Search Results (10)

The integration of carbon nanostructures with semiconductor nanowires holds significant potential for energy-efficient integrated circuits. However, achieving precise control over the positioning and stability of these interconnections poses a major challenge. This study presents a method for the controlled growth of carbon nanofibers (CNFs) on vertically aligned indium arsenide (InAs) nanowires. The CNF/InAs hybrid structures, synthesized using chemical vapor deposition (CVD), were successfully produced without compromising the morphology of the pristine nanowires. Under optimized conditions, preferential growth of the carbon nanofibers in the direction perpendicular to the InAs nanowires was observed. Moreover, when the CVD process employed iron as a catalyst, an increased growth rate was achieved. With and without the presence of iron, carbon nanofibers nucleate preferentially on the top of the InAs nanowires, indicating a tip growth mechanism presumably catalysed by a gold-indium alloy that selectively forms in that region. These results represent a compelling example of controlled interconnections between adjacent InAs nanowires formed by carbon fibers. Full article

As an alternative to noble metal hydrogenation catalysts, pure molybdenum carbide displays unsatisfactory catalytic activity for arene hydrogenation. Precious metals such as palladium, platinum, and gold are widely used as additives to enhance the catalytic activities of molybdenum carbide, which severely limits its potential applications in industry. In this paper, iron-promoted molybdenum carbide was prepared and characterized by various techniques, including in situ XRD, synchrotron-based XPS and TEM. while the influence of Fe addition on catalytic performance for toluene hydrogenation was also studied. The experimental data disclose that a small amount of Fe doping strongly enhances catalytic stability in toluene hydrogenation, but the catalytic performance drops rapidly with higher loading amounts of Fe. Full article

The green synthesis of nanoscale materials is of special interest to researchers all over the world. We describe a simple, robust, inexpensive, and environmentally friendly approach to the synthesis of gold, silver, and iron nanoparticles using a variety of biomolecules/phytochemicals as potential reducers and stabilizers. The green approach to the controlled synthesis of nanoparticles with different morphologies is based on the use of plant extracts. Green synthesized nanoparticles can be used as catalysts, photocatalysts, adsorbents, or alternative agents for the elimination of various organic dyes. The kinetic enhancement of nanoparticles for the degradation/removal of dyes could provide significant and valuable insights for the application of biochemically functionalized nanoparticles in engineering. In this review, current plant-mediated strategies for preparing nanoparticles of gold, silver, and iron are briefly described, and morphologically dependent nanoparticles for the degradation of organic pollutants in wastewater are highlighted. Overall, the approach presented in the article supports environmental protection and is a promising alternative to other synthesis techniques. Full article

The photocatalytic degradation of potassium hexacyanoferrate (III) was assessed in a bench-scale compound parabolic collectors (CPC) reactor assisted with a light-emitting diode (LED) UV-A source emitting at 365 nm, and using a modified TiO₂ as a catalyst via the hydrothermal treatment of commercial Aeroxide P25. The experiments were performed under oxic and anoxic conditions in order to observe a possible reduction of the iron. The modified TiO₂ showed a specific surface area 2.5 times greater than the original Aeroxide P25 and its isotherm and hysteresis indicated that the modified catalyst is mesoporous. The bandgap energy (E_g) of the modified TiO₂ increased (3.34 eV) compared to the P25 TiO₂ band gap (3.20 eV). A specific reaction rate constant of 0.1977 min⁻¹ and an electrical oxidation efficiency of 7.77 kWh/m³ were obtained in the photocatalytic degradation. Although the TiO₂ P25 yields a photocatalytic degradation 9.5% higher than that obtained one with the modified catalyst (hydrothermal), this catalyst showed better performance in terms of free cyanide release. This last aspect is a significant benefit since this can help to avoid the pollution of fresh water by reusing the treated wastewater for gold extraction. A photocatalytic degradation of the cyanocomplex of 93% was achieved when the process occurred under oxic conditions, which favored the removal. Summarizing, the hydrothermal method could be a promising treatment to obtain TiO₂-based catalysts with larger specific areas. Full article

Surface-initiated atom transfer radical polymerization (SI-ATRP) is a powerful tool that allows for the synthesis of organic–inorganic hybrid nanomaterials with high potential applications in many disciplines. This review presents synthetic achievements and modifications of nanoparticles via SI-ATRP described in literature last decade. The work mainly focuses on the research development of silica, gold and iron polymer-grafted nanoparticles as well as nature-based materials like nanocellulose. Moreover, typical single examples of nanoparticles modification, i.e., ZnO, are presented. The organic–inorganic hybrid systems received according to the reversible deactivation radical polymerization (RDRP) approach with drastically reduced catalyst complex concentration indicate a wide range of applications of materials including biomedicine and microelectronic devices. Full article

Goethite- and hematite-supported highly dispersed gold catalysts for carbon monoxide oxidation were synthesized by gold precursor adsorption onto the support materials in self-generated alkaline solutions. The support materials were prepared by reacting iron nitrate with excess sodium hydroxide. The residual minor alkali incorporated into the support could provide suitable alkaline conditions at approximately pH 8 for the hydrolysis of tetrachloroaurate anions and the subsequent adsorption process. Gold species underwent autoreduction to achieve activation during the synthesis. An increase in pH or temperature to 80 °C decreased the gold loading of the catalysts. The optimal catalysts could achieve complete oxidation of carbon monoxide at −20 °C. Full article

Gold-iron oxide (Au/FeO_x) is one of the highly active catalysts for CO oxidation, and is also a typical system for the study of the chemistry of gold catalysis. In this work, two different types of iron oxide supports, i.e., hydroxylated (Fe_OH) and dehydrated iron oxide (Fe_O), have been used for the deposition of gold via a deposition-precipitation (DP) method. The structure of iron oxide has been tuned by either selecting precipitated pH of 6.7–11.2 for Fe_OH or changing calcination temperature of from 200 to 600 °C for Fe_O. Then, 1 wt. % Au catalysts on these iron oxide supports were measured for low-temperature CO oxidation reaction. Both fresh and used samples have been characterized by multiple techniques including transmission electron microscopy (TEM) and high-resolution TEM (HRTEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), X-ray absorption near edge structure (XANES) and temperature-programmed reduction by hydrogen (H₂-TPR). It has been demonstrated that the surface properties of the iron oxide support, as well as the metal-support interaction, plays crucial roles on the performance of Au/FeO_x catalysts in CO oxidation. Full article

Gold nanoparticles have been proven to act as efficient catalysts for chemical reactions, such as oxidation and hydrogen production. In this review we focus on a different aspect of the catalysis of gold nanoparticles; single-walled carbon nanotube (SWCNT) synthesis. This is not a traditional meaning of catalytic reaction, but SWCNTs cannot be synthesized without nanoparticles. Previously, gold was considered as unsuitable metal species as the catalyst of SWCNT synthesis. However, gold nanoparticles with diameters smaller than 5 nm were found to effectively produce SWCNTs. We discuss the catalysis of gold and related metals for SWCNT synthesis in comparison with conventional catalysts, such as iron, cobalt, and nickel. Full article

A novel preparation method was developed for the preparation of gold/iron oxide supported catalysts using the bimetallic carbonyl cluster salts [NEt₄]₄[Au₄Fe₄(CO)₁₆] and [NEt₄][AuFe₄(CO)₁₆] as precursors of highly dispersed nanoparticles over different supports. A series of catalysts with different metal loadings were prepared and tested in the complete oxidation of dichlorobenzene, toluene, methanol and in the preferential oxidation of CO in the presence of H₂ (PROX) as model reactions. The characterization by BET, XRD, TEM, H₂-TPR, ICP-AES and XPS point out the way the nature of the precursors and the thermal treatment conditions affected the dispersion of the active phase and their catalytic activity in the studied reactions. Full article

Low-temperature water-gas shift reaction (WGS) using gold catalyst is expected to be an attractive technique to realize an efficient on-site hydrogen production process. In this paper, Au/Fe₃O₄ catalysts for promoting the WGS below 150 °C were developed by a preliminary reduction of Au/iron oxide (Fe³⁺) catalyst utilizing high reactivity of Au nano-particles. The reduction was conducted under a CO, H₂, or CO/H₂O stream at either 140 or 200 °C, and the effect of reduction conditions on the characteristics of the Au/Fe₃O₄ catalyst and on the catalytic activity in WGS at 80 °C was investigated. The reaction progress during the pre-reduction treatment was qualitatively analyzed, and it was found that the iron oxide in Au/Fe₂O₃ calcined at 200 °C was easily reduced to Fe₃O₄ phase in all reduction conditions. The reduction conditions affected the characteristics of both Au and iron oxide, but all of the reduced catalysts had small Fe₃O₄ particles of less than 20 nm with Au particles on the surface. The surface area and content of cationic Au were high in the order of CO, H₂, CO/H₂O, and 140, 200 °C. In the WGS test at 80 °C using the developed catalysts, the activities of the catalysts pre-reduced by CO at 140 or 200 °C and by H₂ at 140 °C were very high with 100% CO conversion even at such a low temperature. These results indicated that factors such as higher surface area, crystallized Fe₃O₄, and cationic Au content contributed to the catalytic activity. Full article