Fe3O4@BiOCl@GO Core/shell heterojunction nanocomposite as a magnetically recyclable photocatalyst for complete visible light degradation and deep mineralization of dyes in wastewater

• A novel Fe₃O₄@BiOCl@GO ternary nanocomposite was successfully synthesized via a facile route. • The composite exhibited enhanced visible-light photocatalytic activity compared to pristine Fe₃O₄ and Fe₃O₄@BiOCl. • Superior performance was achieved for degradation of organic pollutants and bacterial inactivation. • The synergistic effect of magnetic Fe₃O₄, BiOCl heterojunction, and conductive GO promoted charge separation and reusability. • The photocatalyst demonstrated excellent stability and recyclability under repeated cycles. A novel magnetic Fe 3 O 4 @BiOCl@GO core/shell heterojunction photocatalyst was successfully fabricated through a multi-step synthesis route, introducing an innovative integration of magnetic, photoactive, and conductive components within a single hybrid nanostructure. The composite design strategically combines a Fe 3 O 4 magnetic core for rapid recovery, a BiOCl photoactive shell for efficient visible light absorption, and a graphene oxide (GO) layer as a conductive network that accelerates charge transfer and suppresses recombination. Comprehensive characterization by XRD, FE-SEM, TEM, UV–Vis DRS, and VSM confirmed the formation of a well-defined core/shell heterojunction with strong structural coherence and superparamagnetic behavior. Under optimized conditions, complete degradation (100 %) of methyl orange (MO) was achieved within 75 min of visible light irradiation, following pseudo-first-order kinetics. The band gap narrowing and improved interfacial charge separation resulting from GO incorporation were key factors enhancing photocatalytic efficiency. In addition, multiple linear regression analysis was applied to model the effects of operational parameters (irradiation time, initial dye concentration, pH, catalyst dosage, and H 2 O 2 addition) on degradation performance, yielding a strong correlation coefficient (R 2 = 0.918), validating the experimental data, providing a statistically robust fit and predictive capability for process optimization. Moreover, the photocatalyst exhibited excellent magnetic recyclability and structural stability, maintaining high efficiency after repeated cycles. This work introduces an innovative, magnetically separable Fe 3 O 4 @BiOCl@GO heterojunction that integrates waste minimization, facile recovery, and visible light utilization, offering a promising platform for sustainable water purification and treatment of organic pollutants.