Controlled Synthesis, Processing, and Applications of Structural and Functional Nanomaterials: 2D Nanomaterials & Polymer-derived Ceramics
Program Organizers: Haitao Zhang, University of North Carolina at Charlotte; Gurpreet Singh, Kansas State University; Kathy Lu, Virginia Tech; Edward Gorzkowski, Naval Research Laboratory ; Jian Shi, Rensselaer Polytechnic Institute; Kejie Zhao, Purdue University ; Michael Naguib, Tulane University

Wednesday 2:00 PM
October 2, 2019
Room: D134
Location: Oregon Convention Center

Session Chair: Kathy Lu, Virginia Tech; Michael Naguib, Tulane University

2:00 PM  Invited
Oxidation and Stabilization of 2D MXene Nanosheets: Xiaofei Zhao1; Touseef Habib1; Evan Prehn1; Aniruddh Vashisth1; Smit Shah1; Yexiao Chen1; Zeyi Tan1; Jodie Lutkenhaus1; Miladin Radovic1; Micah Green1; 1Texas A&M University
    Practical uses of MXenes, such as Ti3C2Tx, remains challenging as these nanosheets are known to oxidize and degrade quickly from reacting with water and dissolved oxygen. Here, we examine oxidation of MXene nanosheets in various media (air, liquid, and solid) via multiple types of measurements to assess their shelf stability. The oxidation rate of MXene nanosheets were observed fastest in liquid media and slowest in solid media and can be accelerated by exposure to UV light. We also demonstrate an effective method to retard the oxidation of colloidal Ti3C2Tx MXene nanosheets by introducing antioxidants such as sodium L-ascorbate. The success of the method is evident in the conductivity and colloidal stability of Ti3C2Tx. Even in the presence of water and oxygen, the electrical conductivity of Ti3C2Tx nanosheets treated with sodium L-ascorbate was orders of magnitude higher as compared to untreated ones after 21 days.

2:30 PM  
Facile and Scalable Fabrication of Free-standing Reticulated 3D Graphene Foam via Freeze Drying: Tony Thomas1; Xiaolong Lu1; Benjamin Boesl1; Arvind Agarwal1; 1Florida International University
    Graphene foam (GrF) has become the most sorted nano-filler in the fabrication of multi-functional polymer composites. There have been numerous work in the synthesis of free standing 3D GrF. 3D GrF fabricated through CVD technique is a widely used nano-filler. CVD involves series of chemical processes, resulting in an expensive 3D GrF. Hence not many researchers have the luxury to indulge in GrF based material development. This presentation highlights a simple 2-step fabrication of 3D GrF using 2D graphene nano-platelets (GNP) via freeze drying technique. As-produced 3D GNP has a reticulated micro porous structure. The work also considers the influence of 3D GNP foam on the thermal and mechanical properties of polymers like polydimethylsiloxane (PDMS) and shape memory polymer (SMP) when used as a nano filler. The presentation mainly highlights the competitive edge of 3D GNP over the 3D GrF fabricated by CVD as a nano filler material.

2:50 PM  
Two-dimensional Titanium Carbonitride MXene as Electrocatalyst for Hydrogen Evolution Reaction: Kun Liang1; Anika Tabassum1; Michael Naguib1; 1Tulane University
    As a carbon-free clean energy, hydrogen is a promising alternative to traditional fossil fuels. Currently, electrochemical/photoelectrochemical hydrogen evolution reaction (HER) from water is presenting attractive prospect to generate hydrogen. Until now, Pt group metals are believed to be the most effective catalysts. However, the high-cost of precious metal catalysts become a huge obstacle to produce hydrogen in large-scales. Therefore, advanced precious-metal-free catalysts are needed for HER. As a new family of 2D transition metal carbides and carbonitrides, MXenes show unique combinations of properties, which are benefit for electrochemical catalysts of HER. In this study, we report a nonprecious metal catalyst based on MXenes for high-efficiency HER. A Ti3CN nanosheet was achieved through a wet chemistry etching treatment and a delaminating process, which presented high-performance for HER in acid electrolyte. The investigation of MXenes opens up a promising paradigm for the conscious design of high-performance nonprecious metal catalyst for hydrogen generation.

3:10 PM  
3-D Assembled MnO2 Nanosheets and Conversion to Tunnel-structured MnO2: Scott Misture1; Peter Metz1; Madeleine Flint1; Robert Koch1; Alec Ladonis1; Peng Gao1; 1Alfred University
    Ceramics with 2-dimensional crystal structures have recently been the topic of intense study for electrochemical charge storage, with many materials amenable to exfoliation to form 2-D nanosheets. 2-D MnO2 nanosheets were prepared via exfoliation of high-perfection starting microcrystalline powders and reassembled into 3-D porous structures. As capacitor electrodes, these materials reach over 350 F/g when we intentionally reduce the nanosheets to form a fixed quantity of trivalent Mn ions. X-ray total scattering was teamed with X-ray spectroscopy, Raman and related tools were used to probe both the mesostructure and the atomic defects of MnO2 nanosheet assemblies perturbed by different aqueous treatments. Heating converts the porous 3-D array of nanosheets into tunnel-structured MnO2, yielding hierarchical porosity; that is, the mesopores remain and new tunnels are created. We further show conversion to Mn2O3 with unique droplet microstructure, also of remarkably high surface area.

3:30 PM Break

3:50 PM  
Nanocomposites TiO2-layered Hydroxides. Structure and Photocatalytic Decomposition of Vanillin and Methyl Orange: Andrei Jitianu1; Thomas Haughey2; Naphtali O'Connor1; Edruce Edouarzin1; Mihaela Jitianu2; 1Lehman College, City University of New York; 2William Paterson University
    Various organic compounds can be decomposed in aqueous solution by titanium dioxide (TiO2) under near ultraviolet light into carbon dioxide and water. When TiO2 absorbs ultraviolet radiation, it produces pairs of electrons and holes. The key for an ongoing photooxidation process is avoiding accumulation of the electrons on particles that ultimately leads to recombination with the holes by creating nanocomposites with lamellar mixed hydroxides. Those layered hydroxides have the general formula [Mg(II)1-xAl(III)x(OH)2]x+(Ax/m)m-nH2O, where Am- is a compensating anion. The sol-gel process was employed to synthesize the TiO2-based nanocomposites. TiO2 precursor was Titanium (IV) isopropoxide, whereas the mixed hydroxides were generated in situ from the corresponding nitrates, using urea. The photocatalytic test reactions were performed under visible light (575 nm), using molecules with two different structures, vanillin and methyl-orange. The nanosized composites photocatalytic properties were correlated with specific structural features of the organic compounds investigated.

4:10 PM  
Defect Effects on the Enhanced Photocatalytic Properties of 2D MoO3 Nanoflakes: Haitao Zhang1; Soheil Razmyar1; 1University of North Carolina at Charlotte
    Two-dimensional (2D) MoO3 nanostructures were produced by using a scalable liquid exfoliation method with different alcohol-water solutions. The resulting nanoflakes have different dimensions and defect structures tailorable by the mixing ratio of the solutions, as shown by the materials structure characterization and optical property measurement. Combined with the photothermal study, the detailed reaction mechanism for the low-temperature protonation was revealed. Sub-bandgap defects provide the visible light absorption to initialize the reaction under the visible light irradiation. The usually slow reaction is expedited by the photothermal heating to achieve evident reaction rate without providing any additional heating. The low-temperature reaction has a great potential to produce substoichiometric semiconductors with tunable plasmonic behaviors at low cost. The reaction mechanism can be extended to a variety of photocatalytic processes of MoO3 nanostructures, with enhanced efficiencies to harvest and convert solar energy into chemical energies.

4:30 PM  
Polymer Intercalation Synthesis of GlycoBoehmite Nanosheets: Nelson Bell1; Mark Rodriguez1; Jessica Kruichak1; Bernadette Hernandez1; Igor Kolesnichenko1; Paul Kotula1; Edward Matteo1; 1Sandia National Laboratories
     Novel alumina nanosheets based on the aluminum oxyhydroxide boehmite phases were prepared using glycothermal routes, in which the boehmite phase is altered by chemisorption of the glycol solvent in place of the interlayer hydroxyl groups, creating glycoboehmite. Two new phases that incorporate either polyvinylpyrrolidone or hydroxylpropyl cellulose polymers were found to expand the b-axis of the unit cell beyond the value created from synthesis in the glycothermal solvent itself. These intercalation polymers are non-ionic and interact by wetting interactions and hydrogen bonding, rather than by chemisorption or chelation with the aluminum ions in the structure. The ion absorption capacity was evaluated for environmental remediation applications of these materials. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.

4:50 PM  Cancelled
Oxygen Vacancies in Nanostructured Metal-oxide Gas Sensors: Mohamad Al-Hashem1; Sheikh Akbar1; Patricia Morris1; 1Ohio State University
    Metal oxide nanomaterials are attractive structures for use in health and safety or energy applications. The electronic properties of these materials are closely related to their defects. Oxygen vacancies created during heat treatment processes are often reported to improve gas sensing properties. In this study, SnO2 nanowires have been synthesized by a vapor-liquid-solid process and subjected to different annealing treatments to study how surface and bulk oxygen vacancies can affect sensing. Electrical measurements (DC and AC) are employed to study the effect of different treatments on the behavior of the sensors towards oxidizing and reducing gases. Careful circuit analysis of AC measurements, along with supporting evidence from other spectroscopic techniques such as cathodoluminescence, has enabled a better understanding of the role of oxygen vacancies in metal oxide gas sensors. The framework for an open access database of resistive type gas sensors (ODORS), which is underway, will also be presented.