Photothermally-driven thermo-oxidative degradation of low density polyethylene: heterogeneous heating plus a complex reaction leads to homogeneous chemistry

Recent advances in oxidative degradation of plastics

Oxidative degradation is a powerful method to degrade plastics into oligomers and small oxidized products. While thermal energy has been conventionally employed as an external stimulus, recent advances in photochemistry have enabled photocatalytic oxidative degradation of polymers under mild conditions. This tutorial review presents an overview of oxidative degradation, from its earliest examples to emerging strategies. This review briefly discusses the motivation and the development of thermal oxidative degradation of polymers with a focus on underlying mechanisms. Then, we will examine modern studies primarily relevant to catalytic thermal oxidative degradation and photocatalytic oxidative degradation. Lastly, we highlight some unique studies using unconventional approaches for oxidative polymer degradation, such as electrochemistry.

Environmental behaviors and degradation methods of microplastics in different environmental media

Microplastics, as a group of emerging contaminants, are widely present in environmental media and have the potential to endanger the ecological environment and human health. Due to the inconsistencies and difficulties inherent in the analysis of microplastic particles, global monitoring data on the distribution of microplastics in the environment are still far from sufficient. The fate and migration of microplastics in the environment are also uncertain. Therefore, there have been increasing reviews on the distribution, biological effects, migration, and health risks of microplastics. However, reports focusing on the degradation of microplastics are still rare. Understanding and commanding the environmental behavior of microplastics are of great significance to explore the treatment of microplastic pollution. Although some preliminary studies on microplastics have been carried out, there is still an urgent need to conduct a comprehensive study on environmental behaviors and degradation methods of microplastics in different environmental media. This article summarizes the recent advances on microplastics, basically includes the distribution and ecological impact of microplastics in soil and water environments, then elaborates the migration behavior and influencing factors of microplastics, and focuses on the research progress of microplastics degradation methods. On this basis, the problems existing in the current research and the future development directions have been proposed. This review could provide a more systematic reference for the development and research of microplastics in the future.

Degradation of polyvinyl chloride microplastics via an electro-Fenton-like system with a TiO2/graphite cathode

Nowadays, microplastic pollution has been brought into focus for its hazards to aquatic life. However, researches on the electrocatalytic treatment for efficient degradation of microplastics are still insufficient. Herein, an electro-Fenton like (EF-like) technology based on TiO₂/graphite (TiO₂/C) cathode was put forward to degrade polyvinyl chloride (PVC), a typical microplastic in water. It exhibited a remarkable performance on PVC degradation via cathodic reduction dechlorination and hydroxyl radical (OH) oxidation simultaneously. Besides, the effects of reaction temperature and initial PVC concentration were investigated. Under optimal conditions, the dechlorination efficiency of PVC reached 75 % after potentiostatic electrolysis at -0.7 V vs. Ag/AgCl for 6 h. The intermediate products were explored during the degradation of PVC microplastics. The surface morphologies and molecular weight of PVC changed accordingly. Based on these results, a possible degradation process for PVC was proposed. This work demonstrated that such a heterogeneous EF-like technology using TiO₂/C cathode was hopefully to provide an eco-friendly method for microplastic wastewater treatment.

Nanoparticle-based photothermal heating to drive chemical reactions within a solid: using inhomogeneous polymer degradation to manipulate mechanical properties and segregate carbonaceous by-products

Photothermal heating via metal nanoparticles is utilized to degrade polyethylcyanoacrylate (PECA), which undergoes a thermally-driven depolymerization process, resulting in (i) monomer loss from the sample, (ii) repolymerization to form shorter chains (oligomer), and (iii) formation of carbonaceous by-products which are graphene-like and luminescent. These unique PECA properties are used to demonstrate the heterogeneous temperature distribution present during photothermal processing and the results are compared to degradation via conventional methods where a uniform temperature is present. Photothermal heating results in formation of pockets of depolymerized material around each nanoscale heating site. The characteristic size of these photothermally-generated mechanical defects is determined from changes in the material's tensile strength. Changes in mass loss and molecular weight are utilized to determine the fraction of the sample that has depolymerized: distributing this volume equally to each heating site (based on the nanoparticle concentration) results in a volume that matches the defect size from independent mechanical measurements. In this way, macroscopic measurements elucidate the mesoscopic pattern of photothermal degradation. Sample morphology on scales from millimeters to nanometers is assessed via optical and electron microscopy. The carbonaceous by-products of degradation form in the hot region around each nanoparticle during photothermal heating, as revealed by transmission electron microscopy studies. Heterogeneous heating is also evident from optical images where starch granules, employed as an inert dilute additive to enhance PECA mechanical properties, also become luminescent due to degradation in "hot spots" created by the overlap of warm regions from nearby nanoparticle sites. Beyond the fundamental knowledge gained by these studies, the results demonstrate the ability to manipulate the connection between mechanical properties and chemical degradation which is important for developing new strategies for management of polymeric waste.