Combination Effect of Cation Vacancies and O2 Adsorption on Ferromagnetism of Na0.5Bi0.5TiO3（100） Surface:ab initio Study

The combination effect of cation vacancies and O2 adsorption on ferromagnetism of Na0.5Bi0.5TiO3（100） surface is studied by using density functional theory. An ideal Na0.5Bi0.5TiO3（100） surface is non-magnetic and the cation vacancy could induce the magnetism. By comparing the formation energies for Na, Bi and Ti vacancy, the Na vacancy is more stable than the others. Therefore, we focus on the configuration and electric structure for the system of O2 molecule adsorption on the Na0.5Bi0.5TiO3（100） surface with a Na vacancy. Among the five physisorption configurations we considered, the most likely adsorption position is Na vacancy. The O2 adsorption enhances the magnetism of the system. The contribution of spin polarization is mainly from the O 2p orbitals. The characteristics of exchange coupling are also calculated, which show that the ferromagnetic coupling is favorable. Compared with the previous calculation results, our calculations could explain the room-temperature ferromagnetism of Na0.5Bi0.5TiO3 nanocrytalline powders more reasonably, because of taking into account adsorbed oxygen and cation vacancies. Moreover, our results also show that adsorption of O2 molecule as well as introduction of cation vacancies may be a promising approach to improve multiferroic materials.

Thermogravimetric Study on Oxygen Adsorption/Desorption Properties of Double Perovskite Structure Oxides REBaCo_2O_(5+δ)(RE= Pr,Gd,Y)

The oxygen adsorption/desorption properties of double perovskite structure oxides PrBaCo2O5＋δ,GdBaCo2O5＋δ,and YBaCo2O5＋δ were investigated by the thermogravimetry（TG）method in the temperature range of 400~900 ℃.The calculated oxygen adsorption/desorption surface reaction rate constants ka and kd of these double perovskite structure oxides were larger than the commonly used cubic perovskite oxides,such as Ba0.95Ca0.05Co0.8Fe0.2O3-δ and Ba0.5Sr0.5Co0.8Fe0.2O3-δ,whereas,the oxygen permeation flux was comparable to that of the latter,which was attributed to the smaller difference of oxygen vacancy in oxygen and nitrogen atmosphere（Δδ/Vmol）in these double perovskite structure oxides.The large oxygen adsorption/desorption rate constants of GdBaCo2O5＋δ and PrBaCo2O5＋δ made them nice catalyst coating materials,on other membrane surfaces,to improve the oxygen permeability.

Effects of B and N dopings and H_2O adsorption on structural stability and field emission properties of cone-capped carbon nanotubes

The effects of B and N dopings and H2O adsorption on the structural stability and the field emission properties of cone-capped carbon nanotubes （CCCNTs） were investigated by using the density-functional theoretical calculation. The adsorption of H2O can increase the structural stability and decrease the gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital （HOMO-LUMO gap） of the CCCNTs. The strength of total electric field on the top of the H2O-adsorbed CCCNTs is larger than that of the B-doped and the N-doped CCCNTs, electrons will be emitted primarily from the H2O-adsorbed CCCNTs at the same applied voltage. Therefore, the H2O adsorption can lower the threshold voltage for the CCCNTs. While the B and the N dopings produce opposite effects. The HOMO-LUMO gap of the N-doped CCCNTs is the widest among all the gaps of the CCCNTs.

First-principle calculations of interaction of O_2 with pyrite, marcasite and pyrrhotite surfaces

The interaction of O2 with pyrite, marcasite and pyrrhotite surfaces was studied using first-principle calculations to obtain the oxidization mechanisms of these minerals. The results show that the adsorption energy of O2 on pyrrhotite surface is the largest, followed by that on marcasite surface and then pyrite surface. O2 molecules adsorbed on pyrite, marcasite and pyrrhotite surfaces are all dissociated. The oxygen atoms and surface atoms of pyrite, marcasite and pyrrhotite surfaces have different bonding structures. Due to more atoms on pyrrhotite and marcasite surfaces interaction with oxygen atoms, the adsorption energies of O2 on pyrrhotite and marcasite surfaces are larger than that on pyrite surface. Larger values of Mulliken populations for O？Fe bond of pyrrhotite surface result in relative larger adsorption energy compared with that on marcasite surface.

A density-functional theory investigation on desorption of O_2 on Sn(111) and its comparison with initial oxidation on the X(111)(X=Si,Ge,Sn,Pb) surfaces

The first-principles calculations are performed to investigate the adsorption of O2 molecules on an Sn（lll） 2 × 2 surface. The chemisorbed adsorption precursor states for O2 are identified to be along the parallel and vertical channels, and the surface reconstructions of Sn（111） induced by oxygen adsorption are studied. Based on this, the adsorption behaviours of O2 on X（111） （X=Si, Ge, Sn, Pb） surfaces are analysed, and the most stable adsorption channels of O2 on X（111） （X=Si, Ge, Sn, Pb） are identified. The surface reconstructions and electron distributions along the most stable adsorption channels are discussed and compared. The results show that the O2 adsorption ability declines gradually and the amount of charge transferred decreases with the enhancement of metallicity.

Experimental and density functional theory study of the adsorption of N_2O on ion-exchanged ZSM-5: Part II. The adsorption of N_2O on main-group ion-exchanged ZSM-5

The adsorption and desorption of N 2 O on main-group ion-exchanged ZSM-5 was studied using temperature-programmed desorption （TPD） and density functional theory （DFT） calculations. TPD experiments were carried out to determine the desorbed temperature T max corresponding to the maximum mass intensity of N 2 O desorption peak and adsorption capacity of N 2 O on metal-ion-exchanged ZSM- 5s. The results indicated that T max followed a sequence of Ba 2＋ Ca 2＋ Cs ＋ K ＋ Na ＋ Mg 2＋ and the amount of adsorbed N 2 O on main-group metal cation followed a sequence of Ba 2＋ Mg 2＋ Ca 2＋ Na ＋ K ＋ Cs ＋ . The DFT calculations were performed to obtain the adsorption energy （E ads ）, which represents the strength of the interaction between metal cations and the N-end or O-end of N 2 O. The calculation results showed that the N-end of the N 2 O molecule was favorably adsorbed on ion-exchanged ZSM-5, except for Cs-ZSM-5. For alkali metal cations, the E ads of N 2 O on cations followed the order which was the same to that of T max ： Cs ＋ K ＋ Na ＋ . The calculated and experimental results consistently showed that the adsorption performances of alkaline-earth metal cations were better than those of alkali metal cations.

Preparation of MnO2-Al2O3 adsorbent with large specific surface area for fluoride removal

MnO2-Al2O3 （MOAO） binary nanocomposite with a 1：3 MnO2 to Al2O3 molar ratio was synthesized by impregnation technique using mesoporous alumina （MA） precursor. The MOAO product consisted of MA and amorphous MnO2. The manganese valence in MOAO was ＋4, indicative of MnO2 being coated on the surface of MA during the impregnation process. MOAO had a large specific surface area （385.266 m^2/g） and wormhole-like mesoporous structure. The average pore size, which could be precisely controlled over the range of 3.4-4.1 nm. The optimum removal of fluoride was obtained when the initial pH was in the range of 4-10. The defluorination efficiency of MOAO was far superior to that of MA when the initial fluoride concentration exceeded 40 mg/L. The large surface area and bimodal porous structure of MOAO after coating MnO2 may be responsible for the high removal efficiency in the defluorination process.

Co-adsorption of gaseous benzene, toluene, ethylbenzene,m-xylene(BTEX) and SO_2 on recyclable Fe_3O_4 nanoparticles at 0–101% relative humidities

We herein used Fe3O4 nanoparticles（NPs） as an adsorption interface for the concurrent removal of gaseous benzene, toluene, ethylbenzene and m-xylene（BTEX） and sulfur dioxide（SO2）, at different relative humidities（RH）. X-ray diffraction, Brunauer-Emmett-Teller, and transmission electron microscopy were deployed for nanoparticle surface characterization.Mono-dispersed Fe3O4（Fe2O3·Fe O） NPs synthesized with oleic acid（OA） as surfactant, and uncoated poly-dispersed Fe3O4 NPs demonstrated comparable removal efficiencies.Adsorption experiments of BTEX on NPs were measured using gas chromatography equipped with flame ionization detection, which indicated high removal efficiencies（up to（95 ± 2）%） under dry conditions. The humidity effect and competitive adsorption were investigated using toluene as a model compound. It was observed that the removal efficiencies decreased as a function of the increase in RH, yet, under our experimental conditions, we observed（40 ± 4）% toluene removal at supersaturation for Fe3O4 NPs, and toluene removal of（83 ± 4）% to（59 ± 6）%, for OA-Fe3O4 NPs. In the presence of SO2, the toluene uptake was reduced under dry conditions to（89 ± 2）% and（75 ± 1）% for the uncoated and coated NPs, respectively, depicting competitive adsorption. At RH 〉 100%,competitive adsorption reduced the removal efficiency to（27 ± 1）% for uncoated NPs whereas OA-Fe3O4 NPs exhibited moderate efficiency loss of（55 ± 2）% at supersaturation.Results point to heterogeneous water coverage on the NP surface. The magnetic property of magnetite facilitated the recovery of both types of NPs, without the loss in efficiency when recycled and reused.

CO_2 adsorption using TiO_2 composite polymeric membranes:A kinetic study

CO2is the main greenhouse gas which causes global climatic changes on larger scale. Many techniques have been utilised to capture CO2. Membrane gas separation is a fast growing CO2 capture technique, particularly gas separation by composite membranes. The separation of CO2 by a membrane is not just a process to physically sieve out of CO2 through the controlled membrane pore size. It mainly depends upon diffusion and solubility of gases, particularly for composite dense membranes. The blended components in composite membranes have a high capability to adsorb CO2. The adsorption kinetics of the gases may directly affect diffusion and solubility. In this study, we have investigated the adsorption behaviour of CO2 in pure and composite membranes to explore the complete understanding of diffusion and solubility of CO2 through membranes. Pure cellulose acetate（CA） and cellulose acetatetitania nanoparticle（CA-TiO2） composite membranes were fabricated and characterised using SEM and FTIR analysis. The results indicated that the blended CA-TiO2 membrane adsorbed more quantity of CO2 gas as compared to pure CA membrane. The high CO2 adsorption capacity may enhance the diffusion and solubility of CO2 in the CA-TiO2 composite membrane, which results in a better CO2 separation. The experimental data was modelled by Pseudo first-order, pseudo second order and intra particle diffusion models.According to correlation factor R2, the Pseudo second order model was fitted well with experimental data. The intra particle diffusion model revealed that adsorption in dense membranes was not solely consisting of intra particle diffusion.

Influence of Cl substitution on the electronic structure and catalytic activity of ceria

Cl-containing cerium dioxide(Ce O2) catalysts have been found to exhibit unique catalytic activities. In the present work, using density functional theory calculations with the inclusion of on-site Coulomb correction, we systematically studied the effect of Cl on the physicochemical properties of Ce O2 surfaces by substituting one subsurface O with Cl. The calculated results show that substituting an O atom with a Cl atom results in structural distortion and the reduction of one surface Ce4+ cation to Ce3+. The protruding Ce3+ cation greatly improves the adsorption energy of O2 to produce an active O2- species, and maintains the catalytic oxidation cycle of CO on Ce O2(110). These results may help us obtain a better understanding of Cl-ceria interacting systems and provide some guidance for the design of effective Ce O2-based catalysts.

Improved photoelectric properties of BiOBr nanoplates by co-modifying SnO_2 and Ag to promote photoelectrons trapped by adsorbed O_2

It is highly desired to improve the photoelectric property of nanosized BiOBr by promoting the photogenerated charge transfer and separation. Herein, SnO2 and Ag comodified BiOBr nanocomposites(Ag-SO-BOB) have been prepared through a simple one-pot hydrothermal method.Surface photovoltage response of BiOBr nanoplates has 4.1-time enhancement after being modified with SnO2 nanoparticles. Transient-state surface photovoltage(TS-SPV) and the atmosphere-controlled steady-state surface photovoltage spectroscopy(AC-SPS) confirmed that this exceptional enhancement of the photovoltage response can be ascribed to the coupled SnO2 acting as platform for accepting the photoelectrons from BiOBr so as to prolong the lifetime and enhance charge separation. Remarkably, the surface photovoltage response can be further enhanced by synchronously introducing Ag nanoparticles, which is up to 15.4-times enhancement compared with bulk BiOBr nanoplates. The enhancement can be attributed to the improved O2 adsorption by introducing Ag to further enhance charge separation. Finally, the synergistic effect of SnO2 and Ag co-modification enhances the surface photovoltage response due to the enhanced charge separation and promoted O2 adsorption, which is also confirmed through photoelectrochemistry and photocatalytic experiment.