Bismuth oxyiodide (BiOI) has attracted much attention as a kind of novel functional material because of its highly anisotropic crystal structure and promising optical properties. However, the low photoenergy conversion efficiency of BiOI highly limits its practical applications owing to its poor charge transport. Tailoring the crystallographic orientation has emerged as an effective way to modulate the charge transport efficiency, while there is nearly no report on BiOI. In this study, (001)- and (102)-oriented BiOI thin films were synthesized for the first time with mist chemical vapor deposition at atmospheric pressure. The photoelectrochemical response for the (102)-oriented BiOI thin film was much better than that of the (001)-oriented thin film, owing to the enhanced charge separation and transfer efficiency. The intensive surface band bending and larger donor density for (102)-oriented BiOI were the main origins of the efficient charge transport. Besides, the BiOI-based photoelectrochemical-type photodetector exhibited excellent photodetection performance with a high responsivity of 78.33 mA W–1 and a detectivity of 4.61 × 1011 Jones for visible light. This work provided fundamental insights into anisotropic electrical and optical properties in BiOI, which would be beneficial for the design of bismuth mixed-anion compound-based photoelectrochemical devices.
Photocatalytic nitrogen fixation, converting atmospheric nitrogen into ammonia under ambient conditions, offers a sustainable alternative to the Haber-Bosch process. Herein, the hydrothermal and solvothermal methods to prepare the heterojunction based on BiOCOOH nanosheets and BiOBr nanosheets (BiOCOOH/BiOBr) have been reported. The BiOBr nanosheets epitaxially grow along the nanosheets structure of BiOCOOH. The BiOCOOH/BiOBr heterojunction exhibit photogenerated electron–hole separation properties, which was ascribed from the suitable bandgap values for photocatalytic nitrogen fixation. The NH 3 yield of BiOCOOH/BiOBr heterojunction (63.7 μmol·g −1 ·h −1 ) was about 9 times higher than that of pure BiOCOOH with addition of 0.75 mL of methanol as a sacrifice solvent. Moreover, it is confirmed that the texture coefficient of the (102) BiOBr facet between BiOCOOH and BiOBr is positively correlated with photocatalytic performance, which verifies the growth law of BiOBr on BiOCOOH and explains the formation of the heterojunction from a new perspective. The oxygen vacancies from the (102) BiOBr facet can facilitate the adsorption of nitrogen molecules with a stable adsorption energy of 0.1 eV by density functional theory calculations. This study may offer new perspectives for the design of a series of photocatalytic nitrogen fixation catalysts, particularly in terms of crystal facet control and oxygen vacancy-enhanced nitrogen adsorption.
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