Modeling dye degradation kinetic using dark- and photo-Fenton type processes

Dark- and photo-Fenton type processes, Fe²⁺/H₂O₂, Fe³⁺/H₂O₂, Fe⁰/H₂O₂, UV/Fe²⁺/H₂O₂, UV/Fe³⁺/H₂O₂ and UV/Fe⁰/H₂O₂, were applied for the treatment of model colored wastewater containing two reactive dyes, C.I. Reactive Blue 49 and C.I. Reactive Blue 137, and degradation kinetics were compared. Dye degradation was monitored by the means of UV/VIS, adsorbable organic halides (AOX) and total organic carbon (TOC) analysis, thus determining decolorization and dechlorination of triazine structure, as well as mineralization of model colored wastewater. Both dark- and photo-Fenton type processes were proven to be very efficient for color removal; ≥98% was achieved in all cases. Significant improvements in the mineralization of studied dyes were achieved by the assistance of UV light, as it was expected. It was demonstrated that the degradation kinetic of applied dyes depended on the presence of UV light, as well as type of iron catalyst and dye structure. On bases of the obtained experimental results, the mathematical models were developed describing dye degradation kinetics in all studied systems. Since UV light was used in order to enhance the efficiency of dark-Fenton type processes, mathematical model describing dye degradation by UV photolysis providing the values of quantum yields for each of the dye was developed and incorporated in model for photo-Fenton type processes. A sensitivity analysis for the evaluation of importance of each reaction used in mathematical models was also performed.     

Treatment of a mixture of three pesticides by photo- and electro-Fenton processes

In the present work, a comparative study of a mixture of three pesticides (chlortoluron, carbofuran and bentazon) has been investigated by advanced oxidation processes such as photo-Fenton and electro-Fenton. These processes are based on the in situ production of hydroxyl radical, a highly strong oxidant, which allows the degradation of organic pollutants until their mineralization into CO₂ and H₂O. For the photo-Fenton process, the effect of key parameters such as initial catalyst (Fe³⁺) concentration and hydrogen peroxide (H₂O₂) dosage were studied. Under optimal operating conditions, the evolution of total organic carbon (TOC) has been investigated for the two processes. Obtained results showed that more than 90% of TOC removal was obtained after only 2 h of photo-Fenton treatment whereas the electro-Fenton process needed 8 h of treatment. Nevertheless, the comparison of cost treatment shows that the photo-Fenton process is more expensive than electro-Fenton. The evolution of pesticide's concentration during treatment was determined by high performance liquid chromatography (HPLC). Inorganic ions released such as chloride, nitrate, sulphate and ammonium ions are identified and their kinetic evolution was measured by ion chromatographic analyses.     

Ag@CoFe2O4/Fe2O3 nanorod arrays on carbon fiber cloth as SERS substrate and photo-Fenton catalyst for detection and degradation of R6G

In this study, Ag nanoparticles loaded CoFe₂O₄/Fe₂O₃ nanorod arrays on carbon fiber cloth have been successfully fabricated by a hydrothermal route followed by a calcination treatment and photochemical reduction process. The as-prepared composite has been characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and X-ray photoelectron spectroscopy (XPS). The obtained Ag@CoFe₂O₄/Fe₂O₃ nanorod arrays show excellent SERS performance, which provides enhancement factors (EF) as high as about 1.2 × 10⁸ for Rhodamine 6G (R6G). The SERS signals collected over a 20?µm × 20?µm area show relative standard deviation lower than 12%, suggesting good SERS signal uniformity. In addition, the Ag@CoFe₂O₄/Fe₂O₃ nanorod arrays can be used as an effective photo-Fenton catalyst photocatalytical degradation of R6G. It was found that 99.15% of R6G can be degraded in an hour. This bifunctional composite that can act both as SERS substrates and as photo-Fenton catalyst would facilitate the cleaning and recycling of SERS substrates for reusing through a photocatalytic process, as well as facilitate the integration of rapid detection and effective degradation of organic pollutants.     

UVA-LED assisted persulfate/nZVI and hydrogen peroxide/nZVI for degrading 4-chlorophenol in aqueous solutions

Photocatalytic degradation of 4-chlrophenol (4-CP) using UVA-LED assisted persulfate and hydrogen peroxide activated by the nZVI (Nano Zero Valent Iron) in a batch photocatalytic reactor was investigated. The reaction involved a lab-scale photoreactor irradiated with UVA-LED light emitted at 390 nm. The efficiency of the reaction was evaluted in terms of 4-CP degradation and mineralization degree at different pH of solution, initial concentrations of nZVI, persulfate, hydrogen peroxide and 4-CP. In UVA-LED/H₂O₂/nZVI process, complete degradation of 4-CP (>99%) and 75% mineralization was achieved at pH of 3, hydrogen peroxide concentration of 0.75 mM, nZVI dosage of 1mM and initial 4-CP concentration of 25mg/L at the reaction time of 30 min. The optimum conditions obtained for the best 4-CP degradation rate were at an initial concentration of 25mg/l, persulfate concentration of 1.5mM, nZVI dosage of 1mM, pH of 3 and reaction time of 120min for UVA-LED/persulfate/nZVI process. It was also observed that the 4-CP degradation rate is dependent on initial 4-CP concentrations for both processes. The pseudo-first-order kinetic constant at 25mg/L initial concentration of 4-CP was found to be 1.4×10^?1 and 3.8×10^?2 in UVA-LED/H₂O₂/nZVI and UVA-LED/persulfate/nZVI processes, respectively. Briefly, the UVA-LED/H₂O₂/nZVI process enhanced the degradation rate of 4-CP by 3.67-times in comparison to UVA-LED/persulfate/nZVI process at 30min contact time, which serves as a new and feasible approach for the degradation of 4-CP as well as other organic contaminants containing wastewater.     

Mechanism and kinetic study for the degradation of lindane by photo-Fenton process

Because application of classical treatment methods cannot allow an easily Lindane (gamma 1α,2α,3β,4α,5α,6β-hexachlorocyclohexane) degradation, development of more powerful water treatment techniques, like advanced oxidation processes (AOPs), was necessary. The degradation of lindane (γ-HCH) has been studied using the photo-Fenton reaction. The degradation kinetics under irradiation was optimized in respect to H₂O₂ concentration and Fe²⁺ concentration at a constant lindane concentration. The degradation rate follows pseudo-first order kinetics with respect to lindane and organic clorine mineralization. Application of photo-Fenton system also assures total organic carbon removal with 95% efficiency at 2 h irradiation. The possible pathways of lindane photodegradation is also proposed.     

Augmenting the photocatalytic performance of cobalt ferrite via change in structural and optical properties with the introduction of different rare earth metal ions

In the present study, synthesis of different rare earth (RE) doped cobalt ferrite nanoparticles was done via facile sol-gel auto-combustion method using four different RE metal ions: Eu, Gd, Dy and Nd. The RE substituted cobalt ferrite nanoparticles were then characterized using FT-IR, powder XRD, HR-TEM, SAED, EDX, VSM and DRS techniques. From the characterization results, a significant variation in the structural, magnetic and optical properties of pure cobalt ferrite was observed with the introduction of different RE metal ions. This change in the properties was emerged due to the distortion of the ferrite crystal lattice due to replacement of smaller ionic radii Fe³⁺ ions with the comparatively larger ionic radii RE³⁺ metal ions. The catalytic activity of the fabricated RE doped cobalt ferrite nanoparticles was studied for the photo-Fenton degradation of cationic and anionic dyes. Under visible light irradiation, the as prepared RE doped nanoparticles exhibited great enhancement in the photo-Fenton degradation of dye molecules as compared to pure cobalt ferrite nanoparticles. The enhancement in the degradation rate was ascribed to the generation of defects in the crystal lattice, lower crystallite size and reduced band gap energy values which facilitated the facile transfer of photo-generated holes and electrons. Best catalytic results were obtained for CoNd_0.08Fe_1.92O₄ for SO dye (k?=?2.23?×?10^?1 min^?1) which were found to be around 9 times higher than the pure cobalt ferrite nanoparticles (k?=?0.23?×?10^?1 min^?1).     

Fenton‐ and Fenton‐Like AOPs for Wastewater Treatment: From Laboratory‐To‐Plant‐Scale Application

Abstract

Fenton‐and Fenton‐like AOPs systems have been utilized for the oxidative degradation of some chlorinated pollutants such as chloral hydrate or 1,1,1‐trichloroethane, and for the treatment of real industrial wastewaters. Both ferrous sulfate (FeSO₄ · 7 H₂O) and Mohr's salt (NH₄)₂Fe(SO₄)₂. 6 H₂O have been used as Fe²⁺ ion sources. With Mohr's salt (MS) the Fenton‐and Fenton‐like reaction has been successfully carried out under acidic (pH 3) and neutral (pH 7) reaction conditions. The new Fenton‐like system utilizes zero‐valent iron (Fe^o) instead of ferrous sulfate has been applied for the 1,1,1‐trichloroethane and chloral hydrate degradation. Similarly, the application of catechol‐ and hydroquinone‐driven Fenton reaction for the degradation of chloral hydrate under acidic and neutral pH is a new Fenton‐like AOPs approach. The photo‐Fenton‐like reactions such as Fe³⁺/hν, Fe²⁺/H₂O₂/hν, and ferrioxalate system have been also studied for the degradation of chloral hydrate. As an irradiation source a daily light or sun light have been used. In comparison with photoreactor experiments the best system was observed to be Fe³⁺/hν. In some experiments the influence of standing time prolongation after Fenton reaction on the final degradation efficiency due to hydrolysis of intermediates such as phosgene (CCl₂?O) has also been studied. The Fenton reaction was successfully utilized for the treatment of real industrial wastewaters, in two cases even in plant‐scale applications.     

3D rectangular WO3 hybridized by PrFeO3 nanoparticles with efficient dual charge transfer for enhanced photo-Fenton-like activity

In this work, zero-dimensional (0D) high crystalline PrFeO₃ worm nanocrystals were loaded over a three-dimensional (3D) rectangular WO₃ to construct a 0D/3D PFO/W Z-scheme heterojunction by an in situ ultrasonic synthetic process. This heterojunction exhibited excellent photocatalytic activities towards the degradation of organic pollutants such as rhodamine B (RhB), Methylene blue (MB), and tetracycline hydrochloride (TC) in the presence of small amounts of H₂O₂ under visible-light irradiation. For example, the k value of PFO/W + H₂O₂ was about 67, 107, 45, 27, 11 and 14 times higher than pure H₂O₂, PrFeO₃, WO₃, PFO/W nanocomposite, PrFeO₃+ H₂O₂ and WO₃+H₂O₂ respectively during the degradation of MB. The trapping experiments and ESR measurements identified that the generated ·OH, ·O₂⁻, and h⁺ were the active species involved in the catalysis. Further, the ·OH radical could be continuously generated by Fe³⁺/Fe²⁺ and W⁶⁺/W⁵⁺ conversion and played the dominant role in the degradation of organic pollutants. The superior photocatalytic performance of the PFO/W + H₂O₂ system was derived from the synergistic effect of the Z-scheme heterostructure and dual photo-Fenton-like oxidation (Fe³⁺/Fe²⁺ and W⁶⁺/W⁵⁺). A possible mechanism was postulated based on the results obtained. In summary, this study provided new insights into synthesizing an effectively heterogeneous 0D/3D Z-scheme dual photo-Fenton-like catalyst for water clarification.     

Degradation of 2,4-dichlorophenol in aqueous solution by sono-Fenton method

This study presents the results of the Sono-Fenton process for the degradation of 2,4-dichlorophenol (DCP). The influential parameters such as H₂O₂, Fe²⁺ and pH for the Sono-Fenton process were investigated. Sono-Fenton method was found to be the best one for degradation efficiency of DCP when compared with that of the Fenton process. The optimum concentrations for the degradation of DCP using conventional Fenton’s method were found to be 20 mg/L of Fe²⁺ and 580 mg/L of H₂O₂ at pH 2.5. In the case of Sono-Fenton, the optimal concentrations were found to be 10 mg/L of Fe²⁺ and 400 mg/L of H₂O₂ at pH 2.5. Sono-Fenton method resulted in the reduction of required Fe²⁺ concentration (50%) and H₂O₂ concentration (31%). In addition, this method could be applicable even at pH 5.0 and a degradation efficiency of DCP was 77.6%. Kinetic studies for the degradation of DCP proved that the degradation of DCP tends to follow pseudo first order reaction and the rate constant was found to be 7 × 10⁻⁴ min⁻¹.     

Preparation and modification of polythiophene–organic montmorillonite composite

Polythiophene‐organic montmorillonite (PTP‐OMMT) composites were prepared via Fe³⁺‐H₂O₂ catalytic oxidation system at room temperature in water (medium) within the presence of sodium dodecyl benzene sulfonate. The PTP‐OMMT composite made from 2 g/ml solution of OMMT/TP with reacting for 12 h shown the highest conductivity (3.44 × 10⁻⁵ S/cm). The prepared PTP‐OMMT was modified with aniline (ANI) and pyrrole (PY) under Fe³⁺‐H₂O₂ and ammonium persulfate (APS) oxidation systems. The conductivity of PANI‐(PTP‐OMMT) and PPY‐(PTP‐OMMT) reached the range from 10⁻² S/cm to 10⁻¹ S/cm, showing a growth of 10³ to 10⁴ times. Fourier transform infrared spectroscopy (FTIR) and X‐ray diffraction (XRD) revealed that thiophene enter into OMMT to form intercalation compounding, which undamaged after ANI and PY modification. Thermogravimetric analysis (TGA) comfirmed the improved thermostability of PTP‐OMMT and the decreased thermostability of modified materials. Scanning electron microscopy (SEM) indicated that modified materials under Fe³⁺‐H₂O₂ oxidation system presented regular spherical structures. POLYM. COMPOS., 37:2503–2510, 2016. © 2015 Society of Plastics Engineers     

The oxidation of Fe(II) with Cu(II) in acidic sulfate solutions with air at elevated pressures

The oxidation of ferrous ions in acidic sulfate solutions in the presence of cupric ions at elevated air pressures was investigated in a high-intensity gas–liquid contactor. The study was required for the design of the regeneration steps of the novel Vitrisol^® desulphurization process. The effects of the Fe²⁺ concentration, Cu²⁺ concentration, Fe³⁺ concentration, initial H₂SO₄ concentration, and partial oxygen pressure on the reaction rate were determined at three different temperatures, i.e., T?=?50?°C, 70?°C, and 90?°C. Most of the experiments were determined to be affected by the mass transfer of oxygen, and therefore true intrinsic kinetics could not be fully determined. An increase in Fe²⁺ and Cu²⁺ concentrations, as well as the partial pressure of oxygen and temperature, increased the Fe²⁺ oxidation rate. H₂SO₄ did not influence the Fe²⁺ oxidation rate. An increase in Fe³⁺ concentration decreased the Fe²⁺ oxidation rate. Although determined from experiments partially affected by mass transfer, a first order of reaction in Fe²⁺ was observed, fractional orders in both Cu²⁺ and O₂ were measured, a zero order in H₂SO₄ was determined, and a negative, fractional order in Fe³⁺ was obtained. The activation energy was estimated to be 31.3?kJ/mol.     

The generation of hydroxyl radicals by hydrogen peroxide decomposition on FeOCl/SBA‐15 catalysts for phenol degradation

Iron oxychloride (FeOCl) supported on mesoporous silica (SBA‐15), as a Fenton‐like solid catalyst for phenol degradation, showed supreme activity for production of hydroxyl radical (HO·) by H₂O₂ decomposition, and the generation capacity was comparable to the conventional Fenton reagent (Fe²⁺+H₂O₂). The structure of FeOCl was characterized with spectroscopies. The generation of HO· species during the reaction was detected using 5,5‐dimethyl‐1‐pyrroline N‐oxide trapped electron paramagnetic resonance. Furthermore, the kinetics in detail was driven for the creation and diffusion of HO· by H₂O₂ decomposition over FeOCl, which follows a first‐order rate through a two‐step reaction. With the combination of the catalyst structure and kinetic parameters, the plausible mechanism for H₂O₂ decomposition during the oxidative degradation of phenol was rationalized. As a Fenton‐like solid catalyst, FeOCl/SBA‐15 is a promising alternative for the removal of low‐level organic contaminates from water. © 2014 American Institute of Chemical Engineers AIChE J, 61: 166–176, 2015     

Removal of metsulfuron methyl by Fenton reagent

The removal of metsulfuron methyl (MeS)—a sulfonyl urea herbicide from contaminated water was investigated by advanced oxidation process (AOP) using Fenton method. The optimum dose of Fenton reagent (Fe²⁺/H₂O₂) was 10 mg/L Fe²⁺ and 60 mg/L H₂O₂ for an initial MeS concentration ([MeS]₀) range of 0–80 mg/L. The Fenton process was effective under pH 3. The degradation efficiency of MeS decreased by more than 70% at pH > 3 (pH 4.5 and 7). The initial Fe²⁺ concentration ([Fe²⁺]₀) in the Fenton reagent affected the degradation efficiency, rate and kinetics. The degradation of MeS at optimum dose of Fenton reagent was more than 95% for [MeS] ₀ of 0–40 mg/L and the degradation time was less than 30 min. The determination of residual MeS concentration after Fenton oxidation by UV spectrophotometry was affected by the interferences from Fenton reagent. The estimation of residual MeS concentration after Fenton oxidation by high pressure/performance liquid chromatograph (HPLC) was interference free and represented the actual concentration of MeS and does not include the by-products of Fenton oxidation. The degradation kinetics of MeS was modelled by second order reactions involving 8 rate constants. The two reaction constants directly involving MeS were fitted using the experimental data and the remaining constants were selected from previously reported values. The model fit for MeS and the subsequent prediction of H₂O₂ were found to be within experimental error tolerances.     

Comparison of a new immobilized Fe3+ catalyst with homogeneous Fe3+–H2O2 system for degradation of 2,4‐dinitrophenol

BACKGROUND: Heterogeneous Fenton catalysts have been used to treat various organic pollutants in an aqueous environment. The present study has investigated the degradation of 2,4‐dinitrophenol (2,4‐DNP), a priority pollutant generated by such industries as pharmaceuticals, pesticides, pigments and dyes. Degradation of 2,4‐DNP (100 mg L^?1) was studied using Fe³⁺ loaded on Al₂O₃ as a heterogeneous catalyst in the presence of H₂O₂, and the efficiency compared with the homogeneous Fe³⁺/H₂O₂ based Fenton‐like process. The effect of different parameters for both processes, such as catalyst loading, H₂O₂ concentration, initial solution pH, initial substrate concentration and temperature were investigated and the optimum operating conditions determined. RESULTS: Under optimal operating conditions of the homogeneous system ([Fe³⁺] 125 mg L^?1; [H₂O₂] 250 mg L^?1; pH 3; room temperature), 92.5% degradation was achieved in 35 min for an initial 2,4‐DNP concentration of 100 mg L^?1. In the case of immobilized Fe (Fe³⁺–Al₂O₃ catalyst), degradation improved to 98.7% under the condition 10 wt% [Fe³⁺–Al₂O₃] 1 g L^?1 catalyst loading; [H₂O₂] 250 mg L^?1; pH 3; at room temperature for the same duration. CONCLUSIONS: This study demonstrated the stability and reusability of the prepared heterogeneous catalyst. This process is a viable technique for treatment of aqueous solutions containing contaminants. Copyright © 2012 Society of Chemical Industry     

Oxidation of Herbicides in Groundwater by the Fenton Process: A Realistic Alternative for O3/H2O2 Treatment?

Oxidation with O₃/H₂O₂ and Fe²⁺/H₂O₂ are optional for the degradation of herbicides and pesticides in water. The choice of which process will be applied depends upon the degree of degradation of organic micropollutants and the process conditions related to the formation of oxidation by-products, and also on the total costs and the safety and reliability of the process. Under real conditions, atrazine and some phenylureaherbicides were oxidized with O₃/H₂O₂. Comparable experiments under conditions of different pH, iron and DOC content were performed with Fe²⁺/H₂O₂, in order to gain information on the influence of these parameters. The oxidation results of both processes as well as the formation of bromate as one of the oxidation by-products are described. It was found that 80% of atrazine and >99% of some phenylureaherbicides could be degraded with O₃/H₂O₂ at pH 7.8 (H₂O₂/O₃ ratio 3.7 g/g). Under these conditions, bromate was formed up to 5 μg/1. Comparable results were obtained with Fe²⁺/H₂O₂ at a pH value of 5.5, whereas the formation of bromate was kept below 0.2 μg/L.     

Parametric Study and Process Evaluation of Fenton Oxidation: Application of Sequential Response Surface Methodology and Adaptive Neuro-Fuzzy Inference System Computing Technique

The Fenton oxidation is rarely used industrially due to its high operating cost, large chemical consumption, excessive sludge production, and operability only within a narrow pH range. Therefore, there is a need to evaluate the Fenton oxidation to maximize its ability to degrade high-strength dye wastewater at reduced operating cost. Optimization tools are among the most commonly used tool to maximize the degradation of pollutants. The current study aims at evaluating the applicability of response surface methodology (RSM) and adaptive neuro-fuzzy inference system (ANFIS) to optimize the degradation of Remazol brilliant blue through the Fenton oxidation. The effects of four operating parameters including dye concentration, retention time, and mass ratios of Dye:Fe²⁺ and H₂O₂:Fe²⁺ were evaluated by applying RSM. According to the RSM results, color and chemical oxygen demand (COD) removal of 99.9% and 84%, respectively, were obtained at 120?min at the COD value of 795?mg/L, mass ratios of Dye:Fe²⁺?=?16, H₂O₂:Fe²⁺?=?15 and pH?=?3. ANFIS was also used to evaluate the most influential operating parameters on the COD removal based on the RSM results. The ANFIS results showed that the mass ratio of H₂O₂:Fe²⁺ had the most significant contribution to the COD removal. High R² values (≥90%) indicated that the predictions of RSM and ANFIS models for COD removal were acceptable. In conclusion, this study demonstrated that RSM and ANFIS were able to determine the most significant operating parameters and optimum ratios of pollutant:oxidant:catalyst, which reduced the operating cost directly.     

Gaseous Elemental Mercury Removal Using Combined Metal Ions and Heat Activated Peroxymonosulfate/H2O2 Solutions

Several novel oxidation removal processes of elemental mercury (Hg⁰) from flue gas using combined Fe²⁺/Mn²⁺ and heat activated peroxymonosulfate (PMS)/H₂O₂ solutions in a bubbling reactor were proposed. The operating parameters (e.g., PMS/H₂O₂ concentration, Fe²⁺/Mn²⁺ concentration, solution pH, activation temperature, and Hg⁰/NO/SO₂/O₂/CO₂ concentration), mechanism and mass transfer-reaction kinetics of Hg⁰ removal were investigated. The results show that heat and Fe²⁺/Mn²⁺ have significant synergistic effect for activating PMS and PMS/H₂O₂ to produce free radicals to oxidize Hg⁰. Hg⁰ removal is strongly affected by PMS/H₂O₂ concentration, Fe²⁺/Mn²⁺ concentration, activation temperature, and solution pH. · and ·OH produced from combined heat and Fe²⁺/Mn²⁺ activated PMS/H₂O₂ play a leading role in Hg⁰ removal. Under optimized experimental conditions, Hg⁰ removal efficiencies reach 100, 94.9, 66.9, and 58.9% in heat/Fe²⁺/PMS/H₂O₂, heat/Mn²⁺/PMS/H₂O₂, heat/Fe²⁺/PMS, and heat/Mn²⁺/PMS systems, respectively. Hg⁰ removal processes in four systems belong to fast reaction and were controlled by mass transfer under optimized experimental conditions. © 2018 American Institute of Chemical Engineers AIChE J, 65: 161–174, 2019     

Effect of UV Radiation on the Removal of Carboxylic Acids from Water by H2O2 and O3 in the Presence of Metallic Ions

The effect of UV radiation on the removal of formic, oxalic and maleic acids from water by metallic ion (Fe²⁺ or Cu²⁺)/H₂O₂ and metallic ion/O₃ was studied and compared. The results showed that metallic ion/O₃/UV has higher efficiency than metallic ion/H₂O₂/UV for oxalic acid removal. UV radiation significantly increases the efficiency of metallic ion/H₂O₂ for formic and maleic acids removal while its effect on the efficiency of metallic ion/O₃ for formic acid removal is minor_. However, at pH 2, O₃ alone showed higher efficiency than metallic ion/H₂O₂/UV for formic acid removal. Contrary to the relative efficiency of metallic ions in the previous systems, Cu²⁺ exhibited higher rate than Fe²⁺ for the removal of the degradation products of maleic acid by O₃. UV radiation exhibited a minor effect on the efficiency of Cu²⁺/O₃, while it exhibited a large effect on the efficiency of Fe²⁺/O₃ for the removal of the degradation products of maleic acid.     

Degradation of amoxicillin in aqueous solution using nanolepidocrocite chips/H2O2/UV: Optimization and kinetics studies

Degradation of amoxicillin (AMX) by nanolepidocrocite chips/H₂O₂/UV method as a new photo-Fenton like process was investigated and optimized by response surface methodology (RSM). The optimal conditions were initial AMX concentration of 10 mg l⁻¹ and initial H₂O₂ concentration of 60 mg l⁻¹ at pH of 2 under UV radiation for 120 min. The general photo-Fenton process mechanism was applied to propose a new kinetic model for AMX degradation. According to this model, the reaction constant between AMX and OH was obtained 4.55 × 10⁵ M⁻¹ s⁻¹. Also, nanolepidocrocite showed good catalytic activity even after four successive degradation cycles.     

Lipid hydroperoxide measurement by oxidation of Fe2+ in the presence of xylenol orange. Comparison with the TBA assay and an iodometric method

Study of the role of hydroperoxides and lipid peroxidation in disease requires simple and sensitive methods for direct hydroperoxide measurement. We report on a technique for measuring hydroperoxide which relies upon the rapid hydroperoxide-mediated oxidation of Fe²⁺ under acidic conditions. Fe³⁺ forms a chromophore with xylenol orange which absorbs strongly at 560 nm, yielding an apparent E₅₆₀ (for H₂O₂, butyl hydroperoxide and cumene hydroperoxide) of 4.3×10⁴ M⁻¹ cm⁻¹. The assay was validated in a study of liposomal lipid peroxidation and shown to give results comparable with those obtained by an iodometric method or by measuring conjugated dienes. The assay involving thiobarbituric acid, by comparison, underestimates lipid peroxidation and does not measure hydroperoxideper se.