Turn-On Fluorescence Sensing Of Pb（Ⅱ） Based On In-situ Growth Of MAPbBr₃ Perovskite

Organic-inorganic hybrid lead halide perovskite with excellent optoelectronic properties has emerged as a promising material for colorimetric or fluorescence sensing.However,as one of the most toxic heavy metals in ecological environment,Pb(Ⅱ)may cause persistent pollution and potential danger to surroundings and human health,which limits the applications of perovskite.Owing to the defect-tolerant nature of perovskite,ligand-free formation of lead halide perovskite nanocrystals in mesoporous templates can bring out bright photoluminescence.Highly fluorescent methylammonium lead bromide(MAPbBr3)perovskite could in-situ grow in sulfydryl functionalized mesoporous alumina film,homemade Al(OH)3 and cellulose membrane,where methylammonium bromide(MABr)meets the sulfydryl-captured lead.In this work,the turn-on fluorescence sensing of lead could be applied to the analyses of environmental water and children’s stationery with high selectivity,low method detection limit and simple operation.The dissertation includes five chapters:Chapter I,introduction.The harm of heavy metal element lead and the significance of detection are briefly introduced.The fluorescence sensing of lead,different types of material to enhance the stability of lead halide perovskite and the applications of lead halide perovskite in ion analysis are mainly introduced.On this basis,the research ideas and contents of this paper are put forward.Chapter II,highly selective turn-on fluorescence sensing of Pb(Ⅱ)in sulfydryl functionalized mesoporous alumina film.Pure lead halide perovskites(without any ligand)decompose easily in air.The perovskite with high stability,high fluorescence quantum yield and high defect tolerance synthesized in mesoporous alumina template can resist the influence of illumination,water vapor and oxygen under atmospheric conditions.In-situ growing MAPbBr3 perovskite in the meso-Al2O3-SH film provides a sensitive turn-on fluorescence sensing for Pb(Ⅱ)in water.After a series of optimizations,the linear relationship between the PL intensity and the Pb(Ⅱ)concentration ranged from 0.01 to 1.0 mg/L.The method detection limit was found to be 5 ×10-3mg/L.The sensitivity of this method meets the requirement for the detection of Pb(Ⅱ)in drinking water samples following the National Test Standard of China.In addition,the MAPbBr3 perovskite synthesized in the template had little change among 37 days in air,exhibiting excellent stability.The method is suitable for on-site analysis and off-line detection of Pb(Ⅱ)in domestic water and environmental water samples.Chapter III,turn-on fluorescence sensing of lead in sulfydryl functionalized Al(OH)3 substrate.In this chapter,Al(OH)3 thin-film was synthesized on the surface of glass by liquid phase deposition method.After sulfhydryl functionalization,insoluble Al(OH)3 substrate with a relatively large surface area could be used for the enrichment of Pb(Ⅱ),and as the substrate for the growth of lead halide perovskite.And then the fluorescence intensity of derived perovskite could be detected.After a series of optimizations,the logarithm of the fluorescence signal intensity showed a good linear relationship with the content of Pb2+ in the range of 100 to 1500 mg/kg,with the method detection limit of 40 mg/kg.Compared with the mesoporous Al2O3 template,Al(OH)3 thin-film can be prepared in large quantities with low cost,and espescially suitable for the analysis of Pb(Ⅱ)in children’s stationery of crayons.Chapter IV,turn-on fluorescence sensing of lead in sulfydryl functionalized flexible cellulose membrane.The porous cellulose filter membranes were used as the substrate for the growth of perovskite.The staggered channels can not only provide the growth environment for perovskite,but also act as a barrier to reduce the influence of air,temperature,and humidity.Sulfydryl functionalized cellulose substrate showed good stability in the high salt aqueous.In addition,the flexible cellulose membrane was suitable for swab method.Green fluorescence could be observed under 365 nm UV light when more than 1 μg lead was adsorbed on the cellulose membrane and on-site derivated by MABr.Chapter V,summary and outlook.The significance of the research work is summarized and prospected.In this dissertation,our work focus on the different sulfhydryl functionalized substrates and in situ growing MAPbBr3 perovskite for the turn-on fluorescence sensing of lead.The hydroxyl group on the surface of substrate could be passivated by the stable Pb-S bond,which enhanced the stability of the detection system.The methods using substrate-confined formation of perovskite may also be extended to other analytical sensing applications,such as environmental monitoring and biological medicine,on-site or off-line analyses.