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Publisher's version (útgefin grein), The electrochemical CO2reduction reaction (CO2RR) on RuO2and RuO2-based electrodes has been shown experimentally to produce high yields of methanol, formic acid and/or hydrogen while methane formation is not detected. This CO2RR selectivity on RuO2is in stark contrast to copper metal electrodes that produce methane and hydrogen in the highest yields whereas methanol is only formed in trace amounts. Density functional theory calculations on RuO2(110) where only adsorption free energies of intermediate species are considered,i.e.solvent effects and energy barriers are not included, predict however, that the overpotential and the potential limiting step for both methanol and methane are the same. In this work, we use bothab initiomolecular dynamics simulations at room temperature and total energy calculations to improve the model system and methodology by including both explicit solvation effects and calculations of proton-electron transfer energy barriers to elucidate the reaction mechanism towards several CO2RR products: methanol, methane, formic acid, CO and methanediol, as well as for the competing H2evolution. We observe a significant difference in energy barriers towards methane and methanol, where a substantially larger energy barrier is calculated towards methane formation than towards methanol formation, explaining why methanol has been detected experimentally but not methane. Furthermore, the calculations show why RuO2also catalyzes the CO2RR towards formic acid and not CO(g) and methanediol, in agreement with experimental results. However, our calculations predict RuO2to be much more selective towards H2formation than for the CO2RR at any applied potential. Only when a large overpotential of around −1 V is applied, can both formic acid and methanol be evolved, but low faradaic efficiency is predicted because of the more facile H2formation., This work was supported by the Icelandic Research Fund (grant no. 196437-051), the Research Fund of the University of Iceland and the ‘Nordic Consortium for CO2 Conversion’ (NordForsk project no. 85378, http://site.uit.no/nordco2).

Density functional theory calculations were used to explore reactivity trends of the electrochemical CO2 reduction reaction (CO2RR) toward methanol, methane, methanediol, and formic acid on 12 transition metal dioxide (TMO) surfaces in their rutile structure. The (110) facet of the TMOs was used as a model system to investigate the thermodynamic limiting potentials of CO2RR. Activity and selectivity volcano plots for various products were obtained through the scaling relations of adsorbed intermediates. RhO2 is predicted to be a good catalyst for production of formic acid with low onset potential of around −0.2 V. In addition to its high activity, hydrogen evolution reaction (HER) is predicted to not limit its efficiency due to weak hydrogen binding free energy on this oxide. CrO2 is another promising candidate for CO2RR with onset potential of around −0.3 V toward most of the products. CrO2 seems to be more interesting than RhO2 for production of methanol, methane, and methanediol as it adsorbs HCOOH on ...

Publisher's version (útgefin grein)., CO2 can be reduced electrochemically to form valuable chemicals such as hydrocarbons and alcohols using copper electrodes, whereas the other metal electrodes tested so far mainly form CO or formate, or only the side product, H2. Accurate modeling of electrochemical reaction rates including the complex environment of an electrical double layer in the presence of an applied electrical potential is challenging. We show here that calculated rates, obtained using a combination of density functional and rate theory, are in close agreement with available experimental data on the formation of the various products on several metal electrodes and over a range in applied potential, thus demonstrating the applicability of the theoretical methodology. The results explain why copper electrodes give a significant yield of hydrocarbons and alcohols, and why methane, ethylene, and ethanol are formed in electroreduction rather than methanol, which is the main product when H2 gas reacts with CO2 on copper catalyst. The insight obtained from the calculations is used to develop criteria for identifying new and improved catalysts for electrochemical CO2 reduction., We thank Marc Koper, Jens K. Nørskov, Andrew Peterson, Jan Rossmeisl and Anna Garden for helpful discussions. This work was supported by Nordic Energy Research through the “Nordic Initiative for Solar Fuel Development”, the Icelandic Research Fund, the University of Iceland Doctoral Scholarship Fund, and the Academy of Finland FiDiPro program (grant 263294).

An atomic scale model of the electrical double layer is used to calculate the mechanism and rate of electrochemical reduction of CO2 as well as H2 formation at a Pt(111) electrode. The water layer contains solvated protons and the electrode has excess electrons at the surface. Density functional theory within the generalized gradient approximation is used to describe the electronic structure while the mechanism and activation energy of the various elementary reactions is obtained by calculating minimum energy paths using the nudged elastic band method. The applied electrical potential is deduced from the calculated work function. The optimal reaction mechanism for CO2 reduction to either methane or methanol is found and the estimated rate compared with that of the competing reaction, H2 formation. When the free energy of only the intermediates and reactants is taken into account, not the activation energy, Pt(111) would seem to be a good electrocatalyst for CO2 reduction, significantly better than Cu(111). This, however, contradicts experimental findings. Detailed calculations reported here show that the activation energy for CO2 reduction is high for both Heyrovsky and Tafel mechanisms on Pt(111) in the relevant range of applied potential. The rate-limiting step of the Heyrovsky mechanism, *COOH + H+ + e− → *CO + H2O, is estimated to have an activation energy of 0.95 eV at −0.9 V vs. standard hydrogen electrode. Under the same conditions, the activation energy for H2 formation is estimated to be only 0.5 eV. This explains why attempts to reduce CO2 using platinum electrodes have produced only H2. A comparison is made with analogous results for Cu(111) [J. Hussain et al., Procedia Comput. Sci., 2015, 51, 1865] where a reaction mechanism with low activation energy for CO2 electroreduction to methane was identified. The difference between the two electrocatalysts is discussed.

Associative desorption of hydrogen at edges and facets on Pt nano-particles (NPs) was studied using density functional theory. The goal was to identify catalytically active sites on Pt NPs for the hydrogen evolution reaction. Since NPs used in catalysis typically contain over a thousand atoms, calculations of whole particles are too demanding and the adsorption sites were instead modeled by periodic face centered cubic slabs representing an array of edges between two (111) micro-facets or edges between (111) and (100) micro-facets. The width of the facets in the periodic representations was systematically increased to reach converged results for binding and activation energy. For maximum hydrogen coverage, edges between (111) micro-facets were found to be several orders of magnitude more active than edges between (100) and (111) micro-facets or flat terraces. Unlike the missing row Pt(110)-(2 × 1) surface, which has sometimes been used as a simple model for edges between (111) micro-facets, the converged edge model does not show the recently reported reentrant behavior in desorption mechanism (Gudmundsdottir et al., Phys Rev Lett 108:156101, 2012).

Upon addition of tetrachloroauric(III) (HAuCl(4)) to a solution of cetyltrimethylammonium bromide (CTAB), a perfect transparent yellow colored and yellowish-precipitate appears within the time of mixing, indicating the formation of a complex between HAuCl(4) and CTAB. Morphology of gold nanoparticles in situ via chemical reduction of title reaction has been determined by using conventional techniques. The position and shape of the surface plasmon resonance (SRP) band strongly depends on the [ascorbic acid], [HAuCl(4)], [CTAB] and mixing ratio of the reactants. Sub-, post- and dilution-micellar effects are accountable to the aggregation and/or adsorption of gold nanoparticles onto the surface of CTAB. The morphology of particles was altered by changing the [reactants] as well as [CTAB]. A mechanism of nanoparticle formation has been proposed comprising different steps of particle growth.

The impact of electrolytes, stabilizing and/or capping agents on morphology of colloidal silver nano-materials (AgNPs) has been studied spectroscopically. Sodium thiosulfate acts as reducing-, stabilizing- and damping-agents. Stoichiometric ratios of S2O32− and Ag+ ions were responsible to the formation stable and prefect transparent dark yellow colored AgNPs. The S2O32−-stabilized AgNPs were significantly more stable in inorganic electrolytes (NaNO3, Na2SO4, Na2CO3 and KBr). S2O32− is adsorbed more strongly than the used other anions. The addition of cetyltrimethylammonium bromide (CTAB) and sodium dodecylsulfate (SDS) has significant effects on the absorbance of S2O32−-stabilized AgNPs which can be rationalized in terms of electrostatic attraction and repulsion between the adsorbed S2O32− ions on to the surface of AgNPs and cationic and/or anionic head groups of used surfactants, respectively. Transmission electron microscopy images suggest that AgNPs are polydispersed, spherical and exhibiting an interesting irregular morphology.

Silver nanoparticles were prepared by a simple chemical reduction method using ascorbic acid and starch as reducing and stabilizing agents, respectively. The effect of starch, silver ions and ascorbic acid was studied on the morphology of the silver nano-particles using UV-visible spectrophotometry. The initial reaction time min and amount of starch were important parameters for the growth of Ag-nanoparticles. The morphology was evaluated from transmission electron microscopy (TEM). The truncated triangle nano-plates (from 17 to 30 nm), polyhedron, spherical with some irregular shaped Ag-nanoparticles were formed in presence of starch. Particles are aggregated in an irregular manner, leads to the formation of butterfly-like structures of silver. Starch acts as a stabilizing, shape-directing and capping agent during the growth processes. Silver nanoparticles adsorbed electrostatically on the outer OH groups of amylose left-handed helical conformation in solution.

All-component molecular dynamics studies were used to probe a library of oseltamivir molecularly imprinted polymer prepolymerization mixtures. Polymers included one of five functional monomers (acrylamide, hydroxyethylmethacrylate, methacrylic acid, 2-(triflouromethyl)acrylic acid, 4-vinylpyridine) and one of three porogens (acetonitrile, chloroform, methanol) combined with the crosslinking agent ethylene glycol dimethacrylate and initiator 2,2′-azobis(2-methylpropionitrile). Polymers were characterized by nitrogen gas sorption measurements and SEM, and affinity studies performed using radioligand binding in various media. In agreement with the predictions made from the simulations, polymers prepared in acetonitrile using either methacrylic or trifluoromethacrylic acid demonstrated the highest affinities for oseltamivir. Further, the ensemble of interactions observed in the methanol system provided an explanation for the morphology of polymers prepared in this solvent. The materials developed here offer potential for use in solid-phase extraction or for catalysis. The results illustrate the strength of this in silico strategy as a potential prognostic tool in molecularly imprinted polymer design.

In this paper we report the effect of aniline concentrations on the growth and size of silver nanocrystals using aniline and silver nitrate as reductant and oxidant, respectively. UV-Vis spectroscopy, transmission electron microscopy (TEM) and selected areas electron diffraction (SAED) have been employed to characterize silver nanoparticles. The TEM images show that silver nanocrystals are roughly spherical and of uniform particle size, and the average particle size is ca. 25 nm. A broad surface plasmon resonance band appears at 400 nm. The rings patterns are in good agreement with the standard values of the facecentered-cubic form of silver nanocrystals. This is attributed to the adsorption of aniline and /or interparticle interaction onto the surface of Ag-nanocrystals through electrostatic interactions between the lone-pairs electrons of –NH2 and positive surface of Ag- nanoparticles. Copyright © 2011 VBRI press.

This paper describes a simple procedure based on the modified silver-mirror process for the preparation of colloidal silver quantum dots (diameter ≤7nm). All reactions were monitored with respect to reaction time by using UV-visible studies to understand the growth kinetics and the influence of different [ammonia], [glucose] and temperature on the formation of silver nanoparticles. Shape of the reaction-time curves (sigmoid facing up and sigmoid facing down) strongly depend on the [NH3]. Glucose concentrations have no significant effect on the progress of the reaction. For the nucleation and growth processes, surface plasmon absorbance is directly proportional and increase-decrease with increasing [NH3], respectively. Transmission electron microscopy (TEM) results show that the quantum dots are aggregated in an irregular manner, resulting in the formation of branches-like structures of silver. The activation energy, enthalpy and entropy of activation have been evaluated. Mechanism consistent with the observed kinetics results has been suggested.

Colloidal silver nanoparticles were prepared by reducing silver nitrate with oxalic acid in presence of cetyltrimethylammonium bromide (CTAB). The synthesized silver particles show an intense surface plasmon band in the visible region. The work reported in this paper describes the effect of concentration of various additives (NaCl, NaBr, NaNO3, Na2SO4 and NaH2PO4) and ammonia on the growth and stability of Ag-nanoparticles. In all the cases the rate decreases as the [electrolytes] or [ammonia] increases. The nature, polarizability and coordinating ability of the anions play vital roles for nucleus formation and the growth process, which subsequently form different size particles. Transmission electron microscopy, selected areas electron diffraction, and UV-visible spectroscopy have been employed to characterize Ag-nanoparticles. The effect of the following variables on the particle size and size distribution was investigated: the [oxalic acid], [CTAB] and [Ag+].The nanoparticles are stable in NaNO3 and NaH2PO4 solutions; but NaCl, NaBr and Na2SO4 causes their aggregation.

Investigations regarding renal clearance and urinary excretion of ciprofloxacin were carried out in buffaloes, cows, sheep, and goats. The drug was administered intramuscularly at a dose of 5 mg/kg body weight. The plasma and urine concentrations of the drug were determined with HPLC. Renal clearance of endogenous creatinine was used as an index of glomerular filtration rate (GFR). In buffaloes, it was 0.72 ± 0.15 (mean ± SE), in cows 0.36 ± 0.09, in sheep 1.33 ± 0.35, and in goats 1.87 ± 0.38 mL/min/kg. The renal clearance of ciprofloxacin in buffaloes was 0.47 ± 0.08, in cows 0.29 ± 0.08, in sheep 0.39 ± 0.06, and in goats 0.98 ± 0.17 mL/min/kg. Besides glomerular filtration, ciprofloxacin was reabsorbed from the renal tubules of all ruminants and actively secreted in buffaloes. The cumulative percentage of intramuscular dose of ciprofloxacin excreted into the urine over 10 h in buffaloes was 10.04 ± 1.17, in cows 7.22 ± 1.12, in sheep 11.26 ± 1.74, and in goats 13.03 ± 2.07. Species difference in the urinary excretion of ciprofloxacin revealed that the excretion of the drug was highest in goats, followed by sheep, buffaloes, and cows. This species variation in the percentage of urinary excretion in these ruminants coincides with their respective GFR being the highest in goats and lowest in cows.

UV–Vis spectroscopy, transmission electron microscopy (TEM) and selected area electron diffraction (SAED) have been employed to characterize silver nanoparticles (AgNPs) using aniline and silver nitrate as reductant and oxidant, respectively. A broad surface resonance plasmon (SRP) band appears at 400 nm, indicating that the AgNPs are spherical. The TEM images show that AgNPs aggregated in an unsymmetrical manner, leading to the formation of beautiful silver nanocrystals. Aniline adsorbed onto the surface of Ag-nanocrystals through electrostatic, van der Walls forces and hydrogen bonding. Cetyltrimethylammonium bromide (CTAB) acted as a stabilizer and/or capping agent.

Stable silver nanoparticles were synthesized by the reduction of silver ions with a Paan (Piper betel) leaf petiole extract in absence and presence of cetyltrimethylammonium bromide (CTAB) and sodium dodecyl sulphate (SDS). The reaction process was simple and convenient to handle, and was monitored using ultraviolet-visible spectroscopy. Absorbance of Ag-nanoparticles increases with the concentrations of Paan leaf extract, acts as reducing, stabilizing and capping agents. The polyphenolic groups of petiole extract are responsible to the rapid reduction of Ag(+) ions into metallic Ag(0). The results indicated that the shape of the spectra, number of peaks and its position strongly depend on the concentration of CTAB, which played a shape-controlling role during the formation of silver nanoparticles in the solutions, whereas SDS has no significant effect. The morphology (spherical, truncated triangular polyhedral plate and some irregular nanoparticles) and crystalline phase of the particles were determined from transmission electron microscopy (TEM) and selected area electron diffraction (SAED).

The shape-directing role of cetyltrimethylammonium bromide, CTAB, is reported to the green synthesis of Ag-nanoparticles for the first time using Neem (Azadirachta indica) leaf extract. UV–vis spectroscopy, transmission electron microscopy (TEM), and selected area electron diffraction (SAED) patterns were used to monitor the growth kinetics, morphology and crystalline nature of Ag-nanoparticles, respectively. It was observed that the growths of Ag-nanoparticles are stopped within 40 min of reaction time. The Ag-nanoparticles are polydispersed spherical and exhibiting an interesting triangle, flat, plate-like hexagonal and some irregular morphology in presence of different [CTAB]. Hexagonal particles aggregated in a systematic manor, leads to produce a fine tiles-like arrangement of Ag-nanoparticles with dimensions between 10 and 37 nm. The nature of reaction–time curves to the reduction of Ag+ ions by Neem leaf extract are much different than those observed by us in our earlier studies using different bio-reductants.

This paper describes a simple preparation of single-crystalline Ag-nanoparticles including plates, and wires in water by truncated triangular particles for the first time during the reduction of [Ag(NH3)2]+ complex with glucose at room temperature. Silver particles were characterized by means of the conventional transmission electron microscopy (TEM) and UV-VIS spectroscopy. Cetyltrimethylammonium bromide, CTAB, plays a number of roles during the redox process by solubilizing the reactants, controlling the nucleation and/or growth of nanoparticles, stabilizing the thus-prepared Ag-nanoparticles and minimizing the formation of Ag2O, AgCl, and AgBr precipitates. It was found that the rate constant and absorbance of silver nanoparticles were sigmoidal to the concentration of silver nitrate.