Pretreatment of membrane dye wastewater by CoFe-LDH-activated peroxymonosulfate: Performance, degradation pathway, and mechanism

Abstract

When a membrane is used to treat dye wastewater, dye molecules are continually concentrated at the membrane surface over time, resulting in a dramatic decrease in membrane flux. Aside from routine membrane cleaning, the pretreatment of dye wastewater to degrade organic pollutants into tiny molecules is a facile solution to the problem. In this study, the use of layered double hydroxide (LDH) to activate peroxymonosulfate (PMS) for efficient degradation of organic pollutant has been thoroughly investigated. We utilized a simple two-drop co-precipitation process to prepare CoFe-LDH. The transition metal components in CoFe-LDH effectively activate PMS to create oxidative free radicals, and the layered structure of LDH increases the number of active sites, and thereby considerably enhancing the reaction rate. It was found that the reaction process produced non-free and free radicals, including singlet oxygen (1O2), sulfate radicals (SO4•−), and hydroxyl radicals (•OH), with 1O2 being the dominant reactive species. Under the optimal conditions (pH 6.7, PMS dosage 0.2 g/L, catalyst loading 0.1 g/L), the degradation of Acid Red 27 dye in the CoFe-LDH/PMS system reached 96.7% within 15 min at an initial concentration of 200 mg/L. The CoFe-LDH/PMS system also exhibited strong resistance to inorganic ions and pH during the degradation of organic pollutants. This study presents a novel strategy for the synergistic treatment of dye wastewater with free and non-free radicals produced by LDH-activated PMS in a natural environment.