Presence Of Oxalate Anions Research Articles

Study on the Electrodeposition of Trivalent Chromium Plating Bath in the Presence of Oxalate Anions

Chromium is not easily electrodeposited from aqueous solutions based on trivalent chromium. Hull cell is employed to determine the optimum bath composition, and several electroplating baths were evaluated. The new bath with oxalate and acetate anions produces very good coatings and our results are valuable for the electroplating community and electrochemists. The baths presented a current efficiency of 37%, high covering power at 8.2 cm, low deposition potential of 7.3 V, and deposition rate of 0.4 μm/min. However, the Hull cell required a high current density (30 A/dm2). After 2 h of the electrodeposition process, the pH values change by 0.2 units. In addition, the baths were analyzed after electrolysis to detect Cr(VI), and this cation was not detected. Our study not only has a technological contribution but also presents a new explanation for the nature of these baths. In the literature, the usual explanation of the performance of these baths is based on the formation of complexes between ligands and Cr(III); however, our novel explanation is based on the high stability of water in the first solvation sphere of Cr(III), and we support our suggestions with several references to chromium solvation studies. The ligand-exchange reaction explanation is replaced by the second sphere hypothesis, that is, our explanation is based on the large stabilization energy of Cr−O bonds in [Cr(H2O)6]3+. Figure 1

Evaluation of the Corrosion Inhibiting Capacity of Silica/Polypyrrole-Oxalate Nanocomposite in Epoxy Coatings

Silica/Polypyrrole nanocomposites (SiO2/PPy) incorporating oxalate as counter anion (SiO2/PPyOx) were chemically polymerized in the solution with the presence of pyrrole, silica, and sodium oxalate. Nanocomposites SiO2/PPyOx at different concentrations of oxalate anion were characterized with FTIR, XRD, EDX, TGA, and TEM. The corrosion protective properties for carbon steel of nanocomposites in epoxy coating were studied by electrochemical techniques including electrochemical impedance spectroscopy (EIS) and open circuit potential (OCP). FTIR results of nanocomposites show a slightly red-shift in terms of wavelength compared with the case of PPy and SiO2 spectra. It may be due to a better conjugation and interactions between PPy and SiO2 in nanocomposite structure. TEM image indicated that nanocomposites have spherical morphologies with diameters between 100 and 150 nm. The EIS results showed that |Z| modulus values of epoxy coatings containing SiO2/PPyOx composites reached about 109.7 Ω.cm2, always higher than that of epoxy coating. These results are also confirmed by OCP results. It proves that the presence of oxalate anion can enhance the resistance against corrosion and it has been shown that the content of counter anion strongly affects the anticorrosion ability.

Enhanced visible light photocatalytic performance of Ag3PO4 through doping by different trivalent Lanthanide cations

To explore the efficacy of lanthanides doping on photocatalytic performance of silver orthophosphate, Gd-doped, Dy-doped and Er-doped Ag3PO4 nanoparticles were prepared by co-precipitation method. All synthesized samples were characterized systematically. The photocatalytic activity of pure and M-doped Ag3PO4 (M=Gd, Dy and Er) was compared in degradation of an Anthraquinone dye (Ractive Blue 19). In order to comprehensive comparison, photocatalytic processes by M-doped Ag3PO4 were individually optimized by Response Surface Methodology (RSM). At the optimal conditions proposed by RSM, the photocatalytic degradation efficiency by Gd-doped, Dy-doped and Er-doped Ag3PO4 were 80.4, 92.4 and 57.8%, respectively. Due to the considerable decrease in degradation efficiency in the presence of oxalate anion and p-benzoquinone, photogenerated holes and superoxide anion radicals were detected as the main reactive species in degradation of RB19. The main role of the trivalent lanthanide cations in Ag3PO4 photocatalytic activity enhancement was also discussed.

Effect of gadollunium doping on visible light photocatalytic performance of Ag3PO4: Evaluation of activity in degradation of an anthraquinone dye and mechanism study

Gadolinium (Gd)-doped silver orthophosphate (Ag3PO4) nanoparticles, with spherical morphology, were synthesized by a co-precipitation method and their photocatalytic activities were evaluated in degradation of Reactive Blue 19 (RB19), as a model organic pollutant. The synthesized Ag3PO4 and Gd-doped Ag3PO4 were characterized using X-ray diffraction pattern analysis, scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, diffuse reflectance UV–vis spectroscopy and photoluminescence spectroscopy. In comparison with Ag3PO4, the experimental results revealed a considerable enhancement in photocatalytic activity of Gd-doped Ag3PO4. The optimum mole fraction of Gd loading in Ag3PO4 was 3%. Lower photocatalytic degradation efficiency of RB19 in the presence of oxalate anion and p-benzoquinone indicated the crucial role of photogenerated holes and superoxide anion-radicals in photocatalysis on Gd-doped Ag3PO4. The enhancement of photocatalytic activity was attributed to scavenge the photoexcited electrons, and to suppress their recombination with holes and generation of active oxygen species. A nonlinear empirical kinetic model was introduced to predict the apparent first order rate constant (kapp) as a function of operational parameters, including initial RB19 concentration, Gd-doped Ag3PO4 dosage and light intensity. Degradation byproducts were identified using gas chromatography-mass spectrometry and a probable pathway was proposed. Moreover, Gd-doped Ag3PO4 samples displayed adequate reusability after three successive experiments.

Effect of Oxalate Anions on Zinc Electrodeposition from an Acidic Sulphate Bath

Zinc coatings were electrodeposited on steel substrate. The effect of oxalate anions as chelating agents on nucleation and growth mechanism, surface morphology, predominant texture and corrosion behaviour of zinc electrodeposits was investigated. Evaluation of nucleation mode of zinc in the presence and absence of oxalate anions showed that the instantaneous nucleation is predominant in both cases. From the AFM images, the nuclei densities for zinc deposition were 3.5 × 109 and 2 × 109 cm−2 in the absence and presence of oxalate anions, respectively. These are one order of magnitude higher than those obtained by analysis. Electrochemical impedance spectroscopy revealed that in the bath containing oxalate anions, the growth of deposit is semi-infinite diffusion controlled. While in the absence of oxalate anions, the charge transfer control was governed. In the absence of oxalate anions, the texture components of zinc coating were mostly basal and low angle pyramidal planes, whereas in the presence of oxalate anions, the high angle pyramidal and prism planes were dominant. Furthermore, oxalate anions changed the zinc surface morphology from packets of hexagonal platelets to a granular nature. In the presence of oxalate anions, the zinc coating produced had a better corrosion resistance than that deposited from bath without oxalate anions.

Interaction of Zn(II) with Hematite Nanoparticles and Microparticles: Part 2. ATR-FTIR and EXAFS Study of the Aqueous Zn(II)/Oxalate/Hematite Ternary System

Sorption of Zn(II) to hematite nanoparticles (HN) (av diam=10.5 nm) and microparticles (HM) (av diam=550 nm) was studied in the presence of oxalate anions (Ox2-(aq)) in aqueous solutions as a function of total Zn(II)(aq) to total Ox2-(aq) concentration ratio (R=[Zn(II)(aq)]tot/[Ox2-(aq)]tot) at pH 5.5. Zn(II) uptake is similar in extent for both the Zn(II)/Ox/HN and Zn(II)/Ox/HM ternary systems and the Zn(II)/HN binary system at [Zn(II)(aq)](tot)<4 mM, whereas it is 50-100% higher for the Zn(II)/Ox/HN system than for the Zn(II)/Ox/HM ternary and the Zn(II)/HN and Zn(II)/HM binary systems at [Zn(II)(aq)]tot>4 mM. In contrast, Zn(II) uptake for the Zn(II)/HM binary system is a factor of 2 greater than that for the Zn(II)/Ox/HM and Zn(II)/Ox/HN ternary systems and the Zn(II)/HN binary system at [Zn(II)(aq)]tot<4 mM. In the Zn(II)/Ox/HM ternary system at both R values examined (0.16 and 0.68), attenuated total reflectance Fourier transform infrared (ATR-FTIR) results are consistent with the presence of inner-sphere oxalate complexes and outer-sphere ZnOx(aq) complexes, and/or type A ternary complexes. In addition, extended X-ray absorption fine structure (EXAFS) spectroscopic results suggest that type A ternary surface complexes (i.e., >O2-Zn-Ox) are present. In the Zn(II)/Ox/HN ternary system at R=0.15, ATR-FTIR results indicate the presence of inner-sphere oxalate and outer-sphere ZnOx(aq) complexes; the EXAFS results provide no evidence for inner-sphere Zn(II) complexes or type A ternary complexes. In contrast, ATR-FTIR results for the Zn/Ox/HN sample with R = 0.68 are consistent with a ZnOx(s)-like surface precipitate and possibly type B ternary surface complexes (i.e., >O2-Ox-Zn). EXAFS results are also consistent with the presence of ZnOx(s)-like precipitates. We ascribe the observed increase of Zn(II)(aq) uptake in the Zn(II)/Ox/HN ternary system at [Zn(II)(aq)]tot>or=4 mM relative to the Zn(II)/Ox/HM ternary system to formation of a ZnOx(s)-like precipitate at the hematite nanoparticle/water interface.

Selective photocatalytic reduction of nitrate to nitrogen molecules in an aqueous suspension of metal-loaded titanium(iv) oxide particles

Nitrate was photocatalytically reduced to nitrogen molecules with a high selectivity in a basic aqueous suspension of palladium and copper-loaded titanium(IV) oxide powders in the presence of oxalate anion as a hole scavenger.

Sorption of Zr(IV) on KU-2 Cation Exchanger in the Presence of Oxalate Anions

Sorption of Zr(IV) from 0.1-3.0 M HNO3 aqueous solutions on KU-2 cation exchanger in the presence and in the absence of oxalate anions was studied. It was found that at certain concentrations of oxalate anions Zr(IV) sorption on the cation exchanger increases. Probable mechanisms of this phenomenon are analyzed.

Enhanced Pitting Corrosion Resistance of Aluminum Alloy 7075 in the Presence of Oxalate Anions

Abstract The presence of oxalate in chloride (Cl−)-containing corrosive aqueous media was found to protect aluminum (Al) alloy AA 7075 (UNS A97075). The effect of 0.05 M sodium oxalate on induction...

Precipitation of calcium carbonate in aqueous solutions in the presence of oxalate anions

Precipitation of calcium carbonate in aqueous solutions in the presence of oxalate anions

Photoreduction of deazaflavin. Spectroscopic investigations

Photophysical and photochemical properties of deazaflavin (3,10-dimethylpyrimido[4,5-b]quinoline- 2,4-(3H,10H)-dione) and some of its 1,5-dihydro derivatives have been investigated. Contrary to earlier reports the photodimer of deazaflavin is non-luminescent throughout the temperature range 77-295 K. Excitation of deazaflavin in the presence of oxalate anion (acetate buffer pH 5.0) causes photodimerization with quantum efficiencies exceeding unity. A mechanism involving a triplet excimer of deazaflavin has been proposed for this reaction.