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Despite known toxic properties of phenol and its derivatives, their man-caused release into nature continues. Their importance as building blocks in polymers, pesticides, pharmaceuticals and other industrial chemicals remains a barrier for reducing their introduction into ecosystems. Hence, a considerable effort has been devoted to these organic contaminates removal from water sources. In the present work, we have employed functionalized (5, 5) carbon nanotubes (f-CNTs) for adsorption and remidiation of phenol pollutant from water. Several binding sites (incloding hydroxyl and phenyl groups) were considered due to their ability in π-π stacking and H-bonding interactions with phenol. The adsorption modes and energies of both water and phenol to these sites are evaluated using a general dispersion-corrected density functional (DFT-D3) method. We showed that both water and phenol molecules are weakly bound (weak physisorption) to the outer surface of pristine CNT while they can be adsorbed stronger on the functionalized CNTs. It was found that phenol bound stronger to the CNT-OH than water molecule which was due to the existence of simultaneous π-π stacking and H-bonding in the system. Also, we have prepared a brief report about the solvent effect in the adsorption nature of the more stable systems.The results show that the absorption energy sequence for the absorbing/carbon nanotube complexes in the aqueous phase is similar to the calculated absorption energy for in the gas phase, but adsorption decreased in the aqueous phase. We have also provided a succinct report about the reactivity, energy gap and polarity of the considered systems for all systems. For comparison, we evaluated the adsorption behavior for zigzag OH-CNT (8, 0).The calculation reveal that difference of the binding energy of phenol and water molecules on a zigzag is alike to the armchair CNT system. The phenol adsorption properties onto CNT-OH system in periodic and cluster SWCNT have compared and we were found that the results predicted by the CNT saturated with hydrogen can be comparable to periodic SWCNT. Furthermore, our first-principles calculations demonstrated the importance of dispersion corrections based on weak intermolecular interactions in designing absorbents. Our study offers molecular level understanding of the interactions between water/phenol molecule and CNTs surface and may be informative for toxicity agent adsorption and remediation from environment. [ABSTRACT FROM AUTHOR]

The effective enrichment and detection of organic pollutants in the environment has been attracted much attention because of enormous concerns about human health. Using dispersion-corrected density functional theory (DFT-D2), the interactions between 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin (TCDD) and pristine, defected and Al-doped carbon nanotubes (Al-CNT) were studied. The TCDD molecule was physisorbed on a pure CNT and CNT contain defects with binding energies of about −0.52 eV and −0.34 eV, respectively. The accuracy of our method was validated by hybrid B3LYP levels of theory and it was shown that there is a worthy agreement between two respected methods. However, the binding energy rises to −0.85 eV when TCDD binds to Al-CNT. The increase in binding energy is due to charge transfer from the TCDD molecule to the Al - CNT. Furthermore, the obtained DOS spectra and total charge density indicates that the electronic properties of Al-CNT change considerably by the adsorption of TCDD whereas no such variations are observed for other considered CNTs. Consequently, the Al-CNT is a promising candidate for the TCDD sensing and detection. Our first-principles results present evidences for a rational benchmark for the applicability of the Al-CNT for TCDD adsorption and detection. [ABSTRACT FROM AUTHOR]

Since the successful synthesis of nanocar and its surprising movement on the gold surface, several theoretical investigations have been devoted to explain the interaction properties as well as its movement mechanism on the substrate. All of them failed, however, to gain a clear theoretical insight into the respected challenges because of the weak computational methods implemented for this complex system including heavy metal atoms and giant size of the whole system. In this work, we have investigated the adsorption of fullerene-wheeled nanocar onto a Au (1 1 1) substrate using the comprehensive first-principles density functional theory (DFT) simulations. The binding energy between the nanocar and Au (1 1 1) surface was determined to be −9.43 eV (−217.45 kcal/mol). The net charge transfer from the nanocar to the gold substrate was calculated to be about 9.56 electrons. Furthermore, the equilibrium distances between the Au surface and the C 60 molecule and nanocar chassis were estimated to be 2.20 Å and 2.30 Å, respectively. The BSSE correction was also considered in the binding energy estimation and the result show that the BSSE correction significantly affects the calculated binding energy for such systems. Finally, we have performed ab initio molecular dynamics simulation for a single C 60 fullerene on the gold surface at room temperature. Our first-principles result shows that ambient condition affect remarkably on the adsorption property of fullerene on the gold surface. We also observed that the C 60 fullerene wheel slips by approximately 3.90 Å within 5 ps of simulation time at 300 K. [ABSTRACT FROM AUTHOR]

In the present work, we report a detailed theoretical investigation of a series of metalloporphyrin, MP (M = FeP, CoP and ZnP), molecules interacting with silicon carbide nanotube (SiCNT) by means of density functional theory (DFT) calculations. In all calculations, we used the Perdew–Burke–Erzenhof (PBE) functional as employed in the SIESTA package. The detailed analysis of the structural and electronical properties of various optimized configurations is performed. The results show that among the MPs, adsorption of FeP molecule on the Si site with zigzag orientation is the most energetically preferable with a binding energy of −2.10 eV. Compared to SiCNTs, boron nitride nanotubes (BNNTs) have weaker interaction strength with the FeP molecule with −0.34 eV of binding energy. We have analyzed charge transfer between two interacting species trough well-known Mulliken, Hirshfeld and Voronoi charges analysis for aforementioned systems. The spin-polarized DFT calculations showed that the density of states (DOSs) are spin-polarized for the Fe-BNNT complex while the spin-polarization of the DOS spectra turn out to be less notable for MP-SiCNT complexes. Our results propose that FeP-SiCNT complex could be used for interesting applications in solar cell technology and nano-biosensors while FeP-BNNT complex might be considered for spintronic molecular devices. [ABSTRACT FROM AUTHOR]

The adsorption of hydrogen molecules (H 2 ) on Si-decorated graphene was studied by using density functional theory calculations based on local density approximation (LDA). The accuracy of our method was validated by high level quantum chemical calculation result at MP2 level of theory for similar system. Our calculations show that Si-decorated graphene has high adsorption energy, high net charge transfer values and small connecting distances to graphene surface due to chemisorption. This makes adsorbed Si on the surface as a positive center which can adsorb considerably H 2 molecules. We find that up to 16 H 2 molecules can stably bind to two Si atoms on both side of the graphene sheet with slightly desirable adsorption energy which indicates that the resultant system facilitates the hydrogen desorption at near ambient conditions for practical applications. This newly developed Si decorated graphene with its hydrogen storage capacity of about 15 wt% would be an excellent candidate for hydrogen storage mediums. [ABSTRACT FROM AUTHOR]

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCCD) is one of the most dangerous compounds that infect the environment and hence its removal is crucial for safety in human life. In this work, we have investigated the interaction of TCDD with boron nitride nanotubes (BNNTs) and carbon nanotubes (CNTs) by using the density functional theory (DFT) calculations. Our first-principles results have been validated by experiment and also other theoretical values for the similar system. The adsorption energies for TCDD molecule on the BNNTs and CNT are calculated. It was found that TCDD adsorption ability of BNNT is slightly stronger than that of CNT and TCDD molecule prefers to be adsorbed on BNNTs with molecular axis parallel to the tube axis. The results obtained indicate that TCDD is weakly bound to the outer surface of all the considered nanotubes and the obtained adsorption energy values and binding distance are typical for the physisorption. We also evaluated the influence of curvature and introduced defects on the TCDD adsorption ability of BNNTs. Furthermore, we have analyzed the electronic structure and charge population for the energetically most favorable complexes and the results indicate that no significant hybridization between the respective orbitals of the two entities was accomplished. [ABSTRACT FROM AUTHOR]

The adsorption of DMMP as an intoxicating chemical warfare agent onto the boron nitride nanotube has been investigated by using density functional theory calculations. Several active sites were considered for both interacting systems and full structural optimization was performed to accurately find the energetically favorable state. It is found that DMMP molecule prefers to be adsorbed strongly on the top site above the B atom of a (5, 0) BNNT with a binding energy of about −103.24 kJ mol −1 and an O–B binding distance of 1.641 Å. We have performed a comparative investigation of BNNTs with different diameters and the results indicate that the DMMP adsorption ability for the side wall of the tubes significantly decreases for higher diameters BNNTs. Furthermore, the adsorption properties of DMMP molecule onto the BNNT have been investigated using the ab initio MD simulation at room temperature. Our result showed that BNNTs facilitates the DMMP detection at ambient conditions for practical applications. [ABSTRACT FROM AUTHOR]

The adsorption of hydrogen sulfide (H2S) molecules on non-carbonic (B, Al, and Ga nitride) graphene was studied using a first-principles van der Waals density functional (vdW-DF) method. For the adsorption of a single molecule, we determined the most stable configurations, equilibrium geometries, adsorption energies, and electronic properties by approaching the molecule on the surface of non-carbonic graphenes at different possible sites. The Ga nitride (GaN) graphene was more capable of H2S molecule adsorption than the other graphenes due to the higher binding energy value and shorter bonding distance between the H2S molecule and the graphene surface. Electron transfer calculations confirmed that the electronic properties of GaN graphene changes significantly compared to other graphenes after H2S molecule adsorption. The density of states results indicated a stronger physical hybridization between H2S and GaN graphene. Furthermore, co-adsorption of two H2S molecules on the GaN graphene as a single-layer/bi-layer of adsorbed molecules was examined. Finally, Al and Ga metal atoms decorated on carbonic graphene (Al- and Ga-cargraph) to investigate H2S adsorption. The adsorption of H2S on Al- and Ga-cargraph was weaker than that on the non-carbonic graphenes. Therefore, based on the obtained results, GaN graphene is promising for uses in gas sensor devices for detect H2S. [ABSTRACT FROM AUTHOR]

The adsorption of NH3 on a (5, 0) single-walled SiC nanotube is studied by using the density functional theory approach. The silicon atoms in sites on SiCNT surface is the most stable adsorption site for N pointing of NH3 toward the nanotube surface, with a binding energy of -1.36 eV (-31.35 kcal mol-1) and a Si-N binding distance of 1.972 Å. We also have tested the stability of the NH3-adsorbed SiCNT with ab initio molecular dynamics calculations, which have been carried out at room temperature. Furthermore, the adsorption of NH3 on the single-walled carbon nanotubes has been investigated. Our first-principles calculations predict that the NH3 adsorptive capability of silicon carbide nanotubes is much better than that of carbon nanotubes. This demonstrates that SiCNTs could be a promising material for gas detection and energy storage. [ABSTRACT FROM AUTHOR]

We perform detailed calculations for the adsorption of a single hydrogen molecule by the carbon nanotubes (CNTs) bundles by using Density Functional based Tight Binding (DFTB) method. We have considered an armchair (3, 3) CNTs bundle which consists of seven tubes. It has been found that the binding energy of H2 in the interstitial channels between three tubes site is much higher than the others while, the binding distance of H2 in this site is much smaller than that in other sites. The results also show that H2 molecule become chemisorbed on the outer surface of the tubes via the covalent bonds. Furthermore, the mechanism of the C-H bond formation is studied by density functional based tight binding molecular dynamics simulation which has been carried out at room temperature. [ABSTRACT FROM AUTHOR]