image: undamentals and Challenges for Indirect and Direct Photocatalytic Conversion of Plastic Wastes into Valuable Fuels
Credit: ©Science China Press
Plastics, with excellent chemical stability and acid and alkaline resistance are widely used in our life and industrial production. Plastic brings us convenience, but also brings a lot of trouble to human life. According to the report of United Nations Environment Programme in 2018, all around the world, 430 million tons of plastics are produced every year, and more than two-thirds of these plastic products are disposable plastic products. Based on current trends, plastic pollution will contribute 19% of global greenhouse gas emissions by 2040, and plastic production could triple by 2060. These plastic pollutants will have a serious impact on the ecological environment and human health. Some chemicals used in plastic synthesis, such as antioxidants and plasticizers, may enter human tissues through the biological chain, greatly increasing the chances of cancer in humans. Moreover, plastic waste will also pollute the biological habitats of terrestrial and marine organisms, leading to the destruction of the ecological environment and significantly influencing the ecological balance. Plastics are mainly long chain polymer compounds de-rived from the polymerization of monomers. In our life we often see a variety of plastics, such as PET, PLA, PE, poly-ethylene (PP), polyvinyl chloride (PVC), polyurethane (PUR). With the gradual accumulation of plastic waste, people realize that plastic should be recycled in order not to affect human life.
In the early stage of research, people mainly through incineration disposal, landfill disposal and other traditional ways of plastic treatment, but this will also lead to serious environmental pollution and incomplete treatment of plastic. With the deepening of research, people found that plastic is also a valuable and recyclable carbon resource. Inappropriate treatment of plastics is also a waste of resources. For this reason, researchers are actively exploring methods to recycle plastics under mild conditions. In order to prevent secondary pollution during the plastic recycle process, researchers are focusing on the field of photo-catalysis as a clean and green energy source.
This review details a variety of strategies for converting plastics into valuable chemicals through photocatalysis. In detail, researchers outline the indirect conversion of PET with alkaline-assistant pretreatment. They also review the indirect conversion of PLA with alkaline-assistant and hydrothermal pretreatment. In addition, researchers highlight the indirect conversion of PE with hydrothermal pretreatment. Subsequently, they overview the direct conversion of PE through a two-step process. Besides, they summarize the direct conversion of PLA via an amination strategy. Moreover, they emphasize the direct conversion of PVC by a single ROS strategy. Finally, they offer some challenges and outlooks of photocatalytic conversion of plastics into valuable fuels in the future.