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

•Ag-MWCNT@TiO2 nanocomposites were prepared using one-pot synthesis.•2 wt% Ag-doped nanocomposites showed the best performance in CO2 reduction.•Highest methane formation rate obtained was 0.90 μmol/g-catalyst /h.•Maximum methane formation for 7.5 h reaction was 6.34 μmol/g-catalyst.•Maximum ethylene formation for 7.5 h reaction was 0.68 μmol/g-catalyst.

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 7th and 6th 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.

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