A novel MgCr2O4/WO3 hetero-junction photocatalyst for solar photo reduction of hexavalent chromium Cr(VI)

•New hetero-system MgCr2O4/WO3 was used for photoreduction of the hexavalent chromate.•MgCr2O4 and WO3 were prepared by the sol–gel and chemical precipitation methods.•Hexavalent chromium (30 mg/L) is totally photo-reduced within 120 min at (pH 4) under sunlight.•The kinetics of the photocatalytic reaction of Cr (VI) reduction to Cr (III) followed a first order model.