Tuning Surface-Electron Spins on Fe3 O4 (111) through Chemisorption of Carbon Monoxide.

The adsorption-induced flip of electron spin at interfaces is an important but poorly understood phenomenon for magnetic devices, sensors, and heterogeneous catalysis, due to the difficulties in determining the surface spins at atomic resolution. We present an evolutionary magnetic order searching method that allows efficient identification of the ground state spin configuration of magnetic bulk and surfaces. Using this approach, we have discovered for the first time a set of adsorption-induced near-degenerate surface magnetic states on the Fe3 O4 (111) surface. Molecular adsorption of CO causes a destabilization of the magnetic states of the clean surface leading to a set of near-degenerate surface magnetic states at medium coverage, which causes an abrupt increase of the magnetic entropy on the surface. The empty 2π* orbital of CO, which could accommodate the back donation of the spin density in the Fe d orbitals, plays a key role for the CO adsorption-induced spin transition.

Mechanism of Graphene Formation via Detonation Synthesis: A DFTB Nanoreactor Approach.

With the development of theoretical and computational chemistry, as well as high-performance computing, molecular simulation can now be used not only as a tool to explain the experimental results but also as a means for discovery or prediction. Quantum chemical nanoreactor is such a method which can automatically explore the chemical process based only on the basic mechanics without prior knowledge of the reactions. Here, we present a new method which combines the semiempirical quantum mechanical density functional tight-binding (DFTB) method with the nanoreactor molecular dynamic (NMD) method, and we simulated the reaction process of graphene synthesis via detonation at different oxygen/acetylene mole ratios. The formation of graphene is initiated by the breaking of acetylene (C2H2) molecules by collision into pieces such as H atoms, ethynyl (HC≡C•), and vinylidene (H2C═C:) radicals. It is followed by the formation of long straight carbon chains coupled with a few branched carbon chains, which then turned into  a 2-D framework made of carbon rings. Trace oxygen could modulate the size of the rings during graphene formation and promote the formation of regular graphene with fused six-membered rings as we see, but the addition of high oxygen content makes more C-containing species oxidized to small oxide molecules instead of polymerization. The calculation speed of the DFTB nanoreactor is greatly improved compared to the ab initio nanoreactor, which makes it a valuable option to simulate chemical processes of large sizes and long time scales and to help us uncover the "unknown unknowns".

When Density Functional Approximations Meet Iron Oxides.

Three density functional approximations (DFAs), PBE, PBE+U, and Heyd-Scuseria-Ernzerhof screened hybrid functional (HSE), were employed to investigate the geometric, electronic, magnetic, and thermodynamic properties of four iron oxides, namely, α-FeOOH, α-Fe2O3, Fe3O4, and FeO. Comparing our calculated results with available experimental data, we found that HSE (a = 0.15) (containing 15% "screened" Hartree-Fock exchange) can provide reliable values of lattice constants, Fe magnetic moments, band gaps, and formation energies of all four iron oxides, while standard HSE (a = 0.25) seriously overestimates the band gaps and formation energies. For PBE+U, a suitable U value can give quite good results for the electronic properties of each iron oxide, but it is challenging to accurately get other properties of the four iron oxides using the same U value. Subsequently, we calculated the Gibbs free energies of transformation reactions among iron oxides using the HSE (a = 0.15) functional and plotted the equilibrium phase diagrams of the iron oxide system under various conditions, which provide reliable theoretical insight into the phase transformations of iron oxides.

High coverage adsorption and co-adsorption of CO and H2 on Ru(0001) from DFT and thermodynamics.

The adsorption and co-adsorption of CO and H2 at different coverages on p(4 × 4) Ru(0001) have been computed using periodic density functional theory (GGA-RPBE) and atomistic thermodynamics. Only molecular CO adsorption is possible and the saturation coverage is 0.75 ML (nCO = 12) with CO molecules co-adsorbed at different sites and has a hexagonal adsorption pattern as found by low energy electron diffraction. Only dissociative H2 adsorption is possible and the saturation coverage is 1 ML (nH = 16) with H atoms at face-centered cubic sites. The computed CO and H2 desorption patterns and temperatures agree reasonably with the experiments under ultrahigh vacuum conditions. For CO and H2 co-adsorption (nCO + mH2; n = 1-6 and m = 7, 6, 5, 5, 3, 1), CO pre-coverage affects H adsorption strongly, and each pre-adsorbed CO molecule blocks 2H adsorption sites and H2 does not adsorb on the surface with CO pre-coverage larger than 0.44 ML (nCO = 7); all these are in full agreement with the experiments under ultrahigh vacuum conditions. Our results provide the basis for exploring the mechanisms of catalytic conversion of synthesis gas.

A study on the protective effect of Silybum marianum extract on hepatic ischemia-reperfusion injury.

The objective of the study was to study the protective effect of Silybum marianum extract on hepatic ischemia-reperfusion injury. Rats were randomly divided into five groups; namely Silybum marianum extract high-, medium-, and low-dose protection groups, model group and control group. Hepatic ischemia-reperfusion injury model was prepared. Serum or plasma AST, ALT, MDA, TNF-α, IL-1ß, IL-6 levels were measured. The results revealed that after liver injury, AST, ALT, MDA, TNF-α, IL-1ß, and IL-6 levels significantly increased in succession, showing significant differences. We concluded that inflammatory cytokines participate in liver injury and that Silybum marianum extract can reduce the production of inflammatory cytokines, and thus can have a protective effect on hepatic ischemia and reperfusion.

A comparative study of anti-gastric cancer activity between aqueous extract and ethanol extract of Folium Cordylines Fruticosae.

The active components in Folium Cordylines Fruticosae were extracted by heat reflux method. The solvents used were distilled water and ethanol. The effects of two types of extracts on gastric cancer cells were compared; dry extract yields were calculated, as well as the inhibition rates of gastric cancer MGC-803 cell proliferation and the colony cell counts. The micro-Kjeldahl method was used to measure the cell protein contents and to make a comprehensive comparison. The results showed that the MGC-803 cell inhibition rates of three different concentrations (32.5, 75 and 150 mg/ml) of ethanol extracts increased with the increase of concentration, which was 48.9% at a concentration of 150 mg/ml; aqueous extract of Folium Cordylines Fruticosae had very low inhibitory activity at a low concentration (32.5 mg/ml), which was remained at about 20%. After being affected by two types of extracts, cells had uneven sizes, with very low brightness, while the normal cells presented a uniform full form, with high definition.

[Efficacy observation of nonspecific low back pain treated with the dragon-tiger fighting needling method].

OBJECTIVE: To compare the difference in the clinical efficacy on nonspecific low back pain (NLBP) treated with the dragon-tiger fighting needling method, the uniform reinforcing-reducing method and the intermediate frequency physiotherapy. METHODS: Ninety cases of NLBP were randomly divided into a dragon-tiger fighting needling group (group A), an uniform reinforcing-reducing needling group (group B) and an intermediate frequency physiotherapy group (group C), 30 cases in each one. In the group A, the dragon-tiger fighting needling method was used. In the group B, the uniform reinforcing-reducing method was applied. Two groups of acupoints were prescribed. One group included Shenshu (BL 23), Dachangshu (BL 25), Weizhong (BL 40) and Ashi points. The other group included Qihaishu (BL 24), Guanyuanshu (BL 26), Kunlun (BL 60), Yaoyangguan (GV 3). These two groups of acupoints were used alternatively in the above two groups. In the group C, the intermediate frequency physiotherapy was adopted in the pain area of the lumbar region. The treatment was given once per day in each group. Six treatments made one session. Totally, 2 sessions were required. The Visual Analogue Scale (VAS), the Oswestry Disability Index (ODD and the clinical efficacy were observed in each group. RESULTS: The scores of VAS and ODI were reduced obviously after treatment in each group (P < 0.05, P < 0.01). The score reducing in the group A was much more remarkable than those in the other two groups (all P < 0.05). The clinical curative rate was 30.0% (9/30), 23.3% (7/30) and 16.7% (5/30) in the group A, the group B and the group C, respectively. In comparison, the clinical efficacy in the group A was superior to that in either of the other groups (all P< 0.05). CONCLUSION: The dragon-tiger fighting needling method achieves the much better efficacy on NLBP compared with either the uniform reinforcing-reducing method or the intermediate frequency physiotherapy. It is one of the more effective needling method for analgesia.

A density functional theory study of the CH(2)I(2) reaction on Ag(111): Thermodynamics, kinetics, and electronic structures.

Density functional theory calculation was performed to study the adsorption and reaction of CH(2)I(2) on Ag(111). Thermodynamically favorable reactions of CH(2)I(2) on Ag(111) are C-I bond ruptures and CH(2) coupling to form ethylene. The energy barriers for the C-I bond ruptures of chemisorbed CH(2)I(2) on Ag(111) are 0.43-0.48 eV, whereas the activation energy for the C-H bond rupture of chemisorbed CH(2) on Ag(111) is 1.76 eV. The coupling reaction barrier of neighboring chemisorbed CH(2) to form C(2)H(4) on Ag(111) was much less than those of the C-I bond ruptures of CH(2)I(2)(a) and the migration of chemisorbed CH(2) on Ag(111). The adsorption behaviors of different surface species on Ag(111) were well explained in terms of the charge density difference.

Density function theory study of CO adsorption on Fe3O4(111) surface.

Density functional theory calculations have been carried out for CO adsorption on the Fe(oct2)- and Fe(tet1)-terminated Fe(3)O(4)(111) surfaces, which are considered as active catalysts in water-gas shift reaction. It is found that the on-top configurations are most stable on these two surfaces. Some bridge configurations are also stable in which the new C-O bond formed between the surface O atom and the C atom of CO. The adsorption on the Fe(oct2)-terminated surface is more stable than on the Fe(tet1)-terminated surface. The density of state reveals the binding mechanism of CO adsorption on the two surfaces. Our calculations have also shown that the absorbed CO can migrate from the on-top site to the bridge site or 3-fold site. The oxidation of CO via surface oxygen atoms is feasible, which is in good agreement with experimental results.

CO2 reforming of CH4 on Ni(111): a density functional theory calculation.

CO(2) reforming of CH(4) on Ni(111) was investigated by using density functional theory. On the basis of thermodynamic analyses, the first step is CH(4) sequential dissociation into surface CH (CH(4) --> CH(3) --> CH(2) --> CH) and hydrogen, and CO(2) dissociation into surface CO and O (CO(2) --> CO + O). The second step is CH oxygenation into CHO (CH + O --> CHO), which is more favored than dissociation into C and hydrogen (CH --> C + H). The third step is the dissociation of CHO into surface CO and H (CHO --> CO + H). This can explain the enhanced selectivity toward the formation of CO and H(2) on Ni catalysts. It is found that surface carbon formation by the Bouduard back reaction (2CO = C((ads)) + CO(2)) is more favored than by CH(4) sequential dehydrogenation. The major problem of CO(2) reforming of CH(4) is the very strong CO adsorption on Ni(111), which results in the accumulation of CO on the surface and hinders the subsequent reactions and promotes carbon deposition. Therefore, promoting CO desorption should maintain the reactivity and stability of Ni catalysts. The computed energy barriers of the most favorable elementary reaction identify the CH(4) activation into CH(3) and H as the rate-determining step of CO(2) reforming of CH(4) on Ni(111), in agreement with the isotopic experimental results.

Structures and energies of coadsorbed CO and H2 on Fe5C2(001), Fe5C2(110), and Fe5C2(100).

Density functional theory calculations have been carried out on the CO/H2 coadsorption on the (001), (110), and (100) surfaces of Fe5C2 for the understanding of the Fischer-Tropsch synthesis (FTS) mechanism. The stable surface species changes with the variation of the H2 and CO coverage. Along with dissociated hydrogen and adsorbed CO in 2-, 3-, and 4-fold configurations, methylidyne (C(s)H) (C(s), surface carbon), ketenylidene (C(s)CO), ketenyl (C(s)HCO), ketene (C(s)H2CO), and carbon suboxide (C(s)C2O2) are computed as thermodynamically stable surface species on Fe5C2(001) and Fe5C2(110) containing both surface iron and carbon atoms. These surface carbon species can be considered as the preliminary stages for FTS. On Fe5C2(100) with only iron atoms on the surface layer, the stable surface species is dissociated hydrogen and CO with top and 2-fold configurations. The bonding nature of these adsorbed carbon species has been analyzed.

Chemisorption of CO2 on nickel surfaces.

CO2 chemisorption on the Ni(111), Ni(100), and Ni(110) surfaces was investigated at the level of density functional theory. It was found that the ability of CO2 chemisorption is in the order of Ni(110) > Ni(100) > Ni(111). CO2 has exothermic chemisorption on Ni(110) and endothermic chemisorption on Ni(111), while it is thermally neutral on Ni(100). It is also found that there is no significant lateral interaction between the adsorbed CO2 at 1/4 monolayer (ML) coverage, while there is stronger repulsive interaction at 1/2 ML. On all surfaces, the chemisorbed CO2 is partially negatively charged, indicating the enhanced electron transfer, and the stronger the electron transfer, the stronger the C=O bond elongation. The bonding nature of the adsorbed CO2 on nickel surfaces has been analyzed. The thermodynamics of CO2 dissociative chemisorption, compared with CO and O adsorption, has been discussed, and the thermodynamic preference is in the sequence Ni(100) > Ni(111) > Ni(110).

Density functional theory study of hydrogen adsorption on Fe5C2(001), Fe5C2(110), and Fe5C2(100).

Density functional theory calculations have been carried out for hydrogen adsorption on the (001), (110), and (100) surfaces of Fe5C2. At 1/3 and 2/3 monolyer (ML) on (001), the most stable hydrocarbon species is CsH, while CsH and CsH3 can coexist at 1 ML. On (110), only dissociated hydrogen is found at 2/5 ML, while CsH is the most stable hydrogen carbon species at 4/5 ML, and CsH and CH3 coexist at 6/5 ML. On (001) and (110) surfaces, CsH2 is less stable and can dissociate into CsH or convert into CsH3, respectively. These results are in agreement with the experimental observations. On the metallic Fe5C2(100) surface which lacks surface carbon atoms on the surface monolayer, dissociated hydrogen is found at 1/2 ML, while both dissociated hydrogen and activated H2 are found at 1 ML.