A self-gating proton-coupled electron transfer reduction of hexavalent chromium by core-shell SBA-Dithiocarbamate chitosan composite

We have proposed a novel strategy for the reduction plus adsorption process for hexavalent chromium elimination by thiol functional hybrid materials through a self-gating process. Namely, we exploit that coating dithiocarbamate chitosan at the surface of SBA-15 affords a core-shell composite that undergoes reversible shape transformations while thiol functional groups acted as proton-coupled electron donor for [Cr₂O₇]²⁻. The reduction of [Cr₂O₇]²⁻ to Cr³⁺ was highly efficient and exceptionally rapid, occurred within 5 min with the reduction amount of 899.66 mg of [Cr₂O₇]²⁻ / 1 g of nanocomposite as a record high value. During the reduction of [Cr₂O₇]²⁻, thiol functional groups (-SH) were oxidized into disulfide linkages ([sbnd]S[sbnd]S[sbnd]), and simultaneously chitosan matrix turned into shrunken structure because of the consuming of protons, preventing any release of Cr³⁺. Disulfides can also be reversely reduced to thiols by thiosulphates (S₂O₃²⁻), which was attractive for regeneration and recyclability of the nanocomposite. Moreover, the [Cr₂O₇]²⁻ elimination through self-gating process was highly selective against a huge concentration of background electrolytes. This alternative strategy ensures the outstanding and stable performance in applied fields, and could be conducted in various pollution control techniques like permeable reactive barriers.