Synthesis Of Gold Aerogels With Controllable Facet Content By Size-dependent Surface Reconstruction And Study On The Facet-dependent Performance

Combining the merits of noble metals and aerogels,noble metal aerogels with excellent electrical conductivity,electrochemical properties,continuous porosity,great surface area and low density,have attracted extensive attention in fields of catalysis,sensing,and photoelectric conversion.Currently,many publications about noble metal aerogels are emerged,which make it possible to apply in biological detection and energy storage.Noble metal aerogels can be considered as a bridge between the nano and the macro world and their potential for new applications is almost unlimited.In the past ten years,the works on the surface structure of noble metal aerogels(such as surface facets,defect density,etc.)are in their infancy,although the works on the composition,morphology and surface morphology of them has made great progress.As well as nanoparticles,the electrocatalytic performance of noble metal aerogels largely depends on their surface structures,which will be greatly enhanced in case regulation of surface facets.Theoretically,{100} facets can turn into {110}facets when surface reconstruction occurrs in two types of gold nanoparticles(Au NPs).However,the exact size ratio at which surface reconstruction can occur between two differently-sized Au NPs is unknown.Meanwhile,the type and specific ratio of facets exposed in gold aerogels cannot be accurately analyzed.All of the above problems are extremely unfavorable to study on the relationship between the electrocatalytic performance and surface structure,for example,the relationship between type and specific ratio of facets exposed in gold aerogels,specific avtivity and stability.Based on the above problems,this thesis focused on the preparation of gold aerogels with controlled surface facets.Firstly,a series of gold aerogels(Aum-n and n represent two differently-sized Au NPs,m=6 nm,n=16,30,and 50 nm)were prepared by a two-step sol-gel method.Next,the critical size ratio for the occurrence of the surface reconstruction was determined by analyzing the type and specific ratio of surface facets as well as observing the variations in the size of large Au NPs during the formation process of Aum-n aerogels.Finally,a series of gold aerogels with controlled ratio of {110} facets were prepared by size-dependent surface reconstruction and their face-dependent performance in glucose detection and electro-oxidation of ethylene glycol were observed.The main contents are as follows:In Chapter 2,a series of Aum-n aerogels(m=6 nm,n=16,30 or 50 nm)were firstly synthesized by using two different types of Au NPs at different particle ratios,followed by the analysis of the final ratios of their exposed surface facets by de-convoluting CV measurements.Next,the variations in the size of large Au NPs during the formation of Au6-16 aerogels,Au6-30 aerogels,and Au6-50 aerogels with the highest ratios of {110} facets were investigated respectively.On the basis of the results obtained,it is proposed that the critical condition for surface reconstruction is the size ratio(R)of 5,and the degree of surface reconstruction gradually increases with the increasing of the size ratio.Au6-50 aerogels with the highest ratio of {110}facets(up to 35.5%)showed excellent performance in glucose detection,and beared a short response time of 2 s,an ultrahigh sensitivity(2044.71 mA cm-2 mM-1)and the ultralow limit of detection(0.58 mM).In Chapter 3,AuPNR6-50 aerogels(PNR represents the particle number ratio of 6 nm Au NPs-to-50 nm Au NPs)with controlled {110} facets in the range of 12%-36%were synthesized successfully by adjusting the particle number ratio of 6 nm AuNPs-to-50 nm Au NPs.Next,the performance of the as-prepared AuPNR6-50 aerogels towards ethylene glycol oxidation reaction(EGOR)were investigated and compared.It is found that specific activity increases with the increasing of sum of ratio of {111}and {100} facets while long-term stability increases with the increase of ratio of {110}facets.Additionally,Au24 6-50 aerogels with the highest ratio of {110} facets possessed the boosting long-term stability(up to 95.12%)but still have a comparable specific activity(90.42 mA cm-2)comparision with the previous reports.Finally,it is alsofound that the long-term stability of AuPNR6-50 aerogels towards EGOR highly depends on the the ratio of {110} facets,comparison with the results of other small organic alcohols.Chapter 4 is a summary and prospect of current research work.In summary,in this thesis,gold aerogels with controlled ratio of facets exposed on their surface can be prepared by size-dependent surface reconstruction.Then,their face-dependent performance in glucose detection and electro-oxidation of ethylene glycol were observed.And the performance in glucose detection and electro-oxidation of ethylene glycol can be greatly enhanced by controlling ratio of facets exposed on their surface.