Impact of Active Chlorines and •OH Radicals on Degradation of Quinoline Using the Bipolar Electro-Fenton Process

Electrochemical treatment of simulated wastewater containing nitroaromatic compound with cobalt-titanium electrode

The Co3O4-Ti electrodes were successfully prepared via calcination method to degrade nitrogen-containing (TNP) simulate wastewater in this reaserch. SEM and EDS were employed to analyze the morphology and element composition on Co3O4-Ti electrode, revealing the successful load of cobalt element. Then the electrochemical performance was evaluated by CV and indicated a better redox performance of electrode. Furthermore, five factors as processing time (A), electrolyte concentration (B), pH (C), initial concentration of TNP (D), and current density (E) were systematic studied in electrical treatment process. The removal rate of TN could be 77%. After the optimization work by RSM, the removal rate of TN raised up to 81% with the condition as: A of 180 min, B of 0.05 M, C of 3, D of 400 mg L-1, and E of 20 mA cm-2. The sequence of significants is: C > D > A > E > B. Mechanism analysis revealed that the entire process could be divided into two stages. In the first stage, organic nitrogen compounds were converted into inorganic nitrogen species, such as NO3-N. The oxidation and reduction would react owing to the generating of ·OH at second stage in order to turn the NO3-N into NO2-N, NH4-N or N2. The activation of ·OH on the surface of Co3O4-Ti electrode possesses the exothermic nature with transition theory. The energy calculation of 1.168 eV indicated these reactions could occur spontaneously.

Analysis of factors influencing on Electro-Fenton and research on combination technology (II): a review

The principle of Fenton reagent is to produce ·OH by mixing H2O2 and Fe2+ to realize the oxidation of organic pollutants, although Fenton reagent has the advantages of non-toxicity and short reaction time, but there are its related defects. The Fenton-like technology has been widely studied because of its various forms and better results than the traditional Fenton technology in terms of pollutant degradation efficiency. This paper reviews the electro-Fenton technology among the Fenton-like technologies and provides an overview of the homogeneous electro-Fenton. It also focuses on summarizing the effects of factors such as H2O2, reactant concentration, reactor volume and electrode quality, reaction time and voltage (potential) on the efficiency of electro-Fenton process. It is shown that appropriate enhancement of H2O2 concentration, voltage (potential) and reaction volume can help to improve the process efficiency; the process efficiency also can be improved by increasing the reaction time and electrode quality. Feeding modes of H2O2 have different effects on process efficiency. Finally, a considerable number of experimental studies have shown that the combination of electro-Fenton with ultrasound, anodic oxidation and electrocoagulation technologies is superior to the single electro-Fenton process in terms of pollutant degradation.

Preparation of Ti/SnO2-Sb/La-βPbO2 electrode and its application in the degradation of some pollutants including prednisolone and 8-Hydroxyquinoline

In this work, a novel La-doped βPbO₂ (Ti/SnO₂-Sb/La-βPbO₂) was prepared using electrodeposition method and applied to the degradation of prednisolone (PRD), 8-Hydroxyquinoline (8-HQ), and other typical organic pollutants. Compared with the conventional electrode Ti/SnO₂-Sb/βPbO₂, La₂O₃ doping enhanced oxygen evolution potential (OEP), reactive surface area, stability and repeatability of the electrode. The 10 g L^-1 of La₂O₃ doping exhibited the highest electrochemical oxidation capability of the electrode with [•OH]ss being determined at 5.6 × 10^-13 M. The quenching experiments were conducted to confirm the main oxidizing species (here: •OH) in the electrochemical process. The study showed that the pollutants were removed in the electrochemical (EC) process with different degradation rates and indicated that the second-order rate constant of organic pollutants towards •OH (k_OP,•OH) has a linear relationship with the degradation rate of organic pollutants (k_OP) in the electrochemical process. Another new finding in this work is that a regression line of k_OP,•OH and k_OP can be used to estimate k_OP,•OH of an organic chemical, which cannot be determined using the competition method. k_PRD,•OH and k_8-HQ,•OH were determined to be 7.4 × 10⁹ M^-1 s^-1 and (4.6-5.5) × 10⁹ M^-1 s^-1, respectively. Compared with conventional supporting electrolyte (like SO₄^2-), H₂PO₄^- and HPO₄^2- improved k_PRD and k_8-HQ by 1.3-1.6-fold, while SO₃^2- and HCO₃^- inhibited k_PRD and k_8-HQ significantly, down to 80%. Additionally, the degradation pathway of 8-HQ was proposed based on the detection of intermediates from GC-MS.

OH radical-initiated single-electron transfer for accelerated degradation via carbocation intermediates

Single electron transfer (SET) has made great contributions to a broad range of chemical processes, whose radical cation and carbocation intermediates are important for mechanism studies. Herein, hydroxyl radical (˙OH)-initiated SET was revealed in accelerated degradations, via the online examination of radical cations and carbocations by electrosonic spray ionization mass spectrometry (ESSI-MS). In the green and efficient non-thermal plasma catalysis system (MnO₂-plasma), hydroxychloroquine was efficiently degraded upon SET via carbocations. In the plasma field full of active oxygen species, ˙OH was generated on the MnO₂ surface to initiate SET-based degradations. Furthermore, theoretical calculations revealed that ˙OH preferred to withdraw the electron from the N atom that was conjugated to the benzene ring. This facilitated the generation of radical cations through SET, which was followed by the sequential formation of two carbocations for accelerated degradations. Transition states and energy barriers were calculated to study the formation of radical cations and subsequent carbocation intermediates. This work demonstrates an ˙OH-initiated SET for accelerated degradation via carbocations, providing a deeper understanding and the potential for the wider application of SET in green degradations.

Heterogeneous electro-Fenton using three-dimension Fe-Co-Bi/kaolin particle electrodes for degradation of quinoline in wastewater

Wastewater containing quinoline has become a common pollutant in water and soil environments, which poses a threat to human health due to its carcinogenicity, teratogenicity, and mutagenicity. Quinoline's stability and toxicity hinders its degradation by conventional physicochemical and biological methods. In this contribution, Fe-Co-Bi/kaolin particle electrodes were prepared for the efficient degradation of quinoline in wastewater, and characterized by using scanning electron microscope, X-ray diffraction, pyridine-IR, Brunauer-Emmett-Teller, X-ray photoelectron spectroscopy, and four-probe resistivity test. Parameters affecting the degradation efficiency were optimized to be the particle electrode dosage of 40 g/L, pH 3.5, H₂O₂ addition of 67.6 mmol/L, electrical conductivity of 12.7 ms/cm, and voltage of 20 V. The constructed three-dimensional catalytic particle electrode system (3D-CPE) achieved 92.1% removal rate of chemical oxygen demand (COD) under the optimal conditions. Hydroxyl radicals (•OH) generated in the 3D-CPE process were identified by radical scavenging tests and electron spin response analysis. To unravel the degradation mechanism, the intermediate products were identified by using high performance liquid chromatography-mass spectrometry. The degradation mechanism was discussed with the help of theoretical calculation.