Ferrioxalate Complexes Research Articles

A solar photoFenton process with calcium peroxide from eggshell and ferrioxalate complexes for the degradation of the commercial herbicide 2,4-D in water

The present study focused on the degradation of the commercial herbicide 2,4-D in water by solar photoFenton assisted with ferrioxalate complex and calcium peroxide (CaO2), using an experimental system consisting of a storage tank, a water pump, a solar reactor, and a compound parabolic concentrator (CPC), which collected solar energy of 212.102 kJ/L. The CaO2 was synthesized from eggshells, the influence of the 2,4-D concentration, oxalic acid (H2C2O4), iron (Fe3+), and CaO2 on the degradation of herbicide was evaluated by HPLC, and the intermediates such as 2,4-dichlorophenol, 1,4-benzoquinone, and oxalic acid were determined to confirm the proposed reaction mechanism. The generation of hydroxyl radicals and other reactive species, depends on the molar ratios of oxalate/Fe3+, CaO2/Fe3+, and CaO2/2,4-D. The optimum concentrations for 100 % degradation were 61.5 mg/L 2,4-D, 50.5 mg/L Fe3+, 100.5 mg/L H2C2O4, and 81 mg/L CaO2 with 42.27 % COD and 44.09 % TOC. This study highlights the viability of the solar photoFenton process to degrade the 2,4-D herbicide and aims to promote: the recovery of organic waste such as eggshells, the complexing effect of H2C2O4-Fe3+, the CaO2 as an alternative oxidant, and the application of renewable energy in the treatment of similar contaminants present in wastewater for future research.

A Solar Photofenton Process with Calcium Peroxide from Eggshell and Ferrioxalate Complexes for the Degradation of the Commercial Herbicide 2,4-D in Water

A Solar Photofenton Process with Calcium Peroxide from Eggshell and Ferrioxalate Complexes for the Degradation of the Commercial Herbicide 2,4-D in Water

Optimization of the artificial neuronal network for the degradation and mineralization of amoxicillin photoinduced by the complex ferrioxalate with a gradual and progressive approach of the ligand

In this work, the Ferrioxalate complex was used to mineralize the widely used antibiotic amoxicillin (AMX). The effect of operational parameters such as Fe3+ concentration, the molar ratio (Oxalate/Fe3+), and initial pH was studied for achieving high efficiency of degradation and mineralization. The effect of inorganic ions in the degradation of AMX was also investigated. Optimization of an Artificial Neural Network (ANN) to predict the performance of the process was realized. Neural networks were applied to model AMX degradation using 75 experimental data. Analysis of the results shows that the oxalate: iron ratio is limited to 3 with a Fe3+ concentration of 0.35 mM. In order to avoid this limitation, an alternative solution was adopted to increase the molar ratio with the gradual and progressive use of oxalic acid ligand. Almost total degradation and mineralization of AMX was achieved at the free initial pH of 2.8 and final pH of 6. The study of the effect of inorganic ions showed that bicarbonate and sulfate ions play an important role in contrast to Cl− ions with no noticeable influence. Neural network application resulted in a MSE of 1.1543 × 10-5 and a correlation coefficient r of 0.99 for AMX degradation and MSE of 1.12162 × 10-5 with r of 0.99 for mineralization. The model can describe successfully the percentage of degradation and mineralization of AMX under various conditions. ANN and NSGA-II (Non-dominant Sorting Genetic Algorithm -II) hybrid method to solve a multi-objective problem was proposed to determine the optimal (Fe3+/Ox/UVA) operating and process parameters.

A collaborative strategy for enhanced reduction of Cr(VI) by Fe(0) in the presence of oxalate under sunlight: Performance and mechanism

Nanometer-size zero-valent iron (NZVI) is an efficient reducing agent, but its surface is easily passivated with an oxide layer, leading to reaction inefficiency. In our study, oxalate (OA) was introduced into this heterogeneous system of NZVI, which could form ferrioxalate complexes with the NZVI surface-bound Fe3+ and dissolved Fe3+ in the solution. Photolysis of ferrioxalate complexes can facilitate the generation of Fe2+ from Fe3+ and CO2•- radical, both species have strong reduction capacity. Hence, a “photo-oxalate-Fe(0)” system through sunlight induction was established, which not only prohibited the formation of a surface passivation layer, but also displayed a synergetic mechanism of ferrioxalate photolysis to enhance reduction, exhibiting remarkably higher degradation activity (several times faster) toward the model pollutant Cr(VI) than the mechanism with NZVI alone. Factor tests suggested that both NZVI dosage and OA content markedly affected the reduction rate. Low pH was beneficial to the reduction efficiency. Moreover, recyclability experiment showed that the reduction rate decreased from 0.21706 to 0.03977 min−1 after three cycles of reuse due to the NZVI losing reaction activity generally, but the system still maintained considerable reduction capacity. Finally, a mechanism was revealed whereby NZVI would transform to Fe oxides after the exhaustion of its reductive power, and the photolysis of ferrioxalate to promote the cycling of iron species played the predominant role in providing extra reduction ability. These features confirm that introduction of OA into Cr(VI) reduction by NZVI through sunlight induction is advantageous and promising.

The femtochemistry of the ferrioxalate actinometer

The ferrioxalate actinometer is widely used as an analytical standard to determine the photon flux of light sources in photochemical reactors. Yet, the underlying mechanistic functioning of the actinometer at the molecular level is entirely unknown. Here, we present results from femtosecond UV-pump/mid-infrared-probe spectroscopy to reveal the elementary events including the primary C–C and Fe–O-bond breakages that follow an initial photon absorption by the ferrioxalate complex.

Mineralization of pentachlorophenol by ferrioxalate-assisted solar photo-Fenton process at mild pH

This work reports the use of ferrioxalate complexes to assist solar photo-Fenton treatment of pentachlorophenol (PCP) in aqueous medium at mild pH, which inhibits the precipitation of iron hydroxides and allows working at a low iron dosage. The experimental parameters were optimized by assessing the effect of initial concentrations of H2O2 (0–2.5 mM) and Fe(II) (2–10 mg/L), pH (3.0–9.0) and iron/oxalic acid molar ratios (1:0–1:13.5) on total organic carbon (TOC) removal. Ferrioxalate-assisted solar photo-Fenton achieved 97.5% mineralization in 120 min, clearly outperforming conventional Fenton and solar photo-Fenton. The presence of photosensitive ferrioxalate complexes accounted for the enhancement, as a result of Fe(II) regeneration that accelerated the hydroxyl radical (OH) production. The time course of H2O2 and Fe(II) concentrations was evaluated under different iron/oxalic acid ratios. The five carboxylic acids determined by ion-exclusion HPLC and the eight aromatic by-products identified by GC-MS allowed the proposal of a degradation pathway that included hydroxylation, dechlorination and dimerization steps. Complete chloride ion release was achieved after 90 min of treatment.

Fluorene oxidation by solar-driven photo-Fenton process: toward mild pH conditions.

Polycyclic aromatic hydrocarbons (PAHs) are on the list of priority pollutants to be eliminated from the environment due to their carcinogenic and mutagenic action, chemical stability, and resistance to biodegradation. The aim of this study was to evaluate the degradation of fluorene, a well-known PAH, in aqueous solutions (0.03 and 0.08mgL-1), by means of a solar-driven conventional (PF) and modified photo-Fenton mediated by ferrioxalate complexes (PFF). Photolysis was also employed for comparison purposes. PF reaction was evaluated at different pH values (2.8, 3.5, and 4.0) and iron concentrations (2, 5, 10, and 20mgL-1). On the other hand, PFF studies were conducted at mild pH conditions (4.0, 5.0, and 6.0) and iron content of 2mgL-1, keeping initial iron/oxalate molar ratio at 1:3. In both PF and PFF, the initial hydrogen peroxide/iron molar ratio was maintained at 5. In the presence of methanol as cosolvent for fluorene dissolution, the PF reaction was hampered and no consumption of H2O2 was observed during the reaction carried out at constant pH (2.8). This led to low degradation rates, similar to those achieved by photolysis. Under the same pH but using acetonitrile as cosolvent for fluorene dissolution, fluorene degradation was found to be proportional to the iron content used in the PF experiments. On the other hand, at an invariable iron concentration of 5mg Fe2+ L-1, the increase in pH was accompanied by a decrease in the molar fraction of the most photoactive iron complex (FeOH2+) and ferric hydroxides precipitation, leading to a reduction in the fluorene degradation rate. With regard to the PFF tests, similar fluorene degradation performance was achieved at pH 4 and 5, while at pH 6 iron precipitation became relevant and the degradation rate was slightly slower. PFF has shown to be more efficient than the PF under the same pH (4) and iron concentration (2mgL-1). Moreover, even at near neutral pH (6), fluorine degradation was shown to be feasible by using ferrioxalate complexes.

Role of Fe(III) and Oxalic Acid in the photo-Fenton System for 3-Methylphenol Degradation in Aqueous Solution under Natural and Artificial Light

Abstract The Fenton process has been widely studied in the treatment of wastewater but unfortunately this process can only work under acidic pH conditions. To overcome these disadvantages, the Fenton modified by adding chelating agents such as oxalic acid (Ferrioxalate complex (Fe(III)Ox) since its high solubility in aqueous media can broaden the available pH range of the Fenton reaction to near neutral pH. In this study, The photooxidation efficiencies of 3-methylphenol (3MP) catalyzed by Fe(III) and oxalic acid was investigated. The results show that the photodegradation Of 3MP is slow in the presence of Fe(III) or oxalic acid alone. However, it is markedly enhanced when Fe(III)Ox complex coexist. The concentration of the complex is optimized to the ratio ([Fe(III)Ox] = 3/12). Fe(III)Ox plays a positive role in the photo-Fenton system, especially at higher pH = 5.5. Oxygen is essential to the formation of oxidative species and, as a consequence, for the pollutant degradation. Additionally, the use of tertio-butanol as a scavenger confirmed the intervention of . OH in the 3MP photodegradation. 3MP degradation mechanisms have been elucidated and photoproducts are identified by comparison with authentic products. To get closer to the environmental conditions, the effect of main elements present naturally in the aquatic ecosystem such as humic substances and bicarbonates was examined. The photodegradation of 3MP through Fe(III)Ox system under solar light was significantly accelerated in comparison with artificial irradiation at 365 nm. Measuring chemical oxygen demand (COD) leads to mineralization which decreases the toxicity of 3MP solution. This work also demonstrates that this system is an encouraging method for the treatment of organic pollutants in the natural environment.

Photo-Fenton degradation of a herbicide (2,4-D) in groundwater for conditions of natural pH and presence of inorganic anions.

The effects of four inorganic anions (Cl-, SO42-, HCO3-, NO3-) usually present in groundwater were investigated on the photo-Fenton degradation of 2,4-dichlorophenoxyacetic acid (2,4-D). A kinetic model derived from a reaction sequence is proposed using the ferrioxalate complex as iron source at pH close to natural conditions (pH = 5). It was demonstrated that oxalate not only maintained iron in solution for the natural groundwater system, but also increased the photochemical activation of the process. Results showed that the minimum conversion of 2,4-D for the simulated groundwater after 180 min was 63.80%. This value was only 14.1% lower than the conversion achieved without anions. However, with all anions together, the consumption of hydrogen peroxide (HP) per mole of herbicide showed an increase with respect to the test without anions. Only one kinetic parameter was estimated for each anion applying a nonlinear regression method. Subsequently, these optimized kinetic constants were used to simulate the system behaviour, considering the influence of all the studied anions together. A good agreement between kinetic model predictions and experimental data was observed, with the following errors: RMSE2,4-D = 3.98 × 10-3 mM, RMSEHP = 1.83 × 10-1 mM, RMSEOX = 1.39 × 10-2 mM, and RMSE2,4-DCP = 5.59 × 10-3 mM.

Mineralization of humic acids (HAs) by a solar photo-Fenton reaction mediated by ferrioxalate complexes: commercial HAs vs extracted from leachates.

The mineralization of bio-recalcitrant humic acids (HAs) by a solar photo-Fenton (SPF) process was investigated in aqueous system, in order to understand its abatement in real high-HA content matrices, such as sanitary landfill leachates. SPF reactions were performed in tubular photoreactors with CPCs at lab-scale (simulated solar light) and pilot-scale (natural sunlight). Considering the experimental conditions selected for this work, the formation of insoluble HA-Fe3+ complexes was observed. Thus, to avoid HA precipitation, oxalic acid (Ox) was added, since Fe3+-Ox complexes present a higher stability constant. The effect of different process variables on the performance of SPF reaction mediated by ferrioxalate complexes (SPFF) was assessed with excess of H2O2 (50-250mgL-1), at lab-scale: (i) pH (2.8-4.0); (ii) initial iron concentration (20-60mg Fe3+ L-1); (iii) iron-oxalate molar ratio (Fe3+-Ox of 1:3 and 1:6); (iv) temperature (20-40°C); (v) UV irradiance (21-58WUVm-2); and (vi) commercial-HA concentration (50-200mgCL-1). At the best lab conditions (40mg Fe3+ L-1, pH2.8, 30°C, 1.6 Fe3+-Ox molar ratio, 41 WUV m-2), commercial HAs' mineralization profile was also compared with HAs extracted from a sanitary landfill leachate, achieving 88 and 91% of dissolved organic carbon removal, respectively, after 3-h irradiation (8.7kJUVL-1). Both reactions followed the same trend, although a 2.1-fold increase in the reaction rate was observed for the leachate-HA experiment, due to its lower humification degree. At pilot-scale, under natural sunlight, 95% HA mineralization was obtained, consuming 42mM of H2O2 and 5.9kJUVL-1 of accumulated UV energy. However, a pre-oxidation during 2.8kJUVL-1 (12mM H2O2) was enough to obtain a biodegradability index of 89%, showing the strong feasibility to couple the SPFF process to a downstream biological oxidation, with low chemicals and energetic demands. Graphical abstract ᅟ.

Distinct synergetic effects in the ozone enhanced photocatalytic degradation of phenol and oxalic acid with Fe 3+ /TiO 2 catalyst

Abstract In this work, phenol and oxalic acid (OA) degradation in an ozone and photocatalysis integrated process was intensively conducted with Fe3 +/TiO2 catalyst. The ferrioxalate complex formed between Fe3 + and oxalate accelerated the removal of OA in the ozonation, photolysis and photocatalytic ozonation process, for its high reactivity with ozone and UV. Phenol was degraded in ozonation and photolysis with limited TOC removal rates, but much higher TOC removal was achieved in photocatalytic ozonation due to the generation of OH. The sequence of UV light and ozone in the sequential process also influences the TOC removal, and ozone is very powerful to oxidize intermediates catechol and hydroquinone to maleic acid. Fenton or photo-Fenton reactions only played a small part in Fe3 +/TiO2 catalyzed processes, because Fe3 + was greatly reduced but not regenerated in many cases. The synergetic effect was found to be highly related with the property of the target pollutants. Fe3 +/TiO2 catalyzed system showed the highest ability to destroy organics, but the TiO2 catalyzed system showed little higher synergy.

Study of the intensification of solar photo-Fenton degradation of carbamazepine with ferrioxalate complexes and ultrasound

The intensification of the solar photo-Fenton system with ferrioxalate photoactive complexes and ultrasound applied to the mineralization of 15mg/L carbamazepine aqueous solution (CBZ) was evaluated. The experiments were carried out in a solar compound parabolic collector (CPC) pilot plant reactor coupled to an ultrasonic processor. The dynamic behavior of hydroxyl radicals generated under the different studied reaction systems was discussed. The initial concentrations of hydrogen peroxide and ferrous/oxalic acid and pH were found to be the most significant variables (32.79%, 25.98% and 26.04%, respectively). Under the selected optimal conditions ([H2O2]0=150mg/L; [Fe2+]0=2.5mg/L/[(COOH)2]0=12.1mg/L; pH=5) CBZ was fully degraded after 5min and 80% of TOC was removed using a solar photo-Fenton system intensified with ferrioxalate (SPFF). However, no improvement in the mineralization using SPFF process combined with ultrasound was observed. More mild pH conditions could be used in the SPFF system if compared to the traditional photo-Fenton (pH 3) acidic systems. Finally, a possible reaction pathway for the mineralization of CBZ by the SPFF system was proposed and therein discussed.

Synthesis and characterization of some new ruthenium (II) complexes as photosensitizers in dye-sensitized solar cells

New ruthenium (II) complexes, [Ru(DHZ)2(bpy)], [Ru(SCN)2(bpy)(DMSO)2], [Ru(SCN)2(dmbpy)(DMSO)2] and [RuCl2(salen)]-2, where bpy = 2,2'- bipyridine, DHZ = 1,5-diphenylthiocarbazone, dmbpy = 4,4'-dimethyl-2,2' bipyridine and salen = 2,2'- ethylenebis(nitrilomethylidene)diphenol were synthesized and characterized by elemental analysis, FTIR, UV-Vis spectroscopy and thermal analysis. From data of these investigations the structural formula and the mode of bonding were obtained. These complexes were successfully applied to sensitization of nano-crystalline TiO2 based solar cells (DSSCs). The photovoltaic efficiencies of the studied DSSCs increase in the following order [Ru(DHZ)2(bpy)]< [Ru(SCN)2(bpy)(DMSO)2]< [Ru(SCN)2(dmbpy)(DMSO)2]< [RuCl2(salen)]-2. This increase is in agreement with the light harvesting of these complexes as indicated from their absorption spectra. Ferrioxalate complex enhanced the performance of some investigated cells. Therefore, a mechanism of this improvement has been postulated. Polyaniline as well as iodine doped polyaniline modified FTO electrode has been tested as promising counter electrodes. The efficiencies of the cells using iodine doped polyaniline is higher than that of polyaniline, which is assignable to the high conductivity of iodine.

Ferrioxalate complexes as strategy to drive a photo-FENTON reaction at mild pH conditions: A case study on levofloxacin oxidation

Abstract The present study is about the use of ferrioxalate photoactive complexes as a strategy to drive a photo-Fenton reaction at mild pH conditions, applied to the oxidation of antibiotic levofloxacin (LEV) in pure water and spiked in urban wastewater after secondary treatment. The oxidation ability of the solar photo-Fenton mediated by ferrioxalate complexes (SPFF) was evaluated at different pH values (3.0 to 6.0) for an iron/oxalate molar ratio of 1:3 and using low iron contents (1.0 and 2.0 mg Fe 3+ L −1 ). Additionally, the effect of LEV concentration (2–20 mg L −1 ), iron:oxalate molar ratio (1:3, 1:6 and 1:9), temperature (15–45 °C), UVA irradiance (27.8-59.9 W UV m −2 ), presence of inorganic ions (Cl − , SO 4 2− , HCO 3 − , NH 4 + ), radical scavengers (sodium azide, humic acid and D-mannitol), and others organic ligands, namely citrate and malate, on the SPFF method at pH 5.0 was also assessed. Although the conventional solar photo-Fenton (CSPF) reaction showed similar results to SPFF for pH values ≤ 4, an almost 3.3-fold and 5.7-fold increase in the LEV degradation rate at pH 5.0 and 6.0, respectively, were observed for SPFF when compared to CSPF. This is mainly attributed to the higher photoactivity and solubility of ferrioxalate complexes when compared with ferric ion-water complexes. On the other hand, ferrioxalate complexes exhibited higher photoactivity on LEV removal than ferricitrate and ferrimalate. The presence of phosphate ions in the urban wastewater affected negatively the reaction rate, mainly due to the precipitation of iron as FePO 4(s) , hence a H 2 O 2 /UVC process at different conditions was also explored as an alternative. A pilot-scale assay under natural solar irradiation showed similar results to the ones obtained in the lab-scale photoreactor. Oxalic, formic, citric, and tartronic acids were identified as residual acids in SPFF at pilot scale.

Study on removal of phenol from synthetic wastewater using solar photo catalytic reactor

The present study is devoted to investigate the removal of phenol, which has been selected as a model for the toxic organic compounds by using a parabolic trough collector (PTC) photo catalysis system. The solar photo-catalytic system performance was tested in terms of the phenol removal (%Rphenol) and TOC mineralization efficiency (%MTOC) by using FeSO4 as a catalyst and Oxalic acid as a solar photo assisted agent to enhance the process efficiency. Different operating conditions were studied to investigate the performance of the photo-catalysis system, such as initial phenol concentration, initial H2O2 concentration, FeSO4/Oxalic weigh ratio, pH of solution, and solution flow rate. The operating variables were optimized to obtain a maximum efficiency for the system performance. Results showed that optimum addition of ferrioxalate complexes (3mg/L) enhanced the degradation of phenol by (20–30%) at 120min of illumination time. A quadratic-second-degree polynomial equation was developed for (%Rphenol) and (%MTOC) with correlation coefficients (R2) of 95.26% and 95.2%, respectively.

Strategy for Treating a Landfill Leachate by Integration of Physico-Chemical and Photo-Fenton Processes

This study reports a protocol for the treatment of a sanitary landfill leachate through integration between a stage of coagulation-flocculation, a step of filtration of the resulting suspension, and application of the photo-Fenton process using a ferrioxalate complex and solar irradiation. The best results for turbidity removal by coagulation-flocculation were reached using Al3+ as nitrate salt mainly using concentrations up close 4.4 mmol L-1, at the natural pH of the effluent (pH 7.9), when the removal of 66% of the turbidity was achieved. By using a ferrioxalate complex after adjusting the pH of the effluent to 5, it was possible to circumvent the classical limitations of the Fenton process (related to the pH of the medium limited to between 2.5 and 3.0), performing a removal of 68% of the remaining dissolved organic carbon. The global dissolved organic carbon removal in this process was of 86% after a membrane filtration step before the photo-Fenton process.

Degradation and mineralization of antipyrine by UV-A LED photo-Fenton reaction intensified by ferrioxalate with addition of persulfate

Abstract The intensification of the degradation of antipyrine in aqueous solution by using a UV-A-LED-photo-Fenton reaction intensified by ferrioxalate complexes and with addition of persulfate anions was studied. The efficiency of the reaction was evaluated in terms of antipyrine degradation and mineralization degree at different initial concentrations of hydrogen peroxide, ferrous ion, oxalic acid and persulfate anion. The reaction was carried out using a lab-scale photoreactor irradiated with artificial UV-A-LED light emitting at 365 nm. Artificial neural networks (NNs) were implemented for modelling the degradation process. Under optimal conditions, complete degradation of antipyrine and 93% mineralization was reached in 2.5 and 60 min, respectively. The contribution of HO radicals in this system was evaluated running the reaction in the absence and presence of appropriate quenchers such as tert-butyl alcohol and methanol. In the last step of reaction, possibly different intermediates such as 2-butenedioic acid, butanedioic acid, 4-oxo-pentanoic acid, acetate and formate can be generated which cannot be degraded by HO radicals or their reaction is very slow. This ferrioxalate-mediated system reduces the amount of H2O2 needed (100 mg L−1) for antipyrine degradation and persulfate was not necessary because it could not be activated with UV-A LED nor with Fe2+ since it is quickly converted to Fe3+ forming ferrioxalate complexes.

Enhanced photochemical decomposition of environmentally persistent perfluorooctanoate by coexisting ferric ion and oxalate.

Perfluorooctanoic acid (PFOA), an environmentally persistent pollutant, was found to be quickly decomposed under 254nm UV irradiation in the presence of ferric ion and oxalic acid. To understand the PFOA decomposition mechanism by this process, the effects of reaction atmosphere and concentrations of ferric ions and oxalic acids on PFOA decomposition were investigated, as well as decomposition intermediates. PFOA mainly decomposes via two pathways: (i) photochemical oxidation via Fe(III)-PFOA complexes and (ii) one-electron reduction caused by carboxylate anion radical (CO2 (•-)), which was generated by photolysis of ferrioxalate complexes. Under excess oxalic acid, PFOA decomposition was accelerated, and its corresponding half-life was shortened from 114 to 34min as ferric concentration increased from 7 to 80μM. Besides fluoride ions, six shorter chain perfluorinated carboxylic acids (PFCAs) bearing C2-C7 were identified as main intermediates. The presence of O2 promoted the redox recycling of Fe(3+)/Fe(2+) and thus avoided the exhaustion of the Fe(III).

Photo-Fenton degradation of the herbicide 2,4-D in aqueous medium at pH conditions close to neutrality

A theoretical and experimental study of the photo-Fenton degradation of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) in water is presented. A kinetic model derived from a reaction sequence is proposed using the ferrioxalate complex as iron source for conditions of pH = 5. The kinetic model was employed to predict the concentrations of 2,4-D, 2,4-dichlorophenol (2,4-DCP), hydrogen peroxide (HP) and oxalate (Ox) in a flat plate laboratory reactor irradiated with a solar simulator. Two types of incident irradiation levels were tested by different combinations of attenuation filters. The effects of the oxalate/Fe+3 molar ratio (Ox/Fe), the reaction temperature (T) and the 2,4-D/HP molar ratio (R) on the photo-Fenton process were also investigated. For low radiation level and operating conditions of R = 50 and T = 50 °C, a 2,4-D conversion of 95.6% was obtained after 180 min. Moreover, the 2,4-D conversion was almost 100% in only 120 min when the system was operated under the same operating conditions and high radiation level. From the proposed model and the experimental data, the corresponding kinetic parameters were estimated applying a nonlinear regression method. A good agreement between the kinetic model and experimental data, for a wide range of simulated solar operating conditions, was observed. For 2,4-D, 2,4-DCP, HP and Ox concentrations, the calculated RMSE were 1.21 × 10−2, 5.45 × 10−3, 2.86 × 10−1 and 2.65 × 10−2 mM, respectively.

Photo-Fenton oxidation of 3-amino-5-methylisoxazole: a by-product from biological breakdown of some pharmaceutical compounds.

The present study aims to assess the removal of 3-amino-5-methylisoxazole (AMI), a recalcitrant by-product resulting from the biological breakdown of some pharmaceuticals, applying a solar photo-Fenton process assisted by ferrioxalate complexes (SPFF) (Fe3+/H2O2/oxalic acid/UVA-Vis) and classical solar photo-Fenton process (SPF) (Fe2+/H2O2/UVA-Vis). The oxidation ability of SPFF was evaluated at different iron/oxalate molar ratios (1:3, 1:6, and 1:9, with [total iron] = 3.58 × 10-2mM and [oxalic acid] = 1.07 × 10-1, 2.14 × 10-1 and 3.22 × 10-1mM, respectively) and pH values (3.5-6.5), using low iron contents (2.0mg Fe3+ L-1). Additionally, the use of other organic ligands such as citrate and ethylenediamine-N,N'-disuccinic acid (EDDS) was tested. The oxidation power of the classical SPF was assessed at different pH values (2.8-4.0) using 2.0mg Fe2+ per liter. Furthermore, the effect of AMI concentration (2-20mgL-1), presence of inorganic ions (Cl-, SO42-, NO3-, HCO3-, NH4+), and radical scavengers (sodium azide and D-mannitol) on the SPF method at pH 3.5 was also assessed. Experiments were done using a lab-scale photoreactor with a compound parabolic collector (CPC) under simulated solar radiation. A pilot-scale assay was conducted using the best operation conditions. While at near neutral pH, an iron/oxalate molar ratio of 1:9 led to the removal of 72% of AMI after 90min of SPFF, at pH 3.5, an iron/oxalate molar ratio of 1:3 was enough to achieve complete AMI degradation (below the detection limit) after 30min of reaction. The SPF process at pH 3.5 underwent a slower AMI degradation, reaching total AMI degradation after 40min of reaction. The scale up of SPF process showed a good reproducibility. Oxalic and oxamic acids were identified as the main low-molecular-weight carboxylic acids detected during the pilot-scale SPF reaction. Graphical abstract ᅟ.