Gold Particle Size Research Articles

Versatile film formation and phase transfer of gold nanoparticles by changing the polarity of the media

A simple method to prepare gold particles of different sizes and polydispersities is presented. The diameter of the gold particles ranges from 5 to 50 nm. All systems were prepared in either ethylene glycol or mixtures of ethylene glycol:water without adding any external reducing agent in the presence of sodium docecyl sulfate as a stabilzer and afterward transferred into chloroform or accumulated at interface in the form of film. The absence of water in ethylene glycol is a prerequisite for successful 3-dimensional self-assembly film at the interface. The free standing film was very stable and could be easily transferred on solid support. The probability of the film formation at the interface decreased with the increase in the content of water in the mixture. It was observed that as the polarity of the media increases after a certain extent, Au particles neither get transferred nor accumulated at interface and remained in the form of emulsion. However, addition of NaOH leads to the transfer process. In some cases, the phase transfer has a yield of about 100%. After drying, the particles can be re-dispersed in different nonpolar solvents. The dispersed particles were stable for at least 45 days. Characterization of the particles before and after transfer was performed by using UV/Vis spectroscopy, transmission electron microscopy (TEM), and atomic force microscopy (AFM) techniques.

Reductive dehydration of ethanol to hydrocarbons on Ni- and Au-containing nanocomposites

Monometallic and bimetallic nanocomposites M/Al2O3 (M = NiO, Au, NiO + Au) with metal contents of 0.1–0.65 wt % were prepared by the deposition-precipitation and/or impregnation technique. The surface of the composites was investigated by transmission electron microscopy (TEM), EDX, adsorption spectroscopy (AAS), and XAFS. The features of the M/Al2O3 catalysis of the reductive dehydration of ethanol at 350°C were investigated. The activity of NiO/Al2O3 containing 3.5 nm particles of NiO was 130 h−1. A strong size effect in activity was revealed for Au/Al2O3 nanocomposites with activity increasing from 341 to 1384 h−1 as the size of gold particles decreased from 13–20 to 5 nm. The selectivity of 5-nm particles of Au/Al2O3 to the fraction of C3-C8 hydrocarbons was 11.69 mass %. The growth of M particles due to the segregation of individual metals and/or the formation of mixed (Au + NiO) particles resulted in an increase in the selectivity of C3-C8 up to 34.19 mass %. The causes of the observed catalytic phenomena are discussed considering the reaction mechanisms and the specific structure features of the obtained catalysts.

Influence of Reductants on the Catalytic Properties of Nano-Gold Supported on Mesoporous SBA-15 for Glucose Oxidation

Impregnation and deposition-precipitation (DP) methods were employed for the preparation of Au nanoparticles supported on SBA-15, and the influences of various reductants were systematically surveyed. The dispersion and particle size of gold loaded on SBA-15 were determined by XRD, SEM and TEM. It has been found that reductants have effect on the size and dispersion of Au NPs, resulting in different catalytic properties for aerobic oxidation of glucose. The Au NPs on SBA-15 using KBH4as reductant was approximately 5-6 nm, which exhibited excellent catalytic activity.

36 ENDOCYTOSIS UPTAKE OF LIPOSOMES IN UROTHELIUM CELLS DETECTED BY TRANSMISSION ELECTRON MICROSCOPY

INTRODUCTION AND OBJECTIVES: Intravesical liposomes (phospholipid membrane vesicles) have been used as a drug delivery platform and more recently, empty liposomes has shown promise as a treatment of interstitial cystitis/painful bladder syndrome. The exact mechanism for liposome uptake in bladder cells remains to be investigated and in the present study, we investigated the role of endocytosis in uptake of liposomes by urothelium cells. METHODS: Urothelial cell line (UROtsa) were left to adhere and grow for 48h in 100mm petridishes using Dulbecco modified Eagle medium (DMEM) containing 5% v/v fetal bovine serum with incubation at 37°C in a 5% CO2:95% air atmosphere. Liposomes encapsulating colloidal gold particles size 10nm were prepared by thin film hydration method and were incubated with serum free UROtsa cells for 2h either at 37°C or at 4°C. The morphology of liposome–cell interactions at two temperatures was assessed by transmission electron microscopy. RESULTS: Transmission Electron Microscopy (TEM) images located endocytic vesicles containing liposomes inside the UROtsa cells incubated at 37°C [panel B of attached picture] as indicated by dark stain of colloidal gold particles 10nm. In contrast, only extracellular binding was noticed in cells incubated at 4°C[panel A of attached picture]. Thin section electron micrographs show gold–containing liposomes trapped in intracellular vesicles, and in secondary lysosomes incubated at 37°C with colloidal gold liposomes. Absence of liposome internalization at 4°C indicate the need of energy dependent endocytosis as the primary mechanism of entry of liposomes into urothelium. CONCLUSIONS: Based on these observations, we propose that the main route of entry of liposomes into urothelium cells is by endocytosis and ultrastructural study provide evidence for a possible mechanism by which liposomes can act as drug delivery platform. These findings support the usefulness of liposomes in intravesical drug delivery. Source of Funding: NIDDK R01DK083323

Redispersion of Gold Supported on Oxides

Although many gold heterogeneous catalysts have been shown to exhibit significant activity and high selectivity for a wide range of reactions in both the liquid and gas phases, they are prone to irreversible deactivation. This is often associated with sintering or loss of the interaction of the gold with the support. Herein, we report on the use of methyl iodide as a method of dispersing gold nanoparticles supported on silica, titania, and alumina supports. In the case of titania- and alumina-based catalysts, the gold was transformed from nanometer particles into small clusters and some atomically dispersed gold. In contrast, although there was a drop in the gold particle size on the silica support following CH3I treatment, the size remained in the submicrometer range. The structural changes were correlated with changes in the selectivity and activity for ethanol dehydration and benzyl alcohol oxidation. From these observations, it is clear that this treatment provides a method by which deactivated gold catalysts can be reactivated via redispersion of the gold.

Au, @ZrO2 yolk–shell catalysts for CO oxidation: Study of particle size effect by ex-post size control of Au cores

Gold nanoparticles supported on transition metal oxides are found to exhibit a pronounced particle size effect in CO oxidation. However, the preparation of comparable supported gold nanoparticles with different sizes remains challenging, since the catalytic behavior of these materials is very sensitive to the preparation conditions. To overcome this difficulty, Au, @ZrO2 catalysts with gold core sizes between 5 and 15nm were prepared by partial leaching of gold in an ex-post manner. The material obtained offers a unique comparability for particle size effect studies in CO oxidation. No effect of gold particle size was observed in the studied size range.

Gold supported cryptomelane-type manganese dioxide OMS-2 nanomaterials deposited on AISI 304 stainless steels monoliths for CO oxidation

Gold supported on cryptomelane-type OMS-2 catalysts deposited on AISI 304 stainless steels monoliths have been prepared for the first time, characterised and tested in the CO oxidation reaction. An easy and non-conventional method of incorporation of gold to the cryptomelane solid is used. This method allows the preparation of the monolithic catalysts without altering the structural and textural characteristics of the parent OMS-2 material. Although these catalysts do not show an optimal performance for the oxidation of CO, the presence of small gold particles enhances the catalytic performances of the cryptomelane producing promissory CO oxidation catalysts. The non-conventional gold deposition favours a partial loss of K+ into the channels, resulting in an increment of the average oxidation state of manganese which favours the catalytic behaviour of these kinds of materials. This study can be taken as a starting point to obtain very active gold catalysts supported on OMS-2 materials through the optimisation of the gold–support interaction and the decrease in the gold particle size.

In-situ plasma regeneration of deactivated Au/TiO2 nanocatalysts during CO oxidation and effect of N2 content

Driven by excellent CO oxidation capability of gold nanocatalysts at room temperature, a TiO2 supported Au nanocatalyst (Au/TiO2) was synthesized by deposition–precipitation method. To solve the deactivation issue of Au/TiO2 catalyst during CO oxidation, in-situ regeneration by N2/O2 plasma was employed. Pure O2 plasma could reversibly regenerate the deactivated Au/TiO2 catalyst, however, N2 addition resulted in an extra catalyst poisoning during regeneration. The extra poisoning effect was the most severe at 10% N2 and became much weaker at 80% N2. To investigate the formation of any surface poisoning species [NOy]s on Au/TiO2 catalyst, gaseous product of N2/O2 plasma over fresh Au/TiO2 catalyst was on-line analyzed by FT-IR, followed by catalyst characterization with temperature programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS), UV–vis spectroscopy and diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. The Au/TiO2 catalysts before and after plasma regeneration were also measured by transmission electron microscopy (TEM), in order to exclude the poisoning effect arisen from the change in gold particle size or morphology.

Photopyroelectric (PPE) calorimetry of composite materials

The front photopyroelectric configuration was applied to measure the thermal effusivity of some composite materials, inserted as backing layers in the detection cell. The technique is based on the scanning procedure of the coupling fluid’s thickness (TWRC method). Two particular composite materials were selected for investigation: (i) a liquid one: water based nanofluids with gold nanoparticles and (ii) a solid one: urea—fumaric acid (1:1) cocrystal. The thermal effusivity was found independent on the size and concentration of gold particles. Concerning the urea—fumaric acid cocrystal, the thermal effusivity value of the compound is different from the pure starting materials, indicating the formation of the compound.

Activation and Deactivation of Au–Cu/SBA-15 Catalyst for Preferential Oxidation of CO in H2-Rich Gas

This work aims to develop an efficient catalyst for preferential oxidation (PROX) of CO in a H2-rich gas and obtain a clear structure–property relationship of the catalyst. A Au/CuO/SBA-15 catalyst was designed and prepared via a nanoengineering approach in which the metallic particles of average size 3 nm located in the vicinity of CuO particles were highly dispersed on the SBA-15 support. It was found that the CuO particles could reduce the gold (Au) particle size, stabilize the Au particles, and facilitate the activation of molecular oxygen. Although this catalyst is extremely active for the PROX reaction at room temperature and superior to the Au/SBA-15 and CuO/SBA-15 catalysts, it deactivates easily. Clear experimental evidence showed that CuO was reduced to Cu2O and Cu in the reductive reaction gas mixture, and the Cu further combined/dissolved into the Au particles during the reaction. The alloying of Au and Cu not only decreased the catalytic activity of the Au particles but also reduced the ability of CuO to activate molecular oxygen. Fortunately, this alloying process could be reversed via a simple calcination in air to activate the catalyst. The identification of the catalyst structural evolution and this new contributing factor toward the deactivation of the Au catalysts has provided insights into the field of Au catalysis.

Au/CeO2-SBA-15 catalysts for CO oxidation: Effect of ceria loading on physic-chemical properties and catalytic performances

In this work gold catalysts supported over SBA-15 with different CeO2 loadings (5–30 wt%) were prepared, characterized by N2 physisorption analyses, SAXS, XRD, STEM and XPS techniques and their catalytic performances were evaluated in the CO oxidation, chosen as reaction test. Over a selected catalyst, Au/CeO2(20wt%)-SBA-15, the effect of CO2 and of the mixture (CO2+H2O) on the CO conversion to CO2 was also evaluated.Characterizations by SAXS, XRD, STEM and XPS were carried out on selected spent catalysts after CO oxidation.The results were discussed in terms of relationship between morphological, structural, electronic and catalytic properties as a function of the ceria loading. The CO oxidation activity was strongly affected by gold particle size and gold/ceria interface as well. For gold catalysts supported on ceria-doped SBA-15, the oxygen vacancies in ceria likely act as nucleation sites for gold anchoring and stabilization against sintering. The optimum of the catalytic performances was found for 20wt% ceria loading, likely due to the optimum synergistic interaction between highly dispersed defective ceria oxide and nanosized gold.

Gold-assisted E′ centres formation on the silica surface of Au/SBA-15 catalysts for low temperature CO oxidation

SH-functionalized SBA-15 was synthesized and gold nanoclusters were grafted inside its channels. Different portions of such gold-containing material were subjected to a variety of thermal treatments, including calcination in the 300-560 °C temperature range and further treatments under a hydrogen atmosphere at diverse temperatures (up to 600 °C). The resulting materials were thoroughly characterized by CHS elemental analysis, X-ray diffraction, transmission electron microscopy, N2 physisorption and H2 chemisorption, as well as by Raman, NMR, FTIR and EPR spectroscopies, in order to investigate the influence of the temperature and atmosphere of the pretreatment on the gold particle size and oxidation state, the formation of defective E' centres on the silica support and their ability to induce the formation of reactive O2(-) surface species. Catalytic testing for the CO oxidation reaction was carried out in the 40-150 °C temperature range. Significant differences in catalytic behaviour were observed among the catalysts, which are discussed in the light of the characterization results. A mechanism for the "activation" of the non-reducible ("inert") SBA-15 support involving Au(0)→ Au(+) transformation is proposed, where gold metal plays an essential twofold role: it induces the formation of atomic hydrogen by dissociatively adsorbing H2 and triggers the formation of E' centres by transferring an electron to positively charged silicon species.

Characteristics of a silicon Schottky photodetector produced from colloidal gold nanoparticles

A solution-processed silicon Schottky photodetector fabricated by drop cast film of colloidal gold nanoparticles (NPs) onto n-type monocrystalline silicon wafer is demonstrated. The colloidal gold nanoparticles were synthesised by pulsed Nd:YAG laser ablation of gold target in water at room temperature. Optical absorption and transmission electron microscope (TEM) investigation of the produced gold nanoparticles were carried out. TEM investigation showed synthesised gold particle size of 30 nm. The Schottky junction showed good rectification and photoresponse characteristics. The Schottky barrier height of Au NPs Si contact was calculated from current voltage characteristics and found to be 0.92 eV. The photodetector figures of merit are demonstrated and discussed.

Solvothermal synthesis and photocatalytic application of porous Au/TiO2 nanocomposites

Porous titania networks embedded with gold nanoparticles have been synthesized and tested in photocatalytic applications. A solvothermal method was adopted for the in situ reduction of the gold precursor to gold nanoparticles within a preformed TiO2 matrix synthesized by combining a templating technique and sol–gel chemistry. The titania materials were crystalline with anatase crystals of 13 ± 2 nm in diameter; XRD peaks of metallic gold were observed when the gold content was over 1 wt% (gold crystal diameters of 18–25 nm for 1–8 wt% Au). The variation in gold particle size for different gold content was observed by transmission electron microscopy, which also confirmed highly porous structures of the final Au/TiO2 composites. The actual gold content generally increased with the Au content used during synthesis; was enhanced when the pH of the gold precursor solution increased from 2 to 10; and remained relatively constant with changes in the solvothermal temperature (120–180 °C). UV-Visible diffuse reflectance spectra of the Au/TiO2 showed strong absorption at ∼550 nm due to the successful addition of gold nanoparticles to the titania. The number of surface hydroxyl groups was influenced by solvothermal treatment temperature, synthesis pH and gold content. The addition of gold nanoparticles to the TiO2 significantly suppressed recombination of the photon-induced electron–hole pairs. The photocatalytic efficiency of the composites was assessed by monitoring the photocatalytic degradation of methylene blue in aqueous solution; maximum efficiency was more than double that of the pure TiO2 control when using 2.0 to 4.0 wt% gold solutions at pH 7 and optimized solvothermal conditions of 180 °C for 14 h. The photocatalytic efficiency was significantly altered with the addition of gold and was greatly influenced by the anatase crystal size and relative XRD peak intensity, the gold content, and the capability of the material to decrease photon-induced electron–hole recombination.

Preparation of Layered Double Hydroxide (LDHs)<i>-</i>Supported Gold Catalysts and its Activity and Stability for Low-Temperature CO Oxidation

A new type of gold catalysts have been prepared by supporting gold colloids on layered double hydroxide (MgAl-LDHs) carrier at different pH values. CO oxidation reaction at room temperature was used as probe reaction to test the oxidation activity of the gold catalysts, and X-ray diffraction (XRD), X-ray fluorescence (XRF) and high resolution transmission election microscopy (HRTEM) techniques were used to characterize the physical phase, gold loading, morphology as well as mean diameter of gold particles and particle distribution of the represented gold catalyst samples. Influence of pH value during synthesis of the catalysts on the gold loading and oxidation activity of the gold catalysts was studied. Besides these, the stability of the gold catalysts was investigated by thermal treatment and exposure to air and natural light for a long time. The results indicated that gold colloids can be attached on the carrier easily when pH value was controlled between 6-7, and gold loading in the gold catalysts prepared in this condition was above 1.3wt.%. 100% conversion of CO at room temperature can be obtained when the fresh prepared catalysts had been calcined in the air for 2 h at 473 K. The HRTEM images of the gold catalyst showed that the gold particles were highly dispersed on the surface of the carrier, and the average size of the gold particles was 3.2 nm. After thermal treatment at 723 K or storage 4 weeks in air, gold particle size was still kept less than 5nm and the conversion of CO at room temperature over the aged catalysts achieved 100%.

Au/Y-TiO2 Catalyst: High Activity and Long-Term Stability in CO Oxidation

Gold catalysts supported on TiO2 doped with Y (1, 3, and 6 wt % of Y) were prepared by the deposition-precipitation with urea method. Two yttrium precursors were used: yttrium acetylacetonate and yttrium nitrate. The Y-TiO2 supports prepared by the sol–gel method allowed the formation of solids with high specific surface area. The incorporation of yttrium restricted the growth of TiO2 anatase crystals and hindered the transformation to the rutile phase. The average gold particle size was very similar in all the prepared catalysts (∼3 nm). Au/Y-TiO2 catalysts showed higher activity and stability at room temperature than Au/TiO2 in the CO oxidation reaction. This behavior is related to the strong anchoring of the gold particles on the structural defects and oxygen vacancies of the support caused by the doping of the anatase with yttrium. The variation of the yttrium precursor (acetylacetonate or nitrate) did not have an important effect on the catalytic activity or the temporal stability of the catalysts. I...

CuxCryOz mixed oxide as a promising support for gold – The effect of Au loading method on the effectiveness in oxidation reactions

CuxCryOz containing copper–chromium oxide spinel and CuO was used as a support for gold loaded by different methods: deposition–precipitation using KOH, deposition–precipitation using urea and gold–sol method with tetrakis(hydroxymethyl)phosphonium chloride. The technique of modification with gold determined not only the Au particle size (the smallest if gold–sol method was used) but also the number of oxygen vacancies and copper concentration on the surface. All these parameters were considered in the study of CO, glycerol and methanol oxidation. The size of gold particles is a key feature determining the activity in the oxidation of CO. Glycerol oxidation is also sensitive to this parameter but less than CO oxidation. The oxidation of methanol is not influenced by the presence of gold and it occurs on the CuxCryOz support.

Nano-Au/C Catalysts for the Selective Oxidation of Glucose into Gluconate

Au/C catalyst used for the liquid phase selective oxidation of glucose to gluconate was prepared by gold sol method that includes the preparation of metallic colloid by citrate reduction and subsequent immersion by carbon support. The influence of gold particles of different size on the activity of Au/C catalyst was studied. The results show that the catalyst with good dispersed spherical gold particles has higher catalytic activity. After 16 runs, the conversion of glucose selective oxidation can still achieve over 96% under mild reaction conditions.

Mapping the distributions and quantifying the labelling intensities of cell compartments by immunoelectron microscopy: progress towards a coherent set of methods

An important tool in cell biology is the combination of immunogold labelling and transmission electron microscopy (TEM) by which target molecules (e.g. antigens) are bound specifically to affinity markers (primary antibodies) and then detected and localised with visualisation probes (e.g. colloidal gold particles bound to protein A). Gold particles are electron-dense, punctate and available in different sizes whilst TEM provides high-resolution images of particles and cell compartments. By virtue of these properties, the combination can be used also to quantify one or more defined targets in cell compartments. During the past decade, new ways of quantifying gold labelling within cells have been devised. Their efficiency and validity rely on sound principles of specimen sampling, event counting and inferential statistics. These include random selection of items at each sampling stage (e.g. specimen blocks, thin sections, microscopical fields), stereological analysis of cell ultrastructure, unbiased particle counting and statistical evaluation of a suitable null hypothesis (no difference in the intensity or pattern of labelling between compartments or groups of cells). The following approaches are possible: (i) A target molecule can be tested for preferential labelling by mapping the localisation of gold particles across a set of compartments. (ii) Data from wild-type and knockdown/knockout control cells can be used to correct raw gold particle counts, estimate specific labelling densities and then test for preferential labeling. (iii) The same antigen can be mapped in two or more groups of cells to test whether there are experimental shifts in compartment labelling patterns. (iv) A variant of this approach uses more than one size of gold particle to test whether or not different antigens colocalise in one or more compartments. (v) In studies involving antigen translocation, absolute numbers of gold particles can be mapped over compartments at specific positions within polarised, oriented or dividing cells. Here, the current state of the art is reviewed and approaches are illustrated with virtual datasets.

Polymer/Trimer/Metal Complex Mixtures as Precursors of Gold Nanoparticles: Tuning the Morphology in the Solid-State

The pyrolysis of several physical mixtures of AuCl(PPh3) with polymeric [NP(O2C12H8)]n or cyclic N3P3(O2C12H8)3 phosphazenes, formed as solid powders or films with different molar ratios, have been studied under air and at 800 °C. The characterization of the products has shown that the particle size and morphology are strongly dependent on the nature of the phosphazene, the phosphazene/AuCl(PPh3) molar ratio and on the preparation methodology. Gold nanoparticles (NPs) with mean sizes as small as 3.5 nm were obtained from a [NP(O2C12H8)]n/AuCl(PPh3) 1:1 film. The particle morphology was also strongly dependent on the experimentally conditions of the pyrolysis. Powdered materials exhibit a 3-D irregular morphology in the mixture [NP(O2C12H8)]n/AuCl(PPh3) 3:1 film, and gold foams in the 1:1 ratio, both from the [NP(O2C12H8)]n/AuCl(PPh3) as well as N3P3(O2C12H8)3/AuCl(PPh3) mixtures. These results show for the first time the possibility of controlling morphology and size of gold particles obtained by solid-state reactions.