Development of Rh-Doped Ga₂O₃ Photocatalysts for Reduction of CO₂ by H₂O as an Electron Donor at a More than 300 nm Wavelength

Abstract

Rhodium-doped gallium oxide (Ga 2 O 3 :Rh) that was prepared by a simple coprecipitation method exhibited activity for the photocatalytic conversion of CO 2 by H 2 O under photoirradiation with light of >300 nm wavelength. Although Ga 2 O 3 is a wide-band-gap photocatalyst that is active only under photoirradiation with <300 nm light, the absorption edge shifted to >300 nm as a result of Rh doping. Ag−Cr-loaded Ga 2 O 3 :Rh (0.7 mol %) showed activity for the production of CO (3.9 μmol h −1 ) as a reduction product of CO 2 . The formation of a stoichiometric amount of O 2 indicated that H 2 O acts as an electron donor for the photocatalytic conversion of CO 2 . Characterization using several techniques such as X-ray absorption spectroscopy (XAS) revealed that after doping in Ga 2 O 3 the trivalent Rh species substituted not for the tetrahedral Ga site but for the octahedral Ga site of β-Ga 2 O 3 . From the result of DFT calculations, the new energy level owing to Rh 3+ was within the Ga 2 O 3 band gap. It was concluded that the new absorption due to the Rh d t 2g orbital to the conduction band contributed to the activity of photocatalytic conversion of CO 2 by H 2 O under photoirradiation with light of >300 nm wavelength.

Impact of Al doping on a hydrothermally synthesized β-Ga2O3 nanostructure for photocatalysis applications

“…7(b) shows the relative photocatalytic activities of the b-Ga 2 O 3 nanostructure for different doping materials and concentrations. [16][17][18]26,[57][58][59][60][61] This comparison revealed that the photocatalytic performance of the given Ga 2 O 3 -based photocatalyst increased at certain small amounts of dopants, but decreased with large amounts of dopants. Therefore, an optimal balance between charge separation and recombination via doping approaches is important for Ga 2 O 3 -based photocatalyst.…”

“…26 Cr via Rhodamine B (RhB) degradation under 254 nm, 17 Co via Congo red (CR) degradation under 254 nm, 61 Zn via gas conversion under 254 nm, 18 and Rh via CO 2 conversion under 300 nm. 16…”

“…[16][17][18][19][20][21][22][23] Doping in photocatalysts is a method of suppressing the recombination process, which creates available energy states in the bandgap underneath the conduction band edge and/or above the valence band edge. [16][17][18][19] These additional energy levels in the forbidden bandgap can separate charged carriers and thereby retard the recombination process, allowing more charged carriers to diffuse in the surface and consequently enhances the photocatalytic reactions. 24,25 Thus far, reports have indicated that dopants in Ga 2 O 3 have reduced the bandgap energy of Ga 2 O 3 , which reduce the benets of the high redox potential effects that Ga 2 O 3 posseses.…”

“…24,25 Thus far, reports have indicated that dopants in Ga 2 O 3 have reduced the bandgap energy of Ga 2 O 3 , which reduce the benets of the high redox potential effects that Ga 2 O 3 posseses. [16][17][18][19][20][24][25][26][27] Therefore, it would be benecial to apply a dopant atom that could increase the Ga 2 O 3 bandgap with the dopant concentration. It has been reported that aluminum (Al) can increase the Ga 2 O 3 bandgap upon doping.…”

Phase junction enhanced photocatalytic activity of Ga2O3 nanorod arrays on flexible glass fiber fabric

“…38 Many methods have been investigated to further improve the photocatalytic activity of Ga 2 O 3 , including morphology controlling, doping, surface modication and semiconductor coupling. [39][40][41][42][43][44] Nitu Syed et al reported a two-step method for the synthesis of porous a-Ga 2 O 3 nanosheets from liquid metal gallium, explaining that the excellent photocatalytic activity of a-Ga 2 O 3 originated from the narrowed bandgap caused by trap states. 1 Han et al revealed that the modication of in situ Ag nanoparticles can effectively improve the photocatalytic property of Ga 2 O 3 for hydrogen evolution.…”