Red Emissive Upconversion Carbon Quantum Dots Modifying TiO<sub>2</sub> for Enhanced Photocatalytic Performance
Shokir Khojiev, Gulmira Hojiyeva, Oybek Tursunkulov, Dan Chen, Hemdan S.H. Mohamed, Abduvali Kholikov, Khamdam Akbarov, Jing Liu, Yu Li
Abstract
Carbon quantum dot (CQD) decorated semiconductor materials have become promising photocatalysts in photocatalysis, with a chance to solve energy and environmental crises. Red emissive carbon quantum dots (R-CQDs) have excellent photoluminescence (PL), upconversion, narrowed band structure, electron-accepting, and transmission properties compared to other colors emitting CQDs. In this work, we use the as-synthesized R-CQDs to decorate P25 (R-CQDs/P25) for highly enhanced visible-light photocatalysis. The results show that the photocatalytic performance of the R-CQDs/P25 composites is considerably enhanced with the increasing amount of R-CQDs in the visible-light region. The red emissive upconversion R-CQDs play dual roles as a cocatalyst to separate the photogenerated carriers and an upconversion converter from lower energetic photons to high energetic photons. Various measurements reveal that the R-CQD/P25 photocatalysts have a narrowed band gap, improved charge transfer efficiency, and lower recombination rate, synergistically endowing the R-CQDs/P25 composites with excellent photocatalytic performance. The R-CQD/P25–2.5 composite exhibits the highest photocatalytic activity, which is ∼10 times higher for hydrogen evolution and ∼20 times higher for the photodegradation of methylene blue (MB) compared to pure P25, and its apparent quantum yield (AQY) is 4.94% under 450 nm monochromatic light. This work opens the door for rational design of different fluorescence CQDs and their potential application for solar hydrogen production in a low-cost noble-metal-free system.