Adsorption of methylene blue from aqueous solutions using carboxyl/nitro-functionalized microparticles derived from polypropylene waste

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 degrees 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 degrees 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

Automated summary

This study investigated the feasibility of using waste polypropylene film to prepare functionalized polypropylene microparticles for the adsorption of methylene blue from aqueous solutions. The results showed that increasing polymer dosage, pH, and contact time improved the removal of methylene blue from water. The kinetic and equilibrium studies suggested that the adsorption process followed a chemisorption mechanism, with a maximum adsorption capacity achieved under specific temperature and pH conditions.