The assembly of aqueous gold nanoparticles on the surface of polyurethane (PU) spheres leading to [gold nanoparticle shell]−[polyurethane core] structures is demonstrated. The assembly of gold nanoparticles on the polymer microspheres occurs through interaction of the nitrogens in the polymer with the nanoparticles. Such direct assembly obviates the need to perform additional surface modification of the polymer microspheres, which is an important step in other polymer-based core−shell structure protocols. The nanogold−PU material is then conjugated with the enzyme pepsin, leading to the formation of a new class of biocatalyst. In relation to the free enzyme in solution, the new bioconjugate material exhibited a slightly higher biocatalytic activity and significantly enhanced pH and temperature stability. The use of gold nanoparticle-labeled polymer microspheres in pepsin bioconjugation enables easy separation from the reaction medium and reuse of the bioconjugate over six reaction cycles.

Zirconium pillared clay (PILC) was prepared using montmorillonite as the base clay. Adsorption of tannic acid (tannin) was studied by a batch equilibrium technique, as a function of adsorbate concentration, temperature, pH, agitation speed, particle size of the adsorbent and ionic strength. The process of uptake is governed by diffusion controlled ®rst-order reversible rate kinetics. The higher uptake for the pH range 4.0±6.0 was attributed to external hydrogen bonding between phenolic-OH groups of tannin molecules and the hydrogen bonding sites on the clay. The removal of tannin by adsorption was found to be >99.0% depending on the initial concentration in the pH range of 4.0±6.0. The process involves both ®lm and pore diffusion to different extents. The effects of solute concentration, temperature, agitation speed and particle size on the diffusion rate were investigated. Tannin uptake was found to increase with ionic strength due to the compression of diffuse double layers. The applicability of Langmuir and Freundlich isotherm models has been tested. The maximum adsorption capacity of PILC was found to be 45.8 mmol g À1 of clay and the af®nity constant is 2.9 Â 10 À2 dm 3 mmol À1 at 30°C. Thermodynamic parameters such as DG°,DH°and DS°were calculated to predict the nature of adsorption. The isosteric enthalpies of adsorption were also determined and found to decrease with increasing surface coverage. Regeneration with hot water (60°C) has been investigated for several cycles with a view to recovering the adsorbed tannin and also restoring the sorbent to its original state.

The amine-modified polyacrylamide-grafted coconut coir pith carrying −NH3 +Cl- functional group at the chain end (PGCP−NH3 +Cl-) was investigated as an adsorbent for its possible application for the removal of chromium(VI) from aqueous solution and wastewater. The infrared spectroscopy results were used to confirm the graft copolymer formation and −NH3 +Cl- functional group. The grafting of polyacrylamide onto the coir pith improved the thermal stability of the adsorbent and enhanced the apparent activation energy for the thermal degradation of PGCP−NH3 +Cl-. X-ray diffraction pattern and scanning electron microscopy (SEM) studies were carried out to investigate the crystallinity and morphology of the adsorbent. The decrease in crystalline domains in PGCP−NH3 +Cl- results in the loss of tensile strength of the grafted chain and consequently enhances the free mobility of the grafted chain. Batch adsorption technique using PGCP−NH3 +Cl- was applied for the removal of chromium(VI) anion from aqueous solution and wastewater. The maximum adsorption of 99.4% (12.43 mg/g) took place from an initial concentration of 25.0 mg/L Cr(VI) at 30 °C, pH 3.0, and an adsorbent dosage of 2.0 g/L. The kinetics of sorption of Cr(VI) ions were described by a pseudo-second-order kinetic model. The temperature dependence indicates the exothermic nature of the process. Equilibrium isotherms were determined for different temperatures and the results are analyzed using the Langmuir and Freundlich isotherm equations. Adsorption isotherm experiments were also conducted for comparison using a commercial chloride form Dowex, a strong base (quaternary amine functionality) anion exchanger. Quantitative removal of 22.7 mg/L Cr(VI) in 50 mL of electroplating industry wastewater by 125 mg of PGCP−NH3 +Cl- was observed at pH 3.0. Alkali regeneration was also tried for several cycles with a view to recover the adsorbed metal ions and also to restore the sorbent to its original state.

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Development of simple and reliable protocols for the immobilization of enzymes is an important aspect of biotechnology. Gold nanoparticles are known to bind enzymes, but reuse characteristics of the gold nano−enzyme bioconjugates has hitherto been poor. In this paper, we demonstrate that gold nanoparticles bound at high surface coverage on 3-aminopropyltrimethoxysilane (APTS)-functionalized Na−Y zeolites are excellent candidates for the immobilization of pepsin. The assembly of gold nanoparticles on the zeolite surface occurs through the amine groups present in APTS. Pepsin was then bound to the Na−Y zeolite (core)−Au nano (shell) structures via interaction with the gold nanoparticles leading to a new class of biocatalyst. A highlight of the new biocatalyst wherein the enzyme is supported by a more massive biocompatible surface is the ease with which separation from the reaction medium may be achieved by simple sedimentation. The catalytic activity of pepsin in the bioconjugate was comparable to that of the free enzyme in solution. The pepsin−gold nano−zeolite bioconjugate material exhibited excellent activity over seven successive reuse cycles as well as enhanced pH and temperature stability.