Porous Carbon Membranes Research Articles

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.

Aqueous tetracycline degradation by coal-based carbon electrocatalytic filtration membrane: Effect of nano antimony-doped tin dioxide coating

In this work, a novel electrocatalytic filtration membrane with high degradation efficiency and low cost was fabricated by coating nano antimony-doped tin dioxide (Sb-SnO2) on a porous coal-based carbon membrane (CM) through sol-gel method. The nano Sb-SnO2 is homogeneously distributed on the CM surface and is firmly attached to the CM via C-O-Sn chemical bond. Due to the positive effect of nano Sb-SnO2 coating, the Sb-SnO2/CM possesses excellent electrocatalytic activity and shows a much better tetracycline (TC) degradation performance than CM. The TC removal rate of Sb-SnO2/CM could be achieved 96.5% after 6h operation while that of CM was only 72.8%. Degradation pathway of TC was also explored using HPLC-MS. Furthermore, the effective TC degradation is attributed to the synergistic effects of direct and indirect electrochemical oxidation. During the indirect oxidation process, OH radicals rather than O2- play the dominant role.

Synthesis of Silica Nanoparticles for the Manufacture of Porous Carbon Membrane and Particle Size Analysis by Sedimentation Field‐Flow Fractionation

Silica nanoparticles were synthesized by emulsion polymerization by mixing ethanol, ammonium hydroxide, water, and tetraethyl orthosilicate. An apparatus was designed and assembled for a large‐scale synthesis of silica nanospheres, which was aimed for uniform mixing of the reactants. Then sedimentation field‐flow fractionation (SdFFF) was used to determin the size distribution of the silica nanoparticles. SdFFF provided mass‐based separation where the retention time increased with the particle size, thus the size distribution of silica nanoparticles obtained from SdFFF appeared more accurate than that from dynamic light scattering, particularly for those having broad and multimodal size distributions. A disk‐shaped porous carbon membrane (PCM) was manufactured for application as an adsorbent by pressurizing the silica particles, followed by calcination. Results showed that PCM manufactured in this study has relatively high surface area and temperature stability. The PCM surface was modified by attaching a carboxyl group (PCM‐COOH) and then by incorporating silver (PCM‐COOH‐Ag). The amount of COOH group on PCM was measured electrochemically by cyclic voltammetry, and the surface area, pore size, pore volume of PCM‐COOH‐Ag by Brunauer–Emmet–Teller measurement. The surface area was 40.65 and reduced to 13.02 after loading a COOH group then increased up to 30.37 after incorporating Ag.

Activated hierarchical porous carbon as electrode membrane accommodated with triblock copolymer for supercapacitors

Homopolymer PAN and triblock copolymer PAN-b-PMMA-b-PAN synthesized by RAFT polymerization were used to fabricate activated hierarchical porous carbon membranes by combining phase inversion, carbonization, and HNO3 activation method; during the preparation process, a lot of micro- and meso-pores generated because of phase separation of PAN and microphase separation of PAN-b-PMMA-b-PAN. The hierarchical porous structure shortened ions transport paths and facilitated the rapid migration of electrolyte ions. When the polymer membrane was prepared by the casting solution with 5wt% of PAN-b-PMMA-b-PAN and the electrochemical performance was tested at the current densities from 0.5 to 5Ag−1, a high-end specific capacitance of 297.0Fg−1 and a capacitance retention of 75% were obtained in three-electrode configuration; this specific capacitance remained above 90% of initial value after 2000 cycles at 2Ag−1 in 6M KOH aqueous solution. Moreover, symmetric supercapacitors assembled with the prepared materials achieved high energy density (15.8WhKg−1) and power density (4000WKg−1) in 1M Na2SO4 solution. The unique features and structures endowed the electrode membrane with good capacitive performance in both three-electrode and two-electrode configuration, which can be used as electrode membranes for high-performance energy storage devices and other applications.

Hierarchically porous carbon membranes derived from PAN and their selective adsorption of organic dyes

Porous carbon membranes were favorably fabricated through the pyrolysis of polyacrylonitrile (PAN) precursors, which were prepared with a template-free technique-thermally induced phase separation. These carbon membranes possess hierarchical pores, including cellular macropores across the whole membranes and much small pores in the matrix as well as on the pore walls. Nitrogen adsorption indicates micropores (1.47 and 1.84 nm) and mesopores (2.21 nm) exist inside the carbon membranes, resulting in their specific surface area as large as 1062 m2/g. The carbon membranes were used to adsorb organic dyes (methyl orange, Congo red, and rhodamine B) from aqueous solutions based on their advantages of hierarchical pore structures and large specific surface area. It is particularly noteworthy that the membranes present a selective adsorption towards methyl orange, whose molecular size (1.2 nm) is smaller than those of Congo red (2.3 nm) and rhodamine B (1.8 nm). This attractive result can be attributed to the steric structure matching between the molecular size and the pore size, rather than electrostatic attraction. Furthermore, the used carbon membranes can be easily regenerated by hydrochloric acid, and their recovery adsorption ratio maintains above 90% even in the third cycle. This work may provide a new route for carbon-based adsorbents with hierarchical pores via a template-free approach, which could be promisingly applied to selectively remove dye contaminants in aqueous effluents.

A review of the development of porous substrate-supported carbon membranes

Carbon membranes have attracted extensive attention because of their outstanding performance and excellent stability in the separation of gases, particularly of those with molecular sizes close to that of the membrane pores. However, they suffer from problems such as difficulty in fabrication, low permeability and poor physical strength, which greatly limit their industrial applications. These problems may be solved by supporting the thin carbon membrane on a porous substrate, forming a composite carbon membrane. The properties of the substrate play a key role, especially in the surface properties. A low surface roughness, high porosity, small pore size and fewer defects of the supporting substrate significantly favor membrane fabrication and performance. It is important to develop an effective and low cost surface modification of porous substrates to meet the requirements of membrane fabrication to optimize the selective permeability and economics of the composite carbon membranes. Research progress on the substrate materials, such as material selection, pore size distribution and surface modification, as well as membrane fabrication including precursor selection, coating, carbonization and post-treatment are summarized. [New Carbon Materials 2014, 29(6): 409–418]

A hierarchical porous carbon membrane from polyacrylonitrile/polyvinylpyrrolidone blending membranes: Preparation, characterization and electrochemical capacitive performance

Novel hierarchical porous carbon membranes were fabricated through a simple carbonization procedure of well-defined blending polymer membrane precursors containing the source of carbon polyacrylonitrile (PAN) and an additive of polyvinylpyrrolidone (PVP), which was prepared using phase inversion method. The as-fabricated materials were further used as the active electrode materials for supercapacitors. The effects of PVP concentration in the casting solution on structure feature and electrochemical capacitive performance of the as-prepared carbon membranes were also studied in detail. As the electrode material for supercapacitor, a high specific capacitance of 278.0 F/g could be attained at a current of 5 mA/cm2 and about 92.90% capacity retention could be maintained after 2000 charge/discharge cycles in 2 mol/L KOH solution with a PVP concentration of 0.3 wt% in the casting solution. The facile hierarchical pore structure preparation method and the good electrochemical capacitive performance make the prepared carbon membrane particularly promising for use in supercapacitor.

Hierarchically porous carbon membranes containing designed nanochannel architectures obtained by pyrolysis of ion-track etched polyimide

Well-defined, porous carbon monoliths are highly promising materials for electrochemical applications, separation, purification and catalysis. In this work, we present an approach allowing to transfer the remarkable degree of synthetic control given by the ion-track etching technology to the fabrication of carbon membranes with porosity structured on multiple length scales. The carbonization and pore formation processes were examined with Raman, Brunauer–Emmett–Teller (BET), scanning electron microscopy (SEM) and X-ray diffraction (XRD) measurements, while model experiments demonstrated the viability of the carbon membranes as catalyst support and pollutant adsorbent. Using ion-track etching, specifically designed, continuous channel-shaped pores were introduced into polyimide foils with precise control over channel diameter, orientation, density and interconnection. At a pyrolysis temperature of 950 °C, the artificially created channels shrunk in size, but their shape was preserved, while the polymer was transformed to microporous, amorphous carbon. Channel diameters ranging from ∼10 to several 100 nm could be achieved. The channels also gave access to previously closed micropore volume. Substantial surface increase was realized, as it was shown by introducing a network consisting of 1.4 × 1010 channels per cm2 of 30 nm diameter, which more than tripled the mass-normalized surface of the pyrolytic carbon from 205 m2 g−1 to 732 m2 g−1. At a pyrolysis temperature of 3000 °C, membranes consisting of highly ordered graphite were obtained. In this case, the channel shape was severely altered, resulting in a pronounced conical geometry in which the channel diameter quickly decreased with increasing distance to the membrane surface.

Suspended integration of pyrolytic carbon membrane on C-MEMS

Pyrolytic carbon materials contain high internal surface area, desirable pore structure, and controlled surface functionalities, making them effective for gas purification, separation, storage, and chemical reactions. This research describes a two-step (i.e., photolithography and pyrolysis) procedure to integrate suspended porous carbon membranes on C-MEMS from SU-8 photolithography precursor. The suspended SU-8 film was first generated simultaneously with micro-post array during lithography through controlling exposure parameters. A followed pyrolyzing process converted the structure into carbon microelectrode array with the pyrolytic membrane on top of it. It was demonstrated that stress generated during pyrolysis could be applied to control the porosity of membrane, and such high-porosity membrane can find various applications, especially in the field of filtration, selective gas permeation and carbon microreactors. The electrochemical property of this integrated structure has been explored through cyclic voltammetric measurements. It shows that the specific capacitance increase of almost four times after the pyrolytic carbon membrane integration, which indicates its potential use in energy-related fields.

Easy fabrication and high electrochemical capacitive performance of hierarchical porous carbon by a method combining liquid-liquid phase separation and pyrolysis process

A hierarchical porous carbon membrane was designed and prepared through a method combining liquid-liquid phase separation and then pyrolysis process using polyacrylonitrile (PAN) as precursor. The results of scan electron microscopy, transmission electron microscope and Brunauer-Emmett-Teller characterization reveal that the 3D nanoscaled architecture with hierarchical porous structure was achieved, which not only provide a continuous electron pathway to ensure good electrical contact, but also facilitate ion transport by shortening diffusion pathways. The effect of PAN concentration in casting solution on structure feature of carbon membrane was also studied, indicating that the membrane thickness with different porous structure can be mediated by PAN concentration. As the electrode material for supercapacitor, a high specific capacitance of 277.0Fg−1 was attained at a current density of 5mAcm−2 and long cycle life of 90.0% capacity retention was obtained after 2000 charge-discharge cycles in 2molL−1 KOH solution.

Removal of Microalgae in Ballast Water by Coal-based Porous Carbon Membrane

Introduction of invasive species via ballast water has been identified as one of the greatest threats to oceans.The coal-based porous carbon membrane with low cost for removal of microalgae in ballast water was prepared by carbonization of tubular carbonaceous precursor obtained by extrusion method.Scanning electron microscopy and bubble-pressure method were employed to investigate the morphology and pore structure characteristics of carbon membrane.Effects of microalgae size,transmembrane pressure and crossflow velocity on the steady-state flux were also studied.The results indicate that the as-prepared carbon membrane has smooth surface,rich and uniform porous structure,which are beneficial for removing microalgae in ballast water.A decrease in steady-state flux is observed as the microalgae size increases.High transmembrane pressure is more prone to block the membrane pore and results in the decrease of the steady-state flux.High crossflow velocity is favorable to increase the steady-state flux owing to the inhibition of fouling layer development through the high shear stress on membrane surface.After being treated by coal-based carbon membrane,no microalgae are detected.It indicates that coal-based carbon membrane is of great potential to ballast water treatment.

An Efficient Three‐Dimensional Oxygen Evolution Electrode

Oxygen evolution: A 3D nickel foam/porous carbon/anodized nickel electrode was designed for the oxygen evolution reaction (see picture). The conductive porous carbon membrane, which is derived from a zeolite imidazolate framework, plays a key role as an interlayer to both protect the inner instable Ni foam and support the outermost oxygen-evolving Ni catalyst layer.

Future Prospects of Porous Diamond-Like Carbon Membranes

It is not easy to solve the ongoing issues of worldwide environmental pollution. Polymer-based membranes are widely used for gas separation, filtration, desalination of seawater, wastewater treatment, etc. Chemical, petrochemical, energy and environment-related industries, however, strongly require highly durable membranes applicable under extreme conditions, since the present polymeric membranes gradually or sometimes rapidly deteriorate with time due to undesired swelling, clogging, and chemical reactions. In this review, new porous diamond-like carbon (DLC) membranes are discussed. DLC has been seemed to be extremely dense and it is used mainly for gas barrier applications. In contrast, newly developed DLC membranes have many sub-nanometer pores and extremely high permeability to water and organic solvents.

Preparation of silica nanospheres and porous polymer membranes with controlled morphologies via nanophase separation

We successfully synthesized two different structures, silica nanospheres and porous polymer membranes, via nanophase separation, based on a sol–gel process. Silica sol, which was in situ polymerized from tetraorthosilicate, was used as a precursor. Subsequently, it was mixed with a polymer that was used as a matrix component. It was observed that nanophase separation occurred after the mixing of polymer with silica sol and subsequent evaporation of solvents, resulting in organizing various structures, from random network silica structures to silica spheres. In particular, silica nanospheres were produced by manipulating the mixing ratio of polymer to silica sol. The size of silica beads was gradually changed from micro- to nanoscale, depending on the polymer content. At the same time, porous polymer membranes were generated by removing the silica component with hydrofluoric acid. Furthermore, porous carbon membranes were produced using carbon source polymer through the carbonization process.

Electric Double‐Layer Capacitance of Inverse Opal Carbon Prepared Through Carbonization of Poly(Furfuryl Alcohol) in Contact with Polymer Gel Electrolyte Containing Ionic Liquid

Three‐dimensionally periodic porous carbon membranes are prepared through the carbonization of poly(furfuryl alcohol) in the void spaces of opal materials consisting of monodispersed silica particles. Inverse opal carbon (IOC) membranes are obtained by the removal of silica templates. The obtained IOCs have three‐dimensionally ordered macroporous structures and large specific surface areas due to the mesopores that are formed during the carbonization of the polymer precursor. IOC with three‐dimensionally ordered 50‐nm pores exhibits a large gravimetric capacitance of 120 F g−1, as determined by using an ionic liquid electrolyte, 1‐ethyl‐3‐methylimidazolium bis(trifluoromethane sulfonyl)amide ([C2mim][NTf2]); this capacitance is higher than that of conventional activated carbon. Furthermore, the combination of IOC and an ion gel electrolyte, consisting of network poly(methyl methacrylate) and [C2mim][NTf2], is demonstrated to be effective for achieving a solid‐state, nonvolatile, and high‐capacity electric double‐layer capacitor. Moreover, because of the high ionic conductivity of the ion gel and the continuous ion‐conduction path through the IOC membrane, the IOCs exhibit a large specific capacitance of 100 F g−1 and a good rate capability, even at room temperature. Copyright © 2011 John Wiley & Sons, Ltd.

The Effect of Specific Adsorption of Cations and Their Size on the Charge-Compensation Mechanism in Carbon Micropores: The Role of Anion Desorption

Combined application of cyclic voltammetry (CV) and electrochemical quartz crystal microbalance (EQCM) technique reveals a complicated interplay between the adsorption of ammonium and lower molecular weight tetraalkyl ammonium cations and desorption of Cl(-) anions inside carbon micropores at low surface charge densities, which results in failure of their permselectivity. Higher negative surface charge densities induce complete exclusion (desorption) of the Cl(-) co-ions, which imparts purely permselective behavior on the carbon micropores. The second fundamental effect discovered herein relates to the dominant role of anion desorption (as compared to cation adsorption), that is, overwhelming failure of permselectivity extends to high negative charge densities of the electrode in the presence of bulky tetraalkyl ammonium cations, which tend to be confined in the micropores of the carbon. The results obtained are important for advancement of high power density carbon-based supercapacitors, nanofiltration technologies with porous carbon membranes, and studies of ionic transport across biological membranes.

Ammonia-activated mesoporous carbon membranes for gas separations

Porous carbon membranes, which generally show improved chemical and thermal stability compared to polymer membranes, have been used in gas separations for many years. In this work, we show that the post-synthesis ammonia treatment of porous carbon at elevated temperature can improve the permeance and selectivity of these membranes for the separation of carbon dioxide and hydrocarbons from permanent gases. Hierarchically structured porous carbon membranes were exposed to ammonia gas at temperatures ranging from 850°C to 950°C for up to 10min and the N2, CO2, and C3H6 permeances were measured for these different membranes. Higher treatment temperatures and longer exposure times resulted in higher gas permeance values. In addition, CO2/N2 and C3H6/N2 selectivities increased by a factor of 2 as the treatment temperature and time increased up to a temperature and time of 900°C, 10min. Higher temperatures showed increased permeance but decreased selectivity indicating excess pore activation. Nitrogen adsorption measurements show that the ammonia treatment increased the porosity of the membrane while elemental analysis revealed the presence of nitrogen-containing surface functionalities in the treated carbon membranes. Thus, ammonia treatment at high temperature provides a controlled method to introduce both added microporosity and surface functionality to enhance gas separations performance of porous carbon membranes.

Preparation of porous Carbon Membranes from Phenolic resin

Preparation of porous Carbon Membranes from Phenolic resin

フェノール樹脂粉末及び籾殻粉末からの加圧炭化法による分子ふるい性炭素板膜（ＰＣＭＰ）の調製

A porous carbon membrane plate (PCMP) was prepared from some kinds of phenol resins and rice husks by carbonization in a N2 stream and activation in a CO2 stream under high pressure. Effect of the carbonization/activation time and temperature, heating rate, ratio of the phenol resins and particle diameter of the raw material (rice husks) on density and strength of the PCMP was examined.The PCMPs without crack were prepared when pressurization was ceased at 450°C from both the phenol resins and rice husks. These PCMP were 17 mm in diameter and 3mm in thickness. They had smooth surface and micro pore structure. The pore structure of PCMP was affected by the mixture ratio of the phenol resins. The PCMP with higher density was prepared from the rice husk including more ash (silica).

Nonequilibrium molecular dynamics simulation of gas-mixtures transport in carbon-nanopore membranes.

The numerical simulation of nonequilibrium cotransport of H2 and alkane gas mixtures with very different molecular sizes through a porous carbon membrane structure was implemented. Simulated permeabilities and selectivities in binary diffusive systems (and in one ternary system), at pressure about tens of atmospheres and at operating condition of room temperature or higher, can be predicted from single-gas permeabilities. This suggests that the effect is geometrical and an approximate model of the transport is proposed. It can be used for an estimation of the separation factor of a membrane. Simulations are compared with experimental results of two- and three-component codiffusion and counterdiffusion in a carbon membrane. It is shown that diffusion in a porous molecular network and in a carbon nanotube are completely different. The uniqueness of this work lies in the comparison of simulated, approximate, and experimental results, which enables us to identify the important parameters.