Journal of Colloid And Interface Science (v.333, #1)
Formation mechanism and morphology modulation of honeycomb hybrid films made of polyoxometalates/surfactants at the air/water interface
by Peiqin Tang; Jingcheng Hao (pp. 1-5).
Porous hybrid films of surfactant-encapsulated polyoxometalates with different morphologies have been fabricated simply by water droplets as templating at the air/water interface.Highly ordered honeycomb hybrid films of nanometer-scale polyoxometalates and surfactants were fabricated by a simple solvent-evaporation method at the air/water interface. A good template by micrometer water droplets which are condensed from water vapor because of the quick evaporation of organic solvents plays an important role in the self-patterning of honeycomb films. The morphologies of the thin films can be modulated by the solvent volatility which can not only influence the pore size of the film but also determine whether or not a regular porous structure can be achieved at all. The faster the volatility of organic solvents, the smaller the pores of films. Higher hydrophobicity and larger surface coverage which are induced by the surface encapsulation of a polyoxometalate by cationic surfactants with longer double carbon chains are beneficial to the organization of porous structures. It is also found that the morphologies of the thin films can be changed when the thin films are dropped at different supporting solution interfaces. It is well demonstrated that the morphologies of the fabricated hybrid films are modulated by appropriate controls.
Keywords: Honeycomb film; Surfactant-encapsulated cluster; Polyoxometalate; Morphology modulation; Water droplet
Normalization, comparison, and scaling of adsorption data: Arsenate and goethite
by O.K. Hartzog; V.A. Loganathan; S.R. Kanel; G.P. Jeppu; M.O. Barnett (pp. 6-13).
Various approaches for analyzing adsorption data were examined to determine the best method for reporting and interpreting the results of adsorption experiments and ultimately extrapolating laboratory measurements to the field. The interactions of arsenate and goethite were used as representative adsorbate and adsorbent, respectively, although the general principles are applicable to other adsorbate–adsorbent systems as well. A modeling exercise was conducted first to determine the theoretical principles governing the comparison and scaling of adsorption data. These principles were then tested on a suite of experimental data, both new and previously published.LogKD is significantly more sensitive to variations in adsorbate (AsT) or adsorbent (FeT) concentrations than either adsorbed concentration ( q) or percentage adsorbed. The sensitivity ofKD relative to q occurs due to the non-linearity of the adsorption isotherm at a given pH, since as the equilibrium aqueous concentration approaches zero, q also approaches zero whileKD approaches infinity. Varying AsT and FeT while keeping AsT/FeT fixed yields more consistent values of percentage adsorbed,logKD, and q, although the adsorbate-to-adsorbent ratios used in laboratory studies often have a rather narrow range compared to those possible in the field. Specific surface area is also a better scaling parameter than the mass of adsorbent, especially between systems with differing adsorbents with markedly different specific surface areas (e.g., natural versus synthetic goethite). Our results have significant implications to contaminant transport modeling, as the constantKD approach is the most common method of modeling contaminant transport, while contaminant concentrations in the field are typically low, precisely the conditions whereKD is most sensitive.In this work we examine the factors governing the normalization, comparison, and scaling of adsorption data using arsenate and goethite as a model system. Using a theoretical model and experimental data the article highlights the advantages and limitations of the various approaches commonly adopted for analyzing adsorption data.
Keywords: Adsorption; Arsenic; Arsenate; Goethite; Iron oxides; Scaling; Surface area; Normalization; Adsorbate-to-adsorbent ratio
Adsorption of Cd(II) and Pb(II) from aqueous solutions on activated alumina
by Tarun Kumar Naiya; Ashim Kumar Bhattacharya; Sudip Kumar Das (pp. 14-26).
The ability of activated alumina as synthetic adsorbent was investigated for adsorptive removal of Cd(II) and Pb(II) ions from aqueous solutions. Various physico-chemical parameters such as pH, initial metal ion concentration, and adsorbent dosage level and equilibrium contact time were studied. The optimum solution pH for adsorption of Cd(II) and Pb(II) from aqueous solutions was found to be 5. Kinetics data were best described by pseudo-second order model. The effective particle diffusion coefficient of Cd(II) and Pb(II) are of the order of10−10 m2/s. Values of mass transfer coefficient were estimated as4.868×10−6cm/s and6.85×10−6cm/s for Cd(II) and Pb(II) adsorption respectively. The equilibrium adsorption data for Cd(II) and Pb(II) were better fitted to Langmuir adsorption isotherm model. The thermodynamic studies indicated that the adsorption was spontaneous and exothermic for Cd(II) adsorption and endothermic for Pb(II). The sorption energy calculated from Dubinin–Radushkevich isotherm were 11.85 kJ/mol and 11.8 kJ/mol for the adsorption of Cd(II) and Pb(II) respectively which indicated that both the adsorption processes were chemical in nature. Desorption studies were carried out using dilute mineral acids. Application studies carried out using industrial waste water samples containing Cd(II) and Pb(II) showed the suitability of activated alumina in waste water treatment plant operation.The uptake of Cd(II) by activated alumina is a function of pH, it increases as the pH increases from 2 to 8. As the solution pH>7, the Cd(II) starts precipitation in the solution. This is due to the combination of adsorption as well as precipitation. Therefore the optimum pH is taken as 5.
Keywords: Activated alumina; Pseudo-second order; Effective diffusivity; Langmuir; Desorption; Application studies
An ATR-FTIR study of sulphate sorption on magnetite; rate of adsorption, surface speciation, and effect of calcium ions
by Payman Roonasi; Allan Holmgren (pp. 27-32).
The adsorption of sulphate on magnetite was studied in-situ using ATR-FTIR spectroscopy. Synthetic magnetite particles were deposited on a ZnSe internal reflection element and the spectra of sulphate adsorbed at pH 4–8.5 were recorded. Two different ionic strengths were used viz. 0.01 M and 0.1 M NaCl. The spectra of adsorbed sulphate on magnetite coated ZnSe were compared with the spectra of sulphate solutions at the same pH values and in contact with uncoated ZnSe. The spectrum of adsorbed sulphate at pH 4 showed three maxima at 979, 1044, and 1115 cm−1 indicating a monodentate adsorption in which the Td symmetry ofSO42− is lowered to C3v. At pH 6.5, sulphate adsorbed as an outer-sphere complex with two weak bands appearing at 1102 and 980 cm−1. Moreover, spectra of the adsorbed sulphate at pH 4 were recorded as a function of time and sulphate concentration. The equilibrium absorbance at different concentrations fitted a Langmuir type adsorption isotherm. The Langmuir affinity constant K at pH 4 was determined from the slope and intercept of the Langmuir plot to beK=1.2344×104 M−1 and the Gibbs free energy of adsorptionΔGads0 was estimated from this value to be −33.3 kJ/mol. Kinetic analysis indicated that adsorption at pH 4 is fast, whilst the desorption kinetic at the same pH is very slow. In addition, the effect of Ca ions on sulphate adsorption was also studied. It was shown that Ca ions increased the sulphate adsorption on magnetite at pH 8.5.Sulphate sorption on magnetite was studied by in-situ ATR spectroscopy. The effect of pH, concentration of sulphate, ionic media and time on sulphate adsorption were investigated.
Keywords: Magnetite; In-situ; ATR spectroscopy; Sulphate adsorption; Adsorption kinetics; Adsorption isotherm; Ca ions
Uptake of arsenate by an alginate-encapsulated magnetic sorbent: Process performance and characterization of adsorption chemistry
by Soh-Fong Lim; Yu-Ming Zheng; Shuai-Wen Zou; J. Paul Chen (pp. 33-39).
Arsenate removal by a calcium alginate-encapsulated magnetic sorbent was studied. The morphology, microstructure, and composition properties of the sorbent were explored using X-ray diffraction (XRD) and scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDX). The SEM study demonstrates that there are many protuberances and pores on the sorbent surface; the XRD analysis reveals that the sorbent consists of Fe3O4. The EDX analysis indicates that the adsorption on the surfaces of sorbent is highly location dependent. The interaction characteristics between the arsenic and the functional groups on the sorbent were studied by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). These studies indicate that the lattice oxygen in magnetite and the oxygen in hydroxyl of the calcium alginate play important roles in the sorption of arsenate ions onto the sorbent. More importantly, the XPS analysis demonstrates that the arsenate is reduced to arsenite after its adsorption onto the sorbent. It is proposed that divalent iron and the alcoholic group in alginate provide electrons to arsenate. A conceptual model for the adsorption is proposed to illustrate the mechanisms.Adsorption and reduction occur during arsenate uptake by the alginate encapsulated magnetic sorbent.
Keywords: Adsorption; Arsenate; Arsenite; Calcium alginate-encapsulated magnetic sorbent; Reduction
Synthesis of novel methacrylate based adsorbents and their sorptive properties towards p-nitrophenol from aqueous solutions
by Murat Erdem; Erdinç Yüksel; Turgay Tay; Yasemin Çimen; Hayrettin Türk (pp. 40-48).
The polymeric adsorbents were synthesized from 2-dimethylaminoethyl methacrylate (DMA) and [2-(methacryloyloxy)ethyl]dimethylhexadecylammonium bromide (DMAC16) monomers in the presence of ethylene glycol dimethacrylate (EDMA) cross-linking monomer using suspension polymerization technique and their adsorption efficiencies in the removal of p-nitrophenol from aqueous solutions were investigated. DMAC16 monomer was prepared by means of modification of DMA monomer with 1-bromohexadecane. Adsorption experiments were carried out in a batch system and the experimental parameters were evaluated with respect to pH, agitation time, temperature and initial p-nitrophenol concentration. It was observed that the adsorbent poly[2-(methacryloyloxy)ethyl]dimethylhexadecylammonium bromide ( p-DMAC16) prepared from DMAC16 monomer was more effective in the removal of p-nitrophenol than the adsorbent poly(2-dimethylaminoethyl methacrylate) ( p-DMA) prepared from DMA monomer. The effective pH ranges for the adsorption of p-nitrophenol onto p-DMAC16 and p-DMA were 2–12 and 3–9, respectively. Langmuir and Freundlich adsorption models were used to describe the isotherms and find isotherm constants. The Langmuir model was well agreed with experimental data for both adsorbents. The pseudo-first-order, pseudo-second-order, and intraparticle diffusion kinetic models were used to understand the mechanism of the adsorption process and it fitted very well the pseudo-second-order kinetic model for each adsorbent. Thermodynamic parameters such as activation energy and changes of free energy, enthalpy, and entropy were also evaluated for the adsorption of p-nitrophenol onto each adsorbent. Additionally, reusability of the adsorbents was investigated and the results showed that both adsorbents can be employed many times without a significant loss in their adsorption capacities for the removal of p-nitrophenol from water.Zeta potentials of p-DMAC16 and p-DMA as function of pH and pH dependence of the p-nitrophenol adsorption capacities of the same adsorbents.
Keywords: p; -Nitrophenol; Adsorption; 2-Dimethylaminoethyl methacrylate; [2-(Methacryloyloxy)ethyl]dimethylhexadecylammonium bromide
Acid–base interaction of probes at silica surface. Microcalorimetry and adsorption
by B. Granqvist; G. Hedström; J.B. Rosenholm (pp. 49-57).
The interaction of four benzyl derivatives with silica surface sites in anhydrous cyclohexane is investigated. The strength and extent of adsorption is determined from the Langmuir adsorption isotherm. The enthalpy of immersion is determined microcalorimetrically, which is recalculated to the enthalpy of adsorption. The aim is to distinguish between the Lewis-type (electron exchange) and Brønsted-type (proton exchange) of interaction by selecting methanol–acetone and acetic acid–methylamine, respectively as acid–base substituent in benzene. Moreover, the experiments were performed in anhydrous cyclohexane in order to screen out hydrocarbon interactions from the energy balance. The monomolecular adsorption is also distinguished from the bulk wetting of solids. The results are evaluated in terms of possible proton exchange in anhydrous media.The interaction of four benzyl derivatives with silica surface sites in anhydrous cyclohexane is investigated.
Keywords: Adsorption; Enthalpy of adsorption; Acid–base interaction; Langmuir isotherm; Microcalorimetry; Silica; Lewis acid–base
Fluoride sorption using organic–inorganic hybrid type ion exchangers
by C. Sairam Sundaram; S. Meenakshi (pp. 58-62).
Incorporation of an organic polymer into inorganic exchangers provides a class of hybrid ion exchangers which showed promising fluoride removal capacity.Research in defluoridation of drinking water has thrown more technologies, with adsorption as more popular alternative among the fluoride endemic habitations across the globe. This paper describes the fluoride removal potential of novel sorbent, synthetic hybrid type ion exchangers from drinking water. Synthesized hybrids were characterized using FTIR studies. Batch adsorption studies were performed as a function of contact time, pH and influence of other interfering anions. The values of defluoridation capacities (DCs) of synthesized polyacrylamide Al(III) phosphate (Al-Ex), polyacrylamide Ce(IV) phosphate (Ce-Ex) and polyacrylamide Zr(IV) phosphate (Zr-Ex) were found to be 2144, 2290 and 2166 mg F−/kg, respectively. Ce-Ex has slightly higher DC than Al-Ex and Zr-Ex. The equilibrium data were fitted with isotherm models. Thermodynamic parameters viz.,ΔG°,ΔH° andΔS° were calculated to understand the nature of sorption. Field studies were carried out to find the suitability of these sorbents at field condition.
Keywords: Defluoridation; Hybrid ion exchangers; Isotherms; Thermodynamics
Sorption/desorption of arsenate on/from Mg–Al layered double hydroxides: Influence of phosphate
by Antonio Violante; Marianna Pucci; Vincenza Cozzolino; Jun Zhu; Massimo Pigna (pp. 63-70).
We have studied: (i) the sorption of arsenate on Mg–Al layered double hydroxides (LDHs) containing chloride (LDH-Cl) or carbonate (LDH-CO3) in the absence or presence of phosphate; (ii) the competitive sorption of arsenate and phosphate as affected by reaction time and pH and; (iii) the desorption of arsenate previously sorbed on the LDH by phosphate. The LDH samples were uncalcined (LDH-Cl-20 and LDH-CO3-20) or calcined at 450 °C (LDH-Cl-450 and LDH-CO3-450). More phosphate than arsenate was sorbed onto all the minerals but LDH-Cl-450 sorbed much lower amounts of both the ligands than LDH-Cl-20; vice versa LDH-CO3-450 showed a capacity to sorb arsenate and phosphate much greater than LDH-CO3-20. XRD analysis showed that arsenate was included into the layer spaces of LDH-Cl-20, but not in those of LDH-CO3-20. Competition in sorption between arsenate and phosphate was affected by pH, reaction time, surface coverage and sequence of addition of the ligands. Phosphate showed a greater affinity for LDHs than arsenate. The final arsenate sorbed/phosphate sorbed molar ratio increased with reaction time or by adding arsenate before phosphate, but decreased by increasing pH and by adding phosphate before arsenate. The effect of reaction time on the desorption of arsenate by phosphate was also studied.Sorption isotherms of arsenate and phosphate onto uncalcined and calcined LDH minerals (LDH-Cl and LDH-CO3).
Keywords: Layered double hydroxides (LDHs); Arsenate; Phosphate; Sorption; Competitive sorption; Desorption
Kinetic parameters and mechanisms of the batch biosorption of Cr(VI) and Cr(III) onto Leersia hexandra Swartz biomass
by Jianping Li; Qingyu Lin; Xuehong Zhang; Yan Yan (pp. 71-77).
The hyperaccumulative plant species Leersia hexandra Swartz, particularly, has been considered for its detoxification mechanism for phytoremediation of chromium-contaminated water environments. This study investigates the role of the adsorption mechanism of the L. hexandra Sw. biomass on the removal of chromium ions Cr(VI) and Cr(III) from an aqueous solution. The interaction between chromium ions and the L. hexandra Sw. biomass was characterized by using infrared spectroscopy. The results indicate that the binding process of the chromium ions involves the active participation of ligands present in the biomass, such as acylamide, carbonyl, amino, carboxyl, and hydroxyl groups, to immobilize the chromium ions. Equilibrium biosorption experiments were carried out to investigate the effects of pH values and contact time. Adsorption isotherms were modeled with the Langmuir and Freundlich equations and isotherm constants were calculated. Kinetic experiments showed the rapid process of biosorption and the pseudo-second-order model was successfully applied to predict the rate constant of biosorption. This study firstly discovered the kinetics equilibrium modelling of L. hexandra Sw. biomass on biosorption Cr(VI) and Cr(III).The kinetics equilibrium modeling of L. hexandra Sw. biomass on biosorption Cr(VI) and Cr(III) was discovered. The Freundlich and Langmuir isotherm models were used for chromium ions sorption.
Keywords: Leersia hexandra Swartz; Chromium ions; Adsorption; Mechanisms; Kinetics
Reactions of lysine with montmorillonite at 80 °C: Implications for optical activity, H+ transfer and lysine–montmorillonite binding
by Javier Cuadros; Luca Aldega; Jonathan Vetterlein; Kurt Drickamer; William Dubbin (pp. 78-84).
Adsorption–desorption from smectite changes lysine protonation state from dominantly a zwitterion to dominantly cationic. Thermal treatment of lysine–smectite complexes in moist state increases the binding forces between the two.Amino acid–smectite interaction may have catalyzed prebiotic reactions essential for the emergence of life. Lysine solutions (0.05 M) were reacted with Na-smectite in adsorption–desorption experiments. The lysine–smectite complexes were heated at 80 °C for 10 days to investigate (1) possible slow processes taking place at surface temperature that would be accelerated at higher temperature and (2) processes taking place in hydrothermal systems. Three sets of experiments were performed: thermal treatment in closed tubes and water added regularly; thermal treatment in closed tubes without adding water; and thermal treatment in open tubes and no added water. After lysine desorption (displacement with 0.1 M CaCl2), the solutions were investigated using circular dichroism (CD) and the smectite samples using FTIR and CHN elemental analysis. CD spectra were dependent on the solution pH, which was controlled by lysine protonation state. The lysine protonation state was altered by the adsorption–desorption process, with a higher Lys+/Lys± ratio after desorption. The CD and CHN analyses show that the thermal treatment in a moist state causes stronger smectite–lysine binding. FTIR data suggest that the stronger binding is caused by more or stronger H bonds between –NH+3 lysine groups and smectite basal O atoms.
Keywords: Adsorption–desorption; Amino acid protonation state; Circular dichroism; FTIR; Lysine; Smectite
Hydroxynaphthoic acid isomer sorption onto goethite
by Ellen M. Cooper; Dharni Vasudevan (pp. 85-96).
Hydroxynaphthoic acid isomers sorb at goethite–water interface via the ortho substituted carboxylate and phenolate groups and form either bidendate–mononuclear or bidendate–binuclear complexes.This study used batch and attenuated total reflectance–Fourier-transform infrared (ATR-FTIR) flow-through techniques, along with computational chemistry, to probe the sorption of hydroxynaphthoic acid (HNA) isomers at the goethite–water interface. The HNA isomers employed in this study, 1-hydroxy-2-naphthoic acid and 2-hydroxy-3-naphthoic acid, possessed an intramolecular hydrogen bond (IHB) between their carboxyl and hydroxyl groups, which resulted in coupled vibrational modes. Complimentary information from batch and ATR-FTIR studies suggested surface complexation via a bidentate structure, involving both the carboxylate and phenolate groups, as the dominant mode of sorption. A secondary HNA surfaces species noted only at pH 4 appeared to sorb via the carboxylate group, with the phenolic group involved in IHB or H-bonded to the solvent or surface hydroxyl groups. Despite the lack of unique vibrational modes for the key functional groups our experimental approach was successful in proposing interfacial structures, while acknowledging the limitations with respect to differentiating mono- vs. binuclear complexes. Finally, the spectral similarity of HNA sorbed onto goethite and onto the clay fraction of an iron oxide-rich soil suggested analogous solute interaction in pure phase minerals and soils.
Keywords: Metal oxides; ATR-FTIR; PAH; Surface complexation; Interfacial structure
The effects of urea modification and heat treatment on the process of NO2 removal by wood-based activated carbon
by Svetlana Bashkova; Teresa J. Bandosz (pp. 97-103).
The NO2 adsorption and the retention of NO (product of NO2 reduction by carbon) were studied on urea-modified and heat treated activated carbon samples in dry and moist air.The removal of NO2 on urea-modified and heat-treated wood-based activated carbons was studied. From the obtained results it was found that these modifications, especially when done at 950 °C, have a positive effect on NO2 adsorption and on the retention of NO (the product of NO2 reduction by carbon). The presence of moisture in the system enhances the removal of NO2 but negatively affects the retention of NO. It is possible that the formation of active centers on the carbon surface and some increase in the volume of supermicropores during the high temperature treatment play a significant role in these removal processes. The surface of the carbons was analyzed in terms of thepKa distributions. The qualitative and quantitative analyses of the NO2 adsorption products were carried out by means of FTIR and TA techniques, respectively. The main products found on the carbon surface were theNO3 and NO2 species.
Keywords: Urea; Activated carbon; Nitrogen; Heat treatment; NO; 2; adsorption; NO
Interaction between U(VI) and SrTiO3 surfaces versus temperature
by G. García-Rosales; R. Drot; F. Mercier-Bion; G. Lagarde; E. Simoni (pp. 104-113).
The purpose of this work is the study of the interaction mechanisms between U(VI) ions and SrTiO3 surfaces as a function of pH and temperature (25, 50, 75 and 90 °C) by coupling thermodynamic and spectroscopic approaches. First, the reactivity towards U(VI) for both surface sites of the strontium titanate (TiO andSrO) has been investigated as a function of the temperature. The N2-BET specific area was measured:2.4±0.2m2g−1. The surface site density has been determined from potentiometric titrations (6 sites/nm2 for each siteTiO andSrO). The potentiometric titration data have been simulated, for each temperature, using the FITEQL 4.0 software and the constant capacitance model, taking into account both protonation of theSrOH surface sites and deprotonation of theTiOH ones (one p K model). The intrinsic strontium protonation constant increases with an increasing temperature, while the titanate deprotonation one decreases. Moreover, both enthalpy and entropy changes corresponding to the surface acid–base reactions have been evaluated using the van't Hoff relation. The uranium(VI) ions are sorbed onto SrTiO3 surfaces in the 0.5–5.0 pH range with an initial cation concentration equal to10−4 M. The U(VI) surface complexes were identified by using time-resolved laser-induced fluorescence spectroscopy (TRLFS). For all the studied samples, the fluorescence spectra and the corresponding lifetime values do not change with the pH and the temperature. Two U(VI) complexes sorbed onto SrTiO3 were detected and the corresponding lifetimes are60±5 and12±2μs whatever the temperature (25, 50, 75 and 90 °C). The sorption edges were simulated with the FITEQL 4.0 code. The sorption equilibrium constants of the U(VI)/SrTiO3 system between 25 and 90 °C were obtained with the constant capacitance model (CCM), considering two reactive surface sites. According to the spectroscopic characterization, two types of surface complexes, namely [(SrOH)(TiOH)UO2]2+ and [(TiOH)(TiO)UO2]2+, were considered. Finally, enthalpy (ΔrH°) and entropy (ΔrS°) changes were calculated from the temperature-dependent sorption constants, by the application of the van't Hoff formalism. The formation of the [(SrOH)(TiOH)UO2]2+ surface complex was found to present an endothermic character associated to an increase in the disorder of the system. On the contrary, the formation of the [(TiOH)(TiO)UO2]2+ surface complex led to an exothermic process with only a slight increase in the disorder of the system.Effect of the temperature on the SrTiO3 retention properties towards U(VI). Surface species remained the same but their relative proportions are affected by the temperature.
Keywords: Sorption; SrTiO; 3; Temperature; Uranyl; Potentiometric titration; Surface complexation modeling; Enthalpy; Entropy; TRLFS
Layer structured graphite oxide as a novel adsorbent for humic acid removal from aqueous solution
by Tri Hartono; Shaobin Wang; Qing Ma; Zhonghua Zhu (pp. 114-119).
Layer structured graphite oxide (GO) was prepared from graphite using the Hummers–Offeman method, characterised using N2 adsorption, XRD, XPS, SEM(TEM), and FT-IR, and tested for humic acid (HA) adsorption in aqueous solution. XRD, XPS, and FT-IR measurements indicate the formation of layered structure with strong functional groups of GO. It is also found that the GO exhibits strong and much higher adsorption capacity of HA than graphite. The maximum adsorption capacity of the GO from the Langmuir isotherm is 190 mg/g, higher than activated carbon. For the adsorption, several parameters will affect the adsorption such as solid loading and pH. HA adsorption will decrease with increasing pH and an optimum GO loading is required for maximum adsorption.Layer structured graphite oxide has demonstrated as an effective adsorbent for humic acid removal from aqueous solution.
Keywords: Graphite; Graphite oxide; Humic acid; Adsorption
Zn2Al layered double hydroxides intercalated and adsorbed with anionic blue dyes: A physico-chemical characterization
by Rafael Marangoni; Mustapha Bouhent; Christine Taviot-Guého; Fernando Wypych; Fabrice Leroux (pp. 120-127).
Three different anionic blue organic dyes have been intercalated into the structure of Zn2Al layered double hydroxides, using the co-precipitation method at constant pH. Using the same synthetic procedure, Zn2Al–Cl has been prepared and used as an adsorptive phase to retain the blue dyes from an aqueous solution. All the organic/inorganic (O/I) hybrid LDH compounds were analyzed by X-ray powder diffraction (XRPD), thermal analysis (TG/DTA), elemental analysis, solid state13C nuclear magnetic resonance (CPMAS13C NMR), and Fourier transform infrared spectroscopy (FTIR). In the adsorption experiments, Gibbs free energy Δ G values for the temperatures in a range between 10 and 40 °C were found to be negative, which indicates that the nature of adsorption is spontaneous and shows the affinity of LDH material towards the blue anionic dyes. Additionally a decrease in Δ G values at higher temperature further indicates that this process is even more favorable at these conditions. The enthalpy Δ H values were between physisorption and chemisorption, and it may be concluded that the process was a physical adsorption enhanced by a chemical effect, characterized by a combined adsorption/intercalation reaction, making these O/I assemblies reminiscent of the Maya blue.Three anionic blue organic dyes have been intercalated/adsorbed into Zn2Al layered double hydroxides, confirmed by thermodynamic data, in which enthalpy values were between physisorption and chemisorption.
Keywords: Layered double hydroxides; Dye; Intercalation; Adsorption; Thermodynamic constants
Synthesis of poly(3-hexylthiophene) grafted TiO2 nanotube composite
by M.D. Ming-De Lu; S.M. Sze-Ming Yang (pp. 128-134).
A composite of poly(3-hexylthiophene) (P3HT) grafted on TiO2 nanotubes was synthesized. It was characterized using XRD, TEM, TGA, FTIR and XPS. Cyclic voltammetry (CV) was used to elucidate the electrochemical behavior and evaluate the HOMO and LUMO energy levels. Photoluminescence (PL) measurements show that the emission intensity of P3HT mixed with TiO2 nanotubes was one third of that of random P3HT, while that of P3HT grafted onto TiO2 nanotubes was 10% of random P3HT. The results show that the P3HT grafted onto TiO2 nanotubes is more efficient in photoinduced charge transfer than a physical mixture of P3HT and TiO2 nanotubes, indicating this composite has potential for the fabricating hybrid organic–inorganic solid state solar cells.A composite of poly(3-hexylthiophene) (P3HT) grafted on TiCh nanotube was synthesized, this composite is a promising material for fabrication of hybrid organic–inorganic solid state solar cell.
Keywords: Titania; Poly(3-hexylthiophene); Nanotube; Solar cell material
Study of the interaction between a diblock polyelectrolyte PDMA- b-PAA and a gemini surfactant 12- 6-12 in basic media
by Hongmei Kang; Baoliang Peng; Yanyan Liang; Xia Han; Honglai Liu (pp. 135-140).
The interactions between negatively charged diblock polyelectrolyte PDMA71- b-PAA59 and oppositely charged gemini surfactant hexylene-1,6-bis(dodecyldimethylammonium bromide) (12- 6-12) in basic media were studied using dynamic light scattering, fluorescence spectroscopy, surface tension, and1H NMR. With increased addition of surfactant, the conformation of polyelectrolyte experienced changes from the initial unimer with open-extended PAA block, to the nano-scaled aggregates/complexes with a maximum hydrodynamic diameter (Dh), and finally to the stable complexes with a smallerDh. Accordingly, the value ofDh during the whole process of increasing the surfactant concentration changed from 14–17 nm, to 184 nm, and to the final 70 nm, respectively. This transformation was driven by the electrostatic attractive/repulsive interactions, the hydrophobic interaction between hydrophobic surfactant tails, and the hydrophilicity of PDMA block.
Keywords: Diblock polyelectrolyte; Gemini surfactant; Electrostatic force; Hydrophobic interaction; Conformation
Electrochemically controlled release ofα,β,γ,δ-tetrakis(4- N-methylpyridyl)porphine from layer-by-layer thin films
by Hiroshi Sato; Yoichi Takano; Katsuhiko Sato; Jun-ichi Anzai (pp. 141-144).
The release ofα,β,γ,δ-tetrakis(4- N-methylpyridyl)porphyrin (TMPyP) from layer-by-layer assembled thin films composed of poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA) was electrochemically controlled. The release rate of TMPyP was enhanced when a positive electrode potential (+1.2 to +1.5 V) was applied to the glassy carbon electrode on which TMPyP-loaded PAH/PAA film was coated, while the effect of lower electrode potentials (0 to +1.0 V) was negligibly small. The effect of applied potential on the release rate was more significant at pH 7.4 than in the solutions of pH 8.0 and 9.0. The electrochemically enhanced release of TMPyP was rationalized based on local pH change in the vicinity of the electrode surface, which was induced by electrolysis of H2O.The release of TMPyP from layer-by-layer thin film can be accelerated by applying electric potential.
Keywords: Layer-by-layer film; Controlled release; Electrode potential; Loading and release
Synthesis of cationic polymer-grafted cellulose by aqueous ATRP
by O. Glaied; M. Dubé; B. Chabot; C. Daneault (pp. 145-151).
We describe the synthesis of cellulose fibers densely grafted with the cationic polymer poly[2-(methacryloyloxy)ethyl]-trimethylammoniumchloride (PMeDMA) through aqueous ATRP. The hydroxyl groups present on the cellulose surface were exploited to initiate the ATRP polymerization of MeDMA. We first grafted a bromide initiator, known to be an efficient initiator for ATRP, on the cellulose surface from which the polymer was then directly grown. The resulting fibers/PMeDMA complex was analyzed with infra-red, XPS and SEM techniques and present clear evidences that the polymer is present on the cellulose surface. In order to better characterize the polymer, sacrificial initiators were also added in the mixture and subsequently recovered for analysis. Size exclusion chromatography shows that the polymerization in this heterogeneous medium was controlled. Finally, we show that the mechanical properties of test hand sheets made from modified pulp are markedly improved by the grafting of the cationic PMeDMA.The cationic polymer PMeDMA is grafted onto the surface of cellulose fibers via aqueous ATRP, which leads to better mechanical properties of test paper hand sheets.
Keywords: Atom transfer radical polymerization (ATRP); Cellulose fibers; Cationic polymer
Synthesis and rheological properties of hydrophobically modified polyacrylamides with lateral chains of poly(propylene oxide) oligomers
by Laura M. Gouveia; Bruno Grassl; Alejandro J. Müller (pp. 152-163).
Hydrophobically modified polyacrylamides (HMPAM) were synthesized by aqueous micellar copolymerization using poly(propylene glycol) monomethacrylate, PPGMA, as hydrophobic monomer and sodium dodecyl sulfate, SDS, as surfactant. The hydrophobic monomer to surfactant ratio was varied during micellar synthesis to obtain different hydrophobic block lengths. It was found that the rheology of HMPAM/SDS solutions depends both on the ratio of PPGMA to surfactant and on the concentration of surfactant used in the micellar copolymerization. Also, the rheological behavior of the copolymer solutions was studied as a function of SDS addition and temperature. In the presence of SDS, an increase in zero-shear viscosity was observed that depended on polymer and surfactant concentration. At the highest SDS concentration, the copolymer did not reach the viscosity value exhibited by the solution without surfactant. In the presence of surfactant, HMPAM solutions exhibited a small thermo-thickening behavior when the temperature increases from 25 to 50 °C. Our rheological results evidence that the properties of HMPAM aqueous solution as a function of temperature, are a consequence of the rheological response of both components within the copolymer chain, i.e., hydrophilic (acrylamide) and lateral lower critical solution temperature (LCST) sequences (PPO).Effect of surfactant concentration and temperature on the rheological properties of PAM–PPGMA copolymer synthesized by micellar copolymerization.
Keywords: Hydrophobically modified polyacrylamides; Thermo-thickening behavior; Polypropylene oxide/SDS interaction; Mixed micelles; Polymer-induced micellization
Modification of montmorillonite with aminopropylisooctyl polyhedral oligomeric silsequioxane
by Feng Zhao; Chaoying Wan; Xujin Bao; Bala Kandasubramanian (pp. 164-170).
Sodium montmorillonite (Na-MMT) was modified with various amounts of aminopropylisooctyl polyhedral oligomeric silsequioxane (POSS) and a second surfactant (alkyl ammonium based) via ion-exchange reactions. Interlayer spacing, interlamellar structure, and thermal and surface properties of these organoclays were characterized by wide angle X-ray diffraction, thermogravimetric analysis, and contact angle measurement. The interlayer space of POSS-modified clay (POSS-MMT) was strongly dependent on the arrangement of POSS surfactant but less dependent on the POSS concentration. The sodium ions in Na-MMT were only partially exchanged by protonized POSS due to the steric hindrance effect. In addition, the dual-surfactant-modified clays exhibited increased exchange ratios by controlling the amount of the second surfactant, resulting in a good balance in hydrophobicity and polarity of the modified clays. The resultant organoclays were mixed with polypropylene (PP) via a melt-compounding method. It was found that the dual-surfactant-modified clays with low polarity and similar hydrophobicity to PP were well dispersed in the PP matrix.Montmorillonite is modified with aminopropylisooctyl polyhedral oligomeric silsequioxane (POSS) surfactant and an alkyl ammonium compound to form dual-surfactant-modified organoclays.
Keywords: Montmorillonite; Dual surfactant; Interlayer spacing; Thermal stability; Dispersion
AFM study of the morphologic change of HDPE surface photografted with glycidyl methacrylate
by H.L. Huiliang Wang; J.M. Jianmei Han (pp. 171-179).
The UV-induced grafting of glycidyl methacrylate (GMA) onto high-density polyethylene (HDPE) and the atomic force microscopy (AFM) study of the morphologic change of the grafted surface are reported. The grafting was carried out in GMA acetone solutions with different monomer concentrations. Grafting was much faster in a solution with a higher monomer concentration. FTIR analyses proved that GMA had been successfully grafted onto HDPE. The morphologies of grafted HDPE surfaces changed with UV irradiation time. The monomer concentration had a significant effect on the morphologies of the grafted HDPE surfaces. The HDPE surface grafted in a solution with a higher monomer concentration was much rougher than that grafted in a solution with a lower monomer concentration. The growth models of the grafted granules or clusters are also proposed.Atomic force microscopy (AFM) height image of PE surface photografted in 1 mol/L glycidyl methacrylate (GMA) acetone solution for 2 min.
Keywords: Graft copolymers; High-density polyethylene (HDPE); Morphology; Atomic force microscopy (AFM); Glycidyl methacrylate (GMA)
Surface analysis of pure and complex mucin coatings on a real-type substrate using individual and combined mBCA, ELLA, and ELISA
by Tomas Sandberg; Lisa Mellin; Ulrik Gelius; Karin D. Caldwell (pp. 180-187).
In the past, we introduced the idea of using mucin coatings to improve biomaterials performance. Here, we evaluate non-radioactive methods for the analysis of pure and human host protein-containing (complex) mucin coatings on a real-type substrate (Thermanox). A common protein quantification assay (mBCA) was combined with mass-calibrated, enzyme-amplified assays based on lectin (ELLA) and antibody (ELISA) recognition, to determine the total and specific amounts of surface-associated proteins. Model studies showed the mBCA assay to be of limited use at low mass loads, and steric effects to influence the ELLA at high surface layer densities. Non-specific responses due to substrate interaction were low for the ELLA and ELISAs. Cross-reactions were observed during ELLA analysis of analytes sharing high degree of O-glycosylation. Combined mBCA–ELLA–ELISA analysis suggested that mucin desorption was low upon protein addition and that low concentrations of ELISA-determined protein for the complex coatings could be explained in terms of low accessibility of proteins to the bulk environment. Specifically, a methodology is presented for the determination of the fraction of surface-exposed, presumed bioactive proteins in a complex mucin coating. Finally, X-ray photoelectron spectroscopy and infrared reflectance spectroscopy combined with multivariate data analysis were proven useful in the evaluation of mucin-based coatings.Analysis of total and surface-exposed HSA in composite HSA–mucin coatings.
Keywords: Mucin quantification; mBCA; ELLA; ELISA; Ellipsometry; Jacalin; Complex mucin coating; Surface-exposed protein; Bioactivity; XPS; IRS-MVDA; Principal component analysis (PCA)
Replication of DNA submicron patterns by combining nanoimprint lithography and contact printing
by Yadong Wang; Shook Hui Goh; Xinyan Bi; Kun-Lin Yang (pp. 188-194).
We describe a high throughput method of printing DNA submicron patterns on solid substrates. Combining nanoimprint lithography and contact printing, uniform DNA patterns can be produced with feature sizes from 2 μm down to 250 nm. In this method, poly(methylmethacrylate) (PMMA) with submicron line or dot patterns (produced by nanoimprint lithography) is first chemically functionalized with poly(ethyleneimine) (PEI) to aminate the surface and then a DNA pattern is prepared on the surface. PEI modification leads to higher DNA immobilization and DNA hybridization efficiency due to a higher density of amine functional groups provided by PEI. Next, complementary target DNA hybridized to the PMMA surface can be transferred to an aminated glass slide through contact printing. The transfer mechanism is due to electrostatic attraction (between DNA and amine groups) which can overcome hydrogen bonds between two hybridized DNA molecules. DNA transferred from the PMMA to the glass slide still can hybridize with DNA having a complementary sequence. This method provides a facile and high throughput means of preparing uniform DNA submicron patterns which are difficult to prepare by using conventional solution-based methods.The combination of nanoimprint lithography and contact printing provides a facile and high throughput means of preparing uniform DNA submicron arrays.
Keywords: DNA; Submicron patterns; Nanoimprint; Lithography; Contact printing
Supersaturation driven tailoring of photoluminescence efficiency and size distribution: A simplified aqueous approach for producing high-quality, biocompatible quantum dots
by A. Priyam; S. Ghosh; S.C. Bhattacharya; A. Saha (pp. 195-201).
Supersaturation was found to play a pivotal role during nanoparticle-synthesis and its subtle variation helped achieve two prime objectives: (a) high photoluminescence quantum efficiency (PLQE) and (b) narrow size distribution, thereby obviating the need for post-preparative treatments. Degree of supersaturation of initial synthetic mixture was varied by changing the concentration of reagents while keeping their molar ratio constant at 1:2.5:0.5 for [Cd2+]:[cysteine]:[chalcogenide]. An eight-fold increase in supersaturation caused a sharp focusing of size distribution by 64% for CdS quantum dots (QDs). The as-prepared CdS and CdTe QDs were found to have size distribution as low as 4% at higher supersaturation. For a four-fold increase in supersaturation, PLQE of as-prepared CdTe QDs (4.3 nm) rose by 5 times to a remarkably high value of 54%. The focusing of size distribution with increasing supersaturation was found to work well even in the absence of any stabilizer. A substantial overlap of nucleation and growth was found at low supersaturation (0.5SCdTe), whereas a good separation of the two events is achieved at a higher supersaturation (4SCdTe). This study provides a simplified aqueous route for producing highly monodisperse, photoluminescent and biocompatible nanoparticles.Degree of supersaturation has been found to be an effective tool to achieve two prime objectives of nanoparticle synthesis: (1) high photoluminescence quantum efficiency (PLQE) and (2) narrow size distribution.
Keywords: Quantum dots (QDs); Supersaturation; Photoluminescence quantum efficiency (PLQE); Size distribution; Growth kinetics
Electrostatic interaction between two cylindrical soft particles
by Hiroyuki Ohshima; Atsushi Hyono (pp. 202-208).
An expression for the potential energy of electrostatic interaction between two soft cylinders (i.e., polyelectrolyte-coated cylindrical particles) in an electrolyte solution is derived by applying Derjaguin's approximation to the corresponding interaction energy between two parallel soft plates for the case where the density of fixed charges within the polyelectrolyte layer is low. The interaction between two parallel cylinders and that between two crossed cylinders are considered. The obtained expression covers various limiting cases that include hard cylinder/hard cylinder interaction, cylindrical polyelectrolyte/cylindrical polyelectrolyte interaction, soft cylinder/cylindrical polyelectrolyte interaction, soft cylinder/hard cylinder interaction, and cylindrical polyelectrolyte/hard cylinder interaction.Interaction between soft cylinders.
Keywords: Electrostatic interaction; Cylindrical soft particles; Cylindrical polyelectrolytes; Donnan potential; Derjaguin's approximation
Alumina interaction with AMPS–MPEG copolymers produced by RAFT polymerization: Stability and rheological behavior
by H. Bouhamed; S. Boufi; A. Magnin (pp. 209-220).
Different copolymers of 2-acrylamido-2-methylpropanesulfonic acid sodium salt (AMPS), methoxypolyethyleneglycol methacrylate (MPEG), were prepared using two methods of radical polymerization: classical and RAFT-controlled radical polymerization. The effect of polymer structure and architecture on the adsorption behavior, electrokinetic and rheological properties of the alumina suspensions was investigated. Adsorption isotherms showed that copolymer interaction depended not only on the ratio of the monomers and their distribution within the macromolecular backbone, but also on the method of copolymerization. Electrokinetic analysis indicated that adsorption of the copolymer is accompanied by a shift in the isoelectric point (IEP) towards acid pH values. Above a certain concentration, of the order of 1 wt%, the absolute value of the ζ-potential reaches a saturation plateau. At this stage, the maximum ζ-potential value (in absolute value) depends on both the ratio of the monomers for statistical copolymer and the length of the two blocks in the case of block distribution. The rheological behavior is greatly affected in the presence of added polymer; the viscosity of the alumina suspension decreases and reaches an optimum, which depends on both the ratio of the monomers and their distribution within the macromolecular backbone. The viscoelastic properties of the suspensions were found to be functions of both the structure and the architecture of the copolymer. Adding AMPS–MPEG copolymer increases the stability of the suspension via electrostatic effects, but also via steric effects induced by the polyethylene glycol (PEG) segments. The steric contribution to the stabilization process is much important in the presence of block distribution, which is more efficient as dispersant for concentrated alumina suspensions.Schematic illustration of the configuration of AMPS–MPEG block copolymer on alumina surface.
Keywords: Copolymer; RAFT; Adsorption; Stability; Rheology
Morphology of anisotropic chains in a magneto-rheological fluid during aggregation and disaggregation processes
by P. Domínguez-García; Sonia Melle; M.A. Rubio (pp. 221-229).
Study of cluster morphology during aggregation and disaggregation of microsized magnetic particles when an external magnetic field is applied and switched off.We study the morphology of the chain-like aggregates formed when a external constant and uniaxial magnetic field is applied to a magneto-rheological (MR) fluid. In order to characterize the conformation of the aggregates, we study the evolution of various fractal dimensions during aggregation and disaggregation processes (i.e., when the applied field is switched on and off), using video-microscopy and image analysis. Experiments have been performed by varying the values of two external parameters: the magnetic field amplitude and particle concentration. We found that the box-counting dimension, related with how the aggregates occupy the surrounding space, depends on the ratioR1/R0. During the first stage of the disaggregation process, when the particles are moving by Brownian motion inside the aggregate, Family–Vicsek scaling function is verified.
Keywords: Magneto-rheological fluids; Magnetic colloids; Irreversible aggregation; Fractal aggregates; Box-counting dimension; Projected fractal dimension; Chain disaggregation
Controlled and rapid ordering of oppositely charged colloidal particles
by Vyom Sharma; Qingfeng Yan; C.C. Wong; W. Craig Carter; Yet-Ming Chiang (pp. 230-236).
Oppositely charged colloidal particles in suspension undergo rapid coagulation in the absence of any repulsive component in the interaction potential. With an added steric component serving as the repulsive force it is possible to order oppositely charged particles, which are also weakly charged, in solution. However given the novel features obtainable for an ordered structure from strong oppositely charged particles it becomes imperative to gain a full understanding of methods that can order these particles. Here we report a simple and rapid layer-by-layer method to order strongly and oppositely charged particles. Although this method is in principle scalable to order multiple layers of oppositely charged particles, herein we report ordering of one layer of positively charged particles onto a substrate made of negatively charged particles. This method utilizes a non-ionic surfactant to induce a steric repulsive force between particles and involves spin-coating to disperse and order particles on a very short time scale. The ordered structure obtained through this process is verified as the structure with one of the lowest interaction energies.Ordering of oppositely charged polystyrene (PS) particles with and without a non-ionic, amphiphilic surfactant are presented. Spin coating of positive PS on negative PS without (A) and with (B) Triton X-100.
Keywords: Colloids; Oppositely charged; Non-ionic surfactant; Oder
SERS-active Ag/Au bimetallic nanoalloys on Si/SiO x
by Ramon A. Alvarez-Puebla; Juan P. Bravo-Vasquez; Pavel Cheben; Dan-Xia Xu; Philip Waldron; Hicham Fenniri (pp. 237-241).
Nanoalloys are clusters formed of two or more metallic elements and are of interest for applications in catalysis, spectroscopy, photonics, electronics, and magnetism. The hybridization of the individual plasmonic absorptions of different alloyed metals allows for plasmon tunability and a better coupling of plasmon-excitation line, giving rise to significant increases in the enhancement factor for surface-enhanced Raman scattering (SERS) spectroscopy. Here we report simple fabrication procedures for the preparation of Ag/Au nanoalloys on Si/SiO x substrates, with tunable plasmon resonances. The mechanism and kinetic of the nanoalloy formation and its optical properties were studied by SEM, XPS, SPR, and SERS.
Keywords: Bimetallic nanoalloys; Solid thin films; SERS; 2-Naphthalenethiol
Electrospinning preparation, characterization and photocatalytic properties of Bi2O3 nanofibers
by Changhua Wang; Changlu Shao; Lianjia Wang; Lina Zhang; Xinghua Li; Yichun Liu (pp. 242-248).
Bi2O3 nanofibers with diameter of 70–200 nm were successfully prepared by electrospinning a precursor mixture of polyacrylonitrile (PAN)/bismuth nitrate, followed by calcination treatment of the electrospun polymer/inorganic composite fibers. The resulting Bi2O3 nanofibers were characterized with X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, FT-IR spectra and UV–vis diffuse reflectance spectroscopy. The Bi2O3 nanofibers calcined at 500 °C exhibited β phase, and whereas the nanofibers calcined at 550 and 600 °C both exhibited dominant β phase together with a trace amount of α phase. Photocatalytic experiments indicated that the obtained Bi2O3 nanofibers calcined at 500 °C were highly active for photodegradation of organic pollutants Rhodamine B (RB). Furthermore, the Bi2O3 nanofibers could be easily recycled without decrease of the photocatalytic activity.The Bi2O3 nanofibers with diameters of 70–200 nm are fabricated by electrospinning. The Bi2O3 nanofibers calcined at 500 °C possess high photocatalytic properties and can be conveniently fixed and reclaimed.
Keywords: Bi; 2; O; 3; Nanofibers; Electrospinning; Photocatalytic
Electrochemical preparation and structural characterization of platinum thin film on a polypyrrole film modified ITO electrode
by Li Tian; Yanjuan Qi; Binbin Wang (pp. 249-253).
Platinum nanostructures have been fabricated by electrochemical deposition of platinum onto indium tin oxide (ITO) glass substrate modified with thin polypyrrole film. The crystal size and the number density of the platinum nanoparticles have been examined by varying several deposition parameters, including the thickness of the PPy film and the current densities for platinum deposition. Optimal conditions for uniform growth of nanoparticles well-dispersed on the ITO have been determined, along with insight into the mechanism of crystal growth. The PPy film thickness principally affect the size and number density of the nanoparticles, while the platinum deposition current densities could be used to regulate the shape of the nanoparticles. In addition, the flower-like platinum nanoparticles showed high catalytic activity on electrochemical oxidation of methanol, and its activity was measured to be approximately 1.9 times that of bare platinum.SEM images of the platinum nanostructures deposited at5×10−4Acm−2 for 200 s each on the ITO modified with 40 nm-PPy film.
Keywords: Polypyrrole; Platinum nanoparticle; Electrochemistry
Electrocatalytic oxidation of formic acid and formaldehyde on nanoparticle decorated single walled carbon nanotubes
by V. Selvaraj; A. Nirmala Grace; M. Alagar (pp. 254-262).
TEM images of metal nanoparticles decorated SWCNT obtained by glycerol as reducing agents.A potent catalyst has been prepared consisting of platinum (Pt), and platinum–palladium (Pt–Pd) nanoparticles supported on purified single-walled carbon nanotubes (Pt/CNT and Pt–Pd/CNT). Electrochemical characteristics of formic acid and formaldehyde oxidation on these catalysts are investigated via cyclic voltammetric analysis in mixed 0.5 M HCOOH (or 0.5 M HCHO) and 0.5 M H2SO4 solutions. The results imply that the Pt–Pd/CNT electrodes exhibit a better activity than the corresponding Pt nanoparticles modified SWCNT electrodes. The modified electrode exhibits significant electrocatalytic activity towards formic acid and formaldehyde oxidation, which may be attributed due to the uniform dispersion of nanoparticles on SWCNTs and the efficacy of Pd species in Pt–Pd system. Such nanoparticles modified CNT electrodes exhibit better catalytic behavior towards formic acid and formaldehyde than the corresponding carbon electrodes, indicating that the system studied in the present work is the more promising system for use in fuel cells.
Keywords: Formic acid; Formaldehyde; Single walled carbon nanotubes (SWCNTs); Pt nanoparticles; Pt–Pd nanoparticles; Fuel cells
Interfacial and physico-chemical properties of polymer-supported CdS⋅ZnS nanocomposites and their role in the visible-light mediated photocatalytic splitting of water
by Aparna Deshpande; Pallavi Shah; R.S. Gholap; Narendra M. Gupta (pp. 263-268).
Nano-composite CdS⋅ZnS moieties coated over polyester strip were found to exhibit better visible-light-mediated photo-activity for splitting of water, as compared to corresponding pure CdS or ZnS containing coupons. This increase in activity depended upon the mol ratio of the two component sulphides in a particular sample. HRTEM experiments revealed the presence of 1–3 nm size CdS particles embedded over larger size ZnS clusters, the composite samples thus functioning as a highly dispersed guest–host system. In the case of CdS and ZnS dispersed individually over polyester, average crystallite size was found to be around 5 and 15 nm, respectively. A blue shift was observed in the UV–vis absorption spectrum of CdS on addition of ZnS, in conformation with the quantum size effects. Powder XRD, electron diffraction and XPS studies showed that the nanocomposites were comprised of the face-centered cubic ( α) phases of both CdS and ZnS in a close contact with each other. At the same time, certain solid solution phases, i.e. Cd1− xZn xS, were generated at the interfaces of these two semiconductors. Our study demonstrates that the increase in the number of reaction sites due to smaller size of CdS particles and the micro-structural properties associated with the nanostructured CdS or CdS/ZnS interfaces may together play a vital role in the augmented catalytic activity of CdS⋅ZnS composite photocatalysts.The enhanced activity of CdS⋅ZnS nanocomposites for visible-light-mediated splitting of water is attributable to the microstructural properties of nanosize CdS particles existing at CdS/ZnS interfaces.
Keywords: CdS⋅ZnS nanocomposites; Photocatalytic activity; Splitting of water; Role of microstructural properties
Synthesis of mesoporous TiO2− xN x spheres by template free homogeneous co-precipitation method and their photo-catalytic activity under visible light illumination
by K.M. Parida; Brundabana Naik (pp. 269-276).
TiO2− xN x samples showed higher photo-catalytic activity than Degussa P25 and undoped mesoporous titania under visible light illumination. Sample containing around one atomic % nitrogen showed highest visible light activity among the TiO2− xN x samples.The article presents preparation, characterization and catalytic activity evaluation of an efficient nitrogen doped mesoporous titania sphere photo-catalyst for degradation of methylene blue (MB) and methyl orange (MO) under visible light illumination. Nitrogen doped titania was prepared by soft chemical route i.e. template free, slow and controlled homogeneous co-precipitation from titanium oxysulfate sulfuric acid complex hydrate, urea, ethanol and water. The molar composition of TiOSO4 to urea was varied to prepare different atomic % nitrogen doped titania. Mesoporous anatase TiO2− xN x spheres with average crystallite size of 10 nm and formation of titanium oxynitride center were confirmed from HRTEM, XRD and XPS study. UV–vis DRS showed a strong absorption in the range of 400–500 nm which supports its use in visible spectrum of light. Nitrogen adsorption–desorption study supports the porous nature of the doped material. All the TiO2− xN x samples showed higher photo-catalytic activity than Degussa P25 and undoped mesoporous titania. Sample containing around one atomic % nitrogen showed highest activity among the TiO2− xN x samples.
Keywords: TiO; 2; −; x; N; x; Urea hydrolysis; Homogeneous precipitation; Visible light; Dye degradation; Photo-catalyst
Cobalt-modified mesoporous MgO, ZrO2, and CeO2 oxides as catalysts for methanol decomposition
by Tanya Tsoncheva; Ljubomira Ivanova; Christo Minchev; Michael Fröba (pp. 277-284).
Cobalt oxide-modified mesoporous CeO2, ZrO2, and MgO oxides and their SBA-15 silica analogues were prepared and characterized by XRD, TEM, N2 physisorption, FTIR, and TPR–TG analysis. Their catalytic activity in methanol decomposition to CO and hydrogen was tested. The support effect on the state and catalytic behavior of the loaded cobalt oxide nanoparticles is discussed. The best catalytic activity and selectivity of methanol decomposition to CO and hydrogen are registered for Co/CeO2.Mesoporous oxides are suitable hosts for the preparation and stabilization of cobalt oxide nanoparticles. Their catalytic behavior could be successfully tuned, changing the nature of the support.
Keywords: Mesoporous CeO; 2; MgO and ZrO; 2; SBA-15; Cobalt modification; Methanol decomposition
Photosensitized reduction of water to hydrogen using novel Maya blue-like organic–inorganic hybrid material
by Xiaojie Zhang; Zhiliang Jin; Yuexiang Li; Shuben Li; Gongxuan Lu (pp. 285-293).
On the basis of the understanding that membranes play an important role in the separation of the intermediate photoproducts in the photosynthetic process, a novel efficient hydrogen evolution system was constructed with Maya blue-like organic–inorganic hybrid material as a photocatalyst, in which palygorskite acts as matrix and Eosin Y as a photosensitizer. Under visible light irradiation (λ⩾420 nm), the highest rate of hydrogen evolution and apparent quantum yield are about 3247.2 μmol h−1 (g Eosin Y)−1 and 12.5%, respectively. Negatively charged palygorskite particles could control the photosensitized electron-transfer reaction by means of electrostatic interaction. Based on the activities of hydrogen generation and the experimental measurements of UV–vis absorbance and fluorescence, a probable mechanism for photosensitized hydrogen evolution was postulated.A novel efficient hydrogen evolution system was constructed with Maya blue-like organic–inorganic hybrid material as a photocatalyst, in which palygorskite acts as matrix and Eosin Y as a photosensitizer.
Keywords: Eosin Y; Palygorskite; Photosensitized hydrogen evolution; Visible light irradiation
On the possibility of AgZSM-5 zeolite being a partial oxidation catalyst for methane
by Yasushige Kuroda; Toshinori Mori; Hiroyuki Sugiyama; Yoshinori Uozumi; Katsuhiro Ikeda; Atsushi Itadani; Mahiko Nagao (pp. 294-299).
A silver-ion-exchanged HZSM-5 zeolite sample (Ag(H)ZSM-5) evacuated at 573 K exhibited prominent catalytic behavior in the partial oxidation of CH4 at temperatures above 573 K, exceeding the performance of Ag/SiO2⋅Al2O3 and Ag/SiO2 catalysts. From the infrared (IR) and X-ray absorption fine structure (XAFS) spectra, as well as the dioxygen adsorption measurement, it was concluded that the simultaneous existence of Ag+ ions and small clusters of Ag particles leads to the partial oxidation of methane. Taking the magnitude of the formation enthalpy (per oxygen atom) of Ag2O (ΔH=26 kJ/mol) into consideration, we propose the interpretation that the dioxygen activated on small Ag metal clusters formed in ZSM-5 elaborates a surface oxide layer on small Ag clusters and the thus-formed species is simultaneously and easily decomposed at 573 K or above, and the oxygen activated in this way on the Ag metal spills over and can react with methane that has been activated by the Ag+ ions exchanged in ZSM-5, resulting in the high catalytic activity of the Ag(H)ZSM-5 sample in the partial oxidation of methane. This interpretation is also well evidenced by XAFS and IR data. It is anticipated that this material has the potential to be a promising catalyst in the conversion of natural gas into higher value-added chemicals and fuels.AgZSM-5 exhibited prominent catalytic behavior in the partial oxidation of CH4 to CO and H2 above 573 K and has a potential for acting as the catalyst for the conversion of abundant gases into valuable chemicals.
Keywords: Silver-ion-exchanged ZSM-5-type zeolite; Partial oxidation catalyst for methane; Silver ion; Small silver metal clusters; Fourier transform infrared spectroscopy; X-ray absorption fine structure
Highly dispersed Pt nanoparticles immobilized on 1,4-benzenediamine-modified multi-walled carbon nanotube for methanol oxidation
by Shu-Kun Cui; Dao-Jun Guo (pp. 300-303).
We demonstrate the use of molecular monolayers to enhance the nucleation of electrocatalytically active platinum (Pt) nanoparticles onto multi-walled carbon nanotubes (MWCNTs). The MWCNT is embedded within the 1,4-benzenediamine shell (NH2–MWCNT) with large amounts of amino groups outside on the nanotube surfaces. Subsequent deposition of platinum nanoparticles led to high densities of 2 to 5 nm diameter platinum nanocrystals uniformly deposited along the length of the MWCNTs (Pt/NH2–MWCNTs). The structure and nature of the resulting Pt/NH2–MWCNTs composites were characterized by transmission electron microscopy and X-ray diffraction. Electrochemical measurements show that the molecular monolayers do not impede redox behavior of the electrode, and measurements of the electrocatalytic oxidation of methanol show very high catalytic efficiency compared with commercial E-TEK Pt/C (20 wt%) catalysts, which is crucial for anode electrocatalysis in direct methanol fuel cells.TEM images of the Pt/NH2–MWCNT composites with Pt nanoparticles uniformly decorated on 1,4-benzenediamine-modified multi-walled carbon nanotube.
Keywords: NH; 2; –MWNTs; Platinum nanoparticle; Methanol oxidation; Electrocatalyst
Fabrication and adhesion of biomimetic nanotextures fabricated by local oxidation nanolithography
by Yufei Mo; Mingwu Bai (pp. 304-309).
Functional surfaces with biomimetic nanotexture have aroused much interest because of their great advantages in applications. The nanometer-sized biomimetic textures are fabricated using current induced local anodic oxide (LAO) method. By controlling pulsed bias voltage, pulsewidth and relative humidity, the dimensions of biomimetic textures can be precisely controlled. In our study, an atomic force microscopy (AFM) is used for both fabrication and characterization. Conductive AFM allows fabrication process of biomimetic nanotexture without the need to change masks or repeat entire fabrication process. Furthermore, the adhesive characterization of the biomimetic nanotexture was investigated by a colloidal probe.Schematic of local anodic-oxidation process induced by a biased conductive AFM tip.
Keywords: Biomimetics; Nanotexture; Local anodic oxidation; Atomic force microscopy; Adhesion
Modeling adsorption of liquid mixtures on porous materials
by Matias A. Monsalvo; Alexander A. Shapiro (pp. 310-316).
The multicomponent potential theory of adsorption (MPTA), which was previously applied to adsorption from gases, is extended onto adsorption of liquid mixtures on porous materials. In the MPTA, the adsorbed fluid is considered as an inhomogeneous liquid with thermodynamic properties that depend on the distance from the solid surface (or position in the porous space). The theory describes the two kinds of interactions present in the adsorbed fluid, i.e. the fluid–fluid and fluid–solid interactions, by means of an equation of state and interaction potentials, respectively. The proposed extension of the MPTA onto liquids has been tested on experimental binary and ternary adsorption data. We show that, for the set of experimental data considered in this work, the MPTA model is capable of correlating binary adsorption equilibria. Based on binary adsorption data, the theory can then predict ternary adsorption equilibria. Good agreement with the theoretical predictions is achieved in most of the cases. Some limitations of the model are also discussed.A very good agreement between the MPTA–DRA model and experimental data is observed as indicated by the full lines.
Keywords: Adsorption; Binary and ternary liquid mixtures; Porous materials; Potential theory
Mesostructured SBA-16 with excellent hydrothermal, thermal and mechanical stabilities: Modified synthesis and its catalytic application
by Hui Sun; Qinghu Tang; Yu Du; Xianbin Liu; Yuan Chen; Yanhui Yang (pp. 317-323).
We report a modified method to synthesize SBA-16 mesostructured silica under refluxing condition using block co-polymer poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (F127) as template, cetyltrimethylammonium bromide (CTAB) as co-template, and tetraethyl orthosilicate (TEOS) as silica source. The physiochemical properties of SBA-16 silica were characterized by X-ray diffraction (XRD), nitrogen physisorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and29Si solid-state nuclear magnetic resonance (NMR). The resulting SBA-16 silica exhibited highly ordered mesoporous structure, mono-dispersed spherical morphology, excellent hydrothermal, thermal and mechanical stabilities. It was worth mentioning that the synthesis time can be significantly reduced from 48 h to 8 h, which opened a feasible way to produce SBA-16 silica in a large scale. Moreover, the “super-cage” pore structure of SBA-16 encapsulated gold nanoparticles in a “ship in a bottle” way. The well-confined gold nanoparticles (mean size of 5 nm) with a narrow particle size distribution were highly active in solvent-free benzyl alcohol selective oxidation with molecular oxygen.We describe a modified synthesis of mono-dispersed SBA-16 mesostructured silica. The super-cage structure of SBA-16 encapsulates gold nanoparticles, which show high catalytic activity in benzyl alcohol selective oxidation.
Keywords: SBA-16; CTAB; Refluxing; Stability; Au nanoparticles; Benzyl alcohol oxidation
Preparation of meso–macroporous TiO2 ceramic based on membrane jet-flow emulsification—Influences of triblock copolymers on the processes
by W.H. Wenheng Jing; W.G. Weigang Wang; S.H. Shouhong Wu; W.Q. Wanqin Jin; W.H. Weihong Xing (pp. 324-328).
Meso–macroporous TiO2 ceramics were obtained based on a two-stage ceramic membrane jet-flow emulsification and the influences of the triblock copolymers on the process are discussed in this study. The two α-Al2O3 ceramic membranes with average pore sizes of 0.5 and 1.6 μm were used to control the structure of nonaqueous emulsions. Polyethylene oxide (PEO)–polypropylene oxide (PPO)–polyethylene oxide (PEO) with relative molecular masses of 5800 and 2900 were used as emulsifiers. Monodispersed emulsions with the same average droplet size of 2.6 μm were prepared using the two emulsifiers. However, ordered macroporous structures could only be obtained when the PEO–PPO–PEO of 5800 was used as emulsifier because the lower interfacial tension leans to produce the more stable nonaqueous emulsion. Moreover, the mesoporous structures of 5.4 nm and 7.1 nm could be obtained by the self-assembling block copolymers.Meso–macroporous TiO2 ceramics were obtained based on a two-stage ceramic membrane jet-flow emulsification.
Keywords: Meso–macroporous; Ceramic; Emulsion; Membrane emulsification; Jet flow
A simple approach to the synthesis of hollow microspheres with magnetite/silica hybrid walls
by Jia Liu; Yonghui Deng; Chong Liu; Zhenkun Sun; Dongyuan Zhao (pp. 329-334).
In this paper, we report a simple approach for templating synthesis of magnetic hollow composite microspheres with magnetite/silica walls. This approach is based on the co-sedimentation of polymer microspheres and magnetic colloids followed by impregnation with silica oligomer from tetraethyl orthosilicate and the further removal of the polymer microspheres by pyrolysis. The diameter of the hollow microspheres can be adjusted in range of300 nm–2.0 μm by using polymer microspheres of different sizes and the wall thickness is tunable from 10–50 nm by controlling ratio of magnetite to the polymer microspheres. Magnetic characterizations show that the hollow microspheres have superparamagnetism with magnetization saturation of 10–30 emu/g. HRTEM and N2 adsorption–desorption isotherms reveal that the hollow microspheres have numerous nanopores in the walls with a broad distribution in the range of 2 to 80 nm, which results in a high BET surface (67.6 m2/g) and pores volume (0.14 cm3/g).A simple approach is demonstrated for templating synthesis of magnetic hollow microspheres with magnetite/silica walls via co-sedimentation of polymer microspheres and magnetic colloids and impregnation with silica oligomers.
Keywords: Synthesis; Templating; Hollow microspheres; Mesoporous materials; Magnetic; Sol–gel
Characterization of charge properties of an ultrafiltration membrane modified by surface grafting of poly(allylamine) hydrochloride
by J. Dejeu; B. Lakard; P. Fievet; S. Lakard (pp. 335-340).
A polyethersulfone ultrafiltration membrane was functionalized by a cationic polyelectrolyte, the poly(allylamine) hydrochloride (PAH). The influence of the time of adsorption of PAH on the membrane charge properties was studied. Several characterization techniques were used to investigate the membrane modification. Tangential and transmembrane streaming potential measurements were conducted to characterize the outer and inner surfaces of the membrane, respectively. Both techniques indicated that the surface modification of the membrane was efficient. The charge of the outer surface was reversed (from negative values for the unmodified membrane to positive values for the modified membrane) and the charge of the inner surface was neutralized after adsorption of the cationic polyelectrolyte onto the pore walls. The modification of both the outer surface of the membrane and the pore walls was also put in evidence with membrane potential measurements. It was found that the charge of the PAH-modified membrane is affected by the time of immersion in PAH solution. Experimental data seem to show a fast modification of the membrane for the first 15 min; nevertheless, the modification was more pronounced after 24 h of PAH adsorption. Diffusion experiments carried out with unmodified and modified membranes for four salts (KCl, NaCl, MgCl, and CaCl2) showed a decrease in the salt permeability after functionalization of the membrane. The permeability decrease was greater for 2:1 salts than for 1:1 salts. This decrease was explained by electrostatic interactions.
Keywords: Functionalized membrane; Polyethersulfone; Polyelectrolyte; Streaming potential; Membrane potential
Biocompatible polypeptide microcapsules via templating mesoporous silica spheres
by Aimin Yu; Ian R. Gentle; Gao Qing (Max) Lu (pp. 341-345).
We reported the stepwise formation of biocompatible poly(l-lysine)/poly(l-glutamic acid) (PLL/PGA) multilayer films on mesoporous silica (MS) spheres via layer-by-layer (LbL) self-assembly technique. In-situ QCM revealed the nonlinear (exponential) growth of PLL/PGA multilayer films at both pH 5.5 and pH 7.0 conditions. ξ-Potential measurements of the multilayer coated particles indicated that the multilayer surface was being charge-overcompensated in each adsorption step, thereby facilitating adsorption of the next oppositely charged polypeptide onto the MS spheres. Hollow polypeptide capsules could be obtained by subsequently removing silica cores in HF solution. By using enzyme-preloaded MS spheres as capsule templates, a general approach was developed for encapsulating enzymes in biocompatible microcapsules with high loading and retained bioactivity. The loading amount for several enzymes with different sizes and their bioactivity after encapsulation were also reported.Enzyme preloaded mesoporous silica (MS) particles were used as templates for the layer-by-layer deposition of biocompatible polypeptide multilayer films to prepare microcapsules with high active enzyme loading upon subsequently MS template core removal.
Keywords: Biocompatible hollow capsules; Mesoporous silica; Layer-by-layer
Investigation on surface molecular conformations and pervaporation performance of the poly(vinyl alcohol) (PVA) membrane
by Wei Zhang; Zhennan Zhang; Xinping Wang (pp. 346-353).
A simple method of changing pre-treatment temperature in the course of film formation was used to tune the surface structures of PVA membranes. Surface structure and property of the resulting membranes were characterized by X-ray photoelectron spectroscopy (XPS), sum frequency generation (SFG) vibrational spectroscopy, and contact angle measurements. The results show that PVA have different molecular conformations at the membrane surface while those membranes were prepared at different pre-treatment temperature. At higher pre-treatment temperatures, polar acetoxyl residues and hydroxyl groups of the PVA chains oriented in a more orderly fashion, as induced by the faster evaporation of water. When the membranes were in air, CH3 groups adjacent to the acetoxyl groups covered the surface in order to minimize the surface free energy, while backbones of the PVA were rarely observed. These surfaces exhibited a hydrophilic nature upon contact with water due to rapid surface reconstruction. Conversely, at lower pre-treatment temperatures, the backbone CH2 groups dominated the surface, forming a less hydrophilic surface. When the PVA membranes were employed to separate ethanol/water mixtures, it was found that the PVA membranes with more hydrophilic surface exhibited higher water selectivity. Our investigation indicates that molecular conformations on the membrane surface have considerable influence on pervaporation performance.Surface molecular conformations of PVA membranes have considerable influence on membrane pervaporation performance.
Keywords: Surface molecular conformation; PVA membrane; Pervaporation; SFG; Ethanol/water mixture
Cage-like mesoporous organosilicas with isocyanurate bridging groups synthesized by soft templating with poly(ethylene oxide)–poly(butylene oxide)–poly(ethylene oxide) block copolymer
by Rafal M. Grudzien; Jonathan P. Blitz; Stanislaw Pikus; Mietek Jaroniec (pp. 354-362).
Co-condensation of tris[3-(trimethoxysilyl)propyl]isocyanurate and tetraethyl orthosilicate in the presence of poly(ethylene oxide)–poly(butylene oxide)–poly(ethylene oxide) triblock copolymer afforded cage-like organosilicas with isocyanurate bridging groups, ordered large pores and high surface area.Ordered large-pore organosilicas with isocyanurate bridging groups were synthesized via co-condensation of tetraethyl orthosilicate (TEOS) and tris[3-(trimethoxysilyl)propyl]isocyanurate (ICS) in the presence of poly(ethylene oxide)–poly(butylene oxide)–poly(ethylene oxide) (EO39BO47EO39) B50-6600 template under acidic conditions. It was shown that the extraction of the B60-5500 triblock copolymer with acidified ethanol solution was insufficient to remove completely the template; however, calcination of as-synthesized and extracted samples under air atmosphere at 200 °C, 250 °C and 300 °C caused not only the removal of the polymer but also a substantial decomposition of the ICS groups. In contrast, the heat treatment of extracted organosilicas at 360 °C in flowing nitrogen was able to fully remove the residual template without degradation of the ICS bridging groups. Characterization of the resulting materials by small angle X-ray scattering (SAXS) and X-ray powder diffraction (XRD) revealed that isocyanurate-containing organosilicas have a body-centered cubic symmetry ( Im3m). Argon adsorption–desorption isotherms of these organosilicas revealed cage-like mesopores, high surface areas and large pore volumes. The diameters of spherical cages were found to be very uniform in the range of 12–14 nm. A complete removal of triblock copolymer was confirmed by high-resolution thermogravimetry (TG), Fourier transform infrared spectroscopy (FT-IR) and CHNS elemental analysis (EA). The latter showed that the isocyanurate rings are intact in the framework and their loading is up to 1 mmol g−1. Moreover, these organosilicas were also synthesized using low acid concentration, double amount of polymer and sodium chloride; in this case the template was completely extracted and there was no need for additional heat treatment.
Keywords: Mesoporous organosilica; Argon adsorption; Cage-like mesostructures; Isocyanurate bridging group; Block copolymer template
Effects of charge on osmotic reflection coefficients of macromolecules in porous membranes
by Gaurav Bhalla; William M. Deen (pp. 363-372).
A computational model was developed to predict the effects of solute and pore charge on the osmotic reflection coefficients (σo) of spherical macromolecules in cylindrical pores. Results were obtained for particles and pores of like charge and fixed surface charge densities, using a theory that combined low Reynolds number hydrodynamics with a continuum, point-charge description of the electrical double layers. In this formulation steric and/or electrostatic exclusion of macromolecules from the vicinity of the pore wall creates radial variations in osmotic pressure. These, in turn, lead to the axial pressure gradient that drives the osmotic flow. Due to the stronger exclusion that results from repulsive electrostatic interactions,σo with charge effects always exceeded that for an uncharged system with the same solute and pore size. The effects of charge stemmed almost entirely from particle positions within a pore being energetically unfavorable. It was found that the required potential energy could be computed with sufficient accuracy using the linearized Poisson–Boltzmann equation, high charge densities notwithstanding. In principle, another factor that might influenceσo in charged pores is the electrical body force due to the streaming potential. However, the streaming potential was shown to have little effect onσo, even when it markedly reduced the apparent hydraulic permeability.Osmotic flow induced by macromolecules is affected by molecular and membrane charge. A theory based on continuum hydrodynamics and electrostatics was developed to predict the magnitude of this effect.
Keywords: Streaming potential; Osmotic flow; Hindered transport theory
Incorporation of antigenic GPI-proteins from Leishmania amazonensis to membrane mimetic systems: Influence of DPPC/cholesterol ratio
by Marcelle C. Colhone; Thatyane M. Nobre; Maria Elisabete D. Zaniquelli; Rodrigo G. Stabeli; Pietro Ciancaglini (pp. 373-379).
The reconstitution of membrane proteins into liposomes is a useful tool to prepare antigenic components that induce immunity. We have investigated the influence of the dipalmitoylphosphatidylcholine (DPPC)/cholesterol molar ratio on the incorporation of a GPI-protein from Leishmania amazonensis on liposomes and Langmuir monolayers. The latter system is a well behaved and practical model, for understanding the effect of variables such as surface composition and lipid packing on protein incorporation. We have found that the DPPC/cholesterol molar ratio significantly alters the incorporation of the GPI-protein. In the absence of cholesterol, reconstitution is more difficult and proteoliposomes cannot be prepared, which we correlated with disruption of the DPPC layer. Our results provide important information that could be employed in the development of a vaccine system for this disease or be used to produce other GPI-systems for biotechnological application.Kinetics of L. amazonensis GPI-protein adsorption on a monolayer at 30 mN m−1.
Keywords: Leishmania amazonensis; DPPC; Cholesterol; GPI-proteins; Lipids; Proteoliposomes
Shape and size selective separation of gold nanoclusters by competitive complexation with octadecylamine monolayers at the air–water interface
by Renu Pasricha; Amit Singh; Murali Sastry (pp. 380-388).
The paper presents a time-dependent study of shape-dependent preferential complexation of gold nanoparticles to the octadecyl amine (ODA) monolayers at the air–water interface. Room temperature reduction of chloroaurate ions using lemon grass leaf extract yields a mixture of spherical and triangular nanoparticles, which were used for this study. These nanoparticles have a net negative charge on their surface due to the presence of biomolecules from plant extract and thus a strong attractive electrostatic interaction with the positively charged ODA monolayers drives the complexation process. The extent of preferential complexation of the gold nanoparticles to the ODA monolayers is a function of the charge on the particles and the relative mobility of the nanoclusters in the medium. The complexation process has been followed in real time by a host of techniques such as surface pressure–area(π–A) isotherms, UV–vis–NIR spectroscopy and Brewster angle microscopy. The charge and mobility of the gold nanoparticles was confirmed by measurement of their electrophoretic mobility. Langmuir–Blodgett films of the nanogold–ODA composites have been characterized by UV–vis–NIR spectroscopy, Fourier transform infrared spectroscopy, and transmission electron microscopy. These measurements clearly indicate that the cluster mobility and complexation increase with decreasing cluster size. In the competitive complexation process of large and small gold particles, it was observed that some bigger gold particles were also incorporated into the amine matrix even though the cluster mobility is higher for smaller gold particles.Extent of preferential complexation of the gold nanoparticles to the octadecylamine monolayer is a function of charge on the particles and the relative mobility of the nanoclusters in the medium.
Keywords: Gold nanoparticles; ODA monolayer; Langmuir–Blodgett technique; Competitive complexation
Analytical modeling of capillary flow in tubes of nonuniform cross section
by William W. Liou; Yongqing Peng; Peter E. Parker (pp. 389-399).
The interface rise for the flow in a capillary with a nonuniform cross section distribution along a straight center axis is investigated analytically in this paper. Starting from the Navier–Stokes equations, we derive a model equation for the time-dependent rise of the capillary interface by using an approximated three-dimensional flow velocity profiles. The derived nonlinear, second-order differential equation can be solved numerically using the Runge–Kutta method. The nonuniformity effect is included in the inertial and viscous terms of the proposed model. The present model is validated by comparing the solutions for a circular cylindrical tube, rectangular cylindrical microchannels, and convergent–divergent and divergent–convergent capillaries. The validated model has been applied to capillaries with parabolic varying wall, sinusoidal wall, and divergent sinusoidal wall. The inertial and viscous effects on the dynamic capillary rise and the equilibrium height are investigated in detail.A new analytical model for the time-dependent rise of the capillary interface in nonuniform cross-sectional tubes.
Keywords: Surface tension; Capillary flow; Nonuniform capillaries
Stable polytetrafluoroethylene superhydrophobic surface with lotus-leaf structure
by Weixin Hou; Qihua Wang (pp. 400-403).
The polytetrafluoroethylene superhydrophobic surface with a lotus-leaf structure. The filter paper was firstly used as a template. The stability of the as-prepared material is excellent.A stable polytetrafluoroethylene superhydrophobic surface is prepared with filter paper which is first used as a template. Scanning electron microscope image shows a lotus-leaf like structure appears on the polytetrafluoroethylene surface. Altering the sintering temperature, the microstructure of the as-prepared surface also varied. After treating 12 h in acid, alkali or organic solvents, the as-prepared surface still retains superhydrophobicity and shows excellent stability.
Keywords: Polytetrafluoroethylene; Superhydrophobic; Filter paper; Template
Nanocrystalline Janus films of inorganic materials prepared at the liquid–liquid interface
by Kanishka Biswas; C.N.R. Rao (pp. 404-410).
The interface between toluene and water has been employed to prepare ultrathin Janus nanocrystalline films of metal oxides, metal chalcogenides and gold, wherein the surface on the organic-side is hydrophobic and the aqueous-side is hydrophilic. We have changed the nature of the metal precursor or capping agent in the organic layer to increase the hydrophobicity. The strategy employed for this purpose is to increase the length of the alkane chain in the precursor or use a perfluroalkane derivative as precursor or as a capping agent. The hydrophobicity and hydrophilicity of the Janus films have been determined by contact angle measurements. The morphology of hydrophobic and hydrophilic sides of the film have been examined by field emission scanning electron microscopy.Nanocrystalline Janus films of various inorganic materials have been prepared at the organic–aqueous interface, wherein the surface on the organic-side is hydrophobic and the aqueous-side is hydrophilic.
Keywords: Janus films; Hydrophobic; Hydrophilic; Organic–aqueous interface
Comments on “Adsorption of direct dyes from aqueous solutions by carbon nanotubes: Determination of equilibrium, kinetics and thermodynamics parameters”
by Yuh-Shan Ho (pp. 412-412).
Two most suggested papers for pseudo-second-order kinetic model were published in 1984 and 1995 by Blanchard et al. and Ho, respectively. Blanchard et al. noted the overall exchange reaction of NH+4 ions fixed in zeolite by divalent metallic ions in the solution using a second-order kinetic model. Ho used the pseudo-second-order kinetic model to the copper ion/peat adsorption system. The adsorption involved chemical bonding and cation exchange. In this comment citation error and quotation error were pointed.
Keywords: Initial adsorption rate; Pseudo-second-order kinetic model; Intraparticle diffusion model; Quotation error
Synthesis and characterization of poly(3-methyl thiophene) nanospheres in magnetic ionic liquid
by Songmin Shang; Liang Li; Xiaoming Yang; Lei Zheng (pp. 415-418).
Poly(3-methyl thiophene) nanospheres with their size ranging around 50–60 nm have been synthesized by simply adding monomers into a magnetic ionic liquid.Poly(3-methyl thiophene) nanospheres with their size ranging around 50–60 nm have been synthesized by simply adding monomers into a magnetic ionic liquid, Bmim[FeCl4]. The ionic liquid leads to the formation of uniform nanospheres with a relatively narrow size distribution confined to submicrometer-sized domains. The poly(3-methyl thiophene) nanospheres were characterized by FTIR, Raman and thermogravimetric analysis (TGA). Scanning electron microscopy (SEM) was used to show the morphology of the samples. As compared with the conventional solution polymerization method, the polymerization yield and conductivity of the polymers produced in this magnetic ionic liquid system were improved.
Keywords: Poly(3-methyl thiophene); Ionic liquid; Nanospheres; Polymers
Water rolling and floating upon water: Marbles supported by a water/marble interface
by Edward Bormashenko; Yelena Bormashenko; Albina Musin (pp. 419-421).
Floating of liquid marbles on a water/air interface was studied. The critical density allowing floating marbles containing NaCl solution was established experimentally and compared with its calculated value. A satisfactory agreement between experimental and theoretical values of the critical density is reported. Figure: A water marble floating on NaCl water solution.
Keywords: Water; Marbles; Water/air interface; Floating; Critical density
by Arthur Hubbard (pp. 422-422).