Surface investigations of selective biosorption and reduction of hexavalent chromium ions Cr(VI) over chitosan@MoO₃ and chitosan-cellulose@MoO₃ biocomposite.

Herein we synthesized two novel chitosan-based bicomposites namely chitosan@ MoO3 (Ch@MoO3) and chitosan-cellulose @ MoO3 (Ch-CS@MoO3) to detoxify water polluted with hexavalent chromium through adsorption reduction technology. The bicomposites were characterised using XPS, FT-IR, SEM, EDS, XRD, TGA, BET and DLS. XPS results suggested that Cr(VI) detoxification occurs through the electrostatic attraction and chemical bonding of Cr(VI) to the surface functional groups (Mo6+, -NH2+, -OH+) followed by reduction of Cr(VI) to Cr(III). FT-IR revealed changes in the surface functional groups after adsorption. XRD showed a successful incorporation of MoO3 into chitosan matrix. The surface texture of Ch@MoO3 was homogeneous with small spherical shape while Ch-CS@MoO3 exhibited a rough and dense fiber-like structure as evidenced by SEM characterization. N2 adsorption-desorption isotherm displayed H3-type hysteresis loop and a pore size diameter of 16.4 nm and 14.3 nm for the Ch@MoO3 & Ch-CS@MoO3 respectively. Adsorption capacity (Qmax) values were 128.2 and 52.3 mg/g for Ch@MoO3 and Ch-CS@MoO3 respectively. The metal surface coverage mapping was 5.4 x 1023 and 3.9 x 1020 atoms/m2 for Ch@MoO3 and Ch-CS@MoO3 respectively. Adsorption followed Langmuir isotherm and pseudo-second-order (PSO) kinetics, indicating monolayer chemisorption dominance. The intraparticle diffusion (IPD) model demonstrated a boundary layer control. Thermodynamically, both bicomposites exhibited spontaneous and endothermic biosorption nature.