Hydrothermal integrated chemical treatment of mps for efficient degradation: Mechanistic insight and degradation behavior

Microplastics (MPs) pollution has become a hot topic for researchers due to its common presence in the environment. However, the low efficiency of the existing methods for removing MPs from an environment is a limitation. Advanced oxidation processes are cutting-edge methods for MPs degradation. This review highlights the role of chemical treatments in hydrothermal methods, focusing on mechanisms that enhance MP degradation efficiency. Hydrothermal methods, such as subcritical and supercritical water treatments, break down polymers into smaller molecules, producing 22 % gases and 95.5 % liquids. The integration of chemical reagents such as acids (HCl, H₂SO₄), bases (NaOH, KOH), and oxidizing agents (H₂O₂, KMnO₄) significantly enhances degradation efficiency by catalyzing hydrolysis, oxidation, and depolymerization. Acids facilitate polymer chain cleavage, bases accelerate hydrolysis, and oxidizing agents generate reactive oxygen species (ROS) that mineralize MPs into harmless by-products like CO₂ and water. The degradation behavior of MPs varies by polymer type, with polyethylene (PE) and polypropylene (PP) undergoing thermal degradation and oxidation, while polyethylene terephthalate (PET) and polyvinyl chloride (PVC) are more susceptible to hydrolysis and dechlorination. The analysis of degradation products, including gas-phase hydrocarbons, liquid-phase oils, and solid-phase char, reveals potential for resource recovery, though the toxicity of by-products, such as phthalates and bisphenol A, poses environmental risks. Future research should prioritize the optimization of HICT with respect to scalability, material stability, reactor compatibility, and environmental safety, while also aiming to minimize the formation of toxic by-products. Addressing these challenges will advance sustainable solutions for mitigating MPs pollution and its ecological impacts.