Thermodynamic And Kinetic Control Synthesis Of Cu₂O-Au Composite Material And Its Catalytic Performance

Owing to the multiple functions and synergistic effect,heterogeneous materials have been widely applied in catalysis,biomedical,electronic devices,etc.Among various heterogeneous materials,Cu2O-Au heterogeneous nanostructures have attracted extensive attention due to autologous advantages of cuprous oxide(Cu2O)and Au for actual applications.Cu2O is a kind of cheap material,could be product in enormous quantities,and without any toxicity for biological tissue,which is usually used as a sacrificial template to prepare semiconductor-noble metal nanostructures.Meanwhile,Au nanoparticles possess higher chemical stability,excellent optical property and catalytic activity.The physical and chemical properties of Cu2O-Au heterogeneous materials are related to their structure,composition,morphology and interface characteristics.Thus,the researchers have changed physical parameters in the preparation process,such as reactants ratio,reaction conditions to regulate the structure,morphology and relative content of Cu2O-Au heterogeneous materials,which could have important value for research and application in surface-enhanced raman scattering(SERS),catalysis and adsorption,etc.Based on the above-mentioned background and previous works of our group,a regulated preparation method based on Cu2O nanoparticles with different morphology is reported in this study,which is using as sacrificial template to synthesize the Cu2O-Au heterogeneous materials through galvanic replacement reaction.The Cu2O and Cu2O-Au nanoparticles with different morphology,structure and composition could be obtained by regulating the thermodynamic and kinetic factors during the synthesis process.This work aims at regulating thermodynamic and kinetic in synthesized process to prepare heterogeneous nanomaterials with different morphology,which has an important guiding significance in morphology-control of heterogeneous materials.This study mainly carries out following two aspects of research work:(1)The Cu2O nanoparticles with uniform particle size and good dispersity were synthesized by liquid phase method.In this work,polyvinyl pyrrolidone(PVP)and hydrazine hydrate were respectively used as stabilizer and reducing agent to prepare the Cu2O nanoparticles,which could serve as thermodynamic and kinetic factors to influence the morphology of Cu2O nanoparticles;the species of copper source is another essential effect factor to the morphology and size of Cu2O nanoparticles.Meantime,the reaction temperature also could regulate the morphology of Cu2O nanoparticles,which gradually converts from spherical-like morphology to cubic with increment reaction temperature owing to the acceleration of reaction rate and different growth rate of different crystal planes.As the reduction of p-Nitrophenol(4-NP)by sodium borohydride for model catalytic reaction,the Cu2O nanoparticles with cubic morphology have better catalytic activity in the same catalytic condition,and the catalytic efficiency was increasing with the reducing of particle size of Cu2O.(2)The Cu2O-Au composites were synthesized by galvanic replacement reaction between HAuCl4 and Cu2O,using spherical-like Cu2O NPs with uniform particle size and good dispersity as sacrificial template.The Cu2O-Au composites with different morphology and composition could be synthesized by regulating thermodynamic and kinetic factors,such as solvent type,pH,the amount of HAuCl4 and structure-directing agent(hexadecyltrimethylammonium bromide:CTAB).The results indicated that the particle size of Au nanoparticles in Cu2O-Au is influenced by the solvent type which could regulate the reaction rate of replacement reaction.Besides,the amount of Au source(HAuCl4)is also an crucial factor to dominate the particle size of Au nanoparticles in galvanic replacement reaction.Moreover,CTAB,adsorbed on Au,could regulate the particle size of Au nanoparticles and the interface characteristics between Cu2O and Au.Ultimately,the pH of reaction solution will affects the reaction rate and reaction schedule,which not only affects the particle size of Au nanoparticles on Cu2O template,but also regulates the composite structure of Cu2O-Au nanoparticles.For reducing 4-NP,the catalytic activity of Cu2O-Au is related to their morphology and composition:the catalytic activity of the composite is enhanced with the increase of Au content and the decrease of Au particle size in Cu2O-Au composite materials.