Recent Studies on Chemical Degradation of Microplastics: A Review

Abstract

The microplastic (MP) is a persistent contaminant that is commonly found in water, soil, sediments and air, and is less than 5 mm in size. This review aims to present the summary of recent studies concerning their chemical degradation, which include oxidative, photochemical, hydrolysis, advanced oxidation processes and free-radical. It also discusses the factors that determine the degradation efficiency: polymer composition, pH, crystallinity, catalysts, UV intensity and dose of oxidants. Recent technologies such as Fenton and photo-Fenton oxidation, ozonation, hydrogen peroxide treatment, persulfate activation, photocatalysis and electrochemical oxidation are discussed and compared on the basis of species generated, applicable polymers, advantages, and disadvantages. These methods can speed up the chain scission and partial mineralisation, but some challenges are still left unsolved: incomplete degradation, toxicity of intermediates, recovery of catalysts, energy demand and scale-up. The use of recyclable catalysts, real-environment validation, standardised assessment methods, and integration with biological treatment to realize sustainable microplastic remediation at practical scales with minimal secondary pollution should be emphasised in future research.