Formation and characteristics of cationic-polymer/bentonite complexes as adsorbents for dyes

The adsorption of cationic polymer, i.e., epicholorohydrin-dimethylamine polyamine (EPI-DMA), on bentonite particles was investigated under various conditions of bulk polymer concentration, pH, inorganic salts, and temperature. The resulting high adsorption rate and alkaline solution (pH = 7–11) effect indicated a strong electrostatic interaction between the clay particles and EPI-DMA molecules. Addition of salt can also influence the adsorption of EPI-DMA onto bentonite by affecting the clay particle sizes, the polymer zeta potential and etc. The Freundlich and Langmuir isotherm models were employed and fit the experimental data well in the low EPI-DMA concentration range 0.5–5.0 mg L^− 1. The enthalpy implied by the temperature dependence of adsorption of EPI-DMA on bentonite is 7.93 kJ mol^− 1, suggesting that neither coordination exchange nor chemical bond forces exit in this system. In addition, at high temperatures, larger amounts of EPI-DMA were adsorbed by bentonite, which indicated that increased entropy in the dissolved EPI-DMA molecules contributes to adsorption. The X-ray diffraction (XRD) analysis showed that besides the EPI-DMA molecules intercalated between the layers of bentonite, excess polymer molecules were adsorbed onto polymer loops protruding from the surface of the complex. The TGA and corresponding DSC plots demonstrated that the EPI-DMA polymer had intercalated into the clay layers and thus the EPI-DMA/bentonite was more hydrophobic than natural bentonite. With the addition of EPI-DMA polymer, the negatively charged clay particles increased to a net positive charge and the capacity for dye removal also went up with increasing polymer contents in EPI-DMA/bentonite complexes.     

Adsorption of alizarinate–micelle complexes on Na-montmorillonite

The adsorption on Na-montmorillonite of the monovalent anion alizarinate and its complexes with micelles of cationic surfactants was investigated. Micelles were prepared from octadecyltrimethylammonium (ODTMA) and benzyldimethylhexadecyl-ammonium (BDMHDA). Alizarinate–micelle complexes are much more efficient for the adsorption of the dye than alizarinate alone, e.g., from 0.05 mM alizarinate solution 12.5 mmol per 100 g clay was adsorbed in the presence of micelles, whereas only 4 mmol per 100 g clay was adsorbed in their absence. However, unlike the adsorption of alizarinate on the clay, where its adsorbed fraction increased with the concentration of the clay, in the presence of micelles, the concentration of the clay should be optimized for achieving maximal adsorption of alizarinate. This effect is due to monomer adsorption on excessive clay sites, which leads to the decomposition of micelles, and consequently, the adsorption of alizarinate is reduced.Visible spectra of alizarinate–micelle complexes in water and adsorbed on montmorillonite were recorded. The absorption band of alizarinate in aqueous solutions at 522 nm was red-shifted in the presence of ODTMA and BDMHDA micelles due to the effect of the micelle microenvironment. Further shifts were observed in the presence of montmorillonite indicating that the alizarinate–micelle complexes were adsorbed on the clay. Significant spectroscopic changes were observed after the adsorption of alizarinate–BDMHDA-micelle complex on the clay indicating that the adsorption leads to changes in the micelle. This observation suggests that the dye may serve as a probe in visible-spectroscopy study of the adsorption of micelles on clay minerals.     

Treatment of the production waste water of Konstantinovka Refractory Plant

Conclusions The coagulating action of aluminum sulfate and of the combination of it with polyacrylamide on a suspension of chamotte and clay, leading to a significant increase in particle size of the dispersed phase, was investigated.The presence of a threshold value of the addition of coagulant as an important production parameter determining the unstable suspension type sedimentation of particles was shown.To disturb the stability of the systems and to accelerate the clarification process of waste waters contaminated with chamotte and clay the necessary additions of reagents are 25–50 mg/liter of aluminum sulfate and 5 mg/liter of polyacrylamide.Translated from Ogneupory, No. 6, pp. 42–44, June, 1985.     

CO adsorption energy on planar Au/TiO2 model catalysts under catalytically relevant conditions

The adsorption of CO on planar Au/TiO₂ model catalysts was studied by polarization-modulation infrared reflection–absorption spectroscopy (PM-IRAS) under catalytically relevant pressure (10–50 mbar) and temperature (30–120 °C) conditions, both in pure CO and in CO/O₂ reaction gas mixtures. The adsorption energy of CO on the Au particles was determined by a quantitative analysis of the temperature dependence of the CO absorption intensity in adsorption isobars. The data reveal considerable effects of the Au particle size when pure CO is used; the initial adsorption energy decreases from 74 kJ mol⁻¹ (2 nm mean Au particle diameter) to 62 kJ mol⁻¹ (4 nm). For CO/O₂ gas mixtures, the initial CO adsorption energy is, irrespective of the Au particle size, constant at 63 kJ mol⁻¹ (i.e., the CO adsorption energy is reduced for smaller Au particles), but this effect vanishes for larger Au particles.     

Calcined tetrabutylammonium kaolinite and montmorillonite and adsorption of Fe(II), Co(II) and Ni(II) from solution

Kaolinite and montmorillonite were modified with tetrabutylammonium (TBA) bromide, followed by calcination. The structural changes were monitored with XRD, FTIR, surface area and cation exchange capacity measurements. The modified clay minerals were used for adsorption of Fe(III), Co(II) and Ni(II) ions from aqueous solution under different conditions of pH, time and temperature. The uptake of the metal ions took place by a second order kinetics. The modified montmorillonite had a higher adsorption capacity than the corresponding kaolinite. The Langmuir monolayer capacities for the modified kaolinite and montmorillonite were Fe(III): 9.3 mg g^− 1 and 22.6 mg g^− 1; Co(II): 9.0 mg g^− 1 and 22.3 mg g^− 1; and Ni(II): 8.4 mg g^− 1 and 19.7 mg g^− 1. The modified kaolinite interacted with Co(II) in an endothermic manner, but all the other interactions were exothermic. The decrease of the Gibbs energy in all the cases indicated spontaneous adsorption.     

Saudi Arabian clays for lead removal in wastewater

Three types of local clays–Tabuk, Baha, and Khaiber–were tested for their abilities to adsorb lead ions from wastewater. The effect of pH on the adsorption of lead ions was also investigated. The clays were treated with hydrochloric acid to activate adsorption sites within clay particles. Untreated Tabuk clay had the largest adsorption capacity, about 30 mg lead/g clay, in comparison with those of Baha and Khaiber clays. The smallest adsorption was observed with Khaiber clay, about 10 mg lead/g clay; this may be attributed to the prior existence of lead within the clay. The adsorption of the acid-activated clays was not enhanced compared to those of untreated clays. The Langmuir model described the experimental data for all untreated clays, while the Freundlich model described the experimental data of untreated Khaiber clay and treated Baha clay. The local clays tested in this study, especially Tabuk clay, may be utilized as cost-effective and efficient adsorbent materials for removing heavy metals from wastewater in Saudi Arabia.     

Methods of intensifying the sintering of kaolinitic clay

Conclusions We studied how combined additives improve the sintering of Kirov kaolinite clay. An addition of surface-active agent in the form HAlA still pot residue, and SAlA still pot residue, increased the densification during pressing and more intensively improved the sintering of Kirov kaolinite clay with combined incorporation with talc-magnesite.Incorporating 0.1–0.15% (as MgO) talc-magnesite and 0.3% mixture of still pot residues SAlA and HAlA (in the ratio 1:2) and 0.3% kerosene increases the apparent density from 2.30 to 2.47 g/cm³, and reduces the water absorption of the specimens made from Kirov clay from 6.6 to 3.8%.A high degree of sintering (apparent density 2.44 g/cm³ and water absorption 4.6%) is achieved by the combined use of talc-magnesite and water-soluble still pot residues HAlA.Translated from Ogneupory, No. 4, pp. 59–63, April, 1970.     

Adsorption and binding of the transgenic plant proteins, human serum albumin, β-glucuronidase, and Cry3Bb1, on montmorillonite and kaolinite: Microbial utilization and enzymatic activity of free and clay-bound proteins

Human serum albumin (HSA), β-glucuronidase (GUS), and the Cry3Bb1 protein from Bacillus thuringiensis subsp. kumamotoensis are expressed by genetically-modified plants. Commercial samples of these proteins adsorbed and bound rapidly on the clay minerals, kaolinite (K) and montmorillonite (M). Adsorption increased as the concentration of protein increased and then reached a plateau. The greatest amount of adsorption and binding occurred with the Cry3Bb1 protein, of which there was no desorption: 6.7 ±0.21 μg adsorbed and bound μg^− 1 of M; 2.1 ± 0.39 μg adsorbed and bound μg^− 1 of K. With GUS, 2.2 ± 0.29 μg adsorbed and 1.7 ±0.21 μg bound μg^− 1 of M; 1.5 ± 0.28 μg adsorbed and 1.0 ± 0.03 μg bound μg^− 1 of K. HSA was adsorbed and bound the least: 1.2 ±0.04 μg adsorbed and 0.8 ± 0.05 μg bound μg^− 1 of M; 0.4 ± 0.05 μg adsorbed and 0.4 ± 0.03 μg bound μg^− 1 of K. However, X-ray diffraction analyses indicated that only HSA intercalated M, and none of the proteins intercalated K, a nonswelling clay. When bound, the proteins were not utilized for growth by mixed cultures of soil microorganisms, whereas the cultures readily utilized the free (i.e., not adsorbed or bound) proteins as sources of carbon and energy. The enzymatic activity of GUS was significantly enhanced when bound on the clay minerals. These results indicated that recombinant proteins expressed by transgenic plants could persist and function in soil after release in root exudates and from decaying plant residues as the result of the protection provided against biodegradation by binding on clay minerals.     

Adsorption of poly (4‐sodium styrene sulfonate) on kaolinite clays

The adsorption of polymer on clay particles has great importance in many industrial applications. This work aimed to study the adsorption of anionic polymer, poly (4‐sodium styrene sulfonate), on kaolinite clay surfaces. Three different Egyptian kaolinite clay samples were used. The kaolinite clays were saturated with sodium or calcium cation. It was found that the Freundlich isotherm is applicable for this polymer adsorption on kaolinite. The parameters of the Freundlich equation are very close, indicating a comparable nature for the binding behavior between the different samples of kaolinite and the adsorbed polymer. The adsorption process was examined at different pH values (3, 6, and 9 ± 0.1) to cover the range below and above the point of zero charge of kaolinite surfaces. It was found that, below this point, the polymer adsorption increased, while above it the polymer adsorption decreased. The polymer adsorption on calcium kaolinite was higher than that of sodium kaolinite at the same pH value. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1712–1719, 2006     

Static filtration of purified sodium bentonite clay suspensions. Effect of clay content

The effect of clay content on the static filtration properties of purified Na-montmorillonite suspensions was studied at two different pressures. The results of filtering parameters are as expected. When the clay percentage increases, the thickness (e) of the obtained cake increases, leading to the decrease of water loss (WL), and consequently, to the decrease of permeability (k). These decreases of WL and k are more important for the low applied pressure than for the high one.The differences between values of the different experimental parameters (WL and e) obtained at applied pressures of 5.7×10⁵ and 1.5×10⁵ Pa, as a function of clay content in the initial samples, show some singular points. At the clay content corresponding to the sol–gel transition (SGT), already determined by rheological measurements, ΔWL presents a change in concavity and Δe shows a maximum. Localisation of this maximum seems to be a simple way to detect the SGT by performing static filtration experiments of two series' of clay suspensions at two different pressures.According to the water contents obtained at the two pressures, all the cakes were localised in region (2), defined by Norrish (1954) as the “macroscopic” swelling paste of Na-montmorillonite. At low applied pressure, the texture of the cakes is identified by transmission electron microscopy (TEM). Generally, at low magnification, all samples are globally homogeneous. However, they present some regions more dense than others. At high magnification, the number of layers per particle seems to depend on SGT. Indeed, in the cake corresponding to 1% w/w of clay in the initial suspension, isolated layers are most frequent and particles with two to four layers per particle are scarce. In the cake obtained from the gel (3% w/w of clay) the most frequent stacking is about three layers per particle, and isolated layers almost disappear. In the cake obtained from gel, at the SGT (5.5% w/w of clay) which is the less oriented sample, the most frequent stacking is statistically also around three layers per particle but with a greater number of particles, some isolated layers appear again. After the sol–gel transition, in the cake obtained from the 7% sample (which is the most oriented sample), the number of particles increases but the number of layers in each particle decreases (two layers per particle most frequently occurs), and the number of isolated layers again rises. The frequent distances between the aggregates and particles were estimated on the TEM images of the cakes obtained at 1.5×10⁵ Pa. The distances between the particles of the cakes obtained under 5.7×10⁵ Pa was identified by X-ray diffraction (XRD). All these distances measured by the two techniques are compared with a linear extrapolation of Norrish's (1954) experimental data. At SGT, the cakes obtained at the two pressures correspond to aggregates connected with several distance configurations. However, the cakes obtained from the 3% initial clay content always show two distances (19 and 39 Å) at high pressure. At low pressure, one distance is about 300 Å, and the other is about 65 Å. This last distance disappears in the cake obtained from the more diluted suspension (1%) and only the higher distance persists. The 3% initial clay suspension seems to correspond to a “local osmotic transition”, which occurs between aggregated particles (or small aggregates) in the semi-diluted suspensions and isolated particles and/or layers in the more diluted suspensions.     

Interaction of metal ions with clays: I. A case study with Pb(II)

Pb(II) adsorption was studied under different conditions (pH, time, metal ion concentration, clay amount, temperature) on kaolinite, montmorillonite, and their poly(hydroxo)zirconium (ZrO–kaolinite, ZrO–montmorillonite) and tetrabutylammonium (TBA–kaolinite, TBA–montmorillonite) derivatives. All samples were calcined (ZrO-derivatives at 773 K, TBA-derivatives at 973 K) before using as adsorbents. The data were interpreted assuming first- and second-order kinetics. The rate constants including the pore diffusion rate constant are reported. The adsorption data could be fitted with Freundlich and Langmuir isotherms, and the coefficients indicated favorable adsorption of Pb(II) on the clays. Determination of the thermodynamic parameters, ΔH, ΔS, and ΔG showed the adsorption to be exothermic accompanied by decrease in entropy and Gibbs energy.     

High-pressure adsorption of methane on montmorillonite,kaolinite and illite

Methane (CH₄) adsorption of Ca^2 +-montmorillonite (Mt), kaolinite (Kaol) and illite (Il) at 60 °C and pressures up to 18.0 MPa was investigated, during which the adsorption capacity was evaluated by the Langmuir adsorption model. The influences of adsorbed water and the interlayer distance of the clay minerals on CH₄ adsorption were explored by using heated Mt products with different interlayer distances as the adsorbent. Mt, Kaol and Il showed high CH₄ adsorption capacities, and their maximum Langmuir adsorption capacities were Mt, 6.01 cm³/g; Kaol, 3.88 cm³/g; and Il, 2.22 cm³/g, respectively. CH₄ was adsorbed only on the external surface of Kaol and Il; however, adsorption also occurred in the interlayer space of Mt, which had a larger interlayer distance than the size of a CH₄ molecule (0.38 nm). CH₄ adsorption in the interlayer space of Mt was supported by the lower CH₄ adsorption capacity of heated Mt products (with the interlayer distance < 0.38 nm) than that of Mt at high pressures despite the higher external surface areas of the heated Mt samples. The entrance of CH₄ into the interlayer space of Mt occurred at low pressures, and more CH₄ molecules entered the interlayer space at high pressures. Moreover, the adsorbed water occupied the adsorption sites of the clay minerals and decreased the CH₄ adsorption capacity. These results indicate that clay minerals play a significant role in CH₄ adsorption of shale and indicate that the structure and surface properties of clay minerals are the important parameters for estimating the gas storage capacity of shale.     

Synthesis and intercalation of silver nanoparticles in kaolinite/DMSO complexes

Ag nanoparticles were synthesized in the interlamellar space of a layered kaolinite. Disaggregation of the lamellae of the nonswelling kaolinite was achieved by the intercalation of dimethyl sulfoxide (DMSO). The kaolinite was suspended in aqueous AgNO₃ solution and the adsorbed Ag⁺ ions were reduced on the surface of kaolinite lamellae with NaBH₄ or UV light irradiation. The silver nanoparticles formed were characterized by X-ray diffraction (XRD), small angle X-ray scattering (SAXS), and transmission electron microscopy (TEM). We studied the effects of the two reduction methods on the size and the size distribution of Ag nanoparticles and how clay mineral structure is altered as a consequence of particle formation. It was established that the size of Ag nanoparticles depends on both silver content and the reduction method. Photoreduction of silver led to the formation of relatively large Ag nanoparticles (diameter 8–14 nm).     

Adsorption of difenzoquat on montmorillonite: model calculations and increase in hydrophobicity

The adsorption of difenzoquat (DZ) on montmorillonite was studied at a wide range of concentrations and ionic strengths. Up to difenzoquat loadings of 0.4 mmol/g clay, all the added cation were adsorbed. Maximal adsorbed amounts exceeded slightly the cation exchange capacity (CEC) of the clay (0.8 mol_c/kg). The adsorbed amounts did not change upon increasing the concentration of NaCl in the medium to 500 mM. An adsorption model that combines electrostatic equations with specific binding in a closed system could adequately predict the adsorbed amounts of DZ, even at high ionic strength. Simultaneous adsorption of the divalent cationic herbicide diquat (DQ) and DZ was also determined and the predictions of the model were adequate for total loadings up to the CEC of the clay. At higher loads the model adequately predicts the DZ adsorbed, but underestimates the amounts of DQ adsorbed. The influence of adsorbed DZ on the hydrophobicity of montmorillonite was tested by using the hydrophobic herbicide pendimethalin (PM). The adsorption isotherm of PM on crude montmorillonite is of the S type, indicating very low adsorption at low added amounts, and increasing affinity after part of the surface is covered with the hydrophobic molecules. Adsorption of PM on montmorillonite saturated with DZ up to 80% of the CEC showed a C behavior, indicating a partition mechanism between the solvent and the adsorbent even at low added amounts. The enhanced hydrophobicity of DZ–montmorillonite was also demonstrated in qualitative experiments in a mixed chloroform–water environment: whereas the crude clay mineral stayed in the water phase, DZ–montmorillonite concentrated in the chloroform phase.     

Adsorption behavior of aqueous europium on kaolinite under various disposal conditions

This work investigated the adsorption behavior of europium on kaolinite under various disposal conditions. Batch-wise adsorption and precipitation experiments and equilibrium model calculations were performed over a pH range of 4–10 and CO₂ concentration range of 0%, 0.03%, and 10%. Experimental precipitation behaviors are in agreement with the results of equilibrium model calculations using the geochemical code MINTEQA2. Aqueous species of Eu³⁺ exists mainly at pH 5 or below and solid phases of Eu(OH)₃(s), Eu(OH)CO₃(s), and Eu₂(CO₃)₃·3H₂O(s) are formed at higher pH ranges. Adsorption behavior of Eu on kaolinite in the low pH range can be explained by interlayer ion-exchange reaction. The significant increase in adsorbed amount at pH 5–6 is due to the surface complexation at the edge site of kaolinite. In the high pH range, precipitation of Eu contributes mainly to the adsorption quantity. The rapid decrease in adsorbed amount above pH 7 under 10% CO₂ condition occurs by the formation of anionic europium species of Eu(CO₃) ₂ ^- .The adsorption of Eu on kaolinite could be well interpreted by the Freundlich adsorption isotherm. The data except for the highest equilibrium concentration ranges were also explained by Langmuir isotherm and the maximum adsorbed quantity of Eu on kaolinite,b, is 1.2 mg/g.     

Optimization of kinetic data for two‐stage batch adsorption of Pb(II) ions onto tripolyphosphate‐modified kaolinite clay

BACKGROUND: Most adsorption studies consider only the adsorption of pollutants onto low cost adsorbents without considering how equilibrium and kinetic data can be optimized for the proper design of adsorption systems. This study considers the optimization of kinetic data obtained for the removal of Pb(II) from aqueous solution by a tripolyphosphate modified kaolinite clay adsorbent. RESULTS: Modification of kaolinite clay with pentasodium tripolyphosphate increases its cation adsorption capacity (CEC) and specific surface area (SSA) from 7.81 to 78.9 meq (100 g)^?1 and 10.56 to 13.2 m² g^?1 respectively. X‐ray diffraction patterns for both unmodified and tripolyphosphate‐modified kaolinite clay suggest the modification is effective on the surface of the clay mineral. Kinetic data from the batch adsorption of Pb(II) onto the tripolyphosphate‐modified kaolinite clay adsorbent were optimized to a two‐stage batch adsorption of Pb(II) using the pseudo‐second‐order kinetic model. Mathematical model equations were developed to predict the minimum operating time for the adsorption of Pb(II). Results obtained suggest that increasing temperature and decreasing percentage Pb(II) removal by the adsorbent enhanced operating time of the adsorption process. The use of two‐stage batch adsorption reduces contact time to 6.7 min from 300 min in the single‐stage batch adsorption process for the adsorption of 2.5 m³ of 500 mg L^?1 Pb(II) under the same operating conditions. CONCLUSION: Results show the potential of a tripolyphosphate‐modified kaolinite clay for the adsorption of Pb(II) from aqueous solution and the improved efficiency of a two‐stage batch adsorption process for the adsorption of Pb(II) even at increased temperature. Copyright © 2009 Society of Chemical Industry     

Surface charge heterogeneity of kaolinite in aqueous suspension in comparison with montmorillonite

An analogous study to 2:1 type montmorillonite [Tombácz, E., Szekeres, M., 2004. Colloidal behavior of aqueous montmorillonite suspensions: the specific role of pH in the presence of indifferent electrolytes. Appl. Clay Sci. 27, 75–94.] was performed on 1:1 type kaolinite obtained from Zettlitz kaolin. Clay minerals are built up from silica tetrahedral (T) and alumina octahedral (O) layers. These lamellar particles have patch-wise surface heterogeneity, since different sites are localized on definite parts of particle surface. pH-dependent charges develop on the surface hydroxyls mainly at edges besides the permanent negative charges on silica basal plane due to isomorphic substitutions. Electric double layers (edl) with either constant charge density on T faces (silica basal planes) or constant potential at constant pH on edges and O faces (hydroxyl-terminated planes) form on patches. The local electrostatic field is determined by the crystal structure of clay particles, and influenced by the pH and dissolved electrolytes. The acid–base titration of Na-kaolinite suspensions showed analogous feature to montmorillonite. The initial pH of suspensions and the net proton surface excess vs. pH functions shifted to the lower pH with increasing ionic strength indicating the presence of permanent charges in both cases, but these shifts were smaller for kaolinite in accordance with its much lower layer charge density. The pH-dependent charge formation was similar, positive charges in the protonation reaction of (Si–O)Al–OH sites formed only at pHs below  6–6.5, considered as point of zero net proton charge (PZNPC) of kaolinite particles. So, oppositely charged surface parts on both clay particles are only below this pH, therefore patch-wise charge heterogeneity exists under acidic conditions. Electrophoretic mobility measurements, however, showed negative values for both clays over the whole range of pH showing the dominance of permanent charges, and only certain decrease in absolute values, much larger for kaolinite was observed with decreasing pH below pH  6. The charge heterogeneity was supported by the pH-dependent properties of dilute and dense clay suspensions with different NaCl concentrations. Huge aggregates were able to form only below pH  7 in kaolinite suspensions. Coagulation kinetics measurements at different pHs provided undisputable proofs for heterocoagulation of kaolinite particles. Similarly to montmorillonite, heterocoagulation at pH  4 occurs only above a threshold electrolyte concentration, which was much smaller, only  1 mmol l^− 1 NaCl for kaolinite, than that for montmorillonite due to the substantial difference in particle geometry. The electrolyte tolerance of both clay suspensions increased with increasing pH, pH  6–6.5 range was sensitive, and even a sudden change occurred above pH  6 in kaolinite. There was practically no difference in the critical coagulation concentration of kaolinite and montmorillonite (c.c.c. 100 mmol l^− 1 NaCl) measured in alkaline region, where homocoagulation of negatively charged lamellae takes place. Rheological measurements showed shear thinning flow character and small thixotropy of suspensions at and above pH  6.7 proving the existence of repulsive interaction between uniformly charged particles in 0.01 M NaCl for both clays. The appearance of antithixotropy, the sudden increase in yield values, and also the formation of viscoelastic systems only at and below pH  6 verify the network formation due to attraction between oppositely charged parts of kaolinite particles. Under similar conditions the montmorillonite gels were thixotropic with significant elastic response.     

Adsorption of cationic dyes within spherical particles of poly(N-isopropylacrylamide) hydrogel containing smectite

Spherical particle of poly(N-isopropylacrylamide) hydrogel containing smectite clay (a synthetic saponite) was prepared by the polymerization of N-isopropylacrylamide in aqueous clay suspension. The diameter of the gel particle is 800–1300 nm and the clay content is 11 wt.% (clay/poly(N-isopropylacrylamide)). The gel particle was shown to be useful adsorbent of cationic species from water as a result of strong electrostatic interactions between smectites and the cationic species. Due to the fact that the cation adsorption capacity to the present hybrid hydrogel particles is determined by the cation exchange capacity of clay, the hydrogel particles containing clay are a useful scaffold to immobilize various cationic species to construct functional hybrid gel particles.     

Electrodeposition of nickel/silicon carbide composite coatings on a rotating disc electrode

Composite coatings suitable for protection against wear were prepared by electrodeposition from a nickel Watts solution containing silicon carbide particles maintained in suspension. To obtain a better understanding of hydrodynamic effects on the codeposition process a rotating disc electrode, immersed in a vertical rising flow, was used. The local concentration of embedded SiC along the radius of the disc electrode was studied as a function of suspension concentration, rotation rate and the particle mean diameter. The effect of a rheoactive polymer was also examined. Although it is generally admitted that the particle incorporation rate is governed by a two-step adsorption process, the experimental results show that it is also dependent on the spatial distribution of the wall fluid flow. The normal component of the fluid velocity promotes particle impingement, whereas the parallel component tends to eject the loosely fixed particles. The competition between the forces which tend to maintain particles attached to the surface and the shear force which tends to remove them, depends on several parameters, in particular the surface chemistry and the size of the particles, the flow rate and the current density.List of symbols A, B Tafel coefficients according to metal and particle deposition, respectively - _v volume ratio of the amount of code posited particles (vol %) - _w weight ratio of the amount of codeposited particles (vol %) - C concentration of the particles in suspension in the bath (g dm^–3) - F _adh, F _stagn, F _shear, F _fric forces exerted on particles (adhesion, stagnation, ejection, friction) - overpotential (V) - i current density (A dm^–2) - K Langmuir coefficient (g^–1 dm³) - T constant coefficient in Equation 2 - V _r, V _z radial and normal component of the fluid velocity (cm s^–1) - rotation rate of the disc electrode (rpm) - _c critical rotation rate (rpm)     

Effect of magnetic charging of Ni on electrolytic codeposition of Zn with Ni particles

Composite materials with unique properties can be produced by codepositing an inert phase during a cathodic metal deposition process. The feasibility of codeposition is mainly determined by the interaction of the inert phase and the cathodically deposited metal. When both the inert phase and the cathode or the cathodically deposited metal are ferromagnetic substances, codeposition can be promoted by magnetizing the inert phase prior to codeposition. Codeposition of Zn with Ni particles on a steel cathode from a weakly acidic zinc chloride based bath was investigated. The increased interaction between the magnetically remanent Ni particles and the steel cathode resulted in substantially higher percentages of Ni included in the deposit layer, especially at low concentrations of Ni particles in the bath. The model of Guglielmi, modified for conducting particles, proved to be valid; the value of adsorption parameter k _ad changed with magnetic remanency. Cathodic Zn deposition efficiency decreased with increasing concentration of Ni particles in solution and increasing Ni content in the deposit. The principle outlined can also be applied to systems with nonferromagnetic inert phases by coating these with ferromagnetic substances.List of symbols AG constant (Guglielmi) (V^–1) - BG constant (Guglielmi) (V^–1) - B magnetic field flux density (T) - Br remanent magnetic field flux density (T) - c _p concentration particles in bath (kg m^–3) - d _d deposit layer thickness (m) - F Faraday's constant (C mol^–1) - H magnetic field strength (A m^–1) - i current density (A m^–2) - i ₀ exchange current density (A m^–2) - k _ad Langmuir adsorption constant - M magnetization (A m^–1) - Mr remanent magnetization (A m^–1) - n valence of deposited metal - V _p volume of particles deposited per area of electrode surface (m) - W molecular weight (kg mol^–1) - X _p weight percentage of Ni in deposit - Y _p volume percentage particles in bath Greek symbols _p volume fraction of Ni in deposit - overpotential (V) - _c cathodic efficiency - ₀ magnetic permeability of vacuum (Vs A^–1 m^–1) - _{p, 0} constant for particle deposition (m s^–1) - _m density of metal matrix (kg m^–3) - degree of strong adsorption coverage degree of loose adsorption coverage - degree of loose adsorption coverage