Synthesis, Characterization And Catalytic Performance Of Layered Double Hydroxides Carbon Based Composite Materials

Inorganic nano-carbon materials with sp2-hybridized carbon atoms, have attracted considerable interest in many applications, due to their abundance chemical-thermal stability and electron transfer characteristics. Especially as catalysts, carbon based nanomaterils have many advatanges: Fistly, electron transfer in catalytic process is effective due to the excellent electrical properties; sencondly, the functional groups on the surface of carbon materials and π-π stacking inducing an enhanced oriented chemisorptions of molecules; thirdly, the carbon hydrid catalysts keep stable in structure and catalytic performance; finally, active sites are high dispersed on carbon nanomaterils, which may promote catalyst activity.Rencently, graphtic carbon nitide (g-C3N4) is attracting much attention. Compare with carbon materials, g-C3N4 performance more effective in electron transfer, due to the replacement of C by N. Graphtic carbon nitide as a metal-free catalysts has been invensigated in oxidation catalysis and photocatalysis.Among the new generation of heterogeneous catalysts, layered double hydroxides (LDHs) haved attracted increasing attention, due to its diavalent-trivalent metal cations and charge-compensating anions are easily modulated. The applications of LDH in photocatalysis, electrocatalysis and industry-catalysis have been investigated. Because different M2+ and M3+ metal cations with runable compositions can uniformly distribute and orderly prearrange at an atomic level within the layers or in the interlayer space in the form of metal complexes, well-dispersed metal catalysts can be obtained by reducing calcined LDHs with desired active species.In this thesis, kinds of LDH-carbon hybrid catalysts were easily synthesized as followed:(I) ZnCr-LDH/G nanocomposite material; metal ion can be adsorpted and orientated by graphene oxide (GO), due to many functional groups on GO surface. ZnCr-LDH and graphene hybrid nanocomposites were synthesized through a simple one-step coprecipitation route, which included the nucleation and growth of ZnCr-LDH and the simultaneous reduction of GO in the absence of any additional reducing agents. ZnCr-LDH pieces are high dispersed on graphene sheets. Graphene in composites is well exfoliated by ZnCr-LDH. More photocatalytic active sites CrO6 inside of ZnCr-LDH layers exposed due to the graphene. ZnCr-LDH/G shows high photocatalytic active.(II) B-Ni/C nanocomposites; a new type of carbon supported boron-promoted nickel nanocatalysts were synthesized with good dispersion via in situ self-reduction of hybrid borate-intercalated NiAl-LDH/C. Amorphous carbon in nanocmoposites enhanced electron transfe process. Ni species in B-Ni/C are more favourable to adsorpte C-Cl bond due to strong B-Ni interatction.(III) ZnIn-MMO/C3N4 nanocomposite semiconductors; ZnIn-MMO/C3N4 nanocomposites were synthesized by calcined the Znln-LDH/melamine mixed powder. The highly dispersed MMOs can be formed by calcined LDH, and futher dispersed by g-C3N4 in new composites. The new composite semiconductors show slow electron-hole recombination due to ZnO, In2O3 and g-C3N4 hydrid structure, which make Znln-MMO/C3N4 performance high active in photocatalyst.(IV) NiFe@C3N4 was synthesized via in situ self-reduction of LDH/melamine precursors. The core-shell structure combines the advtange of NiFe alloy and g-C3N4. NiFe@C3N4 nanocomposites are promising catalytic materials.