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 S_x@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 S_x@g-C₃N_(4−y)), as affirmed by the reduced concentrations of S and N in the end product. Thereafter, the Bi₂MoO₆/S_x@g-C₃N_(4−y) photocatalysts (referred to as BS_xN_y) were synthesized via a solvothermal method followed by calcination. Among the prepared samples, the integration of 10% S_x@g-C₃N_(4−y) with Bi₂MoO₆ (referred to as BS_xN_y (II)) demonstrated superior photocatalytic performance. Under optimal conditions, BS_xN_y (II) achieved a remarkable 92.4% degradation efficiency of tetracycline (TCL) in an aqueous solution after 60 min. The degradation rate of BS_xN_y (II) transcended that of pristine S_x@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 O₂˙⁻ 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.