Aqueous Oxalic Acid Research Articles

Poly( N-methylpyrrole) electrodeposited on copper: Corrosion protection properties

Electrochemical synthesis of poly( N-methylpyrrole) films on copper electrodes from an aqueous oxalic acid has been achieved. A potential higher than 2 V (SCE) was needed to generate the polymer, for this reason, the polymer was in the overoxidized state. The inhibiting corrosion properties of this coating on copper were investigated for the first time in aqueous 0.1 M sodium chloride solution using potentiodynamic polarization, Tafel analyses, open-circuit potential and electrochemical impedance spectroscopy. Corrosion protection properties comparable to those of polypyrrole (PPy) films were observed for these films. A physical barrier effect is the most likely protection mechanism.

Synthesis and photocatalytic activity of CuY yFe 2− yO 4–CuCo 2O 4 nanocomposites for H 2 evolution under visible light irradiation

Spinel-type CuY yFe 2− y O 4–CuCo 2O 4 nanocomposites have been successfully synthesized via a facile citric acid (CA)-assisted sol–gel method. And the as-synthesized nanocomposites have been characterized by techniques of X-ray diffraction (XRD), nitrogen adsorption BET method, and transmission electron microscopy (TEM). The samples are composed of primary ultrafine nanoparticles with nearly spherical morphology and mean particle size of about 80 nm. Moreover, the photocatalytic H 2 evolution activity of the as-obtained samples has been evaluated from aqueous oxalic acid solution under visible light irradiation. The influence of photocatalyst type, calcination temperature, Y 3+ doping content, and the durability of the as-obtained photocatalyst have been investigated in detail. The best photocatalytic H 2 evolution activity was obtained over the as-synthesized CuY 0.08Fe 1.92O 4–CuCo 2O 4 nanocomposite.

Influence of phosphate ion dopant on corrosion protection properties of polypyrrole coatings on carbon steel

Polypyrrole (PPy) and polypyrrole-phosphate (PPyP) coatings were electropolymerised onto carbon steel electrodes in aqueous oxalic acid solution using the cyclic voltammetry technique. The electropolymerisation of PPyP was carried out with addition of trisodium phosphate to the supporting electrolyte. Prepared coatings were characterised using scanning electron microscopy. In addition, the ability of the coatings to control the corrosion of carbon steel was studied with the help of a variety of electrochemical methods: open circuit potential monitoring, potentiodynamic polarisation and electrochemical impedance spectroscopy all in 3·5% NaCl solution. All the results have consistently indicated that carbon steel is better protected by the PPyP coating than by the PPy coating.

Synthesis and reactivity of alkenyl- and alkynyl-substituted β,β-dihalo-and β,β,β-trichloroamines

β,β-Dihalo- and β,β,β-trichloroamines, obtained by Lewis acid-promoted Petasis-type reaction of α,α-dichlorinated and α,α,α-trichlorinated imines or reduction of α,α-dihaloaldimines, were subjected to a reactivity study and turned out to be remarkably stable compounds. In general, only the bases KO t Bu and NaOMe cause a 1,2-dehydrochlorination with formation of unsaturated α-chloroimines or unsaturated α,α-dichloroimines. Hydrolysis of the α-chloroimines with aqueous oxalic acid resulted in the formation of the corresponding unsaturated α-chloroketones. The reaction of simple β,β-dihaloamines with NaOMe and KO t Bu generated 2-haloprop-2-enylmines and 2,2-dimethoxypropylamines.

Synthesis of (1S,3R,5R,7S)-Sordidin, the Main Component of the Aggregation Pheromone of the Banana Weevil Cosmopolites sordidus

A synthesis of the banana weevil pheromone component (1S,3R,5R,7S)-sordidin starting from (S)-2-(2-ethyl-1,3-dioxolanyl)propan-1-ol and (R)-4-hydroxypentan-2-one is described. No epimerization was observed for the final, intramolecular, acid-catalyzed cyclization step using aqueous oxalic acid.

Photocatalytic activity evaluation of tetragonal CuFe 2O 4 nanoparticles for the H 2 evolution under visible light irradiation

Copper ferrite (CuFe 2O 4) nanoparticles have been successfully synthesized via a citric acid-assisted sol–gel method. For comparison, CuFe 2O 4 materials were also fabricated by solid-state reaction and co-precipitation method. Techniques of X-ray diffraction (XRD), transmission electron microscopy (TEM) and UV–vis diffuse reflectance spectrum (UV–vis DRS) have been employed to characterize the as-synthesized CuFe 2O 4 products. The CuFe 2O 4 sample prepared by sol–gel approach is composed of almost uniform nanoparticles with a grain size of about 80 nm and crystallized in a tetragonal crystal phase structure. Moreover, the photocatalytic activity of the as-obtained CuFe 2O 4 has been evaluated based on the H 2 evolution from aqueous oxalic acid solution under visible light irradiation. The effects of preparation routes, photocatalyst mass concentration, initial sacrificial reagent concentration and the durability of the as-obtained CuFe 2O 4 have been investigated in detail. The best result of the photocatalytic H 2 evolution activity (1.72 mmol h −1 g cat −1) was obtained over the sol–gel synthesized CuFe 2O 4 nanoparticles when the photocatalyst concentration is 1.0 g l −1 and the oxalic acid concentration is 0.05 M.

Preparation of a titanium dioxide photocatalyst codoped with cerium and iodine and its performance in the degradation of oxalic acid

A novel class of visible light-activated photocatalysts was prepared by codoping TiO 2 with cerium and iodine (Ce–I–TiO 2). The particles were characterized using the Brunauer–Emmett–Teller method, X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy and UV–Visible light absorption. Particles of Ce–I–TiO 2 had greater photoabsorption in the 400–800 nm wavelength range than iodine-doped TiO 2 (I–TiO 2). The effects on the photocatalytic degradation of oxalic acid under visible light or UV–Visible light irradiation were investigated. The photocatalytic activity of Ce–I–TiO 2 calcined at 673 K was significantly higher than that of Ce–I–TiO 2 calcined at 773 K and I–TiO 2 calcined at 673 K in aqueous oxalic acid solution under visible light or UV–Visible light irradiation. Under visible light irradiation, oxalic acid was first adsorbed on the surface of the catalysts rather than reacted with free radicals in the bulk solution, and then oxidized by OH ads to CO 2, which was verified by studying the effects of nitrogen purging and scavengers, as well as by gas chromatography/mass spectrometry.

A Visible Light-Driven Titanium Dioxide Photocatalyst Codoped with Lanthanum and Iodine: An Application in the Degradation of Oxalic Acid

A series of photocatalysts was synthesized by codoping TiO2 with lanthanum and iodine (La−I−TiO2). The structure and properties of the catalysts were studied by X-ray diffraction (XRD), the Brunauer−Emmett−Teller (BET) method, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and UV−vis diffuse reflectance spectra. The prepared anatase-phase La−I−TiO2 (molar ratio 20:20:100) calcined at 400 °C had a BET surface area of 92.9 m2 g−1, and the crystallite size calculated from XRD data was ∼3.57 nm, and it had a remarkable absorption in the visible light range of 400−550 nm. The catalytic efficiency was tested by monitoring the photocatalytic degradation of oxalic acid under visible light irradiation. An optimum molar ratio of 20:100 La/TiO2 was determined for the most efficient inhibition of the recombination of electron−hole pairs and the photocatalytic activity of La−I−TiO2 calcined at 400 °C was significantly higher than that calcined at 500 or 600 °C in aqueous oxalic acid so...

Electrochemical synthesis and characterization of poly(pyrrole- co- o-toluidine)

The electrochemical polymerization of o-toluidine has been investigated in oxalic acid solution. It was shown that the oxidation of monomer could be achieved but this process does not yield a stable, homogenous polymer film on either platinum or mild steel electrodes. Therefore the copolymerization between pyrrole and o-toluidine has been studied as an alternative method for obtaining good quality coating (low permeability and water mobility, high stability), which could also be easily synthesized on steel. For this aim, various monomer feed ratio solutions of pyrrole: o-toluidine 9:1, 8:2 and 7:3 have been examined, in aqueous oxalic acid solution. By using cyclic voltammetry technique, copolymer films were realized on platinum and steel, successfully. The temperature of synthesis solution was found to have a vital role on polymerization and film growth, as much as the monomer feed ratio. The synthesis of homogenous copolymer film could only be achieved under ≤25 °C conditions with using the 9:1 ratio, while the 8:2 ratios could only produce stable films below 5 °C. As the amount of o-toludine increased the required temperature value decreased further, 7:3 ratio could only give a stable copolymer film below 2 °C. The characterization of deposited copolymer coating has been realized by using SEM micrographs, UV–vis and FT-IR spectroscopy techniques and cyclic voltammetry. The protective behaviour of these coatings was also investigated against mild steel corrosion in 3.5% NaCl solution, by means of electrochemical impedance spectroscopy (EIS) and anodic polarization curves. It was found that the monomer feed 8:2 ratio gave the most effective coating against the corrosion of mild steel.

Electrochemical treatment of aqueous oxalic acid solution by using solid polymer electrolyte (SPE) reactor

In this study, the feasibility of electrochemical oxidation of the aqueous oxalic acid solution has been investigated in an electrochemical reactor with SPE and simultaneous hydrogen production has been observed. Experiments were conducted to examine the effects of applied current density, flow rate of solution, pH of the solution, the concentration of supporting electrolyte, the temperature of the solution, types of the electrode and membrane material on removal efficiency. As a result of the studies oxalic acid as COD at the original pH can be treated to meet discharge limits at ambient temperature without any pH adjustment with low energy consumption. COD removal efficiency of 97% has been achieved by using titanium oxide coated with iridium oxide as anode. Since there is no need to use liquid electrolyte in this type of reactor, aqueous oxalic acid solution can be oxidized without adding any supporting electrolyte such as Na2SO4.

Electrochemical synthesis and corrosion performance of poly(pyrrole-co- o-anisidine)

The electrochemical synthesis of poly( o-anisidine) homopolymer and its copolymerization with pyrrole have been investigated on mild steel. The copolymer films have been synthesized from aqueous oxalic acid solutions containing different ratios of monomer concentrations: pyrrole: o-anisidine, 9:1, 8:2, 6:4, 1:1. The characterization of polymer films were achieved with FT-IR, UV–visible spectroscopy and cyclic voltammetry techniques. The electrochemical synthesis of homogeneous-stable poly( o-anisidine) film with desired thickness was very difficult on steel surface. Therefore its copolymer with pyrrole has been studied to obtain a polymer film, which could be synthesized easily and posses the good physical–chemical properties of anisidine. The kinetics and rate of copolymer film growth were strongly related to monomer feed ratio. The introduction of pyrrole unit into synthesis solution increased the rate of polymerization and the substrate surface became covered with polymer film soon, while this process required longer periods in single o-anisidine containing solution. The protective behavior of coatings has been investigated against steel corrosion in 3.5% NaCl solution. For this aim electrochemical impedance spectroscopy (EIS) and anodic polarization curves were utilized. The synthesized poly( o-anisidine) coating exhibited significant protection efficiency against mild steel corrosion. It was shown that 6:4 ratio of pyrrole and anisidine solution gave the most stable and corrosion protective copolymer coating.

Apparent molar volumes of mono- and di-saccharides in water and in aqueous oxalic acid solutions at 293.15, 303.15, 313.15 and 323.15 K

Apparent molar volumes (V Φ ) have been determined for mono- and di-saccharides, [D(+)-glucose, D(-)-fructose and sucrose] in water and in aqueous oxalic acid solutions at different concentrations in the range 0.2-1.0 mol kg -1 by measuring the densities at (293.15, 303.15, 313.15 and 323.15) K. The limiting apparent molar volumes (V 0 Φ ) and experimental slope (S v ) have been obtained in each case and their significance has been discussed briefly. The partial molar volumes (V 0 2 ) have been used to calculate the partial molar volumes of transfer (ΔV 0 Φ ) of mono- and di-saccharides from water to aqueous oxalic acid solutions at different temperatures. The values of limiting apparent molar expansibilities (Φ 0 E ) and that of (∂ 2 V 0 Φ /∂T 2 ) P have been determined from temperature-dependence of V 0 Φ . It is concluded that all the saccharides behave as structure makers in water as well as in aqueous solutions of oxalic acid.

Improving corrosion protection performance of polypyrrole coating by tungstate ion dopants

Polypyrrole ( PPy ) and polypyrrole-tungstate ( PPy - ) coatings were electrodeposited on mild steel (MS) electrodes by cyclic voltammetry (CV) technique. Aqueous oxalic acid solution was used as sup- porting electrolyte for these processes. For the electrodeposition of PPy - , tungstate anion was added to the supporting electrolyte. The surface morphologies of the two types of coated-samples were characterized by scanning electron microscopy (SEM) and line-scan EDX analysis. Furthermore, open circuit potential (OCP) monitoring, polarization and electrochemical impedance spectroscopy methods were performed for comparing the corrosion protection performances. Corrosion studies indicate that dopants can improve corrosion protection properties by taking part in: (i) the passivation process occurred prior to electrodeposition process, (ii) the electrosynthesis process and incorporation into polymer chain.

Poly(2,5‐dimethoxyaniline) films on mild steel for application to glucose biosensor

AbstractPoly(2,5‐dimethoxyaniline) (PDMA) films were electrochemically synthesized on mild steel from an aqueous oxalic acid solution using galvanostatic mode. These films were characterized by potential–time curve, UV‐visible absorption spectroscopy, Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). The enzyme glucose oxidase (GOx) was entrapped into the PDMA film by a physical adsorption method. The resulting PDMA–GOx films were characterized by UV‐visible absorption spectroscopy, FTIR, and SEM. The amperometric response of the PDMA–GOx films was measured as a function of glucose concentration in phosphate buffer solution (pH 7.3). The PDMA–GOx films exhibit a fast and linear amperometric response in the range of 2–20 mM glucose. The maximum current density and Michaelis–Menten constant of PDMA/GOx films are found to be ∼483 μA/cm2 and 1.12 mM, respectively. The shelf stability and thermal stability of these films were also investigated. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008

The activation of heterogeneous Fenton-type catalyst Fe-MFI

Abstract The activation of iron-containing zeolite of MFI structure with mineral and carboxylic acids in heterogeneous Fenton reaction was experimentally studied. The catalytic activity of the zeolite was tested in the hydrogen peroxide decomposition reaction. The activation effect of acids was observed in the following decreasing order: oxalic > acetic > hydrochloric > formic. The catalyst pre-treatment with nitric acid was ineffective. Optimum conditions for the most effective pre-treatment of the zeolite with aqueous oxalic acid solutions were established.

Inhibition of corrosion of mild steel by homopolymer and bilayer coatings of polyaniline and polypyrrole

Homopolymers and bilayers of polyaniline (PAni) and polypyrrole (PPy) coatings have been electropolymerized on mild steel by potentiodynamic synthesis technique in aqueous oxalic acid solutions. Characterization of coatings was carried out by cyclic voltammetry. Corrosion behavior of the polymer coated mild steel electrodes was investigated using linear anodic potentiodynamic polarization, Tafel test and electrochemical impedance spectroscopy (EIS) techniques in various aqueous corrosive solutions. Corrosion test results clearly showed that PPy and PAni/PPy bilayer coatings served as a stable host matrix on mild steel against corrosion. However, bilayers of PAni and PPy did not exhibit good combined properties of each polymer, unlike expected. PPy exhibited the best corrosion resistance among all coatings.

The adsorption and photodegradation of oxalic acid at the TiO2 surface

ATR-FTIR measurements in combination with quantum chemical calculations were performed to study chemical reactions taking place at the surface of a thin TiO2 layer immersed in an aqueous oxalic acid solution under UV(A) illumination. It was found that the adsorption of oxalic acid on TiO2 in the dark can be explained in terms of two surface complexes for the anatase phase. Under UV(A) illumination, one of the adsorbed species on the anatase phase preferably undergoes photo-degradation and at the same time more molecules of oxalic acid are adsorbed at the TiO2 surface which is thus enriched in the second complexation mode. The spectral changes observed under UV(A) illumination are explained in the light of different theories: photo-desorption of water molecules as a thermal mechanism induced by the absorption of photons, surface reconstruction, and newly exposed surface area provided by the de-aggregation of the TiO2 particles.

Poly( N-methyl pyrrole) and its copolymer with pyrrole for mild steel protection

In this study, it was aimed to overcome disadvantages of polypyrrole films like water up taking and resulting low stability, via copolymerization of pyrrole and N-methyl pyrrole and preparing their bilayer films. Poly( N-methyl pyrrole) coating was synthesized electrochemically on mild steel and its corrosion performance has been investigated in 3.5% NaCl aqueous solution, by using electrochemical impedance spectroscopy (EIS), anodic polarization curves and open circuit potential-time relation. This coating was found to have lower protection efficiency than single poly(pyrrole) coating. This case was related to weak adsorption behavior of poly( N-methyl pyrrole) film on mild steel. On the other hand, when this film was applied as a top coat on polypyrrole coated sample; the obtained coating system hindered the attack of corrosive environment and protected mild steel efficiently. The underlying poly(pyrrole) film was strongly adherent and the top poly( N-methyl pyrrole) coat improved barrier property by decreasing permeability and water mobility. Poly(pyrrole-co- N-methyl pyrrole) has also been synthesized from aqueous oxalic acid solutions containing various ratios of these two monomers. The copolymerization rate and protective behavior of copolymer were strongly affected by the monomer concentration ratio. The ratio of 1:3 ( N-methyl pyrrole/pyrrole) gave the most protective copolymer coating and it exhibited better barrier property than single PPy. This was related to introduction of –CH 3 group which creates hydrophobic effect, when compared to –NH group of pyrrole unit. However, the solution with the ratio of 1:1 yielded a coating which had lower protection efficiency than single poly(pyrrole) film. This behavior was attributed to significant decrease in adsorption strength as the ratio of n-methyl pyrrole increased.

Poly(o-anisidine) films on mild steel: electrochemical synthesis and biosensor application

Poly(o-anisidine) (POA) films were synthesized on mild steel from an aqueous oxalic acid solution by electrochemical polymerization of o-anisidine using cyclic voltammetry. These films were characterized by cyclic voltammetry, UV–visible absorption spectroscopy, Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). The enzyme glucose oxidase (GOx) was entrapped into the POA film by a physical adsorption method. The resulting POA–GOx films were characterized by UV–visible absorption spectroscopy, FTIR and SEM. The amperometric response of the POA–GOx films was measured as a function of glucose concentration in phosphate buffer solution (pH 7.3). The POA–GOx films exhibited a fast amperometric response (1–5 s) and a linear response in the range of 2–20 mM glucose. The maximum current density and Michaelis–Menten constant of POA/GOx films were found to be ∼406 µA cm−2 and 1.03 mM, respectively. The shelf stability, operational stability and thermal stability of these films were also investigated.

Polypyrrole films modified with graphite layer on mild steel

Electrochemically synthesized polypyrrole coating was modified with very thin graphite layer and top coated with another polypyrrole film. The corrosion behaviour of this coating has been investigated in aqueous sodium chloride solution. The synthesis of polypyrrole coatings was carried out by cyclic voltammetry technique, from aqueous oxalic acid solution. Electrochemical impedance spectroscopy and potentiodynamic measurements were used for corrosion tests. The cyclic voltammograms obtained in oxalic acid solution and the polarisation curves obtained in sodium chloride solution showed that the stability of coating was improved significantly by graphite layer. The impedance spectra also showed that the corrosion process was controlled by the diffusion rate along the coating, even after 96 h immersion period. The Warburg coefficient values were calculated and used to evaluate the barrier property of coating with time. It was shown that the water up taking process was slowed down by the hydrophobic nature of the graphite layer sandwiched between the two polypyrrole films.