Zhengwei Zhang

Preparation of carbon quantum dots based on starch and their spectral properties

A simple method for the synthesis of water-soluble carbon quantum dots (CQDs) has been developed based on chemical oxidation of starch. The structures and optical properties of the CQDs were characterized by ultraviolet-visible (UV-Vis) spectroscopy, photoluminescence spectroscopy (PL) and transmission electron microscopy. The CQDs were found to emit bright blue fluorescence and disperse uniformly. The effects of ambient temperature, light and pH on the properties of CQDs were studied. The CQDs exhibited good chemical stability, good photostability and pH sensitivity. Furthermore, the interaction between CQDs and bovine serum albumin (BSA) was investigated.

Chemiluminescence determination of potassium bromate in flour based on flow injection analysis.

A novel and highly sensitive flow-injection chemiluminescence method for the determination of potassium bromate (KBrO3) has been developed. This method is based on the luminescence properties of the KBrO3-Na2SO3-quinine sulfate system in acid medium. Optimized experimental conditions and a possible mechanism were investigated. The relative chemiluminescence intensity responded linearly to the concentration of KBrO3 in the range of 7.054 × 10(-6)-1.008 × 10(-4) mol/L with a detection limit of 2.116 × 10(-6) mol/L. The relative standard deviation (RSD) at 5.0 × 10(-5) mol/L KBrO3 (n = 12) was 2.3%. The proposed method was applied successfully to the determination of KBrO3 in flour.

CuInS2/ZnS/TGA Nanocomposite Photocatalysts: Synthesis, Characterization and Photocatalytic Activity

Herein, the CuInS2/ZnS/TGA quantum dots (QDs) were prepared by the oil phase reaction containing thioglycolic acid (TGA) as a functional modification agent under a nitrogen atmosphere. The CuInS2/ZnS/TGA QDs using as the photocatalysts exhibited high photocatalytic activity for the degradation of Rhodamine B (RhB) under ultraviolet irradiation. The photocatalytic conditions were optimized to degrade RhB with superior performances, including the initial RhB and CuInS2/ZnS/TGA QDs concentrations, solution pH values and ultraviolet light intensities. Furthermore, the kinetic equations of photocatalytic reaction and possible photocatalytic degradation mechanism were investigated. The results indicated that it belongs to the typical first order kinetic in accordance with the Langmuir–Hinshelwood mechanism, and the electrons and holes on the surface of the CuInS2/ZnS/TGA microspheres are the main acting forces during the RhB photocatalytic degradation.Graphical Abstract

The synthesis and modification of CdTe/CdS core shell quantum dots

A simple and economical synthesis method of CdTe quantum dots (QDs) has been developed using glutathione as a modifier in an aqueous system. The fluorescent properties of as-prepared CdTe QDs at different reaction times were studied to optimize the synthesis conditions. CdTe/CdS QDs with core-shell structure was obtained by modifying as-synthesized CdTe QDs with refluxing and microwave method, respectively. The properties of the CdTe/CdS QDs were thoroughly investigated by photoluminescence (PL) and inverted fluorescence microscope, and exhibited high fluorescence intensity and good optical property. The study also shows that the microwave synthesis of CdTe/CdS QDs had more dispersed particle size and higher fluorescence intensity.

One‐pot synthesis of fluorescent nitrogen‐doped carbon dots with good biocompatibility for cell labeling

Here we report an easy and economical hydrothermal carbonization approach to synthesize the fluorescent nitrogen-doped carbon dots (N-CDs) that was developed using citric acid and triethanolamine as the precursors. The synthesis conditions were optimized to obtain the N-CDs with superior fluorescence performances. The as-prepared N-CDs are monodispersed sphere nanoparticles with good water solubility, and exhibited strong fluorescence, favourable photostability and excitation wavelength-dependent behavior. Furthermore, the in vitro cytotoxicity and cellular labeling of N-CDs were investigated using the rat glomerular mesangial cells. The results showed the N-CDs have more inconspicuous cytotoxicity and better biosafety in comparison with ZnSe quantum dots, although both targeted the cells successfully. Considering their admirable photostability, low toxicity and good compatibility, the as-obtained N-CDs could have potential applications in biosensors, cellular imaging, and other fields.

A nanosensor made of sulfur–nitrogen co-doped carbon dots for “off–on” sensing of hypochlorous acid and Zn(II) and its bioimaging properties

In this study, we present a facile one-step solvothermal strategy for the fabrication of sulfur–nitrogen co-doped carbon dots (SNCDs) using p-phenylenediamine and cysteamine hydrochloride as the precursors. The as-prepared SNCDs possess well monodispersed and nearly spherical morphology, and present favorable optical performances encompassing strong yellow-green fluorescence and excitation wavelength-independent fluorescence behavior with the maximum excitation/emission wavelength at 420/550 nm. More strikingly, the emission of SNCDs is effectively quenched by hypochlorous acid (HOCl/ClO−), whereas the SNCDs–HOCl aggregate can be released by zinc(II) ions (Zn2+) causing a fluorescence enhancement/recovery process. As such, we designed a SNCD-based fluorescence “off–on” nanosensor for HOCl and Zn2+ detection. The “turn off” mode enables the quantitative analysis of HOCl with a linear range of 0.18–4.22 μM and a detection limit of 0.021 μM. And the quantitative range for Zn2+ detection based on the “turn on” process is from 8.41 to 84.12 μM with a detection limit of 0.30 μM. Moreover, the fluorescent nanoprobe was applied for the assay of HOCl/ClO− and Zn2+ in water samples with satisfactory recovery values and in MCF-7 cell imaging with negligible autofluorescence, indicating its promising application potential in chemical, environmental and biological systems.

Study on the fluorescence resonance energy transfer between CdS quantum dots and Eosin Y

Water-soluble CdS quantum dots (QDs) were prepared using mercaptoacetic acid (TGA) as the stabilizer in an aqueous system. A fluorescence resonance energy transfer (FRET) system was constructed between water-soluble CdS QDs (donor) and Eosin Y (acceptor). Several factors that impacted the fluorescence spectra of the FRET system, such as pH (3.05-10.10), concentration of Eosin Y (2-80 mg/L) and concentration of CdS QDs (2-80 mg/L), were investigated and refined. Donor-to-acceptor ratios, the energy transfer efficiency (E) and the distance (r) between CdS QDs and Eosin Y were obtained. The results showed that a FRET system could be established between water-soluble CdS QDs and Eosin Y at pH 5.0; donor-to-acceptor ratios demonstrated a 1: 8 proportion of complexes; the energy transfer efficiency (E) and the distance (r) between the QDs and Eosin Y were 20.07% and 4.36 nm,respectively.