Removal behavior of hexavalent chromium by mesoporous polydopamine/TiO2 nanosphere photocatalyst under simulated sunlight

The present study employed a straightforward organic-inorganic approach to synthesize spherical mesoporous polydopamine (PDA)/titanium oxide (TiO 2 ) composite material (herein represented by the generic formula of PT-x, where x is the mass of dopamine hydrochloride added) through self-assembly. The morphology, structure and optical properties of PT-x were characterized using various analytical techniques. Moreover, PDA was found to serve multiple functions, including as an adhesive, a light absorber, and an electron (e − ) transport medium. The photocatalytic performance of the synthesized material for removing Cr(VI) was evaluated under simulated sunlight. The results showed that PT-0.5 removed 99.78 % of Cr(VI) within 2.5 h, of which 57.8 % was reduced to Cr(III). After five cycles, PT-0.5 retained a Cr(VI) removal efficiency of approximately 81.76 %. It was revealed that a high concentration of semiquinone and quinone functional groups in PDA facilitated the transfer of photoinduced e − and provided adsorption sites for Cr(VI). In addition, carbon (C) atoms in PDA, belonging to sp 2 hybridized orbitals with strong conductivity, which enabled the photogeneration of e − by the semiconductor material (TiO 2 ) to be transferred to the surface of the material faster, promoted the contact between Cr(VI) and its reduction to Cr(III). The combination of these properties reduced the recombination of photoinduced e − -hole (h + ) pairs in TiO 2 , thereby enhancing the efficiency of the removal of Cr(VI).