Modulating In-Plane Defective Density of Carbon Nanotubes by Graphitic Carbon Nitride Quantum Dots for Enhanced Triiodide Reduction

The catalytic performance of carbon nanotubes has still been hindered by the intrinsic and limited in-plane electrocatalytic active sites, with a focus on improving their catalytic activity by covalent modifications, which require the relatively high energy input to dissociate the in-plane atoms and create the active sites. Herein, an effective route is developed to modulate the in-plane defective density and electronic structure of multi-walled carbon nanotubes (MWCNTs) by ultra-small-sized g-C3N4 quantum dots (CNQDs) with abundant nitrogen species via p-p stacking. The non-covalent bonded CNQDs on MWCNTs endow them with abundant catalytic active sites on the basal plane, still inheriting the intrinsic and fast electron-transfer characteristics of MWCNTs. The optimized CNQDs/MWCNTs-4 heterogeneous catalyst exhibits an optimal photoelectric conversion efficiency of up to 8.30% in probing reaction for triiodide reduction, outperforming the Pt reference (7.86%). The thermodynamic calculations further reveal that the CNQDs integrated on MWCNTs are capable of reducing the reaction energy barrier (?G) of the rate-determining step from I-2 to I- and adsorption state I*. The present study provides an efficient and non-covalent strategy to construct excellent carbon-based catalysts with abundant active sites, which is also enlightening for the preparation and application of other carbon-based catalysts.