Organic Acid Media Research Articles

Synthesis of metal (Ga, Co and Fe) 5,15-bis(pentafluorophenyl)-10-ethoxycarbonylcorrole and their electrocatalytic hydrogen evolution activity

5,15-bis(pentalfluorophenyl)-10-ethoxycarbonylcorrole and their metal complexes (metal = Ga, Co, Fe) had been synthesized and characterized (new complexes). These metal complexes had been used as electrocatalysts for hydrogen evolution reaction (HER) in organic acid and aqueous medium, in which the gallium corrole was firstly used for HER. The results showed that the redox potential of central metal atom for metal-centered metal (eg. Co and Fe) corroles plays a significant role in adjusting catalytic HER activity. Gallium corrole is a ligand-centered HER catalyst, the electronic structure of corrole ligand may play a key role in controlling the electrocatalytic activity.

Eco-friendly oxidation leaching from chalcopyrite powder and kinetics assisted by sodium chloride in organic acid media

The realization of efficient leaching of metal elements in chalcopyrite is of great significance to global industrial development. In this work, an eco-friendly and efficient leaching process was investigated for the leaching of Cu and Fe from chalcopyrite powder. The results showed that the introduction of stirring energy has an adverse effect on the leaching process. 96.13% Cu and 84.35% Fe were leached under the optimal leaching conditions of 0 rpm stirring speed, the solid–liquid ratio of 10 g/L, 0.5 M HAc, 0.4 M NaCl, at 333.15 K for 10 h with timeic addition of H2O2 of 16 mL every 2 h. The kinetics data indicated that the leaching of Cu fitted best to the shrinking core model while the leaching of Fe corresponded to the Avrami equation. Furthermore, all the leaching processes mainly depended on the controlling of diffusion, and reaction order revealed that the volume of H2O2 had the greatest effect on the leaching rates.

Enantioselective Fluorescent Recognition of Free Amino Acids: Challenges and Opportunities.

Fluorescent probes that can discriminate enantiomers of amino acids in organic media or aqueous solution are discussed. This Minireview focuses on recent progress in the studies of three classes of probes including those made of cyclodextrins, 1,1'-binaphthyl compounds, and nanomaterials, and uses them to illustrate the design strategies, applications, and limitations in this area. These probes are potentially useful for rapid analysis of asymmetric reactions for amino acid synthesis as well as the real-time imaging of amino acids in biological systems. The challenges in these applications are analyzed. Working in this field of enantioselective fluorescent recognition of amino acids offers great opportunities to make new scientific discoveries and to develop important practical applications.

Enantioselective Fluorescent Recognition of Free Amino Acids: Challenges and Opportunities

AbstractFluorescent probes that can discriminate enantiomers of amino acids in organic media or aqueous solution are discussed. This Minireview focuses on recent progress in the studies of three classes of probes including those made of cyclodextrins, 1,1′‐binaphthyl compounds, and nanomaterials, and uses them to illustrate the design strategies, applications, and limitations in this area. These probes are potentially useful for rapid analysis of asymmetric reactions for amino acid synthesis as well as the real‐time imaging of amino acids in biological systems. The challenges in these applications are analyzed. Working in this field of enantioselective fluorescent recognition of amino acids offers great opportunities to make new scientific discoveries and to develop important practical applications.

Sonochemical production of nanoscaled crystalline cellulose using organic acids

The present work deals with the production of cellulose nanoparticles through sonochemistry in various organic acidic media.

Improved facile synthesis of mesoporous SBA-15-CTA using citric acid under mild conditions

Unlike being traditionally synthesized in HCl intermediates, in this study, well-ordered 2D hexagonal mesoporous silica (SBA-15) was developed under moderate polycarboxylic acid (e.g. citric acid or oxalic acid) medium without introducing inorganic salts and mineral acids. The key synthesis factors such as the type and concentration of polycarboxylic acids, preparation temperature and crystallization time are systemically studied. It was found that the amount of carboxyl groups inside the organic acid molecules plays a critical role in synthesizing high-quality mesoporous silica products owing to their bridging effects on both nonionic copolymer micelles and silica precursors. The more carboxyl groups the organic acid possesses, the less dosage of organic acid will be used. The citric acid concentration can be as low as 0.0010 molL-1 (pH ​> ​3) for forming the high quality SBA-15-CTA materials (CTA stands for the material prepared under citric acid medium) their microstructure and rod-like particle size can be tailored by varying the acid type and preparation conditions. As-synthesized SBA-15-CTA supported Ni catalysts showed a good potential for dry reforming of methane (DRM) reaction with much less coke formation at 700 ​°C. The synthesis strategy for mesoporous silica under moderate organic acid medium demonstrates a promising prospect for other mesoporous materials preparation and utilizations in catalysis, selective adsorptions, drug delivery, and so on.

Recovery of precious metals from spent Mo–Co–Ni/Al2O3 catalyst in organic acid medium: Process optimization and kinetic studies

In present study, the leaching kinetics of the spent Mo–Co–Ni/Al2O3 catalyst was investigated in the presence of formic acid as an organic leaching agent. Firstly, the spent catalyst was roasted in different roasting temperature (200–700 °C) and time (15–240 min), the maximum metal extraction was achieved that at 500 °C with 90 min. Then, the leaching experiments were carried out to determine the influences of process parameters following; particle size, liquid/solid ratio, formic acid concentration, leaching temperature, leaching time and stirring speed. According to the experimental results, the highest dissolution rates of molybdenum (Mo, 75.82%), cobalt (Co, 96.81%), nickel (Ni, 93.44%) and aluminum (Al, 19.46%) were reached under optimum experimental conditions; particle size +75 − 30 µm; liquid/solid ratio 10 ml/g; formic acid concentration 0.6 M; leaching temperature 80 °C; leaching time 90 min and stirring speed 300 r/min. Moreover, the leaching kinetics clearly reveal that the leaching reaction is controlled by liquid film diffusion and that the activation energy values (Ea) of Co, Ni, Mo and Al were to be 24.49, 25.98, 32.36 and 33.47 kJ/mol, respectively. In conclusion, the leaching process can be conducted in the presence of formic acid for the various industrial wastes in similar structure and composition to Mo–Co–Ni/Al2O3 spent catalyst.

Effects of Some Operating Parameters on Sorption and Desorption Kinetics Related to Spotted Golden Thistle Stalks and Methylene Blue; Isotherm Study at Optimal pH and Sorbent Regeneration

In this work, the sorptive removal assessment of methylene blue by spotted golden thistle stalks was enhanced. Sorption was positively impacted by increasing temperature, initial pH or ionic strength. The sorbent isoelectrical point is 2.6 according to zeta potential measurements. The Elovich and Avrami models best fitted the sorption kinetic data; and an original prediction of equilibrium time is proposed. At 25 °C and for optimal initial pH = 7, the experimental maximal sorption capacity is 75 mg g−1. The Langmuir, Redlich–Peterson, Sips and Tóth models led to good correlations of isothermal data. Desorption percentages are important in both mineral and organic acidic media; the highest levels up to 91% were recorded for 1 × 10−2M HCl solutions. The pseudo second-order model fitted satisfactorily the desorption kinetics. An innovative concept of regeneration is proposed, which promises significant savings of eluent and operating time. The sorbent regeneration assessment showed constant uptake abilities after five cycles of use.

Solvent effects on microstructures and properties of three-dimensional hierarchical TiO2 microsphere structures synthesized via solvothermal approach

One-step solvothermal method has been proved to be a simple and efficient route to synthesize three-dimensional (3D) hierarchical TiO2 microsphere structures, but discrepant properties of the solvent media had been claimed as the major factors determining microstructures and properties of the final products. In this study, several typical solvents, including alkane, aromatic hydrocarbons, halohydrocarbon, ketone, organic acid, mono- and dihydric alcohols, were selected to comprehensively investigate the effect of solvents on the morphology, crystal structure, specific surface area, porous property and light harvesting capability of the final products. According to the experimental results, a good interface separating titanium precursor with aqueous phase in the reaction solution, created by non-polar solvents, or polar solvents which are immiscible with titanium precursor, was the decisive factor for the formation of quasi-3D urchin-like TiO2 microspheres self-assembled from one-dimensional (1D) nanostructures, and concentrated H+ induced by organic acid medium was also helpful. Meanwhile, without the liquid-liquid interface or extremely low solution pH, anatase TiO2 sphere structures with big specific surface area comprising of nanoparticles or nanosheets would be formed, and performed well in photodegradation of pollutants in water.

Enhanced Promiscuity of Lipase-Inorganic Nanocrystal Composites in the Epoxidation of Fatty Acids in Organic Media.

In the present study, Candida antarctica lipase B (CALB) was encapsulated in inorganic nanocrystal composites with flower-like shapes, retaining 92% of its catalytic activity compared to that of native lipase. Surprisingly, CALB-inorganic crystal nanoflowers exhibited promiscuous activity at levels 25- and 4-fold higher than those of native lipase and the commercial immobilized lipase Novozym 435, respectively, as demonstrated by the chemoenzymatic epoxidation of fatty acids conducted in organic media. To the best of our knowledge, we showed for the first time that the promiscuity of enzymes can be significantly improved by enzyme immobilization, suggesting that the enzyme-inorganic nanocrystal composites are a very promising type of immobilized enzyme that can be used to address the challenge of the extremely low efficiency of enzymatic promiscuity.

Extraction of iridium(III) by ion-pair formation with 2-octylaminopyridine in weak organic acid media

ABSTRACTTo extract iridium(III), various physicochemical parameters were studied. 2-Octylaminopyridine was used for the extraction of iridium(III) from acetate medium at 8.5 pH. Quantitative extraction of iridium(III) was achieved via ion-pair formation of cation [2-OAPH+] and anion [Ir(CH3COO)4]−. The stripping of iridium(III)-laden organic phase was carried out 2 M HCl (3 × 10 mL) . The stoichiometry of the extracted ion–pair complex was found to be 1:4:1 (metal: acetate: extractant). The extracted species [2-OAPH+. Ir(CH3COO)4−] is assumed to be an ion association product of [Ir(CH3COO)4] − and [2-OAPH]+. The proposed method was successfully used in the separation of iridium(III) from binary and ternary mixtures. Analysis of various alloy samples was also carried out.

Fabrication of nano-sized copper powders in liquid media via high-energy electrical explosion method: Use of high purity copper recovered from waste jelly-filled cable as raw material

Abstract A novel process for fabrication of nano-sized copper powders in organic oleic acid medium was developed employing a high-energy electrical explosion method. Formation of copper oxides was inhibited by the oleic acid medium during the electrical explosion of copper wires recovered from waste jelly-filled cable as a raw material for synthesis of nano-colloids and final dried nano-sized copper powders. High voltage of 320 V was repeatedly applied between the two horizontal electrodes for 3000 electrical explosions across the horizontal electrodes assembly. The copper powders were finally recovered via dispersion of the colloid by ultra-sonification and subsequent drying in an oven at 60 °C for 1 h and 5 h, respectively. The copper powders thus fabricated were analyzed using FESEM, BET surface area analyzer, TEM and elemental analyzer for determination of morphology, porosity and elemental purity. All of them turned out to be superior compared to similarly produced copper nano-sized powders in deionized water or ethyl alcohol (EtOH) media.

Quantitative Evaluation of the Effects of Moisture Distribution on Enzyme-Induced Acylation of Trehalose in Reduced-Moisture Organic Media

Enzymatic condensation of trehalose and myristic acid in organic media (2-methyl-2-butanol and acetone) with reduced moisture content was evaluated. Monomyristoyl trehalose was synthesized using immobilized lipase B from <em>Candida antarctica</em> (Novozym<sup>®</sup> 435). The product yield was significantly affected by process parameters, such as the initial moisture content in organic media, as well as in immobilized enzymes, and the added concentration of molecular sieves. Up to 25% yield of monomyristoyl trehalose could be attained, depending on the process. The experimental setup used in this study consisted of a multiphase component, i.e., Novozym<sup>®</sup> 435, an organic solvent, and molecular sieves. Moisture adsorbed either onto immobilized enzymes, or molecular sieves, and free moisture content in the organic solvent were characterized using individual experiments. The relationship between process parameters and the quantitative moisture distribution in the system was also investigated. The results presented in this paper indicates that a process design considering moisture distribution in the reaction system is important for understanding the effect of moisture on the reaction as well as for optimizing the process parameters.

Bioinspired Tungsten Dithiolene Catalysts for Hydrogen Evolution: A Combined Electrochemical, Photochemical, and Computational Study.

Bis(dithiolene)tungsten complexes, W(VI)O2 (L = dithiolene)2 and W(IV)O (L = dithiolene)2, which mimic the active site of formate dehydrogenases, have been characterized by cyclic voltammetry and controlled potential electrolysis in acetonitrile. They are shown to be able to catalyze the electroreduction of protons into hydrogen in acidic organic media, with good Faradaic yields (75-95%) and good activity (rate constants of 100 s(-1)), with relatively high overpotentials (700 mV). They also catalyze proton reduction into hydrogen upon visible light irradiation, in combination with [Ru(bipyridine)3](2+) as a photosensitizer and ascorbic acid as a sacrificial electron donor. On the basis of detailed DFT calculations, a reaction mechanism is proposed in which the starting W(VI)O2 (L = dithiolene)2 complex acts as a precatalyst and hydrogen is further formed from a key reduced W-hydroxo-hydride intermediate.

Anthracene coupled thiourea as a colorimetric sensor for F−/Cu2+ and fluorescent sensor for Hg2+/picric acid

A new dual chemosensor (Z)-2-(anthracen-9-ylmethylene)-N-phenylhydrazinecarbothioamide R1 was synthesized by incorporating a thiourea derivative as a binding unit and an anthracene group as a fluorescence signalling unit. R1 selectively binds with Cu2+ and Hg2+ ions in aqueous medium. R1 exhibits highly selective recognition towards F− ion and picric acid in organic medium. Fluorescence quenching was observed in case of R1 with Cu2+ and Hg2+ ions over commonly coexistent metal ions. Furthermore, fluorescence imaging experiments of Cu2+ and Hg2+ ions in living RAW 264.7 cells demonstrate its value of practical applications in biological systems.

Esterification degree of fructose laurate exerted by Candida antarctica lipase B in organic solvents

Sugar esters of fatty acids have many applications as biocompatible and biodegradable emulsifiers, which are determined by their degrees of esterification (DE). Direct esterification of fructose with lauric acid in organic media used commercial immobilized Candida antarctica lipase B (CALB) was investigated for DE. Significant difference of DE was observed between 2-methyl-2-butanol (2M2B) and methyl ethyl ketone (MEK), as di-ester/mono-ester molar ratio of 1.05:1 in 2M2B and 2.79:1 in MEK. Fourier transform infrared (FTIR) spectra showed that the secondary structure of the enzyme binding mono-ester presented distinct difference in 2M2B and MEK. Contents of β-turn and antiparallel β-sheet of CALB in 2M2B were 26.9% and 16.2%, respectively, but 19.1% and 13.2% in MEK. To understand the relationship between the conformational changes and differences of DE, mono-ester and fatty acid were directly employed for synthesis of di-ester. The maximum initial velocity of di-ester synthesis in MEK was 0.59mmolg(enzyme)−1h−1, which was 2.19-fold as greater as that in 2M2B, indicating that CALB conformation in MEK was preferred for the synthesis of di-ester. These results demonstrated that the conformation of CALB binding mono-ester affected by organic solvents essentially determined DE.

Esterification of organosolv lignin under supercritical conditions

An organosolv lignin, extracted in organic acid media, named Biolignin™, was acetylated with acetic anhydride in supercritical carbon dioxide (scCO2). The effect of moisture and specific surface of lignin sample, temperature (50, 80, 100, 150°C), reaction time and the use of a catalyst have been studied using analytical techniques such as FT-IR, quantitative 31P NMR and Differential Scanning Calorimetry (DSC).The reaction appeared to be more efficient when a dried organosolv lignin was used (97% Dry Matter) and with a specific surface of 0.645m2/g. The highest degree of substitution of acetylated samples was obtained after 1h of reaction at a temperature of 100°C (180bar) and in the presence of pyridine as a catalyst.When compared with conventionally acetylated lignin (using a solvent medium), it appeared that supercritical conditions allowed a higher yield of acetylation and a decrease of the glass transition temperature of the lignin.

New Chiral Cyclohexylhemicucurbit[6]uril

The first enantiomerically pure members of the cucurbituril family, (all-S)- and (all-R)-cyclohexylhemicucurbit[6]urils (cycHC), were synthesized in good yield (up to 85%). The crystal structure of this new macrocycle clearly shows its ball-like shape. CycHC monomers adopt a "zigzag" conformation, having apolar cyclohexyls around the openings and polar ureas in the middle. Cyclohexylhemicucurbit[6]urils formed complexes with halides, carboxylic acids and amines and diastereomeric complexes with methoxyphenylacetic acid in organic media. The association constants of cycHC with small organic compounds were evaluated by diffusion NMR in chloroform.

Characterization of Hybrid Sol-gel Coatings Applied over Tinplate

The present work studies the behavior of hybrid sol-gel films based on tetraethyl orthosilicate (TEOS) and vinyltrimethylsiloxane (VTMS) precursors applied over commercial tinplate. In previous works VTMS films obtained by the sol-gel technology were tested to verify their good corrosion performance over short immersion times in a citric acid/sodium citrate buffer solution. However, at longer exposure times the high porosity inherent to organic sol-gel films allows the aggressive media to reach the metallic substrate and start the corrosion process. In order to overcome these limitations, hybrid organic-inorganic sol-gel coatings were obtained using the dipcoating method. This work also studies the influence of the ageing time of the hybrid sol-gel in the formation of a uniform and continuous film. The obtained layers were characterized using a Scanning Electron Microscopy (SEM) and mechanical profilometry. The corrosion performance in organic acid media was tested using polarization curves and Electrochemical Impedance Spectroscopy (EIS) with a 0.1M citric/citrate buffer solution as electrolyte. The results obtained suggest that a minimum ageing time of 10 days is needed to obtain uniform films. The electrochemical measurements indicate a clear improvement on the barrier properties on the hybrid sol-gel compared to the organic ones. A major decrease in the impedance values after 24 hours of immersion indicates that it is necessary to improve the long-term barrier properties to achieve an industrial application.

Dealloying of single-phase Al2Au to nanoporous gold ribbon/film with tunable morphology in inorganic and organic acidic media

In this paper, the dealloying of single-phase Al2Au ribbons and morphological evolution of nanoporosity have been investigated in different inorganic and organic acid solutions. The results demonstrate that the acid strength coupled with the nature of acid anions can significantly influence the dealloying velocity, adatom diffusion and morphological evolution of the resultant nanoporous Au. Compared with those in inorganic acids, the dealloying velocities can be greatly reduced in organic carboxylic acids and severe passivation is prone to occur. The underlying mechanism of passivation occurring at the dealloying front in the organic acids has also been discussed.