Investigating the adsorption mechanism of zinc chloride-modified porous carbon for sulfadiazine removal from water

Abstract

Sulfadiazine (SDZ) is a commonly used antibiotic in medicine, aquaculture, and animal husbandry. However, its misuse has resulted in its release into soil and water environments, posing a gradual threat to the environment and human health. In this study, cotton pulp, poplar sawdust, and corn stover were chosen as raw materials. Zinc chloride (ZnCl2) was used as a modifier to prepare modified porous carbon through pyrolysis at different carbonization temperatures (400 and 800°C). The objective was to investigate the adsorption effect and mechanism of modified porous carbon on SDZ in aqueous environments, as well as the effect of different biomass fractions of the carbon source on the adsorption effect. The physical and chemical properties of the modified porous carbon were characterized by various means of characterization, and the results showed that the high temperature and modification effects made the adsorbent material possess a larger specific surface area and richer pore structure, higher aromaticity, higher degree of graphitization, etc., which would be beneficial for the adsorption of SDZ. Among them, CCPZ800 showed the highest saturation adsorption of SDZ, Q max = 425.45 mg/g. The adsorption experiments were carried out by changing the initial conditions and fitted with kinetic and isothermal adsorption to further explain the adsorption mechanism of modified porous carbon on SDZ in conjunction with the adsorption of SDZ by hydrothermal carbon materials. The results showed that the adsorption of modified porous carbon on SDZ conformed to the quasi-secondary kinetic and Freundlich isothermal adsorption models. Adsorption mechanism of SDZ on modified porous carbon followed a multimolecular layer adsorption, with chemical adsorption being the dominant process. Both physical adsorption and chemical adsorption occurred simultaneously, with the main adsorption mechanism being π–π conjugation. In addition, compositional distribution of biomass from different carbon sources results in variations in pyrolysis mode and pyrolysis products, which in turn affect adsorption. By analyzing the effect of variability in the composition of biomass on the adsorption effect of SDZ, it can be concluded that higher cellulose content in the carbon source leads to a better adsorption effect of SDZ. The study showcases the effectiveness of ZnCl2-modified porous carbon in removing SDZ from water, offering insights into the selection of raw materials for this adsorbent preparation.