A novel heterogeneous photocatalyst for Cr (VI) reduction via planting silicotungstic acid on the surface of calcium tantalate

•The CaxH4-xSi4W12O40/Ca2Ta2O7 was prepared via an in-situ deposition reaction.•The composite exhibited a good photocatalytic efficiency in reducing Cr(VI) ions.•The composite presented a better stability due to the formation of CaxH4-xSi4W12O40.•The agglomeration of H4Si4W12O40 were prevented by Ca-O linkage with Ca2Ta2O7.•A probable mechanism of reducing Cr(VI) is proposed by DFT simulation.