Efficient Electrocatalytic Degradation of 4-Chlorophenol Using a Ti/RuO2–SnO2–TiO2/PbO2–CeO2 Composite Electrode

A review of advanced oxidation process towards organic pollutants and its potential application in fracturing flowback fluid

Fracturing flowback fluid (FFF) including various kinds of organic pollutants that do harms to people and new treatments are urgently needed. Advanced oxidation processes (AOPs) are suitable methods in consideration with molecular weight, removal cost and efficiency. Here, we summarize the recent studies about AOP treatments towards organic pollutants and discuss the application prospects in treatment of FFF. Immobilization and loading methods of catalysts, evaluation method of degradation of FFF, and continuous treatment process flow are discussed in this review. In conclusion, further studies are urgently needed in aspects of catalyst loading methods, macromolecule organic evaluation methods, industrial process, and pathways of macromolecule organics' decomposition.

Application of lead oxide electrodes in wastewater treatment: A review

Electrochemical oxidation (EO) based on hydroxyl radicals (·OH) generated on lead dioxide has become a typical advanced oxidation process (AOP). Titanium-based lead dioxide electrodes (PbO₂/Ti) play an increasingly important role in EO. To further improve the efficiency, the structure and properties of the lead dioxide active surface layer can be modified by doping transition metals, rare earth metals, nonmetals, etc. Here, we compare the common preparation methods of lead dioxide. The EO performance of lead dioxide in wastewater containing dyes, pesticides, drugs, landfill leachate, coal, petrochemicals, etc., is discussed along with their suitable operating conditions. Finally, the factors influencing the contaminant removal kinetics on lead dioxide are systematically analysed.

Electrocatalytic Dechlorination of Dichloromethane in Water Using a Heterogenized Molecular Copper Complex

The remediation of organohalides from water is a challenging process in environment protection and water treatment. Herein, we report a molecular copper(I) complex with two triazole units, CuT2, in a heterogeneous aqueous system that is capable of dechlorinating dichloromethane (CH₂Cl₂) to afford hydrocarbons (methane, ethane, and ethylene). The catalytic performance is evaluated in water and presented high Faradaic efficiency (average 70% CH₄) across a range of potentials (-1.1 to -1.6 V vs Ag/AgCl) and high activity (maximum -25.1 mA/cm² at -1.6 V vs Ag/AgCl) with a turnover number of 2.0 × 10⁷. The CuT2 catalyst also showed excellent stability for 14 h of constant exposure to CH₂Cl₂ and 10 h of CH₂Cl₂ exposure cycling. The control compound, a copper-free triazole unit (T1), was also investigated under the same condition and showed inferior catalytic activity, indicating the importance of the copper center. Plausible catalytic mechanisms are proposed for the formation of C₁ and C₂ products via radical intermediates. Computational studies provided additional insight into the reaction mechanism and the selectivity toward the CH₄ formation. The findings in this study demonstrate that complex CuT2 is an efficient and stable catalyst for the dehalogenation of CH₂Cl₂ and could potentially be used for the exploration of the removal of halogenated species from aqueous systems.

Electrochemical oxidation of aniline using Ti/RuO2-SnO2 and Ti/RuO2-IrO2 as anode

Electrocatalytic properties of anode and the electrolyte composition are important parameters influence the degradation efficiency for aniline wastewater. Ti/RuO₂-SnO₂ and Ti/RuO₂-IrO₂ have been fabricated using thermal decomposition method and experiments in electrolyte containing 0.05 M Na₂SO₄, 0.05 M NaCl and 0.05 M Na₂SO₄+0.005 M FeSO₄ at different current density were conducted to study the influence on aniline degradation. Linear sweep voltammetry (LSV) showed that Ti/RuO₂-SnO₂ had higher oxygen evolution potential and degrade aniline through electrochemical transformation and electrochemical combustion while Ti/RuO₂-IrO₂ degrade aniline mainly through electrochemical transformation. The study showed that Ti/RuO₂-SnO₂ had higher electrocatalytic activity towards the degradation of aniline than Ti/RuO₂-IrO₂ anode in 0.05 M Na₂SO₄ and in 0.05 M NaCl electrolyte. The maximum TOC removal efficiency for Ti/RuO₂-SnO₂ was 64.2% at 40 mA cm^-2 in Na₂SO₄ electrolyte while the average MCE was 1.6% and the average EC_TOC was 1.51 kWh (g TOC)^-1. On the contrary, the maximum TOC removal efficiency for Ti/RuO₂-IrO₂ was 63.1% at 40 mA cm^-2 in NaCl electrolyte while the average MCE was 1.6% and the average EC_TOC was 1.95 kWh (g TOC)^-1. The presence of Fe²⁺ in Na₂SO₄ electrolyte would decrease the TOC removal efficiency except at low current density (20 mA cm^-2) for Ti/RuO₂-SnO₂. These results indicated that Ti/RuO₂-SnO₂ and Ti/RuO₂-IrO₂ anode were suitable in Na₂SO₄ and NaCl electrolyte, respectively, while the presence of Fe²⁺ would inhibit aniline degradation.

Fabrication and characterization of porous titanium-based PbO2 electrode through the pulse electrodeposition method: Deposition condition optimization by orthogonal experiment

Porous titanium-based PbO₂ electrodes were successfully fabricated by pulse electrodeposition method. The primary pulse electrodeposition parameters, including pulse frequency (f), duty ratio (γ), average current density (J_a) and electrodeposition time (t) were considered in this study. An orthogonal experiment was designed based on those four factors and in three levels. SEM images and XRD results suggest that the surface morphology and structure of PbO₂ electrodes could be easily changed by varying pulse electrodeposition parameters. Orthogonal analysis reveals that the increase of f and J_a could decrease the average grain size of PbO₂ electrodes, which is conducive to create more active sites and promote the generation of hydroxide radicals. The electrochemical degradation of Azophloxine was carried out to evaluate the electrochemical oxidation performance of pulse electrodeposited electrodes. The results indicate that the influences of four factors can be ranked as follow: J_a >γ≈ t > f. The higher f, larger J_a and longer t could facilitate the optimization of the integrated electrochemical degradation performance of prepared PbO₂ electrode. The accelerated life time is dominated by J_a and t, coincident with the average weight increase of β-PbO₂ layer. The optimal parameters of pulse electrodeposition turn out to be: f = 50 Hz, γ = 30%, J_a = 25 mA cm^-2, t = 60 min. Together, the consequences of the experiments give assistance to uncover and roughly conclude the mechanism of pulse electrodeposition.

Fabrication of Co/Pr co-doped Ti/PbO2 anode for efficiently electrocatalytic degradation of β-naphthoxyacetic acid

The existence of β-naphthoxyacetic acid (BNOA) pesticide in water system has aroused serious environmental problem because of its potential toxicity for humans and organisms. Therefore, exploiting an efficient method without secondary pollution is extremely urgent. Herein, a promising Ti/PbO₂-Co-Pr composite electrode has been successfully fabricated through simple one-step electrodeposition for efficiently electrocatalytic degradation of BNOA. Compared with Ti/PbO₂, Ti/PbO₂-Co and Ti/PbO₂-Pr electrodes, Ti/PbO₂-Co-Pr electrode with smaller pyramidal particles possesses higher oxygen evolution potential, excellent electrochemical stability and outstanding electrocatalytic activity. The optimal degradation condition is assessed by major parameters including temperature, initial pH, current density and Na₂SO₄ concentration. The degradation efficiency and chemical oxygen demand removal efficiency of BNOA reach up to 94.6% and 84.6%, respectively, under optimal condition (temperature 35 °C, initial pH 5, current density 12 mA cm^-2, Na₂SO₄ concentration 8.0 g L^-1 and electrolysis time 3 h). Furthermore, Ti/PbO₂-Co-Pr electrode presents economic energy consumption and superior repeatability. Finally, the possible degradation mechanism of BNOA is put forward according to the main intermediate products identified by liquid chromatography-mass spectrometer. The present research paves a new path to degrade BNOA pesticide wastewater with Ti/PbO₂-Co-Pr electrode.