Formation Of Oxalic Acid Research Articles

UV-photoprocessing of acetic acid (CH3COOH)-bearing interstellar ice analogues

ABSTRACT Acetic acid (CH3COOH) was detected in the gas towards interstellar clouds, hot cores, protostars, and comets. Its formation in ice mantles was proposed, and acetic acid awaits detection in the infrared spectra of the ice as most of the other complex organic molecules except methanol. The thermal annealing and UV-irradiation of acetic acid in the ice was simulated experimentally in this work under astrophysically relevant conditions. The experiments were performed under ultrahigh vacuum conditions. An ice layer was formed by vapour deposition onto a cold substrate, and was warmed up or exposed to ultraviolet (UV) photons. The ice was monitored by infrared spectroscopy, while the molecules desorbing to the gas phase were measured using a quadrupole mass spectrometer. The transformation of the CH3COOH monomers to cyclic dimers occurs at 120 K, and the crystal form composed of chain polymers was observed above 160 K during warm-up of the ice. Ice sublimation proceeds at 189 K in our experiments. Upon UV-irradiation, simpler species and radicals are formed, which leads to a residue made of complex molecules after warm-up to the room temperature. The possible formation of oxalic acid needs to be confirmed. The photodestruction of acetic acid molecules is reduced when mixed with water in the ice. This work may serve to search for the acetic acid photoproducts in lines of sight where this species is detected. A comparison of the reported laboratory infrared spectra with current JWST observations allows to detect or set upper limits on the CH3COOH abundances in interstellar and circumstellar ice mantles.

Direct photodegradation of internally mixed sodium chloride and malonic acid single aerosols: Impact of the photoproducts on the hygroscopic properties of the particles

Sea-salt aerosols (SSA) are one of the key natural aerosols in our atmosphere, consisting predominantly of sodium chloride (NaCl). Throughout their atmospheric transport, these aerosols undergo complex internal mixing, giving rise to a rich variety of inorganic and organic species, including dicarboxylic acids. This study investigates firstly the composition and deliquescence properties of coarse particles containing pure malonic acid (MA2, CH2(COOH)2) and internally mixed NaCl and MA2, by means of an acoustic levitation system coupled with a Raman microspectrometer. Secondly, we report here the first experimental observation and characterization of the products arising from photochemical reactions under UV–Visible irradiation (338 ≤ λ ≤ 414 nm) in the absence of an oxidant under acoustic levitation conditions in MA2 and NaCl/MA2 aerosols. Furthermore, the impact of photodegradation on the hygroscopic properties of these particles is examined. We confirmed the irreversible formation of monosodium malonate (NaMA, HOOCCH2COONa), which coexists with NaCl or MA2 on non-irradiated particles. We also demonstrated the formation of oxalic acid (OA2, HOOC–COOH) within irradiated MA2 droplets and the appearance of glyoxylic acid (GlyA, HCOCOOH) in NaCl containing droplets. The photolysis process exerts a marked effect on the hygroscopic properties of the particles, resulting in a shift in deliquescence transitions toward higher relative humidity (RH) values. This study contributes to the understanding of the intricate physicochemical processes involved in SSA during their atmospheric transport. Likewise, this work sheds light on the impacts of these types of aerosols on cloud formation and climate change.

New Insights into Urea Electro-Oxidation: Complete Mass-Balances and Proof of Concept with Real-Matrix Effluent

In the present work, all the by-products formed during the urea electrooxidation (UEO) by Ni(III) in alkaline medium are identified and quantified for the first time (e.g., ). Complete mass balances are simultaneously established in both aqueous and gas phases for large urea conversion rates (>80%). The results provide clear evidence (with a maximal deviation of 2%) that, in addition to N-overoxidized by-products are produced during the UEO. Electrolyses conducted with human urine samples under identical operating conditions result in different distributions of N and C-by-products. In particular, the formation of formic and oxalic acids in these latter experiments suggests the presence of different and/or additional mechanistic pathways during the UEO process. The amount of generated at the cathode is also quantified, showing a reduction of 30% in energy consumption when compared with water electrolysis. Finally, this study assesses the energy efficiency of UEO with urea synthetic and real-matrix effluents, thereby contributing to the development of this sustainable process, which enables energy recovery from waste.

Direct synthesis of oxalic acid via oxidative CO coupling mediated by a dinuclear hydroxycarbonylcobalt(III) complex

Oxidative coupling of CO is a straightforward and economic benign synthetic route for value-added α-diketone moiety containing C2 or higher carbon compounds in both laboratory and industry, but is still undeveloped to date. In this work, a rare coplanar dinuclear hydroxycarbonylcobalt(III) complex, bearing a Schiff-base macrocyclic equatorial ligand and a μ-κ1(O):κ1(O’)-acetate bridging axial ligand, is synthesized and characterized. The Co(III)-COOH bonds in this complex can be feasibly photocleaved, leading to the formation of oxalic acid. Moreover, the light-promoted catalytic direct production of oxalic acid from CO and H2O using O2 as the oxidant with good selectivity (> 95%) and atom economy at ambient temperature and gas pressure based on this dicobalt(III) complex have been achieved, with a turnover number of 38.5. The 13C-labelling and 18O-labelling experiments confirm that CO and H2O act as the sources of the -COOH groups in the dinuclear hydroxycarbonylcobalt(III) complex and the oxalic acid product.

Sulfate-associated liquid water amplifies the formation of oxalic acid at a semi-arid tropical location over peninsular India during winter

Aerosol liquid water (ALW) can serve as an aqueous-phase medium for numerous chemical reactions and consequently enhance the formation of secondary aerosols in a highly humid atmosphere. However, the aqueous-phase formation of secondary organic aerosols (SOAs) is not well understood in the Indian regions, particularly in tropical peninsular India. In this study, we collected total suspended particulate samples (n = 30) at a semiarid station (Ballari; 15.15°N, 76.93°E; 495 m asl) in tropical peninsular India during the winter of 2016. Homologous series of dicarboxylic acids (C2–C12), oxoacids (ωC2–ωC9), pyruvic acid (Pyr), and glyoxal (Gly) were determined by employing a water-extraction of aerosol and analyzed using capillary gas chromatography (GC). Results show that oxalic acid (C2) was the most abundant organic acid, followed by succinic (C4), malonic (C3), azelaic (C9), and glyoxylic (ωC2) or phthalic (Ph) acids. Total diacids-C accounted for 1.7–5.8 % of water-soluble organic carbon (WSOC) and 0.6–3.6 % of total carbon (TC). ALW, estimated from the ISORROPIA 2.1 model, showed a strong linear relationship with sulfate (SO42−), C2, C3, C4, ωC2, Pyr, and Gly. Based on molecular distribution, specific mass ratios (C2/C3, C2/C4, C2/Gly, and Ph/C9), linear relationships among the measured organic acids, ALW, organic (levoglucosan and oleic acid), and inorganic (SO42−) marker compounds, we emphasize that diacids and related organic compounds, especially C2, majorly form via aqueous-phase oxidation of precursor compounds including aromatic hydrocarbons (HCs) and unsaturated fatty acids (FAs) originated from biomass burning and combustion-related sources. The present study demonstrates that sulfate driven ALW largely enhances the formation of SOAs via the aqueous-phase reactions over tropical peninsular India during winter.

Catalytic Transformation of Biomass-Derived Hemicellulose Sugars by the One-Pot Method into Oxalic, Lactic, and Levulinic Acids Using a Homogeneous H2SO4 Catalyst

This article presents the conditions for the conversion of hemicellulose with different contents of C6 and C5 carbohydrates and uronic acids based on the OrganoCat process, and the abbreviations M1, M2, and M3 are used. Homogenous catalysis with sulfuric acid (VI) in the concentration range of 0.1–1 M was used in the study to determine its activity on the ability to transform a hemicellulose mixture. The process was carried out using the one-pot technique in the temperature range of 100–250 °C for 1–5 h. Based on the use of the chromatographic technique (HPLC-RID) together with a comparison with standard substances, the resulting chemical compounds were determined and identified from the post-reaction mixtures. The degree of covalence of the raw material, the selectivity of the obtained chemical compounds, and the yield of lactic acid were also determined. Based on the obtained results, lactic acid with the highest yield (64.57%) was obtained after 1 h of the process from the M1 mixture at the temperature of 100 °C with 0.1 M sulfuric acid (VI) as a catalyst. The formation of oxalic acid was also observed, which is present in all post-reaction mixtures, regardless of the composition of the raw material, temperature, and time. Its efficiency was determined at an average level of 90%.

Fates of secondary organic aerosols in the atmosphere identified from compound-specific dual-carbon isotope analysis of oxalic acid

Abstract. Secondary organic aerosols (SOAs) are important components of fine particulates in the atmosphere. However, the sources of SOA precursor and atmospheric processes affecting SOAs are poorly understood. This limits our abilities to improve air quality and model aerosol-mediated climate forcing. Here, we use novel compound-specific dual-carbon isotope fingerprints (Δ14C and δ13C) for individual SOA tracer molecules (i.e., oxalic acid) to investigate the fates of SOAs in the atmosphere at five emission hotspots in China. Coal combustion and vehicle exhaust accounted for ∼ 55 % of the sources of carbon in oxalic acid in Beijing and Shanghai, but biomass burning and biogenic emissions accounted for ∼ 70 % of the sources of carbon in oxalic acid in Chengdu, Guangzhou, and Wuhan during the sampling period. The dual-carbon isotope signatures of oxalic acid and bulk organic carbon pools (e.g., water-soluble organic carbon) were compared to investigate the fates of SOAs in the atmosphere. Photochemical aging and aqueous-phase chemical processes dominate the formation of oxalic acid in summer and in winter, respectively. The results indicated that SOA carbon sources and chemical processes producing SOAs vary spatially and seasonally, and these variations need to be included in Chinese climate projection models and air quality management practices.

Energetic competition in the complexation affinity of paracetamol with water and oxalic acid

The intermolecular interactions of active pharmaceutical ingredients (APIs) are the driving forces of API molecular activity and stability, in vivo receptor binding, environmental transport, and persistence. In manufacturing, API complexation with another molecule to create stable crystalline structures is pursued, but the formation of more energetically stable complexes can lead to undesired consequences. Density functional theory (DFT) was used to describe the role played by hydrogen bonding in the formation of paracetamol and oxalic acid (PCA-OXA) complexes. PCA-OXA hydrogen bonding sites were investigated to determine strength and overall contribution/competition during the initial stages of the nucleation process. Structural and energetic changes were evaluated for 1:1 PCA-OXA, PCA-Water, and OXA-Water complexes both in vacuum and in water environments via explicit and implicit solvation. Results show significant shortening of the hydrogen bonds within the PCA-OXA complex with large changes in energy in the PCA-OXA complexation mechanism. Two out of the four complexation sites play the largest roles in the initial steps of the nucleation process. In an aqueous environment, little to no energetic competition for PCA hydrogen bonds formation with other molecules is observed. Post Hartree–Fock methods (MP2 and CCSD) were used to calibrate and verify the DFT results.

Catalytic formation of oxalic acid on the partially oxidised greigite Fe3S4(001) surface.

Greigite (Fe3S4), with its ferredoxin-like 4Fe-4S redox centres, is a naturally occurring mineral capable of acting as a catalyst in the conversion of carbon dioxide (CO2) into low molecular-weight organic acids (LMWOAs), which are of paramount significance in several soil and plant processes as well as in the chemical industry. In this paper, we report the reaction between CO2 and water (H2O) to form oxalic acid (H2C2O4) on the partially oxidised greigite Fe3S4(001) surface by means of spin-polarised density functional theory calculations with on-site Coulomb corrections and long-range dispersion interactions (DFT+U-D2). We have calculated the bulk phase of Fe3S4 and the two reconstructed Tasker type 3 terminations of its (001) surface, whose properties are in good agreement with available experimental data. We have obtained the relevant phase diagram, showing that the Fe3S4(001) surface becomes 62.5% partially oxidised, by replacing S by O atoms, in the presence of water at the typical conditions of calcination [Mitchell et al. Faraday Discuss. 2021, 230, 30-51]. The adsorption and co-adsorption of the reactants on the partially oxidised Fe3S4(001) surface are exothermic processes. We have considered three mechanistic pathways to explain the formation of H2C2O4, showing that the coupling of the C-C bond and second protonation are the elementary steps with the largest energy penalty. Our calculations suggest that the partially oxidised Fe3S4(001) surface is a mineral phase that can catalyse the formation of H2C2O4 under favourable conditions, which has important implications for natural ecosystems and is a process that can be harnessed for the industrial manufacture of this organic acid.

Low molecular weight dicarboxylic acids, oxocarboxylic acids and α-dicarbonyls as ozonolysis products of isoprene: Implication for the gaseous-phase formation of secondary organic aerosols

Oxidation of isoprene, a major biogenic volatile organic compound emitted from forest canopies, is a potential source of oxalic acid; the dominant species in organic aerosols. We evaluated here ozonolysis of isoprene in dry darkness as a source of oxalic (C2), malonic (C3) and succinic (C4) acids. We found that oxalic acid and methylglyoxal are dominant products within 10 min of reaction followed by glyoxylic, malonic or succinic acids. Interestingly, molecular distributions of oxidation products from early reactions (9–29 min) were characterized by the predominance of methylglyoxal followed by C2, which became dominant after 30 min. The isoprene-derived secondary organic aerosols (SOAs) showed chemical evolution with reaction time towards the molecular characteristics of dicarboxylic acids similar to those of ambient aerosols (C2>C3≥C4). The carbon-based relative abundances of methylglyoxal decreased steadily (40%→30%), while those of C2 increased with reaction time (15%→25%), but no such variations persisted for glyoxal (6–10%). This finding means that methylglyoxal is more important intermediate of oxalic acid than glyoxal. In contrast, smaller variability and lower concentrations of pyruvic and glyoxylic acids than other intermediates indicate that oxalic acid formation under dry conditions follows a different pathway than in aqueous-phase heterogeneous chemistry usually invoked for cloud/fog/atmospheric waters. Here, we propose new reaction schemes for high levels of methylglyoxal and oxalic acid via gas-phase chemical reactions with ozone and OH radicals to better interpret the ambient SOA composition. Furthermore, the relative abundances of C2 exhibit small variability from 1 to 8 h, suggesting its stable character towards the oxidation by hydroxyl radicals.

Summertime atmospheric dicarboxylic acids and related SOA in the background region of Yangtze River Delta, China: Implications for heterogeneous reaction of oxalic acid with sea salts

The diacid chemistry of summertime PM2.5 and the size-segregated aerosols (9-stages) in Chongming Island, a coastal site in the Yangtze River Delta (YRD), China, were investigated. Our results showed that oxalic acid (C2) was the dominant dicarboxylic acid, followed by succinic acid (C4), malonic acid (C3), adipic acid (C6) and phthalic acid (Ph). Two types of haze pollution events were identified during the sampling period, i.e., Event I, which was mainly caused by the local biomass burning emission, and Event II, which was caused by a long-distance transport of the YRD urban pollution. C2 linearly correlated with SO42− and NO3− in Event I but only with O3 in Event II, indicating that oxalic acid formation was dominated by the aerosol aqueous phase oxidation in Event I and by the gaseous phase oxidation in Event II, respectively.65.5% of Cl− in sea salts at the site in the clean period was depleted and robustly correlated with oxalic acid (R2 = 0.74). We proposed a mechanism to explain such a significant Cl− depletion, in which anthropogenic VOC oxidize into oxalic acid and its precursors such as glyoxal and methyglyoxal by a photochemical oxidation, and then oxalic acid and the related compounds subsequently react with sea salts and release HCl into the troposphere. The significant Cl− depletion of sea salts related with the organic acid (C2) in coastal China was found for the first time and should be considered in future studies, because oxalic acid and related SOA in the country are abundant and the released HCl may effectively enhance the oxidation capacity of the atmosphere by photolytically producing Cl radicals.

Electro-Carboxylation of Furfural By CO2 in γ-Valerolactone

The continuous rise of global warming and depletion of fossil fuel resources has led to the development of new ways of valorization of non petro-sourced chemicals. In this objective, it is important to develop electrochemical valorization processes of CO2, a greenhouse gas, for the synthesis of valuable molecules. When the CO2 electroreduction is performed in aqueous media, the competitive HER will decrease the energetic efficiency and the rapid deactivation of reaction intermediates will lead to side products such as CO, formic acid, oxalic acid and small chain hydrocarbons [1]. To circumvent these issues and create value added chemicals, reductive electro-carboxylation reactions can be performed in polar aprotic solvents (DMF, DMSO, acetonitrile or NMP) in the presence of tetraalkylammonim bromide or chloride as electrolytes [2].In this work, we focused on non-aqueous bio-sourced solvent, the γ-valerolactone (GVL), to perform a carboxylation reaction of bio-sourced molecules like furfural by electroreduction of CO2. The reductive electro-carboxylation of furfural was studied at a Pt/C electrode was studied in a bio-sourced GVL with tributylmethylammonium chloride (TBMACl) as electrolyte. The solvent behavior in the CO2 reduction potential range was studied by in situ FTIRS measurements which indicated that GVL reacted at the electrode in the absence of furfural and/or of CO2, while the presence of furfural and/or of CO2 made the solvent much less reactive. The electrochemical study showed that the CO2 electroreduction started at from the high cathodic potential of −0.8 V vs SCE (saturated calomel electrode) and the coupling of electrochemistry with in situ FTIRS demonstrated that it reacted with furfural.The reductive electro-carboxylation was then performed in an electrolysis cell. The cell voltage was maintained at 2.0 V (corresponding to a cathode potential of -1.9 V vs. SCE) for 24 h. In absence of furfural, gas chromatography coupled with mass spectroscopy (GC–MS) analyses revealed the formation of oxalic acid (coupling reaction of CO2) as main reaction product. In the presence of furfural in the reaction medium, a new carboxylated specie, 2-furyl(hydroxy)acetic acid, was identified as the main reaction product. 1H NMR and LC-MS analyses further confirmed the formation of this compound, demonstrating the potentialities of bio-sourced solvents for reduction electro-carboxylation of a bio-sourced molecule by reduction of CO2[3].[1] Y. Hori, Electrochemical CO2 reduction on metal electrodes, in: C. Vayenas, R. White, M. Gamboa-Aldeco (Eds.), Modern Aspects of Electrochemistry, 42, Springer, NewYork 2008, pp. 89–189[2] R. Matthesses, J. Fransaer, K. Binnemans, D.E. De Vos, Electrocarboxylation: towards sustainable and efficient synthesis of valuable carboxylic acids, Beilstein J. Org.Chem. 10 (2004) 2484–2500.[3] Florent Boissou, S. Baranton, M. Tarighi, K. De Oliveira Vigier, C. Coutanceau, The potency of γ-valerolactone as bio-sourced polar aprotic organic medium for the electrocarboxlation of furfural by CO2. J. Electroanal. Chem. 848 (2019) 113257

Response of Root-Exuded Organic Acids in Irrigated Rice to Different Water Management Practices

Knowledge of the composition and volume of root-exuded organic substances is crucial for understanding the biochemical processes in the rhizosphere. The present study was undertaken to quantify organic acids from the roots of drought-tolerant and non-drought-tolerant rice cultivars (DTR and NDTR) and their response to irrigation during different growth periods. Alternating wetting and moderate drying with 4 cm water layer of flood irrigation until the soil water potential reaches −15 kilopascal (kPa) (WMD) significantly enhanced succinic, maleic, citric, malic, oxalic, tartaric, and total organic acids in the two rice cultivars during the trial by 80.59–86.68, 31.62–58.55, 16.55–43.00, 17.89–25.66, 13.68–29.70, 12.40–16.05, and 17.34–21.24%, respectively. Alternate wetting and severe drying with 4 cm water layer of irrigation until the soil water potential reached −30 kPa (WSD) notably decreased formation of maleic, citric, malic, oxalic, tartaric, and total organic acids in the two rice cultivars during the experiment by 5.19–25.15, 13.96–29.92, 20.81–34.88, 32.20–42.51, 12.79–24.66, and 6.67–24.22%, respectively. Acetic acid output between CF (continuous flooding with a 3–4 cm water layer) and WMD treatments in pads with two rice cultivars did not differ. The WSD treatment increased acetic acid exudation by 16.93–25.99% in two rice cultivars during the experiment. The high content of acetic and total organic acids in DTR should be responsible for the smaller loss of total organic acids in the WSD treatment and the high drought tolerance capacity. The results contribute to valuable background knowledge for exploring the role of root exudates in soil-plant relationships.

Ozonolysis of wheat bran in subcritical water for enzymatic saccharification and polysaccharide recovery

The destarched wheat bran was pretreated with ozonolysis, subcritical water (SW), and their combinations to improve its enzymatic digestion and hemicellulose solubilization. Ozonolysis caused lignin destructions and partial leach of hemicelluloses, leading to the formation of oxalic acids. Taking advantage of these effects, the sequential combinations of ozonolysis and SW showed synergy, resulting in a 3-fold hydrolysis outcome relative to the individual SW treatment. Eventually, the combined pretreatment achieved a high hemicellulose removal (86%) and saccharification yield (85% for glucose) under a mild SW condition (160 °C for 30 min). Apart from morphological destructions, FTIR and TGA results indicated different structural changes caused by ozonolysis and SW. Hemicellulose was shown as the major factor hindering enzymatic hydrolysis. Additionally, the soluble polysaccharides generated by these pretreatments were characterized, showing that the single SW pretreatment was better for polysaccharide recovery. These findings may help to maximize the benefits of wheat bran biorefinery.

Electrocatalytic hydrogen production and carbon dioxide conversion by earth abundant transition metal complexes of the Schiff base ligand: (E)-1-((2-dimethylamino)-propylimino)methyl)naphthalene-2-ol

The present work describes an electrocatalytic study for the conversion of carbon dioxide to environmentally benign and industrially important products, as well as the production of hydrogen (green energy) from acids using earth abundant transition metal complexes as catalysts. One cobalt and one nickel complex of the Schiff base ligand (E)-1-((2-(dimethylamino)ethylimino)methyl)naphthalene-2-ol have been used. The cobalt complex (1) has been tested as an electrocatalyst for the reduction of protons in non-aqueous solvent using trifluoro acetic acid (TFA) as a substrate. Complex 1 catalyses the acid reduction at a relatively high potential (−0.7 V) with a turn over frequency of 7.05 s−1 at a 10:1 ratio of the acid to the catalyst. Production of hydrogen gas was detected by gas chromatography. The nickel complex (2) was examined for the electrocatalytic reduction of carbon dioxide. At an applied potential of −2.1 V, the main reduction product is oxalic acid. The acid produced was quantitatively determined by HPLC. The rate of oxalic acid formation is 1.3495 × 10−7 M/min. with a kcat value of 58.03 s−1.

Aromatic Ester-Functionalized Ionic Liquid for Highly Efficient CO2 Electrochemical Reduction to Oxalic Acid.

Electrochemical reduction of CO2 into valuable chemicals is a significant route to utilize CO2 resources. Among various electroreduction products, oxalic acid (H2 C2 O4 ) is an important chemical for pharmaceuticals, rare earth extraction, and metal processing. Here, an aprotic aromatic ester-functionalized ionic liquid (IL), 4-(methoxycarbonyl) phenol tetraethylammonium ([TEA][4-MF-PhO]), was designed as an electrolyte for CO2 electroreduction into oxalic acid. It exhibited a large oxalic acid partial current density of 9.03 mA cm-2 with a faradaic efficiency (FE) of 86 % at -2.6 V (vs. Ag/Ag+ ), and the oxalic acid formation rate was as high as 168.4 μmol cm-2 h-1 , which is the highest reported value to date. Moreover, the results of density functional theory calculations demonstrated that CO2 was efficiently activated to a -COOH intermediate by bis-active sites of the aromatic ester anion via the formation of a [4-MF-PhO-COOH]- adduct, which finally dimerized into oxalic acid.

Colour removal and biodegradability enhancement of biomethanated spent wash from distillery using wet oxidation treatment

In India, high strength spent wash (SW) produced from alcohol distilleries is preferably treated by biomethanation process. However, biomethanated SW (BMSW) still contains intensified dark brown colour, high chemical oxygen demand (COD) and poor biodegradability which requires further treatment before disposal. Wet oxidation (WO) is considered an effective treatment for high strength non-biodegradable wastewaters (COD > 10 g/L). Hence, the present study explored WO of BMSW (pH = 5.7, COD = 65.5 g/L, and total organic carbon (TOC) = 23.5 g/L) in a high pressure batch reactor (0.7 L capacity) at temperatures ranging from 160-220°C and oxygen pressure of 1.1 MPa. At 220°C temperature, TOC, COD and color removals of 39%, 59% and 90%, respectively, were observed after 3 h of reaction period. Meanwhile, biodegradability index (BI) was enhanced from 0.27 to 0.81. Carbon balance calculations showed that the oxidation reaction contribution in TOC removal was enhanced with increase in temperature (64 – 92% of total carbon removal). Fourier transform infrared (FTIR) analysis suggested the precipitation of carbonyl group and nitrogen containing compounds. During the reaction, volatile fatty acids (oxalic acid, malonic acid and acetic acid) formation was also confirmed in the treated wastewater.

Mineralization of Acid Red 1 azo dye by solar photoelectro-Fenton-like process using electrogenerated HClO and photoregenerated Fe(II).

The degradation of Acid Red 1 (AR1) azo dye by solar photoelectro-Fenton-like (SPEF-like) process involving continuously electrogenerated hypochlorous acid (HClO) and photoregenerated Fe(II) to yield hydroxyl radicals, has been studied. The assays were made in a flow plant that included a filter-press cell equipped with a Ti|Ir-Sn-Sb oxide anode, to oxidize Cl- ion to HClO, and a stainless-steel cathode. The cell was coupled to a compound parabolic collector (CPC) photoreactor, in series with a reservoir containing 6L of solution. The influence of the added Fe2+ concentration, current density and initial AR1 content over the performance of the SPEF-like process was systematically studied. The best treatment for 0.196mM AR1 solutions in 35mM NaCl and 25mM Na2SO4 at pH 3.0 was achieved in the presence of 0.40mM Fe2+ under a current density of 15mAcm-2, which yielded total color removal at 120min and 74% COD decay at 480min, with 25% of average current efficiency and 0.076kWh (g COD)-1 of energy consumption. The SPEF-like process was compared with anodic oxidation with electrogenerated active chlorine (AO-HClO), electro Fenton-like (EF-like) and photoelectro-Fenton-like (PEF-like) processes, and it was found that the oxidation power decreased in the sequence: SFEF-like>PEF-like>EF-like>AO-HClO. Ion-exclusion HPLC analysis of electrolyzed solutions revealed the formation of maleic and oxalic acid as final short-chain linear carboxylic acids.

The potency of γ-valerolactone as bio-sourced polar aprotic organic medium for the electrocarboxlation of furfural by CO2

The reductive electro-carboxylation of furfural at a Pt/C electrode was studied in a bio-sourced γ-valerolactone (GVL) solvent using linear scan voltammetry, in situ infrared spectroscopy (in situ FTIRS) under electrode potential control and by chrono-amperometry (CA) with analysis of reaction products. In situ FTIRS measurements indicated that GVL reacted at the electrode in the absence of furfural and/or of CO2, while the solvent became much less reactive in the presence of furfural and/or of CO2. It was also found that CO2 was activated from the high cathodic potential of −0.8 V vs SCE (saturated calomel electrode) and that it reacted with furfural. CA measurements at a cell voltage of 2.0 V, corresponding to a cathode potential higher than −1.66 V vs. SHE (standard hydrogen electrode), were performed for 24 h in the presence of CO2 at the cathode. Gas chromatography coupled with mass spectroscopy (GC–MS) analyses revealed the formation of 2-hydroxyvaleric acid (reaction between GVL and residual water) and oxalic acid (coupling reaction of CO2) as main reaction products in the absence of furfural in the reaction medium. In the presence of furfural in the reaction medium, 2-hydroxyvaleric acid and oxalic acid were detected as traces, whereas a new carboxylated specie, 2-furyl(hydroxy)acetic acid, corresponded by far to the main reaction product (ca. 82%). 1H NMR and LC-MS analyses confirmed the formation of this last compound. Under the experimental conditions described in this article, the electro-activation of CO2 could be performed at high cathode potential in GVL, leading in presence of furfural to the formation of the α-hydroxy-acid.

Persulfate activation by natural zeolite supported nanoscale zero-valent iron for trichloroethylene degradation in groundwater

In the advanced oxidation processes, using persulfate (PS) as a radical precursor for pollutant degradation in groundwater has received increasing attention. In this study, zeolite supported nZVI composites (Z/nZVI) were synthesized through an ion exchange and borohydride reduction method to investigate their ability to activate PS for the TCE degradation. Based on preliminary screening of the PS activation by the Z/nZVI (PS-Z/nZVI) system in terms of TCE degradation, Z/nZVI composite with a zeolite to nZVI mass ratio of 1:1 (Z/nZVI (1)) was optimized as the best composition and chosen for further characterization and examination. Especially, for this PS-Z/nZVI system, PS concentration, solution matrix effects (i.e., solution pH, coexisting anions and natural organic matter) were studied. Characterization results revealed that the aggregation of nZVI particles was alleviated and they were good dispersed on the zeolite sheet with a large SSA (159.49 m2/g) compared to the unsupported nZVI (8.77 m2/g). The synthesized Z/nZVI (1) composite exhibited excellent activated ability towards PS (1.5 mM) and effectively degraded 98.8% of TCE at pH 7 within 120 min. The PS-Z/nZVI system was observed to operate effectively over a wide range of pH (i.e., 4–7) for TCE degradation. Moreover, the presence of nitrates (1 mM) and bicarbonates (10 mM) decreased the TCE degradation efficiency to 91.5% and 59.6%, respectively. Scavenger tests demonstrated that both sulfate and hydroxyl radicals participated in the TCE degradation. The ion chromatography analysis suggested the formation of oxalic acid and formic acid as the reaction intermediates during the TCE degradation process in the PS-Z/nZVI system.