Discharging methylene blue (MB) dye into waste streams has caused severe environmental problems to the aquatic life ecosystem and hence to human beings. Hence, this work investigated the feasibility to use polypropylene (PP) film waste to prepare carboxyl/nitro-functionalized PP microparticles (COOH/NO₂-PP) for the adsorption of MB from aqueous solutions. PP powder was prepared by dissolution/precipitation method from PP film waste, followed by treatment with nitric acid at 130 °C. ATR-FTIR analysis proved the structure of PP and the existence of carboxyl and nitro groups on the surface. The enhancement in surface hydrophilicity of PP after treatment was confirmed by contact angle measurements. The effects of polymer dosage, pH, and contact time on the adsorption process were studied. The results showed that the removal of MB from water increased with increasing these parameters. The kinetic and equilibrium studies showed that the Langmuir isotherm and pseudo-second-order kinetic model fitted the experimental data well. This suggested that the adsorption process was chemisorption. A maximum adsorption capacity of 14.33 mg MB/g-polymer was achieved at 23 °C and neutral pH (6.5). The free energy change had a negative value, which signifies the spontaneity of the adsorption process. Thereby, waste PP can be converted into useful adsorbents for treating cationic dye-polluted water.

Graphic abstract

中文翻译：

---

使用源自聚丙烯废物的羧基/硝基官能化微粒从水溶液中吸附亚甲蓝

将亚甲蓝 (MB) 染料排放到废物流中已对水生生物生态系统和人类造成严重的环境问题。因此，这项工作研究了使用聚丙烯 (PP) 薄膜废料制备羧基/硝基官能化 PP 微粒（COOH/NO ₂-PP) 用于从水溶液中吸附 MB。PP 粉末是通过溶解/沉淀法从 PP 薄膜废料中制备的，然后在 130 °C 下用硝酸处理。ATR-FTIR分析证明了PP的结构以及表面存在羧基和硝基。处理后 PP 表面亲水性的增强通过接触角测量得到证实。研究了聚合物用量、pH 值和接触时间对吸附过程的影响。结果表明，随着这些参数的增加，MB 从水中的去除率增加。动力学和平衡研究表明Langmuir等温线和准二级动力学模型与实验数据拟合良好。这表明吸附过程是化学吸附。最大吸附容量 14。在 23 °C 和中性 pH (6.5) 下达到 33 mg MB/g-聚合物。自由能变化为负值，表明吸附过程是自发性的。因此，废PP可以转化为有用的吸附剂，用于处理阳离子染料污染的水。

图形摘要