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Due to the low concentration of indoor air contaminants,photocatalytic technology shows low efficiency for indoor air purification.The application of TiO2 for photocatalytic removal of formaldehyde is limited,because TiO2 can only absorb ultraviolet (UV) light.Immobilization of TiO2 nanoparticles on the surface of graphene can improve the visible light photocatalytic activity and the adsorption capacity.In this study,rGO (reduced graphene oxide)/TiO2 was synthesized through a hydrothermal method using titanium tetrabutoxide and graphene oxide as precursors,and was used for the degradation of low concentration formaldehyde in indoor air under visible light illumination.Characterization of the crystalline structure and morphology of rGO/TiO2 revealed that most GO was reduced to rGO during the hydrothermal treatment,and anatase TiO2 nanoparticles (with particle size of 15-30 nm) were dispersed well on the surface of the rGO sheets.rGO/TiO2 exhibited excellent photocatalytic activity for degradation of formaldehyde in indoor air and this can be attributed to the role of rGO,which can act as the electron sink and transporter for separating photo-generated electron-hole pairs through interfacial charge transfer.Furthermore,rGO could adsorb formaldehyde molecules from air to produce a high concentration of formaldehyde on the surface of rGO/TiO2.Under visible light irradiation for 240 min,the concentration of formaldehyde could be reduced to 58.5 ppbV.rGO/TiO2 showed excellent moisture-resistance behavior,and after five cycles,rGO/TiO2 maintained high photocatalytic activity for the removal of formaldehyde (84.6％).This work suggests that the synthesized rGO/TiO2 is a promising photocatalyst for indoor formaldehyde removal.