Introducing saccharic acid as an efficient iron chelate to enhance photo-Fenton degradation of organic contaminants

D-glucaro-1,4-lactone improves Diethylnitrosamine induced hepatocellular carcinoma in rats via the uric acid-ROS pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Liuwei dihuang pills is a famous Traditional Chinese Medicine with various anti-cancer properties. Over 50 pharmaceutical manufacturers produce Liuwei dihuang pills in China and an estimated millions of people around the world orally take it every day. D-glucaro-1,4-lactone (1,4-GL) was quantified to be about 12.0 mg/g in Liuwei dihuang pills and a primary bioactive component of it inhibiting the activity of β-glucuronidase in vivo. 1,4-GL can prevent and effectively inhibit various types of cancer. However, its exact mechanism of action remains unknown. The study would justify the traditional usage of Liuwei dihuang pills against cancers.

AIM OF THE STUDY

1,4-GL, a bioactive ingredient derived from Liuwei dihuang pills, a famous Traditional Chinese Medicine, could delay the progression of diethylnitrosamine (DEN)-induced hepatocellular carcinoma (HCC) in rats. The mechanism underpinning the effect, however, remains poorly understood.

MATERIALS AND METHODS

Healthy and HCC rats were treated with or without 1,4-GL (40.0 mg/kg) and 1HNMR-based metabonomic analysis was employed. 10 metabolites in uric acid pathway were quantitatively determined by UPLC-MS/MS. The expression of xanthine dehydrogenase (XDH), SLC2A9 mRNA, and SLC2A9 protein was determined using RT-qPCR and Western Blot. The effect of 1,4-GL on HCC-LM3 cells was verified in vitro. The alterations of ROS activity, SLC2A9 and XDH gene levels were observed in NCTC-1469 cells induced by lipopolysaccharide (LPS) after 1,4-GL treatment.

RESULTS

After the intervention of 1,4-GL, improved pathological morphology, liver lesions in HCC rats was observed with restored serum levels of AFP, AST, ALP, γ-GGT and Fisher's ratio. Hepatic metabonomics revealed that puring metabolism were significantly regulated by 1,4-GL in HCC rats. Uric acid, xanthine and hypoxanthine levels were quantified by UPLC-MS/MS and found to be nearly restored to control levels after 1,4-GL treatment in HCC rats. Changes in xanthine oxidase activity, XDH mRNA expression, and SLC2A9 mRNA and protein expression were also reversed. 1,4-GL treatment in LM3 HCC cells were consistent with the results in vivo. Furthermore, oxidative stress indicators such as T-SOD, GSH, CAT and MDA in serum and liver were improved after HCC rats treated with 1,4-GL. In vitro, 1,4-GL was observed to reduce lipopolysaccharide-induced ROS levels in NCTC-1469 cells with enhanced mRNA and protein expression of SLC2A9 and decreased mRNA level of XDH.

CONCLUSION

The protective effects of 1,4-GL against DEN-induced HCC by reducing uric acid and ROS levels due to down-regulation of uric acid production and up-regulation of SLC2A9 expressions. 1,4-GL may represent a novel treatment that improves recovery from HCC by targeting uric acid-ROS pathway.

Epoxiconazole degradation in water samples: a comparative study of Fenton, photo-Fenton, solar photo-Fenton, and solar photolysis processes

Epoxiconazole (EPO) is classified as a persistent organic pollutant due to its ability to persist in the environment for prolonged periods. Its degradation is pivotal in mitigating its environmental impact. This investigation focuses on assessing the degradation of EPO using various methodologies, namely Fenton, photo-Fenton, solar photo-Fenton, and solar photolysis, conducted in both Milli-Q water and groundwater. These experiments encompassed evaluations at both the standard pH typically used in photo-Fenton reactions and the natural pH levels inherent to the respective aqueous environments. Additionally, EPO degradation products were analyzed after a 60-min reaction. Notably, in systems utilizing groundwater, the inclusion of additional iron was unnecessary, as the naturally occurring iron content in the groundwater facilitated the intended processes. Specifically, in Milli-Q water, solar photo-Fenton demonstrated an EPO degradation efficiency of 97%. Furthermore, the substitution of Milli-Q water with groundwater in Fenton-like processes did not significantly affect the efficacy of EPO degradation. These findings underscore the potential of solar photo-Fenton as an economically viable and environmentally sustainable strategy for EPO degradation.

Progress on mechanism and efficacy of heterogeneous photocatalysis coupled oxidant activation as an advanced oxidation process for water decontamination

The rising debate on the dilemma of photocatalytic water treatment technologies has driven researchers to revisit its prospects in water decontamination. Nowadays, heterogeneous photocatalysis coupled oxidant activation techniques are intensively studied due to their dual advantages of high mineralization and high oxidation efficiency in pollutant degradation. This paved a new way for the development of solar-driven oxidation technologies. Previous reviews focused on the advances in one specific coupling technique, such as photocatalytic persulfate activation and photocatalytic ozonation, but lack a consolidated understanding of the synergy between photocatalytic oxidation and oxidant activation. The synergy involves the migration of photogenerated carriers, radical reaction, and the increase in oxidation rate and mineralization. This review systematically summarizes the fundamentals of activation mechanism, advanced characterization techniques and synergistic effects of coupling techniques for water decontamination. Besides, specific cases that lead researchers astray in revealing mechanisms and assessing synergy are critically discussed. Finally, the prospects and challenges are put forward to further deepen the research on heterogeneous photocatalytic activation of oxidants. This work provides a consolidated view of the existing heterogeneous photocatalysis coupled oxidant activation techniques and inspires researchers to develop more promising solar-driven technologies for water decontamination.

Glucaric Acid Production from Miscanthus sacchariflorus via TEMPO-Mediated Oxidation with an Efficient Separation System

In this study, production and isolation of glucaric acid from lignocellulosic biomass were performed via potassium cation-based TEMPO-mediated oxidation for the ease of glucaric acid isolation. To optimize the oxidation conditions, response surface methodology (RSM) was adopted using standard glucose as the raw material. Among the oxidation conditions, the dosage of oxidant and pH of reaction affected the glucaric acid production, and the optimum conditions were suggested by RSM analysis: 5 °C of reaction temperature, 4.23 equiv dosage of KClO per mole of glucose, and pH of 12. Furthermore, glucaric acid was produced from lignocellulosic biomass-derived enzymatic hydrolysate from Miscanthus under optimum conditions. The impurities such as xylose and lignin in enzymatic hydrolysate inhibited the efficiency of glucose oxidation. As a result, more oxidant was required to produce sufficient glucaric acid from the enzymatic hydrolysate compared to standard glucose. The produced glucaric acid was simply isolated by controlling the pH in the form of glucaric acid monopotassium salt, which showed lower solubility in water, and the purity of isolated glucaric acid was over 99%. The overall mass balance of feedstock to glucaric acid was analyzed, suggesting that 86.38% (w/w) glucaric acid could be produced from initial glucan in feedstock.

Enhanced Fenton-like oxidation (Vis/Fe(III)/Peroxydisulfate): The role of iron species and the Fe(III)-LVF complex in levofloxacin degradation

Traditional Fenton and Fenton-like processes are affected by the sluggish kinetics of Fe(II) regeneration and Fe(III) accumulation. This research revealed that the degradation efficiency of pollutants was significantly increased by adding Fe(III) to the Vis/PS system. A mechanism is proposed in which photosensitivity pollutants can boost Fe(III) to produce Fe(II) under visible light irradiation. Intriguingly, Fe(III) rapidly combines with LVF in aqueous environments to form Fe(III)-LVF complexes. This research confirms that Fe(III)-pollutant complexes are generated. The proportion of complexes are calculated using mathematical models. Furthermore, the production of Fe(IV) is verified in the Vis/PS/Fe(III) system, which also plays a vital role in boosting LVF degradation. Overall, this study provides comprehensive insights into the degradation mechanism of micropollutants, involving hydroxyl radical (OH∙), Fe(IV), and Fe(III)-LVF complexes, providing an efficient and green strategy for contaminant removal during wastewater treatment.

Quantitative probing of reactive oxygen species and their selective degradation on contaminants in peroxymonosulfate-based process enhanced by picolinic acid

The processes of Fe(III) activated peroxymonosulfate (PMS) in degrading contaminants have been extensively studied. Herein, a biodegradable chelating agent, picolinic acid (PICA), was introduced to the PMS/Fe(III) process to improve the reaction efficiency. The emphases of this study were placed on the quantification of steady-state concentrations of reactive oxygen species (ROS). Experiments presented that five types of ROS, including Fe(IV), SO4•-, HO•, 1O2 and O2•- coexisted in this system. Four typical probe compounds were used to quantify the steady-state concentration of ROS under different variables. The steady-state concentration of Fe(IV) ([Fe(IV)]ss) was 3-5 orders of magnitude higher than that of other ROS, followed by 1O2 and SO4•-, whereas HO• had the lowest concentration. The reaction between PMS and PICA was first explored in our study and results showed that 1O2 and O2•- would form in this reaction. Owing to the hybrid oxidation by multiple ROS, this system showed high oxidation capacity, and could effectively degrade a variety of pollutants. The contributions of ROS to the alleviation of pollutants varied depending on their concentrations and specific reactivity of substrates. Generally, organic contaminants with phenol structures were prone to react with Fe(IV). Overall, this study compared the steady-state concentrations of different ROS and revealed the intrinsic ROS formation mechanisms.

Mechanistic Understanding of D-Glucaric Acid to Support Liver Detoxification Essential to Muscle Health Using a Computational Systems Biology Approach

Liver and muscle health are intimately connected. Nutritional strategies that support liver detoxification are beneficial to muscle recovery. Computational-in silico-molecular systems' biology analysis of supplementation of calcium and potassium glucarate salts and their metabolite D-glucaric acid (GA) reveals their positive effect on mitigation of liver detoxification via four specific molecular pathways: (1) ROS production, (2) deconjugation, (3) apoptosis of hepatocytes, and (4) β-glucuronidase synthesis. GA improves liver detoxification by downregulating hepatocyte apoptosis, reducing glucuronide deconjugates levels, reducing ROS production, and inhibiting β-Glucuronidase enzyme that reduces re-absorption of toxins in hepatocytes. Results from this in silico study provide an integrative molecular mechanistic systems explanation for the mitigation of liver toxicity by GA.

Enhanced visible light photo-Fenton catalysis by lanthanum-doping BiFeO3 for norfloxacin degradation

Efficient photo-Fenton removal of antibiotic effluent is a widely followed and significant attempt to deal with the growing environmental pollution. In this study, BiFeO₃ and lanthanum doped BiFeO₃ catalysts were synthesized via one-step hydrothermal method as hydrogen peroxide activator for mineralization of norfloxacin (NOR). Various characterization measurements were used to verify La was successfully doped into the lattice of perovskite and investigated the effect of La doping molar ratio on BiFeO₃ through the characterization of the morphology and physicochemical properties. The degradation experiment and reaction rate constants showed that the La-doped BiFeO₃ particle exhibited superior photo-Fenton catalytic performance to undoped BiFeO₃. Especially, the degradation efficiency of 15% La-doped BiFeO₃ could reach up to 84.94%. And the first order kinetic constant of optimized conditions was 0.01638 min^-1, which was about 6.9 times than that of undoped BiFeO₃.The influence of pH, oxidizer content and catalyst dosage in photo-Fenton reaction were investigated detailedly. Besides, the synthetic catalyst possessed favorable stability and reusability with little metal leaching after many cycles of use. Radical scavenger experiments and electron spin resonance tests were carried out to conclude that the ·OH and holes were regarded as the dominate active species in the catalytic process. The narrow band gap and excellent electron transfer efficiency were the key factors for La-doped BiFeO₃ to have high catalytic efficiency in the photo-Fenton system. Current works demonstrated the great promise of La-doped BiFeO₃ in the elimination of antibiotic organics.

Magnetic recyclable heterogeneous catalyst Fe3O4/g-C3N4 for tetracycline hydrochloride degradation via photo-Fenton process under visible light

Antibiotic pollution of water resources is a global problem, and the development of new treatments for destroying antibiotics in water is a priority research. We successfully manufactured recyclable magnetic Fe₃O₄/g-C₃N₄ through the electrostatic self-assembly method. Selecting tetracycline (TC) as the target pollutant, using Fe₃O₄/g-C₃N₄ and H₂O₂ developed a heterogeneous optical Fenton system to remove TC under visible light. Fe₃O₄/g-C₃N₄ was systematically characterized by SEM, TEM, XRD, FTIR, XPS, DRS, and electrochemical methods. The removal efficiency of 7% Fe₃O₄/g-C₃N₄ at pH = 3, H₂O₂ = 5 mM, and catalyst dosage of 1.0 g/L can reach 99.8%. After magnetic separation, the Fe₃O₄/g-C₃N₄ photocatalyst can be recycled five times with minimal efficiency loss. The excellent degradation performance of the prepared catalyst may be attributed to the proper coupling interface between Fe₃O₄ and g-C₃N₄ which promotes the separation and transfer of photogenerated electrons. Photogenerated electrons can also accelerate the conversion of Fe³⁺ to Fe²⁺, thereby producing more ˙OH. The new Fe₃O₄/g-C₃N₄ can be used as a raw material for advanced oxidation of water contaminated by refractory antibiotics.

Facile fabrication of novel Fe3O4-SnO2-gC3N4 ternary nanocomposites and their photocatalytic properties towards the degradation of carbofuran

Herein, Fe₃O₄-SnO₂ nanoheterojunction has been synthesized and successfully encapsulated in gC₃N₄ matrix using a novel hydrothermal technique. The synthesized material was characterized using sophisticated analytical methods like XRD, TEM, BET, UV-Vis, VSM and XPS to evaluate structural, morphological, optical, magnetic and surface chemical properties. The hybrid nanostructure Fe₃O₄-SnO₂-gC₃N₄ has been utilized for the LED light-induced photocatalytic degradation of carbofuran. The catalyst exhibited notable photocatalytic performance under visible light with an efficiency of ~89% and pseudo first order rate constant of 0.015 min^-1. The result of change in variables like catalyst dose, pollutant concentration, pH and contact time on the photodegradation efficiency and degradation kinetics was studied. The incorporation of Fe₃O₄ improved the magnetic separation of the catalyst after several cycles of operation, thereby improving the practical utility of the catalyst system to tackle organic pollutants.

Enhancing Fenton-like process at neutral pH by Fe(III)-GLDA complexation for the oxidation removal of organic pollutants

N,N-bis(carboxymethyl)glutamic acid (GLDA) was utilized in this study to significantly enhance the Fe(III) mediated Fenton-like oxidation removal of organic pollutants at neutral pH, in which ciprofloxacin (CIP) was used as the model pollutant. The CIP degradation rate in the GLDA/Fe(III)/H₂O₂ system reached 96.5% within 180 min and was nearly 14 times higher than that in the Fe(III)/H₂O₂ system. This enhancement was contributed to the acceleration of the cycle of Fe(III)/Fe(II) caused by GLDA, which was verified by UV-vis spectroscopy, cyclic voltammetry, and radical quenching experiments. The results proved that the GLDA could complex with Fe(III) and greatly modify the redox potential of Fe(III)/Fe(II). Moreover, radical quenching experiments confirmed that •OH and O₂^·- were the mainly species for CIP degradation, and O₂^·- was responsible for 81.9% •OH generation. In addition, H₂O₂ utilization kinetic modeling was also investigated. The optimum parameters of the 100 μM Fe(III)-GLDA complex and 15 mM H₂O₂ were attained by lot-size optimization experiments. Two possible CIP degradation pathways were proposed on the basis of the intermediates identified by MS/MS. The GLDA/Fe(III)/H₂O₂ system performed better than common chelating agents at the same condition, manifesting good potential for environmental concerns.

P-cresol degradation through Fe(III)-EDDS/H2O2 Fenton-like reaction enhanced by manganese ion: Effect of pH and reaction mechanism

P-cresol is a highly toxic phenolic pollutant in coal chemical wastewater. The effective removal of p-cresol is of great significance to the ecological environment. In this study, the degradation of p-cresol by the Fe(III)-EDDS/H₂O₂ Fenton-like reaction modified by Mn²⁺ was investigated. The results showed that the removal rate of p-cresol could be significantly increased by the addition of Mn²⁺ under neutral and weakly alkaline conditions (pH 6.5-8.5). Acidic conditions (pH 3.5) were not conducive to the Fenton-like reaction. This is because a neutral or weakly alkaline environment is conducive to Mn²⁺-EDDS complex formation, which can produce O₂^·- to accelerate the reduction of Fe(III), and the efficiency of p-cresol degradation through a Fenton-like reaction catalyzed by the Fe(III)-EDDS complex is significantly improved. In addition, the degradation of EDDS through ·OH was reduced by O₂^·-, which maintained and stabilized the Mn²⁺-EDDS complex and Fe(III)-EDDS complex. Under neutral conditions, the optimal dosage of Fe(III) is 0.7 mM, and the optimal molar ratios are EDDS/Fe(III) = 1: 1, Mn²⁺/Fe(III) = 1: 1, and H₂O₂/Fe(III) = 15: 1. The addition of free radical clearance isopropanol and CHCl₃ proved that ·OH was the main active substance in the p-cresol degradation process.

Remediation of phenanthrene contaminated soil by ferrous oxalate and its phytotoxicity evaluation

Phenanthrene contaminated soil was remediated by the photochemical process of ferrous oxalate. Without using H₂O₂ and adjusting soil pH, phenanthrene in contaminated soil was degraded effectively by the ferrous oxalate under visible light irradiation. Ferrous oxalate possesses excellent visible light absorption ability which benefits the degradation of phenanthrene in soil under visible light irradiation. Via the Fe(II)/Fe(III) catalytic cycle of ferrous oxalate, H₂O₂ and Fe(II) could be produced continuously and H₂O₂ was further catalyzed by Fe(II) and released hydroxyl radicals (•OH) to degrade the phenanthrene in soil. The dosage of ferrous oxalate, moisture content of soil, and soil thickness were most important factors for degradation of phenanthrene in soil. In addition, a good mixing of ferrous oxalate and soil was vital for enhancing the degradation ratio of phenanthrene. After phenanthrene contaminated soil was treated by ferrous oxalate, the toxicity of treated soil was evaluated via the lettuce cultivation experiments. It was demonstrated the toxicity of phenanthrene contaminated soil was significantly reduced by ferrous oxalate according to the growth indexes of lettuces, including root length, leaf length, and fresh weight. This environment-friendly soil remediation method based on ferrous oxalate has huge potential in the remediation of organic pollutant contaminated soil.

CrVI reductive transformation process by humic acid extracted from bog peat: Effect of variables and multi-response modeling

The present paper reports the efficiency of bog peat-derived humic acid (HA) in the reductive removal of hexavalent chromium (Cr^VI) from aqueous solution as affected by solution pH, the dose of Fe^III and reaction time (numeric variables) and light irradiation (categorical variable). A three-level Box-Behnken design (BBD) applied to design experimental matrix, model the effects and interactions of variables on four determined responses (residual concentration of dissolved Cr^VI, dissolved Cr^III, dissolved Fe^II and total Cr^VI) and optimize the experimental conditions for highest Cr^VI removal efficiency (Cr^VI RE). Reaction mechanisms are also well discussed. Regression models were developed and analyzed by the ANOVA test and models determination coefficient R². Obtained models were significant (F values > 13) and an excellent relationship between experimental and predicted responses (R²: 98.1-99.6%) was observed. The optimum conditions were established corresponding to the residual concentration of dissolved Cr^VI as an index for Cr^VI removal efficiency (RE). In the dark system, the highest Cr^VI RE (98.1%) was obtained under the following conditions: pH = 1, reaction time = 7 d and Fe^III dosage = 0.110 mM. In the light-irradiated system, the optimal Cr^VI RE of 98.3% was observed in pH = 1, reaction time = 5 d and Fe^III dosage = 0.075 mM. Almost all reduced Cr^III remained in the solution even at high pH value. No adsorption or precipitation of Cr^III on the HA surface at pH 5 was confirmed by surface analyses of HA using X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM).

Oxygen reduction reaction electrocatalysis inducing Fenton-like processes with enhanced electrocatalytic performance based on mesoporous ZnO/CuO cathodes: Treatment of organic wastewater and catalytic principle

To treat typical organic wastewater efficiently, a novel Fenton-like processes based on ZnO/CuO composite cathode induced by oxygen reduction reaction (ORR) electrocatalysis with enhanced electrocatalytic performance was established successfully. Electrochemical testing investigation indicated that the ZnO/CuO cathode possessed conspicuous redox peak and better conductivity than uncompounded electrodes. Additionally, the removal efficiency of methylene blue and its chemical oxygen demand (COD) reached 96.4% and 70.8% after 120 min, respectively. Next, the feasibility of the material in practical application was also discussed. Subsequently, electrocatalytic principle based on valence state changes of metal elements on the electrode surface were also studied by x-ray photoelectron spectroscopy (XPS). Redox reactions between the active species H₂O₂ and the species Cu⁺ promoting Fenton-like processes were deduced. Namely, the conversion of Cu(I) and Cu(II) on the electrode surface was accompanied by OH generation. The combination of ZnO and CuO improved the surface morphology, increasing the active site of ORR and the yield of H₂O₂, thus greatly enhanced the Fenton-like activity. Finally, the main intermediates were identified by Gas chromatography-mass spectrometer (GC-MS), and possible pathways for dye degradation were proposed. In short, the research of ZnO/CuO cathode provided great significance for heterogeneous Fenton-like degradation and also showed its application potential in water treatment and remediation.

Oxidation degradation of 2,2',5-trichlorodiphenyl in a chelating agent enhanced Fenton reaction: Influencing factors, products, and pathways

The sodium pyrophosphate (SP)-enhanced Fenton reaction has been proven to have promising potential in remediation of polychlorinated biphenyls in soils by keeping iron ions soluble at high pH and minimizing the useless decomposition of H₂O₂. However, little information can be obtained about the effect of environmental factors on its remediation performance. Thus, the effect of environmental factors on the degradation of 2,2',5-trichlorodiphenyl (PCB18), one of the main PCB congeners in Chinese sites, was investigated in this study. PCB18 degradation was sensitive to pH, which ranged from 39.8% to 99.5% as increased pH from 3.0 to 9.0. ·OH was responsible for PCB18 degradation at pH 5.0, while both ·OH and O₂^- resulted in PCB 18 degradation at pH 7.0 with the calculated reaction activation energy of 73.5 kJ mol^-1. Bivalent cations and transition metal ions decreased PCB18 degradation markedly as their concentrations increased. The addition of humic acid had an inhibitory on PCB18 degradation, but no obvious inhibition of PCB18 removal was observed when the same concentration of fulvic acid was added. The addition of 1 and 10 μM model humic constituents (MHCs) promoted PCB18 degradation, but the addition of 100 μM MHCs decreased PCB18 removal. Biphenyl, two dichlorobiphenyl, and two hydroxy trichlorobiphenyl derivatives were identified as the major degradation products of PCB18 in the Fe²⁺/SP/H₂O₂ system at pH 7.0. Thus, an oxidative pathway contributed by OH and a reductive pathway induced by O₂^- were proposed as the main mechanisms for PCB18 degradation in the SP-enhanced Fenton reaction.

Mitigation of the inhibitory effects of co-existing substances on the Fenton process by UV light irradiation

Co-existing substances (substances not targeted for degradation) can negatively affect wastewater treatment process performance. Here, we quantitatively evaluated the effects of propanal, a common co-existing substance, on the degradation of the azo-dye Orange II, a common pollutant, by the Fenton process to provide data for the development of measures to reduce the effects of co-existing substances on this wastewater treatment process. Inhibition rate (IR; ratio of the reaction rate constants obtained in the absence and presence of propanal) was calculated to examine the effects of propanal on the degradation of Orange II. The IRs for the Fenton process in the first phase and the second phase were 1.6 and 4.2, respectively. However, addition of ultraviolet irradiation to the Fenton process (i.e., the photo-Fenton process) resulted in a comparable IR for the first phase but a markedly lower IR for the second phase. We attributed this to the improvement of the photo-reduction reaction rate due to complexation of propanal with ferric ions, which compensated for the scavenger effects (the trapping of OH radicals) of propanal. Thus, ultraviolet irradiation reduced the inhibitory effects of propanal on the degradation of Orange II by the Fenton process.

Enhancement of photo-Fenton catalytic activity with the assistance of oxalic acid on the kaolin–FeOOH system for the degradation of organic dyes

The Fenton reaction, as an important member of the advanced oxidation processes (AOPs), has gained extensive attention in recent years. However, the practical applications of the traditional Fenton process have been restricted by the poor degradation efficiency and the rigid pH range. In this study, we report a new strategy regarding the photo-Fenton oxidation of Rhodamine B (RhB) by kaolin–FeOOH (K–Fe) catalysts with the assistance of oxalic acid. It was found that the iron–oxalate complex was formed as oxalic acid was introduced into the K–Fe catalyst system by the chelation ability of oxalate. Benefiting from the high photosensitivity of the iron–oxalate complexes, the K–Fe/oxalic acid/H₂O₂/visible light system exhibited excellent catalytic activity towards the degradation of RhB under the optimized reaction conditions [(K–Fe) dosage = 1.0 g L⁻¹, initial pH = 7.2, (oxalic acid) = 1.0 mM, (H₂O₂) = 0.5 mM], and its reaction rate constant for the degradation of RhB was 27.7 times greater than that of the K–Fe/H₂O₂/visible light system. More importantly, the K–Fe/oxalic acid/H₂O₂/visible system showed remarkable degradation efficiency over a wide pH range (3.3–10.8), which was superior to that of the traditional Fenton system. In addition, the degradation efficiency of RhB was found to remain at 94.7% after five cycles. This work is expected to provide an important approach for the application of the Fenton system.

Degradation mechanism of the K–Fe/oxalic acid/H₂O₂/visible light system.

A highly efficient flow-through electro-Fenton system enhanced with nitrilotriacetic acid for phenol removal at neutral pH

Low pH requirement is one of the biggest limitations of the application of traditional Fenton and electro-Fenton (EF) process because Fe^II/Fe^III would precipitate at high pH. In this study, a flow-through EF system operated in batch recirculation mode was constructed. Nitrilotriacetic acid (NTA) was used as a chelating agent in the EF system (NTA/EF) to keep iron soluble at high pH values, producing OH by reaction of H₂O₂ generated in situ with Fe^IINTA that obtained by the reduction of Fe^IIINTA at the cathode. This flow-through NTA/EF system accelerated the mass transfer of target molecules to the electrode surface and showed high efficiency for phenol removal at pH 5-8 with rate constants (k) at around 0.26 min^-1, higher than that of the batch test (k = 0.15 min^-1) and EF process without NTA (k = 0.16 min^-1). The influences of aeration rate, current, flow rate, Fe dose, the ratio of NTA to Fe, pH, and initial phenol concentration on the phenol removal were investigated. The system could be used for at least 3 times for phenol removal without obvious efficiency decline. The flow-through NTA/EF system is promising for the removal of organic contaminants in a wide pH range.

Photo-Fenton and Riboflavin-photosensitized Processes of the Isoxaflutole Herbicide

The proherbicide Isoxaflutole (IXF) hydrolyzes spontaneously to diketonitrile (DKN) a phytotoxic compound with herbicidal activity. In this work, the sensitized degradation of IXF using Riboflavin (Rf), a typical environmentally friendly sensitizer, Fenton and photo-Fenton processes has been studied. The results indicate that only the photo-Fenton process produces a significant degradation of the IXF. Photolysis experiments of IXF sensitized by Riboflavin is not a meaningful process, IXF quenches the Rf excited triplet (³ Rf*) state with a quenching rate constant of 1.5 · 10⁷  m^-1  s^-1 and no reaction is observed with the species O₂ (¹ Δ_g ) or O 2 · - generated from ³ Rf*. The Fenton reaction produces no changes in the IXF concentration. While the photo-Fenton process of the IXF, under typical conditions, it produces a degradation of 99% and a mineralization to CO₂ and H₂ O of 88%. A rate constant value of 1.0 × 10⁹  m^-1  s^-1 was determined for the reaction between IXF and HO˙. The photo-Fenton process degradation products were identified by UHPLC-MS/MS analysis.

Highly efficient treatment of real benzene dye intermediate wastewater by simple limestone and lime neutralization-coagulation with improved Fenton oxidation

Multistage Fenton oxidation is a favored method for the treatment of benzene dye intermediate (BDI) wastewater, but the pH adjustments required after each stage of the Fenton process with a simple way is still a challenge. Limestone pretreatment and lime neutralization-coagulation were used to solve the problem in multistage Fenton process. First, we determined the optimal conditions of Fenton oxidation using the Box-Behnken response surface method. Limestone pretreatment before the multistage Fenton process allowed for simultaneous pH adjustment and 14.15% COD removal. Most notably, the lime cream neutralization-coagulation process effectively adjusted the pH after each stage of the Fenton process. The optimum CaO particle size, lime mass fraction, mixing time, and stirring speed were determined by orthogonal tests. COD removal (89.23%) was obtained when lime cream neutralization-coagulation was applied to the three-staged Fenton process, while only 58.57% COD removal was obtained by the unadjusted single-staged Fenton process. The COD and wastewater color were reduced from 10,600 mg/L and 12,200 multiples to 495 mg/L and 20 multiples, respectively, using the adjusted process. This improved method provides a promising cost-effective way to efficiently treat real BDI wastewater.

Fe1-xZnxS ternary solid solution as an efficient Fenton-like catalyst for ultrafast degradation of phenol

Heterogeneous Fenton-like system has been proved to be an promising alternative to Fenton system due to its easy separation. However, it's a challenge to design heterogeneous Fenton-like catalysts with high activity and great durability. Here, ternary solid solution Fe_1-xZn_xS were prepared via hydrothermal synthesis as heterogeneous Fenton-like catalysts. The Fe_0.7Zn_0.3S sample exhibited state of the art activity for yielding OH by H₂O₂ decomposition, and the ultrafast degradation of phenol was achieved in 4 min at initial acidic condition under room temperature. The phenol degradation rate constant of Fe_0.7Zn_0.3S was 99 and 70 times of ZnS and FeS, respectively. Further, we show that the unique structural configuration of iron atoms, the formation of FeS₂-pyrite with (200) plane, are responsible for the excellent activity. The intermediate products were identified by LC-MS and a possible pathway was accordingly proposed to elucidate the mechanism of phenol degradation by OH. Overall, this work provides an idea for the rational design of the relevant heterogeneous Fenton-like catalysts.

Degradation of organic dyes by a new heterogeneous Fenton reagent - Fe2GeS4 nanoparticle

The heterogeneous Fenton system has become the hotspot in the decontamination field due to its effective degradation performance with a wide pH range. Based on the unstable chemical properties of pyrite, in this article, Fe₂GeS₄ nanoparticles with better thermodynamic stability were prepared by vacuum sintering and high energy ball milling and its potential as Fenton reagent was investigated for the first time. Three determinants of the heterogeneous Fenton system including the iron source, hydrogen peroxide, pH and the degradation mechanism were investigated. The catalyst dosage of 0.3 g/L, initial H₂O₂ concentration in the Fenton system of 50 m mol/L and pH of 7 were chosen as the best operational conditions. An almost complete degradation was achieved within 5 min for methylene blue and rhodamine b while 10 min for methyl orange. The total organic carbon removal efficiencies of Fe₂GeS₄ heterogeneous Fenton system for methylene blue, methyl orange and rhodamine b in 10 min were 56.3%, 66.2% and 74.2%, respectively. It's found that the degradation ability could be attributed to a heterogeneous catalysis occurring at the Fe₂GeS₄ surface together with a homogeneous catalysis in the aqueous phase by the dissolved iron ions.

Remarkable enhancement of Fenton degradation at a wide pH range promoted by thioglycolic acid

Thioglycolic acid efficiently recycles Fe(ii) and significantly enhances the Fenton degradation of organic and microbial pollutants at a broad pH range.

Fenton pre-treatment of rice straw with citric acid as an iron chelate reagent for enhancing saccharification

Rice straw was pre-treated by Fenton action with citric acid for chelation; the pre-treated rice straw was saccharified byRuminiclostridium thermocellumM3.