Synthesis of Nanomaterials
Multiple research groups are involved in synthesis of nanomaterials in the form of particles and coatings. Some of these materials include porous carbons, graphene, carbon nanotubes, gold nanoparticles, titania, and carbon/oxode hybrid materials, as well as those outlined in more detail below.
Carbide-derived-carbons (CDCs) are a growing class of nanostructured carbon materials with properties that are desirable for many applications, such as electrical energy and gas storage. CDCs with structures ranging from amorphous to highly ordered graphitic structures are produced by selective removal of metal or metalloid atoms from a crystalline metal carbide precursor. The carbon structure depends on the synthesis method, applied temperature, pressure and the choice of the carbide precursor. Our group has extensively worked on synthesis of characterization of CDCs for applications in electrochemical energy storage, Hydrogen storage, Methane storage, gas sorption, protein adsorption, tribology, and other applications in the past decade.
Carbon onions are sometimes called carbon nano-onions (CNOs) or onion-like carbon (OLC). Those names cover all kinds of concentric shells, from nested fullerenes to small polyhedral nanostructures. We synthesis carbon onions by annealing (usually in vacuum) of nanodiamond particles. Carbon onions represent one of the least studied carbon nanomaterials, and are seeing a large increase in attention for energy storage applications. Because of their unique 0-D structure, small (<10 nm) diameter, high electrical conductivity and relatively easy dispersion, compared to 1-D nanotubes and 2-D graphene, OLC has been shown to be ideal as a conductive additive to battery and supercapacitor electrodes, or as active material for supercapacitor electrodes for high-power applications and for low temperature devices using ionic liquid electrolytes.
MXenes are a new family of 2D transition metal carbides and/or nitrides discovered and being developed in collaboration with Prof. Barsoum’s group, that can be used in many applications such as energy storage systems (e.g. lithium ion batteries). We labeled the 2D layers of those carbides “MXene” because we produce them by etching A layer from MAX phases and we added the suffix “ene” to emphasize their similarity to graphene. MAX phases are a large family (+60 members) of hexagonal layered ternary transition metal carbides and/or nitrides with composition of Mn+1AXn, where M stands for an early transition metal (such as: Ti, V, Cr, Nb, etc.), A stands for a group A element (such as: Al, Si, Sn, In, etc.), X stands for carbon and/or nitrogen, and n=1, 2, or 3. The etching process is carried out by simply immersing MAX phase in hydrofluoric acid at room temperature. MXenes are produced with compositions of M2X, M3X2, and M4X3. DFT calculations showed that MXenes’ band gap can be tuned by changing the surface termination, for example bare MXene is metallic conductors, while OH or F terminated are semiconductors with small band gap. Multilayer MXenes are electronically conductive with conductivity similar to multilayer graphene. Unlike graphene, MXenes show hydrophilic behavior that allow for easy dispersion in aqueous solutions.
We have shown that MXenes can be intercalated with a variety of organic molecules and inorganic salts which not only enables synthesis of different intercalation compounds but also leads to new applications for these materials. We continue investigating MXene synthesis by exploring structure and surface termination of MXenes in order to define their chemical formulas and control chemical composition and also by studying the intercalation process, understanding the involved mechanisms and the structure of intercalated MXenes. These materials could be used for a wide range of applications including electronic devices, sensors, reinforcement for composites, and energy storage materials.