Electrogeneration of hydrogen peroxide by oxygen reduction using anodized graphite felt

Enhanced electro-fenton degradation of tetracycline pharmaceutical wastewater by N-doped carbon modified titanium membrane aeration: Formation of highly selective singlet oxygen

Singlet oxygen (1O2), the lowest excited electronic state of molecular oxygen, plays an important role in advanced oxidation, but how to directionally enhance the generation of 1O2 is a challenge. In this study,we use membrane aeration electrode modified by carbon-nitrogen for the first time to enhance the generation of 1O2 in the EF (Electro-Fenton) system. The carbon-nitrogen supported tubular titanium membrane (TTM@CN) aeration electrode was prepared by a simple dopamine-loaded one-step sintering method. A membrane aeration EF system was designed with TTM@CN as cathode and netted ruthenium-iridium titanium electrode as anode, and the output of 1O2 was greatly improved. The results of quenching experiments show that the main way of singlet oxygen production is 3O2 → H2O2 → 1O2. In addition, the results of density functional theory (DFT) show that the empty orbital of C above Fermi level in heterojunction is obviously filled, and the density of states tends to shift to the depth of valence band. The system with metal Ti as carrier can quickly transfer electrons to the layer of C, which makes the states density of C increase significantly near Fermi level. It can reduce 3O2 to H2O2 more quickly, and H2O2 can be further converted to 1O2. The system showed excellent degradation performance in a wide pH range (1-12) and excellent stability in 20 cycle experiments, which provided a reference significance for promoting the development of sustainable EF technology.

Treatment of cationic red X-GRL in high-salt printing and dyeing wastewater by an electrocatalytic ozonation system: treatment efficiency and degradation mechanism

High salt concentrations in printing and dyeing wastewaters significantly influence pollutant removal. The function of the electrocatalytic ozonation (MgMn x O y -GAC/EP) system in removing pollutants from high-salt printing and dyeing wastewater was investigated. Under high NaCl concentration, the H2O2 yield in the electrochemical system was maintained at approximately 53 mg L-1. Under optimal treatment conditions, the degradation efficiency of cationic red X-GRL in the MgMn x O y -GAC/EP system reached 100% within 16 min, and the mineralization efficiency achieved 90.8% within 60 min. The specific energy consumption of the MgMn x O y -GAC/EP system was 0.027 kW h per gCOD. The SF of the MgMn x O y -GAC/EP system was 13.04, indicating that MgMn x O y -GAC, EO and O3 had a remarkable synergistic effect in the removal of cationic red X-GRL. The existence of ˙OH, ˙Cl, ˙O2 - and 1O2 in the MgMn x O y -GAC/EP system was demonstrated by quenching and electron paramagnetic resonance experiments. Based on these outcomes, the degradation mechanism of cationic red X-GRL in the MgMn x O y -GAC/EP system under high salt conditions was proposed, which was the action mechanism of multiple free radicals mainly dominated by ˙O2 - and 1O2. After repeated experiments, the MgMn x O y -GAC/EP system accomplished a COD removal efficiency of 84%, which signified its relatively high stability. The MgMn x O y -GAC/EP system achieved a COD removal efficiency of approximately 86% for diverse pollutants. Overall, this study revealed that the MgMn x O y -GAC/EP system has novel prospects for the treatment of organic pollutants in high-salt wastewater.

N, P co-doped graphite felt cathode for efficient removal of ciprofloxacin in an ascorbic acid-coupled electro-Fenton process: Simultaneously enhancing H2O2 generation and Fe3+/Fe2+ cycling

To enhance the contaminant removal efficiency of the electro-Fenton (E-Fenton) process, a nitrogen and phosphorus co-doped graphite felt (NPGF) cathode was synthesized using an anodic oxidation technique. An ascorbic acid-coupled NPGF E-Fenton system was then established for the degradation of ciprofloxacin (CIP). The NPGF cathode featured abundant oxygen-containing functional groups (such as -COOH and -OH), which enhanced the selectivity of oxygen reduction and facilitated the formation of H2O2. The introduction of N and P doping disrupted the charge balance within the carbon framework, accelerating electron transfer. Together, the NPGF electrode and ascorbic acid enhanced the cycling of Fe3+/Fe2+ while preventing the formation of iron sludge. Under optimal conditions (ascorbic acid concentration of 0.3 mM, current density of 2.0 mA cm-2, pH of 3.0, aeration rate of 0.6 L min-1, and Fe2+ concentration of 0.2 mM), CIP was completely removed within 20 min. The NPGF electrode exhibited excellent stability, maintaining 95.35% CIP removal even after 8 cycles. Analysis revealed that singlet oxygen primarily mediated the degradation of CIP, with its concentration measured at 1.23 × 10-7 M. Density functional theory was used to analyze the characteristics and potential attack sites of CIP, enabling the proposal of plausible degradation pathways. Toxicity simulations and Escherichia coli growth inhibition experiments demonstrated a reduction in the toxicity of CIP and its intermediate products. This study offers a valuable reference for improving the efficiency of E-Fenton technology in antibiotic wastewater treatment.

Enhanced H2O2 formation and norfloxacin removal by electro-Fenton process using a surface-reconstructed graphite felt cathode: New insight into synergistic mechanism of defective active sites

The efficient catalytic activity and strong durability possibility of carbon-based three-dimensional fiber materials remains an important challenge in Electro-Fenton advanced oxidation technology. Graphite felt (GF) is a promising electrode material for 2-electron oxygen reduction reaction but with higher catalytic inertia. Anodizing modification of GF has been proved to enhance it electro-catalytic property, but the disadvantages of excessive or insufficient oxidation of GF need further improved. Herein, the surface reconstituted graphite felt by anodizing and HNO₃ ultrasonic integrated treatment was used as cathode to degrade norfloxacin (NOR) and the substantial role of different modification processes was essentially investigated. Compared with the single modification process, the synergistic interaction between these two methods can generate more defective active sites (DASs) on GF surface and greatly improved 2-electron ORR activity. The H₂O₂ can be further co-activated by Fe²⁺ and DASs into •OH_{(ads and free)} and •O₂^- to efficiently degrade NOR. The treated GF with 20 min anodizing and 1 h HNO₃ ultrasound had the highest electrocatalytic activity in a wide electric potential (-0.4 V to -0.8 V) and pH range (3-9) in system and the efficient removal rate of NOR was basically maintained after 5 cycles. Under optimal reaction conditions, 50 mg L^-1 NOR achieved 93% degradation and almost 63% of NOR was completely mineralized within 120 min. The possible NOR degradation pathways and ecotoxicity of intermediates were analyzed by LC-MS and T.E.S.T. theoretical calculation. This paper provided the underlying insights into designing a high-efficiency carbon-based cathode materials for commercial antibiotic wastewater treatment.