Ag-loading on brookite TiO2 quasi nanocubes with exposed {2 1 0} and {0 0 1} facets: Activity and selectivity of CO2 photoreduction to CO/CH4

• CO2 photoreduction over brookite TiO2 quasi nanocubes was conducted in CO2/H2O vapor.
• The brookite nanocubes surrounded by four {2 1 0} and two {0 0 1} exposed crystal facets.
• Ag-loading on nanocubes can enhance the activity/selectivity of CO/CH4 production.
• Activity/selectivity is mainly related to the Ag-loading on the exposed crystal facets.
• Total consumed electron number for CO/CH4 production is used to evaluate activity.

Brookite TiO2 quasi nanocubes (mean size of ∼50 nm) mainly surrounded by four {2 1 0} and two {0 0 1} exposed crystal facets were used as catalyst for the CO2 photoreduction. It is found that the Ag nanoparticle size and its distribution on the exposed facets of the brookite nanocubes are significantly influenced by the Ag-loading levels, which then causing obvious differences in the activity and selectivity of CO2 photoreduction to CO/CH4 generation. At 0.5% Ag-loading, the brookite nanocubes show the highest overall activity with CO/CH4 production rates of 128.8/11.5 ppm h−1, which is 3.89 times higher than that of the pristine brookite. When the Ag-loading level is ≤0.5%, the small Ag nanoparticles are mainly dispersed on the {2 1 0} facets of the brookite nanocubes, which resulting in an enhancement in the selective CO generation; while >0.5% Ag-loading could lead to the formation of Ag nanoparticles aggregated on the {2 1 0} facets with some Ag nanoparticles dispersed on the {0 0 1} facets, and then causing more selectivity for the CH4 generation. This novel phenomenon was explored with the aid of various characterization techniques. The present results provide an important indication about the effects of Ag-loading on the activity and selectivity of CO2 photoreduction reaction over the exposed facets of brookite nanocubes, and demonstrate a strategy for tuning the CO2 photoreduction performance through tailoring the morphology and surface structure of brookite TiO2.

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