共查询到20条相似文献,搜索用时 265 毫秒
1.
In order to synthesize borocarbonitrides of the general formula BC xN where x varies between 1 and 2, we have carried out high-temperature gas phase reaction of BBr 3 with a mixture of ethylene and ammonia. The composition of the product was close to BC 1.6N as shown by x-ray photon spectroscopy (XPS) and electron energy loss spectroscopy (EELS). The products were further characterized by infra-red, Raman and other spectroscopic techniques. The borocarbonitrides obtained from the gas phase reaction have low surface areas, in contrast to those of similar compositions prepared by the urea method. First principles calculations show that the most stable structures of the compositions BCN and BC 2N contain BN-rich and carbon-rich domains where BN 3 and NB 3 units are present. 相似文献
2.
By using first‐principles calculations based on density functional theory, we study the adsorption efficiency of a BC 3 sheet for various gases, such as CO, CO 2, NO, NO 2, and NH 3. The optimal adsorption position and orientation of these gas molecules on the BC 3 surface is determined and the adsorption energies are calculated. Among the gas molecules, CO 2 is predicted to be weakly adsorbed on the graphene‐like BC 3 sheet, whereas the NH 3 gas molecule shows a strong interaction with the BC 3 sheet. The charge transfer between the molecules and the sheet is discussed in terms of Bader charge analysis and density of states. The calculated work function of BC 3 in the presence of CO, CO 2, and NO is greater than that of a bare BC 3 sheet. The decrease in the work function of BC 3 sheets in the presence of NO 2 and NH 3 further explains the affinity of the sheet towards the gas molecules. The energy gap of the BC 3 sheets is sensitive to the adsorption of the gas molecules, which implies possible future applications in gas sensors. 相似文献
3.
Using density functional theory, we investigated the hydrogen storage capacity of Li coated BC 3 honeycomb sheet. Our result indicates 18 H 2 molecules can be adsorbed on BC 3Li 6 complex with a storage gravimetric density of 9.68 wt% and the average adsorption energy reaches 0.206 eV /H 2 . This is desirable for absorbing and desorbing H 2 molecules at near ambient conditions. 相似文献
4.
Density functional theory has been performed to investigate the interaction of H 2 and Pd n clusters ( n = 1–7). The local minima configurations for different H 2 molecule approach modes towards Pd n clusters are presented. Our results show that in some cases H 2 is physically adsorbed around Pd atom, and in other cases H 2 is dissociated to be H atoms. Except for PdH2, Pd n clusters with H atoms dissociatively adsorbed are most stable. For these most stable PdnH2 clusters ( n 2), the binding energy of hydrogen atom decreases as the number of Pd atom increases until n = 4, and when n 4, the binding energy almost keeps constant with the H atoms bound sites changing from Pd–Pd bonds to Pd triangle planes. Besides, the adsorption of H 2 on other low-lying isomers of Pd n clusters is also discussed. 相似文献
5.
In order to reduce the greenhouse effect caused by the rapid increase of CO 2 concentration in the atmosphere, it is necessary to develop more efficient, controllable, and highly sensitive adsorbing materials. In this study, the adsorption behavior of CO 2 on BC 3 nanosheets under an external electric field was explored based on density functional theory (DFT). It was found that CO 2 experienced a transition from physisorption to chemisorption in the electric field range of 0.0060-0.0065 a.u.. In addition, the adsorption/desorption of CO 2 is reversible and can be precisely controlled by switching on/off at the electric field of 0.0065 a.u.. The selective adsorption of CO 2/H 2/CH 4 by BC 3 can also be used to realize gas separation and purification under different electric fields. This study highlighted the potential application of BC 3 nanosheets as a high-performance, controllable material for CO 2 capture, regeneration, and separation in an electric field. 相似文献
6.
The structural and electronic properties of semiconducting BC 19 and AlC 19 heterofullerenes as adsorbents for toxic small gas molecules (H 2S and SO 2) are determined by DFT. Structural parameters, energy gaps, natural population analysis, partial density of state, dipole moments, and vibrational frequencies were extracted. The adsorption process and sensitivity to the gases are increased by doping with B or Al. The results show that AlC 19 is the most sensitive structure. The good sensing of AlC 19 is related to high charge transfer upon gas adsorption. Adsorption of the H 2S on the BC 19 has negligible effects on the electronic properties, to be categorized as “harmless adsorption”. H 2S is weakly adsorbed on BC 19 and AlC 19. The H 2S and SO 2 molecules act as electron donating and electron withdrawing molecules, respectively. Notably, the adsorption processes are highly exothermic. In general, BC 19 is more reactive than C20 and AlC 19 is the most reactive cage. This provides a theoretical basis to fabricate B- and Al-doped C20-based gas sensors. 相似文献
7.
The binding property of hydrogen on organometallic compounds consisting of Co, and Ni transition metal atoms bound to C
m
H
m
rings ( m = 4, 5) is studied through density functional theory calculation. CoC
m
H
m
and NiC
m
H
m
complexes can store up to 3.49 wt% hydrogen with an average binding energy of about 1.3 eV. The adsorption characteristics
of hydrogen to organometallic compounds are investigated by analyzing vibrational spectra of CoC 4H 4(H 2)
n
and NiC 4H 4(H 2)
n
( n = 0, 1, 2). The kinetic stability of these hydrogen-covered organometallic complexes is assured by analyzing the energy gap
between the highest occupied molecular orbitals and the lowest unoccupied molecular orbitals. It is also discussed the application
of 18-electron rule in predicting maximum number of hydrogen molecules that could be adsorbed by these organometallic compounds. 相似文献
9.
A type of Nb 2O 5⋅3H 2O was synthesized and its phosphate removal potential was investigated in this study. The kinetic study, adsorption isotherm,
pH effect, thermodynamic study and desorption were examined in batch experiments. The kinetic process was described by a pseudo-second-order
rate model very well. The phosphate adsorption tended to increase with a decrease of pH. The adsorption data fitted well to
the Langmuir model with which the maximum P adsorption capacity was estimated to be 18.36 mg-P g −1. The peak appearing at 1050 cm −1 in IR spectra after adsorption was attributed to the bending vibration of adsorbed phosphate. The positive values of both
Δ H° and Δ S° suggest an endothermic reaction and increase in randomness at the solid-liquid interface during the adsorption. Δ G° values obtained were negative indicating a spontaneous adsorption process. A phosphate desorbability of approximately 68%
was observed with water at pH 12, which indicated a relatively strong bonding between the adsorbed phosphate and the sorptive
sites on the surface of the adsorbent. The immobilization of phosphate probably occurs by the mechanisms of ion exchange and
physicochemical attraction. Due to its high adsorption capacity, this type of hydrous niobium oxide has the potential for
application to control phosphorus pollution. 相似文献
10.
We explored the aspirin adsorption and their hydrogen evolution reaction (HER) activity in waste water of borocarbonitride sheets. Our results indicate that BCN sheets considered here show HER activity and exhibit superior performance regarding adsorption of aspirin in waste water in comparison with graphene and hexagonal boron nitride (h-BN). The drug molecule (aspirin) possesses a strong affinity to BCN, with the order of binding energy on following the order BCN∼h-BN>graphene. Upon drug adsorption, the band gap of h-BN is found to be reduced by up to 33 %, whereas the bandgaps of graphene and BCN remain unaltered that makes BCN a potential candidate for HER in waste water. 相似文献
11.
The adsorption and dissociation of molecular oxygen on spinel CuCr 2O 4 (100) surface were carried out by first-principles calculations based on density functional theory (DFT). The calculated results indicate that the Cr site is most favorable for atomic oxygen adsorption, with an adsorption energy of 402.8 kJ/mol. For molecular oxygen adsorption, there are three types of favorable interaction modes: O 2 forms bonds with the Cu site or O 2 binds to two Cr sites or O 2 interacts with both Cu and Cr sites simultaneously. The lowest activation energy ( Ea = 35.4 kJ/mol) was found through exploring possible reaction pathways for O 2 dissociation. The relationship between Ea and reaction enthalpy (Δ H) for O 2 dissociation adsorption reactions fits Brønsted-Evans-Polanyi (BEP) behavior. 相似文献
12.
The change in the thermodynamic properties of triclosan adsorption on three activated carbons with the different surface chemistry was studied through immersion calorimetry and equilibrium data; the amount adsorbed of triclosan (Q) during calorimetry was determined and correlated with the energy associated with adsorbate–adsorbent interactions in the adsorption process. It was noted that triclosan adsorption capacity decreases with an increase in oxygenated surface groups. For an activated carbon oxidized with HNO3 (OxAC), the amount adsorbed was 8.50?×?10?3 mmol g?1, for a activated carbon without modification (GAC) Q?=?10.3?×?10?3 mmol g?1 and for a activated carbon heated at 1073 K (RAC1073) Q?=?11.4?×?10?3 mmol g?1. The adsorbed amounts were determined by adjusting the isotherms to the Sips model. For the activated carbon RAC1073, the immersion enthalpy (ΔHimm) was greater than those of the other two activated carbons due to the formation of interactions with the solvent (ΔHimmOxAC?=?? 27.3 J g?1?<?ΔHimmGAC?=?? 40.0 J g?1?<?ΔHimm RAC1073?=???60.7 J g?1). The changes in the interaction enthalpy and Gibbs energy are associated with adsorbate–adsorbent interactions and side interactions such as the adsorbate–adsorbate and adsorbate–solvent interactions.
相似文献
13.
In order to find a solution of energy-related problems, sophisticated hydrogen storing materials are needed as hydrogen is an abundant and environment friendly fuel. We have investigated the hydrogen storage potential of Ng inserted metal acetylide and metal cyanide compounds (metal = Cu, Ag and Au) at the ωB97X-D/cc-pVTZ-PP level of theory. Due to the difference in electronegativity and formal charge on metal atoms in the insertion compounds, the interaction with the hydrogen molecule is expected to be different. The adsorption energies, the free energy of adsorption, natural charges on atomic centers/moieties are obtained through the natural population analysis, and energy decomposition analysis has also been carried out for nH 2···MNgCCH and nH 2···MNgCN (n = 1–3). The hydrogen adsorption capacity of the strongest and the weakest cases has also been investigated. Both the insertion compounds, MNgCCH and MNgCN, are found to adsorb a maximum of three hydrogen molecules on the metal site. The single H 2 adsorbed minimum energy structures of studied compounds show a “T-shaped” orientation while double H 2 adsorbed minimum energy structures are of “Y- shaped” geometry and those of tricoordinated structures resemble “ Td-like” shape. The negative value of Gibbs free energy change suggests the thermodynamical spontaneity of the hydrogen adsorption process. 相似文献
14.
基于密度泛函理论的第一性原理方法,通过计算表面能确定LaFeO 3(010)表面为最稳定的吸附表面,研究了H 2分子在LaFeO 3(010)表面的吸附性质。LaFeO 3(010)表面存在LaO和FeO 2两种终止表面,但吸附主要发生在FeO 2终止表面,由于LaFeO 3(010)表面弛豫的影响,使得凹凸不平的表面层增加了表面原子与H原子的接触面积,表面晶胞的纵向体积增加约2.5%,有利于H原子向晶体内扩散。研究发现,H 2分子在LaFeO 3(010)表面主要存在3种化学吸附方式:第一种吸附发生在O-O桥位,2个H原子分别吸附在2个O原子上,形成2个-OH基,这是最佳吸附位置,此时H原子与表面O原子的作用主要是H1 s与O2 p轨道杂化作用的结果,H-O之间为典型的共价键。H 2分子的解离能垒为1.542 eV,说明表面需要一定的热条件,H 2分子才会发生解离吸附;第二种吸附发生在Fe-O桥位,1个H原子吸附在O原子上形成1个-OH基,另一个H原子吸附在Fe原子上形成金属键;第三种吸附发生在O顶位,2个H原子吸附在同一个O原子上,形成H 2O分子,此时H 2O分子与表面形成物理吸附,H 2O分子逃离表面后容易形成氧空位。此外,H 2分子在LaFeO 3(010)表面还可以发生物理吸附。 相似文献
15.
A large magnetocaloric (MCE) effect has been observed for the ternary compound DyCo 3B 2. This material shows the magnetic ordering below TC = 22 K for H = 0 T. MCE has been determined based on the isothermal magnetization curves measurements and the isomagnetic heat capacity dependence on temperature. The maximum magnetic entropy change −Δ SM = 17.5 J kg −1K −1 and the adiabatic temperature change Δ Tad = 14 K have been observed in the neighborhood of the magnetic phase transition at the magnetic field change of 9 T. The analysis of the magnetic contribution to the specific heat indicates on the important role of the crystal electric field and the anisotropy for the properties of the DyCo 3B 2 compound. 相似文献
16.
The displacement adsorption enthalpies (Δ H) of denatured α-Amylase (by 1.8 mol L −1 GuHCl) adsorbed onto a moderately hydrophobic surface (PEG-600, the end-group of polyethylene glycol) from solutions ( x mol L −1 (NH 4) 2SO 4, 0.05 mol L −1 KH 2PO 4, pH 7.0) at 298 K are determined by microcalorimeter. Further, entropies (Δ S), Gibbs free energies (Δ G) and the fractions of Δ H, Δ S, and Δ G for net adsorption of protein and net desorption of water are calculated in combination with adsorption isotherms of α-Amylase
based on the stoichiometric displacement theory for adsorption (SDT-A) and its thermodynamics. It is found that the displacement
adsorptions of denatured α-Amylase onto PEG-600 surface are exothermic and enthalpy driven processes, and the processes of
protein adsorption are accompanied with the hydration by which hydrogen bond form between the adsorbed protein molecules favor
formation of β-sheet and β-turn structures. The Fourier transformation infrared spectroscopy (FTIR) analysis shows that the
contents of ordered secondary structures of adsorbed α-Amylase increase with surface coverages and salt concentrations increment. 相似文献
17.
Experimental adsorption isotherms were measured and computer simulations were performed to determine the nature of the H 2 gas uptake in the low‐density p‐ tert‐butylcalix[4]arene (tBC) phase. 1H NMR peak intensity measurements for pressures up to 175 bar were used to determine the H 2 adsorption isotherm. Weak surface adsorption (up to ≈2 mass % H 2) and stronger adsorption (not exceeding 0.25 mass % or one H 2 per calixarene bowl) inside the calixarene phase were detected. The latter type of adsorbed H 2 molecule has restricted motion and shows a reversible gas adsorption/desorption cycle. Pulsed field gradient (PFG) NMR pressurization/depressurization measurements were performed to study the diffusion of H 2 in the calixarene phases. Direct adsorption isotherms by exposure of the calixarene phase to pressures of H 2 gas to ≈60 bar are also presented, and show a maximum H 2 adsorption of 0.4 H 2 per calixarene bowl. Adsorption isotherms of H 2 in bulk tBC have been simulated using grand canonical Monte Carlo calculations in a rigid tBC framework, and yield adsorptions of ≈1 H 2 per calixarene bowl at saturation. Classical molecular dynamics simulations with a fully flexible calixarene molecular force field are used to determine the guest distribution and inclusion energy of the H 2 in the solid with different loadings. 相似文献
18.
A mixed proton–electron conducting perovskite made of BaCe 0.95Nd 0.05O 3−δ (BCN) was prepared by EDTA/citric acid complexing method. The precursor was characterized by differential scanning calorimetry (DSC), thermogravimetry (TG), and X-ray diffraction (XRD). In order to learn the perovskite formation process during the calcination, the intermediate, i.e. the sample calcined at 750 °C for 5 h, was investigated by scanning (STEM), energy-filtered (EFTEM), and high-resolution transmission electron microscopy (HRTEM) as well as electron energy-loss spectroscopy (EELS). The results revealed that the perovskite structure was formed via a solid-state reaction between barium–cerium mixed carbonate and cerium–neodymium mixed oxide particles. Dense mixed proton–electron conducting BCN membranes were made by pressing BCN powder followed by sintering. The microstructure of the sintered membranes was investigated by scanning electron microscopy (SEM). Hydrogen permeation through the BCN membrane was studied using a high-temperature permeator. The hydrogen permeation fluxes under wet conditions are higher than those under dry conditions, which is due to increased proton concentrations in the H + hopping via OH groups. The hydrogen permeation increased with increasing hydrogen and steam concentrations in the feed. For a steam concentration of 15 vol.%, the hydrogen permeation flux reaches 0.026 ml/min cm 2. 相似文献
19.
The kinetics of the hydrogenation of methyl oleate on a Ni/α-Al 2O 3 catalyst was studied in the absence of mass-transport limitation, at 398 ≤ T ≤ 443 K and 3.7 ≤ PH2 ≤ 6.5 bar. The kinetic modeling was performed on the basis of elementary step mechanisms involving different regimes of competition between hydrogen and methyl oleate. Admitting a distinction between occupied-sites and covered-sites by the large molecule of methyl oleate, a rigorous proposal was made to link the seemingly separate kinetic models corresponding to the extreme modes of competitive and non-competitive adsorption, without having to draw the common distinction between two types of surface sites. General rate equations were formulated without expressing opinion a priori on whether the adsorption regime is competitive or non-competitive. Then, typical LHHW rate equations for both extreme adsorption regimes were straightforwardly derived as special cases. Statistical results demonstrated the inadequacy of the models approaching non-competitive adsorption to describe the experimental data but results did not allow a definite discrimination between rival models with competitive and semi-competitive adsorption. A mechanistic model featuring dissociative adsorption of hydrogen, molecule of methyl oleate interacting with a single atom of Ni, and second insertion of hydrogen as RDS, proved to be the best candidate to describe the experimental data satisfactorily with physically reasonable parameters. As a distinctive feature, the model considering semi-competitive adsorption gave additional indication that the adsorbed molecule of methyl oleate could cover up to seven surface sites. From this finding, the semi-competitive model seems to be more realistic than the competitive one. 相似文献
20.
The effects of palladium precursors (PdCl 2, (NH 4) 2PdCl 4, Pd(NH 3) 2Cl 2, Pd(NO 3) 2 and Pd(CH 3COO) 2) on the catalytic properties in the selective oxidation of ethylene to acetic acid have been investigated for 1.0 wt% Pd–30 wt% H 4SiW 12O 40/SiO 2. The structures of the catalysts were characterized using X-ray diffraction, N 2 adsorption, H 2-pulse chemical adsorption, infrared spectrometry of the adsorbed pyridine, H 2 temperature-programmed reduction and X-ray photoelectron spectroscopy. The present study demonstrates that the different palladium precursors can lead to the significant changes in the dispersion of palladium. It is found that Pd dispersion decreases as follows: PdCl 2 > (NH 4) 2PdCl 4 > Pd(NO 3) 2 > Pd(NH 3) 2Cl 2 > Pd(C 2H 3O 2) 2, which is nearly identical to the catalytic activity. This indicates that the dispersion of palladium plays an important role in the catalytic activity. Furthermore, density of Lewis ( L) and Brönsted ( B) acid sites are also strongly dependent on the palladium precursors. It is also demonstrated that an effective catalyst should possess a well combination of Brönsted acid sites with dispersion of palladium. 相似文献
|