Oxalic acid

About: Oxalic acid is a research topic. Over the lifetime, 11584 publications have been published within this topic receiving 173263 citations. The topic is also known as: ethanedioic acid & H2ox.

Effects of some carboxylic acids on the Fe(III)/UVA photocatalytic oxidation of muconic acid in water

Abstract: Aqueous solutions of muconic acid, taken as model compound, have been exposed to UVA radiation in the presence of Fe(III) and some carboxylic acids: citric, maleic, malic, malonic, succinic, tartaric and oxalic acids. Both black light lamps and solar light were used as a source of UVA radiation. Carboxylic acids studied can be classified into three groups according to the formation or not of photocatalytic or non-photocatalytic active ferricarboxylate complexes. Only carboxylic acids forming ferricarboxylate complexes that absorb in the UVA region are able to improve the photocatalytic oxidation rate of muconic acid since their photolysis likely yields free radicals that act as oxidants. Thus, citric, tartaric, malic and oxalic acids form photoactive ferricarboxylate complexes in the UVA region while malonic acid forms complexes that do not absorb light above 320 nm. Finally, succinic and maleic acids do not form complexes and, as a consequence, their presence do not improve muconic acid oxidation rate. Also, the presence of photoactive ferricarboxylate complexes improves the mineralization rate. Thus, working with black light, after 2 h reaction, TOC conversion increases from about 25% in the absence of carboxylate complexes up to approx. 48 and 75% in the presence of tartrate and oxalate complexes, respectively. The results are even better when solar light is used since total mineralization is reached after 2 h treatment. In this case, a linear correlation between muconic acid half life and 365 nm average intensity of solar radiance was observed. Fe(III)/UVA photocatalytic oxidation resulted to be more effective than TiO 2 /UVA photocatalytic oxidation at the conditions applied in this work.

Hydrogen peroxide evolution during V-UV photolysis of water

Abstract: Hydrogen peroxide evolution during the vacuum-ultraviolet (V-UV, 172 nm) photolysis of water is considerably affected by the presence of oxalic acid (employed as a model water pollutant) and striking differences are observed in the absence and in the presence of dioxygen.

X-Ray Diffraction and μ-Raman Investigation of the Monoclinic-Orthorhombic Phase Transition in Th1−xUx(C2O4)2·2H2O Solid Solutions

Abstract: A complete Th(1-x)U(x)(C(2)O(4))(2).2H(2)O solid solution was prepared by mild hydrothermal synthesis from a mixture of hydrochloric solutions containing cations and oxalic acid. The crystal structure has been solved from twinned single crystals for x = 0, 0.5, and 1 with monoclinic symmetry, space group C2/c, leading to unit cell parameters of a approximately 10.5 A, b approximately 8.5 A, and c approximately 9.6 A. The crystal structure consists of a two-dimensional arrangement of actinide centers connected through bis-bidentate oxalate ions forming squares. The actinide metal is coordinated by eight oxygen atoms from four oxalate entities and two water oxygen atoms forming a bicapped square antiprism. The connection between the layers is assumed by hydrogen bonds between the water molecules and the oxygen of oxalate of an adjacent layer. Under these conditions, the unit cell contains two independent oxalate ions. From high-temperature mu-Raman and X-ray diffraction studies, the compounds were found to undergo a transition to an orthorhombic form (space group Ccca). The major differences in the structural arrangement concern the symmetry of uranium, which decreases from C2 to D2, leading to a unique oxalate group. Consequently, the nu(s)(C-O) double band observed in the Raman spectra recorded at room temperature turned into a singlet. This transformation was then used to make the phase transition temperature more precise as a function of the uranium content of the sample.

Comparative study of the electrocatalytic oxidation and mechanism of nitrophenols at Bi-doped lead dioxide anodes

Abstract: The electrocatalytic oxidation of o -nitrophenol ( o -NP), m -nitrophenol ( m -NP) and p -nitrophenol ( p -NP) has been studied at Bi-doped lead dioxide anodes on acid medium by cyclic voltammetry and bulk electrolysis. The results of voltammetric studies indicated that these nitrophenol isomers were indirectly oxidized by OH radical in the solutions. Within the present experimental conditions used (50 mg of nitrophenol L −1 , pH 4.3, 30 mA cm −2 , 303 K), the complete decomposition of nitrophenols (NPs) was achieved. The electrocatalytic oxidation of NPs lay in the order: p -NP > m -NP > o -NP. Molecular configuration including the electron character and hydrogen bonds of NPs significantly influenced the electrocatalytic oxidation of these isomers. Hydroquinone, catechol, resorcinol, benzoquinone, aminophenols, glutaconic acid and maleic acid and oxalic acid have been detected as soluble products during the electrolysis of NPs. The possible degradation pathways of these isomers were proposed. The first stage is the release of nitro group from the aromatic rings. As a consequence, hydroquinone, catechol, resorcinol and benzoquinone are formed. These organic compounds are oxidized initially to carboxylic acids (glutaconic acid, maleic acid and oxalic acid) and later to carbon dioxide and water. Simultaneously, the reduction of NPs to aminophenols takes place at the cathode.