Fenton-like degradation of nalidixic acid with Fe(3+)/H2O 2

Simultaneous Emerging Contaminant Removal and H2O2 Generation Through Electron Transfer Carrier Effect of Bi─O─Ce Bond Bridge Without External Energy Consumption

Conventional advanced oxidation processes (AOPs) require significant external energy consumption to eliminate emerging contaminants (ECs) with stable structures. Herein, a catalyst consisting of nanocube BiCeO particles (BCO-NCs) prepared by an impregnation-hydrothermal process is reported for the first time, which is used for removing ECs without light/electricity or any other external energy input in water and simultaneous in situ generation of H2O2. A series of characterizations and experiments reveal that dual reaction centers (DRC) which are similar to the valence band/conducting band structure are formed on the surface of BCO-NCs. Under natural conditions without any external energy consumption, the BCO-NCs self-purification system can remove more than 80% of ECs within 30 min, and complete removal of ECs within 30 min in the presence of abundant electron acceptors, the corresponding second-order kinetic constant is increased to 3.62 times. It is found that O2 can capture electrons from ECs through the Bi─O─Ce bond bridge during the reaction process, leading to the in situ production of H2O2. This work will be a key advance in reducing energy consumption for deep wastewater treatment and generating important chemical raw materials.

Removal enhancement of persistent basic fuchsin dye from wastewater using an eco-friendly, cost-effective Fenton process with sodium percarbonate and waste iron catalyst

In this comprehensive investigation, we evaluate the efficacy of the Fenton process in degrading basic fuchsin (BF), a resistant dye. Our primary focus is on the utilization of readily available, environmentally benign, and cost-effective reagents for the degradation process. Furthermore, we delve into various operational parameters, including the quantity of sodium percarbonate (SPC), pH levels, and the dimensions of waste iron bars, to optimize the treatment efficiency. In the course of our research, we employed an initial SPC concentration of 0.5 mM, a pH level of 3, a waste iron bar measuring 3.5 cm in length and 0.4 cm in diameter, and a processing time of 10 min. Our findings reveal the successful elimination of the BF dye, even when subjected to treatment with diverse salts and surfactants under elevated temperatures and acidic conditions (pH below 3). This underscores the robustness of the Fenton process in purifying wastewater contaminated with dye compounds. The outcomes of our study not only demonstrate the efficiency of the Fenton process but highlight its adaptability to address dye contamination challenges across various industries. Critically, this research pioneers the application of waste iron bars as a source of iron in the Fenton reaction, introducing a novel, sustainable approach that enhances the environmental and economic viability of the process. This innovative use of recycled materials as catalysts represents a significant advancement in sustainable chemical engineering practices.

Advances in magnetic materials for microplastic separation and degradation

The widespread use of plastics in modern human society has led to severe environmental pollution with microplastics (MP/MPs). The rising consumption of plastics raises the omnipresence of microplastics in aquatic environments, which carry toxic organic matter, transport toxic chemicals, and spread through the food chain, seriously threatening marine life and human health. In this context, several advanced strategies for separating and degrading MPs from water have been developed recently, and magnetic materials and their nanostructures have emerged as promising materials for targeting, adsorbing, transporting, and degrading MPs. However, a comprehensive review of MP remediation using magnetic materials and their nanostructures is currently lacking. The present work provides a critical review of the recent advances in MP removal/degradation using magnetic materials. The focus is on the comparison and analysis of the MP's removal efficiencies of different magnetic materials, including iron/ferrite nanoparticles, magnetic nanocomposites, and micromotors, aiming to unravel the underlying roles of magnetic materials in different types of MP degradation and present the general strategies for designing them with optimal performance. Finally, the review outlines the forthcoming challenges and perspectives in the development of magnetic nanomaterials for MP remediation.

Coupling of the optimized electro-Fenton-like process with pulsed laser ablation method to produce bimetallic nanoparticles of Fe°/Cu° and Fe°/Zn° in treatment of thiophene aqueous samples

In this study, an electro-Fenton-like method in the presence of iron particles was used for degradation of toxic thiophene pollutant from aqueous samples with performance >99%. In an electrolytic reactor, the effect of current density, H2O2 dosage, and pH of the sample on the treatment efficiency was investigated and optimized using the response surface method in the experimental design methodology. The conditions were optimized in current density of 20 mA/cm2, H2O2 dosage 500 ppm and pH = 3.0. In this process, a laser pulse ablation was used to produce iron nanoparticles in the electro-Fenton reactor to decrease the treatment time. Also, two bimetallic iron-copper and iron-zinc were used to investigate the synergistic effect of bimetallic catalyst on degradation efficiency of thiophene. The removal of thiophene nearly 100% can be provided in the presence Fe0.5/Cu0.5, Fe0.5/Zn0.5 and Fe alone in 10, 15 and 20 min, respectively. Also, the effect of hydroxyl scavenger and the consumption of catalysts were studied in the proposed procedure. Techniques of gas chromatography-flame ionization detector (GC-FID), gas chromatography-sulphur chemiluminescence detector (GC-SCD) and total sulphur analyser were used to follow thiophene degradation. A thiophene petrochemical wastewater was treated by the proposed method, and the results showed a significant reduction in amounts of chemical oxygen demand (COD) and biochemical oxygen demand (BOD).

A Detailed Insight into the Effects of Morphologies of Cerium Oxide on Fenton-like Reactions for Different Applications

As an exceptional Fenton-like reagent, cerium oxide (CeO2 ) finds applications in biomedical science and organic pollutants treatment. The Fenton-like reaction catalyzed by CeO2 typically encompasses two distinct processes: one resembling the classical Fenton reaction, wherein cerium (Ce3+ ) triggers the decomposition of hydrogen peroxide (H2 O2 ) to yield reactive oxygen species (ROS), and the other involves the complexation of H2 O2 on the Ce3+ surface, leading to the formation of peroxides. However, the influence of diverse CeO2 morphologies on these two reaction pathways has not been comprehensively explored. In this study, CeO2 exhibiting three typical morphologies, rods, cubes, and spheres, were prepared. The generation of ROS and peroxides was evaluated using the 3,3,5,5-tetramethylbenzidine (TMB) oxidation reaction and the reduction current of H2 O2 , respectively. Moreover, the impacts of pH variations and CeO2 /H2 O2 concentrations on the production and conversion of these two reaction products were investigated. To corroborate the distinctions between the resultant products and their applicability, apoptosis assays and acid orange 7 (AO7) degradation analyses were performed. Notably, CeO2 rods exhibited the highest proportion of Ce3+ , predominantly engaging in complexation with H2 O2 to foster peroxide formation, thereby facilitating the robust degradation of AO7. However, the generated peroxides appeared to occupy Ce3+ sites, thereby impeding the H2 O2 decomposition process. Conversely, Ce3+ species on the surface of CeO2 cubes were primarily involved in H2 O2 decomposition, leading to heightened ROS production, and thus showcasing substantial potential for damaging A549 tumor cells. It is worth noting that the ability of these Ce3+ species to form peroxides through complexation with H2 O2 was comparatively reduced. In summation, this study sheds light on the intricate interplay between distinct CeO2 morphologies and their divergent impacts on Fenton-like reactions. These findings expand our comprehension of the influences on its reactivity of CeO2 morphologies and open new insights for applications in diverse domains, from organic dye degradation to tumor therapy.

Taguchi L16 (44) orthogonal array-based study and thermodynamics analysis for electro-Fenton process treatment of textile industrial dye

Reactive orange 16 (RO16) is the most widely used azo dye in Textile industry. Complex aromatic structures and resistivity to biological decay caused the dye pollutants incompletely treated by the conventional oxidative methods. The current study presents the electro-Fenton-based advanced oxidation treatment of RO16 dye and the process optimization by Taguchi-based design of experiment (DOE). Using a 500 mL volume lab-scale experimental setup, the process was first studied for the principal operational parameters (initial dye concentration (q); [H2O2]/[Fe+2] (R); current density (ρ); and temperature (T)) effect on decolourization (D R ) and COD removal (C R ). Then, by means of the L16 (44) orthogonal array (OA) formation, standard mean and signal-to-noise (S/N) ratio, the process was optimized for the response variables. The result showed the optimized result at q = 100 mg/L, R = 100, ρ = 8 mA/cm2, and T = 32 °C; with D R and C R as 90.023 and 84.344%, respectively. It was found that the current density affects the process most, followed by [H2O2]/[Fe+2] ratio, initial dye concentration, and temperature i.e., ρ > R > q > T. Also, with the analysis of variance (ANOVA), model equations for D R and C R were developed and its accuracy was verified for experimental results. At optimized conditions, the first order removal rate constants (k a ) were found from batch results. Additionally, the thermodynamic constants (ΔH e , ΔS e , and ΔG b ) were also calculated for the nature of heat-energy involved and temperature effect study on dye degradation. The results showed that the process was thermodynamically feasible, endothermic, and non-spontaneous with a lower energy barrier (E A  = 46.7 kJ mol−1).

The principle of detailed balancing, the iron-catalyzed disproportionation of hydrogen peroxide, and the Fenton reaction

The iron-catalyzed disproportionation of H₂O₂ has been investigated for over a century, as has been its ability to induce the oxidation of other species present in the system (Fenton reaction). The mechanisms of these reactions have been under consideration at least since 1932. Unfortunately, little or no attention has been paid to ensuring the conformity of the proposed mechanisms and rate constants with the constraints of the principle of detailed balancing. Here we identify more than 200 publications having mechanisms that violate the principle of detailed balancing. These violations occur through the use of incorrect values for certain rate constants, the use of incorrect forms of the rate laws for certain steps in the mechanisms, and the inclusion of illegal loops. A core mechanism for the iron-catalyzed decomposition of H₂O₂ is proposed that is consistent with the principle of detailed balancing and includes both the one-electron oxidation of H₂O₂ by Fe(III) and the Fe(II) reduction of HO₂˙.

A review on Fenton process for organic wastewater treatment based on optimization perspective

Water pollution caused by organic wastewater has become a serious concern worldwide. Fenton oxidation process is one of the most effective and suitable methods for the abatement of organic pollutants. However, the process has three obvious shortcomings: the narrow working pH range, the high costs and risks associated with handling, transportation and storage of reagents (H₂O₂ and catalyst), the significant iron sludge related second pollution. In order to overcome these shortcomings, various optimized Fenton processes have been widely studied. Therefore, a summary of the study status of Fenton optimization processes is necessary to develop a novel and high efficiency organic wastewater treatment method. Based on the optimization perspective, taking shortcomings of Fenton process as a breakthrough, the fundamentals, advantages and disadvantages of single Fenton optimization processes (heterogeneous Fenton, photo-Fenton and electro-Fenton) for organic wastewater treatment were reviewed and the corresponding reaction mechanism diagrams were drawn in this paper. Then, the feasibility and application of the coupled Fenton optimization processes (photoelectro-Fenton, heterogeneous electro-Fenton, heterogeneous photoelectro-Fenton, three-dimensional electro-Fenton) for organic wastewater treatment were discussed in depth. Additionally, the effect of some important operation parameters (pH and catalyst, H₂O₂, organic pollutants concentration) on the degradation efficiency of organic pollutants was studied to provide guidance for the optimization of operation parameters. Finally, the possible future research directions for optimized Fenton processes were given. The review aims to assist researchers and engineers to gain fundamental understandings and critical view of Fenton process and its optimization processes, and hopefully with the knowledge it could bring new opportunities for the optimization and future development of Fenton process.

A green method to synthesize flowerlike Fe(OH)3 microspheres for enhanced adsorption performance toward organic and heavy metal pollutants

Dyestuffs and heavy metal ions in water are seriously harmful to the ecological environment and human health. Three-dimensional (3D) flowerlike Fe(OH)₃ microspheres were synthesized through a green yet low-cost injection method, for the removal of organic dyes and heavy metal ions. The Fe(OH)₃ microspheres were characterized by thermal gravimetric analysis (TGA), Fourier transform infrared (FT-IR), and transmission electron microscopy (TEM) techniques. The adsorption kinetics of Congo Red (CR) on Fe(OH)₃ microspheres obeyed the pseudo-second-order model. Cr⁶⁺ and Pb²⁺ adsorption behaviors on Fe(OH)₃ microspheres followed the Langmuir isotherm model. The maximum adsorption capacities of the synthesized Fe(OH)₃ were 308, 52.94, and 75.64mg/g for CR, Cr⁶⁺, and Pb²⁺ respectively. The enhanced adsorption performance originated from its surface properties and large specific surface area of 250m²/g. The microspheres also have excellent adsorption stability and recyclability. Another merit of the Fe(OH)₃ material is that it also acts as a Fenton-like catalyst. These twin functionalities (both as adsorbent and Fenton-like catalyst) give the synthesized Fe(OH)₃ microspheres great potential in the field of water treatment.

Removal of azo dye using Fenton and Fenton-like processes: Evaluation of process factors by Box-Behnken design and ecotoxicity tests

The conventional treatment of textile effluents is usually inefficient in removing azo dyes and can even generate more toxic products than the original dyes. The aim of the present study was to optimize the process factors in the degradation of Disperse Red 343 by Fenton and Fenton-like processes, as well as to investigate the ecotoxicity of the samples treated under optimized conditions. A Box-Behnken design integrated with the desirability function was used to optimize dye degradation, the amount of residual H2O2 [H2O2residual], and the ecotoxicity of the treated samples (lettuce seed, Artemia salina, and zebrafish in their early-life stages). Dye degradation was affected only by catalyst concentration [Fe] in both the Fenton and Fenton-like processes. In the Fenton reaction, [H2O2residual] was significantly affected by initial [H2O2] and its interaction with [Fe]; however, in the Fenton-like reaction, it was affected by initial [H2O2] only. A. salina mortality was affected by different process factors in both processes, which suggests the formation of different toxic products in each process. The desirability function was applied to determine the best process parameters and predict the responses, which were confirmed experimentally. Optimal conditions facilitated the complete degradation of the dye without [H2O2residual] or toxicity for samples treated with the Fenton-like process, whereas the Fenton process induced significant mortality for A. salina. Results indicate that the Fenton-like process is superior to the Fenton reaction to degrade Disperse Red 343.

Benzene oxidation by Fe(III)-catalyzed sodium percarbonate: matrix constituent effects and degradation pathways

Complete degradation of benzene by the Fe(III)-activated sodium percarbonate (SPC) system is demonstrated. Removal of benzene at 1.0 mM was seen within 160 min, depending on the molar ratios of SPC to Fe(III). A mechanism of benzene degradation was elaborated by free-radical probe-compound tests, free-radical scavengers tests, electron paramagnetic resonance (EPR) analysis, and determination of Fe(II) and H2O2 concentrations. The degradation products were also identified using gas chromatography-mass spectrometry method. The hydroxyl radical (HO.) was the leading species in charge of benzene degradation. The formation of HO. was strongly dependent on the generation of the organic compound radical (R.) and superoxide anion radical (O.). Benzene degradation products included hydroxylated derivatives of benzene (phenol, hydroquinone, benzoquinone, and catechol) and aliphatic acids (oxalic and fumaric acids). The proposed degradation pathways are consistent with radical formation and identified products. The investigation of selected matrix constituents showed that the Cl and HCO₃ had inhibitory effects on benzene degradation. Natural organic matter (NOM) had accelerating influence in degrading benzene. The developed system was tested with groundwater samples and it was found that the Fe(III)-activated SPC has a great potential in effective remediation of benzene-contaminated groundwater while more further studies should be done for its practical application in the future because of the complex subsurface environment.

Enrofloxacin Transformation on Shewanella oneidensis MR-1 Reduced Goethite during Anaerobic-Aerobic Transition

Antibiotics pollution has become a critical environmental issue worldwide due to its high ecological risk. In this study, rapid degradation of enrofloxacin (ENR) was observed on goethite in the presence of Shewanella oneidensis MR-1 during the transition from anaerobic to aerobic conditions. The abiotic reactions also demonstrated that over 70% with initial concentration of 10 mg L^-1 ENR was aerobically removed within 5 min by goethite with adsorbed Fe(II), without especial irradiation and strong oxidants. The results of spin trap electron spin resonance (ESR) experiments provide evidence that Fe(II)/Fe(III) complexes facilitate the generation of •OH. The electrophilic attack by •OH opens the quinolone ring of ENR and initiates further transformation reactions. Five transformation products were identified using high performance liquid chromatography-quadrupole time-of-flight mass spectrometry and the ENR degradation process was proposed accordingly. The identification of ENR transformation products also revealed that both the surface adsorption and the electron density distribution in the molecule determined the reactive site and transformation pathway. This study highlights an important, but often underappreciated, natural process for in situ degradation of antibiotics. With the easy migration of the goethite-MR-1 complex to the anaerobic/aerobic interface, the environmental fates of ENR and other antibiotics need to be seriously reconsidered.

Oxidative degradation of nalidixic acid by nano-magnetite via Fe2+/O2-mediated reactions

Organic pollution has become a critical issue worldwide due to the increasing input and persistence of organic compounds in the environment. Iron minerals are potentially able to degrade efficiently organic pollutants sorbed to their surfaces via oxidative or reductive transformation processes. Here, we explored the oxidative capacity of nano-magnetite (Fe3O4) having ∼ 12 nm particle size, to promote heterogeneous Fenton-like reactions for the removal of nalidixic acid (NAL), a recalcitrant quinolone antibacterial agent. Results show that NAL was adsorbed at the surface of magnetite and was efficiently degraded under oxic conditions. Nearly 60% of this organic contaminant was eliminated after 30 min exposure to air bubbling in solution in the presence of an excess of nano-magnetite. X-ray diffraction (XRD) and Fe K-edge X-ray absorption spectroscopy (XANES and EXAFS) showed a partial oxidation of magnetite to maghemite during the reaction, and four byproducts of NAL were identified by liquid chromatography-mass spectroscopy (UHPLC-MS/MS). We also provide evidence that hydroxyl radicals (HO(•)) were involved in the oxidative degradation of NAL, as indicated by the quenching of the degradation reaction in the presence of ethanol. This study points out the promising potentialities of mixed valence iron oxides for the treatment of soils and wastewater contaminated by organic pollutants.