Surface Charge Alteration in Carbon Dots Governs the Interfacial Electron Transfer and Transport

Abstract

Photoinduced electron transfer (PET) is a widely studied phenomenon in nanoscale carbon dots (CDs) due to the availability of free electrons on their surfaces. It is often treated as a molecular ruler to understand the interaction between nearby donor and acceptor pairs. The current report highlights the modulation of the electron transfer (ET) process in redox-treated CDs with an acceptor molecule, menadione (MD), when subjected to a microemulsion method. In the presence of cationic CTAB micellar heterogeneity, the ET kinetics get markedly altered due to the controlled diffusion dynamics of the reactant inside the microemulsion. In CTAB micellar media, reduced CDs (RCDs) show a higher ET efficiency with MD compared to the oxidized CDs (OCDs), owing to the substantial change in their surface charge and the stronger Coulombic interaction with the micellar interface. Moreover, the presence of CTAB moieties with RCDs greatly influences the local conductance and the electrical band gap at the single molecular level as noticed from current sensing atomic force microscopy measurements compared to OCDs. The current–voltage (I–V) measurements are observed to be nonlinear, revealing both direct and Fowler–Nordheim (FN) types of tunneling, while the presence of MD abruptly enhances the conductance linearly, curtailing the FN tunneling.