微塑料对水环境中亚甲基蓝的吸脱附行为研究

Adsorption-desorption Behavior of Methylene Blue onto Microplastics in Water Environment

微塑料与典型亲水性有机污染物——亚甲基蓝(MB)在水环境中普遍存在,对水生态系统产生了负面影响。结果表明,当温度为25℃,100.0 mg微塑料置于10 mg/L的100 m L MB时,aged PP最大吸附量高达4.18 mg/g。与aged-PP、aged-PE和aged-PVC不同,aged-PS对MB的吸附等温线符合Freundlich模型,其吸附机制主要是不均匀表面形成的多层吸附(物理化学吸附),而aged-PP、aged-PE和aged-PVC对MB的吸附机制则主要是静电作用和化学键作用(化学吸附)。4种微塑料对MB的吸附能力随吸附条件变化较大,提高溶液的pH可以提高4种微塑料的MB吸附量,但增加溶液的盐浓度则可导致其吸附量明显减小。饱和吸附MB的aged-PVC在模拟胃肠道液中MB的脱附率最高,可达58.1%,其次是aged-PVC(39.51%)、aged-PE(25.96%);aged-PP的脱附率最低,为18.49%。这一结果表明,PP等老化后的微塑料,有可能成为MB进入水环境和生物组织的重要载体。

Microplastics and typical hydrophilic organic pollutants-methylene blue(MB) are ubiquitous in water environment, which have a negative impact on aquatic ecosystems. Results showed the maximun adsorption capacity is 4.18 mg/g when 100 mL of MB at a concentration of 10 mg/L was adsorbed by 100.0 mg aged PP microplastics at a temperature of 298 K.Different from aged-PP, aged-PE and aged-PVC, the adsorption isotherms of MB on aged-PS fitted with the Freundlich model well, and the adsorption mechanism was mainly the multilayer adsorption(physical and chemical adsorption) formed on the uneven surface, while the adsorption mechanisms of MB on aged-PP, aged-PE and aged-PVC were mainly electrostatic and chemical bond(chemical adsorption). MB adsorption capacity of the four microplastics varies greatly with the adsorption conditions. Increasing the p H of the solution can improve the MB adsorption capacity of the four types of microplastics, however, increasing the salt concentration of the solution can lead to a significant decrease in the adsorption capacity. MB desorption rate of aged-PS saturated with MB in simulated gastrointestinal fluid was the highest, reaching 58.1%, followed by aged-PVC(39.51%) and aged-PE(25.96%). The desorption rate of aged-PP was the lowest, which was 18.49%. This result shows that the aged microplastics such as PP may become an important carrier for MB to enter the water environment and biological tissues.