Overturning photoreduction product of CO2 by defect- and COOH-functionalized multi-wall carbon nanotubes

We functionalize MWCNTs with defects and COOH groups to form MWCNTs30 through a novel discharge process. In the photoreduction of CO2 with pure H2O in the absence of sacrificial reagent, with CdS as light absorber, MWCNTs30 triggers a selective CH3OH production, with a CH3OH selectivity of 100% and an internal quantum efficiency of 3.9%, but CO is the only C-based product by using pristine MWCNTs without functionalization. The defects on MWCNTs30 are active sites for enhancing CO2 adsorption, H2O dissociation to produce H and H transfer to CO2, thus boosting CO2 hydrogenation to CH3OH. The COOH groups on MWCNTs30 provide H for promoting CO2 hydrogenation to CH3OH. The multiple roles of defects and COOH groups overturn the photoreduction product from CO to CH3OH. The results open a new way to achieve more efficient photoreduction of CO2 in the absence of noble metal and sacrificial reagent. [Display omitted] •MWCNTs enhanced the photoreduction of CO2 in the absence of sacrificial reagent.•MWCNTs overturned the photoreduction product of CO2 from CO to CH3OH.•Defects on MWCNTs were active sites for hydrogenating CO2 into CH3OH.•COOH groups on MWCNTs provided H for promoting CO2 hydrogenation to CH3OH.