Novel Applications with Asphaltene Electronic Structure

Asphaltenes are the molecular components of Asphalts and have polyaromatic hydrocarbon (PAH) structures similar to nanographenes. Thus, organic-based dye sensitized solar cells can be produced from asphaltenes. In addition, graphene based structures doped with transition metals can be synthesized from asphaltenes. These materials are simple to synthesize and inexpensive relative to other methods for doping graphene. Thus, what is considered a “Waste Material - Tar” can now be utilized in several important applications. These novel materials from asphaltene are also termed Discotic Liquid Crystals (DLC) and now have great potential in many areas, because of novel and valuable properties, easy synthesis and low cost

HRTEM and Molecular Modeling of the MoS 2-Co9 S 8 Interface: Understanding the Promotion Effect in Bulk HDS Catalysts

As environmental regulations increase, more selective transition metal sulfide (TMS) catalytic materials for hydrotreating applications are needed. Highly active TMS catalysts become more and more desirable triggering new interest for unsupported Co-promoted MoS2-based systems that have high volumetric activity as reported here. Contrary to the common observation for alumina-supported MoS2-based catalysts, we found in our previous studies with dibenzothiophene (DBT) hydrodesulfurization (HDS) that the catalytic activity is directly proportional to the increase of surface area of the sulfide phases (Co9S8 and MoS2) present in Co-promoted MoS2 unsupported catalysts. This suggests that activity is directly connected with an increase of the contact surface area between the two sulfide phases. Understanding of the nature of the possible interaction between MoS2 and Co9S8 in unsupported catalytic systems is therefore critical in order to get a more generalized overview of the causes for synergy. This has been achieved herein through the detailed characterization by XRD, XPS, and HRTEM of the highly active Co9S8/MoS2 catalyst resulting in a proposed model for a Co9S8/MoS2 interface. This model was then subjected to a DFT analysis to determine a reasonable description of the surface contact region between the two bulk phases. Modelling of the interface shows the creation of open latent vacancy sites on Mo atoms interacting with Co and formation of direct Co-Mo bonds. Strong electron donation from Co to Mo also occurs through the intermediate sulfur atom bonded to both metals while an enhanced metallic character is also found. These changes in coordination and electronic properties are expected to favor a synergetic effect between Co and Mo at the proposed localized interface region between the two bulk MoS2 and Co9S8 phases.CONACYT, Mexico 207997MRTI of UTEP, Cotton Trust UTEPMicrolectronics Research Lab of UT-Austin and Departamento de Educacion y Cultura of Gobierno del Estado de ChihuahuaMicroelectronics Research Cente

Synthesis of Ag-Au Nanoparticles by Galvanic Replacement and Their Morphological Studies by HRTEM and Computational Modeling

Bimetallic nanoparticles are important because they possess catalytic and electronic properties with potential applications in medicine, electronics, and chemical industries. A galvanic replacement reaction synthesis has been used in this research to form bimetallic nanoparticles. The complete description of the synthesis consists of using the chemical reduction of metallic silver nitrite (AgNO3) and gold-III chloride hydrate (HAuCl) salt precursors. The nanoparticles display round shapes, as revealed by high-resolution transmission electron microscope (HRTEM). In order to better understand the colloidal structure, it was necessary to employ computational models which involved the simulations of HRTEM images

Enhancement of Multiwalled Carbon Nanotubes’ Electrical Conductivity Using Metal Nanoscale Copper Contacts and Its Implications for Carbon Nanotube-Enhanced Copper Conductivity

Herein, we present an experimental/computational approach for probing the interaction between metal contacts and carbon nanotubes (CNTs) with regard to creating the most efficient, low resistance junction. Tungsten probes have been coated with copper or chromium and the efficiency of nanocontact transport into multiwalled carbon nanotubes (MWCNTs) has been investigated experimentally, using scanning tunneling spectroscopy and nanoscale two-point probe I-V measurements, and in silico, employing DFT calculations. Experimental I-V measurements suggest the relative conductivity of the metal-CNT interaction to be Cu > W > Cr. It has been found that copper when in contact with MWCNTs results in a high density of states at the Fermi level, which contributes states to the conduction band. It was observed that the density of states also increased when chromium and tungsten probes were in contact with CNTs; however, in these cases the density of states increase would only occur under high voltage/high temperature situations. This is demonstrated by an increase in the experimental electrical resistance when compared to the copper probe. These results suggest that in future copper tips should be used when carrying out all intrinsic conduction measurements on CNTs, and they also provide a rationale for the ultraconductivity of Cu-CNT and Cu-graphene composites

Novel Catalysts and Processing Technologies for Production of Aerospace Fuels from Non-Petroleum Raw Materials

Transportation fuels production (including aerospace propellants) from non-traditional sources (gases, waste materials, and biomass) has been an active area of research and development for decades. Reducing terrestrial waste streams simultaneous with energy conversion, plentiful biomass, new low-cost methane sources, and/or extra-terrestrial resource harvesting and utilization present significant technological and business opportunities being realized by a new generation of visionary entrepreneurs. We examine several new approaches to catalyst fabrication and new processing technologies to enable utilization of these nontraditional raw materials. Two basic processing architectures are considered: a single-stage pyrolysis approach that seeks to basically re-cycle hydrocarbons with minimal net chemistry or a two-step paradigm that involves production of supply or synthesis gas (mainly carbon oxides and H2) followed by production of fuel(s) via Sabatier or methanation reactions and/or Fischer-Trpsch synthesis. Optimizing the fraction of product stream relevant to targeted aerospace (and other transportation) fuels via modeling, catalyst fabrication and novel reactor design are described. Energy utilization is a concern for production of fuels for either terrestrial or space operations; renewable sources based on solar energy and/or energy efficient processes may be mission enabling. Another important issue is minimizing impurities in the product stream(s), especially those potentially posing risks to personnel or operations through (catalyst) poisoning or (equipment) damage. Technologies being developed to remove (and/or recycle) heteroatom impurities are briefly discussed as well as the development of chemically robust catalysts whose activities are not diminished during operation. The potential impacts on future missions by such new approaches as well as balance of system issues are addressed

Electronic states and metallic character of carbide Co/MoS2 catalytic interface

We report computer assisted density functional theory computations of electronic states in carbide Co9S8/MoS2 interface model. The interface model was previously proposed using crystallographic information from experimental high-resolution TEM observations; and directly observed by in-situ heating to confirm carbon deposit occurs at the sulfur edge of Co9S8/MoS2 which creates a thin carbide layer. In here, the total energy for carbon adsorption results eight times more favorable to occur at sulfur edge in comparison to molybdenum or cobalt replacement by permutation of carbon atoms as contained in C, CH, CH2 species by exothermic energies. Amorphous carbon excites 2pz orbitals as observed on density of states near Fermi level (FE), and 13% decreased in terms of charge carriers available, causing to decrease its chemical catalytic reactivity and bending ofMoS2 slabs as carbon starts to accumulate at the sulfur edge mainly, which is attributed to charge distribution around the adsorption site caused by the foreign atoms, confirmed by electron density plots, that acts as ‘electron traps’. This helps us concluding that carbon replacement can induce change of selectivity in direct desulfurization pathway

Synthesis and Evaluation of Porous Semiconductor Hexaniobate Nanotubes for Photolysis of Organic Dyes in Wastewater

We present the chemical synthesis of hexaniobate nanotubes using two routes, (1) starting material K4Nb6O17 and (2) parent material of H4Nb6O17 via ion exchange. The as-synthesized materials were exfoliated by adjusting the pH to 9–10 using tetra-n-butylammonioum hydroxide (TBA+OH−), leading to a formation of hexaniobate nanotubes. In order to understand morphology a full characterization was conducted using SEM, HRTEM, BET and powder-XRD. The photocatalytic activity was evaluated using photolysis method using Bromocresol Green (BG) and Methyl Orange (MO) as model contaminants. Results indicate a nanotube porous oxide with large porous and surface area; the photocatalytic activity is about 95% efficient when comparing with commercial TiO2