Graphene and Chemically Modified Graphene

Chemically Modified Graphene: We recently showed that sodium storage capacity of chemically modified graphene depends on the distance between the individual layers that can be tuned by heating it in argon or ammonia gas. For example, reduced graphene oxide sheets, or rGO, produced at high temperature have near zero sodium capacity, while reduced graphene oxide sheets produced at 500 degrees C have the maximum capacity. (JPC, see publications for details) (Media Coverage: Featured in ScienceDaily)

Graphene: In the past we have demonstrated synthesis of large area graphene films on Cu and Ni substrates in less than 30 min. Further, the as-synthesized films were directly utilized as electrode material and their electrochemical behavior was studied in a lithium half-cell configuration. FLG on Cu (Cu-G) showed reduced lithium intercalation capacity when compared with SLG, BLG and Bare-Cu suggesting its substrate protective nature (barrier to Li-ions). While graphene films on Ni (Ni-G) showed better Li-cycling ability similar to that of other carbons suggesting that the presence of graphene edge planes (typical of Ni-G) is important in effective uptake and release of Li-ions in these materials. (ACS-Appl. Mater. Interfaces, see publications for details) (Media Coverage: Featured in IEEE Spectrum, ChemViews , R&D MAGAZINE, GRAPHENE TIMES)

Two-Dimensional Layered Chalcogenides

Separation of bulk TMDCs into few-layer two-dimensional (2-D) crystals is of interest because of their high surface area for certain chemical processes and size-dependent optical and electronic characteristics. Our group has been involved in developing methods for physical separation of weakly bonded layered materials by use of a variety of solvents. We recently demonstrated liquid phase exfoliation of WS2 and MoS2 in superacid. We also studied their electrochemical behavior in a lithium half-cell configuration that showed a three-step charge–discharge behavior, characteristic of a conversion reaction (JPCL and Scientific Reports see publications for details) (Media Coverage: Featured in NEWSWISE and IEEE-Spectrum)

Laser-Matter Interaction: Coatings for High Power Laser Radiometry

Carbon nanotubes (CNT) and polymer-derived ceramics (PDCs) are of interest due to their unique multifunctional properties. CNTs, however, tend to lose their well-defined structure and geometry at about 400 °C in air. PDCs on the other hand are structureless in X-ray diffraction but show high chemical and thermal stability in air (up to ~1400 °C). Our recent work demonstrate synthesis of a composite nanowire structure consisting of polymer-derived silicon boron-carbonitride (Si–B–C–N) shell with a multiwalled carbon nanotube core. This was achieved through a novel process involving preparation of a boron-modified liquid polymeric precursor through a reaction of trimethyl borate and poly (ureamethylvinyl) silazane under normal conditions; followed by conversion of polymer to ceramic on carbon nanotube surfaces through controlled heating. Chemical structure of the polymer was studied by liquid- Nuclear Magnetic Resonance (NMR) while evolution of various ceramic phases was studied by solid-NMR, FTIR and X-ray photoelectron spectroscopy. Thermogravimetric analysis, followed by Raman spectroscopy and transmission electron microscopy revealed high temperature stability of the carbon nanotube core in flowing air up to 1000 °C. Aim is to design a composite material with high optical absorbance (in the IR range) and high resistance to damage by laser irradiation (as much as 100 kW) (JACerS, see publications for details)

Molecular Precursor Derived Ceramics: Microwave Irradiation for Synthesis of Si(B)CN-MWCNT Composite