Effect of Nitrogen Doping Level on the Performance of N‐Doped Carbon Quantum Dot/TiO2 Composites for Photocatalytic Hydrogen Evolution

Carbon quantum dots (CQDs) have attracted widespread interest for photocatalytic applications, owing to their low cost and excellent electron donor/acceptor properties. However, their advancement as visible‐light photosensitizers in CQDs/semiconductor nanocomposites is currently impaired by their poor quantum yields (QYs). Herein, we describe the successful fabrication of a series of nitrogen‐doped CQDs (NCDs) with N/C atomic ratios ranging from 0.14–0.30. NCDs with the highest N‐doping level afforded a remarkable external QY of 66.8 % at 360 nm, and outstanding electron transfer properties and photosensitization efficiencies when physically adsorbed on P25 TiO2. A NCDs/P25‐TiO2 hybrid demonstrated excellent performance for hydrogen evolution in aqueous methanol under both UV and visible‐light illumination relative to pristine P25 TiO2. Controlled nitrogen doping of CQDs therefore represents a very effective strategy for optimizing the performance of CQDs/semiconductor hybrid photocatalysts. Dots the way, a‐ha, a‐ha, I like it: N‐doped carbon quantum dots (NCDs) with high N/C atomic ratios (0.14–0.30) were fabricated by a facile hydrothermal process. N‐doping suppressed nonradiative quenching in the NCDs, delivering photoluminescence quantum yields as high as 68 %. NCDs/P25‐TiO2 composites showed good activity for photocatalytic H2 evolution under both UV and visible illumination, which can be attributed to efficient excitation wavelength‐dependent interfacial charge transfer.