Growth Of Au Nanoparticles Research Articles

Electron irradiation effects on the nucleation and growth of Au nanoparticles in silicon nitride membranes

The formation of Au nanoparticles (NPs) in Au+ ion-implanted silicon nitride thin films and membranes was investigated as a function of post-implantation thermal treatments or room temperature electron irradiation at energies of 80, 120, 160, and 200 keV. The samples were characterized by Rutherford Backscattering Spectrometry and Transmission Electron Microscopy. High-temperature thermal annealing (1100 °C, 1 h) resulted in the formation of Au particles with a mean diameter of ≈1.3 nm. In comparison, room-temperature electron irradiation at energies from 80 to 200 keV caused the formation of larger Au particles according to two growth regimes. The first regime is characterized by a slow growth rate and occurs inside the silicon nitride membrane. The second regime presents a fast growth rate and starts when Au atoms become exposed to the back free surface of the membrane. Realistic binary electron-atom elastic collision cross-sections were used to analyze the observed nanoparticle growth and membrane sputtering phenomena. The results obtained demonstrate that binary electron-atom elastic collisions can account for the microstructure modifications if the critical displacement energies for the sputtering of N and Si atoms are around 14 ± 3 eV, and the displacement energy for surface located Au atoms is approximately 1.25 ± 0.2 eV. Irradiation experiments using focused electron probes demonstrate that the process provides fine control of nanoparticle formation, resulting in well-defined sizes and locations.

Evaporation of Gold on NaCl Surfaces as a Way To Control Spatial Distribution of Nanoparticles: Insights on the Shape and Crystallographic Orientation

Herein, the growth of Au nanoparticles on NaCl surfaces as a way to control their spatial distribution is explored, giving new insights into the shape and relative orientation of the resulting nanoparticles through modern electron microscopy techniques. Their morphological features depending on the geometry of the NaCl surface site they nucleated on are described in detail. Also, hitherto unreported small but systematic angular deviations in the range of 1–4° from the exact epitaxial orientation were observed. A theoretical approach based on straightforward elastic energy considerations and yet capable of accounting for the experimental results was developed. The production of metallic nanoparticles is a fundamental subject in the development of nanotechnology, and the fine control of the shape and spatial distribution is an important issue for the applicability of nanoparticles. Furthermore, in spite of the extensive research on this topic, some key features such as the precise mechanism controlling particle shape and particle-substrate orientation are still not well understood as evidenced by the results of this work. Thus, a clear understanding of the role played by the diverse factors involved in epitaxial growth is required to produce nanoparticles with finely tailored properties.

Understanding seed-mediated growth of gold nanoclusters at molecular level

The continuous development of total synthesis chemistry has allowed many organic and biomolecules to be produced with known synthetic history–that is, a complete set of step reactions in their synthetic routes. Here, we extend such molecular-level precise reaction routes to nanochemistry, particularly to a seed-mediated synthesis of inorganic nanoparticles. By systematically investigating the time−dependent abundance of 35 intermediate species in total, we map out relevant step reactions in a model size growth reaction from molecularly pure Au25 to Au44 nanoparticles. The size growth of Au nanoparticles involves two different size−evolution processes (monotonic LaMer growth and volcano-shaped aggregative growth), which are driven by a sequential 2-electron boosting of the valence electron count of Au nanoparticles. Such fundamental findings not only provide guiding principles to produce other sizes of Au nanoparticles (e.g., Au38), but also represent molecular-level insights on long-standing puzzles in nanochemistry, including LaMer growth, aggregative growth, and digestive ripening.

Growth of Au Nanoparticles on 2D Metalloporphyrinic Metal-Organic Framework Nanosheets Used as Biomimetic Catalysts for Cascade Reactions.

Inspired by the multiple functions of natural multienzyme systems, a new kind of hybrid nanosheet is designed and synthesized, i.e., ultrasmall Au nanoparticles (NPs) grown on 2D metalloporphyrinic metal-organic framework (MOF) nanosheets. Since 2D metalloporphyrinic MOF nanosheets can act as the peroxidase mimics and Au NPs can serve as artificial glucose oxidase, the hybrid nanosheets are used to mimic the natural enzymes and catalyze the cascade reactions. Furthermore, the synthesized hybrid nanosheets are used to detect biomolecules, such as glucose. This study paves a new avenue to design nanomaterial-based biomimetic catalysts with multiple complex functions.

Extending LaMer's mechanism using open system for increasing forced and controlled growth of Au nano particles: Desired decreasing Fe3O4 nano particles size during simultaneous synthesis in optimized conditions

The most effective parameters were found to obtain Au/Fe3O4 nano particles (NPs)-oleylamine composite. Having Au NPs with the controlled maximum mean size under the forced conditions was the main aim of this study. We used the continuous flow rates of oleylamine 75% to produce Au NPs under an open system by extended LaMer mechanisms. This process decreased the mean size of Fe3O4 NPs synthesized simultaneously, by classic LaMer mechanism. The Fe3O4 NPs production was carried out without continuous adding of any iron reactant, viz. as a closed system. In the absence of gold ions, the mean size of the synthesized Fe3O4 NPs using 2.5ml/min oleylamine was about 35.0nm at 2.0±0.5 °C after 120min. This mean size was decreased to 27.2, 21.4, 16.8 and 8.7nm, when Au NPs were simultaneous prepared using 0.5, 0.75, 1.5 and 2.5ml/min of oleylamine, respectively, at the same conditions. Surface Plasmon Resonance (SPR) adsorption was used to evaluate Au NPs production at first 30min, while Small Angle X-ray Scattering (SAXS) method was used to monitor the reaction progression for near-real time analysis of increasing the growth of Au NPs up to 280min, at the optimum conditions. Changing the properties of Fe3O4 NPs during processes was determined by studying Magnetization, Potentiometric titration, Inductive heating and Zeta potential.

Polydopamine induced in-situ growth of Au nanoparticles on reduced graphene oxide as an efficient biosensing platform for ultrasensitive detection of bisphenol A

Bisphenol A (BPA) is one of the most prevalent environmental endocrine disrupting chemicals with potential estrogenic activity. Herein we report a facile electrochemical sensing strategy for ultrasensitive detection of BPA based on the hybrid of AuNPs decorated reduced graphene oxide (RGO). This Au@PDA-RGO hybrid was synthesized by in-situ growth of AuNPs induced by polydopamine (PDA) on RGO. Since PDA acts as a moderate reducing agent and an effective linker, AuNPs scatter well on RGO with controllable density, homogeneous size and uniform distribution. With the aid of chitosan (Chit), an electrochemical tyrosinase (Tyr) biosensor based on Au@PDA-RGO was constructed on glassy carbon electrode (Tyr/Au@PDA-RGO-Chit/GCE). This immobilization matrix possesses high conductivity, large active areas and a suitable biological microenvironment. As a result, the constructed Tyr biosensor exhibited good analytical performance for BPA with a high sensitivity of 0.2569AM−1, a wide linear range from 12.5nM to 3.68μM, and a low detection limit of 0.10nM (S/N=3). This method was also applied to detect BPA in plastic products, showing good agreement with the values detected by HPLC-MS/MS.

The formation of CdS quantum dots and Au nanoparticles

Abstract We report on microsecond-resolved in-situ SAXS experiments of the early nucleation and growth behavior of both cadmium sulfide (CdS) quantum dots in aqueous solution including the temperature dependence and of gold (Au) nanoparticles. A novel free-jet setup was developped to access reaction times as early as 20 μs. As the signal in particular in the beginning of the reaction is weak the containment-free nature of this sample environment prooved crucial. The SAXS data reveal a two-step pathway with a surprising stability of a structurally relaxed cluster with a diameter of about 2 nm. While these develop rapidly by ionic assembly, a further slower growth is attributed to cluster attachment. WAXS diffraction confirms, that the particles at this early stage are not yet crystalline. This growth mode is confirmed for a temperature range from 25°C to 45°C. An energy barrier for the diffusion of primary clusters in water of 0.60 eV was experimentally observed in agreement with molecular simulations. To access reaction times beyond 100 ms, a stopped-drop setup -again contaiment- free is introduced. SAXS experiments on the growth of Au nanoparticles on an extended time scale provide a much slower growth with one population only. Further, the influence of ionizing X-ray radiation on the Au particle fromation and growth is discussed.

Synthesis and characterizations of Au-C60 nanocomposite

Au-C60 nanocomposite thin film (Au nanoparticles embedded in fullerene C60 matrix) is synthesized by thermal co-evaporation method and subsequent thermal annealing from 150 °C to 300 °C. A very small concentration of Au (∼2 at.%) is chosen in order to minimize the deterioration of the physical and chemical properties of fullerene C60 due to the presence of metal. Spherical shaped Au nanoparticles with a diameter of 2.1 ± 0.04 nm are clearly seen in the TEM images of the nanocomposite annealed at 200 °C. A broad surface plasmon resonance peak at ∼581 nm emerges in UV-visible absorption spectrum due to the evolution of Au nanoparticles at a temperature of 250 °C, which is further blue shifted at ∼554 nm with a narrower FWHM at 300 °C. The presence of Au nanoparticles is also confirmed by X-ray diffraction with Au (111) and Au (200) fcc reflections. Thermally induced transformations of fullerene C60 matrix at high temperatures is studied by Raman spectroscopy on pure fullerene C60 films (without metal). The blue shift of LSPR at a temperature of 300 °C is ascribed to the transformation of fullerene C60 matrix into amorphous carbon and is explained in terms of Mie theory. TEM results show the growth of Au nanoparticles in fullerene matrix at higher temperatures due to the enhanced diffusion of Au atoms and Ostwald ripening.

Superior Catalytic Performance of Gold Nanoparticles Within Small Cross-Linked Lysozyme Crystals.

Bionanomaterials synthesized by bioinspired templating methods have emerged as a novel class of composite materials with varied applications in catalysis, detection, drug delivery, and biomedicine. In this study, two kinds of cross-linked lysozyme crystals (CLLCs) with different sizes were applied for the in situ growth of Au nanoparticles (AuNPs). The resulting composite materials were characterized by light microscopy, scanning electron microscopy, transmission electron microscopy, thermogravimetric analysis, and X-ray photoelectron spectroscopy. The catalytic properties of the prepared materials were examined in the catalytic reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP). It was found that the size of the AuNPs increased with an increase in Au loading for both small and large crystals. In addition, small crystals favored homogeneous adsorption and distribution of the metal precursors. And the size of the AuNPs within small crystals could be maintained below 2.5 nm by managing the HAuCl4/lysozyme molar ratio. Furthermore, the lysozyme functional groups blocked the AuNP activity sites, therefore reducing their catalytic activity. This effect was more pronounced for small AuNPs. Moreover, the mass transfer of reactants (4-NP) from solution to AuNPs within the crystals restricted their catalytic reduction, leading to superior catalytic performance of the AuNPs within small cross-linked lysozyme crystals (Au@S-CLLCs) compared to those within large cross-linked lysozyme crystals (Au@L-CLLCs) at similar Au loadings. Finally, an increase in Au loading clogged the crystal channels with increased quantities of larger AuNPs, thus impeding the catalytic performance of Au@S-CLLCs.

(Invited) Development of Newfangled Nanotechnologies By Introducing Ionic Liquid to Vacuum Devices

One of fascinate features that ionic liquid (IL) possesses is extremely low vapor pressure, which enable us to put IL in a vacuum chamber. There are many vacuum devices that have been designed for solid samples, as a matter of course. However, an ability to make wet condition in vacuum system by introducing IL into it allows us to develop newfangled technologies in analytical chemistry and nanomaterial synthesis fields. In this paper, two topics on in situ electron microscope observation of reactions in IL and facile way to synthesis nanoparticles using a sputtering instrument onto IL are described. Regarding the use of IL for electron microscope observation, we have found the fascinate fact that IL drops give scanning electron microscope (SEM) images without any charging.1 In other words, IL behaves like a conducting material for electron microscope observation. It was also found that IL behaves like a transparent material for SEM observation when its thickness is less than 1 micro meter. Based on these facts, we started to develop ways to conduct in situ electron microscope observation of chemical reactions. Electrically conducting polypyrrole film deposited on an electrode surface was the first sample and changes in its thickness upon redox reaction in IL electrolyte were observed by SEM.2 As another electrochemical reaction, we attempted to observe deposition of Ag metal on an electrode from IL containing Ag+ ions. Nucleation and nuclear growth were dominant when Ag deposition was moderately conducted. Howerver, when the deposition rate was accelerated so as to make the diffusion-controlled condition, growth of Ag metal with dendriform was clearly observed.3 When we observed IL dissolving Na[AuCl4] by SEM, it was found that Au particles appeared in the IL, resulting from reduction of Au ions by electron beam irradiation.4 On the basis of this finding, attempt was made to observe generation and growth of Au nanoparticles by a transmission electron microscope (TEM). Figure 1 shows time course of two Au nanoparticles (diameter = ca. 5 nm). Each particle shows fringes reflecting crystal lattice of Au and it is obvious that coalescence gives a larger Au nanoparticles by production of one Au crystal from two crystals.5 The metal sputtering instrument is useful for depositing a metal thin layer on a substrate surface. The sample was limited to solid materials because the metal sputtering must be conducted under reduced pressure. Our first attempt was to subject IL to Au sputtering and observation of the resulting IL by TEM, giving us a chance to discover synthesis of Au nanoparticles suspended in IL.6 Nanoparticles of several kinds of metals and metal oxides including alloy nanoparticles can be prepared by this method.7 The noble nanoparticles including Au and Pt can be adsorbed on carbon substance surfaces by putting IL containing metal nanoparticles on the substance and heating it. This way is exploitable for preparation of Pt-carbon catalysts for fuel cells.8 Furthermore, adsorption of Pt nanoparticles on surfaces of carbon nanotubes (CNTs) was possible by the similar way as shown in Figure 2.9 Electrochemical measurements of the prepared Pt nanoparticle-adsorbed CNTs revealed that this material possesses distinct catalytic activities toward O2 reduction.

Peptide Sequence Effects Control the Single Pot Reduction, Nucleation, and Growth of Au Nanoparticles

Peptides have demonstrated unique capabilities to fabricate inorganic nanomaterials of numerous compositions through noncovalent binding of the growing surface in solution. In this contribution, we demonstrate that these biomolecules can control all facets of Au nanoparticle fabrication, including Au3+ reduction, without the use of secondary reagents. In this regard using the AuBP1 peptide, the N-terminal tryptophan residue is responsible for driving Au3+ reduction to generate Au nanoparticles passivated by the oxidized peptide in solution, where localized residue context effects control the reducing strength of the biomolecule. The process was fully monitored by both time-resolved monitoring of the growth of the localized surface plasmon resonance and transmission electron microscopy. Nanoparticle growth occurs by a unique disaggregation of nanoparticle aggregates in solution. Computational modeling demonstrated that the oxidized residue of the peptide sequence does not impact the biomolecule’s ability t...

Nano-sized gold particles dispersed on HZSM-5 and SiO2 substrates for catalytic oxidation of HCHO

Au catalysts supported on HZSM-5 and SiO2 prepared by a deposition–precipitation (DP) method with ammonia as the precipitant were very active for HCHO complete oxidation at room temperature under humid air. The treatment atmosphere exerted significant effects on the catalytic performance. The catalysts treated in H2 had better Au dispersions and smaller Au particle sizes than those treated in air, which were crucial for high reactivity. Both catalysts deactivated at high GHSV (600,000mlg−1h−1), due to the growth of Au nanoparticles during the reaction, as well as the accumulation of surface species such as formate intermediates on the catalyst. Our results suggested that small Au particle size and strong metal-support interaction were the key factors for the high activity for HCHO oxidation over Au supported on silica-based materials.

Controlling Au Photodeposition on Large ZnO Nanoparticles.

This study investigated how to control the rate of photoreduction of metastable AuCl2(-) at the solid-solution interface of large ZnO nanoparticles (NPs) (50-100 nm size). Band-gap photoexcitation of electronic charge in ZnO by 370 nm UV light yielded Au NP deposition and the formation of ZnO-Au NP hybrids. Au NP growth was observed to be nonepitaxial, and the patterns of Au photodeposition onto ZnO NPs observed by high-resolution transmission electron microscopy were consistent with reduction of AuCl2(-) at ZnO facet edges and corner sites. Au NP photodeposition was effective in the presence of labile oleylamine ligands attached to the ZnO surface; however, when a strong-binding dodecanethiol ligand coated the surface, photodeposition was quenched. Rates of interfacial electron transfer at the ZnO-solution interface were adjusted by changing the solvent, and these rates were observed to strongly depend on the solvent's permittivity (ε) and viscosity. From measurements of electron transfer from ZnO to the organic dye toluidine blue at the ZnO-solution interface, it was confirmed that low ε solvent mixtures (ε ≈ 9.5) possessed markedly higher rates of photocatalytic interfacial electron transfer (∼3.2 × 10(4) electrons·particle(-1)·s(-1)) compared to solvent mixtures with high ε (ε = 29.9, ∼1.9 × 10(4) electrons·particle(-1)·s(-1)). Dissolved oxygen content in the solvent and the exposure time of ZnO to band-gap, near-UV photoexcitation were also identified as factors that strongly affected Au photodeposition behavior. Production of Au clusters was favored under conditions that caused electron accumulation in the ZnO-Au NP hybrid. Under conditions where electron discharge was rapid (such as in low ε solvents), AuCl2(-) precursor ions photoreduced at ZnO surfaces in less than 5 s, leading to deposition of several small, isolated ∼6 nm Au NP on the ZnO host instead.

CeO2-modified Au/TiO2 catalysts with outstanding stability under harsh CO oxidation conditions

The 1.5wt% Au/TiO2 World Gold Council catalyst (WGC) was modified by depositing on its surface a 5.4wt% CeO2 loading by incipient wetness impregnation. Calcination at 673K of the resulting, surface-modified, catalyst yielded a material in which the system of gold particles was not significantly modified with respect to that of the starting 1.5% Au/TiO2 WGC catalyst, neither in terms of its size distribution or metallic dispersion. The latter parameter remained, as in the catalyst prior to CeO2 deposition, in a value about 36%. Both catalysts, Au(1.5%)/TiO2 WGC and CeO2(5.4%)/Au(1.5%)/TiO2, were tested in consecutive CO oxidation reaction loops at increasing final temperatures. In these cycles, the ceria-modified catalyst showed not only a higher activity but, more importantly, a largely enhanced stability against deactivation. Scanning Transmission Electron Microscopy (STEM) studies clearly revealed the presence of nanometer-sized ceria rafts, less than 1nm thick, on the surface of the fresh CeO2(5.4%)/Au(1.5%)/TiO2 catalysts. After the CO oxidation test at the highest temperature, 1223K, the WGC catalyst suffered from a very severe Au nanoparticle sintering whereas Au nanoparticle growth was very much limited in the ceria-modified catalyst after the same aging test. STEM results reveal that a major fraction of the Au nanoparticles (75%), comprising all the smaller ones (<5nm), was contacting the ceria phase. This evidences an important stabilizing effect of the proposed surface modification. Moreover, these results open up possibilities for gold catalysts in applications where high temperatures are reached under working conditions.

Application of oil-swollen surfactant gels as a growth medium for metal nanoparticle synthesis, and as an exfoliation medium for preparation of graphene

Gel is an intermediate phase of solid and liquid, which exhibits properties of both, and this unique feature of gel has made it an excellent choice as a reaction medium for the nanomaterials synthesis. Herein, we report use of oil swollen surfactant gels as reaction medium and exfoliation medium, for the synthesis of metals (Au, Ag) nanoparticles and graphene, respectively. Confined growth of metals (Au and Ag) nanoparticles, has been achieved by exploring tween 80 based surfactant gel as a reaction medium. Au NPs prepared within tween 80 gel were found to be spherical with size ∼5nm, arranged in template micelles. Heating triggered the growth of Au nanoparticles and particles of various shapes including triangles, rods and pentagonal, were produced. Au and Ag containing tween 80 gels were found to be promising as catalysts for the nitrophenol reduction. Apart from separate synthesis of Au and Ag nanoparticles, bimetallic (Au-Ag) nanoparticles have also been synthesized by taking advantage of selective reducing property of tween 80. First time CTAB gel has been utilized as an exfoliation medium for the quick exfoliation of graphite into graphene sheets, eliminating the necessity of any external driving force such as sonication or heating, to reinforce exfoliation.

Fabricating Carbon Nanofiber Electrodes with Embedded Iron Nanoparticles Using Block Copolymers Templates

Due to its high thermal, mechanical and electrochemical stability and good conductivity, carbon is an attractive material for fabrication of many bioelectrochemical devices such as biosensors and biofuel cells. However, carbon’s inert nature makes it difficult to functionalize with biocatalysts; often requiring harsh chemical treatment, such as nitric acid oxidation, to attach reactive amines and carboxylic acids to its surface. Alternatively, metal nanoparticles have been demonstrated to be efficient supports for biocatalysts functionalization. [1-3] Depositing metal nanoparticles on carbon electrodes by physical vapor deposition (PVD) is a viable means of functionalizing carbon electrodes with biocatalyst. However, PVD is an expensive and directional deposition method; this may result in poor surface coverage for 3D carbon electrodes, such as carbon nanofiber mesh electrodes. It has been traditionally difficult to incorporate nanoparticles into carbon nanofibers by embedding them into the polymer precursors prior to pyrolysis, as most metallic nanoparticles will melt at the temperatures needed for carbon pyrolysis (>900 oC). Recent studies, however, points toward a self-assembly approach for fabricating well organized layers of carbon loaded with arrays of platinum nanoparticles patterned by block-copolymers (BCP) templates. [4-6] Herein, we demonstrate an effective method for developing carbon nanofibers meshes embedded with iron nanoparticles, by incorporating a BCP self-assembly approach into our C-MEMS fabrication technique. The main phase of this hybrid method includes electrospinning iron-salt-loaded BCP into nanofiber meshes, and subsequently reducing the iron salts into iron nanoparticles prior to pyrolysis. This cost-effective process will pave the way for fabricating scalable advanced 3-D carbon electrodes that can be applied to biosensors and biofuel cells devices. [1] Zhao, Xin, et al. "Polymer-supported nanocomposites for environmental application: a review." Chemical Engineering Journal 170.2 (2011): 381-394. [2] Zayats, Maya, et al. "Biocatalytic growth of Au nanoparticles: from mechanistic aspects to biosensors design." Nano letters 5.1 (2005): 21-25. [3] Wilner, Ofer I., et al. "Self-assembly of enzymes on DNA scaffolds: en route to biocatalytic cascades and the synthesis of metallic nanowires." Nano letters 9.5 (2009): 2040-2043. [4] Park, Soojin, et al. "From nanorings to nanodots by patterning with block copolymers." Nano letters 8.6 (2008): 1667-1672. [5] Park, Soojin, et al. "Macroscopic 10-terabit–per–square-inch arrays from block copolymers with lateral order." Science 323.5917 (2009): 1030-1033. [6] Jang, Yu Jin, et al. "Nanostructured Metal/Carbon Hybrids for Electrocatalysis by Direct Carbonization of Inverse Micelle Multilayers." ACS nano 7.2 (2012): 1573-1582.

Gold Nanoparticles Stimulated Surface Plasmon Resonance Effects in Erbium-Zinc-Sodium-Tellurite Glass

Modifying the optical characteristics of rare earth (RE) doped inorganic glasses by stimulating surface plasmon resonance (SPR) via controlled growth of metal nanoparticles (NPs) is an outstanding quest in glass plasmonics. Glasses with composition 70TeO2-20ZnO-10Na2O-(x)Er2O3-(y)Au (x = 0.0 and 1.0 mol%; y = 0.0 and 0.6 mol% both in excess) are synthesized using melt-quenching technique and characterized. Influences of heat treatment temperature on the growth of Au NPs and their subsequent impacts on Raman spectral features modifications are inspected. The amorphous nature of glass is confirmed by using XRD. TEM reveal the non-spherical Au NPs with average diameter vary from 7.4 to 10.3 nm. Surface plasmon band is evidenced around 627 - 632 nm. Raman spectra demonstrate the presence of Er-O and Zn-O bond, anti-symmetric vibrations of Te-O-Te bonds and stretching modes of non-bonded oxygen exists in TeO3 and TeO3+1 unit. The amplifications in Raman signals by a factor of 1.39, 1.40, 0.88 and 1.29 and 1.25 corresponding to the peak centered at 262, 382, 536, 670 and 725 cm-1 are attributed to the contribution of a surface plasmon (SP) generating a strong, localized and secondary field. The excellent features of the results suggest that our systematic method of controlled NPs growth may constitute a basis for improving the spectral features of tellurite glasses useful for the development of efficient and economic up-converted lasers.

Modeling the atomistic growth behavior of gold nanoparticles in solution.

The properties of gold nanoparticles strongly depend on their three-dimensional atomic structure, leading to an increased emphasis on controlling and predicting nanoparticle structural evolution during the synthesis process. In order to provide this atomistic-level insight and establish a link to the experimentally-observed growth behavior, a kinetic Monte Carlo simulation (KMC) approach is developed for capturing Au nanoparticle growth characteristics. The advantage of this approach is that, compared to traditional molecular dynamics simulations, the atomistic nanoparticle structural evolution can be tracked on time scales that approach the actual experiments. This has enabled several different comparisons against experimental benchmarks, and it has helped transition the KMC simulations from a hypothetical toy model into a more experimentally-relevant test-bed. The model is initially parameterized by performing a series of automated comparisons of Au nanoparticle growth curves versus the experimental observations, and then the refined model allows for detailed structural analysis of the nanoparticle growth behavior. Although the Au nanoparticles are roughly spherical, the maximum/minimum dimensions deviate from the average by approximately 12.5%, which is consistent with the corresponding experiments. Also, a surface texture analysis highlights the changes in the surface structure as a function of time. While the nanoparticles show similar surface structures throughout the growth process, there can be some significant differences during the initial growth at different synthesis conditions.

Differential role of PVP on the synthesis of plasmonic gold nanostructures and their catalytic and SERS properties

Differential role of PVP modified with halide ions has been meticulously studied for in situ tuning of Au nanoparticle growth utilizing XRD measurements together with FTIR data, thus quantifying their catalysis and SERS applications.

Controlled fabrication and enhanced visible-light photocatalytic hydrogen production of Au@CdS/MIL-101 heterostructure

A novel and highly efficient three-component Au@CdS/MIL-101 heterostructure was successfully synthesized. The MIL-101(Cr) with large surface area was introduced as a matrix for the well-dispersed growth of Au nanoparticles, and the CdS was selectively coated on the Au nanoparticles. Under visible light irradiation, the Au@CdS/MIL-101 heterostructure presents superior hydrogen evolution rate over the pure CdS, CdS/MIL-101 and Au/MIL-101 composites. The Au@CdS/MIL-101 heterostructure exhibits an unusual H2 production rate of 250μmolh−1/10mg, which is 2.6 times higher than that of pure CdS. The performance enhancement of Au@CdS/MIL-101 heterostructure can be attributed to the following reasons: (i) the large surface area of MIL-101(Cr) can effectively disperse the Au and CdS nanoparticles, resulting in more active adsorption sites and reaction centers. (ii) the strong surface plasmon resonance absorption of Au could accelerate the charge transfer and extend the light response spectrum of CdS. This three-component Au@CdS/MIL-101 heterostructure combining the large surface area of MOF and the surface plasmon resonance of Au into a single structure may provide a potential way to design highly efficient and solar-energy-harvesting photocatalysts.