Shenghai Zhou

Fabrication of a nitrogen-doped graphene quantum dot from MOF-derived porous carbon and its application for highly selective fluorescence detection of Fe3+

Nitrogen doping of carbon quantum dots results in improved fluorescence performance and a wider range of applications in photocatalysis, sensors, bioimaging, etc. Herein, a water-soluble and well-crystallized nitrogen-doped graphene quantum dot (N-GQD) has been obtained by using a MOF-derived carbon (ZIF-8C) as a new source of graphitic sheets. The preparation is based on a rapid, eco-friendly and efficient acid vapour cutting strategy, which is different from previously reported solution chemistry routes. The as-prepared N-GQD is photoluminescent and exhibits an excitation-independent behaviour. Because of the presence of O-functional groups on the surface, the obtained N-GQD can serve as a fluorescent sensing probe for highly selective detection of Fe3+ ions with a detection limit of 0.08 μM (at a signal-to-noise ratio of 3). This work would enable new opportunities for the wider use of MOF-based materials and also contribute to the fluorescent analysis of Fe3+.

Graphene quantum dots: recent progress in preparation and fluorescence sensing applications

Fluorescent graphene quantum dots (GQDs) have attracted tremendous attention because of their unique 2D layered structure, large surface area, good water solubility, tunable fluorescence, high photostability, excellent biocompatibility and low toxicity, which make them promising candidates for applications in various fields. In this review, we summarize the latest progress in research on GQDs, focusing on their preparation via both top-down and bottom-up routes and application in fluorescence sensing of inorganic ions, organic molecules and biomaterials. This review provides insight into GQDs to inspire their further development, including their controllable preparation and use in a wider range of sensing applications, by the large community of researchers focusing on graphene.

One-step synthesis of isoreticular metal–organic framework-8 derived hierarchical porous carbon and its application in differential pulse anodic stripping voltammetric determination of Pb( ii )

A novel nanoporous carbon material (NPC) was prepared by simple pyrolysis of an isoreticular metal–organic framework-8 (IRMOF-8) at 1000 °C. The obtained NPC possessed a three-dimensional hierarchy of micro-, meso-, and macropores, a high surface area of 1715 m2 g−1 and a large pore volume of 1.70 cm3 g−1. By using Nafion and bismuth films as co-modifiers, the obtained NPC was further used for the fabrication of a sensitive NPC–Nafion/bismuth composite modified glassy carbon electrode (NPC–Nafion/Bi/GCE) for electrochemical determination of Pb(II) in aqueous solution. The synergistic effect of the Nafion and Bi films, as well as the high activated surface area, hierarchical porous texture, and good electrical conductivity of the NPC contributed to the enhanced electrochemical response of Pb(II) at the NPC–Nafion/Bi/GCE during differential pulse anodic stripping voltammetry. Under the optimum conditions, the fabricated electrode exhibited two linear ranges varying from 1–7 μg L−1 and 7–70 μg L−1, respectively. The detection limit was estimated to be 0.8 μg L−1 (at a signal-to-noise ratio of 3) for Pb(II), which was about 12 times lower than the guideline value set by the World Health Organization (WHO) for drinking water. The NPC–Nafion/Bi/GCE showed high reproducibility, with relative standard deviations of 6.2% and 3.4% for multiple successive measurements of 10 and 50 μg L−1 Pb(II), respectively. The composite electrode was successfully used in the analyses of Pb(II) in tap-water samples, and good recoveries were obtained for various spiked values.

Time-efficient syntheses of nitrogen and sulfur co-doped graphene quantum dots with tunable luminescence and their sensing applications

Heteroatom doped graphene quantum dots (GQDs) are particularly promising in bioimaging and fluorescent sensing because of their better photoluminescence tunability compared to pristine GQDs. Herein, two nitrogen and sulfur co-doped GQDs (N,S-GQDs) with varied fluorescence emission wavelength were synthesized via HNO3 vapour cutting route, in which a porous polythiophene-derived carbon served as the sulfur source while the HNO3 vapour was presented as the scissor and the nitrogen source. The as-prepared N,S-GQDs exhibited blue and yellow-green coloured fluorescence, owing to their varied morphologies and surface states resulted from varied reaction temperature. Compared to the typical top-down syntheses via hydrothermal or solvothermal routes, the present HNO3 vapour cutting method is prominently efficient in time expense and product separation. An application of the obtained greenish-yellow N,S-GQDs for highly selective and sensitive fluorescent detection of Fe3+ was demonstrated, with a linear range of 0–130 μM and a detection limit of 0.07 μM. The protocol reported here can also be readily applied for facial synthesis of other heteroatom doped GQDs.

Luminescent properties and sensing performance of a carbon quantum dot encapsulated mesoporous silica/polyacrylonitrile electrospun nanofibrous membrane

A novel turn-off and label-free fluorescent sensor based on a carbon quantum dot encapsulated mesoporous silica/polyacrylonitrile (CDs/mesoSiO2/PAN) electrospun nanofibrous membrane for the determination of Fe(III) was evaluated. Compared with that of the free-state CDs, the fluorescent behavior of the embedded CDs was altered because of the involvement of mesoSiO2/PAN electrospun nanofibers as a supporting matrix. On the basis of previously reported understandings, the photoluminescent (PL) mechanism of the CDs had been further studied. It is evident that the fixed blue emission of CDs occurs from the carbon defect states, whereas the excitation-dependent emission at longer wavelengths is related to confinement effects of the CDs. Moreover, compared with the free-state CDs, the CDs/mesoSiO2/PAN nanofibrous membrane exhibits a more stable PL signal, improved anti-photobleaching performance, and better pH adaptability because of the possible hydrogen bonding between the SiOH groups in nanofibers and the surface oxygen-containing groups of the CDs, which create an adequate chemical environment for the preservation of the carbon defect states in luminescence generation as well as the active sites for Fe(III) binding. Applying the CDs/mesoSiO2/PAN membrane for the determination of Fe(III) in tap water samples indicates that it can work efficiently as a PL sensor.

A protocol of self-assembled monolayers of fluorescent block molecules for trace Zn(II) sensing: structures and mechanisms

2D epitaxial nanostructures formed by functional molecules at interfaces/surfaces have attracted considerable research interest because of their promising applications in catalysis, photonics, electronic devices, and so on. In this study, we demonstrate for the first time that a monolayer of functional molecules may be used as a fluorescence indicator for heavy metal ions. Self-assembly of bisligand TPE-C4-L2 on highly oriented pyrolytic graphite was performed and the self-assembled monolayer (SAM) was used for trace amounts of Zn(II) sensing with an output signal of fluorescence. In contrast to the Zn(II)-induced fluorescence enhancement of the TPE-C4-L2 block molecule in solution, the self-assembled TPE-C4-L2 film showed quenched fluorescence after Zn(II) was introduced. Using a high-resolution scanning tunneling microscope, the SAM structures of TPE-C4-L2 and its zinc complex were determined. The correlation between their optical properties and structures at the molecular level was also revealed.

A highly selective fluorescence sensing platform for nanomolar Hg(II) detection based on cytosine derived quantum dot

Inspired by low toxicity and good biocompatibility of biomass derived quantum dot (QD), we herein developed a cytosine derived quantum dot, namely cyt-dot, via a one-step hydrothermal synthesis. The as-prepared cyt-dot emits blue fluorescence (FL) containing abundant oxygen (20.6at.%) and nitrogen (24.1at.%) contents. The cyt-dot based sensing platform shows exclusive selectivity for Hg(II) while being insensitive towards Fe(III) and Ag(I), which are important interference that usually cannot be ruled out. The detection limit for Hg(II) is of 11nM, which is very close to the guideline value of 10nM allowed by the U.S. Environmental Protection Agency in drinking water. In real water sample analyses, the present sensing platform can fulfil satisfied recoveries ranging from 100% to 108%. Besides, the acidity of solution has almost no effect on the sensing performance of the cyt-dot in a pH range of 5-8, suggesting its potential applications in sensing and bio-imaging.