Investigation on adsorption behavior of bovine serum albumin (BSA) on superabsorbent composite is critical for many analytical and biomedical applications. In this study, a novel poly(methacrylic acid)-grafted cellulose/bentonite (PMAA-g-Cell/Bent) superabsorbent composite was synthesized by graft copolymerization reaction of methacrylic acid on cellulose (Cell) in the presence of bentonite (Bent) using N,N′-methylenebisacrylamide as a cross-linker. The original Cell and Bent and composite were analyzed using FTIR, XRD, SEM, TG, and potentiometric titrations. The ability of the composite to adsorb BSA from aqueous solutions has been studied at different optimized conditions. The optimum pH range for the maximum uptake of BSA was 4.5. Maximum adsorption of the BSA, i.e., 99.7%, was achieved from an initial concentration of 10.0 mg/L using 1.0 g composite at pH 4.0. The equilibrium time of adsorbing BSA was about 3 h. Experimental kinetic data were tested with pseudo-first-order and pseudo-second-order kinetic equations. The experimental data fitted very well with the pseudo-second-order kinetic model, indicating the coexistence of chemisorptions and physisorption. It was also found that the film diffusion played an important role in the rate control of the adsorption process. The applicability of the Langmuir, Freundlich, and Sips isotherms was used to try to describe the experimental isotherm equilibrium data. The BSA adsorption isotherm was best represented by the Sips model, which indicates a multilayer adsorption at lower concentration and monolayer at higher concentration. The equilibrium sorption capacity of 196.15 mg/g was determined from the Sips isotherm. The results of the six-time consecutive adsorption−desorption cycles showed the feasibility of repeated use of this composite.

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The removal and recovery of thorium(IV) [Th(IV)] ions from aqueous solutions were investigated using poly(methacrylic acid)-grafted-cellulose/bentonite (PMAA-g-Cell/Bent) superabsorbent composite through batch adsorption experiments. Surface characterizations of the adsorbent were investigated. The adsorbent showed significant Th(IV) removal (>99.7%) at pH 5.0. The influence of coexisting ions on the adsorption of Th(IV) was studied. Mass transfer aspects of Th(IV) adsorption onto PMAA-g-Cell/Bent were evaluated. The Sips adsorption isotherm described the adsorption data very well, with a maximum adsorption capacity of 188.1 mg/g. Thermodynamic parameters such as standard enthalpy (ΔH°), standard entropy (ΔS°), standard free energy (ΔG°), activation energy (E a), isosteric enthalpy (ΔH x ), and entropy (ΔS x ) were calculated. Tests with a seawater sample revealed the effectiveness of PMAA-g-Cell/Bent for adsorptive removal of Th(IV) from aqueous solutions. Desorption experiments showed that 0.1 M HNO3 can effectively desorb adsorbed thorium ions with a contact time of 3 h. A single stage batch reactor is designed for commercial applicability of the adsorbent.

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