Yakang Jin

C2N: an excellent two-dimensional monolayer membrane for He separation

Using the first-principles density functional theory (DFT) and molecular dynamics (MD) simulations, we investigate the He separation performance of a porous C2N monolayer synthesized recently. The DFT calculations demonstrate that the porous C2N monolayer is stable enough to be used as a gas separation membrane and the porous C2N monolayer with a suitable pore size presents a surmountable energy barrier (0.13 eV) for He molecules passing through the membrane. Furthermore, the porous C2N monolayer shows an exceptionally high selectivity for He/Ne (Ar, CH4, CO2, N2, etc.) in a wide range of temperatures. Besides, using MD simulations we demonstrate that the porous C2N monolayer exhibits a He permeance of 1 × 107 GPU at room temperature, which is much higher than the value (20 GPU) in current industrial applications. Therefore, the porous C2N monolayer should be an excellent candidate for He separation from natural gas, due to its high selectivity and excellent permeability.

Theoretical Prediction of Hydrogen Separation Performance of Two-Dimensional Carbon Network of Fused Pentagon

Using the van-der-Waals-corrected density functional theory (DFT) and molecular dynamic (MD) simulations, we theoretically predict the H2 separation performance of a new two-dimensional sp(2) carbon allotropes-fused pentagon network. The DFT calculations demonstrate that the fused pentagon network with proper pore sizes presents a surmountable energy barrier (0.18 eV) for H2 molecule passing through. Furthermore, the fused pentagon network shows an exceptionally high selectivity for H2/gas (CO, CH4, CO2, N2, et al.) at 300 and 450 K. Besides, using MD simulations we demonstrate that the fused pentagon network exhibits a H2 permeance of 4 × 10(7) GPU at 450 K, which is much higher than the value (20 GPU) in the current industrial applications. With high selectivity and excellent permeability, the fused pentagon network should be an excellent candidate for H2 separation.

Theoretical study of a tunable and strain-controlled nanoporous graphenylene membrane for multifunctional gas separation

Using van der Waals corrected density functional theory (DFT), we theoretically predict the performance of a strain-controlled graphenylene membrane in multifunctional gas separation. By applying lateral strain to this membrane, we find that the transition points between “closed” and “open” states for CO2, N2, CO, and CH4 passing through graphenylene membrane occur under 3.04%, 4.20%, 5.12%, and 10.78% strain, respectively. The H2 permeance is remarkably enhanced through tensile strain, and it reaches 2.6 × 10−2 mol s−1 m−2 Pa−1 under 3.04% strain, which is about 6 times higher than that with unstrained graphenylene membrane. At strain levels between 3.04% and 4.20%, this membrane can be used to separate CO2/N2. In particular, at strain levels of 4.20%, the permeance of CO2 for this strained membrane can reach 1.03 × 10−7 mol s−1 m−2 Pa−1 as well as 15.4 selectivity for CO2/N2, which are both higher than the industrially acceptable values of the permeance and selectivity. In addition, with a strain magnitude from 5.12% to 10.78%, a graphenylene monolayer can be used as a CH4 upgrading membrane. Our results demonstrate the promise of a tunable, multifunctional graphenylene gas-separation membrane, wherein the sizes of the nanopores can be precisely regulated by tensile strain. These findings may be useful for designing tunable nanodevices for gas separation and other applications.

Mechanism of oil molecules transportation in nano-sized shale channel: MD simulation

Unconventional energy, such as shale oil and gas, opens up a new avenue for alleviating the pressure on the use of conventional energy, enabling a sustainable development of economy and industry. We firstly explored the mechanism of oil molecules transportation in a nano-sized shale channel by molecular dynamic simulations. It is demonstrated that the competition between the oil adsorption strength to the shale surface and the driving force from gas flooding (N2) plays the dominant role in the oil translocation process in the shale channel. The encapsulated oil molecules would be expelled by gas flooding when the gas pressure reaches a critical value. Besides, it is found that the pressure of the gas flooding, shale channel pore size, N2 amount, temperature and shale component all have an important effect on the translocation process of oil molecules inside the shale channel, whose oil-driving efficiency is characterized by oil displacement distance and oil displacement loss. This work lays a theoretical foundation to achieve effectively and efficiently exploiting oil. Besides, the result may shed light on explaining many industrial processes and natural phenomena in nano-sized channels, including viscous liquid transport or diffusion through membranes, energy conversion devices, biological molecules (hemoglobin, protein, DNA) translocation and so forth.

Self-Assembly of Hydrofluorinated Janus Graphene Monolayer: A Versatile Route for Designing Novel Janus Nanoscrolls.

With remarkably interesting surface activities, two-dimensional Janus materials arouse intensive interests recently in many fields. We demonstrate by molecular dynamic simulations that hydrofluorinated Janus graphene (J-GN) can self-assemble into Janus nanoscroll (J-NS) at room temperature. The van der Waals (vdW) interaction and the coupling of C-H/π/C-F interaction and π/π interaction are proven to offer the continuous driving force of self-assembly of J-GN. The results show that J-GN can self-assemble into various J-NSs structures, including arcs, multi-wall J-NS and arm-chair-like J-NS by manipulating its original geometry (size and aspect ratio). Moreover, we also investigated self-assembly of hydrofluorinated J-GN and Fe nanowires (NWs), suggesting that Fe NW is a good alternative to activate J-GN to form J-NS. Differently, the strong vdW interaction between J-GN and Fe NW provides the main driving force of the self-assembly. Finally, we studied the hydrogen sorption over the formed J-NS with a considerable interlayer spacing, which reaches the US DOE target, indicating that J-NS is a promising candidate for hydrogen storage by controlling the temperature of system. Our theoretical results firstly provide a versatile route for designing novel J-NS from 2D Janus nanomaterials, which has a great potential application in the realm of hydrogen storage/separation.

Surface Effect on Oil Transportation in Nanochannel: a Molecular Dynamics Study

In this work, we investigate the dynamics mechanism of oil transportation in nanochannel using molecular dynamics simulations. It is demonstrated that the interaction between oil molecules and nanochannel has a great effect on the transportation properties of oil in nanochannel. Because of different interactions between oil molecules and channel, the center of mass (COM) displacement of oil in a 6-nm channel is over 30 times larger than that in a 2-nm channel, and the diffusion coefficient of oil molecules at the center of a 6-nm channel is almost two times more than that near the channel surface. Besides, it is found that polarity of oil molecules has the effect on impeding oil transportation, because the electrostatic interaction between polar oil molecules and channel is far larger than that between nonpolar oil molecules and channel. In addition, channel component is found to play an important role in oil transportation in nanochannel, for example, the COM displacement of oil in gold channel is very few due to great interaction between oil and gold substrate. It is also found that nano-sized roughness of channel surface greatly influences the speed and flow pattern of oil. Our findings would contribute to revealing the mechanism of oil transportation in nanochannels and therefore are very important for design of oil extraction in nanochannels.