A first-principles study of gas molecule adsorption on hydrogen-substituted graphdiyne

Hydrogen-substituted graphdiyne (HsGDY) is a novel alkynyl carbon material with a structure similar to that of graphene. In this paper, the adsorption of four gas molecules (NO, NO₂, NH₃, and N₂) on HsGDY and B-doped HsGDY (B-HsGDY) was studied using density functional theory. The results show that the adsorption of NO and NO₂ on HsGDY and B-HsGDY is characterized by a larger charge transfer, stronger interaction, and higher adsorption energy compared with that of NH₃ and N₂. Based on the doping with B atoms, the adsorption energies of the gas molecules on HsGDY significantly improve, especially that of NO and NO₂. The gas molecule adsorption on both HsGDY and B-HsGDY is physical adsorption and the adsorption selectivity is good and thus may be applied for gas-sensitive NO and NO₂ materials.     

Mott insulator-superfluid phase transition in p-band triangle optical lattices with on-site rotation

In order to exploit the potential applications of graphene as gas sensors, the adsorptions of a series of small gas molecules (such as CO, O₂, NO₂ and H₂O) on pristine graphene (PG) and Si-doped graphene (SiG) have been investigated by ab initio calculations. Our results indicate that the electronic properties of PG are sensitive to O₂ and NO₂ molecules, but not changed much by the adsorption of CO and H₂O molecules. Compared with PG, SiG is much more reactive in the adsorption of CO, O₂, NO₂ and H₂O. The strong interactions between SiG and the adsorbed molecules induce dramatic changes to the electronic properties of SiG. Therefore, we suggest that SiG could be a good gas sensor for CO, O₂, NO₂ and H₂O.     

Adsorption of pairs of NOx molecules on single-walled carbon nanotubes and formation of NO + NO3 from NO2

The adsorption of NO_x(x = 1, 2, 3) molecules on single-walled carbon nanotubes (SWCNTs) is investigated using first-principle calculations. Single NO, NO₂ and NO₃ molecules are found to physisorb on SWCNTs, but molecules can be chemisorbed in pairs on the top of carbon atoms at close sites of SWCNTs. The adsorption energy for pairs of NO or NO₃ molecules is larger than for pairs of NO₂ molecules. The local curvature is found to have a sizable effect on adsorption energies. The possibility of a surface reaction NO₂ + NO₂ → NO + NO₃ is examined and the relative pathway and barrier is calculated. The results are discussed with reference to available experimental results.     

Adsorption of small molecules on transition metal doped rhodium clusters Rh3X (X = 3d, 4d atom): a first-principles investigation

The adsorption behaviours of seven molecules (CO, CO₂, N₂, NO, O₂, N₂O and NO₂) on Rh₃X (X?=Sc-Zn, Y-Cd) clusters are systematically investigated by density-functional calculations. Rh₃X clusters exhibit physical adsorption when interacting with CO₂, CO, N₂ and NO. The adsorption energies (E_ads) can be ranked as follows: NO?>?CO?>?CO_2?≥?N₂. Compared with pure Rh₄ cluster, the adsorption capacity changes with the doping element. Chemical adsorption can be obtained for Rh₃X when adsorbing O₂, N₂O and NO₂. E_ads shows an order of E_ads(O₂)?>?E_ads(NO₂)?>?E_ads(N₂O). When O₂ is adsorbed, energy barrier with doping Tc or Cr atom is substantially reduced, which indicates that chemical reactivity of O₂ on Rh₄ can be significantly enhanced. The doped rhodium clusters can be viewed as good candidates in the discrimination between different gas molecules.     

Tuning the electronic and magnetic properties of germanene by surface adsorption of small nitrogen-based molecules

The structural, energetic and electronic properties of germanene adsorbed with small nitrogen-based molecules, including N₂, NH₃, NO₂ and NO, have been investigated by using first-principles calculations. The results show that all nitrogen-based molecules considered bind much stronger to germanene than to graphene due to the hybridized sp²-sp³ bonding of Ge atoms. The N₂, NO and NO₂ molecules all act as an acceptor, while the NH₃ molecule donates electrons to germanene. We also found sizable band gaps (2–158 meV) are opened at the Dirac point of germanene through N₂, NH₃, and NO₂ adsorptions, but with only slightly destroying its Dirac cone shape. The NO₂ molecule also shows a heavy p-type doping character and makes germanene to be metallic. Moreover, when adsorbed by NO molecule, the germanene can change to be a ferromagnetic half-metal with 100% spin-polarization at the Fermi level. Overall, the different adsorption behaviors of small nitrogen-based gas molecules on germanene provide a feasible way to exploit chemically modified germanene for a wide range of practical applications, such as field-effect transistors, gas sensors and spintronic devices.     

Molecular adsorption of NO on free-standing and on graphene-supported Mo<Subscript>3</Subscript>W<Subscript>5</Subscript> cluster: a density functional theory investigation

The adsorption of molecular NO on the free-standing and graphene-supported Mo₃W₅ cluster is studied using methods from the gradient-corrected density functional theory. Before, the effect of the graphene support on the properties of the metal cluster was investigated. The interaction between the metal cluster and the graphene sheet takes place mainly through W atoms, which form up to three bonds with the support. Interaction energies are in the range from 0.6 to 1.5 eV. An amount of charge of about 0.4–0.5 e\(^-\) is transferred from the cluster to the support. Geometric distortions in the metal aggregate are negligible. An important decrease in the magnetic moment of Mo₃W₅ with respect to its free-standing value is observed after the interaction with the support. Molecular NO adsorbs on sites involving W atoms only, both for the free-standing and the supported metal cluster. Adsorption energies are in a range from 2 to 4 eV. A parallel mode is the preferred mode from an energetic point of view. Moreover, for that parallel adsorption mode, the N–O bond is more effectively activated. Magnetic moments change largely after adsorption indicating important rearrangement in the electronic configuration of the metal cluster. An important amount of electronic charge is transferred both from the free-standing and from the supported metal cluster to NO. The amount of charge transferred seems to be closely related to the activation of the N–O bond. The effect of the graphene sheet on the catalytic properties of Mo₃W₅ seems to be negligible, with the exception of some changes in the electronic configuration of the cluster.     

Controlling spin off state by gas molecules adsorption on metal-phthalocyanine molecular junctions and its possibility of gas sensor

Employing Green's function (GF) technique in combination with spin-polarized density functional theory (DFT), we study the electronic structure and magnetic properties of metal phthalocyanine (MPc) (M?=?Mn, Fe, Co, Ni, Cu, Zn) with or without four different gas molecules (NO, CO, O₂ and NO₂) adsorbing on the M atom of MPc molecule. The corresponding stable adsorption structural configurations and transport properties of MPc molecular junctions are also investigated. Our results indicate that the magnetic moment of MPc for M?=?Mn, Fe and Co can be modified by the specific gas molecule adsorption, which is mainly ascribed to competitive relation of HOMO-LUMO Gap and Hund's rules. However, for M?=?Ni, Cu and Zn, it is difficult to detect gas molecule because the interaction of M atom and these gases is most of weak van der Waals interaction. Remarkably, the spin of MPc molecule can be switched to a magnetic off-state by specific gas absorption, giving rise to a potential application on controllable spintronic devices. In addition, CO, NO, O₂ and NO₂ gas molecules can be detected selectively by measuring spin filter efficiency of these MPc molecular junctions. On the basis of our results, MPc (M?=?Mn, Fe, Co) molecular junctions can be considered as a promising nanosensor device to detect individual gas molecules.     

NO<Subscript>2</Subscript>-sensing properties of La<Subscript>0.65</Subscript>Sr<Subscript>0.35</Subscript>MnO<Subscript>3</Subscript> synthesized by self-propagating combustion

Ultrafine-structure La_0.65Sr_0.35MnO₃ (LSM) powders synthesized by self-propagating combustion method have been used to fabricate sensing electrodes (SEs) for NO₂ mixed-potential sensors based on yttria-stabilized zirconia (YSZ). This type of sensor was found to provide better NO₂ sensitivity at 500 °C than sensors with LSM powders synthesized by traditional solid-state methods. The response values of the sensor have good linear relationship (sensitivity 36.6 mV/decade and linear fit 0.99) with the logarithm of NO₂ concentration varying from 30 to 500 ppm. The influence of sintering temperature (1000, 1100, 1200, and 1300 °C) on sensor response was also examined and was found to have a significant effect on the morphology of LSM-SEs. Moreover, in the presence of NO, CO₂, CO, and NO₂, the sensor exhibited good NO₂ selectivity.     

Evidence for oxygen abstraction from NO<Subscript>2</Subscript> upon thermal scattering from an Al(111) surface

Evidence is presented for the existence of a non-adiabatic reaction channel, namely the abstraction of an oxygen atom from a nitrogen dioxide molecule upon scattering from an aluminium(111) surface. This reaction channel was studied by exposing the sample to an NO₂ molecular beam and subsequently analysing the scattered flux using REMPI spectroscopy. In these experiments, a considerable amount of NO emitted from the surface was detected. The emitted NO has a rotational temperature of ca. 260 K that increases only slowly with surface temperature. In summary, these results provide first evidence for the abstraction reaction NO_2(g)NO_(g)+O_(a) upon NO₂/Al(111) scattering, which may arise when two electrons are rapidly transferred to the incoming molecule while it is unfavourably oriented for concurrent adsorption of both fragments. PACS 82.65.+r; 68.43.-h     

Graphene-based nitrogen dioxide gas sensors

In this study, we demonstrated that graphene could selectively absorb/desorb NO_x molecules at room temperature. Chemical doping with NO₂ molecules changed the conductivity of the graphene layers, which was quantified by monitoring the current–voltage characteristics at various NO₂ gas concentrations. The adsorption rate was found to be more rapid than the desorption rate, which can be attributed to the reaction occurred on the surface of the graphene layer. The sensitivity was 9% when an ambient of 100 ppm NO₂ was used. Graphene-based gas sensors showed fast response, good reversibility, selectivity and high sensitivity. Optimization of the sensor design and integration with UV-LEDs and Silicon microelectronics will open the door for the development of nano-sized gas sensors that are extremely sensitive.     

B-, N-doped and BN codoped C60 heterofullerenes for environmental monitoring of NO and NO2: a DFT study

ABSTRACT

Using density functional theory calculations, we investigate the gas sensing performance of B-, N-doped and BN-codoped C₆₀ fullerenes towards NO and NO₂ molecules. The calculated adsorption energies and net charge-transfer values indicate that NO and NO₂ molecules have a stronger interaction with the BN-codoped fullerenes compared to the B- or N-doped ones. It is also found that the electronic properties of the BN-codoped C₆₀ exhibit a larger sensitivity towards NO and NO₂ molecules. An increase in the concentration of doped/co-doped B and N atoms tends to weaken the gas sensing ability of these systems.     

Enhanced gas-sensing performance of graphene by doping transition metal atoms: A first-principles study

By performing the first-principles calculations, we investigated the sensitivity and selectivity of transitional metal (TM, TMSc, Ti, V, Cr and Mn) atoms doped graphene toward NO molecule. We firstly calculated the atomic structures, electronic structures and magnetic properties of TM-doped graphene, then studied the adsorptions of NO, N₂ and O₂ molecules on the TM-doped graphene. By comparing the change of electrical conductivity and magnetic moments after the adsorption of these molecules, we found that the Sc-, Ti- and Mn-doped graphene are the potential candidates in the applications of gas sensor for detection NO molecule.     

SERS and XPS observation of the adsorption behavior of NO and NO2 on a silver powder surface

The influence of H₂O on the adsorption behavior of NO or NO₂ on a silver powder surface was studied by SERS and XPS at room temperature. Water vapor was found to be responsible for the adsorption of NO on the silver powder surface. When surface species such as Ag₂O are present on the surface, some of the NO₂ molecules are adsorbed on the surface species to produce NO^-₃, whereas NO molecules are adsorbed on a different site to produce NO^-₂.     

基于密度泛函理论研究掺杂Pd石墨烯吸附O2及CO

基于第一性原理的密度泛函理论研究了单个O₂和CO气体分子吸附于本征石墨烯和掺杂钯(Pd)的石墨烯的体系, 通过石墨烯掺Pd前后气体分子的吸附能、电荷转移及能带和态密度的计算, 发现掺Pd后气体分子吸附能和电荷转移显著增大, 这是由于Pd的掺杂, 在本征石墨烯能带中引入了杂质能级, 增强了石墨烯和吸附气体分子间的相互作用; 氧化性气体O₂和还原性气体CO吸附对石墨烯体系能带结构和态密度的影响明显不同, 本征石墨烯吸附O₂后, 费米能级附近态密度变大, 掺Pd后在一定程度变小; 吸附还原性的CO后, 石墨烯费米能级附近态密度几乎没有改变, 表明掺杂Pd不会影响石墨烯对CO的气体灵敏度, 但由于CO对石墨烯的吸附能增大, 可以提高石墨烯对还原性气体的气敏响应速度.     

Boron and nitrogen co-doped graphene nanosheets for NO and NO2 gas sensing

Using dispersion-corrected density functional theory calculations, the adsorption behavior of NO and NO₂ molecules is studied over B-doped and BN co-doped graphene sheets (BC_mN_n-Gr; $m,n=0,1,2,3$ and $m+n=3$). To examine practical gas sensing application and selectivity, the adsorption of H₂O, CO and CO₂ molecules is also studied on the BC_mN_n-Gr surfaces. It is found that the preferred adsorption site for the adsorption of these molecules is above the B atom due to accumulation of a local positive charge. Meanwhile, the incorporation of nitrogen atoms in BC_mN_n-Gr makes a substantial increase in the adsorption energies of NO and NO₂, mainly due to the shift in the Fermi energy and electron (donor) concentration states of these surfaces. According to our results, the electronic structure of BC₃-Gr, BC₂N-Gr and BCN₂-Gr is sensitive to NO and NO₂ as evidenced by relatively large variation of the electronic structure as well as charge-transfer values. To address the curvature effect of BC_mN_n-Gr nanosheets on the adsorption and sensing properties of NO and NO₂, the adsorption of these molecules is also investigated over B-doped and BN-codoped ($6,6$) carbon nanotubes. The calculations also indicate that BN co-doped graphene sheets can be used as an efficient and promising gas sensing material for detecting NO and NO₂ molecules in the presence of H₂O, CO and CO₂.     

Application of photocatalytic technology for NO<Subscript>x</Subscript> removal

Materials that contain a photocatalyst have a semi-permanent capacity for removing harmful gases from the ambient air. It is the purpose of this study to investigate the photocatalytic activity of commercial paints containing TiO₂ nanoparticles towards NO and NO₂. Experiments were carried out in a stainless steel (30 m^-3) walk-in type environmental chamber (Indoortron), under “real world setting” conditions of temperature, relative humidity, irradiation and pollutant concentrations. Two types of nanoparticle TiO₂-containing paints were tested for their depolluting properties: a mineral silicate paint and a water-based styrene acrylic paint. The results showed a significant effect of TiO₂-materials in reducing NO_x. It was found that up to 74% of NO and 27% of NO₂ were photo-catalytically degraded by the mineral silicate paint, while degradation percentage using the styrene acrylic paint reached 91% and 71% for NO and NO₂, respectively. The photo-catalytic rate of NO on the mineral and styrene acrylic paint was calculated to 0.11 μg m^-2 s and 0.18 μg m^-2 s, respectively, indicating higher photocatalytic performance of the organic based material. The effect of relative humidity (RH) was also investigated. An increase of RH from 20% to 50% inhibited the NO_x photocatalysis on the surface of the samples. PACS 81.16.Hc; 81.65.Mq; 82.33.Tb; 82.50.Hp; 82.65.+r     

Adsorption of NO, NO2, pyridine and pyrrole on α-Mo2C(0 0 0 1): A DFT study

Density functional theory computations have been carried out on the adsorption of NO, NO₂, pyridine and pyrrole on the α-Mo₂C(0 0 0 1) surface for understanding the hydrodenitrogenation processes. On the Mo-terminated surface, NO decomposes into surface N and O, and NO₂ dissociates into surface O and NO without any barriers, while the most stable adsorption modes of pyridine and pyrrole have π-face coordination over the three-fold molybdenum hollow sites with strongly destroyed aromatic systems. On the C-terminated surface, adsorbed surface species have been found for NO and NO₂, while destroyed ring systems are found for pyridine and pyrrole. It is found that adsorption on the Mo-terminated surface is much stronger than that on the C-terminated surface.     

In situ,facile synthesis of La<Subscript>0.8</Subscript>Sr<Subscript>0.2</Subscript>MnO<Subscript>3</Subscript>/nitrogen-doped graphene: a high-performance catalyst for rechargeable Li-O<Subscript>2</Subscript> batteries

We have successfully devised a simple method to synthesize La_0.8Sr_0.2MnO₃ with nitrogen-doped graphene composites (LSM/NrGO) and investigated their catalytic performance in the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Interestingly, the LSM/NrGO composites demonstrate outstanding catalytic performance in ORR, including high limiting current density and superior onset potential, compared to bare LSM nanocrystals or nitrogen-doped graphene, showing a performance close to that of commercial Pt/C. Moreover, Li-O₂ batteries assembled based on the LSM/NrGO catalysts exhibited brilliant performance, especially during long-term cycling, where the terminal discharge voltage still exceeded 2.31 V after 360 cycles. The excellent catalytic performance is mainly attributed to the large specific surface area (152.24 m² g^?1) of the materials, which provides many catalytic active sites, and the mesoporous structure (2 to 50 nm), which can facilitate the penetration of oxygen molecules into the surface of the nanoparticles and mass transfer.     

Selectively strong molecular adsorption on boron nitride monolayer induced by transition metal substrate

We studied adsorption of several molecules (CO, CO₂, H₂O, N₂O, NO, NO₂, and O₂) on hexagonal boron nitride (h-BN) monolayers supported on transition metal (TM) surfaces, using density functional calculations. We observed that all the molecules bind very weakly on the pristine h-BN, with binding energies in the range of 0.02–0.03 eV. Interestingly, however, when h-BN is supported on the TM surface, NO₂ and O₂ become strongly chemisorbed on h-BN, with binding energies of >1 eV, whereas other molecules still physisorbed, with binding energies of ～0.1 eV at most. The electron transfer from TM to p_z states of h-BN played a substantial role in such strong bindings of NO₂ and O₂ on h-BN, as these molecules possess unpaired electrons that can interact with p_z states of h-BN. Such selective molecular binding on h-BN/TM originates from the peculiar distribution of the spin-polarized highest occupied and lowest unoccupied molecular orbitals of NO₂ and O₂. Strong molecular adsorption and high selectivity would make the h-BN/TM system possible for a variety of applications such as catalysts and gas sensors.