Jun Zhong

Characterization of multiwalled carbon nanotubes dispersing in water and association with biological effects

Biomedical application potentials of carbon nanotubes-based materials have been investigated intensively in recent years; however, characterization and metrology are still facing great technical challenges when the materials are intended to be used as carriers for therapeutics in aqueous solutions. Systematic characterization on the dispersing carbon nanotubes is urgently required and therefore of significance. In this paper multiwalled carbon nanotubes (MWCNTs) with different average lengths or with different oxidation degrees were dispersed in water and characterized systematically by applying UV spectroscopy, SEM, DLS, TGA, XPS, and FTIR. In particular, the characteristic absorption of the carbon nanotubes was analyzed using resolution-fitting technique to establish relations of wavelength and absorption intensity to the size distribution and surface chemistry. Results indicated that the absorption spectra of MWCNTs could reflect the variation of surface chemistry and length distribution of carbon nanotubes dispersed in water by combining with the other measurements. A vascular endothelium cell line was taken as a model to figure out association between physicochemical features and cytotoxicity of the carbon nanotubes. It was showed that the multiwalled carbon nanotubes with different oxidation degrees and similar length distribution exhibited different interaction files to the cells proliferation in a manner of time dependence and concentration dependence.

Unsaturated-sulfur-rich MoS2 nanosheets decorated on free-standing SWNT film: Synthesis, characterization and electrocatalytic application

Herein, we report a bottom-up solvothermal route to synthesize a flexible, highly efficient MoS2@SWNT electrocatalyst for hydrogen evolution reactions (HER). Characterization revealed that branch-like MoS2 nanosheets containing sulfurrich sites were in situ uniformly dispersed on free-standing single-walled carbon nanotube (SWNT) film, which could expose more unsaturated sulfur atoms, allowing excellent electrical contact with active sites. The flexible catalyst exhibited excellent HER performance with a low overpotential (~150 mV at 10 mA/cm2) and small Tafel slope (41 mV/dec). To further explain the improved performance, the local electronic structure was investigated by X-ray absorption near-edge structure (XANES) analysis, proving the presence of unsaturated sulfur atoms and strong electronic coupling between MoS2 and SWNT. This study provides an in-situ synthetic route to create new multifunctional flexible hybridized catalysts and useful insights into the relationships among the catalyst microstructure, electronic structure, and properties.

Electronic structure study of Li+/OH− modified single-walled carbon nanotubes by soft-x-ray absorption and resonant emission spectroscopy

Li+ and OH− modified single-walled carbon nanotubes (SWNTs) treated with the LiOH water solution have been investigated by soft-x-ray absorption and resonant emission spectroscopy. A reconstruction of the band structure after hydroxyl modification and intensity changes between π and σ states in the resonant emission spectra are presented and discussed. A charge transfer induced valence state near Fermi level has been detected at the resonant excitation energy of 285.5 eV, which indicates the tuning of electronic properties of SWNTs by Li+ adsorption.

An XANES study on the modification of single-walled carbon nanotubes by nitric acid.

X-ray absorption near-edge structure (XANES) spectroscopy has been applied to identify the modification process of single-walled carbon nanotubes (SWCNTs) treated by nitric acid. The carboxyl groups created by the nitric acid treatment have been found to be formed on both the carbonaceous fragments and the side walls of SWCNTs. The carbonaceous fragments could be removed by a following washing treatment with sodium hydroxide. XANES spectra indicate that carbonaceous fragments are the result of the synthesis process and/or of the nitric acid treatment. Tube walls of SWCNTs are weakly oxidized by the nitric acid treatment although, after removing carbonaceous fragments, a direct oxidation process of SWCNTs is observed. Experimental data address the removal of carbonaceous fragments on SWCNTs as an efficient method for side-wall modification of a SWCNT.

Comparison of adsorption behavior for fibrinogen and albumin on single walled carbon nanotubes nonwoven

Fibrinogen and albumin are two of the most important plasma proteins that relate to blood coagulation caused by engineered surfaces. In this paper, the adsorption behavior of albumin and fibrinogen on single-walled carbon nanotubes nonwoven (SWNT nonwoven) was investigated through scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), near edge X-ray adsorption fine structure spectroscopy (NEXAFS) and direct enzyme-linked immunosorbent assay (ELISA) respectively. It was concluded that SWNT nonwoven displayed strong adsorption preference of fibrinogen to albumin. In addition, the immune activity of fibrinogen adhered to the SWNT nonwoven surface was found remained and showed a linear response to the concentration in a certain range.

Valence state evolution of C60 deposited on Sm film

Ultraviolet photoemission spectra of C60 deposited on Sm film were measured. The results indicate that C60 and Sm can combine with each other to form fulleride in the interface at room temperature. The bonding is mainly ionic with some covalent contribution. Both the lowest unoccupied molecular orbital (LUMO) and the LUMO+1 orbital of C60 are occupied at coverages less than about one monolayer. As for the second overlayer, only the LUMO orbital is occupied. The first and second C60 overlayers are metallic and semiconducting, respectively.