Double-vacancy-induced polarization and intensified built-in electric field in S-Scheme heterojunction for removal of antibiotics and Cr (VI)

Antibiotics and heavy metals usually co-exist in wastewater and pose serious environmental hazards. Herein, a series of V_Mo-BMO/O_v-BOB S-scheme heterojunctions with double vacancy (Mo vacancy and photoexcited O vacancy) were constructed via an electrostatic assembly method. The removal efficiency of Cr (VI) and tetracycline (TC) over V_Mo-BMO/O_v-BOB-0.3 was 2.47 and 1.13 times than that of a single system, respectively. In-situ EPR demonstrated that the surface O vacancies could be generated under LED light irradiation. These photoexcited O vacancies (P-O_v) enabled V_Mo-BMO/O_v-BOB composites still exhibit satisfactory activity after five successive cycles and an amplified Fermi level gap. The enhancement could be attributed to the enhanced internal electric field and double-vacancy-induced polarization. Additionally, the density functional theory calculation results suggested that double vacancy induced polarization electric field increases the dipole moment, which was conducive to rapid electron transport. Photoluminescence and time-resolved photoluminescence analysis demonstrated that the introduction of S-scheme heterojunction and double vacancy promoted charge transfer and prolonged the lifetime of carriers. Degradation intermediates and toxicity of products were evaluated. In conclusion, a possible mechanism based on V_Mo-BMO/O_v-BOB S-scheme heterojunction in the simultaneous removal of Cr (VI) and TC was proposed.