重金属存在下微塑料对环丙沙星的吸附特征及机制研究

为了揭示微塑料在重金属与抗生素共存体系中的吸附特征,以聚酰胺(PA)、聚氯乙烯(PVC)为典型微塑料,以环丙沙星(CIP)作为目标抗生素,以Cu、Cd为重金属代表,通过批量吸附试验研究了重金属存在下微塑料对CIP的吸附行为及机理。结果表明:PA和PVC两种微塑料对CIP的吸附同时符合Langmuir方程和Freundlich方程,由Langmuir方程拟合得到的CIP对PA和PVC的最大吸附量分别为1.846 mg·g~(-1)和1.862 mg·g~(-1)。不同pH下两种微塑料对CIP的吸附呈现先增加再降低的趋势,pH为6时吸附量达到最大。重金属Cu、Cd存在下的吸附等温线更符合Langmuir方程,Cu的存在显著促进了微塑料对CIP的吸附,而Cd的存在抑制了微塑料对CIP的吸附,Cu、Cd没有改变吸附量随pH变化的趋势。PVC对CIP的吸附以物理吸附为主,PA吸附CIP的机制包括酰胺基与羰基间氢键的产生,此外静电相互作用、极性作用也是两种微塑料吸附CIP的重要机制。研究表明,重金属Cu、Cd存在下,可以改变微塑料对CIP的吸附量,但不会对PA、PVC吸附CIP的机制产生影响。

The characteristics and mechanisms of microplastic adsorption by ciprofloxacin in the presence of heavy metals

To determine the characteristics of microplastic adsorption when these materials co-occurring with heavy metals and antibiotics, we studied the adsorption behavior and mechanisms of ciprofloxacin(CIP) for polyamide(PA) and polyvinyl chloride(PVC) in the presence of the heavy metals Cu and Cd, based on batch adsorption experiments. The results showed that the adsorption of PA and PVC by CIP conformed to the Langmuir and Freundlich equations. The maximum adsorption capacities of CIP for PA and PVC based on the Langmuir equation were 1.846 mg·g^-1 and 1.862 mg·g^-1, respectively. The adsorption of the two microplastics by CIP at different pH values revealed a trend of initial increase followed by a decrease, with the adsorptive capacity reaching a maximum value at pH 6. In the presence of Cu and Cd, the adsorption isotherms were more in line with predictions of the Langmuir equation. Whereas the presence of Cu inhibited microplastic adsorption by CIP, the presence of Cd promoted a significant increase in adsorption. At a given pH value, there was no significant change in the adsorptive capacity of CIP for microplastics in the presence of Cu or Cd. In addition, electrostatic and polar interactions were identified as important mechanisms underlying the adsorption of the two microplastics by CIP. The adsorption of PVC by CIP was found to be predominantly attributable to physical adsorption, whereas the adsorption of PA involves the formation of hydrogen bonds between amide and carbonyl groups. However, although the presence of heavy metals(Cu and Cd) can modify the adsorptive capacity of CIP for the two assessed microplastics, it does not affect the mechanisms whereby CIP adsorbs PA and PVC.