Photocatalytic Degradation of Alkyl Halide Molecules Promoted by CsPbBr₃ Perovskite Quantum Dots

Abstract

We present a detailed investigation of the photo-assisted halide exchange reaction of CsPbBr3 perovskite quantum dots (PQDs) dispersed in chlorinated solvents. We probe the kinetics of this process and the associated blue shift in the emission properties, by varying the irradiation source, its duration, structure of the solvent molecules, and their corresponding reduction potentials. We further carry out a thorough characterization of the nanocrystal intermediates during the irradiation period until complete saturation, using optical and fluorescence spectroscopy, supplemented with powder X-ray diffraction and X-ray fluorescence spectrometry measurements. This has allowed us to closely track changes in the crystal structure and nanocrystal stoichiometry. Our findings indicate that the PQDs in the sample act as photocatalyst, where they absorb high-energy photons, promoting rapid electron transfer to the alkyl chloride molecules and triggering their dissociative degradation to produce radical alkyl molecules and Cl– anions. The intensity- and time-dependent generation of reactive chloride ions triggers anion exchange in the nanocrystals, concomitant with shifting of the optical characteristics of the PQD dispersions. These findings indicate that PQDs exhibit promising photocatalytic properties that may find use in common organic reactions including dehalogenation.

Overcoming the Photoinduced Solvent-Assisted Anion Exchange Reactions of CsPbBr3 Perovskite Nanocrystals

“…However, in such solvents, the major difficulty is the light-induced solvent-assisted anion exchange of lead halide perovskites. − Son and co-workers reported such anion exchange reactions of CsPbBr 3 with DCM in the presence of light . In a recent report, Mattoussi and co-workers investigated the process in detail and formulated a mechanism . In the presence of light, chloroform/DCM accepts an electron from the conduction band (CB) of CsPbBr 3 and results in the formation of chloride ions .…”

“…37 In a recent report, Mattoussi and co-workers investigated the process in detail and formulated a mechanism. 34 In the presence of light, chloroform/DCM accepts an electron from the conduction band (CB) of CsPbBr 3 and results in the formation of chloride ions. 34 These chloride ions replace Br − ions from their sites in the lead halide perovskites.…”

“…34 In the presence of light, chloroform/DCM accepts an electron from the conduction band (CB) of CsPbBr 3 and results in the formation of chloride ions. 34 These chloride ions replace Br − ions from their sites in the lead halide perovskites. 34 It is well known that the anion exchange process starts at the surface and diffuses into the interior parts of the crystal.…”

“…34 These chloride ions replace Br − ions from their sites in the lead halide perovskites. 34 It is well known that the anion exchange process starts at the surface and diffuses into the interior parts of the crystal. 19 The perovskite crystal structure is generally soft and facilitates the motion of halide ions through the crystal.…”

“…Moreover, these solvents are easily evaporable, and thus, they are widely used for the fabrication of lead halide perovskites on different substrates . However, in such solvents, the major difficulty is the light-induced solvent-assisted anion exchange of lead halide perovskites. − Son and co-workers reported such anion exchange reactions of CsPbBr 3 with DCM in the presence of light . In a recent report, Mattoussi and co-workers investigated the process in detail and formulated a mechanism .…”