Kinetic study of the degradation of rhodamine B using a flow-through UV/electro-Fenton process with the presence of ethylenediaminetetraacetic acid

Comparative study of electro-Fenton and photoelectro-Fenton processes using a novel photocatalytic fuel cell electro-Fenton system with g-C3 N4 @N-TiO2 and Ag/CNT@CF as electrodes

In this study, a novel photocatalytic fuel cell electro-Fenton (PFC-EF) system was constructed using g-C3 N4 @N-TNA and Ag/CNT@CF as electrodes. The composition, structure, and morphology of the electrodes were obtained. The g-C3 N4 @N-TNA, with its 2.37 eV band gap and 100 mV photovoltage, has excellent excitation properties for sunlight. Ag/CNT@CF with abundant pores, CNT 3D nanostructures, and Ag crystals on the surface can improve the electro-Fenton efficiency. A comparative study of rhodamine B (RhB) degradation was performed in this system. It has been shown that electric fields can greatly enhance the oxidation efficiency of both anode photocatalysis and the cathode electro-Fenton process. Under optimal conditions, RhB can be completely removed by the photoelectro-Fenton (PEF) process. The energy consumption of the PEF system was obtained. The electrical energy per order (EE/O) is only 9.2 kWh/m3 ·order, which is only 16.5% of EF and 2.2% of PFC-EF system. The mineralization current efficiency (MCE) of the PEF system reached 93.3% for a 2-h reaction. Therefore, the PEF system has the advantage of saving energy. The kinetic analysis shows that the RhB removal follows a first-order kinetic law, and the reaction rate constant reaches 0.1304 min-1 , which is approximately 5.2 times larger and 4.0 times larger than the electro-Fenton and PFC-EF processes, respectively. RhB removal is a coupling multimechanism in which an electric field enhances photoelectron migration, Ag loading improves H2 O2 generation, UV light coupled with H2 O2 promotes hydroxyl radical (٠OH) generation, and the nanoconfinement effect of CNTs promotes ٠OH accumulation in favor of RhB degradation. PRACTITIONER POINTS: Novel efficiency photocatalytic fuel cell electro-Fenton system was constructed. The electric field greatly enhances the photocatalytic fuel cell electro-Fenton system. Multiple coupling mechanisms of UV/H2O2, UV/Fenton and photo-electro-Fenton have been revealed.

Enhanced Fenton-like efficiency by the synergistic effect of oxygen vacancies and organics adsorption on FexOy-d-g-C3N4 with Fe‒N complexation

d-g-C₃N₄-Fe composites was prepared via a self-assembly and calcination process. According to measurements and density functional theory (DFT) computations, the complexation of iron and pyridinic N of g-C₃N₄ (Fe‒N) occurred with Fe(III)-π interaction, causing more oxygen vacancies (OVs) with more electrons in iron oxides. In the catalyst air-saturated suspension, the adsorbed pollutants complexed surface Fe(III) through their hydroxyl group donated electrons to around OVs, reducing the surface Fe(III) to Fe(II) and were destructed by Fe(III)-π interaction of the complexation. The addition of H₂O₂ mainly acted as acceptor being reduced ^•OH at the OV centers, causing higher degradation rate of pollutants due to both ^•OH and the surface reaction. However, for the adsorbed hydrophobic pollutants onto the sites of peripheral structure in g-C₃N₄, H₂O₂ was mainly decomposed into O₂ by the synergistic effect of iron species and OVs. Therefore, the catalyst exhibited high Fenton-like efficiency for the degradation of hydroxyl-containing pollutants and hydrophobic pollutants mixing with the former. Our results demonstrate that the Fe(III)-π interaction could carry out the oxidation of pollutants on the catalyst surface, decreasing the consumption of H₂O₂, and the role of OVs depends on pollutant adsorption patterns.

Hydroxyl and sulfate radical-based oxidation of RhB dye in UV/H2O2 and UV/persulfate systems: Kinetics, mechanisms, and comparison

The degradation kinetics and mechanisms of Rhodamine B (RhB) dye by ^•OH and SO₄^•- based advanced oxidation processes were investigated. The ^•OH and SO₄^•- radicals were generated by UV photolysis of hydrogen peroxide and persulfate (i.e., UV/H₂O₂ and UV/PS), respectively. The effects of initial solution pH, RhB concentration, oxidant dosage, Fe²⁺ concentration, and water matrices were examined. The results showed that the degradation of RhB followed pseudo-first-order kinetics in both processes, with the UV/H₂O₂ process exhibiting better performance than that of the UV/PS process. Acidic conditions were favorable to the degradation of RhB in both systems. Increasing the oxidant dosage or decreasing the contaminant concentration could enhance the degradation of RhB. Photo-Fenton-like processes accelerated the performance when Fe²⁺ was added into both systems. The removal efficiency of RhB was inhibited upon the addition of humic substances. The addition of Cl^- displayed no significant effect and promoted RhB degradation in UV/H₂O₂ and UV/PS systems, respectively. The presence of NO₃^- promoted RhB degradation, while H₂PO₄^- and C₂O₄^2- showed an inhibitory effect on both UV/H₂O₂ and UV/PS processes. Radical scavenging tests revealed the dominant role of SO₄^•- radicals in the UV/PS system. Furthermore, the evolution of low molecular weight organic acids and NH₄⁺ during the degradation of RhB in these two processes were compared. Both UV/H₂O₂ and UV/PS systems led to similar formation trends of NH₄⁺ and some ring-opening products (e.g., formic acid, acetic acid, and oxalic acid), suggesting some analogies in the decay pathways of RhB by ^•OH and SO₄^•--induced oxidation processes.