Photocatalytic removal of Eu (III) using the synergistic effect between novel Sm-BiVO₄-ZnWO₄ Z-scheme heterojunction and S-doped rGO

Europium [Eu (III)] is listed as a critical element; thus, an eco-friendly and sustainable recovery technique is very crucial for a circular economy process. In this study, the Sm-BiVO 4 -ZnWO 4 -SrGO nanocomposite was synthesized using the hydrothermal method to recover Eu (III) from synthetic wastewater. The synthesized nanocomposite was characterized using XRD, FT-IR, FESEM, EDX, Raman spectroscopy, PL, UV DRS, and Mott-Schottky analysis. The results showed that the Sm-BiVO₄-ZnWO₄-SrGO nanocomposite removed 81.3% of Eu (III) from a starting concentration of 50 mg/L in 240 min, while the individual nanomaterials Sm-BiVO₄, ZnWO₄, and SrGO removed only 31%, 28%, and 21% of Eu (III), respectively. The obtained experimental data fitted well with the Langmuir-Hinshelwood (L-H) kinetic model, yielding a very high correlation coefficient value (R² = 0.97). The result revealed a superior photocatalytic rate constant (K r ) of 0.259 min⁻¹ and a lower L-R adsorption constant of 0.060 mg/L. The enhanced Eu (III) removal efficiency obtained in this study is attributed to the improved charge separation, superior surface activity, increased electron mobility, and more favorable reaction kinetics in the photocatalytic system. Furthermore, Sm-BiVO 4 -ZnWO 4 -SrGO nanocomposite demonstrates strong reusability, remaining effective across 4 reductive sorption cycles.