Journal of Colloid And Interface Science (v.281, #1)
Adsorption and heterocoagulation of nonionic surfactants and latex particles on cement hydrates
by Fabrice Merlin; Hicham Guitouni; Hayette Mouhoubi; Sandrine Mariot; Franck Vallée; Henri Van Damme (pp. 1-10).
The adsorption of nonionic surfactants of the alkylâ€“phenolâ€“poly(ethylene oxide) family and of acrylic latex particles on several anhydrous (but hydrating) or fully hydrated mineral phases of Portland cement was studied. No or negligible adsorption of the surfactant was observed. This was assigned to the ionized character of the surface silanol groups in calciumâ€“silicateâ€“hydrates and to the strongly ionic character of the OH groups in calcium hydroxide and in the calciumâ€“sulfoaluminateâ€“hydrates, which prevents the formation of surfaceâ€“ethoxy hydrogen bonds. In contrast, provided they are properly stabilized by the surfactant, the latex particles form a loose monolayer on the surface of hydrating tricalcium silicate particles. The attractive interaction between the positive mineral surface and the negative latex surface appears to be the driving force for adsorption. In line with this, adsorption is reduced by sulfate anions, which adsorb specifically onto the silicate surface. Compared to tricalcium silicate, portlandite and gypsum interact only marginally with the latex particles. Our results show that the stability of the nonionic surfactant/latex/cement systems is essentially controlled by the latex colloidal stability and the latexâ€“cement interactions, the surfactant having little direct interaction, if any, with the mineral surfaces.
Keywords: Cement; Latex; Nonionic surfactants; Adsorption; Heterocoagulation; Hydrates
Selective and sequential adsorption of bovine serum albumin and lysozyme from a binary mixture on nanosized magnetic particles
by Z.G. Peng; K. Hidajat; M.S. Uddin (pp. 11-17).
Magnetic particles about 10 nm in size were prepared by chemical precipitation under nitrogen and used for the selective and sequential adsorption of bovine serum albumin (BSA) (pI=4.7) and lysozyme (LSZ) (pI=11.1) under different conditions, such as pH and initial protein concentration. The separation ratio of BSA over LSZ at pH 4.6 is about 5, which is about 1.5 times the separation ratio of LSZ over BSA at pH 11.0. Only 10% of the preadsorbed BSA could be displaced by the sequential adsorption of LSZ at pH 11.0. On the other hand, 60% of the preadsorbed LSZ was desorbed due to the sequential adsorption of BSA at pH 4.6. Over 50% desorption of BSA or LSZ could be achieved either by 0.5 M Na2HPO4 or 0.5 M NaH2PO4 after 2 h. Over 80% of the enzymatic activity of LSZ was preserved when it was desorbed from magnetic particles.
Keywords: Nanosized magnetic particles; Bovine serum albumin; Lysozyme; Selective and sequential adsorption; Desorption
The effects of acid and alkali modification on the adsorption performance of fuller's earth for basic dye
by G. Hisarli (pp. 18-26).
The objective of this work was to prepare modified adsorbents from fuller's earth (FE) by acid and alkali treatment for enhancement cationic dye adsorption. Toluidine blue (TB) was selected as adsorbate for evaluating the adsorption performance of fuller's earth samples, which was affected significantly by acid and alkali modification. The adsorption of TB was studied by visible spectra. The absorption band of the monomer at low loading of TB in FE suspension with respect to its maximum in aqueous solution is red-shifted, which is related to accessibility of dye interlamellar space in the presence of positively charged surface sites. Since all surfaces are negatively charged under experimental conditions, this effect has not been observed in acid- and alkali-treated FE suspensions. It was seen that the adsorption capacity of alkali-treated surface (FEAl) for TB was higher than these of acid-treated adsorbent (FEAc) and FE. Scanning electron micrographs (SEM) and X-ray diffraction (XRD) and fluorescence (XRF) spectra were applied to analyze the structure of the raw and modified FE samples. Absence of any identifiable amount of a crystalline compound in the solid reaction products after acid treatment was confirmed by XRD and SEM, whereas the crystalline form of FEAl was preserved. Experimental data for high-concentration regions were well described by Freundlich and Langmuir adsorption equations. The thermodynamic parameters were estimated for FE, FEAc, and FEAl by using temperature dependence of adsorption equilibrium constants.
Keywords: Toluidine blue; Fuller's earth; Acid treatment; Alkali treatment; Adsorption
Removal of 2,4-dichlorophenoxyacetic acid from aqueous solutions by partially characterized organophilic sepiolite: thermodynamic and kinetic calculations
by Gülten Akçay; Mehmet Akçay; Kadir Yurdakoç (pp. 27-32).
The adsorption of 2,4-dichlorophenoxyacetic acid (2,4-D) on organophilic sepiolite (dodecylammonium sepiolite, DAS) was studied as a function of solution concentration and temperature. The observed adsorption rates were found to be equal to the first-order kinetics. The rate constants were calculated for temperatures ranging between 25 and 40â€‰Â°C at constant concentration. The adsorption energies, E, and adsorption capacity,qm, for 2,4-D adsorption on organophilic sepiolite was estimated using the Dubininâ€“Radushkevic equation. Thermodynamic parameters (Î”ga,Î”ha,Î”sa) were determined by a new approximation from the isotherm of 2,4-D adsorption on DAS. Also,Î”S0 andÎ”H0 values were calculated from the van't Hoff equation. These isotherms were modeled according to the Freundlich and Dubininâ€“Radushkevic adsorption equations. The amount of adsorption of this herbicide on organophilic sepiolite was found to be dependent on the relative energies of adsorbentâ€“adsorbate, adsorbateâ€“solvent, and adsorbateâ€“adsorbate interaction.
Keywords: Herbicides; Removal; Adsorption; Thermodynamics; Kinetics; Organophilic sepiolite
Investigation of the factors affecting organic cation adsorption on some silicate minerals
by Ceyda Bilgiç (pp. 33-38).
In this study, the effects of some factors on the adsorption of a basic dye (methylene blue) on bentonite and sepiolite samples were studied. These factors are cation (Na+ and Ca2+) saturation of the samples and pH and ionic strength of the dye solution. The adsorption data were found to conform to the Langmuir equation within the concentration range studied and Langmuir constants were determined for each of the samples. The adsorption capacities of the samples were found to increase with cation saturation. Changes in the pH of the dye solution had no significant influence on the adsorption capacity and adsorption capacities were found to decrease with increasing ionic strength. The maximum sorption capacity of methylene blue exceeded the cation exchange capacity of bentonite and sepiolite.
Keywords: Bentonite; Cation saturation; Ionic strength; Methylene blue adsorption; pH; Sepiolite
Modeling Pb sorption to microporous amorphous oxides as discrete particles and coatings
by Ming Fan; Thipnakarin Boonfueng; Ying Xu; Lisa Axe; Trevor A. Tyson (pp. 39-48).
Hydrous amorphous Al (HAO), Fe (HFO), and Mn (HMO) oxides are ubiquitous in the subsurface as both discrete particles and coatings and exhibit a high affinity for heavy metal contaminants. To assess risks associated with heavy metals, such as Pb, to the surrounding environment and manage remedial activities requires accurate mechanistic models with well-defined transport parameters that represent sorption processes. Experiments were conducted to evaluate Pb sorption to microporous Al, Fe, and Mn oxides, as well as to montmorillonite and HAO-coated montmorillonite. Intraparticle diffusion, a natural attenuating process, was observed to be the rate-limiting mechanism in the sorption process, where best-fit surface diffusivities ranged from 10âˆ’18 to 10âˆ’15 cm2â€‰sâˆ’1. Specifically, diffusivities of Pb sorption to discrete aluminum oxide, aluminum oxide-coated montmorillonite, and montmorillonite indicated substrate surface characteristics influence metal mobility where diffusivity increased as affinity decreased. Furthermore, the diffusivity for aluminum oxide-coated montmorillonite was consistent with the concentrations of the individual minerals present and their associated particle size distributions. These results suggest that diffusivities for other coated systems can be predicted, and that oxide coatings and montmorillonite are effective sinks for heavy metal ions.
Keywords: Lead; Sorption; Intraparticle diffusion; Hydrous aluminum oxide; Hydrous iron oxide; Hydrous manganese oxide; Oxide coating; Montmorillonite
A comparative adsorption study with different industrial wastes as adsorbents for the removal of cationic dyes from water
by Amit Bhatnagar; A.K. Jain (pp. 49-55).
Four adsorbents have been prepared from industrial wastes obtained from the steel and fertilizer industries and investigated for their utility to remove cationic dyes. Studies have shown that the adsorbents prepared from blast furnace sludge, dust, and slag have poor porosity and low surface area, resulting in very low efficiency for the adsorption of dyes. On the other hand, carbonaceous adsorbent prepared from carbon slurry waste obtained from the fertilizer industry was found to show good porosity and appreciable surface area and consequently adsorbs dyes to an appreciable extent. The adsorption of two cationic dyes, viz., rhodamine B and Bismark Brown R on carbonaceous adsorbent conforms to Langmuir equation, is a first-order process and pore diffusion controlled. As the adsorption of dyes investigated was appreciable on carbonaceous adsorbent, its efficiency was evaluated by comparing the results with those obtained on a standard activated charcoal sample. It was found that prepared carbonaceous adsorbent exhibits dye removal efficiency that is about 80â€“90% of that observed with standard activated charcoal samples. Thus, it can be fruitfully used for the removal of dyes and is a suitable alternative to standard activated charcoal in view of its cheaper cost.
Keywords: Rhodamine B; Bismark Brown R; Wastewater; Industrial solid wastes; Adsorbents
Removal of lead ions in drinking water by coffee grounds as vegetable biomass
by Toshimitsu Tokimoto; Naohito Kawasaki; Takeo Nakamura; Jyunichi Akutagawa; Seiki Tanada (pp. 56-61).
In an attempt to reuse food waste for useful purposes, we investigated the possibility of using coffee grounds to remove lead ions from drinking water. We studied the lead ion adsorption characteristics of coffee beans and grounds by measuring their fat and protein content, adsorption isotherms for lead ions, and adsorption rates for lead ions. The number of lead ions adsorbed by coffee grounds did not depend on the kind of coffee beans or the temperature at which adsorption tests were performed. The rate of lead ion adsorption by coffee grounds was directly proportional to the amount of coffee grounds added to the solution. When coffee grounds were degreased or boiled, the number of lead ions decreased. When proteins contained in coffee grounds were denatured, the lead ion adsorption was considerably reduced. The lead ion adsorption capacity of coffee grounds decreased with increased concentration of perchloric acid used for treating them and disappeared with 10% perchloric acid. The experiments demonstrated that proteins contained in coffee beans depend upon the adsorption of lead ion. The present study gave an affirmative answer to the possibility of using coffee grounds, an abundant food waste, for removing lead ions from drinking water.
Keywords: Lead ion; Adsorption; Coffee grounds; Vegetable biomass
Thermodynamic and kinetic investigations of PO3âˆ’4 adsorption on blast furnace slag
by Ensar Oguz (pp. 62-67).
The kinetics of adsorption of PO3âˆ’4 by blast furnace slag were found to be fast, reaching equilibrium in 20 min and following a pseudo-second-order rate equation. The adsorption behavior of PO3âˆ’4 on blast furnace slag has been studied as a function of the solution agitation speed, pH, and temperature. Results have been analyzed by Freundlich, Langmuir, BET, and Dubininâ€“Radushkevich (Dâ€“R) adsorption isotherms. The mean energy of adsorption, 10.31 kJâ€‰molâˆ’1, was calculated from the Dâ€“R adsorption isotherm. The rate constants were calculated for 293, 298, 303, and 308 K using a pseudo-second-order rate equation and the activation energy (Ea) was derived using the Arrhenius equation. Thermodynamic parameters such asÎ”H0,Î”S0, andÎ”G0 were calculated from the slope and intercept of linear plot oflnKD against1/T. TheÎ”H0 andÎ”G0 values of PO3âˆ’4 adsorption on the blast furnace slag show endothermic heat of adsorption. But there is a negative free energy value, indicating that the process of PO3âˆ’4 adsorption is favored at high temperatures.
Keywords: Phosphate; Adsorption; Isotherms; Blast furnace slag
The concept of â€œcapacityâ€? in zeolite ion-exchange systems
by Vassilis J. Inglezakis (pp. 68-79).
In the present paper a study is conducted in order to distinguish the several types of capacity used in the literature on zeolite ion-exchange systems, to verify the use of each capacity type, and to analyze the several experimental methods used for capacity determination. Although the study is focused on zeolite clinoptilolite as a characteristic paradigm, its theoretical approaches and experimental findings and methods could also apply to other zeolites.
Keywords: Zeolites; Capacity; Ion exchange; Clinoptilolite
Properties and structure of manganese oxide-coated clay
by Thipnakarin Boonfueng; Lisa Axe; Ying Xu (pp. 80-92).
In the environment, heavy metals are important contaminants that sorb to and accumulate in soils and sediments. Dominant minerals in the subsurface are oxides and clay, which occur as discrete particles and heterogeneous systems; these surfaces can significantly impact the mobility and bioavailability of metals through sorption. To better understand heterogeneous systems, amorphous (hydrous manganese oxide (HMO)) and crystalline manganese oxides (birnessite and pyrolusite) were coated on montmorillonite. However, the montmorillonite substrate potentially inhibited crystallization of the pyrolusite coating, and also resulted in a poorly crystalline birnessite. Mineralogy and morphology of the coated systems suggest an amorphous structure for HMO and uniform coverage for HMO and birnessite coatings; the presence of Si and Al indicates uncoated areas along intraplanar surfaces. The coating surface charge behaved similarly to that of discrete oxides and clay where the pHznpc of HMO- and birnessite-coated clay were 2.8 and 3.1, respectively. Surface area of the coated systems increased while the pore size distribution decreased as compared to the external surface area and pores of montmorillonite. X-ray absorption spectroscopy (XAS) revealed the local structural environment of Mn in the HMO- and birnessite-coated clay was consistent with the pure phase oxides: for HMO-coated clay 3.1 atoms of oxygen at1.89±0.02Å in the first shell and 2.7 atoms of manganese at2.85±0.02 in the second shell; and, for birnessite-coated clay 6 atoms of oxygen at1.91±0.02Å in the first shell and 6 atoms of manganese at distance2.99±0.02Å in the second shell. Overall, the surface properties suggest that the coating behaves like that of discrete oxides, an important sink for metal contaminants.
Keywords: Manganese oxide; Montmorillonite; Coating; XAFS
Interfacial properties of poly(maleic acid-alt-1-alkene) disodium salts at water/hydrocarbon interfaces
by Marcela D. Urzua; Fernando J. Mendizábal; Walton J. Cabrera; Hernán E. Ríos (pp. 93-100).
The interfacial properties of poly(maleic acid-alt-1-alkene) disodium salts at hydrocarbon/water interfaces are determined. In all the studied systems, the interfacial tension decreases markedly with the polyelectrolyte concentration as the side-chain length increases. The results of the standard free energy of adsorption,Î”Gads0, are a linear function of the number of carbon atoms in the polyelectrolyte side chain. The contribution toÎ”Gads0 per mol of methylene group varies from âˆ’0.64 to âˆ’0.52 kJ/mol for the n-octane/water to n-dodecane/water interfaces.Î”Gads0 data also reveal that the adsorption process is mainly determined by adsorption efficiency. Comparatively, the adsorption effectiveness seems to play a less important role. The theoretical interaction energies calculated for the insertion of one hydrocarbon molecule into the space formed by two neighboring polyelectrolyte side chains are in good agreement with the experimental results. The latter results are consistent with van der Waals-type interactions between the hydrocarbon molecules and the polyelectrolyte side chains.
Keywords: Amphipathic polyelectrolytes; Waterâ€“hydrocarbon interfaces; Adsorption free energies
Interaction forces between cellulose microspheres and ultrathin cellulose films monitored by colloidal probe microscopyâ€”effect of wet strength agents
by Stefano Leporatti; Ronny Sczech; Hans Riegler; Stefano Bruzzano; Joachim Storsberg; Fritz Loth; Werner Jaeger; André Laschewsky; Stephan Eichhorn; Edwin Donath (pp. 101-111).
Colloidal probe microscopy was employed to study forces between cellulose surfaces upon addition of a series of cationic copolymers in aqueous solution, as model compounds for wet strength agents. The content of quaternary ammonium groups and primary amines was systematically varied in the cationic polymers, to distinguish between the importance of electrostatical and H-bonding effects. Cellulose microspheres were glued at the apex of tipless microfabricated cantilevers and used as colloidal probes. Ultra thin cellulose films and cellulose fibres were employed as model surfaces. The cellulose films of a thickness of about 5 nm were spin-coated from cellulose solution onto silicon substrates. The root-mean-square-roughness (RMS) was 0.3â€“0.8 nm. The cationic model polymers were compared to Servamine, a polymer employed as standard wet strength resin in papermaking industries. Force versus separation measurements showed a detailed picture of adhesion and contact breaking. Relatively strong adhesion of the order of 0.3 mJ/m2 was observed with Servamine within a range of approximately 10 nm. At larger distances weak bond breaking and elastic chain pulling were identified. When approaching the surface one to two small jump-in's possibly related to strong binding of Servamine and subsequent attraction could be found in the case of Servamine. In contrast, all the model copolymers showed only a weak adhesion of 8â€“30 Î¼J/m2, i.e., an order of magnitude less than that of Servamine and subsequent elastic rupture domains. The contour length, persistence length and characteristic rupture distances were calculated by means of applying the WLC model. Measurements against cellulose fibres obtained from the production process proved the relevance of the model systems.
Keywords: Colloidal probe microscopy; Adhesion; Cellulose; Wet strength; Polyelectrolytes
Chemisorption of thiolated poly(ethylene oxide) to gold: surface chain densities measured by ellipsometry and neutron reflectometry
by Larry D. Unsworth; Zin Tun; Heather Sheardown; John L. Brash (pp. 112-121).
Physical property studies of surfaces formed by chemisorption of polyethylene oxide (PEO) onto gold are reported. Such surfaces have potential as model materials for elucidation of the mechanism of resistance to protein adsorption by PEO surfaces. Thiolated monomethoxy poly(ethylene oxide) (PEO) was chemisorbed onto gold-coated silicon wafers under various conditions such that different surface chain densities were achieved. Chain density was varied by controlling PEO solubility (proximity to cloud-point conditions) as well as chemisorption time. Films prepared with PEO of molecular weight 750, 2000, and 5000 g/mol were studied. Chain densities determined in the dry state by ellipsometry were found to be in the range of 0.4â€“0.7, 0.33â€“0.58, and 0.12â€“0.30 chains/nm2 for MW 750, 2000, and 5000 PEO, respectively. Chain density was found to decrease with increasing molecular weight and to increase as cloud-point conditions were approached. PEO-layer mass densities and chain densities were determined independently by neutron reflectometry. Under low-solubility conditions and for a 4-h chemisorption time, film mass and chain density values of1.0Â±0.3Â gâ€‰cmâˆ’3 and1.8Â±0.9Â chains/nm2 were found for MW 750 PEO, and0.82Â±0.02Â gâ€‰cmâˆ’3 and0.23Â±0.07Â chains/nm2 for MW 5000 PEO. Ellipsometry data for these systems yielded graft densities of0.63Â±0.13 and0.30Â±0.02Â chains/nm2, respectively. Using the mass densities obtained from the neutron data in the ellipsometry calculations, chain densities of0.6Â±0.3 and0.25Â±0.02Â chains/nm2, respectively, were obtained for the MW 750 and 5000 films. The ellipsometry and neutron data for the MW 5000 system are thus in agreement within experimental error. In general, the chain-density values are much higher than those corresponding to layers of unperturbed random coil PEO (â€œmushroomsâ€?), suggesting that the PEO layers are in the brush regime with the chains in an extended conformation.
Keywords: Ellipsometry; XPS; Poly(ethylene oxide); Chemisorption; Conformation; Cloud point; Surface chain density; Neutron reflectometry
Improved cellular adhesion to acetone plasma modified polystyrene surfaces
by S.A. Mitchell; M.R. Davidson; R.H. Bradley (pp. 122-129).
The plasma polymerization of acetone has been used to modify polystyrene substrates for the controlled growth of human fibroblast cells. The surface modified polystyrene was studied by X-ray photoelectron spectroscopy, water contact angle and atomic force microscopy. This showed the surface oxygen levels and wettability to increase rapidly with exposure to the acetone plasma. High-resolution XPS allowed the determination of the relative amounts of surface hydroxyl, carbonyl and carboxyl groups. This showed that there was little incorporation of carboxyl groups in the deposited films. AFM measurements revealed the films to be conformal with a surface roughness equivalent to that of the underlying polystyrene substrate with film growth rates of approximately 0.5 nmâ€‰minâˆ’1. High edge-definition patterns were produced with a simple masking procedure and allowed the confinement of cells to selected areas of the substrate. These chemically patterned surfaces allowed the study of cells confined to particular regions of the substrate as a function of incubation time.
Keywords: Plasma modification; Polymer surfaces; XPS; AFM; Contact angle; Cell adhesion
Dissolution kinetics of granular calcium carbonate in concentrated aqueous sodium dichromate solution at pH 6.0â€“7.0 and 110â€“130â€‰Â°C
by Tiangui Wang; Zuohu Li (pp. 130-135).
An understanding of the factors controlling calcite dissolution is important for modeling geochemical cycles and impacts of greenhouse gases on climate, diagenesis of sediments, and sedimentary rocks. It also has practical significance in the investigation of behavior of carbonates in petroleum and natural gas reservoirs and in the preservation of buildings and monuments constructed from limestone and marble. A large number of papers have been published on dissolution kinetics of calcium carbonate in aqueous solutions. But few involved the near-equilibrium region, especially at elevated temperatures and in concentrated solutions. In this paper, the dissolution kinetics of calcium carbonate in concentrated aqueous sodium dichromate solutions at pH 6.0â€“7.0 and 110â€“130â€‰Â°C were studied in a 2-L autoclave. The results indicate that the dissolution reaction is mix-controlled, with surface reaction as the prevailing factor. The concentration of calcium ions in solution hardly affects the dissolution rate, but carbon dioxide in the vapor phase inhibits the dissolution reaction. The dissolution rate can be expressed byR=k1aH+2+k2, and the apparent activation energy is 55â€“84 kJâ€‰molâˆ’1.
Keywords: Dissolution kinetics; Calcium carbonate; Aqueous sodium dichromate solution; Elevated temperature
Physicochemical properties and stability of activated sludge flocs under temperature upshifts from 30 to 45â€‰Â°C
by F. Morgan-Sagastume; D.G. Allen (pp. 136-145).
The impacts of temperature shifts from 30 to 45â€‰Â°C on the structural stability and surface charge of activated sludge flocs were assessed in four sequencing batch reactors (SBRs) treating pulp and paper mill effluent. The improvement in floc stability was tested by sludge magnesium enrichment in one SBR and by operating another reactor at a high sludge retention time (SRT) of 33 days. Floc stability was characterized by dissociation constants with solutions of CaCl2, KCl, urea, and ethylenediamine tetraacetate (EDTA). Surface charge was assessed by cationicâ€“anionic titration and metals concentrations were also determined. The temperature shift consistently caused an increase in the negative sludge surface charge from approximately âˆ’0.180 toâˆ’0.300Â meq/g MLSS. Magnesium enrichment and a high SRT of 33 days promoted less negatively charged sludge, dampened the increase in negative sludge surface charge, and yielded structurally stronger flocs; however, sludge deflocculation still occurred. Manganese and iron appeared to be released by sludge under the temperature shift. It was concluded that the temperature shift deteriorates the flocculating physicochemical properties of the sludge and that better floc stability achieved by magnesium enrichment and a high SRT is not enough to stop deflocculation. Further research is required to clarify the origin of the increase in negative sludge surface charge, the role of metals, and the governing factors in sludge deflocculation under such temperature shifts.
Keywords: Activated sludge; Floc stability; Surface charge; Temperature upshifts; Metals; Deflocculation; Dissociation constants
Migration and precipitation of soluble species during drying of colloidal films
by Pär Wedin; Lennart Bergström (pp. 146-154).
The evaporation-induced convection resulted in a transport of dissolved species, a water-soluble polymer (carboxymethylcellulose) and dissolved CaCO3, to the drying front of silica and CaCO3 dispersions where the material eventually precipitates. Scanning electron microscopy and chemical analysis showed that the concentration of carboxymethylcellulose, CMC, is highest in the centre of the dried silica film and decreases towards the perifery. The colloidal films of the monodisperse silica particles displayed a high degree of structural order even at high concentrations of the non-adsorbed polymer CMC, which suggests that any depletion induced interparticle attraction is insufficient to affect the assembly of the colloidal crystal. The CaCO3 particles are slightly soluble and we found that rod-like crystals reprecipitated in the centre of the particle films on top of the polyacrylate-coated particles. Addition of CMC disturbs the formation of distinct crystal shapes which was attributed to a complexation of Ca2+ in solution.
Keywords: Migration; Precipitation; Structure; Silica; CaCO; 3; Colloidal stability; CMC; Carboxymethylcellulose; Polyacrylate; NaPA
Adsorption of poly(acrylic acid) onto the surface of titanium dioxide and the colloidal stability of aqueous suspension
by Shengcong Liufu; Hanning Xiao; Yuping Li (pp. 155-163).
The adsorption of poly(acrylic acid) (PAA) in aqueous suspension onto the surface of TiO2 nanoparticles was investigated. FTIR spectroscopic data provided evidence in support of hydrogen bonding and chemical interaction in the case of the PAAâ€“TiO2 system. Adsorption isotherms demonstrated that part of the PAA initially added to the suspension was adsorbed onto the TiO2 surface, after which there was a gradual attainment of an adsorption plateau. The adsorption density of PAA was found to increase with an increase of PAA molecular weight, while it decreased with an increase of pH. The thickness of the PAA adsorption layer was calculated based on measurements of suspension viscosities in the absence and presence of PAA. It was shown that the thickness of the adsorption layer increased with the increase of pH, PAA molecular weight, and its concentration. The surface charge density, the diffuse charge density, and the zeta potential of TiO2 varied distinctly after PAA adsorption. The shift of pHiep toward a lower pH value was observed in the presence of PAA. PAA was found to stabilize the suspension of TiO2 nanoparticles through electrosteric repulsion. The influence of factors such as PAA molecular weight and its concentration on the colloidal stability of the aqueous suspension was also investigated.
Keywords: Titanium dioxide nanoparticles; Adsorption; Poly(acrylic acid); Colloidal stability
Bimetallic isopropoxides M[Al(OC3H i7)4]3 (Mâ€…=â€…Pr, Nd)â€”catalyzed reduction of 2-octanone and benzophenone
by Sudhindra N. Misra; Ram S. Shukla; Minaz A. Gagnani (pp. 164-170).
Bimetallic alkoxides of praseodymium and neodymium with aluminum, viz., M[Al(OC3H i7)4]3, where Mâ€…=â€…Pr(III)/Nd(III), have been used as catalysts in Meerweinâ€“Ponndorfâ€“Verley (MPV) reduction of 2-octanone and benzophenone in isopropanol to give their corresponding secondary alcohols. The reduction of ketones is investigated by following the absorption spectra involving 4 fâ€“4 f transitions. During the MPV reduction the oscillator strengths(P) and the Juddâ€“Ofelt intensity (TÎ»,Î»=2,4,6) parameters corresponding to each 4 fâ€“4 f band (H43â†’D21,H43â†’P03,H43â†’P13, andH43â†’P23 in praseodymium, andI9/24â†’F3/24,I9/24â†’F5/24,I9/24â†’F7/24,I9/24â†’G5/24, andI9/24â†’G7/24 in neodymium alkoxides) at different time intervals have also been calculated and used in the determination of rates. Rates were calculated in terms of complexation of ketone and isopropanol with M[Al(OC3H i7)4]3 during the MPV reaction, from the changes in both absorbance and oscillator strength with time, and were found to be comparable, verifying the Juddâ€“Ofelt theory. The stronger oxyphilicity of Pr(III) and Nd(III) in M[Al(OC3H i7)4]3 than of their analogue Al(III) in Al(OC3H i7)3 made the bimetallic alkoxides better catalyst in MPV reduction of ketones.
Keywords: Pr[Al(; OC; 3; H; i; 7; ); 4; ]; 3; Nd[Al(; OC; 3; H; i; 7; ); 4; ]; 3; Absorption spectra; 4; f; â€“4; f; transitions; Meerweinâ€“Ponndorfâ€“Verley reductions; Ketones; Kinetics
Adsorption of NO and CO over transition-metal-incorporated mesoporous catalytic materials
by Suresh K. Bhargava; Deepak B. Akolekar (pp. 171-178).
Novel high-surface-area mesoporous catalysts of type Al-MCM-41 containing transition metals such as iron, nickel, cobalt, zinc, copper, and cobalt were prepared and characterized using techniques such as BET, FTIR, ICP-MS, XPS, and XRD. The XPS measurements indicated that the transition-metal particles are located in the bulk or pore channels of the Al-MCM-41 materials. A detailed in situ FTIR investigation undertaken on the adsorption and disproportionation of NO and CO over the transition-metalâ€“Al-MCM-41 mesoporous catalysts indicated the formation of various NO/CO species or complexes with active metal sites. The structure and dynamics of the metal activated complex and reactive species formed during the CO/NO reaction together with advantages of these catalysts and the influence of reaction temperature and pressure have been studied. NO adsorption at room temperature leads to the formation of adsorbed N2O, NO2, MNO2, MNO, and [M(NO)2] complexes. CO adsorption at room temperature leads to the formation of physisorbed carbon dioxide and cationic Lewis acid carbonyl moieties as well as transition-metal carbonyl complexes. The copper mesoporous catalysts prepared by different procedures (ion exchanged and as-synthesized) were compared for their interactions with CO and NO probe molecules.
Keywords: FTIR; NO; CO; Transition metal; MCM-41; Zn; Ni; Fe; Co; Cu; Active metal sites; XPS
Modification of ion-exchange membrane used for separation of protons and metallic cations and characterization of the membrane by currentâ€“voltage curves
by Gwenaël Chamoulaud; Daniel Bélanger (pp. 179-187).
The ionic transport properties of several cations (H+, Na+, and Zn2+) across sulfonated ion-exchange membranes modified with an amine were investigated by the measurement of currentâ€“voltage curves to determine the effect of the surface modification of the membrane. The membrane was modified by chlorosulfonation and amination with a diamine (N,N-dimethylethylenediamine) and an amine (isoamylamine) to form a sulfonamide bond between amine groups and the surface layer. In the case of the modification with the diamine, the terminal amine was protonated in acidic media or quaternized with methyl iodide. The presence of a positively charged layer on the two sides of the membrane strongly decreased the limiting current flowing across the membrane in the presence of a 1:1 electrolyte such as HCl or HNO3 due to an increase of the resistance of the membrane. In the case of divalent cations such as Na+ and Zn2+, electrostatic repulsion also contributes to the decrease of the limiting current. The presence of divalent anions seems to increase the limiting current somewhat due to their preconcentration within the cationic layer, which facilitates their subsequent transport across the membrane. When only one face of the membrane was modified, the currentâ€“voltage measurements showed that the membrane did not behave like a bipolar membrane. For one-side (under forward polarization) and two-side modified membranes, counterions are slightly blocked in the membrane by the cationic layer, which led to a decrease of the membrane conductivity during electrodialysis.
Keywords: Ionic transport; Electroconvection; Cationic layer; Membrane modification; CMX; Protonated layer; Quaternized layer; Hydrophobic layer; Concentration polarization
Effect of calcium and carbonate concentrations on cationic membrane fouling during electrodialysis
by Laurent Bazinet; Monica Araya-Farias (pp. 188-196).
Fouling, which is the accumulation of undesired solid materials at the phase interfaces of permselective membranes, is one of the major problems in electrodialysis. The aim of the present work was to investigate the effect on the fouling of cation-exchange membranes of the composition in calcium and carbonate of a model solution to be treated by electrodialysis. No fouling was observed at 400 and 800 mg/L of CaCl2 in the absence of carbonate, while at only 400 mg/L CaCl2 with carbonate, a deposit was observed. This difference could be explained by the buffering capacity of the carbonate, which affects the treatment duration with and without sodium carbonate. Since the duration was longer with carbonate, more calcium ions were able to migrate across the CMX-S membrane, which explained the higher deposit on its surface. Furthermore, whether there was carbonate in the solution treated by electrodialysis or not, the deposit on the surface of the cationic membrane was calcium hydroxide. However, this fouling formed during conventional ED was easily cleaned by an acid procedure.
Keywords: Electrodialysis; Cationic membrane; Fouling; Calcium hydroxide; Carbonate; Calcium
Solid base for hydrogen sulfide removal in light oil
by Yongfeng Duan; Daohong Xia; Yuzhi Xiang; Xiwen Zhang (pp. 197-200).
Three solid bases, with three kinds of activated carbon as supporters and alkaline materials as active components, were tested for hydrogen sulfide removal in light oil. The solid bases have high intensity and greater adsorption capacity for hydrogen sulfide removal and are more easily regenerated.
Keywords: Hydrogen sulfide; Solid base; Adsorption; Light oil
Observation of wall wettability under imposed flow by fluorescence depolarization: dependence on surface oxygen content and degree of polymer branching
by Cristina M. Quintella; Ana Paula S. Musse; Martha T.P.O. Castro; Cristiane C. Gonçalves; Yuji N. Watanabe (pp. 201-208).
This work was concerned with the dependence of the interfacial tension (Î“SL) on surface degree of oxygen content and on polymer branching degree. The staticÎ“SL was evaluated by contact angle (Î¸c) and the dynamicÎ“SL by fluorescence depolarization of molecular probes seeded in induced flows of monoethylene glycol. The latter results were interpreted using statistical covariant analysis. Two different systems of flowing films were studied: free films flowing on the surfaces on which they impinge and films flowing inside 1-mm-thick microflow cells. The solid surfaces were polyethylene of low density, medium density, high density, and linear with low density, polypropylene, vinyl acetate co-polymer with oxygen content of 15% and 28%, borosilicate, and tin dioxide. Increase in oxygen content of the surface decreased both the static and the dynamicÎ“SL, which demonstrated that the presence of oxygen atoms hindered wetting. Only the dynamicalÎ“SL was sensitive to polymer branching, and it increased as branching degree decreased. This was attributed to the higher hydrogen-atom density at the surface, which favored temporary intermolecular bonds between the surface and the flowing liquid.
Keywords: Fluid microdynamics; Intermolecular forces; PLF; Dynamic interactions; Adhesion; Drag
Energy and hydrodynamic approaches to magnetocapillary instability of nonconducting jets
by Y. Zimmels; L.G. Fel (pp. 209-217).
The field energy and magnetocapillary instability of isothermal incompressible and inviscid nonconducting liquid jets in a uniform magnetic field are considered. The equivalence between static and dynamic approaches at the onset of instability and cutoff wavelength is shown and its implications are discussed. A new dispersion relation for magnetocapillary instability in such jets is derived. This relation differs from that given in the literature. The existence of a critical magnetic field that stabilizes jets with finite susceptibility is established. It is shown that the jet is stabilized by the field irrespective of its being para- or diamagnetic, but the extent of stabilization is different.
Keywords: Plateau problem; Magnetocapillary instability; Nonconducting liquid jet
Interactions between n-octyl and n-nonyl Î²-d-glucosides and Î±- and Î²-cyclodextrins as seen by self-diffusion NMR
by Artur J.M. Valente; Markus Nilsson; Olle Söderman (pp. 218-224).
In this work1H NMR self-diffusion experiments have been performed to determine the self-diffusion coefficients of n-octyl Î²-d-glucoside and n-nonyl Î²-d-glucoside in Î±-cyclodextrin and Î²-cyclodextrin solutions at 25â€‰Â°C. Two questions are addressed. The first concerns the general influence on nonionic surfactant transport properties when cyclodextrins are present in solution. The second question concerns the influence of surfactant-chain length and cyclodextrin cavity volume on the association constant. The self-diffusion coefficients of the alkyl glucosides, in cyclodextrin-containing solutions, depend on the cyclodextrin concentration on account of the formation of complexes. The cyclodextrin diffusion is only mildly influenced, since the complex has similar diffusion coefficients as the free cyclodextrin. There are some obstruction effects at the highest surfactant concentrations which decrease the cyclodextrin diffusion. A set of equations to model the self-diffusion coefficients of the surfactant and cyclodextrin was developed and is presented. On the basis of such equations, properties such as association constants, and micelle and complex diffusion coefficients can be estimated.
Keywords: Cyclodextrin; Alkyl glucosides; Self-diffusion; NMR
Effect of microwave pretreatment of coal for improvement of rheological characteristics of coalâ€“water slurries
by B.C. Meikap; N.K. Purohit; V. Mahadevan (pp. 225-235).
Indian high-ash coal contains Î±-silica components of the mineral matter. When coal is transported in the form of a slurry, Î±-silica adds to the settling properties of coal and enhances erosion of pipelines. As such any technique that will contribute to changing the characteristics of mineral matter by selective demineralization is bound to supplement the knowledge of coal slurries in the science of rheology. One such method is the use of a novel microwave technology, which changes the Î±-silica to less harmful Î²-silica. Thus microwave-treated coal slurry facilitates enhanced flow characteristics and abates the erosion problem in pipeline transport as well as in coal-slurry injection furnaces. This paper reports on the rheological study of closely sized coal particles of medium-volatile, low-ash, low-moisture cleans and high-ash rejects with and without microwave treatment. Viscosity of suspensions of microwave-treated coal was found to be less than that of untreated coal, in the case of both cleans and rejects. Microwave pretreatment thus reduces the viscosity and the pumping cost and opens a new outlook for pipeline transport. An attempt has been made to quantify the improvement of rheological characteristics due to microwave pretreatment.
Keywords: Microwave treatment; Coal slurries; Viscosity; Rheological properties; Slurry transport
Electrokinetic properties of sepiolite suspensions in different electrolyte media
by Mahir Alkan; Ã–zkan DemirbaÅŸ; Mehmet DoÄŸan (pp. 240-248).
The present paper deals with the electrokinetic characterization of sepiolite. A series of systematic zeta potential measurements have been carried out to determine the isoelectric point (iep) and potential-determining ions (pdi), and the effect of mono-, di-, and trivalent electrolytes such as NaCl, KCl, LiCl, NaNO3, NaCH3COO, MgCl2, CaCl2, BaCl2, CoCl2, CuCl2, Pb(NO3)2, Na2CO3, Na2SO4, AlCl3, FeCl3, and Na3PO4 on the zeta potential of sepiolite. Zeta potential has been calculated with the aid of Smoluchowski's equation. Sepiolite yields an isoelectric point at pH 6.6. The zeta potential for the sepiolite has ranged from +23.3 mV at pH âˆ¼2 to âˆ’22.4 mV at pH âˆ¼8 at20Â±2â€‰Â°C in water. The valency of the ions have proven to have a great influence on the electrokinetic behavior of the suspension. Monovalent cations were found to have a weak effect, while di- and trivalent cations made the zeta potential positive. Charge reversal was observed for divalent cations at1Ã—10âˆ’2M and for trivalent cations at3Ã—10âˆ’4M. As a result, it can be said that monovalent cations are indifferent ions when di- and trivalent cations are potential-determining ions.
Keywords: Zeta potential; Sepiolite; Mono- and multivalent cations; Isolectrical point; Potential-determining ion
Soap-free synthesis for producing highly monodisperse, micrometer-sized polystyrene particles up to 6 Î¼m
by Yasuyuki Yamada; Tatsuro Sakamoto; Shunchao Gu; Mikio Konno (pp. 249-252).
A soap-free emulsion polymerization method with the use of an amphoteric initiator, currently proposed by the authors for producing highly monodisperse, micrometer-sized polymer particles, was examined in the polymerization of styrene with a 2,2â€²-azobis [ N-(2-carboxyethyl)-2-2-methylpropionamidine] hydrate initiator and an NH4OH/NH4Cl pH buffer. The pH buffer was used to control the electric surface potential of particles to maintain a stable dispersion of particles and to prevent generation of new particles during the polymerization. Addition of monomer to the reaction system during polymerization could enlarge the average size of polymer particles to 5.7 Î¼m with a coefficient of variation of 1.5%, which is much less than the standard criteria of monodispersity, 10%.
Keywords: Amphoteric initiator; Monodisperse polystyrene particle; Colloidal stability; Soap-free emulsion polymerization; Monomer addition
Chemical remediation of beech condensates
by Mohammed Irmouli; Jean Pierre Haluk (pp. 253-254).
In the present work, beech wood condensates are separated from the aqueous phase. Experimental results reveal an electrostatic interaction between the oppositely charged wood extracts after oxidation and Ca(OH)2. The increase in aqueous phase pH resulted in enhanced removal of wood extracts from water. The polarographic assays were carried out at 25â€‰Â°C using a Gilson oxygraph equipped with a Clark electrode in order to determine the oxygen uptake during the oxidation reaction. The effect of pH is explained based on oxygen uptake. The organic compounds found in the aqueous effluent are responsible for the brown color. The objective of this study is to find the optimum pH to eliminate the wood extracts from the liquid effluents.
Keywords: Condensate; Beech wood; pH
Analytical expressions for the electrical potential near planar, cylindrical, and spherical surfaces for symmetric electrolytes
by Sung-Hwa Lin; Jyh-Ping Hsu; Shiojenn Tseng; Chur-Jen Chen (pp. 255-257).
The conjecture of Tuinier (J. Colloid Interface Sci. 258 (2003) 45) for the electrical potentials near a cylindrical surface and near a spherical surface under the conditions of symmetric electrolyte and large scaled radius are derived by solving the corresponding Poissonâ€“Boltzmann equation. The surface charge densityâ€“surface potential relations for these surfaces are also derived under the conditions of constant surface potential. We show that the level of surface charge density for planar, cylindrical, and spherical surfaces follows the order spherical surfaceâ€…>â€…cylindrical surfaceâ€…>â€…planar surface.
Keywords: Electrical potential; Cylindrical surface; Spherical surface; Symmetric electrolytes; Large scaled radius
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