From Fenton and ORR 2e−-Type Catalysts to Bifunctional Electrodes for Environmental Remediation Using the Electro-Fenton Process

Abstract

Currently, the presence of emerging contaminants in water sources has raised concerns worldwide due to low rates of mineralization, and in some cases, zero levels of degradation through conventional treatment methods. For these reasons, researchers in the field are focused on the use of advanced oxidation processes (AOPs) as a powerful tool for the degradation of persistent pollutants. These AOPs are based mainly on the in-situ production of hydroxyl radicals (OH•) generated from an oxidizing agent (H2O2 or O2) in the presence of a catalyst. Among the most studied AOPs, the Fenton reaction stands out due to its operational simplicity and good levels of degradation for a wide range of emerging contaminants. However, it has some limitations such as the storage and handling of H2O2. Therefore, the use of the electro-Fenton (EF) process has been proposed in which H2O2 is generated in situ by the action of the oxygen reduction reaction (ORR). However, it is important to mention that the ORR is given by two routes, by two or four electrons, which results in the products of H2O2 and H2O, respectively. For this reason, current efforts seek to increase the selectivity of ORR catalysts toward the 2e− route and thus improve the performance of the EF process. This work reviews catalysts for the Fenton reaction, ORR 2e− catalysts, and presents a short review of some proposed catalysts with bifunctional activity for ORR 2e− and Fenton processes. Finally, the most important factors for electro-Fenton dual catalysts to obtain high catalytic activity in both Fenton and ORR 2e− processes are summarized.

Cultivation of microalgae in food processing effluent for pollution attenuation and astaxanthin production: a review of technological innovation and downstream application

“…Normally, such a wastewater treatment plant could treat the FPE produced by a large-sized food processing factory. Some data in previous studies were used to estimate the fate of carbon in FPE treatment ( Lu et al, 2023b ; Fajardo-Puerto et al, 2023 ). Concentration of organic carbon in FPE was set as 2,780 mg L -1 .…”

“…As shown in Figure 1 , in Fenton reaction, a typical chemical oxidation for organics-rich effluent treatment, with the generation of hydroxyl radicals (OH•), organic carbon contained in FPE is converted to CO 2 ( Fajardo-Puerto et al, 2023 ). Accordingly, 8.664 kg CO 2 , which is equal around 4.382 m 3 CO 2 to at 20°C, could be produced during the treatment of 1 m 3 FPE.…”

Recent progress and perspective on electrocatalysis in neutral media: Mechanisms, materials, and advanced characterizations

“…On the other hand, the influence of the Fenton reaction inherent in iron-based catalysts on the ORR process has not been fully resolved. [139] Fe-based catalysts are susceptible to the Fenton reaction, whereas Co-based catalysts are not affected by the Fenton reaction compared with Fe-based catalysts while maintaining considerable ORR performance, making them one of the attractive alternatives to noblemetal-based catalysts. Furthermore, in addition to its excellent ORR activity, it also has exceptional performance in the HER and OER catalytic processes.…”

Facile Synthesis of Carbon-Based Inks to Develop Metal-Free ORR Electrocatalysts for Electro-Fenton Removal of Amoxicillin

“…Traditionally, ORR catalysts based on Pt and Pd are considered the best candidates; however, their high cost makes the use of these in the EF process difficult [21]. Carbon-based materials have been evaluated as ORR catalysts due to their low cost and high selectivity for H 2 O 2 [22]. Qin et al [23] synthesized hollow porous carbon spheres with high activity ORR 2e − (higher than that reported in more advanced Fenton catalysts), which was attributed to the presence of sp 3 carbon and sp 2 defects.…”