Publisher Correction: Mixed matrix formulations with MOF molecular sieving for key energy-intensive separations.

In the version of this Article originally published, the units of the y axis of Fig. 3b were incorrectly given as '106 cm2 s-1'; they should have been '10-8 cm2 s-1'. This has been corrected in the online versions of the Article.

Mixed matrix formulations with MOF molecular sieving for key energy-intensive separations.

Membrane-based separations can improve energy efficiency and reduce the environmental impacts associated with traditional approaches. Nevertheless, many challenges must be overcome to design membranes that can replace conventional gas separation processes. Here, we report on the incorporation of engineered submicrometre-sized metal-organic framework (MOF) crystals into polymers to form hybrid materials that successfully translate the excellent molecular sieving properties of face-centred cubic (fcu)-MOFs into the resultant membranes. We demonstrate, simultaneously, exceptionally enhanced separation performance in hybrid membranes for two challenging and economically important applications: the removal of CO2 and H2S from natural gas and the separation of butane isomers. Notably, the membrane molecular sieving properties demonstrate that the deliberately regulated and contracted MOF pore-aperture size can discriminate between molecular pairs. The improved performance results from precise control of the linkers delimiting the triangular window, which is the sole entrance to the fcu-MOF pore. This rational-design hybrid approach provides a general toolbox for enhancing the transport properties of advanced membranes bearing molecular sieve fillers with sub-nanometre-sized pore-apertures.

Enabling Fluorinated MOF-Based Membranes for Simultaneous Removal of H2 S and CO2 from Natural Gas.

Membrane-based gas separations are energy efficient processes; however, major challenges remain to develop high-performance membranes enabling the replacement of conventional separation processes. Herein, a new fluorinated MOF-based mixed-matrix membrane is reported, which is formed by incorporating the MOF crystals into selected polymers via a facile mixed-matrix approach. By finely controlling the molecular transport in the channels through the MOF apertures tuned by metal pillars and at the MOF-polymer interfaces, the resulting fluorinated MOF-based membranes exhibit excellent molecular sieving properties. These materials significantly outperform state-of-the-art membranes for simultaneous removal of H2 S and CO2 from natural gas-a challenging and economically important application. The robust fluorinated MOFs (NbOFFIVE-1-Ni, AlFFIVE-1-Ni), pave a way to efficient membrane separation processes that require precise discrimination of closely sized molecules.

Molecularly Designed Stabilized Asymmetric Hollow Fiber Membranes for Aggressive Natural Gas Separation.

New rigid polyimides with bulky CF3 groups were synthesized and engineered into high-performance hollow fiber membranes. The enhanced rotational barrier provided by properly positioned CF3 side groups prohibited fiber transition layer collapse during cross-linking, thereby greatly improving CO2 /CH4 separation performance compared to conventional materials for aggressive natural gas feeds.

Synergistic effects of adsorption and chemical reduction towards the effective Cr(VI) removal in the presence of the sulfur-doped biochar material.

In this study, the anaerobic sludge withdrawn from thickener in a sewage treatment plant served as the precursor for sludge-based biochar fabrication, which was further modified via sulfur (S) heteroatom doping (i.e., S-BC). The S atom doping resulted in the adjustment of the physicochemical properties towards the carbon material, endowment of abundant functional groups on biochar surface, and increasing the binding sites between biochar and Cr(VI). Compared to the primary biochar (i.e., biochar without heteroatomic doping, named BC), S-BC exhibited a rough surface and possessed remarkable advantages in ash content, specific surface area, and pore volume. The existence of graphene carbon crystal structure for S-BC was confirmed through S-BC by XRD and FTIR analysis. The studies of adsorption kinetics and isotherms showed that pseudo-second-order kinetics and the Langmuir model more fitted the Cr(VI) removal behavior in the presence of S-BC. Therefore, the chemisorption and monolayer adsorption were the primary mechanisms involved in the Cr(VI) removal process. Additionally, XPS analysis results illustrated the aqueous Cr(VI) was efficiently eliminated through the synergistic effect of chemisorption and reduction to Cr(III) in the presence of S-BC. Moreover, S-BC could still achieve the Cr(VI) eliminating efficiency of 85.31% undergoing five cycles with unchanged functional group and crystal structure via FTIR and XRD analysis. Thus, the results of this study may shed light on a new approach for simultaneous economical sludge disposal and the sustainable remediation of the Cr(VI)-contaminated wastewater.

State-of-the-Art Organic- and Inorganic-Based Hollow Fiber Membranes in Liquid and Gas Applications: Looking Back and Beyond.

The aggravation of environmental problems such as water scarcity and air pollution has called upon the need for a sustainable solution globally. Membrane technology, owing to its simplicity, sustainability, and cost-effectiveness, has emerged as one of the favorable technologies for water and air purification. Among all of the membrane configurations, hollow fiber membranes hold promise due to their outstanding packing density and ease of module assembly. Herein, this review systematically outlines the fundamentals of hollow fiber membranes, which comprise the structural analyses and phase inversion mechanism. Furthermore, illustrations of the latest advances in the fabrication of organic, inorganic, and composite hollow fiber membranes are presented. Key findings on the utilization of hollow fiber membranes in microfiltration (MF), nanofiltration (NF), reverse osmosis (RO), forward osmosis (FO), pervaporation, gas and vapor separation, membrane distillation, and membrane contactor are also reported. Moreover, the applications in nuclear waste treatment and biomedical fields such as hemodialysis and drug delivery are emphasized. Subsequently, the emerging R&D areas, precisely on green fabrication and modification techniques as well as sustainable materials for hollow fiber membranes, are highlighted. Last but not least, this review offers invigorating perspectives on the future directions for the design of next-generation hollow fiber membranes for various applications. As such, the comprehensive and critical insights gained in this review are anticipated to provide a new research doorway to stimulate the future development and optimization of hollow fiber membranes.

Ultraselective glassy polymer membranes with unprecedented performance for energy-efficient sour gas separation.

Membrane-based separation of combined acid gases carbon dioxide and hydrogen sulfide from natural gas streams has attracted increasing academic and commercial interest. These feeds are referred to as "sour," and herein, we report an ultra H2S-selective and exceptionally permeable glassy amidoxime-functionalized polymer of intrinsic microporosity for membrane-based separation. A ternary feed mixture (with 20% H2S:20% CO2:60% CH4) was used to demonstrate that a glassy amidoxime-functionalized membrane provides unprecedented separation performance under challenging feed pressures up to 77 bar. These membranes show extraordinary H2S/CH4 selectivity up to 75 with ultrahigh H2S permeability >4000 Barrers, two to three orders of magnitude higher than commercially available glassy polymeric membranes. We demonstrate that the postsynthesis functionalization of hyper-rigid polymers with appropriate functional polar groups provides a unique design strategy for achieving ultraselective and highly permeable membrane materials for practical natural gas sweetening and additional challenging gas pair separations.

Enhanced CO2/CH4 Separation Performance of a Mixed Matrix Membrane Based on Tailored MOF-Polymer Formulations.

Membrane-based separations offer great potential for more sustainable and economical natural gas upgrading. Systematic studies of CO2/CH4 separation over a wide range of temperatures from 65 °C (338 K) to as low as -40 °C (233 K) reveals a favorable separation mechanism toward CO2 by incorporating Y-fum-fcu-MOF as a filler in a 6FDA-DAM polyimide membrane. Notably, the decrease of the temperature from 308 K down to 233 K affords an extremely high CO2/CH4 selectivity (≈130) for the hybrid Y-fum-fcu-MOF/6FDA-DAM membrane, about four-fold enhancement, with an associated CO2 permeability above 1000 barrers. At subambient temperatures, the pronounced CO2/CH4 diffusion selectivity dominates the high permeation selectivity, and the enhanced CO2 solubility promotes high CO2 permeability. The differences in adsorption enthalpy and activation enthalpy for diffusion between CO2 and CH4 produce the observed favorable CO2 permeation versus CH4. Insights into opportunities for using mixed-matrix membrane-based natural gas separations at extreme conditions are provided.