Journal of Colloid And Interface Science (v.315, #1)
Liquid adsorption of n-octane/octanol/ethanol on SBA-16 silica
by Rico Rockmann; Grit Kalies (pp. 1-7).
SBA-16 silica samples with cubicIm3¯m symmetry were synthesized according to methods reported in literature and characterized by nitrogen adsorption and X-ray diffraction. The adsorption behavior of the n-octane(1)/octanol(2), n-octane(1)/ethanol(3), and octanol(2)/ethanol(3) binary liquid mixtures on SBA-16 was studied over the whole concentration range at 25 °C. Inverted U-shape isotherms were found and described by mathematical functions. The experimental binary data were verified by using a consistency test for the specific free wetting energies on the liquid/solid interface. The ternary adsorption excess isotherms of n-octane(1)/octanol(2)/ethanol(3) at 25 °C were predicted from the binary data. The work presents the first complete and consistent tabular set of binary liquid adsorption data for creating ternary data on ordered mesoporous silica.New experimental results in adsorption of binary liquid mixtures on SBA-16 mesoporous silica are presented. The high adsorption excesses measured promise application of SBA-16 in separation and cleaning processes. Ternary adsorption excesses on SBA-16 are predicted.
Keywords: Adsorption excess; Binary and ternary liquid mixtures; Liquid/solid interface; Ordered mesoporous solid
Modeling adsorption of copper (II) onto fly ash and bentonite complex from aqueous solutions
by Shujing Zhu; Haobo Hou; Yongjie Xue; Na Wei; Qing Sun; Xiaolu Chen (pp. 8-12).
Transportation of copper (II) ions from aqueous solutions to a fly ash and bentonite complex amorphous heterogeneous oxides (AHO: CaO–SiO2–Al2O3–MgO–FeO) system was studied. The particles of the fly ash and bentonite complex AHO system were highly porous and composed of platelike grains. They provide the physical basis for establishing a liquid–solid reaction model applicable to mesoporous solids. The main innovation of this model was in simplifying the powder granules to aggregates of close particles, while the particles act in accordance with the model better. The calculated curves from the models were well in line with the experimental results.Effect of time on Cu2+ adsorption.
Keywords: Mechanochemistry; Amorphous heterogeneous oxides (AHO); Copper (II); Kinetics model; Adsorption
Proton–arsenic adsorption ratios and zeta potential measurements: Implications for protonation of hydroxyls on the goethite surface
by J.S. Zhang; R. Stanforth; S.O. Pehkonen (pp. 13-20).
Successfully modeling the surface charge of goethite and anion adsorption on goethite using a surface complexation model (SCM) alone cannot verify the assumptions of this model. In this study, the assumptions of 2-p K triple layer model (TLM) and two-site 1-p K basic stern model (BSM) were assessed with respect to their ability to interpret both the proton–anion adsorption ratios of dimethylarsinate (DMA), monomethylarsonate (MMA), and arsenate and their effect on the ζ-potential. The proton–DMA adsorption ratio is around 0.9 at pH 4.25 and 1.1 at pH 6.75 at DMA surface coverage ranging from 0 to 2 μmol m−2, and the ζ-potential is independent of DMA adsorption at these two pH values. The proton–MMA adsorption ratio increases to 1.5 at pH 4 and 2.1 at pH 6.75 as the MMA surface coverage decreases to 0.5 μmol m−2. The ζ-potential is less dependent on MMA adsorption at a surface coverage range of 0 to 1.8 μmol m−2, and it then decreases with a further increase in the MMA surface coverage at pH 4 and 6.75. The proton–arsenate adsorption ratio decreases to 2 as the arsenate surface coverage approaches zero, and the ζ-potential decreases linearly with the increasing arsenate surface coverage at pH 4 and 6.75. Neither the 2-p K TLM nor the 1-p K BSM give a consistent interpretation of both the proton–arsenic adsorption ratio and the effect of arsenic on the ζ-potential. The results suggest that the 1-p K MUSIC model in which each type of surface hydroxyls has its own intrinsic proton-affinity constant and only one type of surface hydroxyls is involved in DMA, MMA, and arsenate adsorption is preferably pursued. The protonation degree of reactive hydroxyls estimated from proton–arsenic adsorption ratios is 0.2 at pH 4 and 0 at pH 6.75 in 0.001 M NaNO3.The fraction of various charged hydroxyls on the goethite surface in 0.001 M NaNO3 predicted by the 2-p K TLM model and the two-site 1-p K BSM model.
Keywords: Proton–arsenic adsorption ratio; Zeta potential; Protonation degree; Reactive hydroxyls; Goethite
Surface speciation of Cd(II) and Pb(II) on kaolinite by XAFS spectroscopy
by Markus Gräfe; Balwant Singh; Mahalingam Balasubramanian (pp. 21-32).
Little spectroscopic evidence exists in the literature describing the surface complexation of cadmium (Cd) and lead (Pb) on kaolinite, the dominant clay mineral present in highly weathered soils of tropical and humid climates. X-ray absorption fine structure (XAFS) spectroscopy data at the Cd K and Pb LIII edges were collected on Cd- and Pb-sorbed kaolinite samples and compared to a suite of reference materials including Pb and Cd sorbed on amorphous (am-)gibbsite. Cadmium formed dominantly (>75%) outer sphere complexes on kaolinite and a small fraction of CdOHCl complexes. In contrast Cd adsorbed as an inner sphere complex on gibbsite, suggesting that the Si tetrahedral sheet hindered Cd sorption to the Al octahedral sheet on kaolinite. Lead formed polymeric complexes, which bonded to kaolinite via edge sharing with surface Al octahedra. Two distinct Pb–Al edge-sharing distances on am-gibbsite, as opposed to one on kaolinite, suggested a similar steric hindrance effect for the surface complexation of polymeric Pb complexes on kaolinite. The results of this study show that the Si tetrahedral sheet limited the surface complexation of Cd and Pb on kaolinite, elevating kaolinite's permanent negative charge properties in retaining these heavy metals at its surface.
Keywords: EXAFS spectroscopy; Surface structure; Adsorption; Gibbsite; Polynuclear complexes; Steric hindrance
The removal efficiency of chestnut shells for selected pesticides from aqueous solutions
by G. Zuhra Memon; M.I. Bhanger; Mubeena Akhtar (pp. 33-40).
The removal of selected pesticides such as carbofuran (CF) and methyl parathion (MP) using low-cost abundant sorbent chestnut shells from aqueous solutions has been investigated in the present study. The sorption parameters, i.e., contact time, pH, initial pesticide solution concentration and temperature have been studied. Maximum percent sorption (99±1%) was achieved for (0.38–3.80)×10−4 and (0.45–4.5)×10−4 moldm−3 of MP and CF pesticide solutions respectively, using 0.4 g of sorbent in 100 ml of solution for 30 min agitation time at pH 6. The Freundlich, Langmuir and Dubinin–Radushkevich (D-R) models have been applied, and their constants for methyl parathion and carbofuran, sorption intensity1/n (0.55±0.02 and0.54±0.04), multilayer sorption capacityCm (28.3±0.5 and16.4±0.7)×10−3 moll1−1/ndm3/ng−1, monolayer sorption capacity Q (22.5±0.5 and10.8±0.3)×10−6 molg−1, binding energy, b (2.9±0.2 and5.2±0.5)×104 dm3mol−1, and sorption energy E (11.2±0.1 and11.5±0.2 kJmol−1) have been evaluated respectively. Lagergren, Morris–Weber and Reichenberg equations were employed to study kinetics of sorption process. Thermodynamic parameters Δ H (−5.09±0.1 and22.8±0.4 kJmol−1), Δ S (−4.33±0.0003 and0.09±0.001 kJmol−1K−1) andΔG(303K) (−2.9 and−3.8 kJmol−1) have been calculated for methyl parathion and carbofuran, respectively. The developed sorption procedure has been employed to environmental samples.
Keywords: Chestnut (; Castanea vesca; ) shells; Pesticides; Sorption; Isotherms; Kinetics; Thermodynamics
Humic acid adsorption on fly ash and its derived unburned carbon
by Shaobin Wang; Z.H. Zhu (pp. 41-46).
Fly ash is solid waste from combustion process, containing oxide minerals and unburned carbon. In this investigation, fly ash has been separated into metal oxide mineral section and unburned carbon. The fly ash with different contents of unburned carbon was employed for humic acid adsorption to investigate the influence of unburned carbon on adsorption. It is found that metal oxides and unburned carbon in fly ash exhibit significant difference in humic acid adsorption. The unburned carbon plays the major role in adsorption. Higher content of unburned carbon in fly ash results in higher surface area and thus higher humic acid adsorption. Fly ash and unburned carbon exhibit adsorption capacity of humic acid of 11 and 72 mg/g, respectively, at 30 °C, pH 7. Humic acid adsorption is also affected by ion strength, pH, and temperature. The thermodynamic calculations indicate that the adsorption is endothermic nature withΔH0 andΔS0 as 5.79 kJ/mol and 16.0 J/K mol, respectively.Fly ashes with varying contents of unburned carbon were investigated for humic acid adsorption. Humic acid adsorption is dependent on unburned carbon.
Keywords: Fly ash; Unburned carbon; Humic acid adsorption; Isotherm
Adsorption of arsenic(III) and arsenic(V) from groundwater using natural siderite as the adsorbent
by Huaming Guo; Doris Stüben; Zsolt Berner (pp. 47-53).
Batch and column tests were performed utilizing natural siderite to remove As(V) and As(III) from water. One hundred milligrams of siderite was reacted at room temperature for up to 8 days with 50 mL of 1000 μg/L As(V) or As(III) in 0.01 M NaCl. Arsenic concentration decreased exponentially with time, and pseudoequilibrium was attained in 3 days. The estimated adsorption capacities were 520 and 1040 μg/g for As(V) and As(III), respectively. Column studies show that effluent As was below 1.0 μg/L after a throughput of 26,000 pore volumes of 500 μg/L As water, corresponding to about 2000 μg/g of As load in the filter. Results of scanning electron microscopy (SEM) and transmission electron microscopy (TEM) reveal that high As retention capacity of the filter arose from coprecipitation of Fe oxides with As and subsequently adsorption of As on the fresh Fe oxides/hydroxides. Arsenic adsorption in the filter from As-spiked tap water was relatively lower than that from artificial As solution because high HCO−3 concentration restrained siderite dissolution and thus suppressed production of the fresh Fe oxides on the siderite grains. The TCLP (toxicity characteristic leaching procedure) results suggest that these spent adsorbents were inert and could be landfilled.SEM images of the pristine siderite (A) and the used siderite (B), and TEM image of the used siderite (C) and EDS spectra for the Fe-oxide coating (D).
Keywords: Arsenate; Arsenite; Drinking water; Removal; Retention
Kinetic Monte Carlo study of proton binding at the metal oxide/electrolyte interface
by Piotr Zarzycki (pp. 54-62).
The kinetics of proton binding at the metal oxide/electrolyte interface is studied using the kinetic Monte Carlo method. The influence of system properties (surface site density, interfacial dielectric constant, surface energetic heterogeneity) on the equilibrium and kinetic surface coverage is shown. It is shown that the kinetic properties are much more sensitive to lateral interactions than the equilibrium ones. The assumption of energetic heterogeneity rapidly changes the time scales of the processes as well as the time interval between two subsequent elementary processes. In this paper, the atomistic insight into the kinetics of H+ ion uptake at the metal oxide/electrolyte interface is presented for the first time.
Keywords: Kinetic Monte Carlo; Double electrical layer; Surface heterogeneity; Proton binding
Characterization of solid-phase extraction of Fe(III) by unloaded polyurethane foam as thiocyanate complex
by Gil Nunes de Almeida; Leandro M. de Sousa; Annibal D. Pereira Netto; Ricardo J. Cassella (pp. 63-69).
This work presents a detailed study about the adsorption of iron(III)–thiocyanate complexes onto unloaded polyether-type polyurethane foam (PUF). A novel strategy was employed for this purpose, utilizing the adjustment of the plug cylinder of PUF to the arm of an overhead stirrer. The system was characterized in relation to equilibrium and kinetic aspects and it was modeled by applying Langmuir and Freundlich isotherms. The results obtained showed that adsorption occurs on a monolayer and that external transport of the solute from solution to adsorbent was the rate-determining mechanism. A maximum adsorption capacity of2.06×10−4molFeg−1 was obtained under established experimental conditions (0.5 mol L−1 SCN− and 0.005 mol L−1 HCl). Sequential extraction experiments were carried out by changing PUF in time intervals previously defined (5, 20, and 40 min), and the obtained results showed that it is possible to remove around 95% of the Fe(III) in solution through five consecutive extractions of 5 min with five 200 mg PUF cylinders.Polyurethane foam before (white) and after (red) adsorption of Fe(III) as thiocyanate complex.
Keywords: Iron; Polyurethane foam; Adsorption; Thiocyanate
Orthophosphate and metaphosphate ion removal from aqueous solution using alum and aluminum hydroxide
by D.A. Georgantas; H.P. Grigoropoulou (pp. 70-79).
The removal of orthophosphates (10−2 kg P m−3), condensed phosphates (10−2 kg P m−3), and mixtures of both (5×10−3 kgPm−3 as orthophosphate and 5×10−3 kgPm−3 as metaphosphate) in aqueous solution is studied using alum and aluminum hydroxide. The effects of coagulant dose, pH, temperature, aging of aluminum hydroxide, and presence of different ions are investigated. On the basis of the experimental results, alum is much more efficient in phosphorus removal than aluminum hydroxide even if, in both cases, at the conditions studied, the active coagulant form is Al(OH)3. The differences then could be due to the higher activity of the in situ formed hydroxide. Orthophosphates and metaphosphates seem to have similar behavior vs pH variation: maximum removal is achieved at pH values 5–6 in all cases. On the other hand, in the simultaneous presence of both P forms, orthophosphate and metaphosphate ions have different affinities for the surface sites of aluminum hydroxide, since for both alum and aluminum hydroxide, orthophosphates are preferentially removed compared to metaphosphates, due probably to orientation effects and the charge per P atom. The presence of sodium, potassium, magnesium, sulfate, chloride, and magnesium, at the concentrations studied and for a pH value of 6, does not influence P removal. Temperature variation, between 25 and 60 °C, does not affect alum efficiency but both P forms are increasingly removed with increasing temperature, probably due to polymer Al(OH)3 breaking, producing new surfaces for adsorption. Aging decreases sorption capacity of Al(OH)3, while crystallites of increasing size are formed. Finally adsorption of both P forms is best described by the Freundlich isotherm [KF=(49.1–69.1)×10−3(m3kg−1)1/N,1/N: 0.14–0.19 forT=25–60°C] and [KF=(1.58–2.79)×10−3(m3kg−1)1/N,1/N: 2.17–2.47 forT=25–60°C] for orthophosphate and metaphosphate, respectively.The removal of orthophosphates, metaphosphates, and mixtures of both with alum and aluminum hydroxide, the latter having aged for different time intervals, was investigated at various pH and temperature values.
Keywords: Alum; Aluminum hydroxide; Orthophosphate; Metaphosphate; Condensed phosphates; Coagulation; Adsorption isotherms; Aging
Adsorption of nitrobenzene from aqueous solution by MCM-41
by Qingdong Qin; Jun Ma; Ke Liu (pp. 80-86).
Adsorption of nitrobenzene onto mesoporous molecular sieves (MCM-41) from aqueous solution has been investigated systematically using batch experiments in this study. Results indicate that nitrobenzene adsorption is initially rapid and the adsorption process reaches a steady state after 1 min. The adsorption isotherms are well described by the Langmuir and the Freundlich models, the former being found to provide the better fit with the experimental data. The effects of temperature, pH, ionic strength, humic acid, and the presence of solvent on adsorption processes are also examined. According to the experimental results, the amount of nitrobenzene adsorbed decreases with an increase of temperature from 278 to 308 K, pH from 1.0 to 11.0, and ionic strength from 0.001 to 0.1 mol/L. However, the amount of nitrobenzene adsorbed onto MCM-41 does not show notable difference in the presence of humic acid. The presence of organic solvent results in a decrease in nitrobenzene adsorption. The desorption process shows a reversibility of nitrobenzene adsorption onto MCM-41. Thermodynamic parameters such as Gibbs free energy are calculated from the experimental data at different temperatures. Based on the results, it suggests that the adsorption is primarily brought about by hydrophobic interaction between nitrobenzene and MCM-41 surface.
Keywords: Nitrobenzene; Adsorption; MCM-41; Isotherm; Desorption
Adsorption studies on the removal of Vertigo Blue 49 and Orange DNA13 from aqueous solutions using carbon slurry developed from a waste material
by Vinod K. Gupta; Imran Ali; Vipin K. Saini (pp. 87-93).
Waste material (carbon slurry), from fuel oil-based generators, was used as adsorbent for the removal of two reactive dyes from synthetic textile wastewater. The study describes the results of batch experiments on removal of Vertigo Blue 49 and Orange DNA13 from synthetic textile wastewater onto activated carbon slurry. The utility of waste material in adsorbing reactive dyes from aqueous solutions has been studied as a function of contact time, temperature, pH, and initial dye concentrations by batch experiments. pH 7.0 was found suitable for maximum removal of Vertigo Blue 49 and Orange DNA13. Dye adsorption capacities of carbon slurry for the Vertigo Blue 49 and the Orange DNA13 were 11.57 and 4.54 mg g−1 adsorbent, respectively. The adsorption isotherms for both dyes were better described by the Langmuir isotherm. Thermodynamic treatment of adsorption data showed an exothermic nature of adsorption with both dyes. The dye uptake process was found to follow second-order kinetics.Effect of contact time on the adsorption of Vertigo Blue 49 and Orange DNA13 on carbon slurry (initial concentration: 100 mg L−1).
Keywords: Adsorption; Low cost adsorbent; Color removal; Kinetics; Waste treatment; Vertigo Blue 49; Orange DNA13
Calorimetric study on interaction of water-soluble copolymers with ionic surfactant
by Hu Yan; Hiroka Kawamitsu; Yoshinori Kushi; Teruaki Kuwajima; Keizo Ishii; Naoki Toshima (pp. 94-98).
Using isothermal titration microcalorimetry (ITC), we examined the aggregation behavior of water-soluble copolymers, poly(methoxypolyethylene glycol methacrylate- co-ethyl acrylate)s (PME-EA)s, with ionic surfactant, sodium dodecyl sulfate (SDS). From ITC measurements the values of critical aggregation concentration (cac) and saturation concentration (C2), the concentration at which the aggregation of the copolymers starts to form and reaches saturation, respectively, were determined. Thermodynamic parameters such asΔGagg0,ΔHagg, andTΔSagg0 of the aggregation were deduced. Results indicate that cac of the PME-EA remained constant with increase in the concentration of the copolymers, whileC2 increased linearly. On the other hand, the effect of the weight ratio of the EA unit in the copolymer was such that cac of the PME400-EA decreased, whileC2 increased with increase in the weight ratio. The results suggested that the EA units are the main binding sites of the copolymer with SDS.Using isothermal titration microcalorimetry (ITC), the aggregation behaviors of water-soluble copolymers, poly(methoxypolyethylene glycol methacrylate- co-ethyl acrylate)s (PME-EA)s, with ionic surfactant, sodium dodecylsufate (SDS) were investigated. From ITC measurements the values of critical aggregation concentration (cac) and saturation concentration (C2), respectively, were determined.
Keywords: Isothermal titration calorimetry; Hydrophobic interaction; Water-soluble polymer; Waterborne paint; Ionic surfactant
Surface plasmon resonance spectroscopy study of interfacial binding of thrombin to antithrombin DNA aptamers
by Qianjun Tang; Xiaodi Su; Kian Ping Loh (pp. 99-106).
We have applied surface plasmon resonance (SPR) spectroscopy, in combination with one-step direct binding, competition, and sandwiched assay schemes, to study thrombin binding to its DNA aptamers, with the aim to further the understanding of their interfacial binding characteristics. Using a 15-mer aptamer that binds thrombin primarily at the fibrinogen-recognition exosite as a model, we have demonstrated that introducing a DNA spacer in the aptamer enhances thrombin-binding capacity and stability, as similarly reported for hydrocarbon linkers. The bindings are aptamer surface coverage and salt concentration dependent. When free aptamers or DNA sequences complementary to the immobilized aptamer are applied after the formation of thrombin/aptamer complexes, bound thrombin is displaced to a certain extent, depending on the stability of the complexes formed under different conditions. When the 29-mer aptamer (specific to thrombin's heparin-binding exosite) is immobilized on the surface, its affinity to thrombin appears to be lower than the immobilized 15-mer aptamer, although the 29-mer aptamer is known to have a higher affinity in the solution phase. These findings underline the importance of aptamers' ability to fold into intermolecular structures and their accessibility for target capture. Using a sandwiched assay scheme followed by an additional signaling step involving biotin–streptavidin chemistry, we have observed the simultaneous binding of the 15- and 29-mer aptamers to thrombin protein at different exosites and have found that one aptamer depletes thrombin's affinity to the other when they bind together. We believe that these findings are invaluable for developing DNA aptamer-based biochips and biosensors.The assay schemes used for SPR study of interfacial binding of thrombin to antithrombin DNA aptamers: (A) One-step binding assay. (B) Competition or displacement assay. (C) Sandwich assay plus a signaling step.
Keywords: DNA aptamer; Thrombin; SPR
Adsorption mechanism and dispersion efficiency of three anionic additives [poly(acrylic acid), poly(styrene sulfonate) and HEDP] on zinc oxide
by C. Dange; T.N.T. Phan; V. André; J. Rieger; J. Persello; A. Foissy (pp. 107-115).
Adsorption on ZnO of sodium poly(acrylate) (PAA), sodium poly(styrene sulfonate) (PSS) and a monomer surfactant [hydroxyethylidene diphosphonate (HEDP)] was investigated in suspensions initially equilibrated at pH 7. Results demonstrate interplay in the adsorption mechanism between zinc complexation, salt precipitation, and ZnO dissolution. In the case of PAA, the adsorption isotherm exhibits a maximum attributed to the precipitation of zinc polyacrylate. PSS and HEDP formed high-affinity adsorption isotherms, but the plateau adsorption of HEDP was significantly lower than that of PSS. The adsorption isotherm of each additive is divided into two areas. At low additive concentration (high zinc/additive ratio), the total zinc concentration in the solution decreased and the pH increased upon addition. At a higher additive ratio, zinc concentration and pH increased with the organic concentration. The increase in pH is due to the displacement of hydroxyl ions from the surface and the increase in zinc concentration results from the dissolution of ZnO due to the complexation of zinc ions by the organics. The stability of the ZnO dispersions was investigated by measurement of the particle size distribution after addition of various amounts of polymers. The three additives stabilized the ZnO dispersions efficiently once full surface coverage was reached.Adsorption of sodium polyacrylate on ZnO exhibits a bell shape, it is also associated with a significant change of pH and dissolved zinc concentration.
Keywords: Adsorption; Zinc oxide; Poly(acrylic acid; Poly(styrene sulfonate); Hydroxyethylidene diphosphonate; Dispersion efficiency; Dissolution; Complexation
Formation and properties of composites based on microgels of a responsive polymer and TiO2 nanoparticles
by Cecil A. Coutinho; Vinay K. Gupta (pp. 116-122).
Organic–inorganic composites were prepared with titanium dioxide (TiO2) nanoparticles embedded within colloidal particles of a cross-linked, thermally responsive polymer. To promote the incorporation of unaggregated nanoparticles of TiO2, temperature responsive microspherical gels (microgels) of N-isopropylacrylamide (NIPAM) with interpenetrating (IP) linear chains of poly(acrylic acid) (PAAc) were synthesized. Dynamic light scattering (DLS) measurements revealed that these microgels reversibly shrink and swell in diameter from 300–400 nm to 600–800 nm with temperature. Two types of nanoparticles of TiO2 were immobilized within the IP-microgels—fine TiO2 nanoparticles synthesized by the hydrolysis of titanium(IV) isopropoxide and commercially available Degussa P25. Characterization of the composite was conducted using transmission electron microscopy (TEM) and UV–vis absorption spectroscopy from which it was determined that the extent of loading of the TiO2 within the colloidal particles can be easily manipulated from a low value of 10% (weight) to a value as high as 75%. The TiO2 nanoparticles were in a dispersed state within the microgels and the composites showed rapid (∼minutes) sedimentation, which is useful for gravity separations. By using turbidometry to characterize the settling behavior of the organic–inorganic composites, it was found that the settling time decreases as the content of TiO2 increases within the particles.Composite colloidal particles of inorganic nanoparticles such as TiO2 and a responsive polymeric matrix of thermally responsive microgels of PNIPAM with interpenetrating linear chains of PAA.
Keywords: Microgels; Microcomposites; Titania–polymer colloids
Surface modification for stability of nano-sized silica colloids
by Khoa N. Pham; Damian Fullston; Kwesi Sagoe-Crentsil (pp. 123-127).
The surfaces of commercial 30-nm colloidal silica particles were modified by reacting with functional silanes. The high specific surface area and reactivity of the particles due to the small size make the process susceptible to irreversible aggregation not found previously with larger particles. This study compares surface charge results from different reaction conditions and characterization methods. Measurements of the zeta potential as a function of pH and gelation kinetics shed light on the mechanism of instability in nano-sized silica suspensions. Experimental results showed that very stable particles can be suspended in a nonaqueous solvent after refluxing of the silica particles, while maintaining the original particles physical properties of size and electrochemical behavior. Extremely stable particles are obtained by aminosilane surface modification. Factors affecting susceptibility of small particles to irreversible aggregation caused by a nonaqueous solvent or a high concentration of a trialkoxysilane, including the large amount of reactive silanol groups on the surface gel layer of the particles, are discussed.The surface of nano-sized silica colloids modified with monoalkoxysilane contains a single layer of silane, whereas modification with trialkoxysilane can lead to aggregation.
Keywords: Silica; Colloids; Zeta potential; Surface charge; Surface modification; Alkoxysilane; Stability; Light scattering; Nano-size
Raman spectroscopy and DFT calculations of As(III) complexation with a cysteine-rich biomaterial
by Mônica C. Teixeira; Virgínia S.T. Ciminelli; Maria Sylvia Silva Dantas; Sirlaine F. Diniz; Hélio A. Duarte (pp. 128-134).
Arsenite adsorption onto a protein-rich biomass and, more specifically, the chemical groups involved in the uptake were investigated using Raman spectroscopy and DFT calculations. The study was based on spectroscopic analyses of raw and arsenic-loaded biomass as well as standard samples of amino acids and arsenic salts. The predominant secondary structure of the protein was identified as the β-sheet type, with some contribution from α-helix structures. The participation of sulphydryl groups from cystine/cysteine molecules during the adsorption of arsenite was demonstrated. Only the gauche–gauche–gauche (g–g–g) conformation type of the disulfide bonds was involved in arsenic complexation. The formation of a pyramidal trigonal As(HCys)3 complex was modeled according to the density functional theory (DFT). The agreement of the DFT harmonic frequencies with the RAMAN spectra of the As(HCys)3 complex demonstrated the relevant features of the cysteine-rich biomaterial regarding arsenic uptake as well as of the mechanism involved in the As(III)/biomass interaction at a molecular level. The results also illustrate that Raman spectroscopy can be successfully applied to investigate the mechanism of metal adsorption onto amorphous biomaterials.During arsenite adsorption onto a protein-rich biomass each As(III) atom reacts with three sulfur atoms from cysteine. Three water molecules are released and a pyramidal As–S complex is formed.
Keywords: Arsenite sorption; Biomaterial; Arsenite complexes; Cysteine; Raman spectroscopy; Sulphydryl; DFT calculations
Esterification reactions on the surface of layered silicate clay platelets
by V. Mittal (pp. 135-141).
Montmorillonite platelets were modified with ammonium ions of different chemical architectures in order to study the effect of ammonium ions on the extent of surface reactions with long chain fatty acids. Varying number of hydroxyl groups and the presence of octadecyl chains in the ammonium modifications were the attributes studied. The outcome of the surface esterification was analyzed by thermogravimetric studies, IR spectroscopy and wide angle X-ray diffraction. The extent of surface reaction was observed to be extremely dependent on the chemical architecture of the ammonium ion attached to the surface. Different resulting interlayer polarity and swelling of the modified clay in the solvent owing to the solvent-modification interactions led to different extents of surface esterification. In general, it was observed that increasing the number of hydroxyl groups in combination with the octadecyl chain present in the modification was successful in generating high density brushes on the clay surface which also was responsible for achieving higher basal plane spacing of the montmorillonite platelets owing to the reduction of electrostatic interactions holding them.X-ray diffractograms of montmorillonite before and after surface esterification reactions.
Keywords: Montmorillonite; Exfoliation; Surface reaction; Cation exchange capacity; Surface modification
Nanofibrous and nanotubular supports for the immobilization of metalloporphyrins as oxidation catalysts
by Shirley Nakagaki; Fernando Wypych (pp. 142-157).
Nanofibrous and nanotubular materials, natural and synthetic, are important alternative matrices for the immobilization of metallocomplexes, especially metalloporphyrins, as oxidation catalysts. The process permits a regular and controllable distribution of the active phase at the outer and/or inner surfaces of the tubes, promoting a special environment for the approximation of a substrate to the catalytic active species. The immobilization also prevents the molecular aggregation and bimolecular self-destruction reactions, facilitates the recovery and reuse of the catalyst, reduce de cost of material preparation and environmental concerns. A variety of nanofibrous and nanotubular structures are presented and specific examples of immobilization of iron porphyrins in different supports and their oxidation catalytic activities are presented and discussed.Grafting and immobilization of cationic and anionic porphyrins in zinc hydroxide nitrate (A) and a generic layered double hydroxides (B).
Keywords: Porphyrins; Immobilization; Oxidation catalysis; Fibrous and tubular matrixes
Chemiluminescence of luminol catalyzed by silver nanoparticles
by Hao Chen; Feng Gao; Rong He; Daxiang Cui (pp. 158-163).
Silver nanoparticles (AgNPs) are synthesized by chemical reduction method and characterized by UV–vis spectra, transmission electron microscopy, and high performance particle sizer. We have found that AgNPs could enhance the chemiluminescence (CL) intensity of luminol–H2O2 system. In this reaction, luminol intermediate is generated under alkaline condition on the surface of AgNPs in luminol–H2O2 system and enhances CL intensity. To validate the reaction mechanism, AgNPs are bound with thioglycolic acid (Ag–HSCH2COOH) and then joined to BSA protein (Ag–BSA). We investigate the CL intensity in the presence of Ag–HSCH2COOH or Ag–BSA comparing with that in the presence of AgNPs and conclude the catalytic reaction take place on the surface of AgNPs.The figure shows chemiluminescence spectra of silver nanoparticles of different diameters. Silver nanoparticles could enhance the chemiluminescence intensity of luminol–H2O2 system.
Keywords: Silver nanoparticles; Chemiluminescence; Luminol; Mechanism
Dehydrogenation of ethylbenzene to styrene using Pt, Mo, and Pt–Mo catalysts supported on clay nanocomposites
by Cesar Morán; Eduardo González; Jorge Sánchez; Roger Solano; Gabriela Carruyo; Alexander Moronta (pp. 164-169).
A synthetic clay (TS-1) was modified with a nonionic surfactant (IGEPAL CO-720) and magnesium oxide. The resulting solid was used as a support of Pt, Mo, and Pt–Mo catalysts. The catalysts were prepared by wet impregnation with aqueous solutions of H2PtCl6⋅6H2O and (NH4)6-Mo7O24⋅4H2O. In both monometallic and bimetallic catalysts, the molybdenum content was 3 wt% and the platinum content was 0.5 or 1 wt%. The surface area of the starting material was 454 m2/g and after the modification treatment with IGEPAL it increased up to 649 m2/g, while platinum and molybdenum catalysts showed surface areas between 495 and 550 m2/g. The reduction profiles showed different Pt and Mo species and the existence of metal–support interactions. The reduced catalysts were more active than those in the unreduced form. The most active catalysts for the ethylbenzene dehydrogenation were those of monometallic Pt (0.5 and 1 wt%) with a maximum styrene conversion around 50%. The presence of Mo species masked Pt atoms and reduced the activity.The dehydrogenation of ethylbenzene is an important reaction to produce styrene, which is the raw material to the manufacture of polystyrene. This reaction is carried out industrially several iron oxide catalysts promoted with alkaline ions, especially K+, at 600–700 °C.
Keywords: Clay nanocomposites; Ethylbenzene dehydrogenation; Pt–Mo catalysts
Direct electron transfer and bioelectrocatalysis of hemoglobin on nano-structural attapulgite clay-modified glassy carbon electrode
by Jiming Xu; Wei Li; Qifan Yin; Hui Zhong; Yulan Zhu; Litong Jin (pp. 170-176).
Direct electrochemistry of hemoglobin (Hb) on natural nano-structural attapulgite clay film-modified glassy carbon (GC) electrode was investigated. The interaction between Hb and attapulgite was examined using UV–vis, FTIR spectroscopy, and electrochemical methods. The immobilized Hb displayed a couple of well-defined and quasi-reversible redox peaks with the formal potential (E0′) of about−0.366V (versus SCE) in 0.1 M phosphate buffer solution of pH 7.0. The current was linearly dependent on the scan rate, indicating that the direct electrochemistry of Hb in that case was a surface-controlled electrode process. The formal potential changed linearly from pH 5.0 to 9.0 with a slope value of−48.2mV/pH, which suggested that a proton transfer was accompanied with each electron transfer in the electrochemical reaction. The immobilized Hb exhibited excellent electrocatalytic activity for the reduction of hydrogen peroxide without the aid of an electron mediator. The electrocatalytic response showed a linear dependence on the H2O2 concentration ranging from5.4×10−6 to4.0×10−4M with the detection of2.4×10−6M at a signal-to-noise ratio of 3. The apparent Michaelis–Menten constantKMapp for the H2O2 sensor was estimated to be 490 μM, showing a high affinity.Direct electrochemistry of hemoglobin on natural nano-structural attapulgite clay film-modified glassy carbon electrode was investigated. The interaction between Hb and attapulgite was examined using UV–vis, FTIR spectroscopy and electrochemical methods. The immobilized Hb exhibited excellent electrocatalytic activity for the reduction of hydrogen peroxide without the aid of any other reagents.
Keywords: Chemically modified electrode; Direct electron transfer; Attapulgite clay; Hemoglobin; Biosensor
Selective adsorption of mercury ion by mercaptocarboxylic acid intercalated Mg–Al layered double hydroxide
by H. Nakayama; S. Hirami; M. Tsuhako (pp. 177-183).
Intercalations of mercaptocarboxylic acid and dithiodicarboxylic acid in Mg–Al layered double hydroxide and their adsorption properties for heavy metal ions were examined. During the intercalation of mercaptocarboxylic acids, mercapto group was oxidized, and the corresponding dithiodicarboxylic acids were intercalated in the interlayer space of Mg–Al layered double hydroxide. The intercalation compounds adsorbed mercury and sliver ions effectively, whereas there was no adsorption of copper ion practically.
Keywords: Mg–Al layered double hydroxide; Intercalation; Adsorption; Mercaptocarboxylic acid; Solid-state NMR; Mercury ion
Synthesis and characterization of SBA-3, SBA-15, and SBA-1 nanostructured catalytic materials
by Oscar A. Anunziata; Andrea R. Beltramone; Maria L. Martínez; Lizandra López Belon (pp. 184-190).
A highly ordered large pore mesoporous silica molecular sieve SBA-3, SBA-15, Al-SBA-15, and SBA-1, were developed and characterized by XRD, BET, FTIR, SEM, and NMR-MAS. The catalytic materials were synthesized using different raw materials and operation conditions. These materials contain a regular arrangement of uniform channels with diameters between 1.8 and 10 nm, high specific surface area and high specific pore volume. The designed methods were effective for the synthesis, presenting each mesostructured materials, patterns of XRD and other characteristics corresponding to the reported ones in literature. The new route employed to synthesize Al-SBA-15, generates a catalyst with only aluminum in tetrahedral form, according to the data of27Al NMR-MAS. However, several reports indicated that the coordination of the Al atoms changes below the Si/Al ratio of 45, presenting peaks corresponding to penta and hexa-coordinated aluminum, which are absent in our samples (Si/Al = 50 and 33).SBA-1, SBA-3, SBA-15, and Al-SBA-15 were successfully developed by a new route. Al-SBA-15 (Si/Al, a: 50 and b: 33) posses only AlTh. The main XRD signal appears atd100, 1.2° (2 θ) shifts to 0.9°, for higher Al content.
Keywords: Synthesis; Characterization; SBA-3; SBA-15; Al-SBA-15; SBA-1
Silylated pillared clay (SPILC): A novel bentonite-based inorgano–organo composite sorbent synthesized by integration of pillaring and silylation
by Lizhong Zhu; Senlin Tian; Jianxi Zhu; Yao Shi (pp. 191-199).
This research examines the feasibility of synthesizing inorgano–organo composites based on bentonite-silylated pillared interlayered clays (SPILCs) by pre-pillaring of bentonite with the Keggin ion (hydroxyaluminum polycation) and then silylating with alkylchlorosilanes. The results of organic carbon content analysis, FTIR, XRD, and DTA/TG indicated that the silyl group can be successfully grafted to the inner surface of pillared interlayered clays (PILCs) through reaction with theOH groups of the pillars and the d-spacing of synthesized PILCs and SPILCs were almost the same. SPILCs have both the higher organic carbon content relative to original bentonite and PILCs and the better surface and pore properties relative to surfactants-modified organobentonites. A comparison of the modifier demand of SPILCs and CTMAB-bentonites indicated that the silylation of PILCs was a modifier-economized process for organically modification of bentonite. The heat-resistant temperature of SPILCs, 508 °C for OTS-Al-PILC and 214 °C for TMCS-Al-PILC, are more excellent organobentonites. Unlike the partition-predominated sorption mechanisms of organobentonites, both adsorption and partition are important components of sorption mechanism of SPILCs. The VOC sorption capacity of SPILCs is approximately same with that of organobentonites and the hydrophobicity of SPILCs is superior to that of PILCs.The mechanism for the formation of SPILCs is generally a two-step process: (1) pre-pillaring of bentonite with the Keggin ion, and (2) silylating PILC with alkylchlorosilanes.
Keywords: Pillared interlayered clay; Bentonite; Silylation; Alkylchlorosilane; Sorption
Co- and counter-current spontaneous imbibition into groups of capillary tubes with lateral connections permitting cross-flow
by E. Unsal; G. Mason; D.W. Ruth; N.R. Morrow (pp. 200-209).
A model for co- and counter-current imbibition through independent capillaries has already been developed and experiments conducted to verify the theory [E. Unsal, G. Mason, N.R. Morrow, D.W. Ruth, J. Colloid Interface Sci. 306 (2007) 105]. In this paper, the work is extended to capillaries which are connected laterally and in which cross-flow can take place. The fundamental pore geometry is a rod in an angled round-bottomed slot with a gap between the rod and a capping glass plate. The surfaces of the slot, rod and plate form capillaries and interconnecting passages which have non-axisymmetric cross-sections. Depending on the gap size either (i) a large single meniscus, (ii) two menisci one on each side of the rod, or (iii) three menisci, one between the rod and the glass additional to the ones on each side can be formed. A viscous refined oil was applied to one end of the capillaries and co-current and counter-current spontaneous imbibition experiments were performed. The opposite end was left open to the atmosphere for co-current experiments. When the gap between the rod and the plate was large, the imbibing oil advanced into the tubes with the meniscus in the largest capillary always lagging behind the two menisci in the other two smaller capillaries. For counter-current imbibition experiments the open end was sealed and connected to a sensitive pressure transducer. In some experiments, the oil imbibed into the smaller capillaries and expelled air as a series of bubbles from the end of the largest capillary. In other experiments, the oil was allowed to imbibe part way into the tubes before counter-current imbibition was started. The meniscus curvatures of the capillaries have been calculated using the Mayer and Stowe–Princen method for different cell slot angles and gap sizes using a value of zero for the contact angle. These values have been compared with actual values by measuring the capillary rise in the tubes; agreement was very close. A model for co-current and counter-current imbibition has also been developed. The significance of this model is that some hydraulic/capillary properties are common for both co-current and counter-current imbibition. The experiments give an illustration of behavior expected in a real porous material and verify the importance of the ‘perfect cross-flow’ modification to the ‘bundle of parallel tubes’ model.A model for capillaries which are connected laterally and in which cross-flow can take place is presented. Experiments were also conducted to verify the theory, and the results are given.
Keywords: Cross-flow; Co-current imbibition; Counter-current imbibition; Shape factor; Self-similar front
Design of surface properties of PET films: Effect of fluorinated block copolymers
by F. Pilati; M. Montecchi; P. Fabbri; A. Synytska; M. Messori; M. Toselli; K. Grundke; D. Pospiech (pp. 210-222).
This paper demonstrates that the addition of fluorinated block copolymers to PET solutions can be used to prepare PET films with controlled surface morphology, porosity and chemical composition, by exploiting the phenomenon known as breath figures (BF) formation during a spin-coating procedure. Surface features, such as number, depth and diameter of pores and chemical composition, can be tuned by varying the experimental conditions: relative humidity, solution composition and amount of the fluorinated block copolymer added to the PET solutions (in the range of 0.5–10 wt% with respect to PET). BF patterns are more evident at relatively high concentrations of PET (3 wt%) and content of fluorinated block copolymer (10 wt% with respect to PET) in the solution. According to the obtained results, the fluorinated block copolymer seems to play a role in different steps of the mechanism of BF formation. XPS measurements showed a surface composition much richer in fluorinated segments than expected from bulk composition. The combined surface roughness and surface segregation of fluorinated segments have only a limited effect on the macroscopic wettability of the surfaces.
Keywords: Breath figures; Surface patterning; Poly(ethylene terephthalate); Fluorinated block copolymers; Fluorine-rich surfaces; Porous surfaces
Evolving micro-structures in drying detergent pastes quantified using NMR
by J.D. Griffith; A.E. Bayly; M.L. Johns (pp. 223-229).
Magnetic resonance methods have been used to probe the evolution of the internal micro-structure of an industrially important detergent mixture, as a function of total water content. Measurements of the apparent diffusion coefficient of the water content were obtained as a function of diffusion observation time. These data were interpreted to render the surface-to-volume ratio and tortuosity of the pore space in which the water resided. Pore dimensions were found to decrease as moisture content was reduced, partially as a consequence of solute deposition. Deposition of solute material was confirmed through the application of NMRT1 relaxation measurements. These were analysed using regularisation techniques to yieldT1 population distributions. Average pore sizes as a function of water content were extracted from this data and were in good agreement with the results of the diffusion analysis.Change in the characteristic pore size of the opaque detergent paste as a function of water content.
Keywords: Drying; Diffusion; NMR; Regularisation
Synthesis of biomorphological mesoporous TiO2 templated by mimicking bamboo membrane in supercritical CO2
by Jinhong Li; Xiaoying Shi; Lijuan Wang; Fei Liu (pp. 230-236).
A new approach is presented for preparing biomorphological mesoporous TiO2 templated by mimicking bamboo inner shell membrane via supercritical CO2 (SCCO2) transportation through titanium tetrabutyloxide (TTBO). The analysis of wide-angle X-ray powder diffraction (XRD) showed the prepared TiO2 in phase of anatase, and the small-angle XRD revealed the presence of mesopores without periodicity. The product exhibited the shape of crinkled films and extended in two dimensions up to centimeters. The electron microscopic observation showed that the TiO2 films were around 200 nm in thickness, and across the films there were numerous round or ellipse-shaped mesopores, being 10–50 nm in diameter, which were formed by the close packing of TiO2 particles. High-resolution transmission electron microscope (HRTEM) displayed that the single TiO2 particle size was about 12.5 nm. The UV–vis absorption spectrum was transparent in the wavelength of 320–350 nm for suspensions of the prepared mesoporous TiO2 in ethanol at the concentration of 5.0 mg/l. The mesoporous TiO2 prepared with the aid of SCCO2 exhibited an obvious blue shift compared with the TiO2 prepared by sol–gel infiltration. The possible mechanism for the formation of the mesoporous TiO2 is summarized into a biomimetic mineralization pathway. First, TTBO was transported to the membrane surface via SCCO2, and then condensed. Hydrolysis reactions between the functional groups of organic membrane and TTBO took place to form the nuclear TiO2, and the TiO2 seeds grew around the organic membrane into TiO2 mesoporous materials. The approach provides a low-cost and efficient route for the production of ceramics nanomaterials with unique structural features, which may have potential application in designing UV-selective shielding devices [S. Zhao, X.H. Wang, S.B. Xin, Q. Jiang, X.P. Liang, Rare Metal Mater. Eng. 35 (2006) 508–510].
Keywords: Mesoporous TiO; 2; Biomorphological; Bamboo membrane; Supercritical CO; 2
Thermocapillary convection in double-layer fluid structures within a two-dimensional open cavity
by Nivedita R. Gupta; Hossein Haj-Hariri; Ali Borhan (pp. 237-247).
Thermocapillary convection within a differentially-heated open rectangular cavity containing two immiscible liquid layers is considered in the absence of gravitational effects. The temperature and flow fields in the two layers are computed using domain mapping in conjunction with a finite-difference scheme on a staggered grid. The melt–encapsulant and air–encapsulant interfaces are allowed to deform, with the contact lines pinned on the solid boundaries. The presence of a free surface at the top leads to increased convection in the encapsulant phase while retarding thermocapillary flow in the melt. The intensity of thermocapillary convection in the encapsulated layer is reduced as the viscosity of the encapsulant is increased or the thickness of the encapsulant layer is decreased. Choosing an encapsulant with a greater sensitivity of interfacial tension to temperature (as compared to that of the melt phase) can almost completely suppress thermocapillary convection in the melt. Deformations of the melt–encapsulant interface in an open cavity are found to be larger than those in a closed cavity with a rigid top surface, due to higher pressure gradients realized in the encapsulant phase. In contrast to interface deformation behavior reported earlier for a double-layer system in a closed cavity, the shape of the melt–encapsulant interface is qualitatively similar for all values of the viscosity ratio, with the interface dipping into the melt near the cold wall, and into the encapsulant near the hot wall. For the double-layers considered in this study, a free surface at the top of the encapsulant layer was found to be more effective than a rigid top in reducing the intensity of thermocapillary convection in the melt.A free surface at the top of the encapsulant layer can be more effective than a rigid top in reducing the intensity of thermocapillary convection in the melt.
Keywords: Thermocapillary flow; Marangoni stress; Interface deformation
Quartz resonator signatures under Newtonian liquid loading for initial instrument check
by Nam-Joon Cho; J. Nelson D'Amour; Johan Stalgren; Wolfgang Knoll; Kay Kanazawa; Curtis W. Frank (pp. 248-254).
The quartz crystal microbalance (QCM) has been increasingly utilized in the monitoring of the deposition of thin macromolecular films. Studies in the deposition of polymers, biomaterials, and interfacial reactions under electrochemical environment are some of the conditions for the study of these material and deposition properties at a lipid interface. Numerous studies have shown the difficulties in configuring an experimental setup for the QCM such that the recorded data reflect only the behavior of the quartz crystal and its load, and not some artifact. Such artifacts for use in liquids include mounting stress, surface properties such as hydrophobicity, surface roughness coupling to loading liquids, influence of compressional waves, and even problems with the electronic circuitry including the neglect of the quartz capacitance and the hysteretic effects of electronic components. It is thought useful to obtain a simple test by which the user could make a quick initial assessment of the instrument's performance. When a smooth quartz crystal resonator is immersed from air into a Newtonian liquid, the resonance and loss characteristics of the QCM are changed. A minimum of two experimental parameters is needed to characterize these changes. One of the changes is that of the resonant frequency. The second is characterized by either a change in the equivalent circuit resistance (Δ R) or a change in the resonance dissipation (Δ D). Two combinations of these observables, in terms of either Δ f and Δ R or Δ f and Δ D, which we define as Newtonian signatures ofS1 andS2, are calculated to have fixed values and to be independent of the harmonic and of the physical values of the Newtonian liquid. We have experimentally determined the values ofS1 andS2 using three different QCM systems. These are the standard oscillator, the network analyzer, and the QCM dissipation instrument. To test the sensitivity of these signatures to surface roughness, which is potential experimental artifact, we determined the values ofS1 andS2 for roughened crystals and found that these signatures do reflect that experimental condition. Moreover, these results were qualitatively in accord with the roughness scaling factor described by Martin.The topography of crystals was measured by AFM that had roughness of ∼2, ∼300, and∼600nm, respectively.
Keywords: Quartz crystal microbalance (QCM); Newtonian liquid; Newtonian signatures; Atomic force microscope (AFM)
Dynamics of liquid penetration into capillary tubes
by R. Chebbi (pp. 255-260).
The dynamics of penetration is considered in the case where inertia effects are small. The effect of the contact line speed on the dynamic contact angle is taken into consideration. Analytical solutions are obtained for short and large times, and are found to cover together most of the time domain. The results obtained numerically show good agreement with the asymptotic solutions. The large-time solutions are valid in the case of penetration into horizontal capillaries. The large-time asymptotic solution shows a correction term compared to the Lucas–Washburn equation, which is found to be a limiting case valid for very large times (horizontal capillaries case). The analysis shows how to include gravity effects in the case of penetration into vertical tubes. Excellent agreement is found with available published experimental data.Analytical solutions are obtained for short and large times, along with numerical solutions showing excellent agreement with experimental data, and deviations from the Lucas–Washburn equation.
Keywords: Liquid penetration; Porous medium; Dynamics; Dynamic contact angle; Lucas–Washburn equation; Imbibition; Capillary tube; Washburn equation
Surface potential and resistance measurements for detecting wear of chemically-bonded and unbonded molecularly-thick perfluoropolyether lubricant films using atomic force microscopy
by Manuel Palacio; Bharat Bhushan (pp. 261-269).
The wear of perfluoropolyether (PFPE) lubricants applied on Si(100) and an Au film on Si(100) substrate at ultralow loads was investigated by using atomic force microscopy (AFM)-based surface potential and resistance measurements. Surface potential data is used in detecting lubricant removal and the initiation of wear on the silicon substrate. The surface potential change is attributed to the change in the work function of the silicon after wear, and electrostatic charge build-up of debris in the lubricant. It was found that coatings that are partially bonded, i.e., containing a mobile lubricant fraction, were better able to protect the silicon substrate from wear compared to the fully bonded coating. This enhanced protection is attributed to a lubricant replenishment mechanism. However, an untreated lubricant coating exhibited considerable wear as it contains a smaller amount of lubricant bonded to the substrate relative to the partially bonded and fully bonded coatings. A sample subjected to shear is shown to have improved wear resistance, and this enhancement is attributed to chain reorientation and alignment of the lubricant molecules. The detection of wear of PFPE lubricants on Au by an AFM-based resistance measurement method is demonstrated for the first time. This technique provides complementary information to surface potential data in detecting substrate exposure after wear and is a promising method for studying the wear of conducting films.The wear of perfluoropolyether (PFPE) lubricants applied on Si(100) and a Au film on Si(100) substrate at ultralow loads was investigated by using atomic force microscopy (AFM)-based surface potential and resistance measurements. Surface potential data is used in detecting lubricant removal and the initiation of wear on the silicon substrate. The detection of wear of PFPE lubricants on Au by an AFM-based resistance measurement method is demonstrated for the first time.
Keywords: Wear; Perfluoropolyethers; Lubricants; Surface potential; Atomic force microscopy; Kelvin probe microscopy; Contact resistance
Interfacial properties of colloid–polymer mixtures
by Joris Kuipers; Edgar M. Blokhuis (pp. 270-277).
Density functional theory and a virial approach are used to calculate the surface tension and bending rigidity of the interface between demixed fluid phases for a colloid–polymer mixture. The calculated surface tension compares well with results from computers simulations and experiments. The bending rigidity obtained from both theoretical approaches is negative (≈−0.1kBT), its magnitude increases away from the critical point and it is in reasonable agreement with computer simulations.The surface tension and bending rigidity(k) are calculated using density functional theory and a virial approach. Our calculations are compared with computer simulations and experiments.
Keywords: Colloid–polymer mixture; Surface tension; Bending rigidity; Squared-gradient model; Capillary wave theory
Molecular organization of a water-insoluble iridium(III) complex in mixed monolayers
by Juan J. Giner-Casares; Marta Pérez-Morales; Henk J. Bolink; Eulogia Muñoz; Gustavo de Miguel; María T. Martín-Romero; Luis Camacho (pp. 278-286).
In this work, organized mixed monolayers containing a cationic water-insoluble iridium(III) complex, Ir-dye, [Ir(ppy)2(tmphen)]PF6, (tmphen = 3,4,7,8-tetramethyl-1,10-phenanthroline, and ppy = 2-phenylpyridine), and an anionic lipid matrix, DMPA, dimyristoyl-phosphatidic acid, with different molar proportions, were formed by the co-spreading method at the air–water interface. The presence of the dye at the interface, as well as the molecular organization of the mixed films, is deduced from surface techniques such asπ–A isotherms, Brewster angle microscopy (BAM) and reflection spectroscopy. The results obtained remark the formation of an equimolar mixed film, Ir-dye/DMPA = 1:1. BAM images reveal a whole homogeneous monolayer, with gradually increasing reflectivity along the compression process up to reaching the collapse of this equimolecular monolayer atπ≈37mNm−1. Increasing the molar ratio of DMPA in the mixture, the excess of lipid molecules organizes themselves forming dark flower-like domains of pure DMPA at high surface pressures, coexisting with the mixed Ir-dye/DMPA = 1:1 monolayer. On the other hand, unstable mixed monolayers are obtained by using an initial dye surface concentration higher than the equimolecular one. These mixed Langmuir monolayers have been successfully transferred onto solid substrates by the LB (Langmuir–Blodgett) technique.In mixed Ir-dye/DMPA=1:x films (withx>1), the excess of lipid molecules is segregated with increasing surface pressure. Dark and bright phases are related to pure DMPA and Ir-dye/DMPA regions, respectively.
Keywords: Air–water interface; Langmuir–Blodgett films; Brewster angle microscopy; Reflection–absorption spectroscopy; FTIR spectroscopy; Transition metal complex
Hydroxyapatite nanoparticles as stimulus-responsive particulate emulsifiers and building block for porous materials
by Syuji Fujii; Masahiro Okada; Tsutomu Furuzono (pp. 287-296).
Hydroxyapatite (HAp) nanoparticles with spherical, rod-shaped or fiber-shaped morphologies were synthesized by wet chemical method in aqueous media. Scanning electron microscopy, dynamic light scattering, helium pycnometry, and aqueous electrophoresis techniques were used to characterize the nanoparticles in terms of their particle size and morphology, density and zeta potential, respectively. Stable “Pickering-type” emulsions were prepared using the HAp nanoparticles as a particulate emulsifier and methyl myristate as an oil phase above pH 7.7, but not below pH 6.1. These emulsions were characterized in terms of their emulsion type, mean droplet diameter and morphology using electrical conductivity, light diffraction and optical microscopy. Rapid demulsification could be induced by lowering the solution pH: addition of acid led to dissolution of the HAp nanoparticles attached on oil–water interface and the emulsion was destabilized. HAp nanoparticles precipitated by addition of base to the aqueous phase after demulsification and the HAp particles precipitated worked as an effective particulate emulsifier. This emulsification–demulsification cycle was reversible. Sintering of methyl myristate-in-water emulsion stabilized with the HAp nanoparticles led to a porous HAp material.Hydroxyapatite nanoparticles were used as a pH-responsive particulate emulsifier in order to stabilize “Pickering-type” oil-in-water emulsions. The emulsification–demulsification cycle was reversible by changing the solution pH.
Keywords: Hydroxyapatite; Nanoparticle; Pickering emulsion; Stimulus-responsive; Emulsification; Demulsification; Porous material
Timolol transport from microemulsions trapped in HEMA gels
by Chi-Chung Li; Michael Abrahamson; Yash Kapoor; Anuj Chauhan (pp. 297-306).
Approximately 90% of all ophthalmic drug formulations are now applied as eye-drops. While eye-drops are convenient and well accepted by patients, about 95% of the drug contained in the drops is lost due to absorption through the conjunctiva or through the tear drainage. A major fraction of the drug eventually enters the blood stream and may cause side effects [J.C. Lang, Adv. Drug Delivery Rev. 16 (1995) 39–43; C. Bourlais, L. Acar, H. Zia, P.A. Sado, T. Needham, R. Leverge, Prog. Retinal Eye Res. 17 (1998) 33–58; M.P. Segal, FDA Consumer Mag. (1991)]. The drug loss and the side effects can be minimized by using microemulsion-laden soft contact lenses for ophthalmic drug delivery [D. Gulsen, A. Chauhan, Invest. Ophthalmol. Vis. Sci. 45 (2004) 2342–2347; D. Gulsen, A. Chauhan, Abstr. Pap. Am. Chem. Soc. 227 (2004) U875]. In order for microemulsion-laden gels to be effective, these should load sufficient quantities of drug and should release it a controlled manner. The presence of a tightly packed surfactant at the oil–water interface of microemulsions may provide barrier to drug transport, and this could be used to control the drug delivery rates. In this paper we focus on trapping ethyl butyrate in water microemulsions stabilized by Pluronic F127 surfactant in 2-hydroxyethyl methacrylate (HEMA) gels and measuring the transport rates of timolol, which is a beta-blocker drug that is used for treating a variety of diseases including glaucoma. The results described here show that microemulsion-laden gels could have high drug loadings, particularly for drugs such as timolol base which can either be dissolved in the oil phase or form the oil phase of the microemulsions. However, the surfactant covered interface of the Pluronic microemulsions does not provide sufficient barrier to impede the transport of timolol, perhaps due to the small size of this drug.Pseudo-phase diagram for the six component (ethyl butyrate oil), water+HEMA+NaCl+NaOH (continuous phase) and Pluronic F127 (surfactant) microemulsion at 5.3 °C.
Keywords: Hydrogel; Microemulsions; Transport; Timolol; Pluronic
Effect of long-chain alcohols on SDS partitioning to the oil/water interface of emulsions and on droplet size
by Monica A. James-Smith; Kile Alford; Dinesh O. Shah (pp. 307-312).
The effect of long-chain alcohols (C nOH forn=8, 10, 12, 14, 16, 18) on the partitioning of sodium dodecyl sulfate (SDS) to the oil/water interface in oil-in-water macroemulsions was investigated and related to emulsion droplet size and total interfacial area (TIA) contributed by SDS. Alcohols were solubilized in hexadecane and emulsified in SDS solutions. Ultrafiltration was carried out in centrifuge tubes having nanoporous filters with a 30,000 molecular weight cutoff (MWCO), so that emulsion droplets would not pass through, and only SDS that is in the bulk water phase as monomers or micelles (i.e., not at the interface) could pass through. The results showed a chain-length compatibility effect; the maximum amount of SDS partitioned to the interface when dodecanol (C12OH) was added to the oil. The results also showed that partitioning of SDS is affected only when dodecanol is added. All other alcohols had no significant influence on SDS partitioning to the oil/water interface. Droplet size measurements revealed a minimum in droplet size for emulsions with added C12OH. In order to explain the results, it was proposed that the penetration of alcohol molecules into the interfacial film occur at the interface, resulting in more cohesive molecular packing at the interface, and the minimum droplet size and maximum partitioning of SDS at the oil/water interface for C12OH/SDS emulsion system. The TIA provided by the SDS molecules, as determined from our ultrafiltration method, was two orders of magnitude greater than that calculated from the droplet size measured by light scattering. Possible explanations for this disparity are discussed.Effect of alcohol chain length on the amount of SDS that partitions to the interface of hexadecane-in-water emulsions with added alcohol.
Keywords: Chain-length compatibility; Oil-in-water emulsion; Long-chain alcohols; Total interfacial area provided by SDS molecules; Ultrafiltration; SDS partitioning at the oil/water interface; Droplet size; Light scattering
Does SDS micellize under methane hydrate-forming conditions below the normal Krafft point?
by J.S. Zhang; S. Lee; Jae W. Lee (pp. 313-318).
Sodium dodecyl sulfate (SDS) can accelerate nucleation and growth of gas hydrates in a quiescent system. The objective of this paper is to investigate whether or not SDS micelles form in the meta-stable region of methane hydrates by the direct measurement of aqueous SDS concentration. The SDS solubility in water with high-pressure methane is identical to that under atmospheric pressure at a temperature range of 270–282 K; thus, the Krafft point under these methane hydrate-forming conditions does not shift from the normal Krafft point (281–289 K) under atmospheric pressure. The mole fraction of methane in SDS solution is independent of aqueous SDS concentration at a hydrate-forming condition. These results suggest that at temperatures below the normal Krafft point, no SDS micelles are present in the aqueous phase even in a high-pressure methane environment.Aqueous SDS concentrations at 275 K and under two methane pressures (left) and SDS solubility in liquid water near methane hydrate-forming conditions (thePexp/Pdiss ratio ranges from 1.0 to 1.7) and under atmospheric pressure (right).
Keywords: SDS; Krafft point; Micelles; Methane hydrates
Surface conservation laws at microscopically diffuse interfaces
by Kevin T. Chu; Martin Z. Bazant (pp. 319-329).
In studies of interfaces with dynamic chemical composition, bulk and interfacial quantities are often coupled via surface conservation laws of excess surface quantities. While this approach is easily justified for microscopically sharp interfaces, its applicability in the context of microscopically diffuse interfaces is less theoretically well-established. Furthermore, surface conservation laws (and interfacial models in general) are often derived phenomenologically rather than systematically. In this article, we first provide a mathematically rigorous justification for surface conservation laws at diffuse interfaces based on an asymptotic analysis of transport processes in the boundary layer and derive general formulae for the surface and normal fluxes that appear in surface conservation laws. Next, we use nonequilibrium thermodynamics to formulate surface conservation laws in terms of chemical potentials and provide a method for systematically deriving the structure of the interfacial layer. Finally, we derive surface conservation laws for a few examples from diffusive and electrochemical transport.
Keywords: Surface conservation laws; Transport theory; Interface structure; Asymptotic analysis
Effect of temperature on the rheology of wormlike micelles in a mixed surfactant system
by Durga P. Acharya; Dharmesh Varade; Kenji Aramaki (pp. 330-336).
The formation and rheological behavior of a viscoelastic wormlike micellar solution in an aqueous solution of a mixed surfactant system of alkyl ethoxylate sulfate (AES), C12H25(OCH2CH2)3OSO−3Na+, and polyoxyethylene dodecyl ether, C12EO3, and the unusual effect of temperature on the rheological behavior have been studied. Upon successive addition of C12EO3 to the dilute micellar solution of AES, viscosity increases swiftly and reaches its peak where a viscoelastic solution with nearly Maxwellian behavior is formed. With the further addition of C12EO3, viscosity decreases sharply, which is attributed to the formation of micellar joints. With increasing temperature, the extent of micellar growth increases and the viscosity maximum is achieved at a lower mixing fraction of C12EO3, but the maximum viscosity attained by the system decreases. The evolution of relaxation time and network density of the viscoelastic network also suggests that with increasing temperature, enhanced micellar growth takes place, but an additional, faster relaxation mechanism becomes increasingly favorable at high concentrations of C12EO3. These results can be explained in terms of the increase in free energy of hemispherical end-caps (end-cap energy) of the micelles with increasing temperature.Upon successive addition of trioxyethylene dodecyl ether (C12EO3) to the dilute solution of alkyl ethoxylate sulfate (AES), viscosity increases swiftly and reaches its peak. Enhanced micellar growth takes place with the increase in temperature.
Keywords: Alkyl ethoxylate sulfate; Rheology; Wormlike micelles; Viscoelasticity
Presence of negative charge on the basal planes of New York talc
by E. Burdukova; M. Becker; D.J. Bradshaw; J.S. Laskowski (pp. 337-342).
Potentiometric titration measurements as well as rheological measurements of talc aqueous suspensions indicate that the behavior of the New York talc particles is consistent with the presence of a negative charge on their basal planes. The possibility of the presence of a negative electrical charge on the basal planes of talc particles is analyzed in this paper. Samples of New York talc were studied using electron microprobe analysis and dehydration techniques and the exact chemical formula of New York talc was determined. It was found that there exists a deficiency of protons in the tetrahedral layers of talc, resulting from substitution of Si4+ ions with Al3+ and Ti3+ ions. The comparison of the level of substitution of Si4+ ions with ions of a lower valency was found to be of a similar order of magnitude as that found in other talc deposits. This strongly points to the presence of a negative charge on the talc basal planes.Substitution of Si4+ ions with Al3+ and Ti3+ ions in the tetrahedral layers of New York talc causes the basal planes to carry a negative charge. The charge is sufficient to affect the behaviour of talc in suspension.
Keywords: Talc; Basal planes; Surface charge; Substitution; Point of zero charge; Isoelectric point
Boundary effects on electrophoresis of a colloidal cylinder with a nonuniform zeta potential distribution
by Tzu H. Hsieh; Huan J. Keh (pp. 343-354).
The electrophoretic motion of a long dielectric circular cylinder with a general angular distribution of its surface potential under a transversely imposed electric field in the vicinity of a large plane wall parallel to its axis is analyzed. The thickness of the electric double layers adjacent to the solid surfaces is assumed to be much smaller than the particle radius and the gap width between the surfaces, but the applied electric field can be either perpendicular or parallel to the plane wall. The presence of the confining wall causes three basic effects on the particle velocity: (1) the local electric field on the particle surface is enhanced or reduced by the wall; (2) the wall increases viscous retardation of the moving particle; (3) an electroosmotic flow of the suspending fluid may exist due to the interaction between the charged wall and the tangentially imposed electric field. Through the use of cylindrical bipolar coordinates, the Laplace and Stokes equations are solved analytically for the two-dimensional electric potential and velocity fields, respectively, in the fluid phase, and explicit formulas for the quasisteady electrophoretic and angular velocities of the cylindrical particle are obtained. To apply these formulas, one has only to calculate the multipole moments of the zeta potential distribution at the particle surface. It is found that the existence of a plane wall near a nonuniformly charged particle can cause its translation or rotation which does not occur in an unbounded fluid with the same applied electric field.The electrophoretic motion of a long circular cylinder with a general angular distribution of its surface potential in the vicinity of a large plane wall parallel to its axis is analyzed in two fundamental cases: transverse electric fields applied normal to a conducting plane and parallel to a dielectric plane.
Keywords: Electrophoresis; Nonuniform zeta potential distribution; Circular cylindrical particle; Plane wall; Boundary effect
Dynamic Monte Carlo simulation of aggregation of nanoparticles in the presence of diblock copolymer
by Jianhua Huang; Dachuan Sun (pp. 355-362).
The aggregation of hydrophobic nanoparticles in the presence of diblock copolymers is investigated using dynamic Monte Carlo simulation on a simple cubic lattice. One nanoparticle occupies one lattice site, one block copolymer (A mB m) occupies 2 m sequentially linked sites with m segments of A and m segments of B, and solvents are represented by any unoccupied sites. All of them are self-avoiding and nearest-neighbor interactions are considered. A compact big aggregate, dispersed aggregates wrapped by polymer chains, and an ordered lamellar structure are obtained by varying the concentration of copolymer. The structures are seen to be controlled by competing forces between the interaction of copolymer with nanoparticles and the self-assembly of copolymer in solution. The critical concentration of copolymer needed to form the lamellar structure,Cp,L, decreases with the chain length. It is also found thatCp,L decreases roughly linearly with the concentration of nanoparticlesCn, which can be approximately expressed asCp,L=0.764–0.857Cn whenm=2. The simulation demonstrates that addition of diblock copolymer can effectively control the aggregation of nanoparticles and lead to the formation of a variety of nanostructures.The aggregation of hydrophobic nanoparticles in the presence of diblock copolymers A2B2 is investigated using dynamic Monte Carlo simulation on a simple cubic lattice. Nanoparticles form a large aggregate at low concentration of copolymerCp=0.02 (a) and they form a lamellar structure at high concentrationCp=0.7 (b). Gray beads represent nanoparticles; red and green beads represent A and B blocks of copolymer, respectively.
Keywords: Diblock copolymer; Nanoparticle; Dynamic Monte Carlo simulation
Bifunctional Au@Pt hybrid nanorods
by Shaojun Guo; Liang Wang; Yuling Wang; Youxing Fang; Erkang Wang (pp. 363-368).
The controlled synthesis of bifunctional Au@Pt hybrid nanorods has been realized through a simple wet chemical approach. Transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and UV–vis–near infrared spectroscopy (UV–vis–NIR) were employed to characterize the obtained hybrid nanorods. TEM results indicate that the thickness of Pt nanoislands on the surfaces of gold nanorods can be easily tunable via controlling the molar ratio of Au nanorods to the H2PtCl6. These Au@Pt hybrid nanorods have dual functions, which can be used not only for surface enhanced Raman spectroscopy (SERS), but also to exhibit good catalytic activity for O2 reduction. It is expected that these hybrid nanorods can be used as new functional building blocks to assemble novel three-dimensional (3D) complex multicomponent nanostructures, which are believed to be useful for electrochemical nanodevices.The controlled synthesis of bifunctional Au@Pt hybrid nanorods has been realized through a simple wet chemical approach. These Au@Pt hybrid nanorods have dual functions, which can be used not only for surface-enhanced Raman spectroscopy (SERS), but also to exhibit good catalytic activity for O2 reduction. It is expected that these hybrid nanorods can be used as new functional building blocks to assemble novel three-dimensional (3D) complex multicomponent nanostructures, which are believed to be useful for the electrochemical nanodevices.
Keywords: Gold nanorod; Catalysis; SERS; Hybrid material; Platinum nanoparticle
Temporal evolution of composition and crystal structure of cobalt hexacyanoferrate nano-polymers synthesized in reversed micelles
by Mami Yamada; Takuya Sato; Mikio Miyake; Yoshio Kobayashi (pp. 369-375).
Nanometer-size metal coordination polymers are fascinating to explore, since their unique properties are controlled by a large ratio of surface atoms, which is an entirely different effect from that in a bulk crystal. In this report, we have demonstrated the reaction time-induced structural conversion of nanometer-sized metal coordination nano-polymers (MCNPs). The MCNP selected here was a Prussian blue analogue, cobalt hexacyanoferrate (Fe-CN-Co) with ca. 3 nm. When Fe-CN-Co MCNPs were synthesized in reverse micelles of cationic surfactants, cetyltrimethylammonium halides [CTAX, X=B (bromide), C (chloride)], their color dramatically changed from red to green with increasing the reaction time. We investigated the mechanism of this characteristic color change using XRD, FT-IR, UV–vis spectra, CHN elemental analyses, ICP, and TGA, which indicated that the coordination geometry of CoII ions was changed from a 6-coordinate octahedral (Oh) to a 4-coordinate tetrahedral (Td) with clear crystal distortion. The magnetic behavior of the prepared Fe-CN-Co MCNPs was also reaction-time dependent, as illustrated by SQUID and 57Fe Mössbauer spectra.We have demonstrated the reaction time-induced structural conversion of a nanometer-sized cobalt hexacyanoferrate accompanied by the dramatic change of the material color and the magnetic behavior.
Keywords: Nanoparticle; Metal coordination polymer; Reverse micelle; Crystal; Magnetization
Formation mechanism of supramolecular hydrogels in the presence ofl-phenylalanine derivative as a hydrogelator
by Xinjian Fu; Ningxia Wang; Shengzu Zhang; Hong Wang; Yajiang Yang (pp. 376-381).
A novel chiral hydrogelator,l-phenylalanine derivative can self-assemble in aqueous media at different pH values to form supramolecular hydrogels. The images of the FE-SEM indicate that different aggregates of TC18PheBu in morphology were formed, which further lead to the formation of spherical crystallites as observed by polarized optical microscope (POM). The FT-IR spectra of the supramolecular hydrogels reveal that intermolecular hydrogen-bonding and hydrophobic interactions are the driving forces for the self-assembly of TC18PheBu. Fluorescence spectra of TC18PheBu in aqueous solutions in the presence of pyrene as a probe further confirm the importance of hydrophobic interactions for the self-assembly. The circular dichroism (CD) spectra of TC18PheBu in supramolecular hydrogels in the presence of KF indicate that the hydrogen-bonding interaction can be disrupted by fluoride ions, which further confirm the importance of hydrogen bonding for the self-assembly of TC18PheBu.A novel chiral hydrogelator,l-phenylalanine derivative (TC18PheBu) can self-assemble in aqueous media to form supramolecular hydrogels. Investigation of the formation mechanism of the supramolecular hydrogel indicates that hydrogen bonding and hydrophobic interactions are driving forces through the characterization of POM, FT-IR, fluorescence, and CD.
Keywords: l; -Phenylalanine derivatives; Hydrogelator; Supramolecular hydrogels
Preparation of Ce–TiO2 catalysts by controlled hydrolysis of titanium alkoxide based on esterification reaction and study on its photocatalytic activity
by Tianzhong Tong; Jinlong Zhang; Baozhu Tian; Feng Chen; Dannong He; Masakazu Anpo (pp. 382-388).
The Ce–TiO2 catalysts were prepared by controlled hydrolysis of Ti(OC4H9)4 with water generated “in situ” via an esterification reaction between acetic acid and ethanol, followed by hydrothermal treatment. The samples were characterized by X-ray diffraction (XRD), UV–vis diffuse reflectance spectroscopy (DRS), scanning electron microscopy (SEM), atomic absorption flame emission spectroscopy (AAS), and nitrogen adsorption–desorption methods. Both of undoped TiO2 and Ce–TiO2 samples exclusively consist of primary anatase crystallites, which further form spherical aggregates with diameters ranging from 100 to 500 nm. The photocatalytic activity of Ce–TiO2 was investigated for the photocatalytic degradation of Rhodamine B (RB) aqueous solution both under UV and visible light irradiation. Doping of Ce4+ effectively improves the photocatalytic activity under both UV light irradiation and visible light irradiation with an optimal doping concentration of 0.2 and 0.4%, respectively. The photocatalytic mechanisms of Ce–TiO2 catalysts were tentatively discussed.
Keywords: Titanium dioxide; Photodegradation; Esterification reaction; Visible light; Ce; 4+; doping
A versatile strategy to fabricate hydrogel–silver nanocomposites and investigation of their antimicrobial activity
by V. Thomas; Murali Mohan Yallapu; B. Sreedhar; S.K. Bajpai (pp. 389-395).
In this study, hydrogel–silver nanocomposites have been synthesized by a unique methodology, which involves formation of silver nanoparticles within swollen poly (acrylamide- co-acrylic acid) hydrogels. The formation of silver nanoparticles was confirmed by transmission electron microscopy (TEM) and surface plasmon resonance (SPR) which was obtained at 406 nm. The TEM of hydrogel–silver nanocomposites showed almost uniform distribution of nanoparticles throughout the gel networks. Most of the particles, as revealed from the particle-size distribution curve, were 24–30 nm in size. The X-ray diffraction pattern also confirmed the face centered cubic (fcc) structure of silver nanoparticles. The nanocomposites demonstrated excellent antibacterial effects on Escherichia coli (E. coli). The antibacterial activity depended on size of the nanocomposites, amount of silver nanoparticles, and amount of monomer acid present within the hydrogel–silver nanocomposites. It was also found that immersion of plain hydrogel in 20 mg/30 ml AgNO3 solution yielded nanocomparticle–hydrogel composites with optimum bactericidal activity.We designed a facile in situ methodology for hydrogel–silver nanocomposites in which the formation of silver nanoparticles was found to be throughout the gel networks. The formed nanoparticles in the gel are 24–30 nm in size. The formation of nanosilver particles was confirmed by spectral and electronic microscopic techniques. The developed hydrogel–silver nanocomposites demonstrated excellent antibacterial effects on Escherichia coli.
Keywords: Hydrogel; Silver nanoparticles; Surface plasmon resonance; Nanocomposites; E. coli; Transmission electron microscopy; Silver nitrate; Antibacterial activity; Scanning electron microscopy; Colony-forming unit
Effects of hydrogen peroxide on the electrochemical decomposition of layer-by-layer thin films composed of 2-iminobiotin-labeled poly(ethyleneimine) and avidin
by Katsuhiko Sato; Yukihisa Naka; J. Jun-ichi Anzai (pp. 396-399).
The effects of hydrogen peroxide on the electrochemical decomposition of layer-by-layer thin films composed of 2-iminobiotin-labeled poly(ethyleneimine) (ib-PEI) and avidin were studied. An ib-PEI/avidin thin film prepared on the surface of a platinum (Pt) film-coated quartz resonator was electrochemically decomposed in the presence of hydrogen peroxide (H2O2) in the solution. The resonant frequency of the thin-film-deposited quartz resonator was increased upon application of electric potential (0.4–0.6 V vs Ag/AgCl) to the Pt layer, suggesting that the mass on the quartz resonator was decreased as a result of decomposition of the ib-PEI/avidin film. It was found that decomposition of the film is highly accelerated in the presence of H2O2 compared to the decomposition in the same buffer solution without H2O2, due to a pH change originating from electrochemical oxidation of H2O2 on the Pt surface. The rate of electrochemical decomposition of the ib-PEI/avidin film was highly dependent on the concentration of H2O2, buffer capacity, and pH of the solution.
Keywords: LbL thin film; Layered film; Avidin; Electrochemical decomposition; Quartz crystal microbalance
Reactive two-dimensional layered material with regular chlorine groups
by Ken Yao; Ying Fu; Liyi Shi; Wen Wan; Xiaoqing You; Futao Yu (pp. 400-404).
A novel reactive layered two-dimensional molecular space material [layered chloroacetamide phenyl silica (CAAPhS)] with regular chlorine groups was synthesized by grafting chlorine groups into the layer structure of layered aminophenyl silica. The reactive activity of chlorine groups regularly arranged in the layer structure of layered CAAPhS was confirmed through a substitution reaction with n-butylamine. Layered CAAPhS showed potential as a starting material for the formation of a series of two-dimensional layered materials with various regular functional molecules and organic–inorganic composite materials.
Keywords: Two-dimensional layered materials; Regular chlorine groups; Regular functional groups
by Arthur Hubbard (pp. 405-405).