Gallium Oxide Assisting Ag-Loaded Calcium Titanate Photocatalyst for Carbon Dioxide Reduction with Water

Abstract

An efficient and highly selective photocatalytic conversion of carbon dioxide (CO 2 ) into valuable chemicals such as carbon monoxide (CO) using water (H 2 O) as an electron donor has been much attractive and deeply desired, which requires the development of advanced photocatalysts based on a functional design. As the Ag-loaded calcium titanate (CaTiO 3 , CTO) photocatalyst showed a high selectivity to CO 2 reduction in aqueous solution and the Ag-loaded gallium oxide (Ga 2 O 3 ) photocatalyst showed a higher activity for both H 2 O splitting and CO 2 reduction, herein, a series of composite photocatalyst samples consisting of Ga 2 O 3 and CTO were simply fabricated by calcination of the physical mixtures, followed by loading of a Ag cocatalyst with a photodeposition method. The optimized sample with the Ag cocatalyst exhibited both a high CO formation rate of 56.9 μmol h −1 (higher than that of Ag/Ga 2 O 3 ) and a high selectivity of 95.0% (comparable to Ag/CTO) in the photocatalytic CO 2 reduction with H 2 O. In this composite photocatalyst, most of the electrons generated in the photoexcited Ga 2 O 3 part migrated to the minor CTO particles to contribute to the selective CO 2 reduction reaction, which was evidenced by the selective photodeposition of Ag species on the CTO part. The selective CO formation originates from the property of Ag-loaded CTO photocatalyst as the active part in the composite photocatalyst. The Ga 2 O 3 part functions as an antenna to receive the light and donate the photoexcited electrons to the much decorated Ag/CTO part, where the concentrated electrons would promote CO 2 reduction with high efficiency.

Surface gallium oxide hydroxide species adsorbing carbon dioxide to enhance the photocatalytic activity of silver-loaded calcium titanate for carbon dioxide reduction with water

“…4a), which is similar to a previous report. 7 The Ag(1.0)/CTO sample showed the characteristic peaks of Ag NPs centered at around 540 nm assignable to the localized surface plasmon resonance (LSPR) (Fig. 4b), 14 which is good evidence for the presence of Ag NPs.…”

“…3,4 So far, we have developed some modication strategies, for example, modication of an Ag NP cocatalyst with other metal oxides such as Co 3 O 4 5 and addition of a Pr 6 O 11 layer, 6 where they interacted with the CTO photocatalyst and Ag NPs and contributed to the electron transfer or stabilization of Ag NPs, and modication with a Ga 2 O 3 photoabsorber to provide additional photoexcited carriers to the Ag/CTO photocatalyst. 7 The adsorption of CO 2 on the photocatalytic surface is the important rst step of photocatalytic CO 2 reduction before the successive surface reaction with protons and photoexcited electrons to form CO and H 2 O. Some materials feasible for CO 2 adsorption to increase the CO production rate have been reported.…”

“…3,4 So far, we have developed some modification strategies, for example, modification of an Ag NP cocatalyst with other metal oxides such as Co 3 O 4 5 and addition of a Pr 6 O 11 layer, 6 where they interacted with the CTO photocatalyst and Ag NPs and contributed to the electron transfer or stabilization of Ag NPs, and modification with a Ga 2 O 3 photoabsorber to provide additional photoexcited carriers to the Ag/CTO photocatalyst. 7…”

Metal– and covalent organic frameworks for photocatalytic CO2reduction coupled with H2O oxidation

“…The rapid separation efficiency of photogenerated charge carriers is fundamental to efficient catalysis. 15,16,65 In comparison to other semi-conductor photocatalysts, the MOFs and COFs with porous structures and large surface areas provide more exposed active sites and substrate transport channels, facilitating prompt reactions between charge carriers and substrates, thereby reducing charge diffusion distances and suppressing electron-hole recombination. When employing MOF-based materials as photocatalysts, the main strategy for increasing the lifetime of photo-generated charge carriers is to promote space charge separation in low-lying excited states.…”

“…These thermodynamic and kinetic constraints collectively limit the development of CO 2 RR in water. [14][15][16] In the case of CO 2 RR coupled with WOR, the oxidation products consist of oxygen and hydrogen peroxide, while the reduction products mainly includes C 1 and C 2+ products (Fig. 1).…”