Sulfonated polypropylene microparticles from waste as adsorbents for methylene blue: Kinetic, equilibrium, and thermodynamic studies

Dyes discharged into waste streams have threatened the lives of aquatic ecosystems and human beings. This work studied the effectiveness of converting polypropylene (PP) waste films into sulfonated microparticles (SPP) for removing methylene blue dye (MB) from aqueous solutions. PP waste was recycled into microparticles (8 µm) and sulfonated in sulfuric acid at 100°C for (6 h). FT-IR analysis proved the existence of sulfonic, carboxylic, and C = C groups on the surface of SPP microparticles. The concentration of acid groups, morphology, surface area, and wettability of SPP were investigated. The effects of the adsorbent dosage, contact time, pH of MB solution, temperature, and ionic strength on the adsorption process were studied. The experimental data of the adsorption process fit well with pseudo-second-order kinetic model and Langmuir isotherm disclosing that the adsorption was chemisorption. A maximum adsorption capacity of 45 mg MB g−1 SPP microparticles was realized at 20°C and neutral pH (6.5). The free energy change showed a negative value reflecting the feasibility and spontaneity of the adsorption process. Accordingly, waste PP can be recycled into a valuable adsorbent for the removal of cationic dyes from polluted water after a proper treatment such as sulfonation.