Controlled Synthesis Of Gold-based Nanoparticles And Study On Their Performance In Electrocatalysis And Cancer Photothermal Therapy

Gold nanoparticles(Au NPs)have shown great prospect in applications such as catalysis,energy,biomedical diagnosis and therapy due to their unique physicochemical properties.The properties of Au NPs are determined by their size and morphology.By tuning these properties can further provides great flexibility to tune their performance in these applications.For instance,it has been shown that the catalytic activity and selectivity of Au NPs are strongly dependent on the type of facets exposed on the surface.Since the morphology of the Au NPs can determine the surface structure(ie,the arrangement of atoms on the surface)and the surface atomic composition.Therefore,changing the morphology of Au NPs can provide different surface structure,thereby improving its catalytic performance.In addition,it has been established that altering the size and morphology can dramatically significantly change the surface plasmon resonance characteristics of Au NPs.Enhanced plasmonic sensitivity has been particularly observed for Au NPs with anisotropic shapes,allowing their use in surface-enhanced Raman scattering(SERS),sensing,imaging,and photothermal therapy,etc.Among them,Au NPs have been of particular interests for cancer photothermal therapy owing to their inherent biocompatibility,versatile surface functionalizations,fine-tunable localized surface plasmon resonances and highly photothermal conversion efficiency.Bimetallic gold-palladium nanoparticles(Au-Pd NPs)have exhibited enhanced performance as catalysts for fuel cells,owing to the electronic interactions and synergistic interplay between them,compared with their monometallic counterparts.The catalytic performance of bimetallic Au-Pd NPs catalysts has important relationship with size,morphology,structure and composition.As well known,Pd-based catalysts exhibit an excellent electrocatalytic performance in ethanol oxidation in alkaline media,while Au NPs have the excellent anti-CO poisoning ability and other advantages.Therefore,incorporation of Au into Pd-based catalysts would combine their merit and make up their disadvantages to promote the catalytic activity and stability.Meanwhile,the catalytic activity of NPs is also highly dependent on their surface structure,especially the density of low-coordinated surface atoms,such as atomic steps,ledges and kinks which usually serve as active sites with high catalytic activities.Mental nanoparticles exposed by high-index facets usually contain a high density of atomic steps,ledges and kinks,etc.Therefore,one promising route to obtain the electrocatalysts with high catalytic activity can be achieved through shape-controlled syntheses of NPs with high-index facets.However,from a thermodynamic point of view,the high-index facets of the NPs easily disappears during the growth process to minimize the total surface energy of the NPs.Thus,a simply and efficiently synthesis of NPs with high-index facet stills a huge challenge.In general,bimetallic Au-Pd NPs with excellent performance bear either core-shell(CS)structure or alloy structure.On the one hand,CS structured Au-Pd NPs with ultrathin Pd shells can significantly decrease the amount of Pd and also improve the utilization efficiency of Pd.Moreover,their electrocatalytic performance is also improved due to the electronic coupling between the Au core and the Pd shell.Furthermore,deposition of ultrathined shell on the surface of the cores can keep the crystallographic facet structure of the original core surface.However,the stability of CS Au-Pd NPs still has to be improved due to low CO anti-poisoning ability of monometallic Pd shell.On the other hand,alloy Au-Pd NPs can efficiently remove intermediates by oxidation and significantly improve the anti-CO poisoning ability due to the presence of Au in the AuPd alloy-shells,thus leading to better durability in addition to the enhancement in catalytic activity due to synergetic effects.However,to form alloy structures,two metal precursors have to be reduced simultaneously.Thus,a high amount of Pd precursors is usually necessary for preparation of alloy structured NPs,which would increase the application cost.Moreover,direct synthesis of alloy structured Au-Pd NPs with a predetermined shape,surface structure and composition is still one of the most challenging tasks because of their distinct standard reduction potential and atom sizes.Thus,conformal deposition of ultrathin AuPd alloy-shells onto preformed Au cores with controlled facets may achieve the synthesis of CS Au@AuPd NPs with ultrathin alloy-shells of facet-controlled and adjustable composition,which would combine their merit and make up their disadvantages.On the basis of the current issues mentioned above,in the thesis,firstly,irregularly shaped,concave cuboidal(ISCC)and highly branched trepang-like(HBT)Au NPs were synthesized.On the basis of this,CS Au@AuPd NPs were synthesized and explore their applications in electrocatalysis.Basing on the research,we found that Au@AuPd NPs prepared by co-reduction of a trace amount of Au precursor remained in the growth solution and Pd precursors by ascorbic acid(AA)under the aid of elemental silver reserved on the surface of preformed Au core.Next,a series of Au NPs with different facet structure and morphology were first prepared by using Au NRs as seeds in the growth solution composed of cetyltrimethylammonium chloride(CTAC).Then,a series of CS Au@AuPd NPs with ultrathin alloy-shells of facet-controlled and adjustable composition were prepared by co-reduction of a trace amount of Au and Pd precursors by AA under the aid of elemental silver reserved on the surface of preformed Au NPs.Investigate the compositions and facet of the ultrathin alloy-shells of as-prepared CS Au@AuPd NPs with the electrocatalytic performances.Lastly,we designed and prepared spiky Au NPs with high photothermal conversion efficiency through GSH functionalized Au NRs overgrowth and achieved ideal tumors photothermal therapy.In Chapter 2,firstly,ISCC-and HBT-Au NPs were synthesized by using short and long Au NRs as seeds in the growth solution composed of cetyltrimethylammonium bromide(CTAB).Then,ISCC-and HBT-Au@AuPd NPs with high-index facets were synthesized via Pd overgrowth on pre-formed ISCC-and HBT-Au NPs with a lower concentration of Pd precursors.The AuPd alloy nature of the resulting shells was confirmed by X-ray photoelectron spectroscopy,cyclic voltammogram analysis,and energy dispersive X-ray spectroscopy.Among the irregularly shaped NPs obtained,the ISCC-Au97.5@Au0.5Pd2.0 NPs display the largest electrochemically active surface area(up to 92.11m2 g-1),as their closed-packed agglomeration was prevented,and the best long-term stability with respect to ethanol oxidation(0.50 M)in alkaline media(0.30 KOH)by efficiently removing intermediates.Their mass-and ECSA-normalized current densities(4.15 A mgpd-1 and 4.51 mA cm-2)are about 20.7 times and 6.9 times higher than those of commercial Pd/C catalysts(0.20 A ugpd-1 and 0.65 mA cm-2),respectively.In Chapter 3,in this work,a series of facet-controlled Au NPs(such as,hexoctahedral(HOH-shaped)Au NPs with {651} high-index facets,elongated tetrahexahedral(ETHH-shaped)Au NPs with {730} high-index facet and octahedral(OCT-shaped)Au NPs with {111} low-index facet)were firstly prepared by using Au NRs as seeds in the CTAC growth solution.Then we report the synthesis of HOH-shaped,ETHH-shaped and OCT-shaped Au@AuPd NPs via co-reduction of a trace amount of Au and Pd precursors by AA with aid of an elemental silver reservoir on the surface of the corresponding preformed Au NPs enclosed with different facets.Consequently,surface facets of alloy-shells of the resulting Au@AuPd NPs can be tuned,as they can keep the original surface facets of pre-formed,facet-controlled Au cores.It is found that mass activities and specific activities of three types of Au@AuPd NPs both exhibit "volcano-type" dependence with respect to their Pd content in the surface of ultrathin AuPd alloy-shells.Moreover,HOH-shaped Au@Au0.20Pd2.0 NPs simultaneously bear the best activity and excellent stability due to exposed high-index facets of the AuPd alloy-shell and the proper area ratio of active facets and inactive facets on the surfaces of ultrathin alloy-shells.Furthermore,their ECSA value,mass activity and specific activity are 125.8 m2 g-1,11.9 A mgPd-1 and 9.5 mA cm-2,respectively,which are about 4-fold,31-fold,and 7-fold better than those(28.4 m2 g-1,0.38 A mgPd-1,and 1.34 mA cm-2)of commercial Pd/C catalysts,respectively.Thus,this work not only demonstrates that surface facets of core-shell Au@AuPd NPs can be engineered via co-reduction of a trace amount of Au and Pd precursors by AA under the aid of an elemental silver reservoir on the surface of preformed Au NPs,but also will open a new way to improve electrocatalytic performance of core-shell Au@AuPd NPs by surface engineering.In Chapter 4,The current technical dilemma for Au NPs as photothermal(PT)transducers in cancer therapy is that strong absorption in the second near-infrared(NIK)window is accompanied by strong scattering of the NIR light,which then overrides the absorption,thus significantly weakening the NIR light-to-heat conversion efficiency.Here we successfully prepared spiky Au NPs with a controlled number of spikes,designed according to our simulations and experimentally verified.Their overall sizes and the numbers,lengths and widths of the spikes were judiciously adjusted to locate their surface plasmon resonance peaks in the second NIR window and also to achieve a higher absorption to extinction ratio.As a result,the spiky Au NPs with optimal size and 6 spikes exhibited a record light-to-heat conversion efficiency(78.8%)under irradiation by 980 nm light.After surface PEGylation and conjugation with a lactoferrin(LF)ligand on the resulting spiky Au NPs,they in vivo displayed long circulation time(blood circulation half-life of?300 min)and high tumor accumulation due to their larger surface-to-volume ratio.Therefore,spiky Au NPs allowed complete ablation of tumors without recurrence merely after 3 min light irradiation at 980 run,opening up promising prospects of cancer photothermal therapy.In Chapter 5,we summarize and look forward to the current research work.In summary,we have prepared a variety of Au NPs with different morphologies and facet structures and CS Au@AuPd NPs with ultrathin AuPd alloy shell,which greatly extended the catalysis and biological applications of Au-based NPs.