| The layered double hydroxides (LDHs), also called hydrotalcite-like compounds or anionic clays, are a group of inorganic layered materials which are structurally related to the hydrotalcite-like compounds with certain divalent ions replaced by bivalent ones. In recent decades, LDHs have attracted considerable interest, because of their unique physical and chemical properties, such as high specific surface area, "memory effect", layered structures and good anion exchange capacities. Those properties lead to their extensive applications for catalysts, adsorbents, anion exchangers and so on. In this thesis, we studied the preparation procedure and their applications of the Mg-Al-CO3 LDHs with wide applications. LDHs were synthesized successfully by the method of coprecipitation, and the effect of the preparative conditions on the physical and chemical properties of LDHs were analyzed. Meanwhile, a series of composite photocatalysts were prepared by loading titanium dioxide, silver phosphate and bismuth trioxide on the surface of the LDHs and the photocatalytic activities were studied.The Mg-Al-CO3 layered double hydroxides (Mg-Al-CO3-LDHs) were prepared by the co-precipitation method with the mixture of NaOH and Na2CO3 as precipitated agent and chloride salts as cationic sources, respectively. The effect of the aging time on the crystallinity, particle size, chemical composition, morphology, specific surface area, and pore size distribution of Mg-Al-CO3 LDHs were analyzed in detail. The LDHs were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM) and Brunauer Emmett Teller procedure (BET). The results shows that LDHs prepared at 90℃for 4 h (LDH-90-4) has a higher specific surface area of 103.7 m2/g, while LDHs prepared at 90℃for 8 h (LDH-90-8) exhibits well-formed hexagonal crystals with a relative smooth surface. Anatase TiO2-coated the calcined LDHs (MMOs) with MMO/TiO2 mass ratios at 1:1 and 1:0.5 was prepared by immobilizing TiO2 on LDH-90-4, following with calcination at 500℃. Photocatalytic activities of the resultant composites were evaluated by the photocatalytic decomposition of acid red G (ARG) under UV light irradiation. The composite with the MMO/TiO2 mass ratio of 1:0.5 showed a higher photocatalytic efficiency.The reconstructed layered double hydroxides (R-LDHs) were prepared by the reconstruction of their calcined products (MMOs) in Na2CO3 solution according to the "memory effect". The composites with different FLDH/Ag3PO4 mass ratios were fabricated by loading Ag3PO4 on the surface of the R-LDHs. The powders were characterized by XRD, field-emission scanning electron microscopy (SEM), TEM, and UV-vis diffuse reflectance spectroscopy (UV-vis). The results indicated that the well-distributed Ag3PO4 in a fine crystallite size was formed on the surface of R-LDHs.The photocatalytic activities of the Ag3PO4 immobilized on R-LDHs were significantly enhanced for the degradation of acid red G under visible light irradiation compared to bare Ag3PO4 The composite with the R-LDH/Ag3PO4 mass ratio of 3:1 showed a higher photocatalytic efficiency.Theβ-Bi2O3 decorated Mg-Al mixed metal oxides composites with different concentrations of Bi2O3 were prepared with R-LDH and Bi(NO3)3·5H2O as precursors by mixing R-LDH and Bi(NO3)3·5H2O in different mass ratios and grounding in an agate mortar, followed by calcination. The powders were characterized by X-ray diffraction, field-emission scanning electron microscopy, and UV-vis diffuse reflectance spectroscopy. The phases of bare Bi2O3 and Bi2O3 in the composites wereαandβ, respectively. The photoactivity of photocatalysts was tested by the degradation of methylene blue. All of the composites showed higher photocatalytic activity than bare Bi2O3. The as-prepared composite with R-LDH/Bi2O3 mass ratio of 1:2 showed the best photocatalytic efficiency. |
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