Catalyst Design and Engineering for Enhanced Microplastic Degradation and Upcycling - A Review

Microplastics (MPs) are defined as “synthetic solid particles or polymeric matrices, with regular or irregular shape and with size ranging from 1 μm to 5 mm”. They can originate from a variety of sources, such as synthetic textiles, city dust, tires, road markings, marine coatings, personal care products and engineered plastic pellets etc. During the lifetime of larger plastic debris, smaller and smaller pieces tend to form through degradation. Microplastics are challenging to collect and degrade due to its intrinsic chemical stability and small size. Despite being small in size, they are posing a great threat to both human beings and ecosystem. Besides, these tiny particles easily pass through water filtration systems and end up in the ocean and lakes, posing a potential threat to aquatic life. Extensive research has been conducted to find sustainable plastic alternatives or efficient removal approaches; while it remains in the early stage. To effectively mitigate the adverse effect caused by MPs, one of the solutions is through catalytic degradation with reduced time and energy demand and even gearing toward selective formation of useful products as a circular upcycling strategy. The catalytic approaches can be through photo, thermal, biological or electrochemical routes. Catalyst development for MPs degradation and upcycling lately has been actively conducted, however, a systematic and timely summary is lacking. Therefore, in this review, the design and engineering of novel catalysts with improved activity, selectivity, and stability especially for MPs degradation and upcycling are discussed, aiming to provide a thorough and timely reference for current status of MPs degradation catalysts, reaction mechanism, challenges and future opportunities.