Surface characterization and electrochemical properties of PbO2/SnO2 composite anodes for electrocatalytic oxidation of m-nitrophenol

Optimizing difenoconazole degradation via sequential photoelectrochemical oxidation and biodegradation treatments

The growing global demand for food has intensified the use of pesticides in conventional agriculture, raising concerns about their environmental contamination and persistence. This study proposes an integrated strategy for the degradation of difenoconazole (DFZ), combining photoelectrochemical oxidation (PECO) with biodegradation. A mixed metal oxide anode, Ti/(RuO2)0.8(Sb2O4)0.1(TiO2)0.1 was successfully synthesized via the ionic liquid method, and a mangrove-derived Bacillus sp. isolate was employed in a sequential treatment process. Individually, the Bacillus strain degraded 74.56 % of DFZ1 and 72.52 % of DFZ2, while PECO alone achieved a lower removal efficiency of 32 %. Notably, the sequential application of PECO followed by biodegradation enhanced the degradation rates to 77.81 % for DFZ1 and 74.45 % for DFZ2. Additionally, this combined approach significantly reduced chemical oxygen demand (70.6 %) and toxicity, as evidenced by improved lettuce seed germination indices. These findings underscore the potential of integrating PECO with biodegradation as a promising strategy for the remediation of difenoconazole (DFZ), offering new perspectives for the treatment of recalcitrant triazole compounds in contaminated environments.

Dipropyl ammonium ionic liquids to prepare Ti/RuO2-Sb2O4 anodes at different calcination temperatures

The development of technologies capable of producing efficient and economically viable anodes is essential for the electrochemical treatment of water contaminated with complex organic pollutants. In this context, the use of ionic liquids as solvents to prepare mixed metal oxide (MMO) anodes has proven to be an up-and-coming alternative. Here, we analyze the influence of the temperature of calcination (300, 350, and 400 ºC) on the production of Ti(RuO2)0.8-(Sb2O4)0.2 anodes made using the thermal decomposition method using three ionic liquids (IL) as solvents: dipropyl ammonium acetate (DPA-Ac), dipropyl ammonium propionate (DPA-Pr), and dipropyl ammonium butyrate (DPA-Bu). The decomposition temperature for all IL, accessed by thermogravimetry, is below 200 ºC. Physical and electrochemical analyses demonstrate that the calcination temperature of the anodes is decisive for their durability and electrochemical properties. Anodes prepared with DPA-Bu at 350 ºC show higher stability (around 35 h) than those made with other ILs at temperatures of 300 and 400 ºC and improved results in terms of 4-NP mineralization, where 97% of TOC removal was achieved in 120 min. It could be verified that the calcination temperature and IL employed had a decisive influence on the characteristics of the presented anodes. Therefore, the anode prepared with DPA-Bu at 350 ºC is promising for application in the degradation of organic compounds.

PbO2 materials for electrochemical environmental engineering: A review on synthesis and applications

Lead dioxide (PbO₂) materials have been widely employed in various fields such as batteries, electrochemical engineering, and more recently environmental engineering as anode materials, due to their unique physicochemical properties. Key performances of PbO₂ electrodes, such as energy efficiency and space-time yield, are influenced by morphological as well as compositional factors. Micro-nano structure regulation and decoration of metal/non-metal on PbO₂ is an outstanding technique to revamp its electrocatalytic activities and enhance environmental engineering efficiency. The aim of this review is to comprehensively summarize the recent research progress in the morphology control, the structure constructions, and the element doping of PbO₂ materials, further with many environmental application cases evaluated. Concerning electrochemical environmental engineering, the lead dioxide employed in chemical oxygen demand detection, ozone generators, and wastewater treatment has been comprehensively reviewed. In addition, the future research perspectives, challenges and the opportunities on PbO₂ materials for environmental applications are proposed.

Electrochemical degradation of antibiotic enoxacin using a novel PbO2 electrode with a graphene nanoplatelets inter-layer: Characteristics, efficiency and mechanism

A novel PbO₂ electrode was fabricated by adding graphene nanoplatelets (GNP) inter-layer into β-PbO₂ active layer (called GNP-PbO₂) and utilized to degradation of antibiotic enoxacin (ENO). The GNP-PbO₂ electrode had a much rougher surface than the typical PbO₂ electrode, with smaller crystal size and lower charge-transfer resistance at the electrode/electrolyte interface. Notably, the GNP inter-layer increased the oxygen evolution potential of PbO₂ electrode (2.05 V vs. SCE), which was very beneficial to inhibit oxygen evolution and promote ·OH production. The relatively best operating parameters for ENO removal and energy efficiency were current density of 20 mA cm^-2, initial pH of 7, initial ENO concentration of 100 mg L^-1 and electrode distance of 4 cm. Furthermore, indirect radical oxidation was found to be the main way during electrolysis process. Based on the observed analysis of intermediate products, the main reaction pathways of ENO included hydroxylation, defluorination and piperazine ring-opening. Finally, combinating with the electro-oxidation capability, stability and safety evaluation, we can conclude that GNP-PbO₂ is a promising anode for treatment of various organic pollutants in wastewater.

Fabrication of PbO2 Electrodes with Different Doses of Er Doping for Sulfonamides Degradation

In the present study, PbO₂ electrodes, doped with different doses of Er (0%, 0.5%, 1%, 2%, and 4%), were fabricated and characterized. Surface morphology characterization by SEM-EDS and XRD showed that Er was successfully doped into the PbO₂ catalyst layer and the particle size of Er-PbO₂ was reduced significantly. Electrochemical oxidation of sulfamerazine (SMR) in the Er-PbO₂ anode system obeyed te pseudo first-order kinetic model with the order of 2% Er-PbO₂ > 4% Er-PbO₂ > 1% Er-PbO₂ > 0.5% Er-PbO₂ > 0% PbO₂. For 2% Er-PbO₂, k_SMR was 1.39 h^-1, which was only 0.93 h^-1 for 0% PbO₂. Effects of different operational parameters on SMR degradation in 2% Er-PbO₂ anode system were investigated, including the initial pH of the electrolyte and current density. Under the situation of an initial pH of 3, a current density of 30 mA·cm^-2, a concentration of SMR 30 mg L^-1, and 0.2 M Na₂SO₄ used as supporting electrolyte, SMR was totally removed in 3 h, and COD mineralization efficiency was achieved 71.3% after 6 h electrolysis. Furthermore, the degradation pathway of SMR was proposed as combining the active sites identification by density functional calculation (DFT) and intermediates detection by LC-MS. Results showed that Er-PbO₂ has great potential for antibiotic wastewater treatment in practical applications.

Improved mineralization and total nitrogen reduction by combination of electro-reduction and electro-oxidation for nitrophenol removal

In this work, p-Nitrophenol (p-NP) was electro-chemically removed by using a prepared Co₃O₄/Ti cathode and a BDD anode to achieve the simultaneous reduction of total organic carbon (TOC), total nitrogen (TN) and toxicity. The prepared Co₃O₄/Ti cathode showed higher electro-activity than the Ti cathode towards p-NP reduction with the removal rate higher than 90.6% but without mineralization. The electro-oxidation removed 84.3% of TOC but none of TN. To develop an optimized process for mineralization and TN removal during p-NP electrolysis, the combination of electro-oxidation and electro-reduction were evaluated by using a dual-chamber cell and a single-chamber cell, respectively. As a result of the re-oxidation and re-reduction in the single-chamber cell, the typically used mode of the simultaneous redox, showed a lower removal of TOC and TN than the combination processes as well as an increased toxicity. The TN removal for both combined modes (21.0%-32.9%) was all higher than that of the mode of reduction because the produced inorganic nitrogen such as ammonia and nitrate could be partially oxidized or reduced to nitrogen gas. The results suggested that the combination process could significantly improve the mineralization and TN reduction for p-NP removal, accompanied with 60.3% decrease of acute toxicity for the reduction after oxidation mode.

When MXene (Ti3C2Tx) meet Ti/PbO2: An improved electrocatalytic activity and stability

Stable electrode materials with high catalytic activity are urgently required for electrochemical degradation of refractory organic pollutants in wastewater treatment. Herein, high conductive MXene (Ti₃C₂T_x) was firstly fabricated by electrophoretic deposition (EPD) as an interlayer for preparing a novel PbO₂ electrode. The well-conducted Ti₃C₂T_x interlayer significantly improved the electrochemical performance of the EPD-2.0/PbO₂ (EPD time was 2.0 min) electrode with the charge transfer resistance decreased by 9.51 times, the inner active sites increased by 5.21 times and the ∙OH radicals generation ability enhanced by 4.07 times than the control EPD-0/PbO₂ anode. Consequently, the EPD-2.0/PbO₂ electrode achieved nearly 100% basic fuchsin (BF) and 86.78% COD removal efficiency after 3.0 h electrolysis. Therefore, this new PbO₂ electrode presented a promising potential for electrochemical degradation of BF and the new Ti₃C₂T_x middle layer could also be used to fabricate other efficient and stable anodes, such as SnO₂, MnO₂, TiO₂, etc.

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.

Au@SnO2-vertical graphene-based microneedle sensor for in-situ determination of abscisic acid in plants

For developing electrochemical plant sensors, in-situ detection of hormone levels in living plants is worth attempting. A microneedle array sensor based on Au@SnO₂-vertical graphene (VG)/Ta microelectrodes was constructed for analyzing abscisic acid (ABA) in plants. Graphene was vertically grown on Ta wires with a diameter of 0.6 mm by direct current arc plasma jet chemical vapor deposition with SnO₂ as the Au catalyst carrier. These VG nanosheets were embedded with core-shell Au@SnO₂ nanoparticles, and the formation mechanism of the sensing layer was investigated. Three Au@SnO₂-VG microelectrodes, one Ti wire, and one Pt wire were packed into a microneedle array sensor with a three-electrode system. ABA was then quantitatively detected by direct electrocatalytic oxidation, which involves the synergistic catalytic effects of the abundant catalytic active sites of the Au@SnO₂ nanoparticles and the excellent conductivity of the VG nanosheets. The microneedle array sensor responds to ABA in the pH range 4-7, the response concentration range was 0.012 (or 0.024)-495.2 μM, and the detection limit varied between 0.002 and 0.005 μM. The small size, wide pH range, low detection limit, and wide linear concentration range allow the microneedle array sensor to be inserted into plants for in-situ detection of ABA.

BiVO4 prepared by the sol-gel doped on graphite felt cathode for ciprofloxacin degradation and mechanism in solar-photo-electro-Fenton

In this research, bismuth vanadate-doped graphite felt (GF-BiVO₄) was successfully prepared by sol-gel method, in which BiVO₄ owned superior electro-Fenton (EF) and solar-photo-electro-Fenton (SPEF) performance. Combined with the analysis by X-ray diffractometer (XRD), field emission transmission electron microscopy (FE-TEM), nitrogen adsorption-desorption isotherms and cyclic voltammetry (CV), the changes of electrodes were reflected in structure and physicochemical properties. The doping of monoclinic BiVO₄ endued GF with a higher surface area and more electro-active sites and better electrode activity in comparison to Raw-GF. Then, the GFs were used as cathodes to detect •OH concentration with coumarin (COU) as probe molecule and to evaluate photoelectric performance with ciprofloxacin (CIP) in photocatalysis, EF and SPEF processes. The results demonstrated that the concentration of •OH followed an order of SPEF> EF> photocatalysis, which was consistent with the removal rate of CIP (99.8%, 99.4% and 21.2%, respectively) on GF-BiVO₄ at 5 min. Further, five degradation pathways of CIP in SPEF system were proposed including the attack on piperazine ring, oxidation on cyclopropyl group, decarboxylation and hydroxyl radical addition, oxidation on benzene group and defluorination. The study provides insights into the enhancement of EF and SPEF performance and the degradation pathway of CIP in SPEF.

Anodic oxidation of ciprofloxacin using different graphite felt anodes: Kinetics and degradation pathways

Ciprofloxacin (CIP) is ubiquitous in the environment which poses a certain threat to human and ecology. In this investigation, the physical and electrochemical properties of graphite felt (GF) anodes which affected the anodic oxidation (AO) performance, and the CIP removal effect of GF were evaluated. The GFs were used as anodes for detection of ·OH with coumarin (COU) as molecule probe and removal of CIP in a 150 mL electrolytic cell with Pt cathode (AO-GF/Pt system). The results showed that hydrophilic GF (B-GF) owned higher sp³/sp² and more oxygen-containing and nitrogen-containing functional groups than the hydrophobic GF (A-GF). Moreover, B-GF possessed higher oxygen evolution potential (1.12 V), more active sites and stronger ·OH generation capacity. Above mentioned caused that B-GF exhibited more superior properties for CIP removal. The best efficiencies (96.95%, 99.83%) were obtained in the AO-B-GF/Pt system at 6.25 mAcm^-2 after 10 min (k₁, 0.356 min^-1) and 60 min (k₂, 0.224 min^-1), respectively. Furthermore, nine degradation pathways of CIP in AO-B-GF/Pt system were summarized as the cleavage of the piperazine ring, cyclopropyl group, quinolone ring and F atom by ·OH. It provides new insights into the removal and degradation pathways of CIP with GF in AO system.

Electrocatalytic oxidation of PCP-Na by a novel nano-PbO2 anode: degradation mechanism and toxicity assessment

This study aims at investigating the electrocatalytic oxidation of sodium pentachlorophenate (PCP-Na) using a novel nano-PbO₂ powder anode. The nano-PbO₂ powder (marked as HL-PbO₂) was prepared by a simple hydrolysis process, and hydrothermal treatment was followed to improve the activity of HL-PbO₂. The HL-PbO₂ treated for 24 h by hydrothermal process (HL/HT-PbO₂-24) was confirmed to possess higher crystallinity, higher oxygen evolution potential, and more active sites, resulting in stronger OH radical generation capacity and higher electrochemical activity. Compared with conventional electrodeposited PbO₂ (ED-PbO₂) anode, the HL/HT-PbO₂-24 anode showed higher PCP-Na degradation rate. Under the same operating conditions, the mineralization current efficiency at HL/HT-PbO₂-24 was 2.7 times than that at ED-PbO₂. Five intermediates were detected in PCP-Na degradation solution and possible degradation mechanism of PCP-Na was discussed. In addition, the acute toxicity of PCP-Na degradation solution to zebrafish embryos and the oxidative stress induced in zebrafish embryos/larvae were studied to evaluate the ecological security of electrocatalytic oxidation of PCP-Na.