Transition Metal-Ethylene Complexes as High-Capacity Hydrogen Storage Media

From first-principles calculations, we predict that a single ethylene molecule can form a stable complex with two transition metals (TM) such as Ti. The resulting TM-ethylene complex then absorbs up to ten hydrogen molecules, reaching to gravimetric storage capacity of 14 wt%. Dimerization, polymerizations and incorporation of the TM-ethylene complexes in nanoporous carbon materials have been also discussed. Our results are quite remarkable and open a new approach to high-capacity hydrogen storage materials discovery.Comment: 5 pages, 4 figures, additional content, Phys. Rev. Lett. in pres

Half-metallic properties of atomic chains of carbon-transition metal compounds

We found that magnetic ground state of one-dimensional atomic chains of carbon-transition metal compounds exhibit half-metallic properties. They are semiconductors for one spin-direction, but show metallic properties for the opposite direction. The spins are fully polarized at the Fermi level and net magnetic moment per unit cell is an integer multiple of Bohr magneton. The spin-dependent electronic structure can be engineered by changing the number of carbon and type of transition metal atoms. These chains, which are stable even at high temperature and some of which keep their spin-dependent electronic properties even under moderate axial strain, hold the promise of potential applications in nanospintronics.Comment: 11 pages, 3 figures, 1 table

Hydrogen Absorption Properties of Metal-Ethylene Complexes

Recently, we have predicted [Phys. Rev. Lett. 97, 226102 (2006)] that a single ethylene molecule can form stable complexes with light transition metals (TM) such as Ti and the resulting TMn-ethylene complex can absorb up to ~12 and 14 wt % hydrogen for n=1 and 2, respectively. Here we extend this study to include a large number of other metals and different isomeric structures. We obtained interesting results for light metals such as Li. The ethylene molecule is able to complex with two Li atoms with a binding energy of 0.7 eV/Li which then binds up to two H2 molecules per Li with a binding energy of 0.24 eV/H2 and absorption capacity of 16 wt %, a record high value reported so far. The stability of the proposed metal-ethylene complexes was tested by extensive calculations such as normal-mode analysis, finite temperature first-principles molecular dynamics (MD) simulations, and reaction path calculations. The phonon and MD simulations indicate that the proposed structures are stable up to 500 K. The reaction path calculations indicate about 1 eV activation barrier for the TM2-ethylene complex to transform into a possible lower energy configuration where the ethylene molecule is dissociated. Importantly, no matter which isometric configuration the TM2-ethylene complex possesses, the TM atoms are able to bind multiple hydrogen molecules with suitable binding energy for room temperature storage. These results suggest that co-deposition of ethylene with a suitable precursor of TM or Li into nanopores of light-weight host materials may be a very promising route to discovering new materials with high-capacity hydrogen absorption properties

Functional electrospun polymeric nanofibers incorporating geraniol-cyclodextrin inclusion complexes: High thermal stability and enhanced durability of geraniol

Cataloged from PDF version of article.In this study, solid geraniol/cyclodextrin inclusion complexes (geraniol/CD-IC) were successfully prepared by using three types of native CD (alpha-CD, beta-CD and gamma-CD). The modeling studies for inclusion complexation between CD and geraniol were performed by using ab initio techniques. Both experimentally and theoretically, the cornplexation efficiency between geraniol and gamma-CD was higher; therefore, geraniol/gamma-CD-IC was chosen and then incorporated into polyvinyl alcohol (PVA) nanofibers (NF) via electrospinning. The scanning electron microscopy imaging elucidated that the aggregates of geraniol/gamma-CD-IC crystals were distributed in the PVA NF, whereas bead-free and uniform PVA and PVA/geraniol NF without CD-IC were obtained. Higher thermal stability of geraniol was observed in the electrospun PVA/geraniol/gamma-CD-IC NF, However, geraniol molecules having volatile nature could not be preserved without CD-IC during electrospinning or during storage; therefore, the complete evaporation of geraniol in PVA/geraniol NF was unavoidable even after one day of its production. On the contrary, the loss of geraniol was minimal (similar to 10%) for PVA/geraniol/gamma-CD-IC NF even after storage of these NF for two years owing to inclusion complexation. Our study demonstrated that electrospun NF incorporating CD-IC may be quite applicable in food industry, e.g.: active food packaging or functional foods, due to very high surface area and nanoporous structure of NF; high thermal stability and enhanced durability of active agents and functional food ingredients. (C) 2014 Elsevier Ltd. All rights reserved

Size-dependent alternation of magnetoresistive properties in atomic chains

Cataloged from PDF version of article.Spin-polarized electronic and transport properties of carbon atomic chains are investigated when they are capped with magnetic transition-metal (TM) atoms like Cr or Co. The magnetic ground state of the TM-C-n-TM chains alternates between the ferromagnetic (F) and antiferromagnetic (AF) spin configurations as a function of n. In view of the nanoscale spintronic device applications the desirable AF state is obtained for only even-n chains with Cr; conversely only odd-n chains with Co have AF ground states. When connected to appropriate metallic electrodes these atomic chains display a strong spin-valve effect. Analysis of structural, electronic, and magnetic properties of these atomic chains, as well as the indirect exchange coupling of the TM atoms through non-magnetic carbon atoms are presented. (c) 2006 American Institute of Physics

Functionalization of carbon-based nanostructures with light transition-metal atoms for hydrogen storage

In a recent letter, the unusual hydrogen storage capacity of Ti decorated carbon nanotubes has been revealed. The present paper extends this study further to investigate the hydrogen uptake by light transition-metal atoms decorating various carbon-based nanostructures in different types of geometry and dimensionality, such as carbon linear chain, graphene, and nanotubes. Using first-principles plane-wave method we show that not only outer but also inner surface of a large carbon nanotube can be utilized to bind more transition-metal atoms and hence to increase the storage capacity. We also found that scandium and vanadium atoms adsorbed on a carbon nanotube can bind up to five hydrogen molecules. Similarly, light transition-metal atoms can be adsorbed on both sides of graphene and each adsorbate can hold up to four hydrogen molecules yielding again a high-storage capacity. Interestingly, our results suggest that graphene can be considered as a potential high-capacity H2 storage medium. We also performed transition state analysis on the possible dimerization of Ti atoms adsorbed on the graphene and single-wall carbon nanotube. © 2008 The American Physical Society

Selective and Efficient Removal of Volatile Organic Compounds by Channel-type Gamma-Cyclodextrin Assembly through Inclusion Complexation

Cyclodextrins (CD), produced from enzymatic degradation of starch, are a form of biorenewable cyclic oligosaccharide which has an outstanding capability to form inclusion complexes with a variety of molecules including pollutants due to their toroid-shaped molecular structure. In this study, by a simple reprecipitation method, we obtained "channel-type" packing from γ-CD where CD molecules are stacked on top of each other to form long cylindrical channels. The γ-CD "channel-type" crystals have shown very effective removal of organic volatile compounds (VOCs; aniline and toluene) from the surroundings, whereas cage-type γ-CD could not entrap VOCs from the same environment. Encapsulation capability of channel-type γ-CD is at a ∼2:1 and ∼1:1 molar ratio for aniline/CD and toluene/CD, respectively. Thus, channel-type γ-CD crystals have shown higher removal efficiency for aniline compared to toluene. Channel-type γ-CD is also able to remove aniline selectively from surroundings. Additionally, computational modeling studies suggested that single γ-CD cavity can host two molecules of aniline or toluene for the complexation, yet, aniline is more insistent to make a complex with the γ-CD cavity when compared to toluene. We show that channel-type γ-CD can remove VOCs molecules (aniline and toluene) as efficiently as activated carbon. Hence, being a starch-based biorenewable cyclic oligosaccharide in the form of white powder, the use of "channel-type" γ-CD crystals could be a competitive alternative to activated carbon as an adsorbent for the VOC removal/filtering. © 2017 American Chemical Society

Synthesis of colloidal 2D/3D MoS2 nanostructures by pulsed laser ablation in an organic liquid environment

Two-dimensional MoS2 nanosheets (2D MoS2 NS) and fullerene-like MoS2 nanostructures (3D MoS2 NS) with varying sizes are synthesized by nanosecond laser ablation of hexagonal crystalline 2H-MoS2 powder in organic solution (methanol). Structural, chemical, and optical properties of MoS2 NS are characterized by optical microscopy, scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and Raman and UV-vis-near infrared absorption spectroscopy techniques. Results of the structural analysis show that the obtained MoS2 NS mainly present a layered morphology from micrometer to nanometer sized surface area. Detailed analysis of the product also proves the existence of inorganic polyhedral fullerene-like 3D MoS2 NS generated by pulsed laser ablation in methanol. The possible factors which may lead to formation of both 2D and 3D MoS2 NS in methanol are examined by ab initio calculations and shown to correlate with vacancy formation. The hexagonal crystalline structure of MoS2 NS was determined by XRD analysis. In Raman spectroscopy, the peaks at 380.33 and 405.79 cm-1 corresponding to the E1 2g and A1g phonon modes of MoS2 were clearly observed. The colloidal MoS2 NS solution presents broadband absorption edge tailoring from the UV region to the NIR region. Investigations of MoS2 NS show that the one-step physical process of pulsed laser ablation-bulk MoS2 powder interaction in organic solution opens doors to the formation of two scaled micrometer- and nanometer-sized layered and fullerene-like morphology MoS2 structures. © 2014 American Chemical Society

Antibacterial electrospun zein nanofibrous web encapsulating thymol/cyclodextrin-inclusion complex for food packaging

Thymol (THY)/γ-Cyclodextrin(γ-CD) inclusion complex (IC) encapsulated electrospun zein nanofibrous webs (zein-THY/γ-CD-IC-NF) were fabricated as a food packaging material. The formation of THY/γ-CD-IC (1:1 and 2:1) was proved by experimental (X-ray diffraction (XRD), thermal gravimetric analysis (TGA), 1H NMR) and computational techniques. THY/γ-CD-IC (2:1) exhibited higher preservation rate and stability than THY/γ-CD-IC (1:1). It is worth mentioning that zein-THY/γ-CD-IC-NF (2:1) preserved much more THY as observed in TGA and stability of THY/γ-CD-IC (2:1) was higher, as shown by a modelling study. Therefore, much more THY was released from zein-THY/γ-CD-IC-NF (2:1) than zein-THY-NF and zein-THY/γ-CD-IC-NF (1:1). Similarly, antibacterial activity of zein-THY/γ-CD-IC-NF (2:1) was higher than zein-THY-NF and zein-THY/γ-CD-IC-NF (1:1). It was demonstrated that zein-THY/γ-CD-IC-NF (2:1) was most effective in inhibiting the growth of bacteria on meat samples. These webs show potential application as an antibacterial food packaging material. © 2017 Elsevier Lt

Electrospun nylon 6,6 nanofibers functionalized with cyclodextrins for removal of toluene vapor

Functional nylon 6,6 nanofibers incorporating cyclodextrins (CD) were developed via electrospinning. Enhanced thermal stability of the nylon 6,6/CD nanofibers was observed due to interaction between CD and nylon 6,6. X-ray photoelectron spectroscopy and attenuated total reflectance Fourier transform infrared spectroscopy studies indicated the existence of some CD molecules on the surface of the nanofibers. Electrospun nylon 6,6 nanofibers without having CD were ineffective for entrapment of toluene vapor from the environment, whereas nylon 6,6/CD nanofibrous membranes can effectively entrap toluene vapor from the surrounding by taking advantage of the high surface-volume ratio of nanofibers with the added advantage of inclusion complexation capability of CD presenting on the nanofiber surface. The modeling studies for formation of inclusion complex between CD and toluene were also performed by using ab initio techniques. Our results suggest that nylon 6,6/CD nanofibrous membranes may have potential to be used as air filters for the removal of organic vapor waste from surroundings. © 2015 Wiley Periodicals, Inc