Fluoresecent Colorimetric Sensing Of CsPbBr₃ Inorganic Perovskite Nanocrystals Based On Halide Exchanges

Lead halide perovskite nanocrystals(LHPNCs)have been developed since 2014.Due to their intrinsic ionic salts and lead-halogen composition,they have high molar absorbance coefficient,high defect tolerance,and ultra-fast carrier mobility,and their material structure and optical properties can be precisely controlled through ion exchange,which have aroused great research interest of scientific researchers as well as new thinking on the ion salt nanocrystal.Among LHPNCs family,CsPbBr3 all-inorganic perovskite nanocrystals(CsPbBr3 PNCs)are quite outstanding that they behave better stability and luminescence properties,etc.They also demonstrate promising application prospects in light-emitting devices,solar cells,scintillator,photocatalysis and the other fields,occupying a central position in the current research of LHPNCs.All these have aroused our strong passion for the CsPbBr3 PNCs research.This thesis builds a novel wavelength shift based fluorescent colorimetric sensing system based on the halide exchanges of CsPbBr3 PNCs,complementing the conventional intensity based fluorescent colorimetric sensing as well as broadening the application of CsPbBr3 PNCs in analytical chemistry.The thesis consists of five chapters as follows:In chapter I,the recent development of CsPbBr3 PNCs study has been summol/Larized.The synthesis methods of CsPbBr3 PNCs are fully investigated and analyzed,and the structural and optical properties of CsPbBr3 PNCs are also systematically introduced.Especially,their ion exchange properties are mainly discussed.The applications of CsPbBr3 PNCs including chemical sensing,light-emitting diodes,scintillator and photocatalysis have been summarized.Based on the deep understanding of the intrinsic ionic salts of CsPbBr3 PNCs and their halide exchange properties,the novel wavelength shift based fluorescence colorimetric sensing systems are proposed.In chapter ?,we develop a new method for the controllable and reproducible synthesis of high quality CsPbBr3 PNCs using bromobenzene and alkane amines aliphatic nucleophilic substitution(BANS).In this method,bromobenzene reacts with alkane amines under heating to release HBr.The HBr will be trapped by deacid reagent Cs2CO3 and alkane amines under heating to produce CsBr and PbBr2,which finally generates CsPbBr3 PNCs.The CsPbBr3 PNCs nucleation and growth kinetics is easily controlled via regulating reactivity of bromobenzene and alkane amine.Typically,when 1,3,5-tris(bromomethyl)benzene and oleylamine are used,CsPbBr3 PNCs with a quantum yield of 88%and a narrow full-width at a half-maximum of 22 nm could be produced by loading all reactants into a single reaction vessel under continuous heating in an ambient atmospheric condition.The whole synthesis can be completed within 10 min with high simplicity and reproducibility.This method breaks through the obstacle of poor reproducibility resulted from the fast nucleation and growth of CsPbBr3 PNCs,and could be amplified to realized gram scale synthesis.The highly reproducible synthesis of CsPbBr3 PNCs is of great significance to improve the accuracy of CsPbBr3 PNCs based fluorescent colorimetric sensing(FCS),giving full play to the advantages of high efficiency and simplicity of FCS.In chapter III,the halide exchanges between CsPbBr3 PNCs and I-are studied under three different conditions including solid phase-organic,aqueous phase-organic heterogeneous,and organic phase-organic homogeneous phases.CsPbBr3 PNCs could achieve rapid halide exchange with the I-of oleylamine iodine under the homogeneous condition,resulting in a fast fluorescence color changes from green to orange,then to red.The wavelength shift is linear to I-concentration.A wavelength shift based fluorescence colorimetric "iodine ruler" based on the halide exchange of CsPbBr3 PNCs are developed.The "iodine ruler" demonstrates the advantages of high visual resolution,fast response and high sensitivity.Combined with redox reaction between I"and benzoyl peroxide(BPO),the "iodine ruler" could be applied for the highly selective fluorescence colorimetric sensing of BPO.In Chapter IV,considering the high importance of the rapid detection of Cl-in sweat for the diagnosis of fibrotic cysts,we have investigated heterogeneous halide exchange between CsPbBr3 PNCs(n-hexane,organic phase)and NaCl solutions(aqueous phase).The results show that CsPbBr3 PNCs could achieve fast halide exchanges with Cl-of NaCl in the aqueous phase under magnetic stirring at pH 1,accompanying a significant wavelength blue shift and vivid fluorescence color changes.In this study,a wavelength shift based fluorescence colorimetric sensing of Cl-based on the halide exchange of CsPbBr3 PNCs are developed in order to realize the rapid detection of Cl-in sweat.Compared with the other conventional fluorescence colorimetric methods,this method is of high accuracy without any pretreatment,which demonstrates promising application prospects.In Chapter V,since the intrinsic ionic salt properties of CsPbBr3 PNCs limit their stability in polar solvents and hinder their analytical applications,in this chapter,CsPbBr3@SiO2 perovskite nanocomposites(CsPbBr3@SiO2 PNCCs)are synthesized by the benzyl bromide nucleophilic substitution strategy mentioned above.The CsPbBr3@SiO2 PNCCs present good alcohol polarity stability and could be stably dispersed in ethanol.Then,the homogeneous halide exchange between CsPbBr3@SioO2 PNCCs(ethanol)and NaCl solution(aqueous phase)is studied.The results show that CsPbBr3@SiO2 PNCCs achieve fast halide exchange with Cl-of NaCl in the aqueous phase without any magnetic stirring and pH regulation,which is helpful for Cl-detection.Compared with the above-mentioned heterogeneous detection,this method greatly simplifies the detection processes and provides a new idea for further broadening the fluorescence colorimetric sensing using CsPbBr3 PNCs halide.