Dongliang Gao

Size‐Dependent Enhancement of Electrocatalytic Oxygen‐Reduction and Hydrogen‐Evolution Performance of MoS2 Particles

MoS2 particles with different size distributions were prepared by simple ultrasonication of bulk MoS2 followed by gradient centrifugation. Relative to the inert microscale MoS2, nanoscale MoS2 showed significantly improved catalytic activity toward the oxygen-reduction reaction (ORR) and hydrogen-evolution reaction (HER). The decrease in particle size was accompanied by an increase in catalytic activity. Particles with a size of around 2 nm exhibited the best dual ORR and HER performance with a four-electron ORR process and an HER onset potential of -0.16 V versus the standard hydrogen electrode (SHE). This is the first investigation on the size-dependent effect of the ORR activity of MoS2, and a four-electron transfer route was found. The exposed abundant Mo edges of the MoS2 nanoparticles were proven to be responsible for the high ORR catalytic activity, whereas the origin of the improved HER activity of the nanoparticles was attributed to the plentiful exposed S edges. This newly discovered process provides a simple protocol to produce inexpensive highly active MoS2 catalysts that could easily be scaled up. Hence, it opens up possibilities for wide applications of MoS2 nanoparticles in the fields of energy conversion and storage.

One-pot facile fabrication of carbon-coated Bi2S3 nanomeshes with efficient Li-storage capability

AbstractLayered bismuth sulfide (Bi2S3) has emerged as an important type of Li-storage material due to its high theoretical capacity and intriguing reaction mechanism. The engineering and fabrication of Bi2S3 materials with large capacity and stable cyclability via a facile approach is essential, but still remains a great challenge. Herein, we employ a one-pot hydrothermal route to fabricate carbon-coated Bi2S3 nanomeshes (Bi2S3/C) as an efficient Li-storage material. The nanomeshes serve as a highly conducting and porous scaffold facilitating electron and ion transport, while the carbon coating layer provides flexible space for efficient reduction of mechanical strain upon electrochemical cycling. Consequently, the fabricated Bi2S3/C exhibits a high and stable capacity delivery in the 0.01–2.5 V region, notably outperforming previously reported Bi2S3 materials. It is able to discharge 472 mA·h·g−1 at 120 mA·g−1 over 50 full cycles, and to retain 301 mA·h·g−1 in the 40th cycle at 600 mA·g−1, demonstrating the potential of Bi2S3 as electrode materials for rechargeable batteries.

Graphene Oxide as a Multifunctional Platform for Raman and Fluorescence Imaging of Cells.

Fluorescence and Raman bimodal imaging and Raman multifrequency imaging of Hela cells are carried out with the help of two kinds of graphene oxide-based hybrids. As a multifunctional platform, graphene oxide acts as not only a Raman probe, but also as a substrate for Raman and fluorescent probes to load on.

Anisotropic etching of graphite flakes with water vapor to produce armchair-edged graphene.

A one-step anisotropic etching method is developed to specifically obtain armchair-edged graphene directly from graphite flakes on various substrates. The armchair edge structure of the produced graphene is verified by the atomic resolution images obtained from the fluid mode peakforce tapping AFM and the relatively high intensity of D band in the Raman spectra.

Preparation and electrocatalytic properties of triuranium octoxide supported on reduced graphene oxide

Triuranium octoxide-reduced graphene oxide (U3O8/rGO) hybrids have been prepared by a two-step solution-phase method. The presence of GO is essential in order to obtain pure phase U3O8. The U3O8/rGO hybrids exhibited excellent electrocatalytic activity for the oxygen reduction reaction. The electron transfer number was calculated to be ∼3.9 at −0.7 V (vs. Ag/AgCl) from the slope of the Koutecky-Levich plots. The U3O8/rGO hybrids were more stable than commercial Pt/C catalysts. Furthermore, when methanol was present, the U3O8/rGO hybrids still retained high activity. In addition, the U3O8/rGO hybrids can also catalyze the reduction of hydrogen peroxide.

Reduced graphene oxide decorated with Bi2O2.33 nanodots for superior lithium storage

Bismuth oxides are important battery materials owing to their ability to electrochemically react and alloy with Li, which results in a high capacity level, which substantially exceeds that of graphite anodes. However, this high Li-storage capability is often compromised by the poor electrochemical cyclability and rate capability of bismuth oxides. To address these challenges, in this study, we design a hybrid architecture composed of reduced graphene oxide (rGO) nanosheets decorated with ultrafine Bi2O2.33 nanodots (denoted as Bi2O2.33/rGO), based on the selective and controlled hydrolysis of a Bi precursor on graphene oxide and subsequent crystallization via solvothermal treatment. Because of its high conductivity, large accessible area, and inherent flexibility, the Bi2O2.33/rGO hybrid exhibits stable and robust Li storage (346 mA·h·g–1 over 600 cycles at 10 C), significantly outperforming previously reported Bi-based materials. This superb performance indicates that decorating rGO nanosheets with ultrafine nanodots may introduce new possibilities for the development of stable and robust metal-oxide electrodes.

Surface-Enhanced Raman Spectroscopy of Carbon Nanotubes in Aqueous Solution

Carbon nanotubes (CNTs) exhibit intrinsic spectroscopic properties and are potential Raman and NIR florescence probes for bioimaging. However, the weak Raman intensity greatly obstructs such applications. Surface-enhanced Raman scattering (SERS) has shown to be an effective way to increase the Raman signal. SERS has been widely studied for solid samples. However, solid state is distinctly different from the environment in biosystems. Herein, we studied the SERS of Au- nanoparticle-decorated CNTs in aqueous solution, which offers a similar environment to biosystems. We found that the func- tionalization of CNTs with -SH groups can improve the attachment of Au nanoparticles on tube surfaces thus benefit the SERS effect. The particle size is another important issue for SERS. Particles of 50 nm show much stronger enhancement than those of 12 nm. The Raman intensity of CNTs increases with the increase of the concentration of Au nanoparticles. Hexame- thylene diamine molecules can act as the bi-linkers between Au nanoparticles, compressing the interparticle distance. This was proved by the red-shift of the band at ca. 540 nm and the appearance of a broad band around 700 nm in the absorption spectra of Au nanoparticles. Therefore the addition of hexamethylene diamine can further increase the Raman signal of CNTs by the strong coupling of the surface plasma from the Au nanoparticles with very small interparticle distances. Two kinds of commonly used small molecule Raman probes p-aminothiophenol and Rhodamine B both show remarkably enhanced Raman intensity when added to the aqueous dispersion of Au/CNT hybrids. This shows that these Raman probe molecules can ab- sorb onto the Au/CNT hybrids and their Raman spectra are able to be greatly enhanced by Au nanoparticles decorated on CNTs. Because various Raman bands from either CNTs or Raman probe molecules can be used for Raman imaging, this kind of Raman probe molecule/Au/CNT tri-component hybrid systems may be used as a potential nanostructured platform for multiplexed Raman imaging based on SERS effect. Keywords carbon nanotubes; gold nanoparticles; surface enhanced Raman scattering (SERS); Raman spectroscopy for aqueous solution