Articles de revues sur le sujet « Gold/Gallium/Calcium catalysts »

In order to reconstruct the crystallization conditions of the gallium epidote analogue Ca2Al2Ga(Si3O12)(OH) from the Tykotlova gold-sulphide ore occurrence in the Polar Urals, for the first time, a series of epidote-gallium epidote solid solutions were synthesized. The parameters of the unit cell were calculated for these phases, and IR and Raman spectra were obtained. It was concluded that gallium is predominantly in position M3, which allows us to consider the gallium epidote as an independent mineral specie. Stable Ga-containing aluminosilicate and silicate phases in the Ca-Ga-Al-Fe-Si-O system were obtained as by-products of the synthesis (analogs of the grossular-andradite garnet and calcium feldspar).

Gold supported hydroxyapatite (HA) and calcium deficient hydroxyapatite (CDHA) was studied for the room temperature CO oxidation. Nanostructured gold catalyst has been prepared by deposition precipitation method, whereas HA was synthesized by microwave synthesis. Inorder to understand the influence of surface properties of HA, support HA was synthesized with different Ca/P ratios (1.67, 1.62, 1.57, 1.534 and 1.5). The gold supported catalysts were characterized by XRD, BET, ICP-OES and TEM. Typical results indicate that gold supported 1.57 HA shows higher activity compared to other HA catalysts (1.67, 1.62, 1.534 and 1.5) which may be due to the presence of optimum number of acidic and basic sites.

Gold catalysts based on SBA-15, NbSBA-15 (Nb introduced in one pot synthesis) and Nb₂O₅/SBA-15 (prepared by impregnation of SBA-15) were doped with calcium species introduced before Au loading and were tested in gas-phase methanol oxidation.

Non-coking stable alkaline earth metal (M = Mg, Sr, and Ba) modified Ga-NaY catalysts were prepared by ionic-exchange and tested in oxidative dehydrogenation (ODH) of n-octane using air as the source of oxygen. The role of the alkaline earth metals in NaY was to poison the acid sites while enhancing the basic sites responsible for ODH. The exception was the calcium modified NaY, which was more acidic than the parent NaY, coking and unstable under the ODH conditions used in this study. The role of gallium was to enhance the dehydrogenation pathway and improve the stability of NaY. The sequence of increasing selectivity to octenes followed the order: CaGa-NaY < Ga-NaY< MgGa-NaY < SrGa-NaY < BaGa-NaY. The highest octene selectivity obtained was 37% at iso-conversion of 6 ± 1% when BaGa-NaY was used at a temperature of 450 °C. The activity of the catalysts was directly proportional to the reducibility of the catalysts, which is in agreement with expectations.

AbstractThe bio-relevant metals (and derived compounds) of the Periodic Table of the Elements (PTE) are in the focus. The bulk elements sodium (Na), potassium (K), magnesium (Mg), and calcium (Ca) from the s-block, which are essential for all kingdoms of life, and some of their bio-activities are discussed. The trace elements of the d-block of the PTE as far as they are essential for humans (Mn, Fe, Co, Cu, Zn, Mo) are emphasized, but V, Ni, Cd, and W, which are essential only for some forms of life, are also considered. Chromium is no longer classified as being essential. From the p-block metals only the metalloid (half-metal) selenium (Se) is essential for all forms of life. Two other metalloids, silicon and arsenic, are briefly mentioned, but they have not been proven as being essential for humans. All metals of the PTE and a plethora of their compounds are used in industry and many of them are highly toxic, like lead (Pb), which is discussed as a prime example. Several metals of the PTE, that is, their ions and complexes, are employed in medicine and we discuss the role of lithium, gallium, strontium, technetium, silver, gadolinium (the only f-block element), platinum, and gold.

Fine chemistry historically relies on the fossil fuel industry, implying oil extraction and refining [1]. The rarefaction of this resource and adverse environmental consequences of its extraction motivate research for alternative sources of chemicals. Low carbon footprint chemicals can be synthesized from nonedible biomass waste [2]; cellulose extracted from biomass can therefore play an important role, being a clean and widely accessible carbon source. One can extract D-Glucose (units that constitute cellulose) from cellulose and obtain numerous chemicals of interest, such as sorbitol [3][4] or gluconic acid [5][6] (gluconate in alkaline media), respectively by selective reduction or oxidation. Searching for high-performance non-enzymatic catalysts to perform such reactions brought us to study the activity and selectivity of gold and nickel in alkaline media. At the anode, results from differential electrochemical mass spectrometry (DEMS) seem to indicate that the glucose oxidation on a gold surface initiates by its dissociative adsorption (dehydrogenation): the dihydrogen (H2) produced likely originates from the formation of metastable H adsorbates (Had) [7] that diffuse onto the surface [8] and recombine into H2. In parallel, the adsorbed glucose oxidizes into value-added products such as gluconic acid, through a mechanism proposed from in situ (Fourier Transform InfraRed spectroscopy, FTIR) and ex situ (products analysis by High Performance Liquid Chromatography, HPLC) observations, and on the evaluation of the number of exchanged electrons using the rotating ring disk electrode (RRDE). Confronting the experimental data to a microkinetics model enables to validate the proposed mechanism and to estimate the kinetics rate constants. At the cathode, the glucose reduction reaction (GRR) into sorbitol competes with the hydrogen evolution reaction (HER). The HER activity of nickel strongly depends on its surface oxidation state [9], which can be tuned to search the best selectivity towards sorbitol. Combining high value-added compounds production with H2 as by-product allows to improve the overall energy efficiency of this electrolysis. [1] P. G. Levi and J. M. Cullen, “Mapping global flows of chemicals: from fossil fuel feedstocks to chemical products,” Environ. Sci. Technol., vol. 52, no. 4, pp. 1725–1734, 2018, doi: 10.1021/acs.est.7b04573. [2] D. Saygin, D. J. Gielen, M. Draeck, E. Worrell, and M. K. Patel, “Assessment of the technical and economic potentials of biomass use for the production of steam, chemicals and polymers,” Renew. Sustain. Energy Rev., vol. 40, pp. 1153–1167, 2014, doi: 10.1016/j.rser.2014.07.114. [3] B. García, J. Moreno, G. Morales, J. A. Melero, and J. Iglesias, “Production of sorbitol via catalytic transfer hydrogenation of glucose,” Appl. Sci., vol. 10, no. 5, 2020, doi: 10.3390/app10051843. [4] X. Guo et al., “Selective hydrogenation of D-glucose to D-sorbitol over Ru/ZSM-5 catalysts,” Chinese J. Catal., vol. 35, no. 5, pp. 733–740, May 2014, doi: 10.1016/S1872-2067(14)60077-2. [5] H. S. Isbell, H. L. Frush, and F. J. Bates, “Manufacture of calcium gluconate by electrolytic oxidation of dextrose,” Ind. Eng. Chem., vol. 24, no. 4, pp. 375–378, 1932, doi: 10.1021/ie50268a003. [6] S. Anastassiadis and I. Morgunov, “Gluconic acid production,” Recent Pat. Biotechnol., vol. 1, no. 2, pp. 167–180, May 2007, doi: 10.2174/187220807780809472. [7] M. M. Jaksic, B. Johansen, and R. Tunold, “Electrochemical behaviour of gold in acidic and alkaline solutions of heavy and regular water,” Int. J. Hydrogen Energy, vol. 18, no. 2, pp. 91–110, Feb. 1993, doi: 10.1016/0360-3199(93)90196-H. [8] J. Cornejo-Romero, A. Solis-Garcia, S. M. Vega-Diaz, and J. C. Fierro-Gonzalez, “Reverse hydrogen spillover during ethanol dehydrogenation on TiO2-supported gold catalysts,” Mol. Catal., vol. 433, pp. 391–402, 2017, doi: 10.1016/j.mcat.2017.02.041. [9] A. G. Oshchepkov et al., “Nanostructured nickel nanoparticles supported on vulcan carbon as a highly active catalyst for the hydrogen oxidation reaction in alkaline media,” J. Power Sources, vol. 402, no. June, pp. 447–452, 2018, doi: 10.1016/j.jpowsour.2018.09.051. Figure 1

There are thirty-five (35) metals with public health implications due to occupational or residential exposure; twenty-three (23) of these are called heavy elements or metals. They are Antimony, Arsenic, Bismuth, Cadmium, Cerium, Chromium, Cobalt, Copper, Gallium, Gold, Iron, Lead, Manganese, Mercury, Nickel, Platinum, Silver, Tellurium, Thallium, Tin, Uranium, Vanadium, and Zinc. Interestingly, minute amount of these elements are common in our environment and diet and are actually necessary for a balanced health, but increased consumption may cause acute or chronic toxicity (poisoning). Allergies are not uncommon and repeated long-term exposure to these metals such as Zinc, Lead, Chromium, Selenium, Nickel, Cobalt and Cadmium may cause cancer. The alarming perceived increase of these pollutants around the south-western regions of Nigeria have necessitated the need to evaluate water and sediment samples of Osun river, popularly known for its cultural practices and activities. The physicochemical properties of samples such as pH, TDS EC, Total Dissolved Solid (TDS), Conductivity, Total Hardness, Sodium, Potassium, Phosphate, Nitrate, Chloride were analyzed and result showed compliance with recommended WHO standards. Trace and heavy metal composition in water using standard methods indicates the presence of Calcium (5.11±0.04ppm), Magnesium (0.54±0.004ppm), Potassium (1.28±0.01ppm) and Iron (0.05±0.00ppm) while sediment sample contained high composition of Zinc (21.99±2.67ppm), Iron (261.6±2.00ppm) and Manganese (105.6+0.50ppm). Results obtained from proximate analysis of both water and sediment samples, shows that there are no heavy metals presence in Osun River that could pose a threat to public health. Rather, there are more minerals and nutrients in availability which implies that water sample lacks considerable pollutants and can be certified healthy for moderate consumption and domestic uses which is within permissible value limits of WHO standards. Ashaolu V. O. | Research Scholar, Department of Chemistry, LIFE, Loyola College, Chennai-600034

ABSTRACTVarious shaped single-crystalline gallium nitride (GaN) nanostructures were produced by chemical vapor deposition method in the temperature range of 900–1200 °C. Scanning electron microscopy, transmission electron microscopy, electron diffraction, x-ray diffraction, electron energy loss spectroscopy, Raman spectroscopy, and photoluminescence were used to investigate the structural and optical properties of the GaN nanostructures. We controlled the GaN nanostructures by the catalyst and temperature. The cylindrical and triangular shaped nanowires were synthesized using iron and gold nanoparticles as catalysts, respectively, in the temperature range of 900 – 1000 °C. We synthesized the nanobelts, nanosaws, and porous nanowires using gallium source/ boron oxide mixture. When the temperature of source was 1100 °C, the nanobelts having a triangle tip were grown. At the temperature higher up to 1200 °C the nanosaws and porous nanowires were formed with a large scale. The cylindrical nanowires have random growth direction, while the triangular nanowires have uniform growth direction [010]. The growth direction of the nanobelts is perpendicular to the [010]. Interestingly, the nanosaws and porous nanowires exhibit the same growth direction [011]. The shift of Raman, XRD, and PL bands from those of bulk was correlated with the strains of the GaN nanostructures.

AbstractImmobilization of proteins and enzymes on solid supports has been utilized in a variety of applications, from improved protein stability on supported catalysts in industrial processes to fabrication of biosensors, biochips, and microdevices. A critical requirement for these applications is facile yet stable covalent conjugation between the immobilized and fully active protein and the solid support to produce stable, highly bio-active conjugates. Here, we report functionalization of solid surfaces (gold nanoparticles and magnetic beads) with bio-active proteins using site-specific and biorthogonal labeling and azide-alkyne cycloaddition, a click chemistry. Specifically, we recombinantly express and selectively label calcium-dependent proteins, calmodulin and calcineurin, and cAMP-dependent protein kinase A (PKA) with N-terminal azide-tags for efficient conjugation to nanoparticles and magnetic beads. We successfully immobilized the proteins on to the solid supports directly from the cell lysate with click chemistry, forgoing the step of purification. This approach is optimized to yield low particle aggregation and high levels of protein activity post-conjugation. The entire process enables streamlined workflows for bioconjugation and highly active conjugated proteins. Graphical Abstract

ABSTRACTPrecious metals are choice materials for a myriad of applications due their high electrical conductivity, resistance to corrosion, and ligand binding specificity. Indispensable in modern electronics fabrication, precious metals also enjoy widespread use as catalysts, support substrates, and sensor elements. Recent progress towards metallization on diminishing size regimes has imposed increasingly stringent demands upon thin film preparation methodologies. Metallization techniques employed in ultra large scale integration (ULSI) device fabrication, nanoelectromechanical systems (NEMS), and arrayed nanosensors will require unparalleled control of surface morphology, deposition rate, and substrate adhesion without sacrificing throughput or cost effectiveness. Furthermore, precious metal films of this type are essential for fundamental investigations aimed at elucidating the intricate nature of interfacial topics ranging from self-assembled monolayers (SAMs) to heterogeneous catalysis. In contrast to complex and expensive vacuum methods of metallization, research in our laboratory has focused on the preparation of precious metal thin films on semiconductor substrates via electroless deposition. Thin and thick films of gold, platinum, and palladium nanoparticles have been prepared as a result of the immersion of germanium and gallium arsenide substrates into dilute, aqueous solutions of tetrachloraurate (III), tetrachloroplatinate (II), and tetrachloropalladate (II), respectively. This methodology yields nanostructured precious metal films with control over surface morphology and deposition rate. Moreover, metal films prepared in this manner exhibit excellent adhesion to the underlying semiconductor substrate. The resultant films were characterized utilizing scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and scanning probe microscopy (SPM). This method provides for the facile interfacing of metal nanostructures with group (IV) and III-IV compound semiconductor surfaces.

AbstractBioactive glasses (BGs) have been a focus of research for over five decades for several biomedical applications. Although their use in bone substitution and bone tissue regeneration has gained important attention, recent developments have also seen the expansion of BG applications to the field of soft tissue engineering. Hard and soft tissue repair therapies can benefit from the biological activity of metallic ions released from BGs. These metallic ions are incorporated in the BG network not only for their biological therapeutic effects but also in many cases for influencing the structure and processability of the glass and to impart extra functional properties. The “classical” elements in silicate BG compositions are silicon (Si), phosphorous (P), calcium (Ca), sodium (Na), and potassium (K). In addition, other well-recognized biologically active ions have been incorporated in BGs to provide osteogenic, angiogenic, anti-inflammatory, and antibacterial effects such as zinc (Zn), magnesium (Mg), silver (Ag), strontium (Sr), gallium (Ga), fluorine (F), iron (Fe), cobalt (Co), boron (B), lithium (Li), titanium (Ti), and copper (Cu). More recently, rare earth and other elements considered less common or, some of them, even “exotic” for biomedical applications, have found room as doping elements in BGs to enhance their biological and physical properties. For example, barium (Ba), bismuth (Bi), chlorine (Cl), chromium (Cr), dysprosium (Dy), europium (Eu), gadolinium (Gd), ytterbium (Yb), thulium (Tm), germanium (Ge), gold (Au), holmium (Ho), iodine (I), lanthanum (La), manganese (Mn), molybdenum (Mo), nickel (Ni), niobium (Nb), nitrogen (N), palladium (Pd), rubidium (Rb), samarium (Sm), selenium (Se), tantalum (Ta), tellurium (Te), terbium (Tb), erbium (Er), tin (Sn), tungsten (W), vanadium (V), yttrium (Y) as well as zirconium (Zr) have been included in BGs. These ions have been found to be particularly interesting for enhancing the biological performance of doped BGs in novel compositions for tissue repair (both hard and soft tissue) and for providing, in some cases, extra functionalities to the BG, for example fluorescence, luminescence, radiation shielding, anti-inflammatory, and antibacterial properties. This review summarizes the influence of incorporating such less-common elements in BGs with focus on tissue engineering applications, usually exploiting the bioactivity of the BG in combination with other functional properties imparted by the presence of the added elements.

Nanotechnology has been a rapidly growing field of advanced science at the inception of this century. Nanotechnology of advanced materials, polymers, principally revolves around endeavours to plan materials at a sub-atomic level to accomplish alluring properties and applications at a naturally visible level. Nanotechnology can be used for the advancement of technologies, ranging from communication and information, health and medicine, future energy, environment and climate change to transport and cultural heritage, personal protective equipment (PPE), fuels, fuel cells, biosensors, disease sensors etc. Nanomaterials will lead to a new approach to manufacturing materials and devices. Faster computers, advanced pharmaceuticals, controlled drug delivery, biocompatible materials, nerve and tissue repair, crackproof surface coatings, better skin care and protection, more efficient catalysts, better and smaller sensors, even more efficient telecommunication. For example, a low risk solution using antibody modified bismuth nanoparticle, in combination with an X-ray dose equivalent to a chest X-ray specifically, has been shown to kill the common bacterium Pseudomonas aeruginosa in a set up designed to resemble a deep wound in human tissue. Nanosized gold particle could catalyse the oxidation of carbon monoxide better than anything previously known. Heparin functionalized nanoparticles have been use for targeted delivery of anti-malarial drugs. Heparin is abundant and cheap, compared to treatments that involve antibodies, an important consideration, since malaria is most common in developing countries. A bone repairing nano-particle paste has been developed that promises faster repair of fractures and breakages. DNA containing two growth genes is encapsulated inside synthetic calcium phosphate nanoparticles. In a remarkable demonstration of the extreme limits of nanoscale engineering, researchers have used the tip of a scanning tunnelling microscope to cleave and form selected chemical bonds in a complex molecule. Many medicinal and industrial endeavours have seen the use of Nanotechnology. Nanoparticles can attach to SARS COV-2 viruses, disrupting their structure and so kill the virus. These and other more recent advances in nanotechnology will be presented at this conference.