Improved visible-light photocatalytic activity of NaTaO3 with perovskite-like structure via sulfur anion doping

• S2− causes slight lattice expansion of NaTaO3 unit cell.
• S2− causes a lattice transition tendency of NaTaO3 from monoclinic to cubic phase.
• S anion doping narrows the band gap of NaTaO3.
• S-doped NaTaO3 display remarkably improved visible-light photocatalytic activity.
• S-doped NaTaO3 is photo-stable and broad pH adaptable under natural solar radiation.

A novel sulfur anion-doped NaTaO3 photocatalyst with nanocubic morphology, at an average size of 200–500 nm or so, was synthesized by a simple hydrothermal process. The as-prepared samples were characterized by various techniques, such as X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), UV–vis diffuse reflectance spectra (UV–vis DRS) and photocatalytic degradation evaluation. The results indicate that the as-prepared NaTaO3 is assigned to monoclinic lattice, which is much closer to cubic phase than conventional orthorhombic perovskite structure. And doping of S anions would cause, to some extent at least, expanded unit cell and distorted lattice structure from monoclinic into cubic phase, whose TaOTa band angle is much closer to 180°, resulting in the higher mobility of photo induced charge carriers. Narrowed band gap and splitting slopes are observed in S-doped NaTaO3 by UV–vis DRS, confirming the visible-light adsorption capability and the upward shifted valence band edge, which come from the overlapping of S 3p orbitals and Ta 5d orbitals. In virtue of the crystalline and electronic structures, the resultant S-doped NaTaO3 samples, as compared with pure NaTaO3, exhibit remarkably improved visible-light photocatalytic activity and similar UV-light photocatalytic activity, during the photocatalytic degradation of methyl orange. In addition, S-doped NaTaO3 also displays reliable recycling photocatalytic performance and satisfying solar catalytic activity for the organic pollutant. On the basic of above experimental phenomena, a possible mechanism for sulfur anion doping in NaTaO3 perovskite-like structure is also presented.

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