The aim of the present study is to investigate the possibility of using phosphorous-doped graphene (P-Gr) as an efficient and selective sorbent for capture and storage of CO2. Density functional ...theory calculations indicate that in the absence of the electric field, CO2 weakly interacts with the P atom of P-Gr. However, when an electric field of 0.013–0.020 au is applied, CO2 is strongly chemisorbed over P-Gr. Meanwhile, the chemisorbed CO2 can be easily released from the P-Gr surface as the electric field is removed. This indicates that the storage and release of CO2 may be controlled by applying an electric field in the range of 0.013–0.020 au. According to our results, P-Gr can selectively capture CO2 from a CO2/N2 mixture under the electric field due to the difference between the adsorption energies of CO2 and N2.
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•The P atom can be stably incorporated in graphene.•CO2 is physisorbed over P-Gr in the absence of the electric field.•The storage/release of CO2 is possible by applying an external electric field.•CO2 capture by P-Gr can be controlled by the strength and sign of electric field.
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•Incorporation of pyridinic nitrogen atoms around the Pd atom enhances the catalytic activity of Pd-doped graphene.•CO oxidation over Pd supported nitrogen-doped graphene proceeds via ...the termolecular Eley-Rideal (TER) mechanism.•The pyridinic N atoms makes a shift in the d-band center of the Pd atom towards the Fermi level.•CO oxidation through the TER mechanism is a thermodynamically favorable process.
Single-metal catalysts have attracted particular interests in recent years due to their outstanding catalytic activity in CO oxidation reaction. In the present study, periodic DFT calculations are performed to investigate possible reaction mechanisms for oxidation of CO over a single Pd atom incorporated nitrogen-doped graphene. According to our results, the formation energy of a single-vacancy decreases by incorporation of pyridinic nitrogen atoms in graphene. The Pd atom can be stably anchored over the vacancy site, as evidenced by the large energy barriers for diffusion of the Pd atom to its neighboring sites. It is found that the incorporation of nitrogen atoms makes a significant increase in the adsorption energy of O2 and CO molecules over the supported Pd atom. The latter can be attributed to the shift in the bonding states of the Pd towards the Fermi level, which facilitates the charge-transfer from the 4d orbitals of this atom to the 2π∗ orbitals of O2 and CO molecules. The CO oxidation over the Pd atom supported nitrogen-doped graphene can proceed via three different mechanisms; namely, Eley-Rideal (ER), Langmuir-Hinshelwood (LH) and termolecular Eley-Rideal (TER) mechanisms. Our calculations reveal that the TER mechanism is preferred over the LH and ER, due to its smaller activation energy. The CO oxidation via the TER mechanism is a thermodynamically favorable process over the supported Pd atom, due to a large negative change in the Gibbs free energy of this reaction. The findings of this study can be useful to design more efficient single-atom catalysts to remove toxic CO molecules.
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•A single Co atom can be stably anchored over a monovavancy nitrogen-doped graphene.•CO2 hydrogenation proceeds via the formate (HCOO) intermediate.•The activation energy for the ...rate-determining-step of this reaction is 0.51 eV.•The formation of side products (CO and H2O) is almost impossible or proceeds with great difficulty.
The catalytic hydrogenation of CO2 molecule over a single Co atom incorporated nitrogen-doped graphene is investigated using dispersion-corrected density functional theory calculations. It is found that a Co adatom can be effectively stabilized over a mono- or di-vacancy defective nitrogen-doped graphene due to strong hybridization between the Co-3d and N-2p states near the Fermi level. The high energy barrier for the diffusion of Co atom suggests that the resulting structures are stable enough to be used in the hydrogenation of CO2. Our results indicate the Co atom incorporated over a mono-vacancy defective nitrogen-doped graphene (CoN3-Gr) has a large tendency to activate H2 and CO2 molecules due to localization of a relative large positive charge on the Co atom. The hydrogenation of CO2 over CoN3-Gr starts with the coadsorption of H2 and CO2, followed by the formation of a formate (HCOO) intermediate. This needs an activation energy of 0.31 eV, which indicates it can easily proceed at ambient temperature. In the next step, the HCOO moiety is converted to HCOOH by overcoming an energy barrier of 0.51 eV. Our results indicate that the formation of side products, i.e. CO and H2O, is almost impossible or proceeds with great difficulty due to the corresponding large activation energy. The results of this study suggest that CoN3-Gr can be regarded as a highly active and promising catalyst for hydrogenation of CO2 at room temperature.
In recent years, noncovalent interactions involving group-14 elements of the periodic table acting as a Lewis acid center (or tetrel-bonding interactions) have attracted considerable attention due to ...their potential applications in supramolecular chemistry, material science and so on. The aim of the present study is to characterize the geometry, strength and bonding properties of strong tetrel-bond interactions in some charge-assisted tetrel-bonded complexes. Ab initio calculations are performed, and the results are supported by the quantum theory of atoms in molecules (QTAIM) and natural bond orbital (NBO) approaches. The interaction energies of the anionic tetrel-bonded complexes formed between XF₃M molecule (X=F, CN; M=Si, Ge and Sn) and A
anions (A
=F
, Cl
, Br
, CN
, NC
and N₃
) vary between -16.35 and -96.30 kcal/mol. The M atom in these complexes is generally characterized by pentavalency, i.e., is hypervalent. Moreover, the QTAIM analysis confirms that the anionic tetrel-bonding interaction in these systems could be classified as a strong interaction with some covalent character. On the other hand, it is found that the tetrel-bond interactions in cationic tetrel-bonded p-NH₃(C₆H₄)MH₃⁺···Z and p-NH₃(C₆F₄)MH₃⁺···Z complexes (M=Si, Ge, Sn and Z=NH₃, NH₂CH₃, NH₂OH and NH₂NH₂) are characterized by a strong orbital interaction between the filled lone-pair orbital of the Lewis base and empty BD*
orbital of the Lewis base. The substitution of the F atoms in the benzene ring provides a strong orbital interaction, and hence improved tetrel-bond interaction. For all charge-assisted tetrel-bonded complexes, it is seen that the formation of tetrel-bond interaction is accompanied bysignificant electron density redistribution over the interacting subunits. Finally, we provide some experimental evidence for the existence of such charge-assisted tetrel-bond interactions in crystalline phase.
The selective epoxidation of ethylene on Pd-doped C3N nanosheet (Pd@C3N) is investigated using dispersion-corrected DFT calculations. The electronic resonance between the Pd and its neighboring C ...atoms is shown to significantly activate the adsorbed O2 and C2H4 molecules on Pd@C3N. According to our results, the coadsorption of O2 and C2H4 molecules on Pd@C3N is more energetically feasible than a single O2 or C2H4 adsorption. The oxidation of ethylene on Pd@C3N is accomplished via two mechanisms, i.e., bimolecular (B-LH) and trimolecular Langmuir–Hinshelwood (T-LH). In both pathways, the ethylene oxide formation is favored over the acetaldehyde formation. The obtained activation barriers are comparable to those reported for Au-based catalysts. Moreover, the epoxidation of ethylene has a faster kinetics than the formation of acetaldehyde. Also, the effects of temperature and entropy are studied on the rate-determining steps of the B-LH and T-LH mechanisms.
•A single Pd atom can strongly bind to N-defective C3N monolayer.•Ethylene epoxidation is preferred kinetically over acetaldehyde formation.•The ethylene epoxidation has a fast kinetics over Pd-doping C3N.•The activation energies obtained are comparable to those of Au catalysts.
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•The oxidation of CO by O2 molecule is investigated over Al- and Ge-embedded graphene.•The first reaction pathway of the CO oxidation over both surfaces should proceed with the ER ...mechanism.•Ge-embedded graphene can be used as a more efficient catalyst for oxidation of CO than Al- embedded graphene.
In the present study, by means of density functional theory (DFT) calculations, the catalytic oxidation of CO by O2 molecule is investigated over Al- and Ge-embedded graphene. The large atomic radius of these dopant atoms can induce a local surface curvature and modulate the electronic structure properties of the graphene sheet through the charge redistribution. It is found that the adsorption of molecular O2 over Al- or Ge-embedded graphene is stronger than that of CO molecule. The CO oxidation reaction by molecular O2 on Al- and Ge-embedded graphene is comparably studied. The results indicate that a two-step process can occur, namely, CO+O2→CO2+Oads and CO+Oads→CO2. Furthermore, the computed activation energy (Eact) for the first reaction on Ge-doped graphene is lower than that of Al-doped one, and the formation of second CO2 molecule on both surfaces can occur rapidly due to its low energy barrier (0.1eV).
The present study focuses on development of pure and Ru-doped TiO2 nanofibers as potential candidates for humidity sensing. Electrospun technique is used for fabrication of the nanofibers to evaluate ...their humidity sensing properties via QCM method. The obtained nanofibers are analyzed by X-ray diffraction and scanning electron microscopy techniques. The humidity adsorption kinetics and the mechanism of sensing humidity are explored, in details. The results of X-ray analyses reveal that TiO2 nanofibers with a mixture of anatase and rutile structures are successfully synthesized. Additionally, Ru reduces the crystalline size and intensity of the TiO2 peaks. The QCM results show that Ru-doping enriched the humidity sensing performance of TiO2 nanofibers. According to the DFT calculations, the introduction of Ru atoms into TiO2 leads to a sizable increase in the adsorption energy of the water molecule. It is also found that the Ru-doping makes an increase in the charge-transfer from the water molecule into the surface, which can result in an enhanced sensing response of TiO2 by decreasing the electrical resistance.
•Ru-doped TiO2 nanofibers was fabricated by Electrospun technique.•XRD results reveal that Ru reduces the crystalline size and intensity of the peaks.•Ru-doping enriched the humidity sensing performance of TiO2 nanofibers.•DFT results shows that the Ru increase the adsorption energy of the water molecule.•Ru-doping increase the charge transfer from the water molecule into the surface.
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•The metal-free reduction of N2O on carbon-doped BN nanosheet (C-BNNS) is studied by periodic DFT calculations.•N2O is spontaneously decomposed over C-BNNS.•The activation energy for ...the reduction of N2O by CO or SO2 is small and comparable with those of over noble metal catalysts.
We report for the first time, the catalytic activity of the experimentally available carbon-doped boron nitride nanosheet (C-BNNS) towards the reduction of N2O in the presence of CO or SO2 molecule. According to our density functional theory calculations, C-doping can introduce high spin density into BN monolayer which is mainly localized over the C and its neighboring N atoms. The Hirshfeld charge density analysis reveals that the electron-rich C-BNNS acts as an electron donating support to activate N2O molecule which is an important step in the reduction of N2O. The N2O reduction reaction starts with the dissociative adsorption of N2O over the C-BNNS surface, yielding the N2 molecule and an activated oxygen moiety (Oads) adsorbed over the C atom. The reaction then proceeds via the elimination of Oads by a CO or SO2 molecule. The obtained low activation energies clearly indicate that the metal-free C-BNNS surface can be regarded as a highly active catalyst for the reduction of N2O. The results of this study may open new avenues in searching low cost and highly active BN-based catalysts for low temperature reduction of N2O.
H2 storage and capture are critical components in the development of clean and sustainable hydrogen energy. The current work investigates the H2 adsorption properties and storage on the Al-decorated ...porphyrin-like small porous C24N24 cluster using density functional theory calculations. Each Al site in the Al6C24N24 cluster can adsorb up to five H2 molecules, with an average adsorption energy of −0.30 eV. The impact of temperature and pressure on the hydrogen storage capacity of Al-decorated C24N24 clusters is also studied. A Kubas type mechanism and electrostatic interactions are found to be essential in the adsorption of H2 molecules on the Al-decorated C24N24. According to our findings, Al6C24N24 has a gravimetric density of 7.1 wt% H2. These findings demonstrate that the Al-decorated C24N24 may be a potential candidate for reversible H2 storage under normal conditions.
The development of effective drug delivery vehicles is essential for the targeted administration and/or controlled release of drugs. Using first-principles calculations, the potential of alkali metal ...(AM = Li, Na, and K) decorated C
fullerenes for delivery of 5-fluorouracil (5FU) is explored. The adsorption energies of the 5FU on a single AM atom decorated C
are -19.33, -16.58, and -14.07 kcal mol
for AM = Li, Na, and K, respectively. The results, on the other hand, show that up to 12 Li and 6 Na or K atoms can be anchored on the exterior surface of the C
fullerene simultaneously, each of which can interact with a 5FU molecule. Because of the moderate adsorption energies and charge-transfer values, the 5FU can be simply separated from the fullerene at ambient temperature. Furthermore, the results show that the 5FU may be easily protonated in the target cancerous tissues, which facilitates the release of the drug from the fullerene. The inclusion of solvent effects tends to decrease the 5FU adsorption energies in all 5FU-fullerene complexes. This is the first report on the high capability of AM decorated fullerenes for delivery of multiple 5FU molecules utilizing a C
host molecule.
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