Fabrication of CdS/P2MoxW18-x nanospheres with type II heterostructure for photocatalytic reduction of hexavalent chromium

A serial of CdS/POM (POM denotes polyoxometalate: P2MoxW18-x, x = 3, 9, 15) nanospheres were fabricated through electrostatic self-assembly method. For the first time, the semiconductor properties of the three poly-oxometalates were investigated to direct the rational design of the type-II heterojunction photocatalysts. The morphology and semiconducting properties of the as-prepared materials were characterized by using X-ray powder diffraction, scanning electron microscopy, UV-vis diffuse reflectance spectra, Mott-Schottky plots, surface photovoltage spectroscopy and time-resolved photocurrent curves. The band gap of P2Mo3W15, P2Mo9W9 and P2Mo15W3 is taken respectively to be 2.34 eV, 2.26 eV and 2.15 eV. The average diameters of CdS and CdS/P2MoxW18-x (X = 3, 9, 15) nanospheres are all around 80-100 nm, and CdS/P2MoxW18-x (X = 3, 9, 15) nano- spheres have better photoelectric performance than pure CdS. The formation of type II heterostructure between CdS and P2MoxW18-x could promote the separation and transfer of photoinduced electron-hole pairs, so the photocatalytic activities of CdS/POM nanospheres for Cr(VI) reduction were improved significantly. Among them, the CdS/P2Mo15W3 photocatalyst exhibited the highest photocatalytic yield of 64% for the Cr(VI) removal. Our study provides new insight into developing novel CdS/P2MoxW18-x nanocomposite photocatalysts for environmental applications.