Carbon dot/non-conducting polymer composites for the photocatalytic degradation of organic dyes in wastewater: a review

Abstract Organic dyes found in wastewater negatively affect human, animal, and environmental health; therefore, they must be removed. One of the most promising approaches to dye removal is photocatalysis, where catalysts use light to generate electron–hole pairs that react with water and dissolved oxygen to produce powerful reactive oxygen species for oxidative degradation. Conventionally, photocatalysts are semiconductor metal oxide nanoparticles; however, because of their large band gaps, they have poor electron–hole generation efficiencies. Here, we investigate the viability of carbon dots as alternative photocatalysts. Research shows that heteroatom doping and surface functionalisation can be used to modify their electronic structure, allowing them to effectively utilise a much wider range of the electromagnetic spectrum to more efficiently produce the needed reactive oxygen species. Unfortunately, the propensity of carbon dots to aggregate reduces their photocatalytic efficiency; however, this can be prevented through the use of support materials. Due to the ability to obtain strong interfacial interactions with carbon dots, polymers have been identified as suitable supports. In particular, non-conducting polymers have recently been shown to be quite useful, modifying the electronic structure of the composite system by acting as electron traps. Furthermore, polymers exhibit good sorption properties: adsorbing water and oxygen molecules to promote reactive oxygen species generation; adsorbing dye molecules to allow more efficient degradation; and adsorbing the degradation products, enabling a more holistic approach to dye removal. Graphical Abstract