Selective methane production from visible-light-driven photocatalytic carbon dioxide reduction using the surface plasmon resonance effect of superfine silver nanoparticles anchored on lithium titanium dioxide nanocubes (Ag@LixTiO2)

This study focused on the results of applying the strong surface plasmon resonance (SPR) effect of silver (Ag) particles anchored on cubic phase LixTiO2 to the carbon dioxide (CO2) photoreduction reaction. The study demonstrated the importance of three aspects: First, the cubic TiO2, which activated the [101] facet, was successfully produced. Secondly, Li+ ions were introduced as Frenkel defects in some lattices to create oxygen defects. These vacancies increased the adsorption of carbon dioxide and sped up the rate-determining step in the CO2 reduction reaction. In other words, they induced the easy conversion of CO2 to CO, which is the first reduction product. Finally, the loading of Ag nanoparticles onto the LixTiO2 cubic surface the improved photocatalytic activity through SPR effects, and in particular led to selective conversion of CO2 to methane (CH4). Quantitatively, the yield of CH4 from CO2 using the Ag@Li0.075TiO2 particles was 49 mu mol/g after 10 h of reaction, which was 8.2 and 1.5 times higher than that of cubic TiO2 (6 mu mol/g) and Li0.075TiO2 (33 mu mol/g) under UV-light. Additionally, its activity did not decrease under visible lights of 420 and 620 nm with the similar CH4 yields of 42 and 34 mu mol/g after 10 h, respectively. In particular, the production ratio of CH4 and CO using cubic TiO2 and LixTiO2 were about 1:1, with no selectivity for either product. However, after metallic Ag nanoparticles were loaded, the product selectivity shifted towards CH4, and the product ratio of CH4 to CO was about 3:1. Furthermore, the Ag@Li0.025TiO2 particles exhibited a strong SPR effect (in particular, direct electron transfer), which contributed to maintaining the charge separation and the lifetime of the catalyst over a long period. Catalytic deactivation was not observed during five cycles of recycling tests.