The Synthesis And Characterization Of Mesoporous Tungsten Oxide And Tungsten Sulfide Materials

Non-silica-based mesoporous materials have becomed an focus of sysnthesis gradually because of potential values in many fields such as optics, electricity, magnetics, chemical sensors and catalysis. Mesostructured tungsten oxide and tungsten sulfide are synthesized by room-temperature method and hydrothermal techniques, employing the surfactant cetyltrimethyl ammonium bromide(CTAB) as templates. X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform-infrared spectra (FT-IR), X-ray fluorescence spectrum(XRFS) are employed to characterize the mesostructured materials. In my work, mesoporous tungsten oxide materials are synthesized by hydrothermal techniques empolying sodium tungstate as the precursors. The effect of the value of PH, the surfactant amount, hydrotherm time and hydrotherm temperature have been investigated systematically in the preparation of mesoporous material. The value of PH is considered a key factor. In strong acid condition (PH=1) the hexagonal phase can be synthesized. In acid conditions(PH=2-4) mesostructured tungsten oxide can't be synthesized. In weak acid-alkaline conditions (PH=5-11) the hexagonal phase can be synthesized too. XRD, SEM, FT-IR and XRFS, however, demonstrate some difference between the hexagonal phase prepared in strong acid condition (PH=1) and the hexagonal phase prepared in weak acid-alkaline conditions(PH=5-11). For both, the most optimal synthesis conditions were as follow: CTAB/Na2WO4=0.10, hydrotherm time 2d, hydrotherm temperature 110oC. Calcination and ultraviolet illumination have been empolyed to remove the surfactant templates. Mesoporous strusture has been destructed at calcining temperature 400oC. XRD, FT-IR and XRFS demonstrated the framework were WO3 . The templates cannot be removed completely after ultraviolet treatment.By room-temperature method, mesoporous tungsten oxide materials are synthesized empolying sodium tungstate as the precursors. The influence of the value of PH, the surfactant amount and room-temperature reaction time are investigated systematically in the preparation of mesoporous material. The value of PH also is a key factor. In acid condition (PH=1-4) the hexagonal phase can be synthesized . In the range of PH=5-8.5 mesostructured tungsten oxide can't be synthesized . In the range of PH=9-11 the lamellar phase can be obtained. When the value of PH is 9.5 the lamellar phase with high intensity can be obtained. The conditions favorable to the synthesis of mesostructured tungsten oxide at PH=1 are CTAB/Na2WO4 0.10-0.30, room-temperature reaction time 1-4d.In hydrothermal condition, mesoporous tungsten sulfide materials have been synthesized empolying sodium tungstate and thioacetamide as tungsten and sulfide sources respectively . Empolying glacial acetic acid as the acid medium the lamellar phase can be synthesized . Empolying hydrochloric acid as the acid medium, the most optimal hydrotherm temperature is 110oC and the most optimal ratios is surfactant: tungsten sources:sulfide sources=3:6:20. Hydrotherm time is a key factor to the phases formed. When the time is shorter(1-3d) two coexisting phases (the hexagonal phase and the lamellar phase )have been obtained. When the time is longer(4-9d), however, only the hexagonal phase is formed. And the optimal hydrotherm time is 7d. Mesoporous structure has been destructed when calcining temperature was up to 400oC. XRD, FT-IR and XRFS reveal that a small amount of WO3 may exist in the framework .