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A Triple-Function Bismuth Oxochromate Photocatalyst

A photocatalyst with the chemical formula Bi8(CrO4)O11 was synthesized and exhibited wide-spectrum solar energy conversion, efficient water oxidation and pollutant degradation.

Conventional photocatalysts suffer from poor solar-to-chemical energy conversion and the inability to utilize the entire visible light spectrum due to a large bandgap. In recent years, several mixed-anion and oxide materials have been developed as attractive wide-spectrum photocatalysts, using orbital hybridization to narrow the bandgap and widen the absorption spectrum of the material.

However, narrowing the bandgap of a photocatalyst weakens the driving force for redox reactions, especially water oxidation and pollutant degradation, because these reactions involve a complicated multi-electron process. The inability to reconcile these two contradictory demands has confounded scientists for the longest time.

Recently, researchers from Tsinghua University and Hubei University of Technology jointly reported in the Beijing-based National Science Review the synthesis of a bismuth oxochromate photocatalyst Bi8(CrO4)O11 that has satisfied both these requirements.

Owing to hybridization of Cr’s 3d orbitals with O’s 2p orbitals, the conduction band minimum of Bi8(CrO4)O11 was shifted down and the bandgap narrowed, allowing absorption up to the entire visible region (~678 nm) with a theoretical solar spectrum efficiency of 42.0%.

Moreover, attributed to the giant internal electric field induced by its large dipole moment, Bi8(CrO4)O11 realized evidently rapid separation of photogenerated electron-hole pairs, thus showing highly efficient photocatalytic water oxidation activity. Its average O2 evolution rate reached 14.94 μmol/h, about 11.5 and 4.0 times higher than that of Bi2WO6 nanosheets and commercial WO3 nanoparticles. It also registered a notable apparent quantum yield of 2.87% at 420 nm (even 0.65% at 650 nm), superior to many reported wide-spectrum photocatalysts.

Most remarkably, its strong oxidation ability also enables the simultaneous degradation and complete mineralization of environmental pollutant phenol. Its degradation reaction constant could reach 0.119/min, about 23.0 and 2.9 times higher than benchmark materials CdS and P25-TiO2, respectively. Even under 650 nm red light irradiation, Bi8(CrO4)O11 was noted to still be able to degrade and mineralize phenol, a feat few wide-spectrum photocatalysts have achieved. [APBN]