Enhancing Light Absorption and Prolonging Charge Separation in Carbon Quantum Dots via Cl-Doping for Visible-Light-Driven Photocharge-Transfer Reactions

Abstract

Limited light absorption beyond the UV region and rapid photocarrier recombination are critical impediments for the improved photocatalytic performance of carbon quantum dots (CQDs) under visible-light irradiation. Herein, we demonstrate single-step microwave-assisted syntheses of O-CQDs (typical CQDs terminated by carboxylic and hydroxyl functional groups) from a sucrose precursor and Cl-doped CQDs (Cl-CQDs) from a sucralose precursor in short reaction times and without using obligatory strong acids for Cl doping. The doping of Cl into the CQDs is observed to widen the absorption range and facilitate an enhanced separation of photoexcited charge carriers, which is confirmed by the results of optical absorption, photothermal response, and pump-probe ultrafast transient absorption spectroscopy measurements of the O-CQDs and Cl-CQDs. The photoexcited charge carriers with their longer lifetimes in Cl-CQDs enabled the quick degradation of methylene blue dye, rapid conversion of Ag + ions to metallic Ag nanoparticles on the CQD surfaces, and reduction of GO to a welldispersed rGO through the photoelectron transfer reactions under visible-light irradiation. The facile Cl doping strategy, hybridization of Ag nanoparticles or rGO to CQDs, and the elevated charge separation mechanism would open up new avenues in designing CQD-based materials for futuristic applications.

One-Step Green Solvothermal Synthesis of Full-Color Carbon Quantum Dots Based on a Doping Strategy

“…The second one is related to the surface states formed by various surface functional groups. The third is the synergistic effect of the carbon core and surface functional groups. ,− In this work, the double peaks of PL excitation spectra coincide with π → π* absorption peaks of the graphitized carbon core and n → π* absorption peaks of surface groups. This result indicates that the PL processes of CQDs are related to electronic transitions and there is strong coupling between core and surface functional groups.…”

“…For instance, N-doped CQDs, which were prepared with benzene-ammonia derivatives as the N source, − had relatively higher luminous efficiency and tunable luminescence. Chlorine (Cl) atom doping can provide additional energy levels, thereby generating multicolor fluorescence and optimizing the structure as well as luminescence properties of CQDs. − Therefore, doping heteroatoms efficiently and moderately is a possible solution for the “two crucial issues” of CQDs.…”

Halogen-Doped Carbon Dots: Synthesis, Application, and Prospects

“…To overcome the limited light absorption outside the UV region and extremely fast photocarrier recombination of CQDs, Murali et al [ 76 ] prepared Cl-CQDs from sucralose via microwave assisted synthesis. As shown in Figure 6 B, Cl doping increased the absorption range and promoted the separation of the photoexcited carriers.…”

Recent Advances in Quantum Dots for Photocatalytic CO2 Reduction: A Mini-Review

“…Carbon QDs (CQDs), with their sizes in the range of 20 nm, have attracted much attention for their photoluminescence properties and co-catalyst role in different photocatalytic reactions. They exhibit low toxicity, good chemical stability, and exceptional water solubility compared to widely used semiconductor photocatalysts (CdS, TiO 2 , etc) (Murali et al, 2021). Importantly, CQDs possess upconversion photoluminescence property that allows the utilization of NIR light.…”