Hydrogen adsorption on pristine, defected, and 3d-block transition metal-doped penta-graphene

© 2016 Hydrogen Energy Publications LLC The effects of different crystallographic defects and substitutional doping of 3d-block transition metals (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn) on the electronic properties and hydrogen molecule (H2) interaction of penta-graphene (PG) were investigated using density functional theory calculations. Electronic properties of PG show strong dependence on PG\u27s structural configuration and the type of metal dopants used. Doping PG with transition metals (TM) may be used to change PG from being a wide band gap semiconductor to a narrow band gap semiconductor or a semimetal. PG have H2 adsorption energies (Eads) that are superior to graphene, with Eads between −0.7 eV and −0.9 eV depending on the adsorption site. Transition metals act as proton rich dopant, and induced positive electrostatic potential in its adjacent regions. Thus, doping improve H-2 adsorption, especially when substituted on sp2 hybridized carbon site. The V-doped and Ti-doped sheets, with Eads of −0.351 eV and −0.319 eV, respectively, show the greatest potential for on-board reversible solid-state hydrogen molecule storage application

Theoretical investigation on the solubilization in water of functionalized single-wall carbon nanotubes

An important technique to increase the solubility and reactivity of carbon nanotube is through functionalization. In this study, the effects of functionalization of some single-walled carbon nanotubes (SWCNTs) were investigated with the aid of density functional theory. The SWCNT model used in the study consists of a finite, (5, 0) zigzag nanotube segment containing 60 C atoms with hydrogen atoms added to the dangling bonds of the perimeter carbons. There are three water-dispersible SWCNTs used in this study that were functionalized with (a) formic acid, as a model of carboxylic acid, (b) isophthalic acid, as a model aromatic dicarboxylic acid, and (c) benzenesulfonic acid, as a model aromatic sulfonic acid. Binding energies of the organic radicals to the nanotubes are calculated, as well as the HOMO-LUMO gaps and dipole moments of both nanotubes and functionalized nanotubes. Binding was found out to be thermodynamically favorable. The functionalization increases the electrical dipole moments and results in an enhancement in the solubility of the nanotubes in water manifested through favorable changes in the free energies of solvation. This should lower the toxicity of nanotubes and improve their biocompatibility. Copyright © 2012 Michael Mananghaya et al

Theoretical investigation on single-wall carbon nanotubes doped with nitrogen, pyridine-like nitrogen defects, and transition metal atoms

This study addresses the inherent difficulty in synthesizing single-walled carbon nanotubes (SWCNTs) with uniform chirality and well-defined electronic properties through the introduction of dopants, topological defects, and intercalation of metals. Depending on the desired application, one can modify the electronic and magnetic properties of SWCNTs through an appropriate introduction of imperfections. This scheme broadens the application areas of SWCNTs. Under this motivation, we present our ongoing investigations of the following models: (i) (10, 0) and (5, 5) SWCNT doped with nitrogen (CN x NT), (ii) (10, 0) and (5, 5) SWCNT with pyridine-like defects (3NV-CN x NT), (iii) (10, 0) SWCNT with porphyrine-like defects (4ND-CN x NT). Models (ii) and (iii) were chemically functionalized with 14 transition metals (TMs): Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Pd, Ag, Pt and Au. Using the spin-unrestricted density functional theory (DFT), stable configurations, deformations, formation and binding energies, the effects of the doping concentration of nitrogen, pyridine-like and porphyrine-like defects on the electronic properties were all examined. Results reveal that the electronic properties of SWCNTs show strong dependence on the concentration and configuration of nitrogen impurities, its defects, and the TMs adsorbed. Copyright © 2012 Michael Mananghaya et al

H2O Absorptivity on a Fully 4-crosslinked Polyacrylamide Membrane via Density Functional Theory and Monte Carlo Calculations for Draw Solution Recovery in Forward Osmosis

© 2019 IEEE. The draw solution recovery process is a necessary step in forward osmosis systems, such as the one being applied in the dewatering of microalgae. Among the many draw solution recovery methods, the stimuli-response regeneration technique emerged to be one of the most promising in terms of energy efficiency. However, a material with an excellent capacity to absorb water would be needed for this type of process. This study investigated the water adsorption properties of 4-crosslinked polyacrylamide membrane (PAM) by means of density functional theory and Monte Carlo calculations for potential application in draw solution recovery. A geometrically optimized, stable, and energy minimized 4-crosslinked PAM model was prepared and allowed to be immersed to different amount of water molecules. The adsorption energies of water molecules on PAM were calculated. Results indicate that water molecules are most likely to be adsorbed on the amide groups of 4-crosslinked PAM. It was shown that the addition of lower number of water molecules had the highest probability of water molecules adsorbing on PAM. It was found that the 4-crosslinked PAM can adsorb a minimum of 75 and a maximum of 145 water molecules. Results of the study would be useful as a guide for the synthesis and further characterization of PAM for draw solution recovery in forward osmosis systems, specifically in microalgae dewatering

Ab initio study on hydrogen interaction with calcium decorated silicon carbide nanotube

© 2017 Hydrogen Energy Publications LLC Ab initio study on the viability of calcium decorated silicon carbide nanotube as a hydrogen storage material was conducted. Calcium strongly adsorbs on silicon carbide nanotube (SiCNT) with a significant binding energy of −2.83 eV, thus calcium\u27s low cohesive energy and strong binding with SiCNT may prevent Ca to form clusters with other adsorbates. Bader charge analysis also revealed a charge transfer of 1.45e from Ca to SiCNT resulting to calcium\u27s cationic state, which may induce charge polarization to a nearby molecule such as hydrogen. Hydrogen molecule was then allowed to interact with the calcium adatom where it exhibited charge polarization, induced by the electric field from calcium\u27s positive charge. This resulted to a significant binding energy of −0.22 eV for the first hydrogen molecule. Results reveal that Ca on SiCNT can hold up to 7 hydrogen molecules and can be a promising candidate for a hydrogen storage material

A dynamic Leontief model with stochastic extensions for sustainable jatropha curcas biofuel supply chain

Jatropha biofuel is an excellent candidate for an alternative renewable and clean energy source. However, an increasing number of countries and investors are losing interest in J. curcas mainly because of the challenges they encountered caused by ineffective organization and coordination of the entire supply chains. For this purpose, a time varying input-output model with stochastic extension had been presented which can be used to simulate the supply chain dynamics of J. curcas biofuel. The model incorporates various extensions to the basic Leontief input-output model such as non-square matrix requirement for the technology matrix, adapting behavior based on target and current production levels, a control matrix to intervene on undesirable dynamics, and a Gaussian stochastic parameter that simulates uncontrolled changes in the production capacity which may be brought up by natural calamities and market instabilities. Numerical simulations of two-sector case studies having behavioral matrix patterned after the broad interactions between various sectorial agents were able to replicate the general trends of J. curcas biodiesel supply chain. The coefficients of the control matrix used to eliminate oscillatory dynamics of the system made physical suggestions that are strikingly similar to the ones made by some researchers in the field. With the incorporation of stochastic extension, the model was able to make predictions about the relative extent on how different streams will be affected by sudden random changes that are brought into the system

Tapioca starch based green nanocomposites with environmental friendly cross-linker

Starch based films have drawn considerable attention on food packaging owing to their attractive combination of price, environmental friendliness, and abundance. Nevertheless, the use of starch based films in industrial application were restricted by its poor mechanical properties and naturally intractable behavior. The aims of this work were to develop starch green composite films prepared with sustainable materials in agreement with ecology and economic requirements including environmental satisfactory disposal and to investigate the effects of nanocellulose and citric acid on tensile properties, and thermal properties of tapioca starch green composite films. Through the advance of nanotecnology, nanocellulose recovered from oil palm empty fruit bunches (EFB) by chemical approaches acted as reinforcing material incorporated into tapioca starch green composites. Citric acid was a cross-linking agent added to crosslink the tapioca starch molecules in the films. A series of tapioca starch green composite films with varying amount of nanocellulose (0.5, 1, 2, 3, 4, and 5 phr) as per dry weight of tapioca starch were produced by casting method. Plasticizer such as glycerol was added to improve the processing of tapioca starch green composite films by softening the polymer matrix. Confirmation of nanocellulose characteristics were carried out by using Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), and transmission electron microscopy (TEM). Whereas the effects of nanocellulose and citric acid on tapioca starch green composite films were performed by Instron Universal tensile testing machine and thermogravimetric analyzer (TGA). FTIR analysis on nanocellulose verified that the chemical treatments and acid hydrolysis removed non-cellulosic constituents including hemicelluloses and lignin from empty fruit bunches. XRD diffractograms revealed that the crystallinity of nanocellulose increased from 43.1 % of raw EFB to 65.8 %. TEM images confirmed the diameter of nanocellulose was in nano-sized with needle like structure. The tensile strength and modulus of elasticity of tapioca starch green composite films were enhanced significantly as the amount of nanocellulose increased from 0.5 to 3 phr and decreased for further addition of nanocellulose. While the value of break elongation sharply increased from 9.08 % for neat tapioca starch (TS) films to 109.36 % for crosslinked TS films. Therefore, these results reasonably remarked that nanocellulose from empty fruit bunches and citric acid could improve the tensile of tapioca starch green composite films. However, crosslinked TS/NC films using citric acid slightly lower the thermal stability. Copyright © 2017, AIDIC Servizi S.r.l.

Ca and K decorated germanene as hydrogen storage: An ab initio study

© 2018 Hydrogen Energy Publications LLC The hydrogen storage capacity and performance of Ca and K decorated germanene were studied using density functional theory calculation. The Ca and K adatoms were found to be sufficiently bonded to the germanene without clustering at the hollow site. Further investigation has shown an ionic bonding is apparent based on the charge density difference and Bader charge analysis. Upon adsorption of H2 on the decorated germanene, it was found that the Ca and K decorated systems could adsorb 8 and 9 H2 molecules, respectively. The adsorption energies of H2 molecules were within the Van der Waals energy (400–435 meV), suggesting weak physisorption. The charge density profile revealed that the electron of H2 moved toward the adatom decoration without leaving the local region of H2. This suggests that a dipole-dipole interaction was apparent and consistent with the energy range found. Finally, the gravimetric density obtained from the adsorption of H2 on the decorated germanene shows that this material is a potential for H2 storage media

Structures and UV resistance of Ag/SnO2 nanocomposite materials synthesized by horizontal vapor phase growth for coating applications

The structures and UV resistance of Ag/SnO2 nanocomposite materials was observed in this study for coating applications. Horizontal Vapor Phase Growth (HVPG) was used to synthesize the Ag/SnO2 nanocomposite materials. The ratio between Ag and SnO2 was fixed with stoichiometric mixtures of 0:5, 1:4, 2:3, 3:2, 4:1, and 5:0. Scanning electron microscope–energy-dispersive X-ray spectroscopy (SEM–EDX) was used to evaluate the morphology of the materials. The results were then compared with Density Functional Theory (DFT) analysis. Computational DFT analysis of the SnO2 (110) and Ag (111) cells have verified nanorods formation of the composite material. Moreover, DFT results of Ag/SnO2 confirmed the UV blocking properties from their computed electrical bandgap energies of the range from 2.72 to 4.84eV. The highest UV absorbance of nanocomposite was observed for 1:4 Ag/SnO2 stoichiometric ratio with 8.09 A. The study shows that the ration of SnO2 over Ag increases, the absorbance increases as well. © 2020 The Authors