Fabrication And Applications Of Two-dimensional Layered Materials Supported Noble Metal Nanocomposite Catalysts

Noble metal nanoparticles have attracted much attention due to their unique physicochemical properties and functional properties in the fields of optics,sensing and catalysis.However,nanoparticles with high surface energy,are highly prone to agglomeration and unstable.Two-dimensional layered materials are characterised by their structural simplicity,flexibility,anisotropic features,excellent stability,and unique optical and electronic properties.The exfoliated nanosheets are approximately 1 nm thick,forming a new type of inorganic macromolecular structure with distinctly different physicochemical properties from their three-dimensional bulk macromolecules.They can be used as versatile building blocks to construct multilayer films,porous composites and layered nanocomposites,etc.In this thesis,we mainly focus on layered metal oxides(KSr₂Nb₃O₁₀,KTiNbO₅),α-zirconium phosphate（α-ZrP）and layered double hydroxides（Ni Al-LDH）,and the nanosheets of these two-dimensional layered materials obtained by exfoliation reaction were used as templates.A series of novel binary and ternary noble metal nanoparticles immobilized layered nanocomposites were constructed by tailored designing the synthetic route of"electrostatic loading→in-situ photoreduction→nanosheets restacking".These composites exhibit excellent catalytic performance in various fields such as selective oxidation of alcohols,Heck coupling reaction and degradation of organic pollutants.Details are as follows.（1）Two-dimensional strontium niobate（SrNbO）nanosheets were synthesised by cation exchange assisted liquid exfoliation and used as carriers for immobilised palladium nanoparticles（PdNPs）by electrostatic assembly with Pd（NH₃）₄²⁺precursors and subsequent in-situ photoreduction.PdNPs with an average diameter of 9.22 nm were uniformly dispersed on the surface of SrNbO nanosheets.The obtained Pd-SrNbO composites can be used as an efficient heterogeneous catalyst for the atmospheric pressure oxidation of benzyl alcohol to benzaldehyde at low temperature（80°C）using air as the oxidant and water as the sole solvent.15 mg of Pd-SrNbO composite was added to the reaction system of benzyl alcohol oxidation,and benzyl alcohol was almost completely converted within 6 h,and no by-products such as benzoic acid were generated.The turnover number（TON）and turnover frequency（TOF）of the reaction were208.7 and 34.8 h^-1,respectively.In addition,the composite could be easily recovered by centrifugation and showed good stability in recycling tests.（2）A simple and efficient nanostructured catalyst system was prepared using an exfoliation/restacking method in which PdNPs with an average diameter of 2.84 nm were uniformly dispersed on TiNbO nanosheets.The metal precursors were deposited on the exfoliated TiNbO nanosheets by electrostatic interaction and then reduced to nanoparticles by UV irradiation.The selective oxidation of benzyl alcohol in ultrapure water was achieved with the prepared Pd-TiNbO under alkali-free and atmospheric pressure conditions,using air as the oxidant.The results showed that the catalyst exhibited excellent catalytic activity and selectivity in the aerobic oxidation of benzyl alcohol to benzaldehyde.In addition,the catalyst showed excellent stability in the recycling tests.（3）By usingα-zirconium phosphate（α-ZrP）as the host material,a novel composite Pd-ZrP was prepared by assembling the guest PdNPs with the exfoliatedα-ZrP nanosheets through the exfoliation/restacking method.The PdNPs with an average diameter of 5.17 nm were uniformly dispersed on the surface of theα-ZrP nanosheets,and their particle sizes ranged from 3 to 7 nm.The catalytic performance of the prepared Pd-ZrP composite was evaluated by selecting the Heck reaction of iodobenzene and methyl acrylate as a model reaction under the set reaction conditions.The results showed that the prepared Pd-ZrP composite had excellent catalytic activity.When the composite dosage was 15 mg and the reaction temperature was 100℃,the Pd-ZrP composite had the highest catalytic efficiency（the yield was 99.3%,3 h）.The TON and TOF of the reaction were 468.7 and 937.4 h^-1,respectively.In addition,the composite could be easily recovered by centrifugation and showed good stability in recycling tests.（4）Ag@SrNbO/LDH ternary composite was successfully synthesized by encapsulating Ag NPs between oppositely charged strontium niobate（SrNbO）and Ni Al LDH nanosheets using an exfoliation/restacking method.Ag NPs with an average diameter of 14.30 nm were uniformly dispersed on the surface of the nanosheets.Driven by electrostatic interactions,the two nanosheets alternated layer by layer to form a loosely stacked framework with a large specific surface area.The ternary composite exhibited high catalytic activity and stability for the reduction of 4-nitrophenol（4-NP）using Na BH₄as the reducing agent.After adding Ag@SrNbO/LDH,the color of the reaction mixture completely disappeared within 60 s.The absorbance at 400 nm decreased with time and a new absorbance peak appeared at 300 nm,confirming the formation of 4-aminophenol（4-AP）.In addition,the ternary composite could be easily recovered by centrifugation,and showed excellent stability in the recycling tests.The thesis has 62 figures,17 tables,and 185 references.