Narrow Results

The electron mobility of hexadecafluorophthalocyaninato-copper (F₁₆PcCu) films was evaluated based on field effect measurements in vacuum and in various gas atmospheres. An Arrhenius plot of the mobility showed that the carrier transport followed a thermally activated hopping mechanism with an activation energy of 0.28 eV. The mobility evaluated for freshly prepared films in ultrahigh vacuum was 2.0 × 10⁻³cm²V⁻¹s⁻¹ at room temperature. The electrical conductivity and carrier density were 4.4 × 10⁻⁵S cm⁻¹ and 1.4 × 10¹⁷cm⁻³ respectively. The high carrier density indicated the existence of impurities acting as electron donors in the films. The field effect carrier mobility increased to 5.7 × 10⁻³cm²V⁻¹s⁻¹ in NH₃ atmosphere (100%, 1 atm) and decreased by 75% in the presence of O₂ gas (100%, 1 atm). A quick recovery of mobility was observed when the gas molecules were evacuated, indicating a low capability of gas adsorption.

The adsorption behavior and electronic properties of CO and O₂ molecules at the supported Pt and Eu atoms on (5,5) armchair SWCNT have been systematically investigated within density functional theory (DFT). Fundamental aspects such as adsorption energy, natural bond orbital (NBO), charge transfer, frontier orbitals and the projected density of states (PDOS) are elucidated to analyze the adsorption properties of CO and O₂ molecules. The results reveal that B- and N-doping CNTs can enhance the binding strength and catalytic activity of Pt (Eu) anchored on the doped-CNT, where boron-doping is more effective. The electronic structures of supported metal are strongly influenced by the presence of gases. After adsorption of CO and O₂, the changes in binding energy, charge transfer and conductance may lead to the different response in the metal-doped CNT-based sensors. It is expected that these results could provide helpful information for the design and fabrication of the CO and O₂ sensing devices. The high catalytic activity of Pt supported at doped-CNT toward the interaction with CO and O₂ may be attributed to the electronic resonance particularly among Pt-5d, CO-2$\pi$* and O₂-2$\pi$* antibonding orbitals. In contrast to the supported Eu at doped-CNT, the Eu atom becomes more positively charged, which leads to weaken the CO adsorption and promote the O₂ adsorption, consequently enhancing the activity for CO oxidation and alleviating the CO poisoning of the europium catalysts. A notable orbital hybridization and electrostatic interaction between these two species in adsorption process being an evidence of strong interaction. The electronic structure of O₂ adsorbed on Eu-doped CNT resembles that of O${}_2^{-}$, therefore the transferred charge weakens the O–O bonds and facilitates the dissociation process, which is the precondition for the oxygen reduction reaction (ORR).

It has been proved that effective stimulated reservoir volume (ESRV) is a significant area dominant to the production of the fractured well in unconventional gas reservoirs. Although ESRV properties can be estimated based on the microseismic technology and the analysis of actual fracturing data, the operations are complicated and results are inaccurate. Due to the complex structure of stimulated reservoir volume (SRV) with fractal and chaotic characteristics, a fractal evaluation model for ESRV (ESRV-FEM) of fractured wells in unconventional gas (both tight and shale gas) reservoirs is developed. Multiple gas transport mechanisms, SRV and unstimulated reservoir volume (USRV) are included. According to the pressure transient analysis (PTA), influences of multiple transport mechanisms on gas transport behaviors in ESRV are conducted. Moreover, the fractal index representing the heterogeneity degree is applied to estimate the ESRV under different inter-porosity flow coefficients and storage ratio conditions based on the ESRV-FEM. In addition, the presented ESRV-FEM is validated by an actual field case. The results show that gas adsorption has a significant effect on the radial flow duration time in SRV, and the heterogeneity makes the radial flow on PTA curves no longer show a horizontal line with the value of 0.5. Calculated ESRV sizes are compared with the assumed ones under different fractal indexes. The stronger the heterogeneity, the smaller ESRV is. The ESRV size of a fractured well in shale gas reservoirs is only 52.11% of SRV size when the fractal index equals to 0.6. The ESRV-FEM presented in this paper is expected to provide an effective method for the evaluation of the ESRV of fractured wells in unconventional gas reservoirs.

In study of gas migration process in coal seam, the permeability evolution rule with time has been one of hot topics in the area of coal seam for decades. At present, in view of the time-varying rule of coal seam permeability, the influence of microstructure parameters and adsorption effect are seldom considered simultaneously. In this paper, the fractal seepage model coupled with coal deformation, and the adsorption expansion effect of coal is proposed. A multi-field coupling model is established by considering the influence of matrix and fracture structure. The influence of structural parameters and adsorption constant of main fracture on the time-varying curve of macro permeability are analyzed, including: (1) fractal dimension for fracture lengths; (2) maximum fracture length; (3) Langmuir adsorption strain constant; (4) Langmuir adsorption pressure constant. The results show that, under the influence of in situ stress and adsorption effect, the permeability of coal seam decreases with time. The present results show that the permeability is proportional to the fractal dimension for fracture lengths and the maximum fracture length. The uniformity of permeability distribution is found to be directly proportional to the pressure constant of Langmuir and inversely proportional to the volume constant of Langmuir.

The complex rock fracture structures in reservoirs play an important role during methane extraction. However, there is still a challenge to elucidate the impacts of adsorption–desorption, rock expansion, and thermal conduction on the microstructures under thermal–hydrological–mechanical interactions. In this paper, fractal theory for porous media was applied to characterize the structures of rock fractures, and the fracture fractal dimension $(D_f)$ was adopted to analyze the density of fractures and the microstructural evolution. We developed a coupled thermal–hydrological–mechanical model enabling simultaneous analysis of rock fracture microstructures and multi-physical field effects. Furthermore, we analyzed the evolution of the fracture fractal dimension with the reservoir parameter effects, including: (1) methane extraction process; (2) reservoir stress; (3) pore pressure; and (4) reservoir temperature. We also calculated the effects of physical and mechanical factors on the above parameters, including (1) adsorption constant; (2) the in-situ stress; and (3) thermal expansion coefficient. The present results indicate that various characteristic parameters have multiple effects on the microstructures of rock fractures. It was found that the fractal dimension is inversely proportional to the reservoir stress, the gas pressure, and the reservoir temperature.

Gaining a comprehensive insight into how shale’s pore structure changes due to the extraction of oil from smaller pores is pivotal for understanding the impact of movable oil in shale plays, particularly when estimating reserves. The fractal dimension, a parameter reflecting pore complexity, can be quantitatively employed to explore this aspect. In this research endeavor, we focused on assessing variations in pore structure resulting from oil removal in four samples from the Fengcheng shale Formation in Mahu Sag, China. To achieve this, we utilized two diverse probing techniques: Gas adsorption and small-angle X-ray scattering (SAXS). These methodologies allowed us to analyze pore structure alterations both before and after oil extraction. By comparing data gathered through these approaches, we calculated and compared fractal dimensions across pre- and post-extraction conditions. The outcomes revealed notable differences in fractal dimensions obtained from the two methods. Before extraction, the disparity in fractal dimensions calculated from these techniques ranged from 9.6% to 18.3% across the samples. Post-extraction, this variation decreased to a range of 1.6% to 25.1%. These differences originate from the inherent physics governing each method’s operational mode. Furthermore, both techniques indicated an increase in fractal dimension post-extraction, implying heightened pore complexity. In terms of the gas adsorption method, the increase in fractal dimensions across studied samples ranged from 6.385 to 13.435. Comparatively, for the SAXS method, this increase varied between 2.22% and 18.61%. These findings suggest that the movable oil, whether fully or partially occupying pore spaces or being adsorbed onto mineral/organic matter surfaces, could potentially reduce pore complexity. This study pioneers the role of adsorbed or freely moving oil within both connected and isolated pores of shale plays which is crucial for accurate reserve estimation and economic evaluation of shale plays. By elucidating the intricate interactions between oil and pore structures, our research lays the groundwork for more precise assessments in this critical domain.

The effect of gas adsorption on the electronic properties of MgO and Ca-doped MgO is investigated using ab initio molecular dynamics method. The equilibrium position, adsorption energy, charge transfer, and electronic band structure of MgO and Ca-doped MgO (001) surface in the presence of H₂, O₂, and CO were calculated. It was found that CO and O₂ affect the electronic properties of MgO and Ca-doped MgO, extensively. The MgO and Ca-doped MgO can exhibit semiconductor behavior with a band gap which is smaller than that of the MgO after CO and O₂ adsorption. The obtained results indicate that Ca doping increase the activity and the conductivity of MgO (001) surface.

A series of lanthanide porphyrins, [Ln^III(TPPS^IV)]_n·nH₅O₂ (Ln = La, Sm, Eu; H₂TPPS = tetra(4-sulfonatophenyl)porphyrin), have been synthesized through solvothermal reactions and structurally characterized by single-crystal X-ray diffraction. These compounds are characterized by a condensed three-dimensional (3-D) porous open framework. Magnetic measurements reveal that these compounds show ferromagnetic, antiferromagnetic and paramagnetic behavior, respectively. All of the compounds exhibit highly thermal stability. The FT-IR and adsorption measurement of CO₂ were also studied.

Presented here is the synthesis of three new Schiff-base cryptands, 4–6. Dynamic covalent imine bond formation via the condensation of a dialdehyde (7 or 8) with two different tris-amines allowed for the preparation of 4–6 in 84%, 80% and 83% yield, respectively. These systems were characterized by NMR spectroscopy, mass spectra, and, in the case of 5, single crystal X-ray diffraction analysis. These cages act as selective CO${}_{\mathrm{\text{2}}}$ gas adsorbing materials in the solid state.

Hydrogen storage capacity of a carbon nanotube (CNT) sample is investigated using Elastic Recoil Detection Analysis (ERDA) at constant hydrogen uptake pressure of 5 bar and different adsorption temperatures within 30°C–500°C. The results of hydrogen concentration versus temperature revealed three distinct temperature intervals in which a certain adsorption or desorption mechanism is dominant. Moreover, the results showed that hydrogen storage capacity of CNTs at the applied conditions of pressure and temperature is about 0.1 wt.% which is well below the DOE requirements for a viable hydrogen storage system. The physidesorption activation energy is calculated using the Arrhenius plot to be 6 kJmol^-1.

Here we reported the synthesis of nanoporous carbide-derived carbons (CDCs) from a new precursor, titanium tin carbides (Ti₂SnC), via chlorination at 400–1100${}^{\circ }$C. At low chlorination temperature (400–500${}^{\circ }$C), as-synthesized CDCs mainly consisted of amorphous carbon and chlorides. As the chlorination temperature increased up to 600${}^{\circ }$C, chlorides disappeared, and the main composition of CDCs was amorphous carbon. At high chlorination temperature, there was a trend of graphitization. The microstructure of CDCs was observed and characterized by scanning electron microscopy and transmission electron microscopy. Some graphite-like sheet structures in CDCs were found. Specific surface area (SSA) and pore volume of CDCs increased with chlorination temperature, except an abnormal decrease of the CDC chlorinated at 900${}^{\circ }$C. CDC chlorinated at 1100${}^{\circ }$C had the largest SSA, 1580m²/g. In order to apply these materials as novel hydrogen/methane storage media in the area of energy efficient transport, gas adsorption properties of CDCs were measured. For CDC chlorinated at 1100${}^{\circ }$C, pore volume uptakes are $\sim 206$cm³/g at 60 bar (25${}^{\circ }$C) for methane, and $\sim 442$cm³/g at 35 bar ($-196^{\circ }$C) for hydrogen, respectively. It was suggested that CDCs from Ti₂SnC are promising materials for hydrogen/methane adsorptive storage.