ZnS-containing industrial waste: Antibacterial activity and effects of thermal treatment temperature and atmosphere on photocatalytic activity

ZnS-containing industrial waste (ZnSW) from the mining-metallurgy industry was characterized as a useful photocatalytic material for environmental remediation. The XRD results reveal that the ZnSW contains cubic ZnS (sphalerite) as a major phase and hexagonal ZnS (wurtzite), triclinic FeS₂ (pyrite) and hexagonal SiO₂ (quartz) as minor phases. The antibacterial activity of the ZnSW was tested for four bacterial strains. The antibacterial activity against L. innocua under UV light irradiation is comparable to that observed with MRSA, whereas the inactivation rate against E. coli reaches 99% within 2 h of UV light irradiation. The ZnSW is found to be less effective in the inactivation of S. enteretidis. The impact of thermal treatment temperature (400–1000 °C) and atmosphere (in air and NH₃) on photocatalytic activity of the ZnSW for photodegradation of gaseous acetaldehyde (AcH) and Bisphenol A (BPA) in aqueous solution under simulated solar light were investigated. The sample thermally treated at 500 °C in air completely mineralized AcH and BPA within 4 and 2 h of the photocatalytic reaction, respectively, due to the formation of a ZnS–ZnO heterojunction that promoted an effective charge separation. The sample thermally treated at 1000 °C in NH₃ exhibited the highest photocatalytic efficiency in complete photodegradation of AcH and BPA within 3.5 and 1.5 h of the photocatalytic reaction, respectively, because of the introduction of nitrogen and formation of midgap defect states. The present study demonstrates the importance of the thermal treatment temperature and atmosphere for improving the photocatalytic activity of ZnS-containing industrial waste for environmental remediation.