Journal of Colloid And Interface Science (v.357, #2)
Cement: A two thousand year old nano-colloid
by Francesca Ridi; Emiliano Fratini; Piero Baglioni (pp. 255-264).
Cement has been in use for over two thousand years and systematically studied for over a century. Still, a full comprehension of its atomic arrangement and nanostructure is far from being complete.Display Omitted► Cement: the oldest nanomaterial. ► The mechanisms underling the hydration process of cement: water plays a central role. ► Organic polymers affect properties of cement. ► Cement properties depend on its nano and microstructure.Since Roman times, cement is one of the synthetic materials with the largest production and usage by mankind. Its properties allowed the expansion of the Roman Empire and the building of still fascinating works. In spite of the diverse use of cement and the abundant literature accumulated during a century of systematic scientific research on this material, the understanding of its properties is still far from complete. Several issues are still open, ranging from the understanding of the hydration kinetics and the influence of the modern industrial additives, to the deep comprehension of the atomic arrangement and nanostructure of disordered hydrated calcium silicate phase (C–S–H) formed by hydration. This feature article briefly summarizes recent results in the field, highlighting the necessity for a colloidal model of the cement microstructure that, combined with the layer-like structure of the colloidal units, is the most effective approach to fully describe the characteristics of this peculiar material.
Keywords: Cement; C–S–H phase; Nano structure of cement; Alite; Belite; Aluminate; Superplasticizers; Colloidal model; QENS; Calorimetry; NIR
Optical sensing quantum dot-labeled polyacrolein particles prepared by layer-by-layer deposition technique
by Alla N. Generalova; Vladimir A. Oleinikov; Margarita M. Zarifullina; Ekaterina V. Lankina; Svetlana V. Sizova; Michail V. Artemyev; Vitali P. Zubov (pp. 265-272).
Tailored QD loading as a part of polyelectrolyte layers makes it possible to design polymer particles with pH-dependent fluorescence intensity and use these particles for sensitive and selective detection of copper(II) ion.Display Omitted► Fluorescent polymer particles are prepared by LbL technique. ► Close to surface QD deposition results in pH-sensitivity of particle fluorescence. ► Bioligands as outermost shell determine the fluorescence properties of particles. ► The outer shell of BSA allows the particle design for detection of Cu(II) ion.Optical sensing polymer particles with tailored semiconductor nanocrystal (QD) loading are prepared by layer-by-layer deposition technique (LbL). Polyacrolein particles of 1.2μm diameter are used as solid support for deposition of hydrophilic CdSe/ZnS nanocrystal/polyelectrolyte multilayers formed by electrostatic interactions. The pH-dependent fluorescence of QDs and pH-dependent conformations of polyelectrolytes, which likely passivate the surface state of nanocrystals, allow a creation of both mono- and multiplex coded polymer particles with pH-dependent fluorescence intensity. Bovine serum albumin (BSA) as outermost layer makes it possible to design the optical sensing polymer particles with reversibly responded fluorescence at pH variations. The fluorescence of such polymer particles with BSA outer layer is sensitive to copper(II) ion while the fluorescence of these particles is practically insensitive to the other divalent cations (Zn2+, Ca2+, Ba2+, Co2+, Mg2+). The detection limit of Cu2+ is about 15nM. Adaptation of LbL method to prepare QD-labeled polymer particles with enhanced complexity (e.g. several types of QDs, multiple biofunctionality) is expected to open new opportunities in biotechnological applications.
Keywords: Polyelectrolytes; Polyacrolein particles; Quantum dots; pH-sensitivity; Copper(II) detection
Enhancing the hydrophilic and antifouling properties of polypropylene nonwoven fabric membranes by the grafting of poly( N-vinyl-2-pyrrolidone) via the ATRP method
by Chanchan Wang; Ranran Feng; Fenglin Yang (pp. 273-279).
SEM images of membrane samples: (a–c) PNVP-modified membranes with 0, 2, and 4h grafting time, respectively.Display Omitted► Hydrophilic polymer poly(N-vinyl-2-pyrrolidone) (PNVP) was successfully grafted on the surfaces of polypropylene NWF membranes by atom-transfer radical polymerization. ► The modified membranes became more hydrophilic after the introduction of PNVP. ► The modified membranes had better antifouling properties than the original NWF membrane. ► The bacterial adhesion was suppressed largely after the introduction of PNVP.In this work, the surface characteristics of poly( N-vinyl-2-pyrrolidone) (PNVP)-modified nonwoven fabric (NWF) membranes and the effects of the surface characteristics on the membranes antifouling properties were investigated. Effects of grafting time, grafting temperature, and monomer concentration on the grafting degree of PNVP were systematically investigated. The effect of grafting degree on the surface characteristics was also investigated. Scanning electron microscopy (SEM) was used to characterize the structural and morphological changes on the membrane surface. The water contact angles decreased from 113±1.2° to 52±3°, which means that the hydrophilicity of the modified NWF was enhanced with increasing PNVP grafting degree. The surface free energy was calculated, which showed an increase after modification. Static bovine serum albumin (BSA) adsorption experiments were carried out, which showed a decrease of 82.5%. Permeation experiments of water and supernatant solution of active sludge were carried out to determine the antifouling characteristics against the extracellular polymeric substance. Results demonstrated that the modified NWF had higher permeation fluxes and lower flux loss in comparison with the original NWF. Bacterial adhesion on the membrane surface was largely suppressed after the introduction of PNVP.
Keywords: Nonwoven membrane; Atom-transfer radical polymerization (ATRP); Poly(; N; -vinyl-2-pyrrolidone); Hydrophilicity; Antifouling property; Bacterial adhesion
Luminescent, mesoporous, and bioactive europium-doped calcium silicate (MCS: Eu3+) as a drug carrier
by Yong Fan; Shanshan Huang; Jinhua Jiang; Guogang Li; Piaoping Yang; Hongzhou Lian; Ziyong Cheng; Jun Lin (pp. 280-285).
The emission intensities of Eu3+ in the drug carrier system vary with the released amount of IBU, making the drug release easily tracked and monitored.Display Omitted► Luminescent and mesoporous europium-doped calcium silicates were synthesized. ► The system exhibits luminescence of Eu3+ under UV irradiation after the drug loading. ► The drug release situation can be tracked by the change of the luminescence intensity.Luminescent, mesoporous, and bioactive europium-doped calcium silicate (MCS: Eu) was successfully synthesized. The obtained MCS: Eu3+ was performed as a drug delivery carrier to investigate the drug storage/release properties using ibuprofen (IBU) as the model drug. The structural, morphological, textural, and optical properties were well characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), N2 adsorption/desorption, and photoluminescence (PL) spectra, respectively. The results reveal that the MCS: Eu exhibits the typical ordered characteristics of the mesostructure. This composite shows a sustained release profile with IBU as the model drug. The IBU-loaded samples still present red luminescence of Eu3+ (5D0–7F1,2) under UV irradiation. The emission intensities of Eu3+ in the drug carrier system vary with the amount of released IBU, making the drug release easily tracked and monitored. The system demonstrates a great potential for drug delivery and disease therapy.
Keywords: Drug delivery; Luminescence; Calcium silicate; Mesoporous; Bioactive
A facile route to growth of γ-MnOOH nanorods and electrochemical capacitance properties
by Zhongchun Li; Hongling Bao; Xiaoyu Miao; Xuhong Chen (pp. 286-291).
Single crystal nanorods of γ-MnOOH were successfully prepared via a novel solvothermal process based on the redox reaction between KMnO4 and DMF without extra surfactant or template.Display Omitted► A novel and facile solvothermal route was developed to synthesis of γ-MnOOH nanorods. ► Single crystal γ-MnOOH nanorods were prepared without surfactant or template. ► The synthetic route requires only two reagents and can exquisite control over the morphologies of γ-MnOOH. ► γ-MnOOH nanorods have a good electrochemical capability.Single crystal nanorods of γ-MnOOH with lengths up to hundreds of nanometers were successfully prepared employing a novel solvothermal process based on the redox reaction between potassium permanganate (KMnO4) and N, N-dimethyl ammonium formate (DMF) without extra surfactant or template. The as-prepared products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and Fourier transformed infrared spectroscopy (FTIR). The electrochemical properties of γ-MnOOH nanorods were investigated by cyclic voltammetry and galvanostatic charge–discharge performance measurements. Specific capacitance ( Cs) calculated from the galvanostatic discharge curve was 131.9Fg−1 for γ-MnOOH nanorods at the current density of 0.5Ag−1. The electrochemical experiment results demonstrate that γ-MnOOH nanorods should be a good candidate as electrode material for supercapacitor.
Keywords: γ-MnOOH; Synthesis; Nanorod; Capacitance
Coagulation and stabilization of sterically functionalized magnetite nanoparticles in an organic solvent with different technical polymers
by Martin Rudolph; Urs A. Peuker (pp. 292-299).
Polymers in an organic solvent based nanoparticle dispersion can cause coagulation or stabilization through depletion interactions and adsorption effects which is important for polymer composite synthesis influencing primary particle concentration.Display Omitted► Thermo gravimetric analyses can quantify the content of primary particles. ► PVB adsorbs and stabilizes magnetite nanoparticle dispersions in organic solvents. ► PC has a stronger destabilization effect compared to PMMA for same coil sizes. ► Primary particle concentration decreases with increasing polymer concentration. ► Extinction and DLS analyses reveal formation of larger structures by PVB adsorption.This experimental study deals with the colloidal stability of sterically functionalized magnetite nanoparticles in a low dielectric constant organic solvent with different concentrations of technical grade polymers. Those dispersions are the starting point of a solution and spray drying process chain to synthesize highly filled nanocomposite materials with nanoparticle volume concentrations exceeding 10%. We introduce a thermo gravimetric method together with light extinction and dynamic light scattering measurements to gain quantitative information on the concentration of primary particles and the mechanism of destabilization or stabilization by polymer addition. Poly(vinyl butyral) is found to stabilize the dispersion considerably caused by stronger interactions with the fatty acid coated magnetite particles quantified by means of adsorption measurements. Both poly(methyl methacrylate) as well as two grades of poly(bisphenol A carbonate) are found to destabilize the dispersion due to depletion flocculation over the entire concentration range investigated However there is a significant quantity of a stable fraction of primary nanoparticles in the supernatant after depletion flocculation occurred. This fraction of primary particles is increasing with decreasing polymer concentration. We furthermore point out important concerns and limitations for the composition of and concentrations in such complex colloidal systems for use in industrially relevant processes.
Keywords: Nanoparticle stability; Polymers; Depletion; Nanocomposites; Thermogravimetric analysis; Primary particles; Poly(carbonate); Poly(methyl methacrylate)
The viscosity of dilute poly(N-isopropylacrylamide) dispersions
by Anya J. Howe; Andrew M. Howe; Alexander F. Routh (pp. 300-307).
The volume fraction dependence of the low shear viscosity for a dilute dispersion of soft porous particles is determined experimentally and theoretically.Display Omitted► The intrinsic viscosity for porous particles displays a deviation from hard particle behavior. ► Behavior demonstrated experimentally, numerically and analytically. ► Using responsive particles allows temperature control over rheology.The viscosity of dilute aqueous dispersions of poly(N-isopropylacrylamide) microgel particles is measured by capillary viscometry. The viscosity increases with particle mass fraction and on reducing temperature, particularly below the volume phase transition temperature (VPTT) of 32°C. Converting the particle loading to volume fraction via the change in hydrodynamic size, the slope of the viscosity–volume fraction graph exhibits an increasing value beyond that for the equivalent effective hard-sphere size as the particles swell. This increase is due to the porosity of the particles. Two microgel samples of different collapsed size (124 and 59nm at 50°C) are investigated and the deviation from hard-sphere behavior is greater for the smaller particles.
Keywords: Intrinsic viscosity; Microgels; Stokes flow
Oleic acid assisted glycothermal synthesis of cuboidal Ba0.6Sr0.4TiO3 nanocrystals and their ordered architectures via self-assembly
by Yang Xiaowei; Zeng Yanwei; Mo Leiqing; Han Longxiang (pp. 308-316).
The size-controllable and highly monodispersed cuboidal barium strontium titanate (BST) nanocrystals have been successfully synthesized through a glycothermal approach with no mineralizers but oleic acid as growth-directing agent.Display Omitted► Through a glycothermal process with oleic acid as surfactant, the size-controllable and highly monodispersed cuboidal BST nanocrystals can be synthesized. ► The selective adsorption of OA on the facets with lower plane indices directed BST to grow into uniform cuboidal nanocrystals. ► The uniform cuboidal BST nanocrystals create a chance for the ferroelectric oxide nanocrystals to self-assemble into nanoscale electronic devices.The size-controllable and highly monodispersed cuboidal barium strontium titanate (BST) nanocrystals have been successfully synthesized through a glycothermal process with no mineralizers but oleic acid as growth-directing agent. The synthesized BST nanocrystals under different glycothermal conditions were structurally characterized by XRD, IR, FESEM, TEM and HRTEM and investigated with respect to the effects of key influencing factors including the amount of oleic acid, duration of glycothermal process and 1,4-butanediol/water volume ratio in the reaction media on the formation of BST nanocrystals and their size and morphological evolution. It has been found that the oleic acid incorporated into the glycothermal system plays a decisive role in promoting the formation of cuboidal nanocrystals. It allows the BST nanocrystals to form via a nucleation-growth mechanism instead of in situ reactions and the selective chemical adsorption of oleic acid molecules on the facets with lower plane indices of newly-built BST nuclei directs them to grow into uniform cuboidal BST nanocrystals. The duration of glycothermal reactions and the polarity of reaction media can remarkably affect the dynamic process of the formation of BST nanocrystals. These regularly-shaped and highly monodispersed nanocrystals show a spontaneity of self-assembling into 2D ordered architectures when they were dispersed in organic solvents like cyclohexane and droped onto a hydrophobic surface of substrates, which creates a chance for the ferroelectric oxide nanocrystals to self-assemble into nanoscale electronic devices.
Keywords: Barium strontium titanate; Cuboidal nanocrystals; Glycothermal synthesis; Surfactant-mediated crystal growth; 2D self-assembled architecture
A microemulsion-template-interfacial-reaction route to copper sulfide hollow spheres
by Denghui Jiang; Wenbin Hu; Haoran Wang; Bin Shen; Yida Deng (pp. 317-321).
Copper sulfide hollow spheres can be obtained directly since the reaction of two reactants respectively dissolved in two different phases of an o/w microemulsion only occurs at the oil/water interface.Display Omitted► Copper sulfide hollow spheres have been successfully synthesized. ► The reaction only occurs at the interface of an oil-in-water microemulsion. ► To form hollow spheres it is vital to establish a steady interfacial reaction rate. ► The size of the hollow spheres can be tailored by changing the content of oil phase.CuS hollow spheres have been successfully synthesized through a facile microemulsion-template-interfacial-reaction route using copper naphthenate as metal precursor and thioacetamide as the source of S2−. In this way, hollow spheres could be obtained directly since the reaction of two reactants respectively dissolved in two different phases of an oil-in-water (o/w) microemulsion only occurs at the oil/water interface. Therefore, it is a key for forming hollow spheres to optimize the interfacial reaction rate by controlling reaction conditions. Furthermore, the size of the hollow spheres can be tailored by changing the content of oil phase. In this study, the average diameter of the CuS hollow spheres can be adjusted from 110 to 280nm by changing the content of oil phase from 0.5ml to 1.5ml. In addition, the reaction temperature is a very important factor for forming CuS hollow spheres and the appropriate reaction temperature is about 50°C.
Keywords: Copper sulfide; Hollow spheres; Microemulsion; Interfacial reaction
Spectral properties of rhodamine 6G in smectite dispersions: Effect of the monovalent cations
by Adriana Czímerová; L’uboš Jankovič; Juraj Bujdák (pp. 322-330).
Spectral properties of R6G in the dispersion of montmorillonite, saturated with various monovalent cations depend on the type of the cations.Display Omitted► Spectral properties of R6G in the dispersion of montmorillonite, saturated with various monovalent cations depend on the type of the cations. ► Adsorption of the dye cations is a very fast process. ► R6G molecular aggregates formed in montmorillonite colloidal systems bear both the features of H- and J-aggregates. ► Significant effects of the properties of inorganic ions and swelling properties montmorillonite on R6G molecular aggregation were observed.Montmorillonite monoionic forms with alkali metal andNH4+-cations were prepared by ion exchange. The hydration properties and binding of the ions to montmorillonite surface and the swelling properties of the mineral specimens were analyzed. Whereas Na+- and Li+-ions were fully hydrated over a large range of conditions, large size K+,NH4+, and mainly Rb+ and Cs+ ions were apt to bind directly to the oxygen atoms on the mineral surface. The forms with large ions exhibited reduced hydration and swelling and the absence of macroscopic swelling of the respective aqueous colloids. The interaction of laser dye rhodamine 6G (R6G) in montmorillonite colloids was investigated by absorption and steady-state fluorescence spectroscopies. Significant effects of the properties of both the inorganic ions and swelling properties of colloidal dispersions on R6G molecular aggregation were observed. Large amounts of the molecular aggregates were formed in the colloids of Na+- and Li+-montmorillonites. The aggregates absorbed light at significantly lower wavelengths (∼460nm) with respect to the light absorption by monomers (535nm). Fluorescence spectroscopy provided a key evidence for the assignment of the type of the aggregates: The emission of the aggregates at relatively low energies proved these assemblies are rather a mixed H-/ J-type than ideal H-aggregates. The presence of parent inorganic cations of larger size led to a significant lowering of the amount of the R6G aggregates in favor of the monomers. Investigations of the evolution of the dye aggregation with time indicated basic features of dye aggregation reaction: The size of parent inorganic ions did not affect the reaction mechanism, but rather limited the extent of the reaction. Probably the forms with large inorganic ions, such as Rb+ and Cs+, did not provide sufficient surface for the formation of the large size assemblies of the dye. This property can be explained in terms of strong association of the large alkali metal ions to clay mineral surface, as well as to reduced swelling in the colloidal systems of respective forms.
Keywords: Smectite; Dye cations; Interactions; Colloid properties; Alkali cations; Rhodamine 6G
Evolution of fluorescence resonance energy transfer between close-packed CdSeS quantum dots under two-photon excitation
by Wenzhi Wu; Hong-An Ye; Yachen Gao; Qing Chang; Zhiren Zheng; Yanqiang Yang (pp. 331-335).
Contour plot of luminescent intensity for mixed CdSeS QDs film under infrared laser excitation.Display Omitted► Doped quantum dots for the enhancement of up-conversion luminescence. ► Energy transfer using two-photon excitation. ► The FRET rate from donors to acceptors is estimated as 0.03ns−1 by Dexter theory. ► Potential applications for biological and medical imaging.Energy transfer (ET) processes between quantum dots (QDS) were investigated by means of steady-state and time-resolved up-conversion luminescence measurements. Two types of CdSeS QDs with different Se/S molar ratios at the similar sizes of ∼4.5nm emit green and orange up-conversion luminescence at infrared laser excitation, separately. The power dependence and nanosecond luminescent decays of QDs films demonstrated that up-conversion luminescence was attributed to two-photon absorption and ET process occurred from green-emitting QDs to orange-emitting QDs. The ET rate was estimated quantitatively to be 0.03ns−1 by Dexter theory. The decrease of ET rate is due to Se doped substituted in the Sulfur sites. The band-edge excitonic state is predominating at the initial time evolution and responsible for peak shift and ET. The surface emission of orange-emitting QDs becomes slower, and is attributed to the trapping of electrons from QDs donors.
Keywords: CdSeS; Quantum dots; Fluorescence resonance energy transfer; Excitonic state
Transition from transparent aerogels to hierarchically porous monoliths in polymethylsilsesquioxane sol–gel system
by Kazuyoshi Kanamori; Yasunori Kodera; Gen Hayase; Kazuki Nakanishi; Teiichi Hanada (pp. 336-344).
A transition of pore structures from mesoporous to macro/mesoporous in polymethylsilsesquioxane monolithic gels has been investigated in sol–gel systems containing nonionic surfactant.Display Omitted► Monolithic porous polymethylsilsesquioxane gels are prepared by sol–gel. ► Macropores and mesopores are controlled by an addition of nonionic surfactant. ► Transparent aerogels are formed with high concentration of surfactant. ► Hierarchically porous gels are formed with low concentration of surfactant.A transition from hierarchical pore structures (macro- and meso-pores) to uniform mesopores in monolithic polymethylsilsesquioxane (PMSQ, CH3SiO1.5) gels has been investigated using a sol–gel system containing surfactant Pluronic F127. The precursor methyltrimethoxysilane (MTMS) undergoes an acid/base two-step reaction, in which hydrolysis and polycondensation proceed in acidic and basic aqueous media, respectively, as a one-pot reaction. Porous morphology is controlled by changing the concentration of F127. Sufficient concentrations of F127 inhibit the occurrence of micrometer-scale phase separation (spinodal decomposition) of hydrophobic PMSQ condensates and lead to well-defined mesoporous transparent aerogels with high specific pore volume as a result of the colloidal network formation in a large amount of solvent. Phase separation regulates well-defined macropores in the micrometer range on decreasing concentrations of F127. In the PMSQ-rich gelling domain formed by phase separation, the PMSQ colloidal network formation forms mesopores, leading to monolithic PMSQ gels with hierarchical macro- and meso-pore structures. Mesopores in these gels do not collapse on evaporative drying owing to the flexible networks and repulsive interactions of methyl groups in PMSQ.
Keywords: Polymethylsilsesquioxane; Sol–gel; Macroporous; Mesoporous; Aerogels; Hierarchically porous gels
Non-ionic, thermo-responsive DEA/DMA nanogels: Synthesis, characterization, and use for DNA separations by microchip electrophoresis
by Xihua Lu; Mingyun Sun; Annelise E. Barron (pp. 345-353).
(a) Volume-phase transitions of polyDEA and DEA/DMA nanogels of four different co-monomer compositions (70%/30%, 60%/40%, 50%/50%, and 40%/60%, w/w).D h is the average diameter of the nanogels as a function of temperature whileD ho is the average diameter of nanogels at 20°C, (b) de-swelling ratios of polyDEA and DEA/DMA co-polymer nanogels of four different compositions (70%/30%, 60%/40%, 50%/50%, and 40%/60%, w/w).Display Omitted► DEA/DMA co-polymer nanogels obtained in only in a certain narrow range of synthesis temperatures. ► Nonionic DEA/DMA nanogels display tunable phase transition temperatures of between 26 and 67 °C. ► Concentrated, 8% w/v dispersions of DEA/DMA nanogels show optical clarity at room temperature. ► Nanogel-doped networks enable ultra-fast high resolution DNA analysis by chip electrophoresis.Thermo-responsive polymer “nanogels” (crosslinked hydrogel particles with sub-100nm diameters) are intriguing for many potential applications in biotechnology and medicine. There have been relatively few reports of electrostatically neutral, thermosensitive nanogels comprising a high fraction of hydrophilic co-monomer. Here we demonstrate the syntheses and characterization of novel, non-ionic nanogels based on random N, N-diethylacrylamide (DEA)/ N, N-dimethylacrylamide (DMA) copolymers, made by free-radical, surfactant-free dispersion polymerization. The volume-phase transition temperatures of these DEA/DMA nanogels are strongly affected by co-monomer composition, providing a way to “tune” the phase transition temperature of these non-ionic nanogels. While DEA nanogels (comprising no DMA) can be obtained at 70°C by standard emulsion precipitation, DEA/DMA random co-polymer nanogels can be obtained only in a particular range of temperatures, above the initial phase transition temperature and below the critical precipitation temperature of the DEA/DMA copolymer, controlled by co-monomer composition. Increasing percentages of DMA in the nanogels raises the phase transition temperature, and attenuates and broadens it as well. We find that concentrated DEA/DMA nanogel dispersions are optically clear at room temperature. This good optical clarity was exploited for their use in a novel DNA sieving matrix for microfluidic chip electrophoresis. An ultrafast, high-efficiency dsDNA separation was achieved in less than 120s for dsDNA ranging from 75bp to 15,000bp.
Keywords: Abbreviations; DEA; N; ,; N; -diethylacrylamide; DMA; N; ,; N; -dimethylacrylamide; MALLS; multi-angle static laser light scattering; NIPA; N; -isopropylacrylamide; PCS; photon correlation spectroscopy; DLS; dynamic light scattering; VPTT; volume-phase transition temperature; LCST; lower critical solution temperature; PDI; polydispersity indexNanogels; DEA; DMA; LCST; Microchip electrophoresis; DNA separations
Effective functionalization of multiwalled carbon nanotube with amphiphilic poly(propyleneimine) dendrimer carrying silver nanoparticles for better dispersability and antimicrobial activity
by E. Murugan; G. Vimala (pp. 354-365).
Two multiwalled carbon nanotube hybrids MWCNTs-APPI and MWCNTs-APPI-AgNPs were synthesized. The better dispersability of MWCNTs-APPI in aqueous/organic solvents and the antimicrobial activity of MWCNTs-APPI and MWCNTs-APPI-AgNPs have been achieved.Display Omitted► Functionalization of MWCNTs with amphiphilic poly(propyleneimine) dendrimer. ► Deposition of silver nanoparticles on MWCNTs-APPI. ► Dispersability of MWCNTs-APPI in aqueous and organic solvents without sonication. ► In vitro antimicrobial activity of MWCNTs-APPI and MWCNTs-APPI-AgNPs.Two multiwalled carbon nanotube hybrids have been prepared: (a) multiwalled carbon nanotubes (MWCNTs) functionalized with amphiphilic poly(propyleneimine) dendrimer (APPI), viz. MWCNTs-APPI, and (b) silver nanoparticles (AgNPs)-deposited multiwalled carbon nanotubes functionalized with an amphiphilic poly(propyleneimine) dendrimer (MWCNTs-APPI-AgNPs). The degree of covalent functionalization of APPI in MWCNTs and deposition of AgNPs in MWCNTs-APPI were examined by Fourier transform infrared spectroscopy, zeta potential, scanning and high-resolution transmission electron microscopy, energy-dispersive spectroscopy, thermogravimetric analysis, and Raman spectroscopy. The amount of APPI functionalized on MWCNTs determined by thermal gravimetric analysis was about 67% which enables an effective dispersability in aqueous and organic solvents without sonication and these solutions were stable for 6months without undergoing aggregation of MWCNTs. The electronic properties of the hybrid materials were not altered drastically as verified by the Raman studies. The antimicrobial activities of MWCNTs-APPI and MWCNTs-APPI-AgNPs against three different bacteria, viz. Bacillus subtilis, Staphylococcus aureus, and Escheriachia coli illustrated excellent activity.
Keywords: Multiwalled carbon nanotube; Amphiphilic poly(propyleneimine) dendrimer; Silver nanoparticles; Dispersability; Antimicrobial activity; Thermogravimetric analysis
Cellular uptake and subcellular localization of highly luminescent silica-coated CdSe quantum dots – In vitro and in vivo
by M. Vibin; R. Vinayakan; Annie John; C.S. Rejiya; V. Raji; Annie Abraham (pp. 366-371).
The efficient cellular uptake and localization characteristics of silica-coated CdSe QDs were performed in stem cells (RADMSCs).Display Omitted► Silica-coated CdSe QDs exhibits strong fluorescence under biological conditions. ► Efficient cellular uptake and localization characteristics of QDs in cancer cells. ► Efficient cellular uptake and localization characteristics of QDs in stem cells. ► In vivo studies confirmed the distribution maxima of QDs.With excellent optical properties, quantum dots (QDs) have been made as attractive molecular probes for labeling cells in biological research. The purpose of the present work is to explore the possible role of silica-coated cadmium selenide (CdSe) QDs in the in vitro and in vivo cellular uptake and their subcellular localization. The in vitro uptake characteristics of silica-coated CdSe QDs were performed in cultured New Zealand rabbit adipose tissue-derived mesenchymal stem cells (RADMSCs) and Human cervical cancer cells (HeLa) using fluorescence microscopy after staining with 4,6-diamidino-2-phenylindole (DAPI). The in vitro results showed that the silica-coated CdSe QDs were efficiently taken up by the cells and it was localized in the intracellular vesicles giving strong fluorescence from the cytoplasm and nearby nucleus. Subsequently, the in vivo localization and distribution of QDs were studied by the hematoxilin stained semithin cryosections of tissues (∼15μm thickness) under fluorescence microscopy and ultrathin sections of tissues (∼100nm thickness) under confocal laser scanning microscopy at the distribution maxima. Our in vivo results confirmed the effective cellular uptake and even distribution pattern of QDs in tissues. Overall, these in vitro and in vivo results are represented with focus on internalization, subcellular localization and distribution of the QDs, in view of their potential applications in biomedical field.
Keywords: Cellular uptake; Confocal laser scanning microscopy; Fluorescence; HeLa cells; Quantum dots
Thermo sensitive behavior of cellulose derivatives in dilute aqueous solutions: From macroscopic to mesoscopic scale
by Mohamed Fettaka; Rachid Issaadi; Nadji Moulai-Mostefa; Isabelle Dez; Didier Le Cerf; Luc Picton (pp. 372-378).
By pyrene fluorescence spectrophotometry, a double step thermal transition has been evidenced in dilute regime for the copolymer MHPC suggesting that each LCST group (i.e. methyl and hydroxypropyl) undergoes its own transition at this mesoscopic scale. At the same time, by investigation at macroscopic scale (e.g. optical density), only one transition occurs.Micropolarity index ( I1 /I3) vs. temperature: HPC (▪) MHPC (▾) and MC (△).NaCl 0.5M, [polymer concentration]=0.5gL−1Display Omitted► Evidence of HPC, MC and MHPC thermo association in dilute solution. ► Link between association kinetic and rate of temperature sweep. ► Two transitions for MHPC at mesoscopic scale, only one at macroscopic scale. ► Any influence of MC on HPC transition temperature in mixture.Thermal behaviors of thermo sensitive hydroxypropyl cellulose (HPC), methyl cellulose (MC) and methyl hydroxypropyl cellulose (MHPC) solutions have been investigated in dilute regime of concentration ( C< C*) by means of optical density (OD), Quasi Elastic Light Scattering (QELS) and Pyrene Fluorescence Spectroscopy (PyFS) measurements. The importance of controlling the rate of a temperature sweep regarding to the kinetic of association has been demonstrated. MHPC copolymer exhibits only one thermal transition at macroscopic scale (OD and QELS) but two distinct thermal transitions have been evidenced at mesoscopic scale (PyFS) suggesting a double association step for each thermo associative group (i.e. hydroxypropyl and methyl). In HPC/MC mixture, HPC undergoes its own thermal transition. The presence of MC leads to a shift of the temperature of HPC precipitation toward higher temperature even in dilute regime.
Keywords: Cellulose ethers; LCST; Thermo sensitive; Pyrene Fluorescence Spectroscopy
Facile synthesis and step by step enhancement of blue photoluminescence from Ag-doped ZnS quantum dots
by Sonal Sahai; Mushahid Husain; Virendra Shanker; Nahar Singh; D. Haranath (pp. 379-383).
We report step by step enhancement of blue-photoluminescence from Ag doped ZnS quantum dots useful for applications involving full-colour displays, white-light emitting devices, bio-imaging and other medical diagnostics.Display Omitted► Significantly enhanced blue photoluminescence from ZnS:Ag+ quantum dots is presented. ► UV photolysis and polysulphide hydrothermal treatment enhanced the PL intensity to 250%. ► Presented results are different from those reported earlier for nano-ZnS:Ag+ system. ► Strong blue PL finds applications in displays, lighting, bio-medical sciences etc.Our results pertaining to the step by step enhancement of photoluminescence (PL) intensity from ZnS:Ag,Al quantum dots (QDs) are presented. Initially, these QDs were synthesized using a simple co-precipitation technique involving a surfactant, polyvinylpyrrolidone (PVP), in de-ionised water. It was observed that the blue PL originated from ZnS:Ag,Al QDs was considerably weak and not suitable for any practical display application. Upon UV (365nm) photolysis, the PL intensity augmented to ∼170% and attained a saturation value after ∼100min of exposure. This is attributed to the photo-corrosion mechanism exerted by high-flux UV light on ZnS:Ag,Al QDs. Auxiliary enhancement of PL intensity to 250% has been evidenced by subjecting the QDs to high temperatures (200°C) and pressures (∼120bars) in a sulphur-rich atmosphere, which is due to the improvement in crystallanity of ZnS QDs. The origin of the bright-blue PL has been discussed. The results were supported by X-ray phase analysis, high-resolution electron microscopy and compositional evaluation.
Keywords: Zinc sulphide; Quantum dot; Photoluminescence; UV photolysis; Hydrothermal method
Time-resolved and spatially-resolved infrared spectroscopic observation of seeded nucleation controlling geopolymer gel formation
by Ailar Hajimohammadi; John L. Provis; Jannie S.J. van Deventer (pp. 384-392).
Synchrotron radiation infrared spectromicroscopy provides spatially-resolved analysis of connectivity within aluminosilicate gels whose structure has been tailored by seeding with various oxide nanoparticles.Display Omitted► Nanoparticle seeding provides structural control of aluminosilicate gel. ► Infrared microscopy shows local differences in gel molecular structure. ► Nanostructure influences gel mechanical properties.The effect of seeded nucleation on the formation and structural evolution of one-part (“just add water”) geopolymer gels is investigated. Gel-forming systems are seeded with each of three different oxide nanoparticles, and seeding is shown to have an important role in controlling the silica release rate from the solid geothermal silica precursor, and in the development of physical properties of the gels. Nucleation accelerates the chemical changes taking place during geopolymer formation. The nature of the seeds affects the structure of the growing gel by affecting the extent of phase separation, identified by the presence of a distinct silica-rich gel in addition to the main, more alumina-rich gel phase. Synchrotron radiation-based infrared microscopy (SR-FTIR) shows the effect of nucleation on the heterogeneous nanostructure and microstructure of geopolymer gels, and is combined with data obtained by time-resolved FTIR analysis to provide a more holistic view of the reaction processes at a level of detail that has not previously been available. While spatially averaged (ATR–FTIR) infrared results show similar spectra for seeded and unseeded samples which have been cured for more than 3weeks, SR-FTIR results show marked differences in gel structure as a result of seeding.
Keywords: Geopolymer; Aluminosilicate; Gel; Nucleation; Seeding
Micellar effects on the alkaline hydrolysis of isatin and its derivatives
by Abdullah S. Al-Ayed; Mohd. Sajid Ali; Hamad A. Al-Lohedan; Adel M. Al-Sulaim; Zuheir A. Issa; Kabir-ud-Din (pp. 393-399).
The rate of alkaline hydrolysis of isatin and its derivatives shows a tendency to a maximum as the concentration of cationic surfactant, CTACl, increases. Added anionic surfactant, SDS, inhibits the rate of alkaline hydrolysis.Display Omitted► The presence of a hydrophobic group in isatin accelerates the rate of alkaline hydrolysis. ► Alkaline hydrolysis of isatin can be controlled by using cationic as well as anionic surfactants. ► The hydrolysis can also be inhibited by the addition of salts.Herein we have investigated the hydrolysis of 1 H-indol-2,3-dione (isatin, I) and its derivatives of different hydrophobicities, viz. N-dimethylaminomethyl indol-2,3-dione (II), N-morpholinomethyl indol-2,3-dione (III), N-pipridinomethyl indol-2,3-dione (IV), N-heptylaminomethyl indol-2,3-dione (V), N-dodecylaminomethyl indol-2,3-dione (VI), N-hexylanilinomethyl indol-2,3-dione (VII), N-decylanilinomethyl indol-2,3-dione (VIII), and N-hexadecylanilinomethyl indol-2,3-dione (IX), in the presence of an excess amount of sodium hydroxide. All the isatin derivatives were synthesized in the laboratory. The progress of the reactions was studied by exploiting UV–visible spectrophotometry. The observed rate constant, kw, increases linearly on increasing the hydroxide ion concentration, indicating first-order dependence on [OH−]. The effects of surfactants, cationic (cetyltrimethylammonium chloride, CTACl), and anionic (sodium dodecyl sulfate, SDS) were also investigated. The rate of reaction increased on increasing the concentration of CTACl and, after reaching a maximum, it started decreasing. Conversely, anionic micelles of SDS inhibited the rate of hydrolysis of isatin and its derivatives. The results of the effect of CTACl were analyzed using a pseudophase ion-exchange model while the inhibition by SDS was analyzed using a simple Menger–Portnoy model. The effects of added salts, such as NaBr, NaCl, and (CH3)4NBr, were also seen on the isatin hydrolysis. It was found that the addition of salts decreased the rate enhancement efficiency of the CTACl.
Keywords: Isatin and its derivatives; Cationic surfactant; Anionic surfactant; Alkaline hydrolysis; Micellar catalysis
Unique liquid crystal behavior in water of anionic fluorocarbon–hydrocarbon hybrid surfactants containing oxyethylene units
by Masanobu Sagisaka; Yoshie Fujita; Yusuke Shimizu; Chie Osanai; Atsushi Yoshizawa (pp. 400-406).
A hybrid surfactant, 8F-B2ES, having two oxyethylene units in one of the tails, formed lamellar aggregates, which were distorted at temperatures below 40°C, implying genration of quasi ion channel.Display Omitted► A hybrid surfactant 8F-B2ES having oxyethylene units in one of the tails was synthesized. ► 8F-B2ES forms vesicles, which became distorted at temperatures below 40°C. ► Hydrohpilicity of the 8F-B2ES bilayers increased with decreasing temperature. ► These unique properties suggest the possibility to generate oxyethylene-based quasi ion channels.This study reports the unique aqueous lyotropic liquid crystal behavior of an anionic hybrid surfactant, 8F-B2ES, which has 2-[2-(butyloxy)ethyloxy]ethyl and 1 H,1 H,2 H,2 H-perfluorodecyl tails. An 8F-B2ES-analog hybrid surfactant with no oxyethylene units (8F-DeS) and a symmetric fluorinated double-tail surfactant with two 2-(1 H,1 H,2 H,2 H-perfluorohexyloxy)ethyl tails (4FEOS) were used as control surfactants in examining the effects of the oxyethylene units and of the hybrid structure on the liquid crystal behavior. Polarized microscopic observations showed the formation of a lamellar liquid crystal phase for each surfactant/water mixture at surfactant concentrations higher than 10wt.%. In the case of the 30wt.% 8F-B2ES/water mixture, two types of spherical aggregates were observed at temperatures higher than 40°C: one was a typical lamella liquid crystal with a maltese cross-texture, and the other was optically isotropic. Interestingly, when the 8F-B2ES lamellar phase was cooled to below 40°C, the lamellar aggregates were distorted and the isotropic droplets became anisotropic. As this unique liquid crystal behavior was not observed for aqueous mixtures of the control surfactants, the oxyethylene units in the hybridized hydrocarbon tail play an important role in the behavior. This study also examined the effect of the oxyethylene units on microenvironmental polarity in the hybrid surfactant bilayer via fluorescence spectral measurements of pyrene solubilized in each lamellar phase. The polarity of the 8F-B2ES bilayer at 70°C was found to be that of a hydrocarbon surfactant lamellar phase, and increased gradually with decreasing temperature. The polarity became the same as that of hydrophilic spherical micelles below 40°C, despite the presence of the lamellar aggregates. Since the polarity in the 8F-DeS bilayer was independent of temperature, and as low as that of a typical hydrocarbon surfactant bilayer, hydration of the 8F-B2ES oxyethylene units would increase the polarity, and then loosen the 8F-B2ES packing within the bilayer. This probably led to distortion of the lamellar aggregates.
Keywords: Lamella phase; Dehydration; Hybrid surfactant; Microsegregation; Ion channel
Organization of amphiphiles
by Uma Dash; Pramila K. Misra (pp. 407-418).
The effects of nonionic surfactants polyoxyethylated octyl phenols in surfactant mixtures with ionic surfactants cetyltrimethylammonium bromide (CTAB) and sodium dodecyl sulphate (SDS) are found to be antagonistic in nature.Display Omitted► Antagonism behavior has been noted between nonionic and ionic surfactants of varying hydrophobicity. ► The formation of hydrophobic complexes and association of the ionic surfactants with the nonionic surfactant have been evidenced to account for the antagonism. ► A schematic model for these interactions has been suggested.The effects of nonionic surfactants OP-10 and OP-30 (polyoxyethylated octyl phenols with 10 and 30 oxyethylene groups, respectively) in surfactant mixtures with ionic surfactants hexadecyltrimethylammonium bromide (CTAB) and sodium dodecyl sulphate (SDS) have been investigated by a conductometric method in conjunction with fluorescence, surface tension, zeta potential, and DLS measurements. The interactions are found to be antagonistic in nature for each of the systems; i.e., micellization of CTAB as well as SDS is hindered on addition of the nonionic surfactants. The antagonism is found to be more prominent in the presence of OP-10 compared to that of OP-30. Two types of mechanistic paths, path A operating below the critical micellar concentration and path B operating beyond the critical micellar concentration of nonionic surfactants, have been suggested. In path A, the retardation in micellization has been attributed to a decrease in monomeric concentration of the ionic surfactants from solution as a result of the formation of a hydrophobic complex between nonionic and ionic surfactants. In path B, the decrease in monomer concentration is due to the solubilization of the ionic surfactant in micelles of the nonionic surfactants in a 1:1 stoichiometric ratio. A theoretical treatment to the interaction in each ionic–nonionic pair yields a positive value of the interaction parameter supporting the concept of antagonism. The formation of the hydrophobic complex is supported by fluorescence and surface tension measurements. A schematic representation of the stabilization of these hydrophobic complexes has been suggested. The association of ionic surfactants by nonionic micelles is suggested by zeta potential and DLS studies.
Keywords: Polyoxyethylated octyl phenols; Polarity parameter; Thermodynamics of micellization; Excimer formation; Aggregation number; Hydrophobic complex; Interaction parameter; Size of the aggregates; DLS and zeta potential studies
Comparison of the structure and the transport properties of low-set and high-set curdlan hydrogels
by Marc-André Gagnon; Michel Lafleur (pp. 419-427).
Low-set and high-set curdlan gels prepared from the same aqueous suspension.Display Omitted► Microscopic structure and the transport properties of low- and high-set curdlan gels. ► Low-set gels are more heterogeneous at the microscopic level than high-set ones. ► The diffusion coefficient distribution reflects the sampled volume by each analyte. ► The gel structural differences are not correlated with their transport properties.Curdlan, a bacterial polysaccharide, can form different types of thermogels, having the very same chemical composition, but whose structures depend on the incubation temperature. Structural characterization of 10% (w/v) low-set and high-set curdlan gels was carried out by Fourier transformed infrared (FT-IR) imaging and environmental scanning electron microscopy (eSEM) in the hydrated state. Considerable differences were observed between the two gels, the high-set one being overall more homogeneous. The self-diffusion coefficients of a series of analytes of different sizes (water, phosphate, glucose-6-phosphate, polyphosphate, polyethylene glycol, and dextran labelled with rhodamine B) were measured in aqueous solution(Dssln) and in both types of curdlan gels(Dsgel) using1H and31P pulsed field gradient nuclear magnetic resonance (PFG NMR) spectroscopy. The mutual-diffusion coefficients(Dmgel) of dextran in the curdlan gels were determined from release experiments based on fluorescence spectroscopy. The dependence of the relative diffusion coefficient(DsgelDssln) on the size of the analyte, expressed by its hydrodynamic radius (R h), could be expressed byDsgelDssln∝exp(-Rh0.46), valid for both types of gels. The self-diffusion measurements for the largest investigated analytes were not compatible with a single diffusion coefficient and, therefore, were analysed using an approach based on a normal distribution of self-diffusion coefficients. In the hydrogels, broadening of the self-diffusion coefficient distribution increased as a function of the analyte size. This phenomenon was associated with the limited distance travelled by the analytes during the measurements, and it is inferred that the distribution of diffusion coefficients is representative of the distribution of local environments of the individual analyte. It was found that the structural differences observed between both types of curdlan gels are not correlated with the gel transport properties, highlighting the complexity of the relationship between structural details and transport properties in gels.
Keywords: Hydrogel; Transport properties; Structure; Diffusion; PFG NMR
Simple chiral urea gelators, ( R)- and ( S)-2-heptylurea: Their gelling ability enhanced by chirality
by Jong-Uk Kim; Dieter Schollmeyer; Martin Brehmer; Rudolf Zentel (pp. 428-433).
Pure enantiomeric ( R)- and ( S)-2-heptylurea gelatinize nonpolar solvents and water by forming a 3D network of 1D fibrous supramolecular structures, while the racemate precipitates in lamellar crystals.Display Omitted► We synthesize pure enantiomeric ureas, ( R)- and ( S)-2-heptylureas. ► We examine gelling behaviors of the chiral ureas in various solvents. ► The gelling ability of the pure compounds are superior to that of the mixture. ► The superiority is due to the 1D fibrous morphology of the pure enantiomers. ► Instead, the racemic mixture crystallizes into 2D shapesWe present the first report on the synthesis of chiral ureas, ( R)- and ( S)-2-heptylurea, and their gelling behaviors. The ureas were prepared by the reactions of chiral amines and phenyl carbamate in the presence of triethylamine. On cooling from homogeneous solutions, the chiral ureas form gels in water and various nonpolar organic solvents, such as cyclohexane, toluene, and tetrachloromethane, while the racemate gelatinize only toluene and tetrachloromethane among the solvents we examined. The gelling ability of the enantiomeric urea is higher than the racemate, as the critical gelling concentrations in toluene, for example, were 0.2% and 0.7% (wt/wt), respectively. The enhanced gelling ability of the enantiomeric ureas is due to the 1D supramolecular structure formed during gelation. In contrast, the racemate crystallizes into two-dimensional lamellae, where the ( R)- and ( S)-2-heptylurea exist alternatingly in a plane ( P21/c space group). Powder X-ray diffraction pattern of the enantiomeric urea showed that it has a different crystal lattice from that of the racemate, implying that the steric effect by the methyl group at the chiral center prevents the pure enantiomers from having 2D hydrogen bonding networks, which lead to sheet-like structures for the racemate and the achiral analog. Thus the pure enantiomers self-organize into one-dimensional fibrous structures. The simplicity and the ambidextrous gelling behaviors of the chiral ureas in forming both hydrogels and organogels present numerous possibilities for future applications.
Keywords: Chiral ureas; Gel; Self-assembly
Effect of sodium salicylate, sodium oxalate, and sodium chloride on the micellization and adsorption of sodium deoxycholate in aqueous solutions
by Sujit Das; Jahar Dey; Teiborlang Mukhim; Kochi Ismail (pp. 434-439).
The binding behavior of sodium ions to deoxycholate micelles is similar in the presence of chloride and salicylate ions, but different in the presence of sodium oxalate.Display Omitted► Salicylate and chloride have similar effects on sodium deoxycholate micellization. ► Oxalate ions affect differently sodium deoxycholate micellization. ► Effect of oxalate on counterion binding to deoxycholate micelles is quite different. ► No obvious role of salicylate on deoxycholate micellization on its choleretic effect.The salicylate ion increases the rate of bile flow (choleretic effect) and bile salts are known to affect the colonic absorption of oxalate. Owing to this physiological relevance of salicylate and oxalate ions, critical micelle concentration (cmc) values of sodium deoxycholate (NaDC) were determined in aqueous sodium oxalate, sodium salicylate, and sodium chloride solutions by using surface tension, fluorescence, and EMF methods. The results indicate, besides a counterion effect, the influence of coanions on the cmc. In the range from 25 to 40°C, cmc increases almost linearly with temperature. In the temperature range from 30 to 40°C, the counterion binding constant β of NaDC micelles has the same value (0.17±0.01) in the presence of sodium chloride and sodium salicylate. On the other hand, in sodium oxalate solution β=0.05±0.02 when oxalate concentration is less than or equal to c* and β=0.48±0.04 above c*, where c*≈0.038molkg−1. EMF measurements also supported this type of counterion binding to NaDC micelles in sodium oxalate solutions. In sodium oxalate solution, at c* a change in the shape of deoxycholate micelles is expected to take place. Salicylate, oxalate, and chloride coanions have a similar effect on the adsorption of NaDC. This study reveals that the choleretic effect of salicylate is not due to the influence of salicylate ions on the micellization of NaDC.
Keywords: Sodium deoxycholate; Salicylate; Oxalate; Critical micelle concentration; Counterion binding constant; Surface excess
Synthesis, performance, and modeling of immobilized nano-sized magnetite layer for phosphate removal
by Adva Zach-Maor; Raphael Semiat; Hilla Shemer (pp. 440-446).
A novel homogeneous porous layer of magnetite nanoparticles (<4nm) was synthesized on modified charcoal granular activated carbon for extremely high efficiency of phosphate adsorption.Display Omitted► A novel nano-sized magnetite impregnated GAC was synthesized for PO4 removal. ► A comprehensive characterization of the nFe-GAC was conducted. ► The homogeneous porous layer of nano-Fe3O4 exhibited remarkable adsorption capacity. ► Magnetite formation and phosphate adsorption mechanisms are proposed. ► A detailed kinetic analysis is presented.A homogeneous layer of nano-sized magnetite particles (<4nm) was synthesized by impregnation of modified granular activated carbon (GAC) with ferric chloride, for effective removal of phosphate. A proposed mechanism for the modification and formation of magnetite onto the GAC is specified. BET results showed a significant increase in the surface area of the matrix following iron loading, implying that a porous nanomagnetite layer was formed. Batch adsorption experiments revealed high efficiency of phosphate removal, by the newly developed adsorbent, attaining maximum adsorption capacity of 435mg PO4/g Fe (corresponding to 1.1mol PO4/mol Fe3O4). It was concluded that initially phosphate was adsorbed by the active sites on the magnetite surface, and then it diffused into the interior pores of the nanomagnetite layer. It was demonstrated that the latter is the rate-determining step for the process. Innovative correlation of the diffusion mechanism with the unique adsorption properties of the synthesized adsorbent is presented.
Keywords: Iron oxide; Adsorption; Granular activated carbon; Isotherm; Mössbauer spectroscopy
The activity and selectivity of catalytic peroxide oxidation of chlorophenols over Cu–Al hydrotalcite/clay composite
by Shiwei Zhou; Chuantao Gu; Zhenying Qian; Jinguang Xu; Chuanhai Xia (pp. 447-452).
The catalyst was a polymer of hydrotalcite and clay, with a large number of cavities and crevices on the surface, which showed high activity for catalytic wet peroxide oxidation of CPs.Display Omitted► The catalytic peroxide oxidation of CPs in the first step was selective. ► The content and position of chlorine influenced the oxidation rate of CPs. ► The hydrotalcite/clay composite exhibited high catalytic activity. ► There was an appropriate concentration ratio among catalyst, H2O2, and CPs.Liquid phase catalytic oxidation of chlorophenols (CPs) was carried out over Cu–Al hydrotalcite/clay composite at ambient temperature and pressure using hydrogen peroxide as oxidant. The results showed that the catalyst had high catalytic activity, with complete oxidation of 4-CP within 40min at 40°C. The content and position of chlorine on the aromatic ring had significantly different effects on the oxidation rate of CPs, with the rate sequence of phenol>monochlorophenol (MCP)>dichlorophenol (DCP)>trichlorophenol (TCP), 3-CP>2-CP>4-CP, and 3,5-DCP>3,4-DCP>2,5-DCP>2,4-DCP>2,6-DCP. This was ascribed to the interactions among σ-electron withdrawing conductive effect, π-electron donating conjugative effect, and steric hindrance effect of chlorine. It was evidenced that the catalytic peroxide oxidation of CPs in the first step was selective and rate-limiting, where chlorinated 1,4-benzoquinones formed.
Keywords: Catalytic wet peroxide oxidation (CWPO); Selective oxidation; Copper-based catalyst; Hydrotalcite/clay composite; Chlorophenol (CP)
Copper(II) influence on flumequine retention in soils: Macroscopic and molecular investigations
by David Pérez Guaita; Stéphanie Sayen; Stéphanie Boudesocque; Emmanuel Guillon (pp. 453-459).
Coexistence of flumequine and copper in the environment enhances the antibiotic adsorption through a ternary complex onto soils at environmentally relevant pH values, thus reducing its mobility.Display Omitted► Flumequine is classified at environmentally relevant pH as a slow-mobile compound in soils. ► Copper enhances flumequine retention onto soils. ► EXAFS and XANES spectra evidence the formation of a ternary complex. ► Formation of a ternary complex leads to an increase of the adsorbed flumequine amount.The coadsorption of flumequine (fluoroquinolone antibiotic) and copper(II) on a alkaline soil sample (collected from the Champagne–Ardenne region, France) was studied at macroscopic and molecular scales by means of batch experiments and X-ray absorption spectroscopy. The retained antibiotic amount onto the soil surface increases (from 2- to >20-fold) with the copper concentration due to the formation of a CuII–flumequine ternary surface complex, which leads to the accumulation of flumequine into soils. Flumequine can be classified at environmentally relevant pH values as a slow-mobile compound in soils and a very slow-mobile compound in the presence of copper, even at relatively low concentrations.
Keywords: Antibiotic; Flumequine; Copper; Soil; Adsorption; Ternary complex; EXAFS
Sorption of aqueous antimony and arsenic species onto akaganeite
by F. Kolbe; H. Weiss; P. Morgenstern; R. Wennrich; W. Lorenz; K. Schurk; H. Stanjek; B. Daus (pp. 460-465).
Comparison of the adsorption isotherms of antimony species onto the commercial GEH (black circles) and onto the synthesized akaganeite (SynA, white circles).Display Omitted► Adsorption isotherms of arsenic and antimony species onto akaganeite. ► pH influence on the sorption of different inorganic and organic arsenic and antimony species. ► Competing reactions with the sorption of arsenate, antimonite, and phosphate.Two akaganeite materials were tested for the removal of antimonate, trimethyl antimonate, arsenate, arsenite, and dimethyl arsenate from water: a commercial product (GEH) and a synthesized akaganeite. The two materials show similar qmax values, but differ in theirK L values. This could be a result of their different crystal sizes indicated by sharper XRD reflections of the synthesized akaganeite compared with GEH. Batch experiments were carried out using all species to investigate the influence of the pH on their sorption onto the commercial material. The best results for the removal of antimonate and arsenate were achieved under acidic conditions, while the sorption of arsenite has an optimum at pH 7. The maximum loadings vary from 450mgg−1 (antimonate at pH 2.2.) to 2mgg−1 (trimethyl antimonate at pH 7). Competition reactions (up to a 10-fold excess of the competitor ion) were studied with antimonate, arsenate, and phosphate. The sorption capacity of arsenate decreases up to 12.5% by adding phosphate (ratio 1:10), but the addition of antimonate did not influence the sorption of arsenate. Conversely, the sorption of antimonate decreases due to the addition of 10-fold concentration of arsenate (31%) or phosphate (27%).
Keywords: Arsenic species; Antimony species; Sorption isotherms; Sorption competition; Water treatment
Adsorption of polycyclic aromatic hydrocarbons from aqueous solutions by modified periodic mesoporous organosilica
by Carla B. Vidal; Allen L. Barros; Cícero P. Moura; Ari C.A. de Lima; Francisco S. Dias; Luiz. C.G. Vasconcellos; Pierre B.A. Fechine; Ronaldo F. Nascimento (pp. 466-473).
Structural formulas of the sources of silica (without CH2CH3 groups) BTEB (a), FTE (b), and idealized schematic of primary structure of mesoporous organosílicas (c).Display Omitted► A PMO is synthesized using Si sources and surfactants as structure-directing agents. ► PMO have structures that allow molecules to be held into their nanotubes. ► The viability of using the PMO for PAH removal from aqueous solution is presented.A novel procedure was developed for the synthesis of a periodic mesoporous organosilica (PMO), which was used to remove polycyclic aromatic hydrocarbons (PAHs) from aqueous solutions. Adsorption equilibrium isotherms and adsorption kinetics experiments were carried out in solutions of PAHs (2–60mgL−1), using the PMO as adsorbent. Adsorption models were used to predict the mechanisms involved. The adsorption kinetics data best fitted the pseudo-first-order kinetic model for naphthalene, and to the pseudo-second-order model for fluorene, fluoranthene, pyrene, and acenaphtene. The intraparticle model was also tested and pointed to the occurrence of such processes in all cases. The isotherm models which best represented the data obtained were the Freundlich model for fluoranthene, pyrene, and fluorene, the Temkin model for naphthalene, and the Redlich–Peterson model for acenaphtene. PAHs showed similar behavior regarding kinetics after 24h of contact between adsorbent and PAHs. FTIR, XRD, BET, and SEM techniques were used for the characterization of the adsorbent material.
Keywords: PAHs; Adsorption; PMO; Adsorption models
Perchlorate removal by granular activated carbon coated with cetyltrimethyl ammonium bromide
by Jian-hong Xu; Nai-yun Gao; Yang Deng; Ming-hao Sui; Yu-lin Tang (pp. 474-479).
More perchlorate was adsorbed by GAC-CTAB, more bromide was produced. 31% of adsorbed perchlorate over the initial percholrate of 0.082–0.490mmol/L was exchanged with bromide in CTAB.Display Omitted► The K in Freundlich adsorption isotherm increased with CTAB content increase. ► The optimal perchlorate adsorption by GAC-CTAB typically occurred at pH 2–3. ► Some of adsorbed perchlorate was exchanged with bromide in CTAB.In this study, granular activated carbon (GAC) coated with cetyltrimethyl ammonium bromide (CTAB) (GAC-CTAB) was synthesized to remove perchlorate from water via adsorption. Laboratory-scale batch experiments were performed to study the factors affecting the perchlorate adsorption by GAC-CTAB, including the CTAB content and solution pH, and explore the mechanisms behind the adsorption phenomenon. The novel GAC-CTAB material was characterized by scanning electron microscopy (SEM), zeta potential measurement and Brunauer–Emmett–Teller (BET) analysis. The characterization tests showed that CTAB was deposited on the GAC surface, pHpzc of the material was between 2.0 and 3.0, and the BET specific surface area was reduced from 925 to 729m2/g with the increasing CTAB content from 0 to 0.034mmol CTAB/g GAC. The adsorption process was better described by a pseudo-second-order kinetics model and the Freundlich adsorption model. The CTAB content and solution pH significantly influenced the kinetics and chemical equilibrium of the adsorption. When the CTAB content was increased from 0.0.023 to 0.135mmol CTAB/g GAC, the K in the Freundlich adsorption isotherm increased from 0.071 to 0.19mmol/g. The optimal adsorption typically occurred at pH 2–3, close to the pHpzc of the solution. Finally, the mechanisms for the adsorption of perchlorate on GAC-CTAB were associated with surface complexation, electrostatic interaction and ion exchange.
Keywords: Perchlorate; Cetyltrimethyl ammonium bromide; Adsorption; Ion exchange
Backside SERS studies of inhibitor transport through polyelectrolyte films on Ag-substrates
by Haybat Itani; Monika Santa; Patrick Keil; Guido Grundmeier (pp. 480-486).
Comparison of backside geometry SERS signal was done between samples: bare Ag-substrate, pure polyelectrolyte film, film cured at 180°C and film with the incorporation of Ag nanoparticles.Display Omitted► Backside SERS studied the transport of inhibition molecules through a polymer film. ► Barrier properties of polyelectrolyte films can be modified by post treatment. ► Incorporation of Ag nanoparticles induced trapping effect on the transport of MBI. ► Electrochemical Impedance Spectroscopy showed significant decrease in water uptake for cured sample at 200°C.In situ backside surface enhanced Raman spectroscopy (in situ-SERS) was newly employed for the study of the transport of inhibiting molecules through a polymer film. The barrier properties of layer-by-layer polyelectrolyte films (PE) composed of polyacrylic acid and polyallylamine hydro-chloride layers on Ag-surfaces were compared between untreated, thermally crosslinked, and Ag-nanoparticles containing samples. IB-SERS enabled the study of the transport of 2-mercaptobenzimidazole (MBI) as an inhibitor through the film. Water barrier properties of the treated PE films determined by Electrochemical Impedance Spectroscopy were correlated to the MBI diffusion kinetics. The PE stability against MBI diffusion and thermal treatment was analyzed by Infra-Red Reflection Absorption Spectroscopy (IRRAS). IRRAS showed that the thermally treated PE films formed chemical crosslinking via amide bonds and lowered the diffusion of water and the water uptake in the films. Moreover, the MBI diffusion kinetics can be followed by means of SERS. However, MBI adsorption at the PE film/metal interface was not detected after the heat treatment. In this case the adsorbed PE on the Ag surface was not substituted by the competing adsorption of MBI. Moreover, the presence of Ag-nanoparticles in the film decelerated MBI diffusion to the SERS substrate due to the trapping effect of MBI molecules.
Keywords: In situ backside surface enhanced Raman spectroscopy; Polyelectrolytes; Layer-by-layer; Diffusion; Amide formation; Electrochemical Impedance Spectroscopy
Cd(II) biosorption using Lessonia kelps
by Carmen Boschi; Holger Maldonado; Martha Ly; Eric Guibal (pp. 487-496).
Modeling of uptake kinetics using the model of resistance to intraparticle diffusion (Crank’s equation).Display Omitted ► Lessonia kelps are efficient sorbents for copper and nickel. ► Characterization of biosorbent by FT-IR spectroscopy and SEM–EDAX. ► Langmuir equation for modeling sorption isotherm. ► Crank equation for fitting uptake kinetics. ► Greater impact of sorbent dosage and metal concentration against particle size and temperature. Lessonia kelps ( L. trabeculata and L. nigrescens) have been successfully used for the recovery of Cd(II) from near neutral solutions. The biomass was pre-treated with calcium chloride for stabilization of alginate-based compounds. SEM–EDAX analysis and FT-IR spectrometry analysis were used for identifying the modifications of the biomass. Sorption isotherms were performed at the optimum pH (i.e., pH 6) and the maximum sorption capacity reached up to 1 and 1.5mmolCdg−1 for L. nigrescens ( L.n.) and L. trabeculata ( L.t.), respectively. The Langmuir equation fits well experimental data. The temperature (in the range 20-40°C) had a more marked effect on affinity coefficient than on maximum sorption capacity. The influence of particle size, sorbent dosage, metal concentration and temperature was evaluated on uptake kinetics. The kinetic profiles that were modeled using the Crank equation (i.e., the resistance to intraparticle diffusion) were hardly affected by the temperature and the particle size contrary to the sorbent dosage and the metal concentration, which show greater impact. The pseudo-second order rate equation was also tested for the modeling of uptake kinetics.
Keywords: Lessonia; kelp; Cadmium; pH effect; Sorption isotherm; Uptake kinetics; Intraparticle diffusion
Effect of titania structure on the properties of its supported copper oxide catalysts
by Haiyang Zhu; Lin Dong; Yi Chen (pp. 497-503).
Different surface structures of anatase and rutile result in different reductions and catalytic behaviors of dispersed copper oxide species for NO reduction by CO.Display Omitted► Rutile TiO2 with a relatively high surface area was used as support. ► Reduction behavior of dispersed CuO species was influenced by TiO2 structure. ► Dispersed CuO species on rutile was stepwise reduced by H2 in TPR. ► This reduction behavior of may be responsible for its high NO reduction activity.Anatase and rutile have the same chemical composition as TiO2 but different crystalline structures (space group ofD4h19-I41 for anatase andD4h14-P42 for rutile, respectively), which result in different surface structures and can be used ideally to investigate the effects of support and surface structure on the properties of their supported catalysts. In this work, anatase- or rutile-supported copper oxide catalysts (signed as Cu-A and Cu-R, thereafter) prepared by the impregnation method were characterized by X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) surface area, X-ray photoelectron spectroscopy (XPS), and H2 temperature-programmed reduction (H2-TPR) to study the support effect of titania on the physicochemical properties and catalytic properties for the NO reduction by CO of these supported copper oxide catalysts. The results indicated that (1) copper oxide presented different dispersion capacities on anatase or rutile; (2) dispersed copper oxide species on anatase and rutile also showed different reduction behaviors; i.e., one-step reduction for dispersed copper oxide species in Cu-A and stepwise reduction for that in Cu-R; (3) the NO+CO activity test suggested dispersed copper oxide and small CuO particles on rutile are the main active species under the current reaction conditions and copper oxide supported on rutile is more active than that on anatase, which might result from Cu+ species in Cu-R sample formed during the reaction due to its stepwise reduction behavior.
Keywords: Copper oxide; Anatase; Rutile; Surface interaction; Surface structure
Kinetic separation of carbon dioxide and methane on a copper metal–organic framework
by Zongbi Bao; Sufian Alnemrat; Liang Yu; Igor Vasiliev; Qilong Ren; Xiuyang Lu; Shuguang Deng (pp. 504-509).
Fractional adsorption uptake of CO2 (top) and CH4 (bottom) on the Cu–MOF adsorbent showing a kinetic selectivity of 26 at 298KDisplay Omitted► Kinetic separation of CO2 and CH4. ► Microporous Cu–MOF. ► Kinetic selectivity. ►Adsorption.Separation of carbon dioxide and methane is an important issue in upgrading low-quality natural gas. Adsorption equilibria and kinetics of CO2 and CH4 on a copper metal–organic framework (MOF), Cu(hfipbb)(H2hfipbb)0.5 [H2hfipbb=4,4′-(hexafluoroisopropylidene) bis(benzoic acid)], were investigated to evaluate the feasibility of removing CO2 from CH4 in a pressure swing adsorption process using this new MOF adsorbent. The heat of adsorption of CO2 on the Cu–MOF at zero-coverage (29.7kJ/mol) is much lower than those on a carbon molecular sieve and a zeolite 5A adsorbent; and the heat of adsorption of CH4 on the Cu–MOF (21.4kJ/mol) is similar to that on the zeolite 5A adsorbent and smaller than that on a carbon molecular sieve. The Cu–MOF being investigated has apertures of (∼3.5×3.5Å), which favors the kinetically controlled separation of CO2 and CH4. The kinetic selectivity is found to be 26 at 298K, and the overall selectivity (combining the equilibrium and kinetic effects) is about 25 for an adsorption separation process. These results suggest that the Cu–MOF adsorbent is an attractive alternative adsorbent for the CO2/CH4 separation.
Keywords: Kinetic selectivity; CO; 2; /CH; 4; separation; Adsorption; Membrane; Cu–MOF; Microporous; Pressure swing adsorption
The role of mineral surface chemistry in modified dextrin adsorption
by Audrey Beaussart; Agnieszka M. Mierczynska-Vasilev; Sarah L. Harmer; David A. Beattie (pp. 510-520).
AFM images of HOPG (left) and copper-activated sphalerite (right) bare surfaces (top) and exposed to SO Dextrin polymer solution (bottom). Insets show receding water contact angles of the 4 samples.Display Omitted► Styrene oxide (SO) and phenyl succinate (PS) dextrins adsorbing on mineral surfaces. ► Mineral surfaces have been characterized by XPS and contact angle measurements. ► Surface chemistry alters polymer uptake and subsequent effect on wettability. ► PS Dextrin has the most potential to separate ZnS and graphite in flotation.The adsorption of two modified dextrins (phenyl succinate dextrin – PS Dextrin; styrene oxide dextrin – SO Dextrin) on four different mineral surfaces has been studied using X-ray photoelectron spectroscopy (XPS), in situ atomic force microscopy (AFM) imaging, and captive bubble contact angle measurements. The four surfaces include highly orientated pyrolytic graphite (HOPG), freshly cleaved synthetic sphalerite (ZnS), and two surfaces produced through surface reactions of sphalerite: one oxidized in alkaline solution (pH 9, 1h immersion); and one subjected to metal ion exchange between copper and zinc (i.e. copper activation: exposed to 1×10−3M CuSO4 solution for 1h). XPS measurements indicate that the different sphalerite surfaces contain varying amounts of sulfur, zinc, oxygen, and copper, producing substrates for polymer adsorption with a range of possible binding sites. AFM imaging has shown that the two polymers adsorb to a similar extent on HOPG, and that the two polymers display very different propensities for adsorption on the three sphalerite surface types, with freshly cleaved sphalerite encouraging the least adsorption, and copper activated and oxidized sphalerite encouraging significantly more adsorption. Contact angle measurements of the four surfaces indicate that synthetic sphalerite has a low contact angle upon fracture, and that oxidation on the timescale of one hour substantially alters the hydrophobicity. HOPG and copper-activated sphalerite were the most hydrophobic, as expected due to the carbon and di/poly-sulfide rich surfaces of the two samples, respectively. SO Dextrin is seen to have a significant impact on the wettability of HOPG and the surface reacted sphalerite samples, highlighting the difficulty in selectively separating sphalerite from carbonaceous unwanted minerals in flotation. PS Dextrin has the least effect on the hydrophobicity of the reacted sphalerite surfaces, whilst still significantly increasing the wettability of graphite, and thus has more potential for use as a polymer depressant in this separation.
Keywords: Polymer adsorption; Flotation; AFM; Graphite; Sphalerite; Dextrin
On steady two-fluid electroosmotic flow with full interfacial electrostatics
by WooSeok Choi; Ashutosh Sharma; Shizhi Qian; Geunbae Lim; Sang Woo Joo (pp. 521-526).
Electroosmotic velocity profile of conducting (top) and nonconducting (bottom) fluid layer. Depending upon electrokinetic properties, hydrodynamic shear can be overcome to result in backward flow.Display Omitted► Hydrodynamic and electrostatic interactions incorporated. ► Counterintuitive flow found through the electrostatic interaction of the interface. ► The interfacial electrostatic effects can induce reverse flow. ► A formula for quantitative control of electroosmotic pumping provided.A two-fluid electroosmotic flow in a microchannel is studied by considering full hydrodynamic and electrostatic interactions on the interface. Jumps in electrical potential and in charge density across the interface, in particular, are found to create counterintuitive flow behavior through the electrostatic interaction of the interface with the external field imposed. The interfacial electrostatic effects are shown to induce flow reversal within physically reasonable parametric ranges. It is also shown that the electrostatic properties of the interface must be carefully considered in electroosmotic pumping lest the nonconducting fluid should stay stationary or flow in an unintended direction. A formula for quantitative control of electroosmotic pumping is provided.
Keywords: Electroosmosis; Interface; Maxwell stress; Two-fluid
The effect of interfacial microstructure on the lipid oxidation stability of oil-in-water emulsions
by Maryam Kargar; Fotios Spyropoulos; Ian.T. Norton (pp. 527-533).
Lipid oxidation was monitored by measuring the concentration of primary lipid oxidation product, using the peroxide value method. Increasing silica particles concentration at the interface, results in decrease in the rate of lipid oxidation due to ability of silica particles to form a thick interfacial layer around droplets.Display Omitted► O/W emulsions stabilised by sodium caseinate, Tween 20 and silica particles. ► Lipid oxidation rate was monitored over extended time. ► Silica particles at the interface are able to reduce the lipid oxidation rate. ► CAS can reduce the rate of oxidation through its ability to scavenge free radicals.A novel approach to reduce lipid oxidation in oil-in-water emulsions has been taken and involves the manipulation of the emulsions’ interfacial microstructure. Oil-in-water emulsions stabilised by sodium caseinate (CAS), Tween 20 and silica particles were prepared and their lipid oxidation stability was assessed over a week. Lipid oxidation was monitored by measuring the concentration of primary lipid oxidation product, using the peroxide value method and secondary lipid oxidation products formation were evaluated with the p-anisidine technique. Oil-phase volume fraction and emulsifier type both play key roles in influencing the rate of lipid oxidation. Decreasing the oil fraction from 30% to 5% was found to promote lipid oxidation as a result of an increase in the amount of pro-oxidant iron per gram of oil. It was further shown that, CAS in the continuous phase reduces lipid oxidation at pH 7 due to its metal chelating ability. In addition, the results show that, emulsions stabilised with silica particles (at pH 2) inhibit lipid oxidation to a greater extent than emulsions stabilised with surfactants alone. The present study demonstrates that emulsions’ physical properties such as oil-phase volume fraction, droplet size and droplet interfacial microstructure are all formulation parameters that can be used to significantly reduce the rate of lipid oxidation.
Keywords: Lipid oxidation; Oil-in-water emulsions; Pickering emulsions; Interfacial microstructure; Surfactant; Chelators
Pressure-driven flow in open fluidic channels
by Nicholas Davey; Adrian Neild (pp. 534-540).
Fast and stable flow is developed through both a ribbon (bottom left) and bulge (top right) fluid profile, at high rates (500μL/min, along a 30mm long 1mm channel) the ribbon deforms due to the pressure head (bottom right).Display Omitted► High flow speeds are demonstrated in open fluidic channels. ► Ribbons of fluid distort slightly to account for the pressure head. ► Stable bulges display strong recirculation patterns potentially suitable for mixing. ► Applications in air-borne contaminate detection and interfacing to fluidic systems. ► The approach is in keeping with recent striving for simplification in microfluidics.At the boundary between a hydrophilic and hydrophobic surface coating a large contact angle hysteresis exists which can be used to retain fluid on a flat surface, a similar effect exists at the edge of a solid surface. In this work, pressure-driven flow is used to create fluid flow through a fluid volume confined along a 1mm wide strip of glass. Very high flow rates are shown to be achievable, reaching a value of 500μL/min over a 30mm length; at such values the maximum flow velocity is found through modeling to be 0.13m/s. By consideration of the minimum energy state the shape a certain fluid volume will adopt on a strip of material are well known for static fluids, we demonstrate flow through the two key types, the case resembling a section of a cylinder and the case of a pronounced bulge. This combination of fluid constrained though locations of high contact angle hysteresis combined with induced flow allows applications in detection of air-borne contaminants, the detection of changing fluid composition, and easy interfacing between microfluidic system and external tools.
Keywords: Surface tension; Pressure-driven flow; Contact angle; Fluid/gas interface; Open microfluidics
Fast microwave-assisted synthesis of tailored mesoporous carbon xerogels
by E.G. Calvo; E.J. Juárez-Pérez; J.A. Menéndez; A. Arenillas (pp. 541-547).
Visual illustration of the different stages involved in the organic xerogels synthesis with the determination of the gelation point and the observed mesoporosity of carbon xerogels in a wider pH for the microwave than for conventional synthesis.Display Omitted► Mesoporosity can be tailored using MW synthesis of carbon xerogels. ► A wider range of pH than conventional methods can be used with MW synthesis. ► MW synthesis allows straightforward determination of the gelation point. ► Faster and cheaper production of carbon xerogels can be achieved using MW synthesis.Resorcinol–formaldehyde carbon xerogels with several initial pH were synthesized using two different heating methods (conventional and microwave heating). The effect of the pH of the precursor solution and the method of synthesis employed on the textural and chemical properties of the final materials was evaluated. It was found that both methods produce tailored carbon xerogels depending on the initial pH and that the pores of the carbon xerogels become larger as the initial pH decreases. High pHs result in exclusively microporous carbon xerogels, while a decrease in the amount of NaOH added, i.e. lower pH, causes the materials to evolve firstly into micro–mesoporous samples and then into micro–macroporous carbon xerogels. The main difference between the two heating methods studied, apart from the duration of the synthesis (i.e. approximately 5h for the microwave-assisted synthesis as opposed to several days by conventional methods) lies in the meso–macroporosity of the resulting materials, since microwave radiation produces mainly mesoporous carbon xerogels with a specific mesopore size over a wider range of pH than conventional synthesis. For example, the pH range for mesoporous MW samples is 4.5–6.5 while equivalent samples that are conventionally synthesized require an initial pH of between 5.8 and 6.5. This work also illustrates a simple and precise method for determining the gelation point (t g) of different pH resorcinol–formaldehyde mixtures, based on varying the energy consumed by the microwave device during the synthesis of organic gels, without the need for other more complicated techniques.
Keywords: Microwave-assisted synthesis; Gelation point; Carbon xerogels; Mesoporous materials
Separation of plasmid DNA isoforms by highly converging flow through small membrane pores
by David R. Latulippe; Andrew L. Zydney (pp. 548-553).
Converging flow field causes elongation of the supercoiled plasmid and transmission through small pores in ultrafiltration membrane.Display Omitted► First demonstration of separation of plasmid DNA isoforms using ultrafiltration. ► Novel separation mechanism based on differences in elongational flexibility. ► Separation characteristics very different than in SEC or agarose gels. ► Opportunities for large-scale purification of supercoiled isoform for gene therapy.Plasmid DNA isoforms can be separated by both agarose gel electrophoresis and a variety of chromatographic methods, but both of these approaches have significant shortcomings in terms of scalability, throughput, and/or resolution. This study provides the first demonstration that the supercoiled, linear, and open-circular isoforms of plasmid DNA can be effectively separated based on differences in their elongational flexibility in the highly converging flow field that is established during membrane ultrafiltration. Data were obtained with plasmids from 3 to 17kbp in size using commercially available cellulose ultrafiltration membranes with pores an order of magnitude smaller than the DNA root-mean-square radius of gyration. High-resolution separations were achieved by controlling the filtrate flux between the critical flux values required for transmission of the individual isoforms. The separation behavior in ultrafiltration was very different than that observed in size exclusion chromatography or agarose gel electrophoresis due to differences in the underlying separation mechanisms. The simplicity of the ultrafiltration process makes this approach attractive for a wide range of applications, including large-scale purification of plasmid DNA for gene therapy.
Keywords: DNA; Ultrafiltration; Elongational flow; Plasmid isoforms; Supercoiled DNA
Simple preparation of a cadmium selenide–montmorillonite hybrid
by Areeporn Ontam; Nithima Khaorapapong; Makoto Ogawa (pp. 554-557).
In comparison with bulk CdSe, the near band-edge emission of CdSe–HDTMA–montmorillonite was blue-shifted, implying the thermal redistribution of the excited electron in surface defects of CdSe nanoparticles and their relaxation.Display Omitted► Immobilization of organically modified cadmium selenide into montmorillonite was investigated. ► The intercalated cadmium selenides were plate-shaped nanoparticles with a diameter of ca. 3–6nm. ► A blue shift of near band-edge emission was observed in the PL spectrum of the hybrid on heating.The immobilization of organically modified cadmium selenide on montmorillonite was investigated by the reaction of modified cadmium selenide nanoparticles with montmorillonite. The intercalation of the nanoparticles was indicated by the expansion of the interlayer space and spectroscopic observations. The diffuse reflectance absorption spectrum of the product showed absorption onset at 567nm. In comparison to the bulk cadmium selenide, the blue shift of the absorption onset of the hybrid was ascribed to the quantum size effect of the modified cadmium selenide nanoparticles. This study provides a new method for introducing nanoparticles into the interlayer space of layered inorganic materials.
Keywords: Cadmium selenide; Hybrid; Montmorillonite; Nanoparticle; Optical properties; Self-assembly