Sulfate radical-based advanced oxidation processes (SR-AOPs) are a highly promising technology for water treatment, and their processing capacity is affected by the catalyst. However, the existing catalysts are mostly powder-based and cannot meet the requirements of recovery and mass transfer in practical applications. Catalytic filtration membrane is a functional membrane that combines catalysis and filtration. It provides a support for the catalyst to ensure its recovery, and restricts the reaction to pores, facilitating a close contact between pollutants and active sites, thereby achieving efficient utilization of peroxymonosulfate. Sepiolite is an excellent catalyst carrier because of its excellent thermal stability, great adsorption capacity, and abundant acid-base sites. In addition, sepiolite is a high-quality film-making material with fibers interwoven into a mesh structure in the same or different directions. In the paper, we prepared a CuO/sepiolite catalytic filtration membrane (CuO/sepiolite) with excellent catalytic performance via impregnation-filtering coating-drying-calcination. In addition, the performance and activation mechanism of catalyzing peroxymonosulfate method were also investigated.

0.1g sepiolite was dispersed in 20 mL of 20 mmol/L Cu(NO₃)₂ solution to obtain a suspension A. The suspension A was heated at 30 ℃ and stirred continuously for 3 h. The mixed suspension was filtrated through polyethylene (PE) microfiltration membrane (0.45 μm) and dried at 60 ℃ for 12 h to obtain a precursor. The dried precursor was placed in a muffle furnace and heated at 400 ℃ for 2 h to obtain a catalytic membrane. The catalytic membrane was cut into a circle with a diameter of 50 mm (named CS). A series of catalytic membranes were prepared at different calcination temperatures (i.e., 300, 400, 500, 600 ℃ and 700 ℃) (named CS-X, where X represents the calcination temperature).

The chemical composition of the samples was determined by X-ray fluorescence spectroscopy (XRF). The Cu content was quantitatively measured by an acid dissolution method combined with inductively coupled plasma atomic emission spectroscopy (ICP-AES). The crystal structure was analyzed by X-ray powder diffraction (XRD). The functional groups on the surface of catalytic filtration membranes were detected by Fourier transform infrared spectroscopy (FTIR). The microstructure and structural characteristics of the membrane material were determined by scanning electron microscopy (SEM) and high-resolution transmission electron microscopy.

A lab-scale catalytic filtration system was established to evaluate the catalytic performance of the CS. The inside diameter of filtration is 50 mm and the valid test area of CS is 19.6 cm². The simulated wastewater flowed through the catalytic filtration from top to bottom at a certain flow rate. Before catalytic degradation, a feed PNP solution firstly flowed through the catalytic filtration system to achieve adsorption-desorption equilibrium, and then the catalytic reaction was started by adding a specific mass of peroxymonosulfate (PMS). After a specific interval, filtrate was collected for measurement of absorbance, ion leaching concentration and TOC in alkaline conditions. The removal ratio (R) is calculated by

The catalytic filtration membrane (CS-400) has the optimum catalytic performance when the calcination temperature is 400 ℃ and the concentration of copper nitrate solution is 20 mmol/L. After the continuous catalytic degradation of 15 L of p-nitrophenol solution at a concentration of 10 mg/L, the performance of CS-400 catalytic filtration membrane does not show any degradation, and its structure is not damaged. Hydroxyl radical is the main reactive oxygen species for the degradation of p-nitrophenol in this catalytic reaction system. The CuO/sepiolite catalytic filtration membrane is a potentially valuable peroxymonosulfate catalyst with the promising applications in wastewater treatment.

A novel CuO/sepiolite catalytic filtration membrane was prepared according to the process route of impregnation-filtering-forming-drying-calcination for activating peroxymonosulfate. When the calcination temperature was 400 ℃ and the concentration of Cu(NO₃)₂ was 20 mmol/L, the prepared catalytic filter membrane (CS-400) had the best catalytic performance. After the continuous catalytic degradation of 15 L of p-nitrophenol solution at a concentration of 10 mg/L, the performance of the CS-400 catalytic filtration membrane did not show significant degradation, and its structure was not significantly corroded. The hydroxyl radical is the main reactive oxygen species for the degradation of p-nitrophenol in this catalytic reaction system, and the CuO/sepiolite catalytic filtration membrane is a potentially valuable peroxymonosulfate catalyst for the application in wastewater treatment.