Abstract:

A novel NaTaO_3-xS_x catalysts were successfully synthesized by one-step hydrothermal method using Ta₂O₅ as starting material and Na₂S₂O₃ as sulfur source. Its catalytic mechanism and reaction process were tested by degradation experiment. The samples were characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XRS), UV-Vis diffuse reflectance spectra (UV-Vis DRS) and X-ray diffraction (XRD). The results showed that the as-prepared S-doped NaTaO₃ did not display obvious variations to the surface charge and micro-morphology of NaTaO₃. UV-Vis diffuse reflectance spectrum analysis indicated that S^2- partially substitute of O^2- ions in the lattice to form Ta-S-Ta bonds, and the light response range of the doped NaTaO_3-xS_x samples extends to the visible region. The results of degradation experiment indicated that NaTaO_3-xS_x exhibited much higher activity than that of pure NaTaO₃. The reason is that in the crystal lattice of NaTaO_3-xS_x, S^2- ions replace part of the O^2-ions, which form a mixed valence band energy levels. The results of GC-MS showed that the monohydroxylated species (m/z = 304) results in the production at m/z = 156, 226 and 276, which is further degraded into species of m/z = 212 and 156. Finally, the photogenerated oxidative species forming over S-doped NaTaO₃ catalyst surface further decompose these intermediates into the final carbon dioxide and some non-toxic inorganic products (SO₄^2-, NO₃^- and NH₄⁺). In addition, in a ten-time recycling test, S-doped NaTaO₃ displayed reliable recycling photocatalytic performance, whose photocatalytic efficiency kept at a high level and only existed very slight drop, due to the loss of photocatalyst during the reclaiming process.

Key words: perovskite, nonmetal element doping, NaTaO₃, photocatalysis