Controlled Synthesis And Assembly Of Gold-based Nanoparticles And Study Of The Applications Based On Their Optical Properties

The noble metal nanomaterials(NMs)have many valuable application prospects in the fields of environmental monitoring,surface enhanced Raman scattering(SERS),optical imaging,biosensing and photoelectrocatalysis(PEC)due to their unique physical and chemical properties,which have been widely studied.The size,morphology,surface defects,elemental composition,surface ligands,and particle arrangement of noble metal NMs have a tremendous effect on their various properties.Gold nanoparticles(Au NPs)have a wide range of applications in the field of analytical detection due to their good biocompatibility,chemical stability and surface plasmon resonance effects.Among them,the ultra-small size of Au NPs with larger specific surface areas and a high proportion of surface-active atoms,have better detective sensitivity,which have attracted special attention.In addition,the mono-dispersity of nanoparticles,the sol stability and the type of ligands on their surface have a significant effect on their applications.For example,the ultra-small-sized Au NPs prepared by using strong ligands in the oil phase is stable,but the ligands on the NP surface is strong,and require complicated post-treatment processes before being applied in the field of analysis and detcction.While the soluble weak ligand-modified-Au NPs have the advantages of easy surface function and controllable size.Therefore,it is of great significance to prepare soluble,high-yield,high-stability,ultra-small-sized Au NPs by a simple method for applications of detection by utiliz:ing their spectral changes.Although the silver nanoparticles(Ag NPs)have excellent SERS effect,the excellent plasmonic property of Ag NPs has not been fully utilized in practical applications because of their poor stability against nonideal chemical environments(eg,oxidizing environments).In contrast,Au NPs have good chemical stability.Therefore,AuAg alloyed nanoparticles(AuAg ANPs)can be mixed by Au and Ag at the atomic scale,which combines the excellent plasmon resonance effect of Ag NPs and the good chemical stability of Au NPs,further realizing the applications in complex chemical environment.At present,the preparation of high-quality AuAg ANPs is mainly achieved by high-temperature sintering annealing and template sacrificial method,but the corresponding equipment and economic cost are very high in complexity steps.In addition,since the reactivity of the two elements of Au and Ag from the precursors to the atomic is different,it is often necessary to use a strong ligand to adjust the proportion of the NP elements,and the use of strong ligands will affect the subsequent SERS performance test of the NPs.Therefore,it is valuable to realize the in-situ preparation of monodispersed,controllable size and composition of AuAg ANPs by a one-step method using non-toxic,low-cost and biocompatible ligand in soluble environment.And it is worth to implement reliability detection based on its SERS spectra in practical applications.However,due to the poor quality of the SERS substrate,the uniformity and reproducibility of the SERS signal cannot be guaranteed.Therefore,the quantitative detection based on SERS is still a huge challenge.The uniform preparation of Au-based noble metal NPs is one of the prerequisites for ensuring the reproducibility of SERS substrates.While the construction of a periodically arranged SERS substrate such as a macroscopic film of monolayer,closed-packed nanoparticles(MFs of MCP-NPs)based on Au-based NPs provides the possibility of SERS quantitative detection.In addition,the detection sensitivity and chemical stability of the SERS substrate in practical applications are also critical,which has a certain correlation with the size,element composition and surface roughness of the MCP-NPs.At present,among several methods for preparing MFs of MCP-NPs,the interfacial self-assembly of nanoparticles has the advantages of no need extra substrate and force,controllable interparticle-gaps,and simple operation of equipment,which has great practical value.However,the current method is only mature for the close-packed self-assembly of oil-soluble NPs.The uniform preparation of oil-soluble Au-based noble metal NPs often use large amounts of strongly hydrophobic ligands,resulting in a complicated post-treatment process on the surface of the NPs.For water-soluble Au-based NPs that are easy to surface functionalize,it is still difficult to achieve dense packing arrangement due to the effect of the surface charge.Currently,how to use a common method to prepare water-soluble,Au-based noble metal NPs of different sizes,morphologies and compositions into high-quality MFs of MCP-NPs as SERS substrates to ensure the reproducibility of their SERS spectra;and on the basis of this,the application of SERS-based photothermal sensing technology has important research value.Based on the above problems,this paper takes the controllable preparation and application of Au-based NMs as the research goal.Firstly,using tris(hydroxymethyl)aminomethane(TB)as a reducing agent,Au NPs with a size range of 5.5 to 17.8 nm were successfully prepared by one-step seeded growth method,which realized the precise adjustment of the size of small-sized Au NPs.Next,we introduced Fe2-ions assisted Citrate to reduce the precursors of gold and silver,and in situ prepared AuAg ANPs(11 to 25 nm)and core-shell(CS)AuAg ANPs(30 to 80 nm)by one-pot method.Then,based on the precise control of small-sized Au NPs and(CS)AuAg ANPs,the phase transfer or interface transfer of the Au-based NPs is carried out by ligand exchange.It is prepared into high quality MFs of MCP-Au NPs and applied to SERS substrate.Finally,we systematically explored the performance of MFs of MCP-Au-based NPs with different sizes,compositions and surface topologies as SERS substrates,and their applications in ultra-low concentration rapid detection and SERS-based temperature sensors.The maim contents of this paper are as follows(Chapter 1 is the introduction):In Chapter 2,firstly,using TB as reducing agent and 3.5 nm Au NPs as seeds to investigate the influences of temperature,pH value,and the amount of HAuCl4 precursors and Au NP-seeds during the growth of small-sized Au NPs.Then,the colloidal stability of the as-prepared Au NPs(TB-Au NPs)was tested in the presence of high concentration salt solution.Subsequently,based on the gold leaching mechanism,the obtained Au NPs were prepared as sensors for detecting the concentration of lead ions in the aqueous solution,and study their linear detection ranges.Finally,in the actual environment such as complex soil leachate,the selective detection of lead ions was verified.The results show that Au NPs with a size range of 5.5 to 17.8 nm can be successfully prepared by one-step seeded-growth method,and the size can be accurately adjusted according to the understanding of the growth mechanism.The resulting Au NPs have good colloidal stability.Sensors prepared with 5.5,10 and 15 nm of Au NPs enables linear detection of lead ions in aqueous solutions at concentrations ranging from 0.1 nM to 5 pM.Among them,in the presence of a variety of interfering ions,the 5.5 nm of Au NP-sensors achieved ultra-low detection sensitivity(0.1 nM)of Pb2-ions,and achieved a high detection rate of lead ion in actual soil extract.In Chapter 3,firstly,one-pot method was used to directly synthesis of AuAg ANPs(11 to 25 nm)and CS AuAg ANPs(30 to 80 nm),by using Fe2+-assisted citrate co-reducing HAuCl4 and AgNO3.Furthermore,the growth mechanism of the AuAg ANPs was investigated by tracking the changes of the spectra and element distributions during the growth process.Then,the SERS activity and the chemical stabilities in corrosive environment of the resulting different size of(CS)AuAg ANPs were tested.Finally,the selected ANPs with both SERS activity and stability was applied to the actual detection in corrosive environments,and their SERS sensitivity and durability were explored.It has been found that Fe2+ ions play a vital role in particle nucleation and growth during the growth of(CS)AuAg ANPs.The size and composition of the NPs can be adjusted by controlling the ratio of Fe2+ ions to gold and silver precursors.Among them,the 25 nm of AuAg ANPs exhibited excellent SERS activity and chemical stability in the test.It can be applied to the SERS detection of organic pollutants such as benzidine and p-cresol(a typical substance in actual industrial wastewater)in artificial industrial wastewater,which can achieve low concentration detection(10-9 M)and good durability(24 h)in corrosive environment.In Chapter 4,firstly,oil-soluble Au-based NPs were obtained by surface ligand exchange of the prepared high-quality water-soluble Au-based NPs with a suitable concentration of hydrophobic ligands(say,oleylamine).Subsequently,the preparation of MFs of MCP-Au-based NPs was realized by interface assembly technology.Then,it was applied to SERS substrates,and the homogeneity and sensitivity in SERS detection were systematically explored.Finally,the MFs of MCP-Au NPs was prepared into SERS-based temperature sensors,and the linear detection of temperature was explored.It was found that,because of the uniform distribution of "hot spots" in macroscopic areas,the MFs of MCP-Au-based NPs exhibits good spectral uniformity and reproducibility in SERS detection.Among them,the MFs of MCP-R-AuAg ANPs have a fast and strong adsorption capacity for the probe molecules,achieving a breakthrough in SERS detection sensitivity(10-13 M);and achieving rapid detection(10 min)of ultra-low concentration(10-12 M)probe molecules in corrosive chemical environment.Besides,The SERS-based temperature sensors prepared by MFs of MCP-Au NPs realized linear sensing of temperature in a wide range of 33-130 ℃ with good repeatability.In Chapter 5,we have summarized and forecasted the above works.In summary,in this paper,the controllable synthesis and assembly of Au-based NPs such as small-sized Au NPs and(CS)AuAg ANPs are realized.The environmental monitoring based on colorimetric method and SERS,and the preparation of SERS-based temperature sensors are realized.