Effects of pH value and hydrothermal treatment on the microstructure and natural-sunlight photocatalytic performance of ZnSn(OH)6 photocatalyst

The ZnSn(OH)₆ nanocubes were prepared under different pH (3–12.4) by liquid precipitation, well characterized and further used for wastewater treatment. The results indicated that the ZnSn(OH)₆ nanocubes prepared at pH = 11.1 possessed of uniform size distribution and excellent photocatalytic activity, the degradation efficiency to MB reaches 76.3% after 5 h natural sunlight irradiation. Subsequently, the prepared ZnSn(OH)₆ nanocubes was further thermal treated (200 °C, 24 h) in four different solvents, containing deionized water, stock solution, mixed solution (V_water: V_ethanol: V_{glacial acetic acid} = 3:1:1) and ethanol, named as H-1, H-2, H-3 and H-4, respectively. H-2 and H-3 showed superior photocatalytic performance and the removal efficiency of MB improved to be almost 100%, as well as red-shifted light absorption edge and the band gap energies reduced 0.9 and 0.93 eV, respectively. Moreover, free radical capture experiments showed that the h⁺ and ·O₂⁻ are the main active species for the ZnSn(OH)₆ nanocubes and H-2, respectively, while all these three ·OH, ·O₂⁻ and ¹O₂ radicals for H-3. Those results suggested that both pH regulation and thermal treatment could efficiently improve the microscopic morphology, crystal structure and photocatalytic activity of the ZnSn(OH)₆, which might pave the way for the artful design of other high-performance catalysts.