| Photocatalytic hydrogen evolution from water splitting using solar energy is of great significance because it can save resources, protect environment, alleviate the energy crisis and achieve sustainable development. Tantalates have attracted much attention in the field of photocatalytic hydrogen evolution because of their unique crystalline structure and electronic structure. However, most of them can only works under UV light irradiation owing to their wide bandgaps, which greatly limits the utilization of the sunlight. Doping metal ions is an effective way to broaden the light absorption range of wide band gap semiconductors. Thus in the present work, Cu(II) and Cu(II)/W(VI) doped NaTaO3 were prepared to extend the absorption scope of NaTaO3 into visible region. The visible light photocatalytic hydrogen production was evaluated in a methanol aqueous solution. Main results are as follows:First, Visible light response NaTa1-xCuxO3 (x=0.00-0.10) powders with different doping amounts were synthesized by a solid-state reaction process and characterized by XRD, SEM, XPS and UV-Vis. The results show that Cu exists as a form of Cu(Ⅱ) in NaTa1-xCuxO3. NaTa1-xCuxO3 exhibits an orthorhombic perovskite phase. The absorbing onset of NaTa1-xCuxO3 shifts to longer wavelength with increasing x. This indicates that NaTa1-xCuxO3 have clear visible light absorption properties. At x=0.10, the redshift reached a maximum value. The photocatalytic activies of NaTa1-xCuxO3 after loading NiO as a co-catalyst for hydrogen evolution were envaluated in a methanol aqueous solution. The morphology and the interfacial structures of the NiO-loaded NaTa1-xCuxO3 were characterized by TEM and HRTEM. The 0.3 wt.% NiO-loaded NaTa0.92Cu0.08O3 achieves the highest visible light photocatalytic activity (69.0μmol h-1 g-1) with a long-term stability. The doping of Cu(Ⅱ) and the junctions formed between NiO and NaTa1-xCuxO3 play important roles in enhancing the visible light activity.Based on NaTa1-xCuxO3, copper and tungsten codoped NaTaO3 (NaTaO3:Cu/W), was prepared by the solid state method and the effects of the molar ratio of Cu to W (λ) and the total doping concentration (X) used in the synthetic process on the phase structure, morphology, optical absorption properties as well as photocatalytic activity for hydrogen production from methanol aqueous solutions under visible light have been studied. The results show that the metallic dopants exist as forms of Cu(Ⅱ) and W(VI) in NaTaO3:Cu/W, respectively. The codoping of Cu and W into NaTaO3 does not affect the crystal structure, but distorts the crystal lattice and decreases the characteristic steps on the surface. With increasing X at a constantλ, the increased doping ions make the (020) diffraction peak gradually shifted to higher angles as well as the red shift of the absorption edge to the visible light range. However, further increase of X results in the shift of the (020) diffraction peak to lower angle. This indicates that excessive metallic ions can not be doped into the lattice effectively. There is a maximum X value (Xmax) for the doping of Cu, W into NaTaO3. Whenλ= 1:2,1:3 and 1:4, Xmax is 8%,6% and 4%, respectively. NaTaO3:Cu/W exhibits the optimum photocatalytic activity for hydrogen evolution at X=Xmax. When X is fixed, the photocatalytic activity mainly depends on the control of Cu(II) over the band gap and the charge balance effect of W(Ⅵ). NaTaO3:Cu/W withλ= 1:4, X= 4% shows the highest activity of 1.35μmol h-1 g-1. It indicates that the codoping of Cu and W ions into NaTaO3 at an appropriateλcan maintain the charge balance to a great extent, suppressing the formation of oxygen defects in the lattice and inhibiting the recombination of photogenerated electrons and holes so that the photocatalytic activity for hydrogen production is improved.
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