Synthesis And Physical Properties Of Inorganic Photoelectronic Functional Composite Materials

Inorganic photoelectronic functional composite materials have been one of the important research directions in the fields of materials science due to its excellent physical properties and broad application prospects. With the development of nano science and technology, ordered mesoporous based inorganic photoelectronic functional composites have attracted great attention in recent years. Mesoporous materials with uniform pore size, high surface area and easily functional surface have attracted great interest from scientists for the possibility of peculiar optical, electrical, magnetic and other physical characteristics when the second phase is incorporated into the pores. Generally, mesoporous composite materials provide a new way for the synthesis and application of new materials, and the related research has great theoretical and practical significance.AgI is the first solid state electrolyte discovered, and the extensive investigations into its unique ionic conductivity have promoted the progress in solid-state ionics. With the development of the materials science, interestingly, the conductivity of AgI was found to depend on the components in the composites AgI-X.Along with the improvement of the preparation technology, various AgI-X composites with enhanced ion transport and optical properties were successfully prepared.In this paper, we first reported the preparation of γ-Fe2O3/SBA-15and AgI/SBA-15mesoporous composite materials with SBA-15as the matrix, and their optical and magnetic properties were studied further. Secondly, the AgI-KI ternary compounds, AgI-K2AgI3and Agl-KAg4I5composites were prepared, and the optical and ion transport properties of these composites were analyzed. The detailed studies are as follows.(1) Double solvent method was used to prepare γ-Fe2O3SBA-15mesoporous composite materials with SBA-15as the matrix material. XRD and FT-IR results show that the nanoparticles encapsulated in mesoporous silica are y-Fe2O3. Low-angle XRD and N2adsorption porosimetry results indicate that the y-Fe2O3/SBA-15mesoporous composites keep the ordered hexagonal mesoporous structure of SBA-15. It can be seen from UV-vis absorption spectra that Eg of y-Fe2O3/SBA-15mesoporous composite can be adjusted by the different γ-Fe2O3loadings in SBA-15, and the optical absorption edges show a blue shift with the iron concentration decreasing, which should result from the size effect of γ-Fe2O3nanoparticles in samples. Besides, VSM results indicate that the as-obtained nanocomposites exhibit superparamagnetic behavior, and the value of saturation magnetization (Ms) for the samples increase with the iron concentration increasing, which should correspond with the particle size’s increasing.(2) Heat diffusion method was used to prepare AgI/SBA-15mesoporous composite materials with SBA-15as the matrix material. XRD results show that AgI encapsulated in SBA-15is AgI cluster when AgI content is lower than15wt%; when AgI content is higher than15wt%, AgI nano-crystal can be observed. EDS、EPR and PLE results indicate the existence of Ag clusters in AgI/SBA-15mesoporous composite, which disperse on the surface of AgI. In addition, a blue shift on the absorption edge as well as the formation of a band tail is observed in the reflectance spectra. The blue shift is due to quantum size effect and the band tail is likely to be caused by the unsaturated dangling bonds on the AgI boundary. Morever, a PL emission located at about620nm is found, which has not been reported elsewhere. The examinations of excitation and recombination process indicate that the620nm emission is most likely to be due to the transition process between the excited state of Ag clusters and the hole-trap state in AgI.(3) Solid state reaction method was used to prepare K2AgI3-AgI composites with AgI and KI. XRD results show that K2AgI3-AgI composites are mainly composed of K3AgI3, and also contain a small amount of AgI. The absorption band around3.27eV in optical absorption spectrum and the value of g in EPR spectrum indicate that the STHs exist in the as-prepared K2AgI-AgI sample. A broad luminescence band centered at about608nm at180K with large Stokes shift was found. When the temperature rised to about300K, an obvious PL blue-shift, PL intensity weakening, and an emission band broadening were observed. It is suggested that the emission at about608nm may originate from the recombination of self-trapped excitons.(4) Solid state reaction method was used to prepare KAg5particles and KAg4I5-AgI composites with AgI and KI. XRD results show that KAg4I5is unstable and likely to decompose into β-AgI and K2AgI3at room temperature. KAg4I5is an excellent solid state electrolyte at room temperature, while β-AgI is not. When temperature is above β→α phase transition temperature,β-Agl becomes α-Agl and turns to be a fast ion conductor (ionic conductivity is about10-’S/cm). The ion conductivity of KAg4I5-AgI composites corresponds with β→α phase transition, when temperature is below β→αphase transition temperature, the ion conductivity of KAg4I5-AgI composites is the weighed value of KAg4I5and β-AgI; when temperature is above β→αphase transition temperature, the ion conductivity of KAg4I5-AgI composites is higher than that of both pure KAg4I5and pure α-Agl. It is suggested that the interaction between KAg4I5and α-AgI produce the Ag+and holes with higher mobility located in phase interfaces. The conductivity-temperature curves for a heating-cooling circle of KAg4I5-AgI composites forms a loop, and the temperatures of β→αphase transition lagged behind both heating process and cooling process. In heating process, the lag of temperature inβ→αphase transition is attributed to the hindrance of pre-generated homogeneous AgI around the interfaces; while in cooling process, the lag of temperature in α→βphase transition is supposed to be from the influence of shear stress formed in phase transition from a-AgI (bcc (100)) to β-AgI (hep dense packing).