Visible-light absorptivity of a zincoxysulfide (ZnOxS1−x) composite semiconductor and its photocatalytic activities for degradation of organic pollutants under visible-light irradiation

Abstract

It has been generally known that ZnS and ZnO were unable to absorb visible light due to their wide band-gap energy, however, we attempted to develop a visible-light sensible photocatalyst by making their composite semiconductor, which was named as ZnO x S 1− x . It was confirmed that the composite showed enhanced visible-light absorptivity and we expected this has been caused by small band-gap energy (2.4 eV) resulted from hybrid orbitals in valence band of ZnO x S 1− x . Therefore, we presented a rational model for band structure of ZnO x S 1− x and verified the photocatalytic activity for degradation of an organic pollutant under visible-light irradiation. This work reports the development of a visible-light sensible photocatalyst and the photocatalytic degradation of organic pollutants under visible-light irradiation. A composite semiconductor of ZnS and ZnO was prepared through co-precipitation process of Zn(NO 3 ) 2 in the mixed solution of aqueous Na 2 S and NaOH followed by calcination at 400 °C in N 2 atmosphere. It was revealed that the composite semiconductor was a solid solution of ZnS and ZnO, a zincoxysulfide (ZnO x S 1− x ) having advanced visible-light absorptivity. It was assured that the visible-light absorptivity was caused by modification of band structure while the solid solution had been prepared, thus we suggested a reasonable band structure model involved in a zincoxysulfide. To observe its photocatalytic activity under visible-light illumination, photodegradation test was done and we confirmed that zincoxysulfide showed predominant photocatalytic activity due to its superior visible-light absorptivity to pure ZnS and ZnO.