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 (TiO2) 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 sp2 hybridized orbitals with strong conductivity, which enabled the photogeneration of e- by the semiconductor material (TiO2) 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 TiO2, thereby enhancing the efficiency of the removal of Cr(VI).