## 1 Introduction  
Today, the presence of organic pollutants in water is a major problem for human, animal and environmental health [1]. Chlorophenols (CPs) are organochlorides of phenol recognized as priority pollutants by the US Environmental Protection Agency. These compounds are very toxic and can cause many environmental problems due to their widespread use and release into the environment. These have been detected in surface water, groundwater, landfills, disposal sites and sludge produced in treatment plants [2]. CP are also found in bactericides, insecticides, herbicides, and fungicides [3]. In addition, CP can be produced as by-products during various processes, such as disinfection of drinking water by chlorination process. The presence of CP in gases emitted from incinerators has been also identified [4]. Therefore, treatments of CP-contaminated wastewaters and CP removal before the discharge of wastewaters is essential. Water and wastewater treatment methods are generally divided into three categories: physical, chemical, and biological. The physical methods include filtration, adsorption, flotation by air, extraction, flocculation, and sedimentation; the biological methods are aerobic (such as activated sludge) and anaerobic degradation; and the chemical methods include oxidation, ion exchange, and chemical precipitation [5; 6; 7]. These methods have disadvantages such as their high investment costs, high energy consumption, low operating speed, volatile emissions, toxic sludge production, complex equipment maintenance, etc. [8; 9]. One of the most important applied methods to purify pollutants are the advanced oxidation processes (AOPs). In the AOPs methods, hydroxyl (\"OH), sulfate (SO4\"), and superoxide (O2\") free radicals are produced, leading to the breakdown of pollutants and turning them into simple and low risk molecules. The advantages of this method include its non-toxicity, high oxidizing power of active radicals, no sludge production, short life of radicals, no corrosion of equipment, and its simple application [10]. Oxidants such as persulfate (PS) and hydrogen peroxide (H2O2) can be used. Persulfates are low-cost and environmentally stable oxidants that exist in both proxymonosulfate (PMS) and prooxydisulfate (PDS). PS produces SO4\" radicals, which have a higher oxidation power (\(E^{0}\) = 2.5-3.1 V) than hydroxyl radicals (\(E^{0}\) = 1.89-2.72 V) [11]. These oxidants can be activated by different methods, such as heating, ultraviolet irradiation, and ultrasound (with different frequencies) [12; 13]. In traditional AOPs like the Fenton process, the H2O2 and PS ions were applied with homogeneous iron salt as catalysts to produce \"OH and SO4\" radicals. However, the main disadvantages of the Fenton process are the additional purification of iron ions, handling produced sludge, and effluents neutralization [14]. Nanoparticles are used in AOPs as nanocatalysts to increase the process efficiency. Methods such as filtration and centrifugation are often used to separate these nanoparticles, which have the disadvantages of being time-consuming and interrupting processes. To solve these problems, magnetic nanocatalysts can be used. These are synthesized by various methods such as sol-gel, heat decomposition, radiation, microwave, biological synthesis, and co-precipitation. The advantages of magnetic nanocatalysts include their easy synthesis, lack of toxicity, high chemical stability, and simple separation under a magnetic field without the use of chemicals and filtration. To make AOPs more efficient, magnetic nanocatalysts can be used in combination with various oxidants. Among all these procedures, the activation of PS by magnetic nanocatalysts is less complex and cheaper. It is carried out without the need for external energy [2]. Iron in magnetic nanocatalysts is one of the metals that is generally used to activate PS according to the following reactions [15].