Synthesis, characterization, and kinetic study of activated carbon modified by polysulfide rubber coating for aqueous hexavalent chromium removal

[Display omitted] •Thiol-modified activated carbon was synthesized by coating polysulfide rubber on AC (AC-PSR).•AC-PSR showed higher aqueous Cr(VI) adsorption capacity than virgin AC.•Effects of pH, initial Cr(VI) concentration, time, and adsorbent dose were studied.•Both adsorbents showed biphasic intraparticle diffusions for Cr6+ removal while AC-PSR was superior in longer contact times.•AC-PSR maintained ∼98% Cr(VI) removal efficiency even after four cycles of regeneration and reuse. Activated carbon (AC) is a widely used adsorbent with a limited selectivity for chromium species. In this study, polysulfide rubber (PSR) polymer was synthesized, characterized by FTIR, and coated on F400 granular AC to obtain AC-PSR. The material properties of this composite adsorbent were investigated using SEM, TEM, EDS, TGA, BET isotherm, and XPS. The effectiveness of AC-PSR for aqueous Cr(VI) removal was investigated, and compared against virgin AC. The results showed that despite a 23% decrease in the surface area of AC after PSR coating, AC-PSR had a higher capacity for Cr(VI) adsorption. Adsorption followed a pseudo-second-order biphasic diffusion model for both AC and AC-PSR. The reaction rate constants showed that despite faster initial kinetics between AC and Cr(VI) during the film diffusion step, AC-PSR exhibited faster kinetics during the intraparticle diffusion step. The Langmuir isotherm model was found to be the best model to describe the experimental data, which showed a higher adsorption capacity for AC-PSR (QM,AC=3.472mg/g vs. QM,AC-PSR=8.929mg/g) and a stronger binding between Cr(VI) and AC-PSR (bA,AC=0.391L/mg vs. bA,AC-PSR=0.696L/mg). Regenerated AC-PSR showed an 8% increase in Cr(VI) removal efficiency after the first cycle, and then maintained a ∼98% Cr(VI) removal for three additional successive cycles.