عنوان مقاله [English]
BACKGROUND AND OBJECTIVE: The high use of pesticides in agriculture and the entry of some of these compounds in water and products has led to one of the main strategies in agriculture, increasing the health of the community using less pesticides and, consequently, producing a healthy product and in the future, isolation of pesticides in contaminated water before release in the environment. The poison in agriculture is a chemical substance designed to kill pests. The poison in the food chain is sometimes condensed up to many thousand times, and most of them, especially if they have an aromatic ring, cannot be easily decomposed. The purpose of the study was to remove methylene blue from aqueous solution by beta-cyclodextrin / Zinc oxide composite.
MATERIALS AND METHODS: Beta-cyclodextrin / Zinc oxide nanocomposite was synthesized by sol-gel method in aqueous solution under nitrogen atmosphere and successfully identified using FTIR, SEM and XRD techniques. The maximum methylene blue absorbance wavelength was determined using a UV-VIS spectrophotometer and a range of 400 to 800 nm wavelength range at 665 nm. The methylene blue adsorption on β-cyclodextrin /Zinc oxide composite was evaluated discontinuously. The initial pH (1, 4, 7, 9 and 12), the initial amount of adsorbent (0.005, 0.01, 0.015 and 0.02 grams), the initial methylene blue concentration (5, 10, 20 and 30 mg/L), and contact time up to 40 minutes as well as the desorption process were studied. Langmuir, Freundlich, and Tempkin isotherm adsorption models were investigated. Experimental data were studied with different kinetic models. Thermodynamic parameters in surface adsorption including Gibbs free energy change (ΔG0), entropy change (ΔS0) and enthalpy change (ΔH0) were measured by examining the adsorption process at several different temperatures.
RESULTS: The lowest amount of adsorption was observed at pH 7 and highest in acidic pH=1. It seems that increasing methylene blue adsorption in acidic pH is due to the conversion of the pigment to anion, which results in more potent adsorption. Up to 15 minutes after the start of the process, adsorption is performed at more and then performed at a lower rate. The adsorption takes to equilibrium after 30 minutes. The maximum adsorption capacity occurs at a concentration of 5 milligrams per liter than the contaminant in the presence of 0.005 grams per liter of absorbent material at 20 degrees Celsius. The process of adsorption is accompanied by the reduction of entropy. The thermodynamic constants of ΔH0 and ΔS0 are 55.15 kJ / mol and 195.62 j/k.mol respectively. At 20 ° C, the amount of ΔG0 is 2131.65 j/k.mol and increases with increasing temperature up to 37 ° to 5457.19 j/k.mol. The Tempkin isotherm has a good correlation with experimental data with a correlation coefficient of 0.9818 and a constant KT of 0.493. The kinetic model of pseudo-second order with a correlation coefficient of 0.9578 and a constant speed of 0.07 min-1M-1 is a suitable kinetic model for describing absorption.