Water desalination of a new three-dimensional covalent organic framework: a molecular dynamics simulation study.

Preparing a nanoporous membrane with high density and ordered pore sizes which allows high water permeability and salt rejection rate is the key to realize highly efficient desalination. However, preparing a nanoporous membrane with high density and order pore sizes is still extremely hard due to the limitation of experimental techniques. Recently, a 3D covalent organic framework (3D-COF) material named as the 3D-OH-COF with good crystallinity and large specific surface areas has been synthesized. Based on the structural features of the 3D-OH-COF, we speculate that it may be a good candidate for the desalination application derived from its high-density sub-nanometer pore. In this work, using molecular dynamics simulations, the possibility of the 3D-OH-COF for desalination application was explored, the influence of membrane thickness on its desalination performance was also studied, and the detailed structure and dynamics of ions and water transport in the channel of the 3D-OH-COF was discussed. The results show that the rectangular channel structure and charged H atoms are responsible for the excellent salt rejection rate (100%) and high water flux (41.44 Lit cm-2 day-1 MPa-1), respectively. Furthermore, the water flux is three orders of magnitude higher than that of the commercial reverse osmosis membrane and is four times higher than that of the theoretically reported monolayer nanoporous MoS2 membrane. It is also about 28% higher than that of the recently reported 2D-CAP membrane. This work theoretically confirms that the 3D-OH-COF is a promising membrane material for desalination applications and the underlying molecular mechanisms are clarified.

Alternating electric field-induced ion current rectification and electroosmotic pump in ultranarrow charged carbon nanocones.

Pumping fluid in ultranarrow (sub-2 nm) synthetic channels, analogous to protein channels, has widespread applications in nanofluidic devices, molecular separation, and related fields. In this work, molecular dynamics simulations were performed to study a symmetrical sinusoidal electric field-induced electroosmotic pump in ultranarrow charged carbon nanocone (CNC) channels. The results show that the CNC channels could rectify the ion current because of the different ion flow rates in the positive and negative half circles of the sinusoidal electric field. Electroosmotic flow (EOF) rectification yielded by the ion current rectification is also revealed, and net water flow from the base to the tip of the CNC channels is observed. The simulations also show that the preferential ion current conduction direction in the ultranarrow CNC channels (from base to tip) is opposite to that in conical nanochannels with tip diameters larger than 5 nm (from tip to base). However, the preferential EOF direction is the same as that of large conical nanochannels (from base to tip). We also investigated the influences of ion concentration and the amplitudes and periods of the sinusoidal electric field on the EOF pump. The results show that high ion concentration, large amplitudes, and long periods are desired for high EOF pumping efficiency. Finally, through comparison with a constant electric field and a pressure-induced water pump, we prove that the EOF pump under an alternating electric field has a higher pump efficiency. The approach outlined in this work provides a general scheme for pumping fluid in ultranarrow charged conical nanochannels.

Transcriptomics Integrated with Metabolomics Unveil Carotenoids Accumulation and Correlated Gene Regulation in White and Yellow-Fleshed Turnip (Brassica rapa ssp. rapa).

Turnip (Brassica rapa ssp. rapa) is considered to be a highly nutritious and health-promoting vegetable crop, whose flesh color can be divided into yellow and white. It is widely accepted that yellow-fleshed turnips have higher nutritional value. However, reports about flesh color formation is lacking. Here, the white-fleshed inbred line, W21, and yellow-fleshed inbred line, W25, were profiled from the swollen root of the turnip at three developmental periods to elucidate the yellow color formation. Transcriptomics integrated with metabolomics analysis showed that the PSY gene was the key gene affecting the carotenoids formation in W25. The coding sequence of BrrPSY-W25 was 1278 bp and that of BrrPSY-W21 was 1275 bp, and BrrPSY was more highly expressed in swollen roots in W25 than in W21. Transient transgenic tobacco leaf over-expressing BrrPSY-W and BrrPSY-Y showed higher transcript levels and carotenoids contents. Results revealed that yellow turnip formation is due to high expression of the PSY gene rather than mutations in the PSY gene, indicating that a post-transcriptional regulatory mechanism may affect carotenoids formation. Results obtained in this study will be helpful for explaining the carotenoids accumulation of turnips.