不同微塑料对亚甲基蓝的吸附行为

Adsorption behavior of methylene blue on diverse microplastics

微塑料易成为水中染料污染物的载体而形成复合污染,增加污染物的环境危害性.目前,关于微塑料对染料污染物的吸附研究十分有限.本文以亚甲基蓝(MB)为染料污染物的典型代表,系统的研究了聚苯乙烯(PS)、聚氯乙烯(PVC)和聚甲基丙烯酸甲酯(PMMA)的3种微塑料对MB的吸附行为和吸附机理,分析了溶液pH、盐度、腐殖酸、粒径、温度和自然水样对吸附的影响.结果表明,不同微塑料对MB的吸附能力顺序为:PMMA> PVC> PS.微塑料对MB的吸附过程用准二级动力学模型和Langmuir等温模型拟合较好,表明微塑料对MB的吸附为单分子层化学吸附.静电相互作用力和CH/π相互作用会促进微塑料对MB的吸附. PMMA和PVC与MB之间存在极性作用. PVC对MB的吸附还受卤素键的影响,PS和MB之间存在π–π相互作用.不同微塑料对MB的吸附性能存在差异,主要与微塑料的比表面积和官能团有关.溶液pH通过影响微塑料表面所带电荷进而影响吸附性能;NaCl和腐殖酸会与MB竞争微塑料表面的吸附位点;升高温度能促进PMMA和PVC对MB的吸附,却抑制PS对MB的吸附.相对于纯水体系,微塑料在自然水环境下对MB的吸附能力明显下降.

Microplastics might be prone to accumulate dye pollutants in the aquatic environment,increasing their potential environmental risks. However, there were rare studies on the interaction between microplastics and dye pollutants. In this study, the interaction between methylene blue(MB)and microplastics(polystyrene(PS), polyvinyl chloride(PVC), and polymethyl methacrylate(PMMA)) were thoroughly investigated, and the effects of pH, salinity, humic acid, particle size,temperature, and natural aquatic environment were considered. The adsorption capacity of MB on microplastics followed the order PMMA > PVC > PS. The sorption process for microplastics to MB could be well described by the pseudo-second-order model and Langmuir model, revealing that the adsorption was monolayer chemisorption. Electrostatic interaction and CH/π interaction could promote the adsorption of MB on microplastics. PMMA and PVC could combine with MB through polar interaction. The adsorption of PVC to MB was affected by halogen bonding, and there was a π-π interaction between PS and MB. The specific surface area and functional groups of microplastics were the main factors affecting the adsorption performance of MB on microplastics. The sorption process exhibited a pronounced pH dependency due to the effect of pH on the surface charge of the microplastics. The presence of NaCl and humic acid could compete with MB for adsorption sites on the surface of microplastics. High temperature promoted the adsorption of MB on PVC and PMMA but inhibited that of PS. Moreover, the adsorption capacities of MB on microplastics were significantly reduced in the natural aquatic environment(Xiang River).