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.

Substrate dependent photocatalytic performance of TiO2/MWCNT photocatalysts

Abstract: Titanium dioxide multiwall carbon nanotube (TiO2/MWCNT) composite photocatalysts were synthesized by the hydrolysis of titanium containing precursor adsorbed on the surface of MWCNT. Annealing was applied to convert amorphous titania oxide-hydroxide to crystalline material. The prepared photocatalysts were characterized with TEM, XRD and Raman spectroscopy. XRD and Raman results showed that only anatase-phase titanium dioxide is present in the samples. Generally this is the preferred phase as it is photocatalytically more active than all other TiO2 phases. TEM investigations revealed that the prepared photocatalysts have well defined structures; the MWCNTs were decorated with TiO2 nanoparticles. The photocatalysts were tested in aqueous-phase photocatalytic reactions using sol–gel prepared TiO2 as references. The choice of model compounds was based on their aromatic and polar characteristics. The concentration of the model compounds (phenol and oxalic acid) was measured by HPLC technique. These investigations showed that photocatalytic activity does depend on the model compound and the percentage of MWCNT content. The sample containing 5% MWCNT was the most efficient for oxalic acid decomposition under UV irradiation while the sample containing 1% MWCNT performed the best in phenol decomposition under our experiment conditions. For both model compounds, there are MWCNTs containing samples which are better than the similar way prepared TiO2 reference samples.

The release of iron-bearing minerals and dissolution of feldspars by heterotrophic bacteria of bacillus species

Abstract: Dissolution of aluminosilicates and Fe-oxyhydroxide minerals from granitic eluvium using bacteria of Bacillus genus was monitored with solution chemistry, granulometric and X-ray analyses as well as microscopic techniques to determine the effects of these bacteria on crystal surface and releasing mechanism of K, Si, Fe, and Al from minerals. Feldspars, quartz and micas are dominant minerals in granitic eluvium (GE). Oxyhydroxides of Fe are found in the intergranular spaces of minerals, contaminating and making most feldspar raw materials unsuitable for commercial applications. Bacteria of Bacillus spp. decrease pH of leaching medium by production of organic acids. These organic acids are directed by glycocalyx of adherent bacteria to specific sites on mineral surface (e.g. to crystal defects). The impregnated iron minerals are released by bacterial destruction of intergranular and cleavage spaces of silicate grains. This bacterial activity results in the release of Fe, Si, and K from feldspar and Fe oxyhydroxides. However pH of leaching medium is adjusted to neutral value in regular intervals during bioleaching to maintain bacterial activity. The decrease of fine-grained fraction is the result of bacterial destruction of GE. Despite the impoverishment of the distribution of fine-grained fraction, there was observed the increase of the surface area offeldspar grains from the value 3. 65 m 2 /g to value 4. 82 m 2 /g. This fact confirms the activity of bacteria of Bacillus genus together with hydrolysis in point corrosion of mineral grains. After 120 days of bioleaching, 31 % Fe extraction from granitic eluvium was observed. It was also possible to accelerate this process by using 0.1 Moxalic acid after 1 month's bacterial pretreatment. Moreover, the bacterial pretreatment facilitated the access of oxalic acid to Fe-bearing minerals and showed a possibility to use the oxalic acid in lower concentration. This fact is important especially from the view of producing less-agressive effluent to the environment and decreasing of costs in subsequent recyclation of oxalic acid.

Sources and atmospheric processes impacting oxalate at a suburban coastal site in Hong Kong: Insights inferred from 1 year hourly measurements

Abstract: Oxalic acid is one of the most abundant dicarboxylic acids in the atmosphere, receiving a great deal of attention due to its potential influence on cloud condensation nucleus activities. In this work, we report 10 months of hourly oxalate measurements in particulate matter of less than 2.5 µm in aerodynamic diameter (PM2.5) by a Monitor for Aerosols and Gases in ambient Air at a suburban coastal site in Hong Kong from April 2012 to February 2013. A total of more than 6000 sets of oxalate and inorganic ion data were obtained. The mean (±SD) oxalate concentration was 0.34 (±0.18) µg m−3, accounting for 2.8% of the total ion mass and 1.5% of the PM2.5 mass. Seasonal variation showed higher concentrations in fall and winter (0.54 and 0.36 µg m−3, respectively) and lower concentrations in spring and summer (~0.26 µg m−3). Different from the inorganic ions, a shallow dip in the oxalate concentration consistently occurred in the morning after sunrise (around 9:00 A.M.) throughout all seasons. Our analysis suggests that this was likely due to photolysis of oxalate-Fe (III) complex under sunlight. In summer, a small daytime peak was discernable for oxalate and nitrate. This characteristic, together with a more evident diurnal variation of O3, indicates comparatively more active photochemical oxidation in summer than other seasons. High correlations were observed between oxalate and non-sea-salt SO42− (NSS) (R2 = 0.63) and Ox (O3 + NO2) (R2 = 0.48), indicating significant commonality in their secondary formation. Positive matrix factorization analysis of oxalate and other real-time gas and particle-phase component data estimates that secondary formation processes, including secondary gas or aqueous oxidation processes (49%), oxidation processes of biomass burning emissions (37%), accounted for the majority of PM2.5 oxalate. A backward trajectories cluster analysis found that higher oxalate/NSS ratios were associated with low pollution samples under the influence of marine air masses while the ratios were lower in high pollution samples that were typically associated with continental air masses passing through areas of high anthropogenic emissions. Isolating the “low pollution marine” aerosols across the entire data set indicates that oxalate production increased in the summer compared to other seasons, suggesting either more active marine emissions of oxalate precursors or stronger photochemical processes in the summer.