Synthesis Of Se-based Nanomaterials And Their Catalytic & Thermoelectric Properties

Environmental pollution and energy crisis are two challenges mankind facing with. Catalytic degradation of wastewater is one of focuses in the field of environmental governance, while thermoelectric (TE) material is a new kind of energy materials which can convert waste heat into electricity. In this dissertation, different Se-based nanomaterials have been synthesized by hydrothermal method or colloidal oil-phase method, and their potential applications have been investigated in the field of wastewater treatment and thermoelectric application.The main research contents are as follows:1. Hydrothermal synthesis of Co0.85Se-TiO2 nanofilms and their catalytic activity for p-nitrophenol reduction and hydrazine hydrate deconpositionBased on our previous report about Co0.85Se nanofilms, Ti(OC4H9)4 being used as Ti precursor, water and ethylene glycol as conjunct solvent, Co0.85Se-TiO2 nanofilms with heterojunction were successfully prepared with the aid of NH3·H2O via hydrothermal method. Effects of NH3·H2O on the synthesis of Coo.85Se-Ti02 nanofilms were investigated. The as-synthesized samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and selective-area electron diffraction (SAED). The results demonstrate that TiO2 nanoparticles with a size of about 10 nm are succesfully loaded on the surface of graphene-like Co0.85Se nanofilms. Brunauer-Emmett-Teller measurement shows that the obtained nanocomposites have a larger specific surface area (199.3 m2 g-1) than that of single Co0.85Se nanofilms (55.17 m2g-1) and TiO2 nanoparticles (19.49 m2 g-1). The catalytic tests indicate Co0.85Se-TiO2 nanofilms have the highest activity for p-nitrophenol (4-NP) reduction and hydrazine hydrate decomposition within 10 min and 8 min, respectively, compared with the corresponding precursor Co0.85Se nanofilms and TiO2 nanoparticles. The recycle tests show Coo.85Se-TiO2 nanofilms have stable conversion efficiency for 4-NP reduction. The reason for the enhancement catalytic activity of nanocomposites was studied.2. Colloidal synthesis of Cu2SnSe3-Ag^ CuFeSe2-Ag nanocomposites and their thermoelectric propertiesBased on our previous work, monodispersed Cu2SnSe3 (CTSe)、CuFeSe2 (CISe) and Ag nanocrystals were prepared via colloidal oil-phase method, respectively. XRD and TEM were used to characterize their structure、composition and morphology. The results show that the as-synthesized CTSe and CISe nanocrystals both were about 8 nm in size, while the synthesized Ag nanoparicles (Ag NPs) were 4 nm and can be well dispersed in chloroform. A series of specific proportion of Ag were doped into CTSe and CISe via a simple and novel drip method, and CTSe-Ag、CISe-Ag nanocomposites were obtained. The nanocomposites were compacted into dense wafers for thermoelectric measurements. The results display that sample CTSe-1% mol Ag show the best figure-of-merit zT (zT=0.18,655 K) among CTSe-based samples. As to the CISe-based samples, we have studied their thermoelectric power properties. The results indicte that sample CISe-1% mol Ag displayed the best thermoelectric power performance in high temperature (>550 K), while sample CISe-5% mol Ag showed the best power performance in the temperature below 550 K.3. Colloidal Synthesis of monodispersed CuAgSe nanocrystals and their thermoelectric propertiesSelenium powder dissolved into mix solution of oleylamine and dodecanethiol at room temperature with stirring were injected into hot solution of oleylamine (OM), including CuCl and AgNO3, at a given temperature for a certain time, and CuAgSe nanocrystals were successfully prepared via colloidal oil-phase method for the first time. XRD、EDX、TEM were used to test their composition and morphology. Impacts of reaction temperature、reaction time and solvent species on synthesis of CuAgSe were studied, and the optimal reaction condition was confirmed. The surface organic group of samples before and after wash was confirmed by FT-IR measurement. Enough amounts of CuAgSe nanoparticles were collected, and their surface organic groups were removed. TG-DTA was used to test their thermostability, which then guided us to determine the proper temperature for hot press (HP) operation and thermoelectric measurements. The thermoelectric performance was tested with dense wafers compacted from CuAgSe nanocrystals. The results exhibit that CuAgSe have good performance in thermoelectric, with its zT value up to 0.35. With the temperature increasing to 478 K, it then changes into a phase (>478 K) in crystal structure, and its zT value increases fast to 0.44 at 567 K. Interestingly, CuAgSe will change from β phase to a phase at 478 K, along with N type semiconductor changing into P type semiconductor, which indicates the potential application in thermal-control device. As to the annealed sample of CuAgSe, N-P conversion phenomenon didn’t happened, and its zT value increased with temperature rising, which could be up to 0.72 at 567 K, showing good thermoelectric performance.