Determination of Kinetic, Isotherm, and Thermodynamic Parameters of the Methamidophos Adsorption onto Cationic Surfactant-Modified Zeolitic Materials

In the present study, a natural clinoptilolite was conditioned with NaCl solution and subsequently modified with different cationic hexadecyltrimethylammonium surfactant concentrations for methamidophos removal. The surfactant-modified zeolitic material with maximum methamidophos adsorption capacity was chosen, and the effect of several parameters such as contact time and initial pesticide concentration were performed by batch system. Other parameters such as the effect of adsorbent dosage, pH, and temperature were also evaluated. Natural, NaCl-conditioned, and the best surfactant-modified zeolitic materials were systematically characterized by several analytic techniques such as scanning electron microscopy with energy dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, and BET-specific surface area by N2 physisorption measurements. The zero point charge was also determined in each studied zeolitic material. Derived results showed a maximum methamidophos adsorption of 1.385 mg/g onto zeolitic material surfactant-modified with 25 mmol/L at 20 °C. The experimental adsorption kinetics and isotherms data were well adjusted with pseudo-second order and Langmuir isotherm models in its not linearized form, respectively. The amount of adsorbent and pH in the surfactant-modified zeolitic material influences the pesticide adsorption capacity. Thermodynamic parameters indicated that methamidophos adsorption on surfactant-modified zeolitic material at 25 mmol/L was an exothermic in nature process, not spontaneous, and with decreased randomness. The obtained results in the present research contribute as study of methamidophos adsorption behavior with zeolitic materials application as an alternative removal method for organophosphates pesticides.