In situ formation of surface sulfide species and its role in enhancing the photocatalytic and photoelectrochemical properties of wide bandgap ZrO2

Abstract

Development of visible light active photocatalysts for hydrogen generation from water is important for the effective utilization of solar energy. In this paper, we demonstrate visible light photocatalytic activity (>410nm) for wide bandgap ZrO2 when irradiated in the presence of Na2S and Na2SO3 (SS) as sacrificial reagents instead of methanol. When irradiated with fluorescent lamp (UV<3%), the activity is much higher in the presence of SS (nearly 20 times more) than in the presence of methanol. No significant improvement in hydrogen evolution is observed when other sacrificial reagents like lactic acid and methyl amine are used. Current-voltage (I–V) characteristics show a significant increase in the photocurrent for Si/ZrO2 when SS is used as electrolyte, indicating the increased availability of electrons. The switching characteristics studies show that the switching current increases with increase in light exposure time and the current increases to twice that of the initial current for an exposure of about 1000s. When KCl is used as electrolyte no significant switching effect is observed. Surface analysis clearly indicates the presence of S2− bonded to ZrO2 after photocatalysis experiment, which suggests the in situ formation of sulfide/oxysulfide species on the surface of ZrO2 when irradiated in the presence of SS. UV–vis absorption spectrum of irradiated ZrO2 in the presence of SS shows increased visible light absorption compared to other samples. Present study leads to a new result of in situ formation of sulfide/oxysulfide on ZrO2 when irradiated in the presence of SS, which enhances the visible light photocatalytic activity.