Mixed matrix membranes with fast and selective transport pathways for efficient CO2 separation.

To improve CO2 separation performance, porous carbon nanosheets (PCNs) were used as a filler into a Pebax MH 1657 (Pebax) matrix, fabricating mixed matrix membranes (MMMs). The PCNs exhibited a preferential horizontal orientation within the Pebax matrix because of the extremely large 2D plane and nanoscale thickness of the matrix. Therefore, the micropores of the PCNs provided fast CO2 transport pathways, which led to increased CO2 permeability. The reduced pore size of the PCNs was a consequence of the overlapping of PCNs and the polymer chains penetrating into the pores of the PCNs. The reduction in the pore size of the PCNs improved the CO2/gas selectivity. As a result, the CO2 permeability and CO2/CH4 selectivity of the Pebax membrane with 10 wt% PCNs-loading (Pebax-PCNs-10) were 520 barrer and 51, respectively, for CO2/CH4 mixed-gas. The CO2 permeability and CO2/N2 selectivity of the Pebax-PCNs-10 membrane were 614 barrer and 61, respectively, for CO2/N2 mixed-gas.

Constructing Unique Cross-Sectional Structured Mixed Matrix Membranes by Incorporating Ultrathin Microporous Nanosheets for Efficient CO2 Separation.

Ultrathin microporous nanosheets denoted as Zn-tetra-(4-carboxyphenyl)porphyrin (Zn-TCPP) were synthesized and incorporated into a Pebax MH 1657 (Pebax) polymer to fabricate mixed matrix membranes (MMMs) for efficient CO2 separation. The Zn-TCPP nanosheets with a microporous structure provide high-speed channels for fast CO2 transport and shorten the diffusion pathways, both contributing toward high CO2 permeability. Furthermore, scanning electron microscopy results indicate that the ultrathin Zn-TCPP nanosheets with an ultrahigh aspect ratio (>200) tend to arrange horizontally in the Pebax matrix. The obtained unique cross-sectional structure of the MMMs functions as a selective barrier, allowing repeated discrimination of gases due to the tortuous interlayer of horizontal nanosheets, thus improving the selectivity of the MMMs. In addition, the horizontally arranged microporous nanosheets were found to strongly interact with the membrane matrix and endowed the MMMs with excellent interfacial compatibility, which improved the CO2 permeability and eliminated unselective permeation pathways. Significantly, the optimized CO2 separation performance of the MMMs surpassed the 2008 Robeson's limit.

Application Value of Magnetic Resonance Perfusion Imaging in the Early Diagnosis of Rat Hepatic Fibrosis.

OBJECTIVE: To assess the application value of perfusion-weighted imaging (PWI) in early diagnosis, quantitation, and hepatic fibrosis staging by analyzing the related parameters in hepatic fibrosis. METHODS: A total of 60 rats were randomly divided into the hepatic fibrosis and control groups, and carbon tetrachloride (CCL4) was used to establish the liver fibrosis model. All rats underwent PWI examination, and the trend of the time-signal intensity curve (TIC, automatically generated by the software) was observed. Also, the perfusion parameters, maximum signal reduction ratio (SRRmax), time to peak (TTP), and mean transit time (MTT), were analyzed and compared with pathological staging. RESULTS: The TIC curve was characterized by slow wash-in and wash-out with a low and wide peak. The PWI perfusion parameters were statistically significant in specific groups (P < 0.05): SRRmax values (control group and F3, F4), TTP, and MTT values (control group and F2-F4, F1 and F3, F1 and F4, and F2 and F4 in addition to TTP values for F1 and F2). Pearson's correlation analysis showed a negative correlation of SRRmax with hepatic fibrosis stage (r = -0.439, P < 0.05), while TTP and MTT values were positively correlated with hepatic fibrosis stage (TTP, r = 0.798; MTT, r = 0.647; all P < 0.001). CONCLUSIONS: PWI perfusion parameters reflect the degree of hepatic fibrosis, especially TTP and MTT, and PWI is recommended for the early diagnosis of liver fibrosis for timely intervention and treatment of the disease and delaying its progression.

Mixed-Matrix Membranes Containing Carbon Nanotubes Composite with Hydrogel for Efficient CO2 Separation.

In this study, a carbon nanotubes composite coated with N-isopropylacrylamide hydrogel (NIPAM-CNTs) was synthesized. Mixed-matrix membranes (MMMs) were fabricated by incorporating NIPAM-CNTs composite filler into poly(ether-block-amide) (Pebax MH 1657) matrix for efficient CO2 separation. The as-prepared NIPAM-CNTs composite filler mainly plays two roles: (i) The extraordinary smooth one-dimensional nanochannels of CNTs act as the highways to accelerate CO2 transport through membranes, increasing CO2 permeability; (ii) The NIPAM hydrogel layer coated on the outer walls of CNTs acts as the super water absorbent to increase water content of membranes, appealing both CO2 permeability and CO2/gas selectivity. MMM containing 5 wt % NIPAM-CNTs exhibited the highest CO2 permeability of 567 barrer, CO2/CH4 selectivity of 35, and CO2/N2 selectivity of 70, transcending 2008 Robeson upper bound line. The improved CO2 separation performance of MMMs is mainly attributed to the construction of the efficient CO2 transport pathways by NIPAM-CNTs. Thus, MMMs incorporated with NIPAM-CNTs composite filler can be used as an excellent membrane material for efficient CO2 separation.