Recent advances of CDs-based ternary heterojunctions for enhancing photocatalytic performance in the degradation of organic pollutants: A review

Wastewater containing organic pollutants, such as dyes, antibiotics or pesticides, is a major environmental problem. Photocatalysis is an effective, environmentally friendly and economically viable method for degrading hazardous organic pollutants in wastewater. Among the heterojunction systems, the ternary heterojunction system is the most effective system due to its higher electron transfer, excellent redox capacity and light-harvesting ability, which are advantageous in photocatalytic degradation of organic pollutants. Carbon dots (CDs) are often used as a component in ternary heterojunctions due to their strong absorption within the various regions of the solar spectrum, tunable band structure and up-conversion photoluminescence (UCPL) properties. The optical properties of CDs-based ternary heterojunctions enable faster migration of multiple carriers, effective utilization of sunlight and a shorter migration pathway which enhances the organic pollutant photodegradation efficiency. A profound understanding of the synergistic effects between CDs and semiconductors in ternary heterojunction systems as photocatalysts for organic pollutants degradation is essential for future development. In this review, we comprehensively discuss recent advances of CDs derived from various precursors and their utilization in ternary heterojunction photocatalysts. Furthermore, we conduct a critical analysis on the synergistic effect between CDs and semiconductors for fabricating photocatalysts with optimal organic pollutant degradation performance. In addition, we elaborate on the charge transfer reaction mechanisms and several factors that influence the performance of CDs-based ternary heterojunctions. We also present research gaps in the use of CDs-based heterojunctions for organic pollutant degradation and state future perspectives and research areas. This review provides an insightful discussion on the development of CDs-based ternary heterojunctions for organic pollutant degradation.