Enhanced photochemical activity and stability of ZnS by a simple alkaline treatment approach

In this study, a simple alkaline treatment method is developed to greatly improve the photochemical properties of ZnS. It is found that after treating ZnS with NaOH solution, the obtained sample (3 M-ZnS) has a larger pore size (12.5 nm) and a larger BET area (51.2 m(2) g(-1)), compared with untreated ZnS (3.8 nm, 27.6 m(2) g(-1), respectively). Moreover, alkaline treatment also increases zinc vacancies (V-Zn), which up-shift the conduction band (CB) and down shift the valence band (VB) positions. V-Zn causes a defect energy level above the VB of ZnS, thus causing additional light absorption; it can also act as a trap for the photogenerated holes. V-Zn not only improves the charge separation efficiency, but also reduces the oxidative ability of holes. Compared with untreated ZnS, the degradation activity of 3 M-ZnS increases by 55% for MB dye in wastewater after 40 minutes of UV light irradiation ( 420 nm); most importantly, the resistance to photocorrosion of 3 M-ZnS increases by 210% compared with that of untreated ZnS. This low-cost strategy could be used for the mass production of efficient photocatalysts, which can be used for dye cleanup from wastewater.