Frabication Of Layered Double Hydroxides (LDHs) Composites And Their Photocatalytic Properties Study

Photocatalysis is one of promising techniques in the field of environment and energy, and thefabrication of novel photocatalysts is one of research hotpots. In this study, a series of layereddouble hydroxides (LDHs) composites were fabricated by the methods of intercalation,immobilization, self-assembly and in-situ growth, and then employed as photocatalysts fordegradation of organic pollutants. For materials, based on the physicochemical properties ofLDHs and the components, a series of LDHs composites were fabricated and theirmicrostructure were deciphered by spectroscopy and experimental methods. For advancedoxidation processes (AOP), it provides new methods and information for the heterogenizationof complex catalysts, immobilization of nanoparticles and the expansion of the photocatalyticapplication of graphene. The main contents are as follows:1. Intercalation of Fe(III) complexes [Fe(Ox)3]3-and [Fe(Cit)2]3-in MgAl-LDHs had beencarried out by different routes: direct self-assembly, reconstruction and anion exchange. Theresult of XRD indicated that these two kinds of Fe(III) complexes intercalated LDHs(LDHs/Fe-complexes) could be successfully synthesized by anion exchange obtaining twowell crystallized LDHs both with a large basal spacing. The chemical environment of iron ionin the intercalated Fe complexes was determined by FTIR, XPS XAFS, BET (N2adsorption-desorption), TG-DSC and SEM. Measurement of adsorptive and heterogeneousphoto-Fenton degradation of methylene blue (MB) were conducted to investigate theproperties of adsorption and photocatalysis. Additionally, our previous study of hydroxylFe/Al interacted montmorillonites (a cationic clay) were compared to analyze their respectiveadvantages and disadvantages for using as heterogeneous catalysts.2. The organic LHDs/TiO2composites with various mass ratios were prepared by thereconstruction of mixed metal oxides to photodegrade dimethyl phthalate (DMP). Thephysicochemical properties of the obtained products were analyzed by XRD, XPS, and SEM.According to the experimental results of adsorptive and photodegradation of DMP, theorganic LDHs with flaky structure could effectively adsorb the DMP molecules and theadsorption isotherm by the composites modeled well with the Langmuir equation. Theenrichment of DMP onto the composites and the external hydroxyl groups of the composites produce a synergistic effect leading to greatly enhance the rate of DMP photocatalyticdegradation by the obtained composites.3. The synthesis of layer-by-layer ordered nanohybrid with sandwich structure was based onelectrostatically driven self-assembly between the negatively charged carboxyl graphenemonolayer and the positively charged ZnAl-layered double hydroxides nanosheets. Thecharacteristics of the layer-by-layer ordered nanohybrid were investigated by SEM, TEM,AFM and XRD. The enhanced photocatalytic activity of the calcined product is determinedby photocatalytic degradation of cationic dye methylene blue (MB) and anionic dye orange G(OG) under visible light. The enhanced photocatalytic efficiency was mainly attributed to theeffective electronic coupling between graphene and calcined ZnAl-LDH. Additionally, thechemical stability of the calcined ZnAl-LDH is significantly improved by hybridization ofgraphene attributed to the protection provided by the closely contacted graphene with highlystability.4. Graphene oxides (GO)@ZnNiAl-LDH composites were prepared by the methods ofgrowth in-situ, and characterized by XRD, SEM and TEM to analyze the structure feature andmorphology. The results showed that the ZnNiAl-LDHs crystallized on the surface ofgraphene in-situ were remarkably smaller than that of pristine ZnNiAl-LDHs. The calcinedproduct graphene@ZnNiAl-LDO composites displayed a broad absorption in the range ofUV-vis region. The obtained composites were applied to photocatalytic oxidation of MB andremoval of Cr(VI) in aqueous solution simultaneously, which confirms thatgraphene@ZnNiAl-LDO composite has a strong adsorption capacity of Cr(VI) and thepresence of Cr(VI) produces a synergistic effect leading to enhance the decolorization of MB.