Yan-Sheng Li

Intercalation-assisted longitudinal unzipping of carbon nanotubes for green and scalable synthesis of graphene nanoribbons

We have demonstrated an effective intercalation of multi-walled carbon nanotubes (MWCNTs) for the green and scalable synthesis of graphene nanoribbons (GNRs) using an intercalation-assisted longitudinal unzipping of MWCNTs. The key step is to introduce an intercalation treatment of raw MWCNTs with KNO3 and H2SO4, making it promising to decrease the strong van der Waals attractions in the MWCNTs bundles and between the coaxial graphene walls of CNTs. Systematic micro Raman, X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) characterizations suggest that potassium, nitrate, and sulfate ions play an important role in the CNT intertube and intratube intercalations during the pretreatment. Detailed scanning electron microscopy (SEM), transmission electron microscopy, XRD, and micro Raman characterizations indicate that the developed methodology possesses the ability to synthesis GNRs effectively with an improved CNT concentration in H2SO4 of 10 mg/ml at 70 °C, which is amenable to industrial-scale production because of the decreased amount of strong acid. Our work provides a scientific understanding how to enhance the GNR formation by accelerating the CNT longitudinal unzipping via suitable molecular intercalation.

Controllable Tailoring Graphene Nanoribbons with Tunable Surface Functionalities: An Effective Strategy toward High-Performance Lithium-Ion Batteries.

An effective, large-scale synthesis strategy for producing graphene nanoribbons (GNRs) with a nearly 100% yield has been proposed using a stepwise, solution-based, lengthwise unzipping carbon nanotube (CNT) method. Detailed Raman and X-ray photoelectron spectroscopy (XPS) analysis suggest that GNRs with tunable density of oxygen-containing functional groups on the GNR surfaces can be synthesized by adjusting the oxidant concentration during the CNT unzipping. The electrochemical characterization reveals that the as-produced GNRs with 42.91 atomic percent (atom %) oxygen-containing functional groups deliver a capacity of 437 mAh g(-1) after 100 cycles at 0.33C, while the as-produced GNRs with higher oxygen-containing functional groups only present a capacity of 225 mAh g(-1). On the basis of the electrochemical assessment and XPS analysis, the funtionals groups (epoxy-, carbonyl-, and carboxyl groups) in GNRs could be the effective contributor for the high-performance Li-ion batteries with appropriate adjustment.

In situ growth of porphyrinic metal–organic framework nanocrystals on graphene nanoribbons for the electrocatalytic oxidation of nitrite

Graphene nanoribbons (GNRs) are incorporated with the nanocrystals of a porphyrinic metal–organic framework, MOF-525, by solvothermally growing MOF-525 in a suspension of well-dispersed GNRs. A nanocomposite, which is composed of the MOF-525 nanocrystals interconnected by numerous one-dimensional GNRs, is successfully synthesized. Due to the excellent dispersity, uniform thin films of the MOF-525/GNR nanocomposite can be simply deposited on conducting glass substrates by using drop casting. The obtained thin film of the MOF-525/GNR nanocomposite is applied for electrochemical nitrite sensors. The MOF-525 nanocrystals serve as a high-surface-area electrocatalyst toward nitrite and the interconnected GNRs act as conductive bridges to provide facile charge transport. The thin film of the MOF-525/GNR nanocomposite thus exhibits a much better electrocatalytic activity for the oxidation of nitrite compared to the pristine MOF-525 thin film.

A high sensitivity field effect transistor biosensor for methylene blue detection utilize graphene oxide nanoribbon

In this work, we developed a field effect transistor (FET) biosensor utilizing solution-processed graphene oxide nanoribbon (GONR) for methylene blue (MB) sensing. MB is a unique material; one of its crucial applications is as a marker in the detection of biomaterials. Therefore, a highly sensitive biosensor with a low detection limit that can be fabricated simply in a noncomplex detection scheme is desirable. GONR is made by unzipping multiwall carbon nanotubes, which can be mass-produced at low temperature. The GONR-FET biosensor demonstrated a sensitivity of 12.5μA/mM (determined according to the drain current difference caused by the MB concentration change). The Raman spectra indicate that the materials quality of the GONR and the domain size for the C=C sp2 bonding were both improved after MB detection. X-ray photoelectron spectroscopy revealed that the hydroxyl groups on the GONR were removed by the reductive MB. According to XPS and Raman, the positive charge is proposed to transfer from MB to GONR during sensing. This transfer causes charge in-neutrality in the GONR which is compensated by releasing •OH functional groups. With high sensitivity, a low detection limit, and a simple device structure, the GONR-FET sensor is suitable for sensing biomaterials.

Toward bandgap tunable graphene oxide nanoribbons by plasma-assisted reduction and defect restoration at low temperature

Simultaneous reduction and defect restoration of graphene oxide nanoribbon (GONR) via plasma-assisted chemistry is demonstrated. Hydrogen (H2) and methane (CH4) gases are continuously dissociated in a plasma to produce atomic hydrogen and carbon-containing ions and radicals carried by the gas flow to react with and remove oxygen functional groups from GONR films. Detailed material characterization confirms that the synergistic effect of simultaneous reduction and defect restoration of GONR occurred during the H2/CH4 plasma treatment. Extensive optical transmittance measurement suggests that the optical energy gap of the as-treated reduced GONR (r-GONR) can be engineered by controlling the plasma exposure time. Systematic electrical measurement indicates that the electrical conductivity of as-treated r-GONR can be enhanced after H2/CH4-plasma treatment. The unique H2/CH4-plasma reduction with characteristics of short process time, high purity, and low temperature compared with conventional thermal and chemical reductions suggests that this nonequilibrium chemical approach can be used for industrial-scale reduction of GONR and graphene oxide (GO).