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

Abstract

A novel heterogeneous photocatalyst CaxH4-xSi4W12O40/Ca2Ta2O7 was prepared by planting silicotungstic acid on the surface of calcium tantalate. The materials are characterized by X-ray diffraction (XRD), scanning electron microspectroscopy (SEM), X-ray photoelectron spectroscopy (XPS), Fourier transformation infrared spectroscopy (FTIR), UV–vis diffuse reflectance spectroscopy (UV–vis), Energy-dispersive X-ray spectroscopy (EDS), BET surface area, and Malvern ZEN3690 Particle Analyzer (ZP). The results recovered Ca2Ta2O7 presented regular octahedron morphology with the cubic phase structure, and H4Si4W12O40 uniformly grew on the surface of Ca2Ta2O7 with the form of CaxH4-xSi4W12O40. The primary Keggin structures of H4Si4W12O40 was found to remain intact as noticed by XRD and FTIR. The modification of H4Si4W12O40 on Ca2Ta2O7 surface contributed the increase in negative zeta potential and red shifts. The as-prepared catalyst exhibited greatly enhanced UV photocatalytic efficiency in the reduction of Cr(VI) ions as high as 94.6% under the optimum conditions (Ca2Ta2O7 to H4Si4W12O40 was 1:2). Moreover, the composite presented an excellent reusability, which was mainly ascribed to the locally formation of water-insoluble CaxH4-xSi4W12O40. A probable mechanism involved in the enhanced reducible activity and well recycled performance via CaO binding linkage of H4Si4W12O40 and Ca2Ta2O7 is proposed by DFT simulation. This work will be significant in the design of heteropoly acid as stable heterogeneous photocatalyst applied to heavy metal ions reduction.