Carbon quantum dots as charge bridges: Photogenerated electrons flow alter microbial interactions and electron...

This study introduced carbon quantum dots (CQDs) into constructed wetland (CW) systems and to propose a previously unreported mechanism in which photogenerated electrons from CQDs act as electron bridges, thereby facilitating their integration into microbial electron transport chains. At the initial stage, the photoelectric conversion capability of CQDs supplied additional photoelectrons, effectively functioning as an extracellular biological electron transport pathway and temporarily increasing the redox potential of the system. Following depletion of the externally supplied photoelectrons, CQDs continued to enhance denitrification by upregulating the activities of key enzymes associated with microbial electron transport chains and the FeSN cycle. As a result, the incorporation of CQDs led to a maximum 3.19-fold increase in the abundance of denitrification-related genes within the microbial community and improved total nitrogen removal efficiency by up to 20%. These findings provide new insights into the application of nano photocatalytic materials in CW systems.