Ionic liquid-assisted hydrothermal preparation of BiOI/BiOCl heterojunctions with enhanced separation efficiency of photo-generated charge pairs and photocatalytic performance

Abstract In this contribution, BiOI/BiOCl heterojunctions were successfully synthesized with the assistance of reactable ionic liquid (IL) 1-propyl-3-methylimidazolium iodide ([PrMIm]I) via a hydrothermal method. The crystal structures, morphologies, chemical compositions, optical properties and separation efficiency of photo-generated charge pairs of the as-prepared BiOI/BiOCl heterojunctions were characterized by various analytic methods. Surface photovoltage spectroscopy (SPS) and photoelectrochemical measurements reveal that the BiOI/ BiOCl heterojunctions exhibit higher separation efficiency of photo-generated charge pairs than the reference BiOCl and BiOI. XPS results reveal that I element exists in the as-prepared samples with a chemical valence of -1, and when the mass ratio of [PrMIm]I/BiOCl is 8%, the sample holds the highest surface hydroxyl content. Photocatalytic performance of the as-fabricated photocatalysts was evaluated by abatement of rhodamine B (RhB) aqueous solution under simulated sunlight irradiation. BiOI/BiOCl heterojunctions exhibit enhanced photocatalytic performance; the 8% sample displays the highest photocatalytic activity. Trapping experiments certify that the superoxide radicals (•O2-) is the predominant active free radicals in the photocatalytic degradation process of RhB over the BiOI/BiOCl heterojunctions. In light of experimental results, a possible Z-scheme photocatalytic degradation mechanism was discussed to elaborate the separation and migration of the photo-induced electron-hole pairs. This study provides a useful reference for ILs assisted fabrication of high efficiency photocatalytic materials.