Light-Induced Hypoxia in Carbon Quantum Dots and Ultrahigh Photocatalytic Efficiency

Abstract

Carbon quantum dots (CQDs) represent a class of carbon materials exhibiting photoresponse and many potential applications. Here, we present a unique property that dissolved CQDs capture large amounts of molecular oxygen from the air, the quantity of which can be controlled by light irradiation. The O2 content can be varied between a remarkable 1 wt % of the CQDs in the dark to nearly half of it under illumination, in a reversible manner. Moreover, O2 depletion enhances away from the air–solution interface as the nearby CQDs quickly regain them from the air, creating a pronounced concentration gradient in the solution. We elucidate the role of the CQD functional groups and show that excitons generated under light are responsible for their tunable adsorbed-oxygen content. Because of O2 enrichment, the photocatalytic efficiency of the CQDs toward oxidation of benzylamines in the air is the same as under oxygen flow and far higher than the existing photocatalysts. The findings should encourage the development of a new class of oxygen-enricher materials and air as a sustainable oxidant in chemical transformations.

Self-assembly of a heterogeneous microreactor with carbon dots embedded in Ti-MOF derived ZnIn2S4/TiO2 microcapsules for efficient CO2 photoreduction

“…18–24 With CDs in a microreactor system, the transportation of photogenerated electrons in the encapsulation system will become faster and more efficient. 25 CDs as electron storage containers may capture more electrons from the semiconductor catalyst and regulate the local charge distribution, thus acquiring more electrons to produce CH 4 . 26 Also, CDs may facilitate the water oxidation reaction to provide more protons for CH 4 instead of H 2 .…”

Spatial Decoupling of Redox Chemistry for Efficient and Highly Selective Amine Photoconversion to Imines

“…In sharp contrast, NBI and H 2 generation on CoP@ZnIn 2 S 4 coaxial nanorods proceeds efficiently and steadily, with NBI selectivity staying around 100% (Figure 2b,c); importantly, the NBI generation rate on CoP@ZnIn 2 S 4 reaches 3.82 mmol g −1 h −1 as compared to 0.08 mmol g −1 h −1 on pristine ZnIn 2 S 4 . Proton nuclear magnetic resonance 1 H NMR (Figure S10a−c) and 13 C NMR (Figure S10d−f) characterizations also confirm that the main products obtained on ZnIn 2 S 4 and CoP@ZnIn 2 S 4 are DBA and NBI, respectively. Three consecutive experiments demonstrate the unique ability of CoP@ZnIn 2 S 4 to maintain its high NBI selectivity, although the generation rates of NBI and H 2 drop slightly due to possible photocorrosion of ZnIn 2 S 4 (Figure 2d).…”

“…Imines that contain an unsaturated CN group are important intermediates for applications in pharmaceuticals, organometallic chemistry, agrochemicals, and coordination polymers. − Oxidative coupling of primary amines and condensation of amines with aldehydes are popular strategies for the synthesis of imines. − Nevertheless, elevated temperatures and acidic (or basic) reaction environments are typically required to drive and catalyze these reactions. Alternatively, light-driven dimerization of primary amines emerges as an attractive approach to imine generation due to its mild reaction conditions, free emission of pollutants. − …”

“…This concept of spatial isolation of redox chemistry and associated design principles for photocatalytic systems present a key progress in photocatalytic transformation of primary amines to imines, and would also offer valuable insights into the selective synthesis of other fine chemicals.The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/jacs.2c12182. Details of the synthesis, SEM and TEM images, XRD patterns, XPS spectra, surface area and pore volume analyses, 1 H and13 C NMR spectra, TPD−MS analysis, DFT calculation, and additional reaction data (PDF) Nanjing 210093, PR China Yuanqi Wang − National Laboratory of Solid State Microstructures, School of Physics, Nanjing University, Nanjing 210093, PR China; Jiangsu Key Laboratory for Nano Technology, College of Engineering and Applied Sciences, Nanjing University, Nanjing 210093, PR China Huiting Huang − Jiangsu Key Laboratory for Nano Technology, College of Engineering and Applied Sciences, Nanjing University, Nanjing 210093, PR China; orcid.org/0000-0001-7906-6122 Jun Wang − National Laboratory of Solid State Microstructures, School of Physics, Nanjing University,…”

Carbon-Dots-Modified Hierarchical ZnIn2S4/Ni–Al LDH Heterojunction with Boosted Charge Transfer for Visible-Light-Driven Photocatalytic H2 Evolution

“…Thus, the coupling of ZnIn 2 S 4 and Ni–Al LDH can predictably construct an efficient heterojunction to promote photocatalytic hydrogen production . Furthermore, the carbon dots (CDs) as a new type of 0D metal-free alternative are often used as electron mediators to enhance the photocatalytic activity in heterojunction catalysts on account of less toxicity, size effect, and excellent charge transfer ability. − In addition, CDs as a cocatalyst can effectively utilize the full spectrum of solar light and possess abundant active sites for photocatalytic H 2 generation . Consequently, CDs modify the ZnIn 2 S 4 /Ni–Al LDHs to construct a ternary catalytic system, which can overcome the rapid charge recombination and boost the electron transfer efficiency.…”