Study On Plant Residues’ Adsorption Behavior And Mechanism On Oxytetracycline

Pharmaceuticals and Personal Care Products(PPCPs) are a kind of environmental pollutants with a "subtle, potential, and cumulative effect", which widely exists in water and soil. As is known to all, soil and sediment have certain adsorptive effect on PPCPs, and the effect is highly related to the organic matter in soil and sediment. The content, types and structures of organic matter affect the adsorption effect, so the study of the effect of different sources of organic matter and its content and structure on the adsorption is very meaningful.Since the organic matters in the sediments of the riverbank of the Weihe River mainly come from plant residues along the bank, this thesis chose six kinds of plant residues, that is, roots, stems, and leaves respectively of widely spread willows and reeds. With oxytetracycline as the representative substance of PPCPs, firstly the six residues were desugared rapidly, and then the original and desugared plant residues were used to do the series adsorption experiments through adsorption kinetics experiments, isothermal adsorption experiments and adsorption thermodynamics experiments on oxytetracycline and structure characterization analysis, such as scanning electron microscope and infrared spectrum. Through the analysis of these experiments, the features of plant residues along the Weihe River adsorbing oxytetracycline are deeper explored and plant residues’ adsorption behavior and mechanism of oxytetracycline before and after desugarization are further illustrated. The results were shown as following:1. The adsorption kinetics of willow residues’ every part towards oxytetracycline conformed to the quasi-first-order model. In addition, the desugared samples appeared to have a relatively slow adsorption rate and large adsorption amount. The isothermal adsorption process in which willow residues’ every part adsorbed oxytetracycline both fitted in the Langmuir model and Freundlich model and the process was a spontaneous endothermic reaction which was mainly physical adsorption. The elemental analysis, scanning electron microscope, Fourier transform infrared spectrum and other characterization methods, showed that the content of organic carbon in the willow residues after the removal of sugar was increased, the polarity decreased, the aroma increased, and the specific surface area increased, which from the microscopic angle further illustrated the reason why the adsorption ability of willow residues was improved after desugarization.2. The adsorption kinetics of reed residues’ every part towards oxytetracycline agreed with the quasi-first-order model and in terms of the adsorption capacity, reed root ranked first, then reed stem, then reed leaf. The Langmuir model and Freundlich model could be applied to depict the isothermal adsorption process in which reed residues adsorbed oxytetracycline and the process, primarily the physical adsorption, was a spontaneous endothermic reaction. The element analysis, scanning electron microscope and Fourier transform infrared spectroscopy and other characterization methods showed increased content of organic carbon in the desugared reed residues, increased aroma, decreased polarity, and increased specific surface area, which was further demonstrated that the removal of sugar was the reason for the increase of the adsorption capacity of the reed’s every part from microcosmic point of view.3. The adsorption kinetics of oxytetracycline that each component of willow and reed residues adsorbed was consistent with the quasi-first-order model. Whether desugarization or not, among the components of the two kinds of plant residues, willow root had the largest adsorption amount of oxytetracycline. Besides, the isothermal adsorption process was in line with the Langmuir model and Freundlich model. And the whole adsorption process was a spontaneous endothermic reaction, which was primarily physical adsorption. Through element analysis, scanning electron microscope and Fourier infrared spectrum and other characterization methods, it was proved that the residues of the two kinds of plants had similar adsorption behaviors and mechanisms in a micro angle.