Construction of Fe3O4@ZIF-8@BiOX (X = Cl, Br, I) heterojunctions toward simultaneous removal of oxytetracycline and Cr(VI) by adsorption-photocatalysis

[Display omitted] •A novel Fe3O4@ZIF-8@BiOX (X = Cl, Br, I) composite photocatalyst was developed.•Synergistic removal of OTC-Cr(VI) was optimized by regulating halide ion type.•Fe3O4@ZIF-8@BiOI masters the fate of pollutants through surface-active substances.•OTC and Cr(VI) interacted on the surface of Fe3O4@ZIF-8@BiOI.•The designed method holds potential for practical wastewater removal and recycling. The magnetic Fe3O4@ZIF-8 with high adsorption properties and easy separation were embedded in BiOX (X = Cl, Br, I) to synthesize Fe3O4@ZIF-8@BiOX using a simple one-pot solvothermal strategy. The crystal structure, surface morphology, photoelectric properties, thermal stability and magnetic response of the three materials were compared and analyzed, and the effect on the removal of OTC and Cr(VI) from single and coexisting systems by adsorption-photocatalysis is discussed. The results show Fe3O4@ZIF-8@BiOI has the highest separation efficiency of photogenerated carriers upon photoexcitation and stronger light absorption capacity, and exhibits better adsorption-photocatalytic activity than the other two materials in the photocatalytic reduction of Cr(VI) (68 % and 65 % removal for single and coexisting systems) and degradation of OTC (86 % and 59 % removal for single and coexisting systems). It is noteworthy that in the coexistence of Cr(VI) and OTC, a slight decrease of removal occurred, which could be due to a competitive effect between two pollutants being greater than the synergistic effect. ∙O2- is the main active substances in the adsorption-photocatalysis process. Finally, this work demonstrates the excellent adsorption and photocatalytic ability of Fe3O4@ZIF-8@BiOI for the simultaneous removal of Cr(VI) and OTC, which has great potential for practical wastewater treatment.