Photocatalytic Properties of Perovskite Quantum Dots and Their Role in the Degradation of Alkyl Halide Molecules

Since the first successful implementation of solution phase growth of colloidal cesium lead halide perovskite nanocrystals (PNCs), interest in these materials has steadily grown. This has been driven by their unique photophysical properties and the ionic nature of the semiconducting cores. One of the most interesting properties of PNCs is the ability to forego anion exchange reactions with the surrounding medium, which offers an alternative route for tuning the photophysical properties of these materials.<br/>We present a detailed study on the photo catalytically assisted anion exchange reaction of CsPbBr₃ PQDs dispersed in alkyl chloride solutions. We found that electron transfer from photoexcited PNCs to the surrounding alkyl chloride molecules triggers their electrochemical degradation which produces alkyl radicals and reactive Cl^- anions in the medium. The resulting reactive chlorides engage in halide exchange reaction with the PNC cores, resulting in blue shift in the absorption and PL emission properties of the samples. We probe the efficiency of the reaction by varying the nature of the photoexcitation source (e.g., laser source vs UV reactor or sunlight) and the relative reduction potential of the alkyl halide molecules used. We supplement our findings with thorough characterization of the nanocrystal intermediates to track changes in the crystal structure and stoichiometry during irradiation, using optical and fluorescence spectroscopy, powder X-ray diffraction and x-ray fluorescence spectroscopy. These findings bode well for testing the photocatalytic properties of PNCs in general and may have implications in the degradation of chlorinated molecules.