Application of Bimetallic Hydroxide/Graphene Composites in Wastewater Treatment

The increasing discharge of antibiotic wastewater leads to increasing water pollution. Most of these antibiotic wastewaters are persistent, strongly carcinogenic, easy to bioaccumulate, and have other similar characteristics, seriously jeopardizing human health and the ecological environment. As a commonly used wastewater treatment technology, non-homogeneous electro-Fenton technology avoids the hazards of H₂O₂ storage and transportation as well as the loss of desorption and reabsorption. It also facilitates electron transfer on the electrodes and the reduction of Fe³⁺ on the catalysts, thereby reducing sludge production. However, the low selectivity and poor activity of electro-synthesized H₂O₂, along with the low concentration of its products, combined with the insufficient activity of electrically activated H₂O₂, results in a low ∙OH yield. To address the above problems, composites of layered bimetallic hydroxides and carbon materials were designed and prepared in this paper to enhance the performance of electro-synthesized H₂O₂ and non-homogeneous electro-Fenton by changing the composite mode of the materials. Three composites, NiFe layered double hydroxides (LDHs)/reduced graphene oxide (rGO), NiMn LDHs/rGO, and NiMnFe LDHs/rGO, were constructed by the electrostatic self-assembly of exfoliated LDHs with few-layer graphene. The LDHs/rGO was loaded on carbon mats to construct the electro-Fenton cathode materials, and the non-homogeneous electro-Fenton oxidative degradation of organic pollutants was realized by the in situ electrocatalytic reduction of O₂ to ∙OH. Meanwhile, the effects of solution pH, applied voltage, and initial concentration on the performance of non-homogeneous electro-Fenton were investigated with ceftazidime as the target pollutant, which proved that the cathode materials have an excellent electro-Fenton degradation effect.