2D materials' membranes with well-defined nanochannels are promising for precise molecular separation. Herein, the design and engineering of atomically thin 2D MXene flacks into nanofilms with a thickness of 20 nm for gas separation are reported. Well-stacked pristine MXene nanofilms are proven to show outstanding molecular sieving property for H 2 preferential transport. Chemical tuning of the MXene nanochannels is also rationally designed for selective permeating CO 2 . Borate and polyethylenimine (PEI) molecules are well interlocked into MXene layers, realizing the delicate regulation of stacking behaviors and interlayer spacing of MXene nanosheets. The MXene nanofilms with either H 2 -or CO 2 -selective transport channels exhibit excellent gas separation performance beyond the limits for state-of-the-art membranes. The mechanisms within these nanoconfined MXene layers are discussed, revealing the transformation from "diffusion-controlled" to "solution-controlled" channels after chemical tuning. This work of precisely tailoring the 2D nanostructure may inspire the exploring of nanofluidics in 2D confined space with applications in many other fields like catalysis and energy conversion processes.fabrication. Hence, MXene is considered to be a novel potential candidate for developing separative 2D-material membranes. However, there are a very few reports on MXene separation membranes. Gogotsi and co-workers first reported MXene membranes for rejection of trivalent cation in solution using nonpressure diffusion. [12] A high water permeance was obtained by applying MXene stacks in the pressure-filtration process, [13] but the membrane can only rejected matters with a size larger than 2.5 nm. Very recently, Wang and co-workers [14] reported the manufacturing of MXene membranes with highly ordered nanochannel structures for high-performance separation of H 2 /CO 2 , which opens the door of applying MXene membranes for molecular separation. It is considered that rationally regulating the nanostructure of 2D channels may, thereby, enlighten the exploring of MXene materials for sub-nanoscale separation with versatile functionalities.Herein, we report the design and engineering of MXene nanofilms with tunable transport channels for gas separation. Ultrathin pristine MXene nanofilms with a thickness down to 20 nm were fabricated by horizontally aligning the exfoliated MXene nanosheets on porous substrates. Molecular sieving channels within pristine MXene nanofilm can be formed to show highly selective H 2 permeation, as shown in Figure 1. Interestingly, these MXene laminates, as functionalized by borate and amine, exhibit different stacking behaviors and tunable interlayer spacing, allowing preferential CO 2 permeation. The resulting separation performance of either H 2 -or CO 2selective MXene nanofilms is beyond the performance limits for state-of-the-art membranes.

Fluorinated membranes based on covalent triazine frameworks are prepared through rational design of aromatic nitrile monomers containing fluorine and ether groups via a sol-gel polymerization process. The CO 2 separation performance is markedly enhanced with the increase of fluorine content in the membrane. With functionalized triazine units, fluorine and ether groups, the carbon molecular sieve membranes obtained after pyrolysis exhibit intrinsic ultra-micropores, high surface areas, and outstanding CO 2 separation performance.

Metrics & MoreArticle Recommendations * sı Supporting Information CONSPECTUS: The discovery of graphene triggers a new era of two-dimensional (2D) materials, which exhibit great potential in condensed matter physics, chemistry, and materials science. Meanwhile, the booming of 2D materials brings new opportunities for the next generation of high-performance (high permeability, selectivity, and stability) separation membranes. Two-dimensional materials with atomic thinness can serve as new building blocks for fabricating ultrathin membranes possessing the ultimate permeation rate. The plane structure with micrometer lateral dimensions provides an excellent platform for the orderly alignment of the nanosheets. Moreover, the apertures of two-dimensional-material membranes (2DMMs), including the in-plane nanopores and interlayer channels, can contribute to the fast and selective transport of small molecules/ions related to molecular separation. Therefore, the emerging 2D materials with various nanostructures, including graphene oxide (GO), zeolite nanosheets, metal− organic framework (MOF) nanosheets, and transition-metal carbides/carbonitrides (MXene), can be assembled into highperformance membranes. Various assembly methods such as filtration, spin coating, and hot dropping have been employed to fabricate 2DMMs, while the processes for separating small molecules/ions tend to demand higher precision, especially in water desalination and gas separation. The nanostructures of 2DMMs and the physicochemical properties of transport pathway need to be finely tuned to meet the requirement. In addition, the stability of 2DMMs, which is critical to the large-scale implementation, must be taken into consideration as well.In this Account, we discuss our recent progress in manipulating molecular transport pathways in 2DMMs by optimizing the assembly behavior of 2D nanosheets, tuning the microstructure of interlayer channels, and controlling the physicochemical properties of the membrane surface. Assembly methods, including vacuum suction assembly, polymer-induced assembly, and external force-driven assembly, have been proposed to construct ordered laminates for molecular transport. The size and chemical structure of interlayer channels were further tailored by strategies such as nanoparticle intercalation, cationic control, and chemical modification. Interestingly, the manipulation of surface properties of 2DMMs was proven to contribute to fast molecular transport through interlayer channels. Moreover, the issues concerning 2DMMs toward practical applications are discussed with an emphasis on the substrate effect, molecular bridge strategy, and preliminary progress in large-scale fabrication. Finally, we conclude this Account with an overview of the remaining challenges and the new opportunities that will be opened up for 2DMMs in molecular separation.

Bicarbonate (HCO3 –), one of the most abundant anions in fresh water, is relatively nontoxic and cheap. In this work, the degradation of organic dyes with simple copper(II) ions as the catalyst in the HCO3 – solution using H2O2 as the oxidant was investigated. It was found that the dyes such as Orange II (AOII), Methyl Orange, Methyl Red, and Toluidine Blue could be efficiently decolorized by the system. The rate of H2O2 decomposition was much slower in the presence of the dyes than that without the pollutants. The formed copper(II) species at different HCO3 – concentrations were calculated, and CuCO3 was suggested to be more reactive. The radical scavenging measurements further implied that the produced higher oxidation state of copper, Cu(III), was to be responsible for the dye decolorization. A possible pathway of AOII degradation was also proposed based on the detected intermediate products by electrospray ionization mass spectrometry. This study can provide us a simple, effective, and economical system ideal for the treatment of toxic and nonbiodegradable organic dyes.

Surface-enhanced Raman scattering (SERS) substrate of Ag nanostructure arrays patterned by porous anodic aluminum oxide (AAO) membrane supported on Al substrate (AAO/Al) were fabricated by electron beam evaporation technique. By introducing Al substrate, the optical and SERS properties of as-prepared AAO/Al-based Ag nanostructure arrays are much different from those of the AAO-based array. By optimizing the thickness of both deposited Ag and AAO membrane, the SERS enhancement factor (EF) of as-fabricated AAO/Al-based Ag nanostructure arrays reached 9.77 × 107 due to the SPR and destructive interference coenhanced effects, which is higher than that of AAO-based Ag nanostructure arrays. Also, the mechanism of SPR and destructive interference coenhanced local EM fields as well as SERS enhancement were demonstrated by FDTD simulation results.

No abstract

Mixed matrix membranes (MMMs) made from inorganic fillers and polymers is a kind of promising candidate for gas separation. In this work, two‐dimensional MXene nanosheets were synthesized and incorporated into a polyether‐polyamide block copolymer (Pebax) matrix to fabricate MMM for CO2 capture. The physicochemical properties of MXene nanosheets and MXene/Pebax membranes were studied systematically. The introduction of MXene nanosheets provided additional molecular transport channels and meanwhile enhanced the CO2 adsorption capacity, thereby enhancing both the CO2 peremance and CO2/N2 selectivity of Pebax membrane. The optimized MXene/Pebax membrane with a MXene loading of 0.15 wt % displayed a high separation performance with a CO2 permeance of 21.6 GPU and a CO2/N2 selectivity of 72.5, showing potential application in CO2 capture.

The UV plasmonic properties of Al shallow pit arrays (ASPA) are investigated by experimental and simulative methods. ASPA with various periods are fabricated by the hard anodization (HA) technique. The measured reflectance spectra of ASPA exhibit a reflectance pit in the UV region, which is red shifted with the increasing period of ASPA and refractive index of the surrounding medium. The dependence of reflectance on the period and refractive index calculated by the finite difference time domain (FDTD) method exhibits the identical evolution trends with measurement results. The angle-dependent reflectance spectrum, spatial electric field, and surface charge distribution calculated by FDTD reveal that ASPA sustains propagating surface plasmons (SPs), the UV reflectance pit corresponds to the propagating SPs mode, and the total field inside the Al shallow pit and its proximity region is enhanced with increasing the period of ASPA, which reveals the origin of the higher sensing performance of ASPA with bigger period and is in accordance with the measured results.