The Investigation Into Synthesis Of Lead Halide Perovskite Nanocrystals And Their Optical And Photocatalytic Properties In Polar Environment

Material science is one of the important disciplines supporting the development of today’s society.Nanotechnology showing a rapid development has entered the vision of the world with the progress of technology.As an essential member of nanomaterials,semiconductor nanocrystalline materials have attracted much attention since their advent,because of their novel optoelectronic physical and chemical properties.In the past decade,the outstanding performance of lead halide perovskite(LHP)materials in optoelectronic devices are awe-inspiring,which ascribes from LHP’s unique physical and chemical properties.Compared with quantum dot materials(such as CdSe,CdS,InP.etc.)which come from Ⅱ-Ⅵ,Ⅲ-Ⅴ or Ⅳ-Ⅵ group.LHP nanocrystals show superior optoelectronic properties,such as high absorption coefficient,high luminescence purity,flexible and adjustable band gap and long-range carrier diffusion ability,and so on.More importantly,LHP nanocrystals are highly defected tolerant materials.The high quantum yields can be obtained without additional surface treatment(such as coating)in the preparation process of LHP nanocrystals.In addition,the synthetic routes for LHP nanocrystals are alternative,simple and low cost.Nowadays,LHP materials have shown great potential and made great progress in the field of optoelectronic devices,such as solar cells,light-emitting diodes,photodetectors etc..However,it lags far behind in other application research(e.g.,photocatalysis).Moreover,the basic research on LHP nanocrystal materials themselves cannot keep up with the development of devices,and there is still a long way to go before the on-demand preparation of materials.Therefore,based on the LHP nanocrystal material itself,a series of reaction systems related to polar solvents were designed and developed,and the reaction mechanism was deeply studied in order to deepen the basic understanding of LHP nanocrystal materials.Besides,investigations in the fields of photocatalysis and anti-counterfeiting were also conducted.In addition,the spaceconfined strategy in perovskite was extended to non-perovskite system(e.g.,Pd nanocubes),which can demonstrate novelty and universality of space-confined strategy.The specific research contents have summarized as follows:1.An immiscible bi-phase system was developed for Mn doping of CsPbX3(X=Cl,Br)nanoplatelets.Systematic studies have shown that the electron-donating oleylamine acts as a shuttle ligand between hexane-water interface,which can drag MnX2 from water to hexane solution and then transfer it to CsPbX3 nanoplatelets.The halide anions play an important role in maintaining proper Mn2+ radius,thus can maintain the structural stability of perovskite octahedrons.By adjusting the thickness of the nanoplatelets,one can tune the amount of Mn doping and,consequently,the exciton-to-dopant energy transfer.Timeresolved optical measurements offer a detailed insight into the exciton-to-dopant energy transfer process.The bi-phase system of non-polar-polar solvents paves a new way for post-processing synthesis of perovskite nanocrystals and an angle for exploring the interaction between perovskite and polar solvents.2.The universality of the water-hexane bi-phase strategy for cation-and anionexchange of LHP was demonstrated.The strategy can not only achieve the continuous adjustment of A-site cations in LHP nanocrystals,but also carry out B-site cation exchange for alternative shapes of LHP.The in-situ optical characterization of the A-site cation exchange reaction shows that the x can be adjusted between 0 and 1 in Cs1-xFAxPbI3.It can be observed clearly that the Cs+ with smaller ion radius is much easier getting access to the lattice of LHP when the precursors in hexane and water are exchanged.In addition,the Mn doping in CsPbX3 nanocubes was also conducted along with monitoring the in-situ doping process in various concentration condition of Mn.This work provides the possibility for a more detailed observation of ion exchange in perovskite.3.we demonstrate that platinum(Pt)decorated lead halide perovskites(MAPbBr3,FAPbBr3,CsPbBr3)photocatalytically produces hydrogen from the vapors of aqueous methanol and biomass.An optimal MAPbBr3 perovskite nanoplatelets(NPLs)film exhibits the highest hydrogen evolution rate of 373 μmolg-1h-1 steadily for～20 hours under solar irradiation.Time-resolved photoluminescence measurements suggest that the superior photocatalytic performance of MAPbBr3 arises from the prolonged charge separation across the homojunction.Such a non-liquid reaction system offers a promising solution to use unprotected metal halide perovskites for light-driven hydrogen production directly.4.For the first time,the space-confined CsPbBr3 nanocrystals have hydrochromic properties.When CsPbBr3 nanocrystals were embedded in a porous array,the reversible transformation between the luminescent CsPbBr3 and non-luminescent CsPb2Br5 can be achieved by moisture supply and removal.The CsPbBr3 nanocrystals were synthesized in situ in the pores of mesoporous SiO2 spheres(around 100 nm in size)which provide the confined space.CsPbBr3@SiO2 showed potential applications in anti-counterfeiting.Due to the small size and negative charge on the surface of mesoporous SiO2 spheres,CsPbBr3@SiO2 can be laser-jet printed with high precision and high speed.Such a material showed good stability in the reversible transformation cycle.This new discovery may not only deepen the understanding of CsPbX3,but also open up a new way to design new applications suitable for CsPbX3 materials.5.The PdNCs@ZIF-8 core-shell structure have been developed and prepared.The surface of Pd nanocubes in the framework of ZIF-8 was functionalized after thermal treatment,and the number of Pd-C species on the Pd surface could be manipulated by different calcination temperature,without the aggregation of Pd nanocrystals and the obvious change of the ZIF-8 framework.The Pd-C formed on Pd NCs@ZIF-8 can strongly inhibit the adsorption of H2,thereby selectively catalyzing propyne to propene.Therefore,the optimized catalyst(i.e.,Pd NCs@ZIF-8-100)exhibits 96.4%propylene selectivity and 93.3%propyne conversion at 35 ℃ and atmospheric pressure.This work can not only provide efficient catalysts for propyne selective hydrogenation,but also provide new ideas for catalytic applications of ZIFs.