Photoreduction properties of novel Z-scheme structured Sr0.8La0.2(Ti1−δ4+Tiδ3+)O3/Bi2MoO6 composites for the removal of Cr(vi)

Abstract

Novel Z-scheme structured Sr_0.8La_0.2(Ti_1−δ⁴⁺Ti_δ³⁺)O₃/Bi₂MoO₆ (LSTBM) composites were prepared via a facile two-step solvothermal method. Several characterization techniques were employed to investigate the phases, microstructures, compositions, valence states, oxygen vacancies, surface oxygen absorption, energy band structures and lifetime of photoproduced carriers. It was found that the lifetime and transfer of the photoproduced carriers of LSTBM were better than those of Bi₂MoO₆ (BMO) and Sr_0.8La_0.2(Ti_1−δ⁴⁺Ti_δ³⁺)O₃ (LSTO). The LSTBM with a molar ratio of BMO/(LSTO + BMO) = 0.07 (denoted as LSTBM7) showed 1.9 and 3.1 times removal rates than those for BMO and LSTO, respectively. Importantly, the built-in electric field in the heterojunction of LSTBM and O_v-s, especially in O_v-s on the higher-Fermi-level side of the heterojunction, had co-played roles in prolonging the lifetime and improving the transfer of photogenerated carriers. The photoproduced e⁻ played a dominant role in reducing Cr(VI) to Cr(III) and the produced Cr(III) tends to form Cr(OH)₃ and adsorb onto the surface of the photocatalyst to decrease the nucleation energy. The possible reduction route for Cr(VI) to Cr(III) over LSTBM7 was figured out. This study implies that inducing O_v-s on the higher-Fermi-level side of the Z-scheme heterojunction is a more effective route for separating the photogenerated electrons and holes and improving the transfer of photogenerated carriers.