Today, the pharmaceutical and health industries have caused the entry of various pollutants into the environment and water resources, and as a result, threaten the health of the people. Therefore, removing them from the environment becomes more important [1–4]. Typically, drugs either absorb activated sludge and enter the sludge digesters and can play a role in inhibiting the biodegradation activity of anaerobic bacteria, or by entering conventional wastewater treatment processes with effluent, entering soil or surface water, groundwater and They are drunk [5–7]. Medicinal compounds, including cardiovascular drugs, are substances that are very useful and despite their side effects, they are widely used in medicine [8–11]. Among these drugs is one of the most widely used cardiovascular drugs called atenolol, which is one of the most widely used drugs due to the prevalence of cardiovascular disease and hypertension. Atenolol is a beta-blocker and is used to treat chronic angina, hypertension, high blood pressure (alone or with other antihypertensive drugs) and to prevent myocardial infarction [12]. About 50 to 60% of the drug is absorbed from the gastrointestinal tract. The drug is low protein-bonded in plasma, the drug is metabolized in small amounts in the liver, the biological half-life of the drug is 6-7 hours and the time required to reach the peak effect is 2-4 hours, 85 to 100% of the drug is unchanged by the kidney It is predicted that large amounts of this compound will be present in household, hospital, pharmaceutical and groundwater sources [13–15] Therefore, it is necessary to provide a simple, sensitive, and fast method to remove drugs from aqueous sources [16–18]. Many methods are used to remove these compounds, including membrane processes such as nanofiltration, ultrafiltration, reverse osmosis, etc., that their disadvantages are high pressure, high cost of the membrane, and most importantly chemical or microbial clogging of the membrane that prevents water from passing through the filter and reducing the flow [19]. Conventional oxidation treatment is another method of removing contaminants by adding an oxidizing agent to a solution containing contaminants. With this oxidation, some of the contaminants are removed and decomposed. In wastewater treatment, oxidizers such as chlorine and other chlorine-containing compounds (such as hypochlorous acid), oxygen, ozone, and hydrogen peroxide are used for oxidation. Chlorine and its derivatives can be used in the role of chemical oxidant in wastewater treatment. However, due to its high oxidation strength, it reacts with aromatic rings and double bond substances, which result in halogenated organic matter, and some of them have the potential for carcinogenic risk. Therefore, the use of chlorine in the decomposition of wastewater organic matter is not appropriate [20, 21], So catalytic oxidation with H2O2 in the presence of an appropriate catalyst is considered.
Transition metal complexes of transfer elements are good catalysts and some of them have high solubility in solution, so they are considered homogeneous catalysts [22, 23]. Although homogeneous catalysts have high activity and selectivity, but the difficulty of separating them from the product limits their industrial applications. And this problem can be solved by heterogeneizing them [24–26]. Homogeneous catalysts can be converted to heterogeneous catalysts by bonding or encapsulation [27, 28].
Zeolites are crystalline aluminosilicates with cavities and channels of the specified size and unique properties such as ion exchange, adsorption, and catalytic activity which are very suitable in industrial applications. [29]. The general oxide formula for NaX zeolite is Na2O.Al2O3.5Si02 and for its unit cell is (Na88Al88Si104O384.172.1H20). The NaX zeolite is of the Fujasite family and the sodalite cages are connected by the secondary prismatic units with a hexagonal base. The size of the cavity and its channels is about 0.74 nm (relatively large), and it is used as a stable size in the production of catalysts [30].
To increase the catalytic activity of the complexes, they can be encapsulated in the pores and cavities of the inorganic polymer structure [31]. Zeolites are unique among all types of compounds with porous and porous structures, because they have a regular crystal structure with high chemical and thermal stability. The proper structure of zeolites has made them a suitable environment for trapping active metal complexes and metal clusters, which use these modified systems as catalysts [32]. There are three methods for encapsulating coordination compounds in the pores and channels of zeolite, including the method and synthesis of zeolite complexation, the template synthesis method and the synthesis method, and the flexible ligand method, simultaneously [33, 34]. In this research work, the flexible ligand method has been used. First, the appropriate metal enters the zeolite structure by ion exchange method, and then the appropriate ligand in terms of size and flexibility is spread in the zeolite structure, in this method. The ligand used in this method must have sufficient flexibility to be stable and not be degraded during adsorption and binding to the exchanged metal in the zeolite pores. The amount of complex produced in the zeolite pores is proportional to the amount of cation exchanged with the sodium cations in the zeolite structure. The excess amount of ligand and metal complex on the outer surface of the zeolite should be separated by a solvent.
Continuing the previous work [i], we describe the synthesis and characterization of the encapsulated Ni (II) and Co (II) complexes of pydcH2 in zeolite-X and their use in the oxidation of atenolol (an organic pollutant in wastewater) with hydrogen peroxide as an oxidant.