Controllable Synthesis Of Colloidal Gold Nanoparticles And Their Ceria-based Micro/Nanocomposites And Their Catalytic Performance For 4-Nitrophenol

With the improvement of people's living conditions,the problem of water poIllutiorn has gradually become one of the major problems that people have to face urgently.China is a country with severe water shortage,and 4-nitrophenol(4-NP)is one of the main culprits in water pollution.How to solve the problem of 4-NP in waste water is becoming more and more imperative for environmentalists and researchers.4-nitrophenol is a very important and common chemical raw material.It is widely used as an intermediate in the production and processing of explosives,rubber,plastics,medicines,pesticides,wood preservatives,dyes,glass fibers,chemical reagents.However,it is also a highly toxic organic compound,which is difficult to degrade in nature,and is also enriched in humans and even highly susceptible to cancer,teratogenicity,and mutagenicity.Gold nanoparticles have been shown to have a good catalytic reduction of 4-NP with the action of sodium borohydride,and its catalytic product,4-aminophenol(4-AP),is an indispensable intermediate for many drugs.However,in recent years,researchers have not been able to find a stable and universal law which can improve the efficiency of colloidal gold nanoparticles in the catalytic reduction of 4-NP greatly,but only chose new ligands f-or the colloidal gold nanoparticle.The main purpose of this paper is to find and explore the universal law of the ef-fect of ligands coated on the surface of gold nanoparticles in the catalytic reduction of-4-NP.and the law will be applied to the treatment of 4-NP in waste water to make further targeted improvement of its catalytic efficiency.The details are as follows:1)Controllable synthesis of ceria nanosheets and colloidal gold nanoparticlesIn the second chapter,we synthesized a novel oval ceria 2D nano-sheet(about 50 n! thickness)by liquid phase synthesis without template.By means of TEM,SEM,XRD.HRTEM and other characterization methods,the influencing factors and forming mechanism in the growth process were discussed,and the optimal experimental conditions were finally explored,and it was confirmed that the material had excellent potential to be a support of noble metal gold catalyst.We also sy'nthesized stable monodispersed colloidal gold nanoparticles(Au@OAm,average particle size:4.5 nm)at 20 ?.Based on this material,we further explore the catalytic property of colloidal gold nanoparticles in the next chapter.2)Study on the influence of chain length of the surface ligands coated on gold nanoparticle in catalytic reduction of 4-NPIn the third chapter,we choose the following three kinds of ligands:11-mercaptoundecanoic acid(MUA)containing 10 carbons,3-mercaptopropionic acid containing 3 carbons(MPA)and S2-without carbon.Three kinds of different colloidal gold nanoparticles(Au@MUA,Au@MPA,Au@S2-)were successfully synthesized by ligand exchange.The number of carbon atoms in a linear chain means the length of the ligand chain.In the process of catalytic reduction of 4-NP,we found that the shorter the length of ligand chain on gold nanoparticles,the higher the catalytic activity of colloidal gold nanoparticles would be.To further prove the above experimental conclusions,we also selected two linear quaternary ammonium salts with different numbers of carbon atom:Dodecyl trimethyl ammonium bro]micde,{DTAB,[(Cl2H2s)(CH3)3N]Br} and Hexyltrimethylaminium bromide,{ HTAB.L(C6HIs)(CH3)3N]Br} were grafted onto the surface of Au@S2-nanoparticles by electrostatic attraction,respectively abbreviated as(Au@S2-+ DTAB)and(Au?S2-?HTAB).In the reaction of the catalytic reduction of 4-NP,it was found that the experimental results were consistent with the previous conclusion.The phenomenon was caused by the steric hindrance of ligands.In addition,the experimental method also realized the transition from long organic ligand to inorganic ligand on the Ssurface of Au NPs,and it was found that Au@S2"NPs had excellent catalytic activity and stability in the process of catalytic reduction from 4-NP to 4-AP.As for the ligand.the price of inorganic sodium sulfide is much lower than that of other organic ligands.From the perspective of industry,this catalyst not only greatly reduce the reaction cost,but also realize the controllable regulation of reaction rate in the process of industrial catalysis by grafting linear quaternary ammonium salt of different chain length.3)Synthesis of supported Au@S2-/CeO2-NS catalyst and its study on catalytic reduction of 4-NPAlthough we found a very excellent colloidal gold nanoparticle catalyst in the previous chapter,for gold as a noble metal,irreversible agglomeration must occur in the catalytic process.In this regard,the two-dimensional oval ceria nanosheet synthesized in the second chapter were used as the support,and the Au@S2-NPs were loaded on its surface by impregnation method.The agglomeration of colloidal gold nanoparticles in the catalytic process was restrained because of the special surface properties and microporous structure of the support material.The service life of gold nanoparticles as catalysts is greatly extended,and the catalytic efficiency is not obviously decreased.