Ji-Shi Wei

Full-Color Light-Emitting Carbon Dots with a Surface-State-Controlled Luminescence Mechanism

Carbon dots (CDs) with tunable photoluminescence (PL) and a quantum yield of up to 35% in water were hydrothermally synthesized in one pot and separated via silica column chromatography. These separated CDs emitted bright and stable luminescence in gradient colors from blue to red under a single-wavelength UV light. They exhibited high optical uniformity; that is, every sample showed only one peak in the PL excitation spectrum, only one peak in the excitation-independent PL emission spectrum, and similar monoexponential fluorescence lifetimes. Although these samples had similar distributions of particle size and graphite structure in their carbon cores, the surface state gradually varied among the samples, especially the degree of oxidation. Therefore, the observed red shift in their emission peaks from 440 to 625 nm was ascribed to a gradual reduction in their band gaps with the increasing incorporation of oxygen species into their surface structures. These energy bands were found to depend on the surface groups and structures but not on the particle size, not as in traditional semiconductor quantum dots. In addition, because of their excellent PL properties and low cytotoxicity, these CDs could be used to image cells in different colors under a single-wavelength light source, and the red-emitting CDs could be used to image live mice because of the strong penetration capability of their fluorescence.

Hierarchical porous carbon materials with high capacitance derived from Schiff-base networks.

A type of hierarchical porous carbon material was prepared using a Schiff-base network as the precursor and ZnCl2 as the activation agent, and their electrochemical performances were investigated in acid and alkaline aqueous solutions, respectively. The as-prepared materials have high surface areas, appropriate distributions of hierarchical pore sizes, and various forms of nitrogen/oxygen derivatives. These structural advantages guarantee the outstanding performances of such carbon materials as electrodes for supercapacitors, which include high specific capacitances, fast current responses, and high cycling stabilities.

Carbon Dots/NiCo2O4 Nanocomposites with Various Morphologies for High Performance Supercapacitors

A series of carbon dots/NiCo2 O4 composites with various morphologies are prepared and tested for supercapacitors. These samples have good electrical conductivities and efficient ions transport paths, so they exhibit high specific capacitances, superior rate performances, and high cycling stabilities. The optimal composite for hybrid supercapacitor exhibits a high energy density up to 62.0 Wh kg-1 .

Red-Emissive Carbon Dots for Fingerprints Detection by Spray Method: Coffee Ring Effect and Unquenched Fluorescence in Drying Process

Brightly red fluorescent carbon dots are synthesized hydrothermally and dissolved in diluted hydrochloric acid solution. Such carbon dots exhibit excitation-independent emission at about 620 nm with quantum yield over 10%, which is visible in daylight. After the carbon dots solution is sprayed to the fingerprints on various solid substrates and dried in air, clear fingerprints can be seen under an ultraviolet lamp and stay stable for 1 day. Detailed characterizations suggest that during the drying process, the coffee-ring effect and the electrostatic interactions between the carbon dots and the fingerprint residues prevent the typical aggregation-induced fluorescence quenching of carbon dots.

Facile synthesis of red-emitting carbon dots from pulp-free lemon juice for bioimaging

In this work, red-emitting carbon dots (R-CDs) with a high quantum yield (QY) of 28% in water were synthesized for the first time by heating an ethanol solution of pulp-free lemon juice. The obtained R-CDs were mono-dispersed with an average diameter of 4.6 nm, and exhibited excitation-independent emission at 631 nm. Meanwhile, these R-CDs featured low cytotoxicity and good photostability, which allow R-CDs to be employed as luminescent probes for in vitro/in vivo bioimaging. In addition, a detailed study on the physical properties and structural compositions of the sodium borohydride (NaBH4) reduced R-CDs with orange emission suggested that surface states on the R-CD surfaces and nitrogen-derived structures in the R-CD cores synergistically caused their intense red luminescence. The low-cost and eco-friendly synthesis method and favorable optical properties of R-CDs make these carbon dots promising for further applications, such as bioimaging and light-emitting diodes.

Highly Efficient Red-Emitting Carbon Dots with Gram-Scale Yield for Bioimaging

Carbon dots (CDs) are a new class of photoluminescent (PL), biocompatible, environment-friendly, and low-cost carbon nanomaterials. Synthesis of highly efficient red-emitting carbon dots (R-CDs) on a gram scale is a great challenge at present, which heavily restricts the wide applications of CDs in the bioimaging field. Herein, R-CDs with a high quantum yield (QY) of 53% are produced on a gram scale by heating a formamide solution of citric acid and ethylenediamine. The as-prepared R-CDs have an average size of 4.1 nm and a nitrogen content of about 30%, with an excitation-independent emission at 627 nm. After detailed characterizations, such strong red fluorescence is ascribed to the contribution from the nitrogen- and oxygen-related surface states and the nitrogen-derived structures in the R-CD cores. Our R-CDs show good photostability and low cytotoxicity, and thus they are excellent red fluorescence probes for bioimaging both in vitro and in vivo.

Self-Assembled ZnO Nanoparticle Capsules for Carrying and Delivering Isotretinoin to Cancer Cells

ZnO@polymer core-shell nanoparticles are assembled into novel capsule shells with diameters of about 100 nm to load isotretinoin (ISO) with a capacity as high as 34.6 wt %. Although ISO, a widely used drug for acne treatment, by itself is not suitable for treating cancer because of its hydrophobicity, our ZnO-ISO composite showed much stronger anticancer activity. The improved cytotoxicity is ascribed to the synergistic effects of the ZnO@polymer and ISO, where the ZnO@polymer helps in the accumulation of ISO in cancer cells on the one hand, and on the other hand, ISO is released completely through ZnO decomposition under acidic conditions of cancer cells. Such a pH-triggered drug-delivery system exhibits a much improved killing of cancer cells in vitro in comparison with the benchmarks, Nintedanib and Crizotinib, two commercial drugs clinically applied against lung cancer.

Preparation of porous carbon electrodes from semen cassiae for high-performance electric double-layer capacitors

A series of sponge-like hierarchical porous carbons are prepared using semen cassiae as the precursor and potassium oxalate monohydrate as the activation agent. These sponge-like carbon materials have high surface areas, wide distributions of pore size, and the appropriate forms of nitrogen/oxygen derivatives. All these advantages in structures and surface states contribute to the outstanding performances of such materials as electrodes for high performance electric double-layer capacitors, which include high specific capacitance, high cycling stability, and high energy density. For example, the optimal sample exhibits a high specific capacitance of 401 F g−1, excellent cycling stability (94.5% retention after 10 000 cycles), high energy density (12.01 W h kg−1) and a high power density (10 200 W kg−1) in 1 M H2SO4 solution.