Preparation of new visible-light driven nanocomposite photocatalysts, X/NaTaO3/Er3+:YAlO3 (X = Ag, Au and Pt), for photocatalytic conversion of Cr(VI)

In order to expand the light response range of wide band-gap semiconductor photocatalyst (NaTaO 3 ) for effective photocatalytic conversion of Cr(VI), an up-conversion luminescence agent (Er 3+ :YAlO 3 ) is combined with NaTaO 3 and a visible-light driven photocatalyst, NaTaO 3 /Er 3+ :YAlO 3 , is prepared. Moreover, several conduction band co-catalysts (Ag, Au and Pt) are deposited the surface of NaTaO 3 /Er 3+ :YAlO 3 , respectively, to facilitate the transfer rate of photo-generated electrons. X-ray diffractometer (XRD), energy dispersive X-ray spectroscopy (EDX) and scanning electron microscopy (SEM) analyses are employed to confirm the morphology, microstructure and composition of the prepared photocatalysts. In addition, UV–vis diffuse reflectance spectra are determined to explore the visible-light absorption properties of Er 3+ :YAlO 3 , NaTaO 3 , NaTaO 3 /Er 3+ :YAlO 3 and X/NaTaO 3 /Er 3+ :YAlO 3 (X   =   Ag, Au and Pt). Photoluminescence (PL) spectra are used to estimate the recombination rate of electron–hole pairs. The effects of irradiation time, photosource kind, solution acidity and used times on the photocatalytic capabilities of NaTaO 3 /Er 3+ :YAlO 3 and X/NaTaO 3 /Er 3+ :YAlO 3 (X   =   Ag, Au and Pt) are investigated in detail. The results show that the uses of up-conversion luminescence agent (Er 3+ :YAlO 3 ) and co-catalysts (Ag, Au and Pt) can promote NaTaO 3 to utilize visible-light to carry out the photocatalytic conversion of Cr(VI). Particularly, the prepared Au/NaTaO 3 /Er 3+ :YAlO 3 nanocomposite with 1.0   wt% Au and 0.3:1.0 molar ratio of Er 3+ :YAlO 3 and NaTaO 3 shows the highest photocatalytic activity in conversion of Cr(VI).