ZnO-graphene composites as practical photocatalysts for gaseous acetaldehyde degradation and electrolytic water oxidation

Afacile, green one-pot hydrothermal method has been developed to prepare ZnO-reduced graphene oxide (rGO) composites with controllable rGO content. Time-resolved photoluminescence spectra revealed that an increased electron-transfer rate constant was observed for ZnO-rGO with increasing rGO contents, suggesting that an increased number of photoexcited charge carriers were separated and available for photocatalysis utilization. The photocatalytic properties of the ZnO-rGO composites were investigated by using gaseous acetaldehyde (CH₃CHO), a typical volatile organic compound (VOC), as the test pollutant. This is the first time that ZnO-rGO composites have been used as photocatalysts for gaseous CH₃ CHO degradation. Compared to pure ZnO, ZnO-rGO composites with suitable rGO contents (1.0 and 3.0 wt%) displayed significantly enhanced photocatalytic activity in both CH₃CHO degradation and CO₂ generation. This enhancement was ascribed to the rGO support that can promote the carrier utilization efficiency of ZnO by readily accepting the photoexcited electrons from ZnO. As a result, abundant photogenerated holes remained on the ZnO and were available for participation in the CH₃CHO photodegradation. Furthermore, the photoactivity of ZnO-rGO toward electrolytic water oxidation was evaluated. The results showed that ZnO-rGO composites achieved 50% increase in water oxidation current over pure ZnO under white light illumination. The demonstration from this work may facilitate the use of ZnO-rGO composites in photodegradation of VOCs as well as for photoelectrochemical applications, which is imperative from the environmental and energetic points of view.