Fenton's Reagent

H2O2 generation by 2-electron oxygen electroreduction reaction (2eORR) has attracted great attention as an alternative to the industry-dominant anthraquinone process. Electro-Fenton (EF) process, which relies on the H2O2 electrogeneration, is regarded as an important environmental application of H2O2 generation by 2eORR. However, its application is hindered by the relatively expensive electrode materials. Proposing cathode materials with low cost and facile synthetic procedures are the priority to advance the EF process. In this work, a composite cathode structure that uses graphitic granular bamboo-based biochar (GB) and stainless steel (SS) mesh (GBSS) is proposed, where SS mesh functions as current distributor and GB supports synergistic H2O2 electrogeneration and activation. The graphitic carbon makes GB conductive and the oxygen-containing groups serve as active sites for H2O2 production. 11.3 mg/L H2O2 was produced from 2.0 g GB at 50 mA after 50 min under neutral pH without external O2/air supply. The O-doped biochar further increased the H2O2 yield to 18.3 mg/L under same conditions. The GBSS electrode is also effective for H2O2 activation to generate ·OH, especially under neutral pH. Ultimately, a neutral Fe-free EF process enabled by GBSS cathode is effective for removal of various model organic pollutants (reactive blue 19, orange II, 4-nitrophenol) within 120 min, and for their partial mineralization (48.4% to 63.5%). Long-term stability of the GBSS electrode for H2O2 electrogeneration, H2O2 activation, and pollutants degradation were also examined and analyzed. This work offers a promising application for biomass waste for removals of organic pollutants in neutral Fe-free EF process.

This study aims to investigate treatment efficiency and evaluate the energy efficacy of integrated electrocoagulation system combined with ozonation, Fenton, and photo-Fenton processes for successful textile dye-bath effluents' treatment. In this regard, the characterization of physicochemical parameters such as pH, turbidity, salinity, total dissolved solids (TDS), total suspended solids (TSS), electrical conductivity (EC), and chemical oxygen demand (COD) was analyzed to estimate removal efficiency of each treatment process. Moreover, the electrical energy consumption of all aforementioned processes was measured individually to work out costeffectiveness. Fenton process appeared to be ineffective for reducing COD and other parameters. While the overall performance of ECS alone showed far better results, COD and color removal efficiencies were 57.4%, and 40%, respectively. However, the application of ECS/O 3 resulted in complete decolorization and almost 99.7% COD removal under optimized operating conditions including ozone flow 300 mg/h, pH 7.1, Temperature 25 • C. ECS/photo-Fenton process resulted in COD, and color removal of 95.6%, and 97%, respectively. Electrical Energy per Order of ECS was found 1.58 kWh/m 3 for minimum removal of dyes and COD. ECS/Ozonation is responsible for 100% decolorization but at a very high cost. ECS/photo-Fenton process proved to be the second-best option in terms of treatment and energy consumption. Hence, an integrated treatment system of ECS with AOPs appeared to be the most feasible and eco-friendly. That could lead to the treated wastewater for reuse and recycling purposes within the industry.

Electrochemical synthesis of H2O2 offers a great potential for water treatment. However, a significant challenge is the development of efficient cathode materials for the process. Herein, we implement a practical electrochemical cathode modification to support efficient H2O2 electrogeneration via the reduction of dissolved anodic O2. Graphite felt (GF) is in situ anodically modified by electrode polarity reversal technique in an acid-free, low-conductivity electrolyte. The modified GF exhibits a significantly higher activity towards O2 reduction. Up to 183.3% higher H2O2 yield is obtained by the anodized GF due to the increased concentrations of oxygen-containing groups and the hydrophilicity of the surface, which facilitates electron and mass transfer between GF and the electrolyte. Another significant finding is the ability to produce H2O2 at a high yield under neutral pH and low current intensity by the modified GF (35% of the charge need to produce the same amount by unmodified GF). Long-term stability testing of the modified GF showed a decay in the electrode’s activity for H2O2 production after 30 consecutive applications. However, the electrode regained its optimal activity for H2O2 production after a secondary modification by electrode polarity reversal. Finally, in situ electrochemically modified GF is more effective for removal of reactive blue 19 (RB19, 20 mg/L) and ibuprofen (IBP, 10 mg/L) by the electro-Fenton process. The modified GF removed 62.7% of RB19 compared to only 28.1% by the unmodified GF in batch reactors after 50 min. Similarly, 75.3% IBP is removed by the modified GF compared to 57.6% by the unmodified GF in a flow-through reactor after 100 min.

The management of contaminants of emerging concern (CECs) in water bodies is particularly challenging due to the difficulty in detection and their recalcitrant degradation by conventional means. In this review, CECs are characterized to give insights into the potential degradation performance of similar compounds. A two-pronged approach was then proposed for the overall management of CECs. Light-driven oxidation processes, namely photo/Fenton, photocatalysis, photolysis, UV/Ozone were discussed. Advances to overcome current limitations in these light-driven processes were proposed, focusing on recent trends and innovations. Light-based detection methodology was also discussed for the management of CECs. Lastly, a cost–benefit analysis on various light-based processes was conducted to access the suitability for CECs degradation. It was found that the UV/Ozone process might not be suitable due to the complication with pH adjustments and limited light wavelength. It was found that EEO values were in this sequence: UV only > UV/combination > photocatalyst > UV/O3 > UV/Fenton > solar/Fenton. The solar/Fenton process has the least computed EEO < 5 kWh m−3 and great potential for further development. Newer innovations such as solar/catalyst can also be explored with potentially lower EEO values.

Major challenges for effective implementation of the Electro-Fenton (EF) water treatment process are that conventional efficient cathodes are relatively expensive, and H2O2 activation by Fe2+ may cause secondary pollution. Herein, we propose a low-cost activated carbon/stainless steel mesh (ACSS) composite cathode, where the SS mesh distributes the current and the AC simultaneously supports H2O2 electrogeneration, H2O2 activation, and organic compounds (OCs) adsorption. The oxygen-containing groups on the AC function as oxygen reduction reaction (ORR) sites for H2O2 electrogeneration; while the porous configuration supply sufficient reactive surface area for ORR. 8.9 mg/L H2O2 was obtained with 1.5 g AC at 100 mA under neutral pH without external O2 supply. The ACSS electrode is also effective for H2O2 activation to generate OH, especially under neutral pH. Adsorption shows limited influence on both H2O2 electrogeneration and activation. The iron-free EF process enabled by the ACSS cathode is effective for reactive blue 19 (RB19) degradation. 61.5% RB19 was removed after 90 min and 74.3% TOC was removed after 720 min. Moreover, long-term stability test proved its relatively stable performance. Thus, the ACSS electrode configuration is promising for practical and cost-effective EF process for transformation of OCs in water.

In this work, the antimicrobial effects of the photo-Fenton process on yeast cells were tested (Saccharomyces cerevisiae), an essential eukaryotic unicellular model of living cells. Near-neutral pH was used in all studies, while iron sulfate and iron citrate were evaluated as iron sources during S. cerevisiae photo-Fenton inactivation under simulated solar light (hv/H2O2/Fe). The following indicators were monitored to decrypt the mechanism of yeast inactivation by neutral photo-Fenton process: cell viability by flow cytometry, damage at DNA level, as well as intracellular and extracellular proteins, assessed by gel electrophoresis. A significant loss of cultivability was monitored through the application of all the different photo-Fenton systems, attributed to the oxidative stresses applied. The mechanisms involved were the homogeneous action of dissolved iron and the heterogeneous action mode of iron oxides. The DNA and protein analyses indicated drastic intracellular damages, while external macromolecules (cell wall and membrane proteins) showed limited degradation. This marked internal photocatalytic processes as the main inactivation mechanism in S. cerevisiae. Different pathways are proposed, forming a general process of inactivation by the near-neutral photo-Fenton systems. © 2015 Elsevier B.V.

We use density functional theory (DFT) and ab initio molecular dynamics to study the conversion of H 2 O into H 2 O 2 in water solution by the Fe IV O 2+ group under room-temperature and-pressure conditions. We compute the free energy of formation of an O(water)−O(oxo) bond using thermodynamic integration with explicit solvent and we examine the subsequent generation of H 2 O 2 by proton transfer. We show that the O−O bond formation follows the standard reactivity pattern observed in hydroxylation reactions catalyzed by high-spin (S = 2) iron(IV)− oxo species, which is initiated by the transfer of one electron from the highest occupied molecular orbital of the moiety attacking the Fe IV O 2+ group, either a −C−H bonding orbital (hydroxylation) or a lone pair of a water molecule (water oxidation). The highly electrophilic character exhibited by the Fe IV O 2+ ion, which is related to the presence of an acceptor 3σ* orbital at low energy with a large contribution on the O end of the Fe IV O 2+ ion, is the crucial factor promoting the electron transfer. The electron transfer occurs at an O(water)− O(oxo) distance of ca. 1.6 Å, and the free energy required to favorably orient a solvent H 2 O molecule for the O(oxo) attack and to bring it to the transition state amounts to only 35 kJ mol −1. The ensuing exoergonic O−O bond formation is accompanied by the progressive weakening of one of the O−H bonds of the attacking H 2 O assisted by a second solvent molecule and leads to the formation of an incipient Fe 2+ −[O−O−H] − [H 3 O + ] group. Simultaneously, three additional solvent molecules correlate their motion and form a hydrogen-bonded string, which closes to form a loop within 5 ps. The migration of the H + ion in this loop via a Grotthuss mechanism leads to the eventual protonation of the [O−O−H] − moiety, its progressive removal from the Fe 2+ coordination sphere, and the formation of free H 2 O 2 in solution.

Pharmaceutical industry often generates highly toxic wastewater and sludge depending upon the used manufacturing process and season. Effluent from pharmaceutical industry has a COD value in the range of 4000 to 1000. Fenton’s reagent is used in the reduction of COD from the pharmaceutical industry wastewater in this study. The ferrous and hydrogen peroxide were used in molar ratio of 1:1, 1:2 and 1:3. Ferrous was added in the form of ferrous sulphate. A reaction time of one hour was decided for the purpose of reducing COD. A magnetic stirrer was used for mixing the Fenton’s reagent and the wastewater sample. Different doses of hydrogen peroxide and ferrous sulphate was added as per the ratio decided. 89% reduction of COD was observed at 7350 mg/L of ferrous sulphate and 900 mg/L of hydrogen peroxide for 1:1 ratio. For a ratio of 1:2 an efficiency of 87% COD reduction was observed at doses of 3267 mg/L of ferrous sulphate and 800 mg/L of hydrogen peroxide. For a ratio of 1:3 maximum reductions of COD was observed in doses of 2450 mg/L of ferrous sulphate and 900 mg/L of hydrogen peroxide. COD reduction was maximum for a reaction time of 1 hour. Also, increase in the reaction time did not aid in COD reduction.