Evaluating the antibiotic adsorption ability of diatomite minerals: the role of treatment agents

Abstract

The uncontrolled use of antibiotics combined with ineffective treatment of antibiotic residues has led to the accumulation of antibiotics in water sources, directly threatening ecosystems. Diatomite is a good absorbent and a friendly and efficient material for removing pollutants from organic matter. In this study, diatomite from Phu Yen, Vietnam, was treated with many different agents, i.e., HCl, H₂SO₄, and NaOH, resulting in good adsorption of various antibiotics, such as tetracycline (TC), ciprofloxacin (CIP), tylosin (TLS), trimethoprim (TMP), and florfenicol (FFC). Furthermore, the TC antibiotic was chosen as a pollutant model to study the adsorption environment, adsorption isotherms, adsorption kinetics, and adsorption thermodynamics. Compared with raw diatomite, diatomite treated with HCl (D-HCl) has superior TC adsorption performance due to the removal of lotus fruit receptacle bud-like particles in the structure, which helps clear the pores and increases the specific surface area. Moreover, the change in surface charge leads to an increase in the electrostatic interaction force with TC. The TC adsorption of D-HCl follows the second-order kinetic model and the Langmuir isotherm model, with a high correlation coefficient of 0.9965 and a maximum adsorption capacity of 90.09 m² g⁻¹ at room temperature. The intra-particle diffusion model with the largest initial rate constant (k_int1) suggests that the TC rapidly occupied the surface active sites of the D-HCl adsorbent. The high secondary rate constant (k_int2) indicates that intragranular diffusion then proceeded immediately, which is consistent with the presence of multiple pore sizes within the D-HCl material. The adsorption thermodynamic parameters also show that the adsorption process occurs naturally, and the bond between TC and the D-HCl surface is a physical bond, indicating that D-HCl has potential for practical applications in removing antibiotics from water sources. Additionally, D-HCl shows promise as a perfect carrier in the field of photocatalysis.