Investigation of Zeolite 4A Modified by CU for Tetracycline Removal from Aqueous Environment

Antibiotics are common drug contaminants due to their high levels in the effluents of pharmaceutical companies and hospitals. Tetracyclines, as a relatively inexpensive bactericidal inhibitor, are one of the most widely used antibiotics for humans and animal food and pharmaceutical supplements, which have led to their widespread release into the environment. In this paper, zeolite 4A, due to its high specific surface area and ion exchangeability has been modified to increase the adsorption capacity of tetracycline using copper ion. Impregnation method as one of the simple and reproducible methods has been used to add copper with different ratios to the zeolite structure. The adsorbent characterizations were investigated using FESEM, FTIR, XRD and BET analyses. Adsorption experiments were performed by investigating the effect of copper to zeolite mass ratio, adsorbent weight, and different pH over time. Adsorption isotherms and kinetics have been investigated to investigate the adsorption capacity and transfer mechanism of tetracycline from liquid bulk to the adsorbent surface and intraparticle diffusion. The specific surface area of the adsorbent increased from 36 m2/g to 635 m2/g during the modification process. The maximum adsorption is achieved at pH 6.8 and the weight ratio of copper nitrate to zeolite is 0.4, which according to Langmuir's theory increases from 41 to about 416 mg/g and for higher copper to zeolite ratio the adsorption capacity decreases. The Freundlich isotherm showed better agreement with the equilibrium data and the second order kinetic model predicted the reaction rate data more accurately. FTIR analysis showed that the electrostatic bond between the carbonyl and phenol groups of tetracycline with copper is one of the main mechanisms of tetracycline adsorption on the modified zeolite. The results showed that copper has significantly increased the adsorption capacity of zeolite by changing the internal structure and reducing the radius of cavities and increasing the specific surface area.