Sm³⁺-Modified ZnWO₄/YVO₄ Heterostructure for Enhanced Photocatalytic Degradation of Crystal Violet and Sulfamethoxazole

Abstract Sm³⁺-modified ZnWO₄/YVO₄ ternary heterostructure was developed as a reusable photocatalyst for photocatalytic treatment of chemically diverse aquatic contaminants, Crystal Violet (CV) and sulfamethoxazole (SMX). The novelty lies in integrating a ZnWO₄/YVO₄ heterointerface with Sm³⁺ modification, thereby combining interfacial charge separation with dopant-induced electronic/defect regulation, while demonstrating applicability to both dye and pharmaceutical pollutants. XRD, Raman, XPS, SEM, TEM/HRTEM, SAED and AFM confirmed the coexistence and crystalline integrity of monoclinic ZnWO₄ and tetragonal YVO₄, successful Sm incorporation, and transformation toward finer, elongated nanostructures. The crystallite size was reduced to approximately 20 nm upon Sm³⁺ modification, as estimated from the XRD data using the Debye–Scherrer equation. UV–Vis analysis showed a reduction in effective optical band gap from 3.05 to 2.87 eV with a red-shifted absorption edge from 406 to 432 nm. TRPL lifetime increased from 3.12 to 5.78 ms, while EIS revealed a marked reduction in charge-transfer resistance to 260 Ω, supporting improved carrier separation and migration. Under irradiation, Sm³⁺/ZnWO₄/YVO₄ achieved 93% CV and 97% SMX degradation within 90 min, compared with 78% and 58%, respectively, for unmodified ZnWO₄/YVO₄. The processes followed pseudo-first-order kinetics with R² values of 0.992 for CV and 0.981 for SMX. Optimal conditions were 20 mg/L catalyst dosage, pH 3 for CV and pH 5 for SMX. The catalyst retained 87% CV and 89% SMX removal after seven cycles. Enhanced activity is attributed to Sm³⁺-assisted charge transfer, reduced recombination, and ROS generation, highlighting potential for reusable wastewater remediation. The findings establish a structure property performance relationship for efficient contaminant removal and practical real-world application.