Enhancement The Aqueous Stability Of Perovskite Nanomaterials And Its Applications

Recently,perovskite quantum dots as promising nanomaterials have been attracted much attention in the research areas such as solar cells and optoelectronic devices,due to its high photoluminescence quantum yield,narrow photoluminescence half peak width,and adjustable photoluminescence.However,perovskite quantum dots also have obvious defects,especially the weak resistance to moisture corrosion and photodegradation.The poor stablilty limits their practical application,especially in electrochemistry.Hence,perovskite quantum dots with various modifications and improvements are reported to obtain better stability.In this thesis,the aqueous phase stability of all-inorganic perovskite nanomaterials CsPbBr₃ nanocrystals?NCs?was studied.To coat waterproof layer was demonstrated to improve the stability of its aqueous phase.The electrochemiluminescence?ECL?of CsPbBr₃ NCs in its aqueous phase were tested.The main contents are outlined below.1.Enhancing aqueous stability and radiative-charge-transfer efficiency of CsPbBr₃perovskite nanocrystals via conductive silica gel coatingThe poor water stability of perovskite nanocrystals limits their electrochemical applications.We report a CsPbBr₃ NCs coated with a waterproof and conductive silicone shell,which enhances its aqueous phase stability and radiative charge transfer efficiency.After introducing a small amount of CsBr aqueous solution into n-hexane containing tetramethoxysilane?TMOS?and Cs₄PbBr₆ NCs,the Cs₄PbBr₆@CsPbBr₃@silica gel?CsBr?hybrid was formed.The outer silica shell can block the contact between the perovskite and the water phase.The presence of Cs⁺and Br^-in the silica shell significantly improves the conductivity of the silica shell.The obtained CsPbBr₃ NCs@silica gel?CsBr?not only significantly enhances its aqueous phase fluorescence stability and ECL luminescence stability,but also has strong ECL luminescence performance after being stored in CsBr salt solution for one month,and shows significantly improved charge injection performance and radiation charge transfer coefficiency.Annihilation ECL indicates that all electrons injected into the perovskite hybrid can recombine with the injected holes to generate light.The annihilation and co-reaction agent ECL and photoluminescence spectra show that encapsulation of CsPbBr₃ NCs in a conductive and waterproof silica shell is beneficial to enhance the water phase stability of perovskite NCs,and the effect on its excited state can be ignored.The core-shell perovskite hybrid was used to detect dopamine molecules with a linear range of 0.01-10?M and a detection limit of 3 nM.2.Monitor reaction kinetics and determination of trace water in hydrophobic organic solvents by a smartphone-based ratiometric fluorescence deviceA smartphone-based ratiometric fluorescence device was designed to monitor the reaction kinetic process under continuous mixing conditions,demonstrated by the hydrolysis of Cs₄PbBr₆NCs.In the presence of water,Cs₄PbBr₆ NCs?non-fluorescent?were converted to CsPbBr₃ NCs?strong fluorescent?.The fluorescence images of CsPbBr₃ NCs were recorded by the camera in smartphone with anthracene as the reference luminophore for ratiometric measured.It was shown that the water triggered convert reaction of Cs₄PbBr₆ NCs to CsPbBr₃ NCs is followed the pseudo-second-order kinetic model.The CsPbBr₃ NCs layer on the surface of the hydrolysate of Cs₄PbBr₆ NCs@CsPbBr₃ NCs prevented Cs₄PbBr₆ NCs core from contact with the aqueous microspheres and the common ion effect of CsBr in aqueous microspheres hindered the hydrolysis of Cs₄PbBr₆ NCs.With increasing water content,the hydrolysis of Cs₄PbBr₆ NCs is promoted to yield more CsPbBr₃ NCs,which can be utilized for trace water determination in hydrophobic organic solvents.By using the brightness ratio of the fluorescence image of CsPbBr₃ NCs and anthracene in the green and blue components as the signal,the portable fluorescence device was used to determinate water in n-hexane,dichloromethane and toluene with the detection limits of 0.0031%,0.0043%and 0.0072%?v/v?,respectively.The device offers the advantages of portability and low cost for the field rapid analysis of trace water in hydrophobic organic reagents.3.Cathodic electroluminescence behavior related of CsPbBr₃ NCs in aqueous phaseUp to now,only the anodic ECL of CsPbBr₃ NCs is reported.The investigation about the cathodic ECL of CsPbBr₃ NCs is still absent.But our experimental results show that the moderate-intensity cathodic ECL signal is measured on the glassy carbon electrode?GCE?modified by CsPbBr₃ NCs,in the presence of?NH₄?₂S₂O₈ as the co-reactant.Compared with the bare GCE,the ECL signal is significantly enhanced.Moreover,during the continuous cyclic voltammetric excitation,the ECL intensity is increased gradually and approached to stable level after four cycles.But the anodic ECL of GCE|CsPbBr₃ NCs is decayed rapidly during the continuous potential cycles.The electrochemical impedance measurements show that the attenuation in adodic ECL signal is not caused by the loss of CsPbBr₃ NCs from the electrode surface,but by the degradation of its ECL performance.At the same time,a strong cathodic ECL signal is measured in GCE|CsPbBr₃ NCs without anode ECL.In addition,the GCE modified with degradated CsPbBr₃ NCs also shows strong cathodic ECL signal,and its intensity is increased with the increasing of scan cycles.Accordingly,we speculate that the cathodic ECL behavior of GCE|CsPbBr₃ NCs in the presence of?NH₄?₂S₂O₈ may be originated from the ECL of S₂O₈^2-.And CsPbBr₃ NCs and/or its decomposition product are the coreactant or promoter for the ECL of S₂O₈^2-.That is to say,CsPbBr₃ NCs is not the true luminophore oin the cathodic ECL in GCE|CsPbBr₃ NCs.It is reasonable to explain why the cathodic ECL behavior of CsPbBr₃NCs is not reported yet.The enhancement mechanism and possible application of this phenomenon may need to be further explored.