Litter extract from Alternanthera philoxeroides as an efficient passivator for oxytetracycline stability in riverbank purple soils
Yinfei Wang, Hongyan Deng, Wenbin Li, Min Li, Jinni Wu, Lei Hou, Jiang-ming Ouyang
Abstract
To study the effect of litter extract (Le) from Alternanthera philoxeroides on the stability of oxytetracycline (OTC) in riverbank purple soil (P), we used different proportions of Le to modify acidic P (Ac-P), neutral P (Ne-P), and alkaline P (Al-P) to obtain Le-modified P (Le-Ac-P, Le-Ne-P, and Le-Al-P). The basic physicochemical properties of Le-modified Ps were determined, and their microscopic morphology was studied using specific surface area detection (SBET), scanning electron microscopy (SEM), energy dispersion spectroscopy (EDS), and Fourier transform infrared (FTIR) spectroscopy. Batch method was used to study the isothermal and thermodynamic characteristics of OTC adsorption on different Le-modified Ps, and the OTC stability differences were compared in terms of the changes in temperature, pH, and ionic strength. Results showed that pH of Le-Ne-Ps and Le-Al-Ps decreased, the SBET of Le-modified Ps decreased, the total organic carbon content of Le-modified Ps increased, and the cation exchange capacity (CEC) of Le-Ac-Ps and Le-Ne-Ps increased with the increased modification proportion of Le. SEM, EDS, and FTIR results all showed that Le modified the surface of different Ps. Langmuir model was more applicable to describe the isothermal adsorption of OTC by different Le-modified Ps than Henry and Freundlich models. The maximum adsorption capacity of OTC by different Le-modified Ps ranged between 5.48–129.10 mmol/kg, and the following trend was observed: Le-Ne-Ps > Le-Ac-Ps > Le-Al-Ps. 20%Le-modified Ps showed excellent adsorption capacity toward OTC. OTC adsorption on different Le-modified Ps decreased with the increase in pH and decrease in temperature. With increased ionic strength, the adsorption stability of OTC increased first and then decreased. OTC adsorption was a spontaneous, endothermic, and entropy-adding reaction. The CEC and pH of Le-modified Ps were the keys to determining the maximum adsorption capacity of OTC.