An all-in-one photocatalyst: Photocatalytic reduction of Cr(VI) and anchored adsorption of Cr(III) over mesoporous titanium@sulfonated carbon hollow hemispheres

Completely removing chromium (Cr) from contaminated water with simultaneous reduction of Cr(VI) and sequestration of Cr(III) is an efficient strategy to restrain its migration in natural water. Herein, sulfonated carbon hemisphere (Labeled as CHS, Inner diameter: 150 nm) worked as a supporter to hold mesoporous TiO2 (MT) nanoparticles (Diameter: 10 nm), constructing a bifunctional catalyst with photocatalytic activity and adsorption capacity. During a typical Cr removal process, efficient photocatalytic reduction Cr(VI) performed alongside the utter adsorption of the generated Cr(III) on the sulfonated CS by ion exchange for the grafted -SO3H+. The reaction rate constant (k) for removing Cr(VI) by TiO2-C-SO3H is 0.04998 min−1, which is 3.72 times higher than that (0.01342 min−1) unmodified TiO2-C, and 23.68 times and that of MT (0.00223 min−1). No residual Cr was determined in the treated water. The highest removal efficiency was achieved when the mass ratio of carbon and TiO2 hemispheres is 0.62%. Two factors contributing to the exceptional reduction efficiency include improved electron-hole separation efficiency endowed by the CHS conductive framework, sensitive light absorption. Ultimately, the -SO3H+ grafted on CHS can immobilize Cr(III) by ion exchange, performing like a resin, which realizes the total removal of Cr(VI) or Cr(III) and restrains the possible hazardous influence.