Design, Fabrication, And Application Investigation Of Noble Metal Nanostructures

During the last two decades, great attentions have been paid to noble metal nanostructures with abundant morphologies, distinct chemicophysical properties, since they could be applied in various fields, such as, optics, photonics, magnetics, catalysis, biomedicine, environment, and new energy. It was well known that the properties of noble metal nanocrystals usually depends on their physical parameters including szies, shapes, dimensions, compositions and structures (i.e. solid or hollow).In principle, one can tailor and fine-tune the properties of a metal nanocrystal by controlling any one of these parameters, but the flexibility and scope of change are highly sensitive to the specific parameter. Based on these, we could effectively pre-design and controllably synthesize noble metal nanomaterials with specific properties and stable structures, which might be applied in many potential fields with higher efficiency and defined purposes, especially electrocatalysis, sensing, biochemical dectection and fuel cells. Fox example, proton-exchange membrane fuel cells (PEMFCs) have increasingly been an important way to resolve the problems of environmental pollution and energy crisis, and among these platinum and its alloy materials have been extensively investigated and used, since they are one kind of effective electrocatalysts both in the anode and cathode of PEMFCs. However, as an electrocatalyst Pt has to face many problems, such as, low Pt storage on Earth, expensive price, higher loading amount and easily deactive, large overprotential and low kinetic activity of ORR, and readily be poisoned by CO under room temperature, which have been the major obstacles for the commerical application of PEMFCs based on such catalysts. But according to the theoretical calculations for the mechanisms of both anodic and cathodic process, one may have the ability of pre-designing and manufacturing catalysts to avoid these problems.Herein, we focused on the development of a simple, versatile and rapid route to fabricate noble metal nanostructure with specific properties, and via a targeted way to prepare metallic catalyst with distinctive surface-structural designing, which were used in both the anode catalytic oxidation and the cathode catalytic reduction of fuel cells, as well as electrochemical sensing and detection, especially, we explored their application prospects in both electrocatalysis and fuel cells. Meanwhile, considering the potential biosafety issues due to the extensively using of noble metal nanomaterials, the cytotoxicity investigation has also been done via a simple model of spherical gold nanoparicles (GNPs) and human lung cancer cell A549, which might provide some suggestions for the applications of noble metal nanomaterials.The results are as follows:(1) Metallic nanostructures with hollow interiors or tailored porosity represent a special class of attractive materials with intriguing chemicophysical properties. This paper presents the fabrication of a new type of metallic nanoporous nanotube structure based on a facile and effective combination of nanocrystal growth and surface modification. By controlling the individual steps involved in this process, such as nanowire growth, surface modification, thermal diffusion, and dealloying, one-dimensional (1-D) metallic nanostructures can be prepared with tailored structural features and pre-designed functionalities. These tubular and porous nanostructures show distinct optical properties, such as tunable absorption in the near-infrared region, and enhanced capability for electrochemiluminescence signal amplification, which make them particularly desirable as novel1-D nanocarriers for biomedical, drug delivery and sensing applications.(2) Considering the residual Ag component in the Au/Ag alloy porous nanotubes (APNTs), we fabricated a kind of Pt/Ag composite porous nantubes (PNTs) with enhanced catalytic actvity toward HCOOH electrooxidation via the simple galvanic replacement between the residual and H2PtCl6-Due to the relatively low content of Ag in the Au/Ag APNTs as well as the effective alloy between Au and Ag, we do think the reduced Pt atoms disperesed on the PNTs surface could be effectively controlled and separated by the surface Au atoms, which could be ascribed to the lower diffusion coefficient of Pt than that of Au. By tuning the amount of Pt precursor, Pt/Au PNTs with different Pt-decorated loading could be easily approached. Structural characterizations with scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray powder diffraction (XRD) reveal a novel nanoarchitecture with multimodal open porosity and excellent structural continuity and integrity. Meanwhile, as a kind of anodic catalysts, CV and other techniques demonstrated that the Pt/Au PNTs possess excellent electrocatalytic activity toward HCOOH oxidation and enhanced tolerance to CO poisoning.(3) Based on the one dimensional Ag nanowires synthesized via a modified polyol process, with a simple electroless plating and selective etching process we sucessfully fabricated Pt/Ag composite porous nanotubes (Pt/Ag PNTs). We have investigated the influence of different amount of Pt precursors toward the final Pt/Ag PNTs structures. It was find that the mechanical strength of the composite PNTs wall sturcture strongly depended on the dosage of H2PtCl6, which presents a positive correlation. Following, the Pt/Ag PNTs were used as an anodic catalyst under alkaline condition and sensing electrode in neutral conditon toward the electrooxidation of ethanol and detection of H2O2, respectively. As for the ethanol oxidation, campared with the commerical Pt/C catalyst, Pt/Ag PNTs possessed the similar electrochemical behaviors, but their intrinsic activity is evidently higher than that of Pt/C. CO stripping in acid sloution showed that Pt/Ag PNTs have much higher tolerance to CO poisoning than Pt/C. During the detection of H2O2, we got find that Pt/Ag PNTs exhibits sensitive respones toward the reduction of H2O2. CV study illustrated that a linear relationship for H2O2determniantion in a concentration range from25μmol/L to4mmol/L, with～0.8μmol/L response sensitivity. These two results revealed that Pt/Ag composite PNTs could be a kind of remarkable alkaline fuel cell catalysts and superior sensing electrode materials.(4) We developed a large scale, simple and rapid route to fabricate Pt/Ag hollow porous nanospheres (HPNSs) which can be served as a supportless ORR catalyst with higher activity than that of commercial Pt/C catalysts. To prepare the HPNSs, firstly Ag@Pt core-shell nanoparticles were fabricated via a one-pot approach of solvent-thermal process, following a selective etching process by concentrated HNO3was employed to get HPNSs. Thermal annealing under relatively moderate condition (～160℃) was adopted to obtain high quality crystalline and stable shells of HPNSs (a-HPNSs), Owing to their ultra-thin wall structure (～3nm), porous shells with high surface-area-to-volume, and their alloy structures, the α-HPNSs exhibited significant enhancement of the ORR catalytic activity over commercial Pt/C catalyst, and the half-wave potential of α-HPNSs is～0.896V (versus a reversible hydrogen electrode, RHE), which is nearly70mV higher than that of Pt/C (～0.828V vs. RHE). Durability examination adopted the same condition and the α-HPNSs showed surprisingly high activity toward ORR. Although the α-HPNSs are particle-like structure, they displayed superior connectivity and conductivity without any substrates during the electrochemical test. Consequently, this method allows simplification of the experimental procedures by avoiding the tedious mixing and optimization of catalysts with supporting materials.(5) Gold nanoparticles (GNPs) were used to evaluate their cytotoxicity toward human lung cancer cells A549. No cell proliferation inhibition was found when the cells were treated by GNPs independently. However, when L-buthionine-sulfoximine (BSO) was used to decrease the expression of glutathione (GSH) in A549cells, GNPs showed evident cytotoxicity to cells. Interestingly, the cytotoxicity of GNPs could be reversed after adding outside source GSH into the system. Whereas GSH plays an important role in eliminating reactive oxygen species (ROS), by monitoring the intracellular levels of ROS, GNPs were observed to generate more intracellular ROS in the presence of BSO. The cytotoxicity caused by GNPs toward lung cancer cells could therefore be partially attributed to the increase in intracellular ROS levels. These results suggest that caution should be paid in the use of GNPs for in vivo tests because GNPs can serve as therapeutic agents in their own right as well as carriers for other drugs and biomolecules.