Metal Precursor Concentration Research Articles

Degradation of Acid Blue 29 in visible light radiation using iron modified mesoporous silica as heterogeneous Photo-Fenton catalyst

The evaluation of heterogeneous Fenton degradation on dye pollutant, Acid Blue 29 (AB29), has been investigated. The solid catalyst prepared by both sol–gel and incipient wetness impregnation methods was developed by occlusion of Fe3+ ions on synthesized mesoporous silica from sodium silicate. The prepared catalysts were characterized for their textural and surface morphology. High concentration of soluble metal precursor with 8.0wt% Fe3+ can be easily deposited on silica. The results showed that the Fe-SiO2 catalyst demonstrated good performance in the degradation of 50ppm Acid Blue 29 (AB29) which was nearly completed in 100min under visible light irradiation with optimum operating conditions at 0.4g Fe-SiO2/L, pH 3.0 and 10mM H2O2. A possible mechanism on visible light irradiated Fenton process was proposed. The catalyst is reusable over four consecutive cycles and minimal leaching of iron ions (<0.5ppm) was observed.

In Vitro Biosynthesis of Metal Nanoparticles in Microdroplets

We report the use of a hydrogel polymer, recombinant Escherichia coli cell extracts, and a microdroplet-based microfluidic device to fabricate artificial cellular bioreactors which act as reactors to synthesize diverse metal nanoparticles (NPs). The combination of cell extracts, microdroplet-based microfluidic device, and hydrogel was able to produce a mass amount of artificial cellular bioreactors with uniform size and shape. For the first time, we report the alternating generation of microdroplets through one orifice for the fabrication of the artificial cellular reactors using the cell extract as inner cellular components and hydrogel as an artificial cellular membrane. Notably, the hydrogels were able to protect the encapsulated cell extracts from the surrounding environment and maintain the functionality of cellular component for the further cellular bioreactor applications. Furthermore, the successful applications of the fabricated artificial cellular bioreactors to synthesize various NPs including quantum dots, iron, and gold was demonstrated. By employing this microfluidic technique, the artificial cellular bioreactors could be applicable for the synthesis of diverse metal NPs through simple dipping of the reactors to the metal precursor solutions. Thus, the different size of NPs can be synthesized through controlling the concentration of metal precursors. This artificial cellular bioreactors offer promising abilities to biofriendly ways to synthesis diverse NPs and can be applicable in chemical, biomedical, and bioengineering applications.

Drying of supported catalysts for low melting point precursors: Impact of metal loading and drying methods on the metal distribution

Supported metal catalysts are used in many industrial processes. Experiments have shown that the metal distribution within the support may be greatly affected by the drying conditions. In this work, we have developed a theoretical model to predict the drying process for high metal load conditions; this was accomplished by building upon a model that was established for low metal loadings. A number of additional phenomena must be accounted for under high metal loadings including the effect of metal precursor concentration on the solution density, solution viscosity, water vapor pressure and solution surface tension. The model predictions of the metal distribution are compared with experimental measurements for a Nickel/Alumina catalyst. It is found that the drying mechanisms for low metal loading conditions and high metal loading conditions are quite different. The constant drying rate stage observed for low metal concentrations does not exist for high metal concentrations. For low metal loadings, the adsorption strength and distribution of liquid in the support must be considered in the model in order to get good experimental agreement. For the conditions we considered, an egg-shell profile was observed for low metal loadings, and the egg-shell profile was enhanced with an increase in the initial metal precursor concentration. For a metal precursor with a high concentration and a low melting point, the metal precursor is dissolved or molten in the liquid phase during drying. In this case, adsorption strength and distribution of liquid in the support are not important, and the metal distribution after drying reaches a nearly uniform profile if the initial metal concentration is above a critical value. Both microwave drying and regular oven drying have been examined in this work. During microwave drying, the catalyst samples can be heated volumetrically so microwave drying resulted in a significantly more uniform metal distribution than regular oven drying.

Controlled Synthesis and Characterization of Nobel Metal Nanoparticles

In this work, monodispersed, well-shaped platinum (3.2 - 6.4 nm), rhodium (2.4 - 5.1 nm), palladium (3.2 - 5.3 nm) nanoparticles capped with poly(vinylpyrrolidone) were synthesized by a polyol reduction method in an ethylene glycol solution at temperature of 190℃. The influences of synthetic parameters on the size and morphology of the noble metal nanoparticles have been systematically investigated. The noble metal nanoparticles were characterized by means of UV-vis, laser scattering particle size distribution analysis (LSPSDA) and transmission electron microscopy (TEM). The experimental results showed that the particle size of metals nanoparticles, the morphology of which was spherical, increased with the raise of metal precursor concentration as well as the amount of PVP. The optimal molar ratio of PVP/metal and metal precursor concentration for the fabrication of Pt, Rh, and Pd nanoparticles with uniform distribution were 10 and 0.1 mM, respectively. The morphologies of the Rh nanoparticles with the size of 5.1 nm were polygons, including hexagons, pentagons, and triangles.

One-pot synthesis of gold/poly(3,4-ethylendioxythiophene) nanocomposite

In this paper, we report the preparation of highly stable gold nanoparticles/poly(3,4-ethylendioxythiophene) nanocomposites by a one-pot chemical route in aqueous medium without surfactants to increase the solubility of the monomer (3,4-ethylendioxythiophene, EDOT) or to stabilize gold nanoparticles (Au NPs). The generation of the nanocomposite was followed by UV–Visible transmission spectroscopy combined with multivariate curve resolution alternating least squares analysis to deconvolute the individual spectra of the different species generated in the synthesis: oligomers, polymer and gold nanoparticles. The plasmon band observed at 530 nm during the synthesis step indicates the generation of gold nanoparticles. The influence of monomer and metal precursor concentration and their concentration ratios on Au NP size were analyzed. The electrochromic properties of the composite were investigated by UV–Visible absorption spectroelectrochemistry, being mainly related to polymer oxidation and reduction. The main difference observed is the hypsochromic shift of the polymer spectra due to the gold nanoparticles inside the polymer. Multicyclic spectroelectrochemical experiments evidence a high stability and adhesion of the nanocomposite.

Thin film growth of yttria stabilized zirconia by aerosol assisted chemical vapor deposition

Thin film growth of yttria stabilized zirconia (YSZ) using atmospheric aerosol assisted chemical vapor deposition (AA-CVD) from β-diketonates is studied. The influence of nature and concentration of metal precursors and solvents on thin film growth, microstructure and composition is investigated as a function of deposition temperature. AA-CVD is able to produce smooth and homogeneous YSZ thin films of controlled thickness and stoichiometry. Amorphous, nanocrystalline or columnar microstructures can be obtained at deposition temperatures between 300 and 650 °C. In the same temperature regime, a transition from surface reaction to diffusion controlled film growth is observed. For applications as gas separating membranes, e.g. for micro-solid oxide fuel cell electrolytes, randomly oriented nanocrystalline microstructures with grain sizes in the range of 10 nm are promising.

Preparation of Nanoporous MgAl2O4 by Combined Utilization of Sol-Gel Process and Combustion of Biorenewable Oil

ABSTRACTNanoporous MgAl2O4 particulates with high porosities were successfully prepared from sol-gel reactions, solvent exchange with castor oil and subsequent combustion and calcination at 700 °C. The products were crystalline and semitransparent. Changes in the metal precursor concentrations allowed control of pore volumes from 0.7 to 1.1 cm3/g and average pore sizes from 14 to 19 nm. The specific surface areas are about 200 m2/g regardless of the precursor concentrations. After heating at 1000 °C for 10 hours, the products kept about 70% of their original pore volume and about 60% of the original surface area. Heating at 1100 °C caused a drastic reduction of pore volume and surface area to 40 and 36%, respectively, as the average particle size increased to 23 nm.

Pt-based composite nanoparticles for magnetic, catalytic, and biomedical applications

This feature article highlights the recent advances in the synthesis of Pt-based binary alloy and core–shell nanoparticles (NPs) for magnetic, catalytic and biomedical applications. These composite NPs are made by thermal decomposition and reduction of metal precursors in a high boiling point organic solvent with their size, shape, composition and shell thickness controlled by metal precursor concentrations, surfactant concentrations and reaction temperatures. The as-synthesized alloy NPs adopt typically the face centered cubic (fcc) structure and can be further converted into the face centered tetragonal (fct) structure upon high temperature annealing. The NP size, shape, composition and structure dependent magnetism and catalysis are further illustrated. The studies show that the fct structured NPs are ferromagnetic and are promising components for magnetic data storage media, and that the core–shell NPs are better catalysts for fuel cell reactions with much enhanced activity and durability, and that the fcc structured FePt NPs have great potential for multimodality imaging and for therapeutic applications.

Synthesis and characterization of the Pt/SiO2 nanocomposite by the sol-gel method

The silica supported platinum nanoparticles was synthesized by using the sol-gel method. The possibility of using diamminedinitro platinum (II) as Pt precursor and effect of metal precursor concentration on the final Pt nanoparticle size was investigated. A stable silica sol was prepared via hydrolysis of tetraethyl orthosilicate (TEOS) as a metal alcoxide and condensation reaction. Subsequently, diamminedinitro platinum (II) was added to sol to form the Pt/silica sol. After drying and calcination of the sol, the Pt/SiO2 nanocpmposite has been obtained. Crystallographic information and crystalline size of the synthesized Pt/SiO2 were determined by X-ray diffraction (XRD) method. Morphology of the nanoparticles and hydrogen-bonding interaction between silanol groups and amine ligands were characterized by SEM and Fourier transform infrared (FTIR) spectra, respectively. Transmission Electron Microscopy (TEM) was employed in evaluating the distribution and size of the platinum nanoparticles in the silica.

Palladium crystals of various morphologies for SERS enhancement

Palladium (Pd) nanostructures with urchin-like, hemispherical, flower-like, and plate-like morphologies were controllably deposited on silicon substrates in aqueous hydrogen fluoride (HF) solution at room temperature. The morphology of the Pd nanostructures changed from urchin-like to hemispherical and flowerlike in the presence of polyvinyl pyrrolidone (PVP, MW = 55 000) and cetyltrimethylammonium bromide (CTAB), respectively. The Pd nanostructures were characterized by transmission electron microscopy, high-resolution transmission electron microscopy, field emission scanning electron microscopy, energy-dispersive X-ray, and X-ray diffraction. The size and shape of palladium nanostructures were investigated as a function of metal precursor concentration, reaction time and organic additive concentration. The possible formation mechanisms were discussed. In addition, the morphology-dependent surface-enhanced Raman scattering (SERS) of the as-synthesized Pd nanostructures were investigated. The results showed that urchin-like Pd nanostructures had the highest SERS activity than the other Pd nanostructures for Rhodamine 6G (R6G) probe molecules.

Ascorbate-Assisted Growth of Hierarchical ZnO Nanostructures: Sphere, Spindle, and Flower and Their Catalytic Properties

A simple solution-based method to prepare mainly flowerlike zinc oxide (ZnO) nanostructures using the ascorbate ion as a shape-directing/capping agent at relatively low temperature (ca. 30 and 60 degrees C) was described. However, we observed that different shapes of hierarchical ZnO nanostructures such as flowerlike, spindlelike, and spherical could be obtained with an increase in the synthesis temperature from 60 to 90 degrees C. The effects of other organic capping agents on the shape of hierarchical ZnO nanostructures were also studied. FTIR, FESEM, and XRD characterization were performed on the formed ZnO nanostructures to understand the role of ascorbate in the growth of flowerlike morphology. The nucleation and growth process can regulate by changing the metal precursor and ascorbate ion concentrations. We were able to identify intermediate nanostructures such as spherical/quasi-spherical and spindle that are very much on the pathway of formation of large, flowerlike ZnO nanostructures. Electron microscopy results indicated that these spherical/quasi-spherical ZnO nanoparticles might aggregate through oriented attachment to produce spindlelike and flowerlike nanostructures. On the basis of these results, a possible growth mechanism for the formation of flowerlike ZnO nanostructures was described. The optical properties of these differently shaped ZnO nanostructures were also described. The catalytic activities of the as-synthesized spherical and flowerlike ZnO nanostructures were tested in the Friedel-Crafts acylation reaction of anthracene with benzoyl chloride. The catalysis results indicated that the catalytic activity of flowerlike ZnO nanostructures is slightly higher than the spherical counterpart.

Carbon supported Pd–Co–Mo alloy as an alternative to Pt for oxygen reduction in direct ethanol fuel cells

Carbon black (CDX975) supported Pd and Pd–Co–Mo alloy nanoparticles are prepared by the reduction of metal precursors with hydrazine in reverse microemulsion of water/Triton-X-100/propanol-2/cyclohexane. The as-synthesized Pd–Co–Mo/CDX975 is heat treated at 973, 1073 and 1173 K to promote alloy formation. The prepared materials are characterized by powder XRD and EDX. Face-centred cubic structure of Pd is evident from XRD. The chemical composition of the respective elements in the catalysts is evaluated from the EDX analysis and observed that it is in good agreement with initial metal precursor concentrations. Oxygen reduction measurements performed by linear sweep voltammetry indicate the good catalytic activity of Pd–Co–Mo alloys compared to Pd. This is due to the suppression of (hydr)oxy species on Pd surface by the presence of alloying elements, Co and Mo. Among the investigated catalysts, heat-treated Pd–Co–Mo/CDX975 at 973 K exhibited good ORR activity compared to the catalysts heat treated at 1073 and 1173 K. This is due to the small crystallite size and high surface area. Rotating disk electrode (RDE) measurements indicated the comparable ORR activity of heat-treated Pd–Co–Mo/CDX975 at 973 K with that of commercial Pt/C. Kinetic analysis reveals that the ORR on Pd–Co–Mo/CDX975 follows the four-electron pathway leading to water. Moreover, Pd–Co–Mo/CDX975 exhibited substantially higher ethanol tolerance during the ORR than Pt/C. Good dispersion of metallic nanoparticles on the carbon support is observed from HRTEM images. Single-cell direct ethanol fuel cell tests indicated the comparable performance of Pd–Co–Mo/CDX975 with that of commercial Pt/C. Stability under DEFC operating conditions for 50 h indicated the good stability of Pd–Co–Mo/CDX975 compared with that of Pt/C.

IN SITU FORMATION OF COBALT NANOCLUSTERS IN SOL–GEL SILICA FILMS FOR SINGLE-WALLED CARBON NANOTUBE GROWTH

A facile method was developed for in situ formation of Co nanoclusters in sol–gel silica thin films spin-coated on Si wafers. The size and density of Co nanoclusters can be controlled by spin-coating speeds, annealing methods, reduction temperatures under H 2, and metal precursor concentrations in tetraethylorthosilicate solutions. The optimized preparation condition, spin-coating speed of 9000 rpm, annealing at 500°C in air followed by reduction at 800°C in H 2, resulted in silica films as thin as 60 nm and Co nanoclusters with a mean diameter of 1.5 nm. Morphological and chemical characteristics of thin films and nanoclusters were studied by atomic force microscopy and X-ray photoelectron spectroscopy, respectively. Subsequently, these Co nanoclusters were successfully used to grow SWCNTs by CO decomposition. Film containing Co monometallic clusters produced SWCNTs of 1.3 nm in diameter, whereas film having Co/Mo bimetallic clusters produced SWCNTs of 0.9 nm. This sol–gel approach allowed not only easy catalyst patterning on a thin film but also a fine-tuning of SWCNT properties, e.g., diameter.

Solvothermal synthesis of crystalline nickel oxide nanoparticles

Nickel oxide (NiO) nanoparticles were synthesized via a solvothermal reaction with nickel(II) acetylacetonate as the metal containing precursor and 2-butanone (methyl ethyl ketone, MEK) as the solvent. The particles were characterized using X-ray diffraction, electron microscopy, Brunauer–Emmett–Teller (BET) surface area measurements and thermal gravimetric analysis (TGA) to determine that the crystal structure, particle size, and the presence of residual organic material upon completion of the reaction. The effect of varying the reaction temperature, time and metal precursor concentration were investigated. A range of optimal reaction conditions; defined here as a high yield, low residual organic content; were determined. A particle size in the range of 5.5–6.5 nm was observed for the optimal reaction conditions. The formation of metallic Ni was also observed for reactions carried out at 225 °C and time durations longer than 24 h. The reaction mechanism for the formation of NiO nanoparticles was investigated using mass spectrometry and a proposed pathway based on a keto-enol tautamerization is presented.

Solution-phase synthesis of nickel phosphide single-crystalline nanowires

We report on the synthesis of single-crystalline Ni 2P nanowires via a solution-phase approach using nickel (II) acetylacetonate as a metal precursor and trioctylphosphine as a phosphorus source. Powder X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) were used to characterize the crystalline structure, morphology and composition of the as-synthesized nanowires. The results show that the as-synthesized nanowires have a uniform width of ca. 6 nm, and a length that can vary from tens of nanometers to several hundred nanometers. These nanowires possess a hexagonal crystalline phase, and predominantly grow along the c-axis. The formation of one-dimensional nanostructures has a close relationship with the concentration of metal precursor and surfactants, and the synthetic methodologies.

Influence of porous morphology on optical dispersion properties of template free mesoporous titanium dioxide (TiO 2) films

This paper focuses the influence of porous morphology on the microstructure and optical properties of TiO 2 films prepared by different sol concentration and calcination temperatures. Mesoporous TiO 2 thin films were prepared on the glass substrates by sol–gel dip coating technique using titanium (IV) isopropoxide. Porous morphology of the films can be regulated by chemical kinetics and is studied by scanning electron microscopy. The optical dispersion parameters such as refractive index ( n), oscillator energy ( E d), and particle co-ordination number ( N c) of the mesoporous TiO 2 films were studied using Swanepoel and Wemple–DiDomenico single oscillator models. The higher precursor concentration (0.06 M), films exhibit high porosity and refractive index, which are modified under calcination treatment. Calcinated films of low metal precursor concentration (0.03 M) possess higher particle co-ordination number ( N c = 5.05) than that of 0.06 M films ( N c = 4.90) due to calcination at 400 °C. The lattice dielectric constant ( E ∞) of mesoporous TiO 2 films was determined by using Spintzer model. Urbach energy of the mesoporous films has been estimated for both concentration and the analysis revealed the strong dependence of Urbach energy on porous morphology. The influence of porous morphology on the optical dispersion properties also has been explained briefly in this paper.

Organic Ligand-Mediated Synthesis of Shape-Tunable Gold Nanoparticles: An Application of Their Thin Film as Refractive Index Sensors

A simple wet-chemical in situ reduction method has been developed for the synthesis of shape-tunable gold nanoparticles (GNPs) using 1,4,8,11-tetraazacyclotetradecane (cyclam) as a reducing-cum-stabilizing agent. The growth of different shaped GNPs occurred at ambient temperature in the absence of any added stabilizers/templates. Transmission electron microscopic analysis of the as-prepared GNPs shows that an increase in the metal precursor concentration in the reaction medium resulted in the formation of triangular or hexagonal nanoplates along with spherical GNPs. The addition of foreign metal ions like Ni2+ or Cu2+ in the reaction medium also affects the shape of the formed GNPs. Mechanistic and kinetic studies of GNPs formation have been studied by UV−vis spectroscopy. We have also demonstrated that the GNPs could easily be deposited on unfunctionalized glass and quartz substrates by a simple dip-coating technique to fabricate thin films that were also characterized by UV−vis spectroscopic and high-re...

RNA-mediated metal-metal bond formation in the synthesis of hexagonal palladium nanoparticles.

RNA sequences have been discovered that mediate the growth of hexagonal palladium nanoparticles. In vitro selection techniques were used to evolve an initial library of approximately 10(14) unique RNA sequences through eight cycles of selection to yield several active sequence families. Of the five families, all representative members could form crystalline hexagonal palladium platelets. The palladium particle growth occurred in aqueous solution at ambient temperature, without any endogenous reducing agent, and at low concentrations of metal precursor (100 micromolar). Relative to metal precursor, the RNA concentration was significantly lower (1 micromolar), yet micrometer-size crystalline hexagonal palladium particles were formed rapidly (7.5 to 1 minutes).

Synthesis of nanostructured materials in supercritical ammonia: nitrides, metals and oxides

In this study, the synthesis of nanostructured particles of nitrides (Cr2N, Co2N, Fe4N, Cu3N, Ni3N), metal (Cu) and oxides (Al2O3, TiO2, Ga2O3) by using supercritical ammonia in the reaction medium is described. The elaboration process is based on the thermal decomposition of metal precursors in a supercritical ammonia–methanol mixture at a range of temperatures between 170 and 290 °C at about 16 MPa. Nitrides are obtained at relatively low temperatures in comparison with classical processes. It is shown that the chemical composition of the produced materials can be controlled by the adjustment of process operating conditions (pressure, temperature, metal precursor concentration and residence time in the elaboration reactor) and by the knowledge of the Gibbs free energy of oxide formation of the studied metal.

Conditions of Formation of Copper Phyllosilicates in Silica-Supported Copper Catalysts Prepared by Selective Adsorption

It is shown that, during the preparation of Cu/SiO2 samples by selective adsorption of copper tetraammine complex [Cu(NH3)4(H2O)2]2+ on silica, two types of supported CuII species form: grafted CuII ions and copper phyllosilicate. The formation of grafted CuII ions results from electrostatic adsorption of CuII ammine complex cations in solution onto the surface of silica particles negatively charged due to the high solution pH. Grafting of CuII ions occurs during the subsequent drying step. The formation of copper phyllosilicate takes place in solution. It results from a reaction between silicic acid arising from silica dissolution and [Cu(OH)2(H2O)4]0 complex in solution. Both CuII species lead to small metal particles after reduction. Several preparation parameters were investigated in this paper: the metal precursor concentration, the pH of the precursor solution, the solution/silica contact time, and the addition of ammonium nitrate to the precursor solution. The amount of copper phyllosilicate depe...