Analysis and Simulation of Adsorption Efficiency of Herbicides Diuron and Linuron on Activated Carbon from Spent Coffee Beans

Abstract

Phenyl urea herbicides such as diuron and linuron are commonly used in agriculture to eliminate weeds. Their uncontrolled use can cause environmental problems. In this study, the adsorption of these herbicides was evaluated using activated carbon from coffee grounds, activated with zinc chloride (AC-ZnCl2, 100% purity), nitric acid (AC-HNO3, 65% purity), and commercially activated (AC-C) carbon for comparison purposes. The spent coffee grounds were transformed into activated carbon through the calcination process. The highest removal efficiency for diuron 40 mg∙L−1 and linuron 31 mg∙L−1 was obtained using the ZnCl2-activated adsorbent, being 100% and 45%, respectively. The best pH range was between 4 and 6. Adsorption kinetic studies showed that pseudo-first and second-order models fit the experimental data, with the adsorption rate increasing rapidly within 60 min for the concentrations tested. Adsorption isotherms indicated that the Langmuir model provided the best fit for diuron, while the Freundlich model was more appropriate for linuron. The efficiency of the adsorption process using activated carbon (AC) was confirmed by the toxicity analysis of diuron and linuron solutions before and after adsorption with AC.