Photoelectro-Fenton treatment of pesticide triclopyr at neutral pH using Fe(III)-EDDS under UVA light or sunlight

The recent development of innovative photoelectro-Fenton processes for the effective and cost-effective remediation of organic pollutants in waters

Wastewaters with toxic and recalcitrant organic contaminants are poorly remediated in conventional wastewater treatment plants. So, powerful processes need to be developed to destroy such organic pollutants to preserve the quality of the aquatic environment. This critical and comprehensive review presents the recent innovative development of photoelectro-Fenton (PEF) covering the period 2019-September 2024. This emerging photo-assisted Fenton-based electrochemical advanced oxidation process (EAOP) is an efficient and cost-effective treatment for water remediation. It possesses a great oxidation power because the in-situ generated hydroxyl radical as oxidant is combined with the photolysis of the organic by-products under UV or sunlight irradiation. The review is initiated by a brief description of the characteristics of the PEF process to stand out in the role of generated oxidizing agents. Further, the homogeneous PEF. PEF-like, solar PEF (SPEF), and SPEF-like processes with iron catalysts are discussed, taking examples of their application to the removal and mineralization of solutions of industrial chemicals, herbicides, dyes, pharmaceuticals, and direct real wastewaters. Novel heterogeneous PEF treatments of such pollutants with solid iron catalysts or functionalized cathodes are analyzed. Finally, novel hybrid processes including PEF/photocatalysis and PEF/photoelectrocatalysis, followed by novel and potent sequential processes like electrocoagulation-PEF and persulfate-PEF, are discussed. Throughout the manuscript, special attention was made to the total operating cost of PEF, which is more expensive than conventional electro-Fenton due to the high electric cost of the UV lamp, pointing to consider the much more cost-effective SPEF as a preferable alternative in practice.

Heterogeneous activation of self-generated H2O2 by Pd@UiO-66(Zr) for trimethoprim degradation: Efficiency and mechanism

The Fenton reaction is recognized as an effective technique for degrading persistent organic pollutants, such as the emerging pollutant trimethoprim (TMP). Recently, due to the excellent reducibility of active hydrogen ([H]), Pd-H2 has been preferred for Fenton-like reactions and the specific H2 activation of Pd-based catalysts. Herein, a heterogeneous Fenton catalyst named the hydrogen-accelerated oxygen reduction Fenton (MHORF@UiO-66(Zr)) system was prepared through the strategy of building ships in the bottle. The [H] has been used for the acceleration of the reduction of Fe(III) and self-generate H2O2. The systematic characterization demonstrated that the nano Pd0 particle was highly dispersed into the UiO-66(Zr). The results found that 20 mg L-1 of TMP was thoroughly degraded within 90 min in the MHORF@UiO-66(Zr) system under conditions of initial pH 3, 30 mL min-1 H2, 2 g L-1 Pd@UiO-66(Zr) and 25 μM Fe2+. The hydroxyl radical as well as the singlet oxygen were evidenced to be the main reactive oxygen species by scavenging experiments and electron spin resonance. In addition, both reducing Fe(III) and self-generating H2O2 could be achieved due to the strong metal-support interaction (SMSI) between the nano Pd0 particles and UiO-66(Zr) confirmed by the correlation results of XPS and calculation of density functional theory. Finally, the working mechanism of the MHORF@UiO-66(Zr) system and the possible degradation pathway of the TMP have been proposed. The novel system exhibited excellent reusability and stability after six cyclic reaction processes.

Assessing the electrochemical degradation of reactive orange 84 with Ti/IrO2-SnO2-Sb2O5 anode using electrochemical oxidation, electro-Fenton, and photoelectro-Fenton under UVA irradiation

Today, water shortage problems around the world have forced the search for new treatment alternatives, in this context, electrochemical oxidation technology is a hopeful process for wastewater treatment, although it is still needed exploration of new efficient and economically viable electrode materials. In this way, mixed metal oxide anodes look like promising alternatives but their preparation is still a significant point to study, searching for finding low-cost materials to improve electrocatalytic efficiencies. In an exploration of this kind of highly efficient materials, this work presents the results obtained using an MMO Ti/IrO2-SnO2-Sb2O5 anode. All the prepared anodes exhibited excellent physical and electrochemical properties. The electrochemical oxidation of 100 mL and 200 mg L-1 Reactive Orange 84 (RO 84) diazo dye was studied using 3 cm2 of such synthesized anodes by applying current densities of 25, 50, and 100 mA cm-2. Faster and more efficient electrochemical oxidation occurred at 100 mA cm-2 with 50 mM of Na2SO4 + 10 mM NaCl as supporting electrolyte at pH 3.0. The degradation and mineralization processes of the above solution were enhanced with the electro-Fenton process with 0.05 mM Fe2+ and upgraded using photoelectron-Fenton with UVA light. This process yielded 91% COD decay with a low energy consumption of 0.1137 kWh (g COD)-1 at 60 min. The evolution of a final carboxylic acid like oxalic was followed by HPLC analysis. The Ti/IrO2-SnO2-Sb2O5 is then an efficient and low-cost anode for the photoelectro-Fenton treatment of RO 84 in a chloride and sulfate media.

Solar photoelectro-Fenton: A very effective and cost-efficient electrochemical advanced oxidation process for the removal of organic pollutants from synthetic and real wastewaters

Recalcitrant and toxic organic pollutants from wastewaters are scarcely removed in conventional wastewater treatment plants. To preserve the water quality, organics need to be removed by developing powerful oxidation technologies. Our laboratory proposed in 2007 a potent electrochemical advanced oxidation process (EAOP) for wastewater remediation, so-called solar photoelectro-Fenton (SPEF). This review summarizes the advances of this emerging technology up to 2022, making evident its effectiveness and cost-efficiency for the destruction of usual organic pollutants. The simultaneous action of generated hydroxyl radicals and the photolysis by sunlight explains the high oxidation power of SPEF respect to other EAOPs. The review is initiated by describing the fundamentals of the process to remark the role of the produced oxidants and the benefits of using solar irradiation in its performance. The photoelectrochemical systems used (bench tank reactor and solar pre-pilot flow plant) and the assessment of the operating variables are discussed. The characteristics of the most common homogeneous SPEF for the degradation and mineralization of several synthetic solutions of industrial chemicals, herbicides, pharmaceuticals, and synthetic organic dyes, as well as of some real wastewaters, are further described. The influence of the photoelectrochemical cell, electrodes, solution pH, electrolyte composition, Fe²⁺ and pollutant concentration, and current density is analyzed. The performance of a homogeneous SPEF-like process with active chlorine and heterogeneous SPEF processes with solid catalysts such as Fe₃O₄ and sodium vermiculite is also discussed. Finally, the advances of homogeneous SPEF combined with other techniques like solar photocatalysis, solar photoelectrocatalysis, anaerobic digestion, and nanofiltration are reported.

Mixed industrial wastewater treatment by the combination of heterogeneous electro-Fenton and electrocoagulation processes

Mixed industrial wastewater treatment efficiency of combined electro-Fenton (EF) and electrocoagulation (EC) processes was investigated in the present study. Alkali modified laterite soil was used as a heterogeneous EF catalyst and found superior performance than the raw laterite soil. Initially, the effect of catalyst dosage, initial pH, and applied voltage on the performance of EF process was carried out. A total of 54.57% COD removal was observed after 60 min of the EF treatment. Further treatment was carried out with EC process at different voltages. A total of 85.27% COD removal after 2 h treatment was observed by combining two electrochemical processes. Performance of EF followed by EC (EF + EC) process was compared with EC followed by EF (EC + EF) process. Even though efficiency is the same, EF + EC is a better strategy than EC + EF as it nullifies the neutralization requirement after EF process in addition to high mineralization efficiency, enhanced biodegradability, and lesser sludge generation.