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

• A facile one-pot hydrothermal method was developed to prepare ZnO–rGO composites.
• The as-prepared ZnO–rGO exhibited pronounced charge carrier separation.
• Significantly enhanced photocatalytic activity in CH3CHO degradation was attained.
• Practical use as photoanode for electrolytic water oxidation was demonstrated.

A facile, 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 CH3CHO 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.

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