Congcong Chen

Facile synthesis of halogenated carbon quantum dots as an important intermediate for surface modification

A simple and efficient method to prepare halogenated carbon quantum dots (CQDs) through solvent-thermal reaction was reported. The halogenated CQDs were synthesized and further surface functionalization with diamines was achieved based on the halogenated CQDs as intermediates. The halogenated CQDs provide an alternative approach for surface modification of CQDs.

Well dispersed single-walled carbon nanotubes with strong visible fluorescence in water for metal ions sensing

A novel and simple method to prepare well dispersed single-walled carbon nanotubes with strong visible fluorescence in water is reported. The visible fluorescence was found to be responsive to pH value and metal ions, and tunable emission ability of oxidized SWCNTs depending on the excitation wavelength and a novel self-excitation and emission process were found.

The visible photoluminescence mechanism of oxidized multi-walled carbon nanotubes: an experimental and theoretical investigation

Dominant components of oxidized products of multi-walled carbon nanotubes were separated by column chromatography, the origin of highly visible fluorescence from carbon quantum dots was revealed, and the nature of weak near-UV-Vis fluorescence of oxidized carbon nanotubes from isolated sp2 carbon clusters was supported among the four proposed explanations through experimental and theoretical approaches. It was found that three dominant components including carbon quantum dots, short and long oxidized carbon nanotubes were produced during the oxidation of carbon nanotubes. The highly visible fluorescence was mainly originated from carbon quantum dots, while short and long oxidized carbon nanotubes only exhibited weak near-UV-Vis fluorescence. For the nature of fluorescence of oxidized carbon nanotubes, two proposed explanations including defects mechanism and an isolated carbon cluster mechanism were compared and discussed through theoretical analysis of corresponding model compounds. It was supported that the fluorescence is dominantly originated from sp2 carbon clusters isolated by sp3 carbons due to oxidation depending on the comparison between experimental data and calculated values. The results also indicated that carbon nanotubes can be transformed to large graphene oxide during oxidation. This work not only clearly demonstrated the origin of highly visible fluorescence in an oxidized carbon nanotube mixture and a reasonable explanation for fluorescence of oxidized carbon nanotubes, but also provided an example to understand visible fluorescent graphene oxide and carbon quantum dots.

Facile synthesis of halogenated multi-walled carbon nanotubes and their unusual photoluminescence

The facile synthesis of halogenated multi-walled carbon nanotubes with Cl, Br and I under high pressure and high temperature was reported, and the unique photoluminescence of the halogenated carbon nanotubes was investigated by means of experimental and theoretical approaches. The one-step and facile method to incorporate these halogens onto nanotubes’ surface involves high temperature and high pressure using a sealed vessel. This method is easily handled using SOCl2, Br2 and I2 as halogen sources and is accessible for the large-scale production of halogenated carbon nanotubes. The concentration of halogen in the samples by this method reaches up to 3–8% in weight. The UV-Vis photoluminescence of these halogenated carbon nanotubes was observed, and attributed to fluorescence, depending on their lifetimes. The fluorescence of the halogenated carbon nanotubes can be remarkably enhanced by the increase of introduced halogen atoms resulting from prolonging the reaction time. Different species of halogen atoms have little influence on the fluorescence emission behaviour, but affect their fluorescence lifetimes. The fluorescence is more likely to originate from sp2 carbon clusters isolated from sp3 carbons formed by the addition of halogen atoms, but a defect mechanism cannot be excluded from the present results. A series of compounds with different aromatic rings were modelled to predict the size of the isolated sp2 carbon clusters by comparing the calculated excitation and emission maximum wavelengths with their experimental data. Basing on these theoretical results, it is thought that the UV-Vis fluorescence of the halogenated carbon nanotubes may originate from the isolated sp2 carbon clusters containing 4–8 aromatic rings.

Multicolour fluorescent graphene oxide by cutting carbon nanotubes upon oxidation

Different sizes of graphene oxide with tunable fluorescence colours were prepared by continuous chemical oxidation with multi-walled carbon nanotubes (MWCNTs) as precursor. The photoluminescence of as-prepared GO was attributed to fluorescence according to their luminescence lifetimes. The as-prepared GO exhibit colourful fluorescence, which can be tuned by the level of oxidation. It is found that the fluorescence emission can be bathochromically shifted with the increase of pH value, and the fluorescence can be strongly quenched by usual heavy metal ions except for Cd2+.

Unusual visible luminescence of aluminium polyoxocations in aqueous solution

Identification of aluminium polyoxocations, MO(4)Al(12)(OH)(24)(H(2)O)(12)(7/8+) (M = Al, Ga and Ge) (K-MAl(12)) and Al(30)O(8)(OH)(56)(H(2)O)(26)(18+) (Al(30)), by their luminescence is reported. The fluorescence behavior of K-Al(13) has been found to differ with different metal ions and anions, implying a new discovery of a potential ion sensor.

Theoretical investigation of formation mechanism of bipyridyl molecule on Ni(111) surface: implication for synthesis of N-doped graphene from pyridine

The formation mechanism of bipyridyl molecule catalyzed by nickel catalyst with pyridine precursor has been studied using density functional theory calculations. The formation of bipyridyl on Ni(111) surface from two pyridine molecules is considered as the initial process of N-doped graphene growth, and the minimum energy pathway for the formation has been investigated in detail. The whole formation processes mainly includes three steps, i.e., the dehydrogenation of the first pyridine, adsorption and dehydrogenation of the second pyridine, and formation of the bipyridyl molecule. It is found that the C-H bond of pyridine could be selectively dissociated while the C-C and C-N bond connections are retained during the catalytic processes. The N-doped graphene formed by pyridine only contains pyridine-like nitrogen atoms, suggesting a possible way to produce N-doped graphene with pure pyridine-like nitrogen atoms. The comparison of formation mechanisms between bipyridyl and biphenyl molecules was carried out, and the results imply a lower temperature process for synthesis of N-doped graphene from pyridine than that for graphene from benzene.