Nanoporous Carbon Membranes Research Articles

Electron-mediated control of nanoporosity for targeted molecular separation in carbon membranes

Carbon molecular sieve (CMS) membranes are considered game-changers to overcome the challenges that conventional polymeric membranes face. However, CMS membranes also confront a challenge in successfully separating extremely similar-sized molecules. In this article, high-precision tuning of the microstructure of CMS membranes is proposed by controlled electron irradiation for the separation of molecules with size differences less than 0.05 nm. Fitting CMS membranes for targeted molecular separation can be accomplished by irradiation dosage control, resulting in highly-efficient C2H4/C2H6 separation for low dosages (∼250kGy, with selectivity ∼14) and ultra-selective H2/CO2 separation for high dosages (1000∼2000kGy with selectivity ∼80).The electron irradiated CMS also exhibits highly stabilized permeability and selectivity for long-term operation than the pristine CMS, which suffers from significant performance degradation due to physical aging. This study successfully demonstrates electron irradiation as a possible way to construct “designer” nanoporous carbon membranes out of the standard components mostly confined to pyrolysis conditions.

Unidirectional ion transport in nanoporous carbon membranes with a hierarchical pore architecture

The transport of fluids in channels with diameter of 1-2 nm exhibits many anomalous features due to the interplay of several genuinely interfacial effects. Quasi-unidirectional ion transport, reminiscent of the behavior of membrane pores in biological cells, is one phenomenon that has attracted a lot of attention in recent years, e.g., for realizing diodes for ion-conduction based electronics. Although ion rectification has been demonstrated in many asymmetric artificial nanopores, it always fails in the high-concentration range, and operates in either acidic or alkaline electrolytes but never over the whole pH range. Here we report a hierarchical pore architecture carbon membrane with a pore size gradient from 60 nm to 1.4 nm, which enables high ionic rectification ratios up to 104 in different environments including high concentration neutral (3 M KCl), acidic (1 M HCl), and alkaline (1 M NaOH) electrolytes, resulting from the asymmetric energy barriers for ions transport in two directions. Additionally, light irradiation as an external energy source can reduce the energy barriers to promote ions transport bidirectionally. The anomalous ion transport together with the robust nanoporous carbon structure may find applications in membrane filtration, water desalination, and fuel cell membranes.

Revealing Molecular Mechanisms in Hierarchical Nanoporous Carbon via Nuclear Magnetic Resonance

Author(s): Mao, H; Tang, J; Xu, J; Peng, Y; Chen, J; Wu, B; Jiang, Y; Hou, K; Chen, S; Wang, J; Lee, HR; Halat, DM; Zhang, B; Chen, W; Plantz, AZ; Lu, Z; Cui, Y; Reimer, JA | Abstract: Hierarchical nanoporous carbons combining pore sizes of different length scales are highly important for separation processes. However, critical questions remain regarding the hierarchical structure regulation and the molecular mechanisms of gaseous adsorbate uptake and interactions within the hierarchical nanoporous carbons. These materials present characterization challenges in that there are no experimental techniques that can elucidate the molecular mechanisms of the organic compounds and CO within the materials. We deployed multidimensional solid-state nuclear magnetic resonance (NMR) to generate maps of guest-framework interactions as a function of adsorbate concentrations and adsorption times. The NMR spectra provide insight toward the design of effective hierarchical pore structures. Our materials show a high volatile organic compounds/CO physisorption capacity, which reveals promising application to carbon-capture strategies to mitigate global warming. 2 2

Power generation by reverse electrodialysis in a single-layer nanoporous membrane made from core-rim polycyclic aromatic hydrocarbons.

Nanoporous graphene and related atomically thin layered materials are promising candidates in reverse electrodialysis research owing to their remarkable ionic conductivity and high permselectivity. The synthesis of atomically thin nanoporous membranes with a narrow pore size distribution, however, remains challenging. Here, we report the fabrication of nanoporous carbon membranes via the thermal crosslinking of core-rim structured monomers, that is, polycyclic aromatic hydrocarbons. The mechanically robust, centimetre-sized membrane has a pore size of 3.6 ± 1.8 nm and a thickness of 2.0 ± 0.5 nm. When applied to reverse electrodialysis, the nanoporous carbon membrane offers a high short-circuit current with an output power density of 67 W m-2, which is about two orders of magnitude beyond that of the classic ion-exchange membranes and current prototype nanoporous membranes reported in the literature. Crosslinked and atomically thin porous polycyclic aromatic hydrocarbon membranes therefore represent new scaffolds that will revolutionize the rapidly developing fields of sustainable energy and membrane technology.

Electro-confinement membrane desalination by nanoporous carbon membrane

In this work, we reported a novel desalination method, electro-confinement desalination (ECMD), combining electric field and confinement effects using nanofiltration carbon membranes (CM) as the electrode. The ECMD method showed high ions rejection and high energy efficiency. It was found that the optimum potential for rejection of SO42− was −0.4 V (SCE), a steady rejection of 94.89% for SO42− being achieved in the cathode chamber when the feed concentration of Na2SO4 was 500 mg L−1 in water. To remove Na+, we set CM anode chamber to treat the effluent water from the cathode chamber. The rejection of SO42− and Na+ reached 100% and 88.86%, respectively. Besides the high removal of ions, the energy consumption was as low as 1.90 × 10−2 KWh m−3. The application of nanoporous CM and electric field made the desalination process concern adsorption desalination (AD), capacitive deionization (CDI) and electric enhanced confinement membrane desalination (CMD). To understand the contribution of the AD, CDI and CMD to desalination, a series of experiments were conducted. It was found that SO42− removal could be achieved 38.62% by AD, 18.50% by CDI and 80.99% by CMD, respectively. This result suggests that high desalination efficiency was stemmed from multi-effects but mainly from electro-confinement.

Poly(Ionic Liquid)-Derived Graphitic Nanoporous Carbon Membrane Enables Superior Supercapacitive Energy Storage.

High energy/power density, capacitance, and long-life cycles are urgently demanded for energy storage electrodes. Porous carbons as benchmark commercial electrode materials are underscored by their (electro)chemical stability and wide accessibility, yet are often constrained by moderate performances associated with their powdery status. Here via controlled vacuum pyrolysis of a poly(ionic liquid) membrane template, advantageous features including good conductivity (132 S cm-1 at 298 K), interconnected hierarchical pores, large specific surface area (1501 m2 g-1), and heteroatom doping are realized in a single carbon membrane electrode. The structure synergy at multiple length scales enables large areal capacitances both for a basic aqueous electrolyte (3.1 F cm-2) and for a symmetric all-solid-state supercapacitor (1.0 F cm-2), together with superior energy densities (1.72 and 0.14 mW h cm-2, respectively) without employing a current collector. In addition, theoretical calculations verify a synergistic heteroatom co-doping effect beneficial to the supercapacitive performance. This membrane electrode is scalable and compatible for device fabrication, highlighting the great promise of a poly(ionic liquid) for designing graphitic nanoporous carbon membranes in advanced energy storage.

Ambient Electrosynthesis of Ammonia: Electrode Porosity and Composition Engineering

AbstractAmmonia, a key precursor for fertilizer production, convenient hydrogen carrier, and emerging clean fuel, plays a pivotal role in sustaining life on Earth. Currently, the main route for NH3 synthesis is by the heterogeneous catalytic Haber–Bosch process (N2+3 H2→2 NH3), which proceeds under extreme conditions of temperature and pressure with a very large carbon footprint. Herein we report that a pristine nitrogen‐doped nanoporous graphitic carbon membrane (NCM) can electrochemically convert N2 into NH3 in an acidic aqueous solution under ambient conditions. The Faradaic efficiency and rate of production of NH3 on the NCM electrode reach 5.2 % and 0.08 g m−2 h−1, respectively. Functionalization of the NCM with Au nanoparticles dramatically enhances these performance metrics to 22 % and 0.36 g m−2 h−1, respectively. As this system offers the potential to be scaled to industrial levels it is highly likely that it might displace the century‐old Haber–Bosch process.

Ambient Electrosynthesis of Ammonia: Electrode Porosity and Composition Engineering.

Ammonia, a key precursor for fertilizer production, convenient hydrogen carrier, and emerging clean fuel, plays a pivotal role in sustaining life on Earth. Currently, the main route for NH3 synthesis is by the heterogeneous catalytic Haber-Bosch process (N2 +3 H2 →2 NH3 ), which proceeds under extreme conditions of temperature and pressure with a very large carbon footprint. Herein we report that a pristine nitrogen-doped nanoporous graphitic carbon membrane (NCM) can electrochemically convert N2 into NH3 in an acidic aqueous solution under ambient conditions. The Faradaic efficiency and rate of production of NH3 on the NCM electrode reach 5.2 % and 0.08 g m-2 h-1 , respectively. Functionalization of the NCM with Au nanoparticles dramatically enhances these performance metrics to 22 % and 0.36 g m-2 h-1 , respectively. As this system offers the potential to be scaled to industrial levels it is highly likely that it might displace the century-old Haber-Bosch process.

Selective Permeation through One-Atom-Thick Nanoporous Carbon Membranes: Theory Reveals Excellent Design Strategies!

Research on the permeation of various species through one-atom-thick nanoporous carbon membranes has gained an unprecedented importance in the past decade, thanks to the development of numerous theoretical design strategies for a plethora of applications ranging from gas separation, water desalination, isotope separation, and chiral separation, to DNA sequencing. Although some of the recent experiments have demonstrated successful performance of such carbon membranes in sieving, many of the suggested applications are yet to be realized in experiments. This review aims to draw the attention of the theoretical as well as the experimental researchers working on two-dimensional carbon materials toward the recent theoretical developments probing the permeation of various species such as atoms, ions, small molecules, and biopolymers like DNA through carbon frameworks like graphynes, graphdiyne, graphenylenes, and various forms of nanoporous graphene, including graphene crown ethers. The underlying guiding principles toward the design of carbon-based membranes for nanofiltration are established using estimates of the adsorption energies, barrier heights for permeation, rates of permeation, selectivities, permeances, etc. The crucial roles of tunneling, temperature effects, chemical functionalities, and dynamical aspects of the nanopores are also highlighted, paving the way to a comprehensive description of the theoretical design strategies for tailoring the applicability of novel nanoporous carbon membranes in sieving and related aspects.

Nitrogen-Doped Nanoporous Carbon Membranes with Co/CoP Janus-Type Nanocrystals as Hydrogen Evolution Electrode in Both Acidic and Alkaline Environments.

Self-supported electrocatalysts being generated and employed directly as electrodes for energy conversion has been intensively pursued in the fields of materials chemistry and energy. Herein, we report a synthetic strategy to prepare freestanding hierarchically structured, nitrogen-doped nanoporous graphitic carbon membranes functionalized with Janus-type Co/CoP nanocrystals (termed as HNDCM-Co/CoP), which were successfully applied as a highly efficient, binder-free electrode in the hydrogen evolution reaction (HER). Benefited from multiple structural merits, such as a high degree of graphitization, three-dimensionally interconnected micro/meso/macropores, uniform nitrogen doping, well-dispersed Co/CoP nanocrystals, as well as the confinement effect of the thin carbon layer on the nanocrystals, HNDCM-Co/CoP exhibited superior electrocatalytic activity and long-term operation stability for HER under both acidic and alkaline conditions. As a proof-of-concept of practical usage, a 5.6 cm × 4 cm × 60 μm macroscopic piece of HNDCM-Co/CoP was prepared in our laboratory. Driven by a solar cell, electroreduction of water in alkaline conditions (pH 14) was performed, and H2 was produced at a rate of 16 mL/min, demonstrating its potential as real-life energy conversion systems.

Synthesis of single-crystal-like nanoporous carbon membranes and their application in overall water splitting

Nanoporous graphitic carbon membranes with defined chemical composition and pore architecture are novel nanomaterials that are actively pursued. Compared with easy-to-make porous carbon powders that dominate the porous carbon research and applications in energy generation/conversion and environmental remediation, porous carbon membranes are synthetically more challenging though rather appealing from an application perspective due to their structural integrity, interconnectivity and purity. Here we report a simple bottom–up approach to fabricate large-size, freestanding and porous carbon membranes that feature an unusual single-crystal-like graphitic order and hierarchical pore architecture plus favourable nitrogen doping. When loaded with cobalt nanoparticles, such carbon membranes serve as high-performance carbon-based non-noble metal electrocatalyst for overall water splitting.

Carbon membranes for efficient water-ethanol separation.

We demonstrate, on the basis of molecular dynamics simulations, the possibility of an efficient water-ethanol separation using nanoporous carbon membranes, namely, carbon nanotube membranes, nanoporous graphene sheets, and multilayer graphene membranes. While these carbon membranes are in general permeable to both pure liquids, they exhibit a counter-intuitive "self-semi-permeability" to water in the presence of water-ethanol mixtures. This originates in a preferred ethanol adsorption in nanoconfinement that prevents water molecules from entering the carbon nanopores. An osmotic pressure is accordingly expressed across the carbon membranes for the water-ethanol mixture, which agrees with the classic van't Hoff type expression. This suggests a robust and versatile membrane-based separation, built on a pressure-driven reverse-osmosis process across these carbon-based membranes. In particular, the recent development of large-scale "graphene-oxide" like membranes then opens an avenue for a versatile and efficient ethanol dehydration using this separation process, with possible application for bio-ethanol fabrication.

Modeling of nitrogen separation from natural gas through nanoporous carbon membranes

This work presents a theoretical investigation of the use of nanoporous carbon membranes for the separation of nitrogen from natural gas. A mathematical model to predict the performance of the membrane is developed. The model is a combination of the well known dusty gas model, which describes the transfer of multi-components mixture in porous media, together with a surface diffusion model. The model is first validated using the literature results for the separation of hydrogen from hydrocarbons mixture. The model is then applied to the nitrogen-hydrocarbons system. The membrane performance is evaluated in terms of nitrogen recovery, methane loss, nitrogen purity, as well as hydrocarbons compositions in both permeate and retentate sides. The model calculation methods are applied for both co-current and counter-current flow configurations. A parametric study is also carried out to investigate the effects of membrane parameters such as feed and permeate pressures and porosity on the membrane performance. The developed model is general and can be applied to various nanoporous membrane flow patterns.

Decoration of porous ceramic substrate with pencil for enhanced gas separation performance of carbon membrane

Carbon membranes have been extensively applied in gas separation field, and the cost and performance of membranes strongly rely on the properties of the substrate material. In this study, effective nanoporous carbon membranes were prepared by pencil coating of the macroporous ceramics, followed by carbonization treatment of polyfurfuryl alcohol (PFA) coated on the pencil-modified ceramics substrates. The decoration of the macroporous ceramics substrates with pencil effectively repairs surface defects and decreases surface roughness, and greatly prevents PFA from penetrating into the ceramics substrates during pyrolysis. The as-prepared carbon membranes showed high gas permeability and permselectivity properties. This work provides an efficient method to fabricate nanoporous carbon membranes with enhanced gas separation performance.

Structure and gas permeation of nanoporous carbon membranes based on RF resin/F-127 with variable catalysts

Abstract

Pyrolysis of Cellulose under Ammonia Leads to Nitrogen-Doped Nanoporous Carbon Generated through Methane Formation

Here, we present a simple one-step fabrication methodology for nitrogen-doped (N-doped) nanoporous carbon membranes via annealing cellulose filter paper under NH3. We found that nitrogen doping (up to 10.3 at %) occurs during cellulose pyrolysis under NH3 at as low as 550 °C. At 700 °C or above, N-doped carbon further reacts with NH3, resulting in a large surface area (up to 1973.3 m(2)/g). We discovered that the doped nitrogen, in fact, plays an important role in the reaction, leading to carbon gasification. CH4 was experimentally detected by mass spectrometry as a product in the reaction between N-doped carbon and NH3. When compared to conventional activated carbon (1533.6 m(2)/g), the N-doped nanoporous carbon (1326.5 m(2)/g) exhibits more than double the unit area capacitance (90 vs 41 mF/m(2)).

Preparation and characterization of supported ordered nanoporous carbon membranes for gas separation

ABSTRACTSupported ordered nanoporous carbon membranes (ONCM) were prepared by coating a membrane‐forming solution of resorcinol‐formaldehyde (RF) resin on plate support through solvent evaporation and pyrolysis. The membrane solution was formed by the organic‐organic assembly of RF resin with Pluronic F127 in the presence of triethyl orthoacetate and catalyst hydrochloric acid. The thermal stability of precursor, the microstructure, functional groups, and morphology and porous structure of resultant support and ONCM were investigated by the techniques of thermogravimetry, X‐ray diffraction, Fourier transformed infrared spectroscopy, scanning electron microscopy/transmission electron microscopy and nitrogen adsorption‐desorption, respectively. Results have shown that the as‐obtained ONCM has well‐developed porous regularity with bi‐modal narrow pore size distribution. ONCM is tightly adhered to the adopted phenolic resin‐based carbon support. Gases permeating through the ONCM are dominated by molecular sieving mechanism. The ideal gas separation factor of the supported ONCM can be reached to 46.4, 4.7 and 3.3 for H2/N2, CO2/N2 and O2/N2, respectively. The supported ONCM obtained in this work exhibits most promising application for permanent gas separation. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 39925.

Direct prototyping of patterned nanoporous carbon: a route from materials to on-chip devices.

Prototyping of nanoporous carbon membranes with three-dimensional microscale patterns is significant for integration of such multifunctional materials into various miniaturized systems. Incorporating nano material synthesis into microelectronics technology, we present a novel approach to direct prototyping of carbon membranes with highly nanoporous structures inside. Membranes with significant thicknesses (1 ~ 40 μm) are rapidly prototyped at wafer level by combining nano templating method with readily available microfabrication techniques, which include photolithography, high-temperature annealing and etching. In particular, the high-surface-area membranes are specified as three-dimensional electrodes for micro supercapacitors and show high performance compared to reported ones. Improvements in scalability, compatibility and cost make the general strategy promising for batch fabrication of operational on-chip devices or full integration of three-dimensional nanoporous membranes with existing micro systems.

Novel Modification of a Macroporous Stainless Steel Tube by Electroless Ni plating for Use as a Substrate for Preparation of Nanoporous Carbon Membranes

Nanoporous carbon (NPC)/Ni–P composite membranes were prepared on electroless Ni-plating-modified porous stainless steel tubes (PSSTs) by carbonizing polyimide or cellulose acetate precursors at 700 °C in a nitrogen atmosphere. The performance of the membranes was evaluated by single-gas permeation and binary-gas mixture separation. The effects of the substrate with or without modification on gas permeation were studied, and the diffusion mechanism of the gases through the membranes was analyzed. The real separation factors of gas mixtures through the NPC/Ni–P composite membranes were much higher than those through the nanoporous carbon membranes (NPCMs) prepared on the unmodified substrate, especially those for H2/CH4 and H2/CO2. The weight loss rate of polymer precursors was investigated by TG/DTG. The specific surface areas of the membranes and the crystallization of the Ni–P alloy layer were characterized by means of the BET and DSC techniques, respectively, indicating that localized electroless Ni pl...

The performance of carbon membranes in the presence of condensable and non-condensable impurities

To fully assess the suitability of nanoporous carbon (NPC) membranes for industrial applications such as carbon capture, it is necessary to understand the impact of impurities commonly present in the feed streams upon the membrane performance. In this work, the effect on the performance of a NPC membrane upon exposure to condensable impurities typically found in natural gas (e.g. water, hexane and toluene) and non-condensable impurities typically found in synthesis gas (e.g. H 2S and CO) has been determined in laboratory experiments. Small reductions in the permeance (less than 30%) and minimal reductions in selectivity have been observed, with the greatest impact at 35 °C and less impact at 100 °C. The performance of a NPC membrane upon exposure to real synthesis gas produced from air-blown coal gasification, as part of the Mulgrave Capture Project, has also been determined. The combined higher concentrations of impurities in these pilot plant experiments resulted in a greater impact on performance at 100 °C with a reduction in CO 2 permeance of around 40% and in CO 2/N 2 selectivity of around 25%. However, these relatively limited reductions in membrane performance suggest that such carbon membranes still offer some promise for pre-combustion applications.