Co-dopant engineering of copper-doped carbon dots: mechanistic control of ROS catalysis

Co-dopant engineering can alter copper-centered redox activity in carbon dots (CDs), but links among composition, coordination structure, electron transfer, and reactive oxygen species (ROS) remain incompletely resolved. This review critically examines Cu-CD systems containing N, Zn, I, or Cl, distinguishing evidence for coupled co-doping from surface association and phase-separated species. It evaluates how carbon-matrix heterogeneity, Cu speciation, co-dopant location, surface functionality, and reaction conditions influence Cu(I)/Cu(II) cycling and ROS generation or scavenging. Studies of photocatalytic oxidation, antioxidant nanozymes, peroxidase-like catalysis, sensing, and ROS-mediated therapy reveal context-dependent responses that cannot be assigned to nominal dopant identity alone. However, differences in synthesis, assays, and structural characterization limit direct comparisons and causal attribution. We identify priorities for coordination-sensitive and operando measurements, accessible-site-normalized kinetics, leaching controls, and independent-batch testing. The proposed framework organizes the available evidence and identifies experimentally testable relationships between structure and catalytic behavior. It is intended to guide hypothesis generation and the design of matched studies; it has not been validated as a model that predicts ROS selectivity or catalytic performance across Cu-CD formulations.