Size dependent photocatalytic activity of ZnS nanostructures prepared by a facile precipitation method

• Size-controlled ZnS crystallites were achieved by adjusting the reaction pH.
• The formation mechanism of ZnS prepared at different pH was discussed.
• Size-related photocatalytic properties of ZnS were shown.

Size-controlled ZnS nanostructures have been synthesized successfully with different reaction pH via a facile homogeneous precipitation method. These samples were characterized by X-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy (TEM), N2-sorption BET surface area, Raman spectra and UV–vis spectroscopy for their structures, morphologies, specific surface area and band gaps values (Eg). Results show that the size of the prepared nanospheres can be controllably tuned by adjusting pH value. Moreover, the size-related mechanism of different samples was also discussed. The degradation of methyl orange (MO) under UV light irradiation was carried out to study the effects of the size on the photocatalytic activity of the prepared samples. It was found that the sample obtained at pH = 7 exhibited the higher photocatalytic activity, which degradation efficiency reaches 99.5% under UV irradiation for 30 min. The big specific surface area of ZnS nanostructures are believed to greatly affect the final degradation efficiency of MO in our research. Moreover, the mechanism of enhanced photocatalytic activity was also investigated and the O2− plays a dominant role during degradation process.