Oxalate enhanced synergistic removal of chromium(VI) and arsenic(III) over ZnFe2O4/g-C3N4: Z-scheme charge transfer pathway and photo-Fenton like reaction

[Display omitted] •Magnetically separable direct Z-Scheme photocatalyst ZnFe2O4/g-C3N4 was prepared.•Simultaneous removal of Cr(VI) and As(III) was achieved in photocatalytic system.•Oxalate could activate ZnFe2O4/g-C3N4 to produce more Fe(II), CO2−, OH and O2−.•There is a synergistic effect between As(III) and Cr(VI) removal. In this work, direct Z-Scheme photocatalyst (ZnFe2O4/g-C3N4) was employed to purify Cr(VI) and As(III) in wastewater. Results showed that Cr(VI) and As(III) was completely removed in a wide pH range of 3–7 under visible light irradiation. During photo reaction, oxalate enhanced the generation of Fe(II) and CO2−, which were beneficial for formation of OH and O2−. In photocatalytic system, Fe(II), photogenerated electron, as well as CO2− contributed to Cr(VI) reduction, OH and O2− were responsible for treatment of As(III). Moreover, ZnFe2O4/g-C3N4 was easily recycled by magnetic separation, and presented an excellent reuse ability in treatment of Cr(VI) and As(III).