One-pot synthesis of Ag-MWCNT@TiO2 core–shell nanocomposites for photocatalytic reduction of CO2 with water under visible light irradiation

This work presents for the first time the preparation of silver (Ag)-doped MWCNT@TiO2 (multi-walled carbon nanotubes@titanium dioxide) core–shell nanocomposites with enhanced visible-light-responsive properties for the application in carbon dioxide (CO2) photoreduction. Comprehensive study was conducted on the synthesis and the photoreactivity performance of the Ag-MWCNT@TiO2 ternary nanocomposites at various Ag loadings ranging from 1 to 4wt% (gram Ag per unit gram of TiO2). The properties of the Ag-MWCNT@TiO2 nanocomposites were characterized thoroughly and their photoreactivity was tested in a continuous CO2 photoreduction system under the irradiation of visible light source. The developed Ag-MWCNT@TiO2 demonstrated excellent activity in the reduction of CO2 into methane and ethylene. 2wt% of Ag was found to be the most suitable loading, giving the highest total methane and ethylene formation of ca. 6.34μmol/g-catalyst and 0.68μmol/g-catalyst, respectively, for a reaction time span of 7.5h along with the maximum hourly formation rate of methane and ethylene of ca. 0.91μmol/g-catalyst/h and 0.048μmol/g-catalyst/h, at the reaction time of 7th and 6th h, respectively. The results showed that the methane yield over 2wt% Ag-MWCNT@TiO2 nanocomposites was approximately 1.60 folds higher than that of the undoped-MWCNT@TiO2 core–shell nanocomposites.