Fabrication of 2D/2D Bi2MoO6/Sx@g-C3N(4-y) type-II heterojunction photocatalyst for enhanced visible-light-mediated degradation of tetracycline in wastewater

Abstract

Aquatic biota and human health are seriously threatened by the dramatic rise in antibiotics in environmental matrices. In this regard, the present study aims to improve knowledge of the combined effects of heterojunction design and defect engineering on the photocatalytic degradation of pharmaceuticals in aqueous matrices. Advantageously, the positioning of the valence band (VB) and conduction band (CB) levels of Sx@g-C3N(4-y), being higher than those of Bi2MoO6, demonstrates the feasibility of forming a type-II heterojunction between these materials. Initially, S and N defects were inserted in S-doped g-C3N4 through an alkali-assisted calcination method (referred to as Sx@g-C3N(4-y)), as affirmed by the reduced concentrations of S and N in the end product. Thereafter, the Bi2MoO6/Sx@g-C3N(4-y) photocatalysts (referred to as BSxNy) were synthesized via a solvothermal method followed by calcination. Among the prepared samples, the integration of 10% Sx@g-C3N(4-y) with Bi2MoO6 (referred to as BSxNy (II)) demonstrated superior photocatalytic performance. Under optimal conditions, BSxNy (II) achieved a remarkable 92.4% degradation efficiency of tetracycline (TCL) in an aqueous solution after 60 min. The degradation rate of BSxNy (II) transcended that of pristine Sx@g-C3N(4-y) and Bi2MoO6 by 4.86 and 3.41 times, respectively. The higher number of active sites and the greater electron-hole pair separation are responsible for this improvement in the rate of TCL degradation. The photocatalyst also exhibited remarkable thermal/chemical stability and possessed reusability, as noted by 84% TCL degradation TCL up to 5 cycles. The radical scavenging experiment indicated "O" _"2" ^"•-" as the primary contributor towards TCL degradation, with h+ and •OH playing a secondary role. Additionally, a seed germination experiment used to measure phytotoxicity determined that the treated effluent was non-phytotoxic, making it suitable for irrigation.