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

(Graph Presented) 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 4 wt% (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. 2 wt% of Ag was found to be the most suitable loading, giving the highest total methane and ethylene formation of ca. 6.34 μmol/g-catalyst and 0.68 μmol/g-catalyst, respectively, for a reaction time span of 7.5 h along with the maximum hourly formation rate of methane and ethylene of ca. 0.91 μmol/g-catalyst/h and 0.048 μmol/g-catalyst/h, at the reaction time of 7^th and 6^th h, respectively. The results showed that the methane yield over 2 wt% Ag-MWCNT@TiO₂ nanocomposites was approximately 1.60 folds higher than that of the undoped-MWCNT@TiO₂ core-shell nanocomposites.