Green Synthesis Of Highly Dispersed Noble Metal Nanocomposites And Their Catalytic Performance

Green synthesis of noble metal nanocatalysts with controllable morphology and size has been the focus of much research.At the same time,due to their excellent chemical and catalytic activities,noble metal nanocatalysts have also been extensively studied in the field of catalysis.However,how to improve the catalytic efficiency,reduce the loading of noble metal nanoparticles,and improve the stability of noble metal nanomaterials are the focus and difficulty for scientific researchers.Based on these,three noble metal nanocomposites including RGO/Mn₃O₄/Pd,Mn₃O₄/PdCu@NC and Pd-Au-P/PDDA/RGO were prepared in this thesis.The composition,morphology and structure of the prepared noble metal nanomaterials were characterized by transmission electron microscopy?TEM?,X-ray diffraction?XRD?,X-ray photoelectron spectroscopy?XPS?,and so on.Selecting oxidation of hydroquinone,reduced p-nitrophenol?4-NP?and electrochemical detection of dopamine?DA?as the model reactions,the catalytic properties and reaction mechanism of the as-prepared materials were studied via electrochemical methods such as cyclic voltammetry?CV?and current-time?i-t?curve method.The main contents include:1.Green synthesis Highly dispersed RGO/Mn₃O₄/Pd nanocomposites and extremely high catalytic performance for hydroquinone oxidation.RGO/Mn₃O₄ was prepared by microwave assisted heating method,and then Pd nanoparticles were loaded by in-situ galvanic replacement reaction.The RGO/Mn₃O₄/Pd catalyst with high dispersibility and uniform particle size was successfully prepared.The oxidation of phenol?HQ?to benzoquinone?BQ?was selected as a model reaction,and the performance of the catalyst under a series of reaction conditions was tested by means of analytical means.Experiments showed that the catalyst could promote the complete oxidation of HQ within 4 min,and its conversion frequency?TOF?reached up to3613 h^-1,which is hundreds of times of the Pd-based and Ag-based catalysts reported in the literature.Furthermore,the catalyst also held a high TOF value when being applied for the catalytic oxidation of phenol derivatives.2.Facile synthesis of Mn₃O₄/PdCu nanoparticles with N-doped carbon coatings as a high-performance catalyst for 4-nitrophenol reduction in environmental applications.On the basis of the preparation of Mn₃O₄,ethylene glycol was used as a mild reducing agent,where P123 was used as a template to support Pd-M?Cu,Au,Ni,Ag?on the surface of Mn₃O₄.Followed by the coating with polydopamine?PDA?,carbonization was achieved at a high temperature form a Mn₃O₄/PdCu@NC composite.Due to the synergistic catalysis between PdCu alloy and Mn₃O₄ support,Mn₃O₄/PdCu@NC catalyst had excellent catalytic activity for the catalytic reduction of 4-nitrophenol?4-NP?,which was significantly higher than Mn₃O₄/PdM@NC?M=Au,Ni,Ag?and commercial Pd/C catalysts.Due to the protection of the NC shell,the prepared catalyst still retained more than 90%conversion efficiency over ten consecutive cycles.3.Green synthesis of ternary Pd-Au-P-PDDA/RGO nanocomposite for electrochemical detection of dopamine.On the basis of PDDA/RGO complex,Pd-Au-P ternary nanoparticles were prepared by gas-liquid interface synthesis.Cyclic voltammetry?CV?test in 0.1 M PBS?pH 6.5?+5 mM DA solution showed that the Pd-Au-P/PDDA/RGO modified electrode had a good electrochemical response to dopamine.By studying the kinetics of dopamine oxidation,it was shown that the electrochemical oxidation of dopamine was irreversible and followed Laviron Equation.By using differential pulse voltammetry?DPV?,it was proved that the synthesized Pd-Au-P/PDDA/RGO sensor had lower detection limit and a wide linear range,which was suitable for the detection of biological and environmental samples.