Microwave-Assisted Synthesis of Bismuth Chromate Crystals for Photogenerated Charge Separation

The conversion of renewable solar energy into chemical energy is an important topic in research. Recently, bismuth chromate (Bi 2 CrO 6 ) has attracted attention in photocatalytic research, particularly for its potential applications in pollutant degradation and water splitting. This layered metal oxide exhibits a narrow optical band gap of approximately 1.9 eV and can utilize most of visible light in the solar spectrum. However, the photocatalytic activity of Bi 2 CrO 6 is relatively low, and its poor charge separation properties restrict its practical applications. Herein, we report a microwave-assisted hydrothermal method for the fabrication of Bi 2 CrO 6 crystals with high crystallinity and uniform morphology. Compared with the conventional preparations, microwave irradiation induces rapid volumetric heating and greatly accelerates nucleation and growth reactions, forming Bi 2 CrO 6 crystals within minutes. Multiple characterization methods, including X-ray diffraction, Raman scattering, and scanning electron microscopy, were employed to examine the crystallinity and morphologies of the samples. Microwave-assisted synthesized Bi 2 CrO 6 crystals showed better water oxidation activity in photocatalytic and photoelectrochemical tests than the conventional samples. Oxygen evolution rates were boosted 7.2 and 3.1 times using AgNO 3 and Fe(NO 3 ) 3 as electron acceptors, respectively. Further investigations showed that microwave-assisted Bi 2 CrO 6 crystals exhibited improved photogenerated charge separation. The average lifetime of photogenerated carriers, calculated from time-resolved photoluminescence results, also showed an increase. Furthermore, using photodeposition of metals and oxides as probes, the spatial separation of photogenerated electrons and holes was demonstrated to take place between {001} top and side facets of the Bi 2 CrO 6 crystal samples. Loading reduction and oxidation cocatalysts onto different facets significantly enhanced the photocatalytic activities. These results enforce the promise of microwave-assisted Bi 2 CrO 6 crystal synthesis for photocatalytic water-splitting applications and present a solution for efficient solar-energy conversion. Download: Download high-res image (64KB) Download: Download full-size image