Bimodal Mesoporous Carbon Research Articles

Wettability, imbibition and interdiffusion of lithium-based water-in-salt electrolytes in nanoporous carbon in relation to energy storage: A neutron radiography study

Superconcentrated lithium salt electrolytes, or lithium-based Water-in-Salt (WiS) electrolytes emerge as alternative electrolytes in supercapacitors and advanced batteries, such as the Li–O2 ones, especially when combined with a mesoporous carbon with very high surface area. In this work, we analyze the wettability, imbibition, and diffusivity of very concentrated lithium salts in a bimodal mesoporous carbon with pores of 5 nm and 25 nm in diameter. For the first time a neutron radiography technique is used to determine the imbibition and interdiffusion of lithium salts in mesoporous carbon. We found that a 20 m LiTFSI aqueous solution wets the surface of graphite and mesoporous carbon better than water. As a consequence, this WiS electrolyte is embedded rather fast in the mesoporous carbon by the action of capillary forces, exhibiting an intrinsic permeability K = (1.16 ± 0.03).10−18 m2. Finally, by resorting to the different cross-section of the 6Li and 7Li isotopes for the neutron capture, we could analyze the diffusion of LiCl in D2O confined in the mesoporous carbon. The interdiffusion coefficient of the confined LiCl is 5.0 10−7 cm2 s−1, corresponding to a tortuosity coefficient τ = 1.32. This moderate confinement effect results from the strong ion association of the LiCl that precludes the electrostatic interactions of Li+ ions with the negative charge on the pore walls. In summary, the combined properties of the lithium-based WiS electrolytes and the mesoporous carbon allow us to glimpse their use in supercapacitors and Li–O2 batteries.

Enhanced adsorption of perfluorooctanesulfonic acid (PFOS) in fluorine doped mesoporous carbon: Experiment and simulation

Per- and polyfluoroalkyl substances (PFAS) are new types of emerging pollutants that have contaminated major water sources of developed and developing countries. Porous carbon-based materials are considered as universal adsorbents of all types of PFAS molecules. We have synthesized bimodal mesoporous carbon with fluorine and nitrogen functionalities for better removal for perfluorooctanesulfonic acid (PFOS) as the model PFAS molecule. All the mesoporous carbons with fluorine functionalities demonstrated the better adsorption of PFOS, and the adsorption amounts were better than that of commercial activated carbon. Kinetics measurements confirmed a remarkable improvement in saturation time of mesoporous carbon (1 h) compared to that commercial carbon (50 h). This mesoporous carbon also successfully removed PFAS from different complex matrices, including influent and effluent wastewater, and landfill leachate. Molecular simulation results revealed that presence of fluorine on the carbon surface increases the hydrophobicity of the carbon surface and Lennard-Jones (LJ) potential of the PFOS with the carbon leading to the enhanced adsorption of PFOS. Simulation study confirms that the presence of fluorine provides a good interaction of PFOS with the carbon surface. Molecular simulation also revealed that, despite nitrogen functionalities decrease hydrophobicity of the carbon surface, it may increase the LJ potential of PFOS with carbon surface leading to enhanced PFOS adsorption. However, as the improvement in LJ potential may be caused by much higher nitrogen content than what is present in the current system, it can be confirmed that the elevated PFOS adsorption is primarily contributed by the fluorine functionalities.

Efficient removal of dyes from aqueous solutions using short-length bimodal mesoporous carbon adsorbents

Ordered mesoporous carbons (OMCs) with controlled mesopore lengths and volumes were synthesized and investigated to remove the model dye methylene blue (MB) from aqueous solutions. The pore size, specific surface area, pore volume, and pore length of OMCs (CMK-3, sCMK-3, and sCMK-5) were analyzed and benchmarked against commercial activated carbon (AC). CMK-3 and sCMK-3 had narrow pore size distributions (PSDs) centered at ∼4.4 nm, whereas the PSD of sCMK-5 was bimodal, derived from the same pores as CMK-3 (∼4.4 nm) and the inner diameter of the carbon nanotubes (∼5.8 nm). The pore length decreased from 743 nm for CMK-3 to 173 nm for sCMK-3 and 169 nm for sCMK-5, facilitating the MB accessibility and efficient utilization of internal mesopores. The MB adsorption on the prepared adsorbents was well described by a pseudo-second-order kinetic model (R2 > 0.999), and the initial adsorption rate (h) on sCMK-5 was 34.07-fold faster than that on commercial AC. The Langmuir model adequately explained the equilibrium adsorption data, and the increase in the Langmuir maximal adsorption capacity (qm) of the OMCs was proportional to the specific surface area. The MB adsorption on sCMK-5 was endothermic and spontaneous, and proceeded primarily through physical adsorption as well as chemisorption reacting with oxygen atoms in hydroxyl groups. The prepared adsorbents were also suitable for polishing textile wastewater containing color-causing substances along with the background organic matter. These OMCs are promising for treating wastewater as efficient adsorbents for large molecular pollutants such as dyes.

Bimodal Mesoporous Carbon Spheres with Small and Ultra-Large Pores Fabricated Using Amphiphilic Brush Block Copolymer Micelle Templates

We report the self-assembly of amphiphilic polystyrene-block-poly(ethylene oxide) (PS-b-PEO) brush block copolymers (BBCPs) into spherical micelles in an ethanol/water mixture as an efficient templating approach to fabricate mesoporous carbon spheres using polydopamine as a carbon source. Mesopore sizes of up to 25 nm are well controlled and are dependent on the molecular weight (Mw) of the BBCP. Such large pores are difficult to obtain using traditional linear block copolymers templates. Furthermore, bimodal mesoporous carbon spheres with two populations of pore sizes (24.5 and 6.5 nm) are obtained using a BBCP coassembled with a small molecule surfactant (Pluronic F127). An oxygen reduction reaction is used to demonstrate that electrocatalytic performance can be tuned by controlling the carbon sphere morphologies. This work provides a novel and versatile method to fabricate carbon spheres with broadly tunable bimodal pore sizes for potential applications in catalysis, separations, and energy storage.

Iron-Catalyzed Selective Denitrification over N-Doped Mesoporous Carbon.

Electrocatalytic denitrification has been considered as one of the most promising technologies to selectively reduce excessive nitrogen oxyanions to benign dinitrogen in polluted water. The development of nonprecious metal catalysts with high performance for the denitrification is imperative but still a great challenge. Herein, we report an iron-based electrocatalyst for high-efficiency and selective denitrification. This nanocatalyst is prepared by template assembly of iron-based metal organic frameworks on surface-functionalized bimodal mesoporous carbon and subsequent pyrolysis under argon atmosphere. It contains well-dispersed FeNx sites and Fe nanoparticles (most of them are wrapped by N-doped graphitic carbon), with high surface area (1080 m2 g-1) and uniform mesopore and micropore (5.0 and 1.7 nm) for the construction of electrodes. Experimental results confirm that the catalyst can achieve an excellent nitrate removal capacity of 3410 mg N/g Fe, along with a reduction efficiency up to 87% and N2 selectivity of 81% in neutral electrolyte (100 mg/L NO3--N and 0.1 M Na2SO4) within 24 h. It is proposed that the active FeNx sites cooperated with sufficient Fe nanoparticles to be conducive to adsorption of O in NO3- on the catalyst for the improved performance. The material also presents long-term durability and good adaptability in the range of pH 5-9 and simulated neutral wastewater, mainly contributed by the protection of the mesostructure and graphitic N-doped carbon. These findings open the door to rational design of nonprecious metal iron-based functional electrocatalysts for water purification and environmental remediation.

Effect of bimodal mesoporous carbon as PtRu catalyst support for direct methanol fuel cells.

Mesoporous carbons (MCs) with different pore sizes were synthesized and evaluated as a catalyst support for fuel cells. The MCs were obtained from resorcinol–formaldehyde precursors, polymerized in the presence of polydiallyldimethylammonium chloride (cationic polyelectrolyte) as a structuring agent and commercial silica (Sipernat® or Aerosil®) as the hard template. The MC obtained with Aerosil® shows a broad pore size distribution with a maximum at 21 nm. On the other hand, the MCs with Sipernat® show a bimodal pore size distribution, with a narrow peak centered at 5 nm and a broad peak with a maximum ca. 30 nm. All MCs present a high specific surface area (800–1000 m2 g−1) and total pore volume ranging from 1.36 to 1.69 cm3 g−1. PtRu nanoparticles were deposited onto the MC support by an impregnation–reduction method with NaBH4 at 80 °C in basic media. The electrochemical characterization reveals improved electrocatalysis towards the methanol oxidation for the catalyst deposited over the carbon with the highest total pore volume. This catalyst also presented the highest CO2 conversion efficiency, ca. 80%, for the methanol oxidation as determined by differential electrochemical mass spectroscopy analysis. Moreover, the catalyst as a fuel cell anode showed the best performance, reaching a power density of 125 mW cm−2 at 90 °C with methanol as fuel and dry O2.

High capacity and rate capability of S/3D ordered bimodal mesoporous carbon cathode for lithium/sulfur batteries

Abstract

Atomic Cobalt on Defective Bimodal Mesoporous Carbon toward Efficient Oxygen Reduction for Zinc–Air Batteries

AbstractSingle‐atom catalysts (SACs) with maximum atom‐utilization efficiency and distinctive properties are emerging as a new frontier in the field of catalysis. Herein, a new strategy for synthesizing stable Co single atoms with content of about 1.52 wt% on defective bimodal mesoporous carbon materials (A‐Co@CMK‐3‐D) is reported. The dispersion and coordination structures of atomic Co species at carbon defect sites are confirmed by both aberration‐corrected high‐resolution transmission electron microscopy (AC‐HRTEM) and X‐ray absorption spectrometry, respectively. The obtained catalyst exhibits efficient electrochemical performance on oxygen reduction reaction (ORR) in an alkaline electrolyte with a half‐wave potential (0.835 V vs RHE), which is comparable to that of Pt/C (0.839 V vs RHE). Furthermore, the Zn–air batteries (ZABs) fabricated by this electrocatalyst display a superior discharging and charging performance with long‐term durability. This work provides a new approach on optimizing SAC‐based carbon materials from multiscale principles (simultaneous regulation of electronic structure and hierarchical morphology) to boost ORR reactivity.

Bimodal mesoporous hard carbons from stabilized resorcinol-formaldehyde resin and silica template with enhanced adsorption capacity

Hard carbon powders with hierarchical mesoporous structure from resorcinol-formaldehyde polymer were successfully prepared by use of double pore forming method. Poly-diallyldimethylammonium chloride (pDADMAC) and commercial silica (Sipernat® 50) were used as structuring agent and hard template, respectively. Through the proposed procedure carbon powder with bimodal mesoporous size distribution (around 4–5 nm and 20–40 nm) and different pore volume ratios can be obtained, by changing the ratio pDADMAC/silica used in the synthesis. Pore volumes between 0.70 and 2.10 cm3·g−1, and specific surface areas between 662 and 998 m2·g−1 were obtained.Raman spectroscopy and X-Ray diffraction analysis showed that all the carbons presented a non-ordered mesopore structure, and a hard carbon micro-structure with roughly 40% of single-layer microstructures, an average of 2.6 stacked graphene layers, and an in-plane graphitic crystallite size around 3.4 nm. We have evaluated the adsorption of methylene blue, as a model of a pollutant dye, on the mesoporous carbons with different pore size distribution, and we found that carbons with bimodal pore size distribution exhibit a remarkable and irreversible adsorption capacity. Microporosity can help to enhance the adsorption capacity, provided that micropores are connected to mesopores, allowing the adsorbate to get deep into the carbon structure. The adsorption kinetic is very fast for carbons with such pore architecture, and can be well described by a three-stage intraparticle diffusion model.

Enhanced electrocatalytic activity and durability of Pt nanoparticles supported on ordered bimodal mesoporous carbon nanowires

Ordered bimodal mesoporous carbon nanowires (OMCWs) is prepared from dual templates that were fabricated by filling silica nanospheres in the channels of porous anodic aluminum oxide (AAO) membranes. The prepared OMCWs material exhibits a large surface area (876.7 m2 g−1), ordered large mesoporous (30 nm) nanostructure and small mesopores on the large mesopore walls. Pt nanoparticles are deposited on OMCWs to form Pt/OMCWs electrocatalyst for methanol oxidation reaction (MOR). In Pt/OMCWs, Pt nanoparticles (∼1.8 nm) are uniformly located on the OMCWs. The Pt/OMCWs catalyst possesses larger electrochemically active surface area (ECSA) (93.3 m2 g−1), higher activity for MOR and better durability compared with the commercial Pt/C catalyst. The good electrochemical performance of Pt/OMCWs is ascribed to the unique bimodal mesoporous structure that could facilitate the rapid mass transfer and enhanced the dispersion of Pt nanoparticles and the one-dimensional structure that could enhance the electron transport.

Selective pore filling of mesoporous CMK-5 carbon studied by XRD: Comparison between theoretical simulations and experimental results

It is possible to infiltrate a guest species selectively in one pore system of bimodal mesoporous CMK-5 carbon by an optimized nanocasting procedure. The selective filling has a drastic impact on the low-angle X-ray diffraction pattern of this novel class of materials. The structures of CMK-5, CMK-5 composite materials (sulfur and SnO2 as guest species), and CMK-3 carbon were simulated to investigate the influence of the pore filling with different guest species on the diffraction pattern and compared with experimental results. Additionally, the impact of structural defects is taken into account. The nature of the guest species strongly influences the relative intensity of the diffraction peaks. It turns out that the diffraction patterns of sulfur-carbon composite materials are nearly identical as those of CMK-3 carbon, which is attributed to a similar electron density of carbon and sulfur. Thus, sulfur is an ideal guest species to investigate the selective pore filling in CMK-5 carbon.

Metal‐Organic‐Framework‐Derived Co Nanoparticles Deposited on N‐Doped Bimodal Mesoporous Carbon Nanorods as Efficient Bifunctional Catalysts for Rechargeable Zinc−Air Batteries

AbstractElectrically rechargeable zinc−air batteries (ZnABs) have received increasing attention as promising energy storage devices, owing to their high theoretical energy density and environmental friendliness. However, it remains a great challenge to develop highly efficient bifunctional catalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Herein, we design and prepare a highly active bifunctional catalyst for ZnABs by using a cobalt metal‐organic framework (Co‐MOF) as the precursor. The catalyst has a desirable nanostructure composed of cobalt nanoparticles deposited on N‐doped bimodal mesoporous carbon nanorods (Co@N‐CNR). This hybrid structure exhibits a higher catalytic activity (a maximum power density of 63 mW cm−2) and cycling stability compared to commercial Pt/C+Ir/C integrated in ZnABs. The high catalytic performance could be attributed to the unique nanostructure composed of Co@N‐CNR, which incorporates the advantageous features of cobalt nanoparticles, mesoporous materials, and N‐CNR towards OER and ORR. The reported advancement provides a new and efficient strategy for the development of rechargeable ZnABs.

Bimodal Mesoporous CMK-5 Carbon: Selective Pore Filling with Sulfur and SnO2 for Lithium Battery Electrodes

Ordered mesoporous CMK 5 carbon exhibits two distinct pore systems that can be modified individually. This work demonstrates how one of the pore system can be selectively filled with elemental sulfur, while the other pore system remains empty. The resulting sulfur-carbon composite material with high residual porosity can be used as the cathode material in lithium-sulfur battery cells. We present a systematic investigation of the loading of CMK 5 carbon with variable relative amounts of sulfur and compare the results to the preparation of SnO2 (as well as TiO2, Mn2O3/Mn3O4, NiO) nanoparticle-loaded CMK 5 carbon.

Synthesis of bimodal mesoporous carbon nanospheres for methyl orange adsorption

Mesoporous materials with bimodal mesopores show advantages in adsorption, energy storage, and catalysis because such unique structures are beneficial to the mass transfer. Here, we describe the synthesis of bimodal mesoporous carbon nanospheres (BMCSs) by using phenolic resin as carbon precursor, triblock copolymer Pluronic F127 as the soft template, and mesoporous silica spheres as hard templates. The BMCSs with uniform spherical morphology, high specific surface area (1489 m2 g− 1), large pore volume (0.92 cm3 g− 1), and bimodal mesoporous structure (3.8 and 6.8 nm) exhibit promising properties for adsorption of methyl orange (MO). The maximum adsorption capacity of the BMCSs is 5.5 × 102 ± 0.2 × 102 mg g− 1, which is higher than that of many adsorbents reported. The kinetics studies show a better fit of pseudo-second-order model. Meanwhile, fitting equilibrium data show that the Langmuir model is more suitable to describe the MO adsorption than Freundlich model.

Enhanced performance of sulfur-infiltrated bimodal mesoporous carbon foam by chemical solution deposition as cathode materials for lithium sulfur batteries

The porous carbon matrix is widely recognized to be a promising sulfur reservoir to improve the cycle life by suppressing the polysulfide dissolution in lithium sulfur batteries (LSB). Herein, we synthesized mesocellular carbon foam (MSUF-C) with bimodal mesopore (4 and 30 nm) and large pore volume (1.72 cm2/g) using MSUF silica as a template and employed it as both the sulfur reservoir and the conductive agent in the sulfur cathode. Sulfur was uniformly infiltrated into MSUF-C pores by a chemical solution deposition method (MSUF-C/S CSD) and the amount of sulfur loading was achieved as high as 73% thanks to the large pore volume with the CSD approach. MSUF-C/S CSD showed a high capacity (889 mAh/g after 100 cycles at 0.2 C), an improved rate capability (879 mAh/g at 1C and 420 mAh/g at 2C), and a good capacity retention with a fade rate of 0.16% per cycle over 100 cycles.

Synthesis of bimodal mesoporous carbon with embedded nickel nanoparticles through pyrolysis of nickel-organic framework as a counter-electrode catalyst for dye-sensitized solar cells

Bimodal mesoporous carbon with embedded Ni nanoparticles (BMCNi) was prepared by thermal pyrolysis of nickel-organic framework (NiOF) in nitrogen environment followed by acid treatment. The coordination complex of NiOF enabled the formation of small mesopores (3.6nm) during pyrolysis. The thermal decomposition and acid treatment generated large mesopores (23.6nm). The small mesopores contributed to high surface area and the large mesopores speeded up the transport of electrolyte species. Fluorine-doped tin oxide electrode with attached BMCNi catalyst possessed good electrocatalytic performance for I−/I3− couple compared with bimodal mesoporous carbon (BMC) only, owing to its high current peak and small voltage separation between anodic and cathodic peaks in cyclic voltammetry test. Ni nanoparticles embedded in BMC could provide electrical conductivity and extra active sites for facilitating the redox reaction. BMC with high surface area acted as not only a catalyst, but also a protective matrix to lessen the corrosion of Ni nanoparticles in I−/I3− electrolyte, leading to an improved electrochemical stability. Consequently, the dye-sensitized solar cell employing BMCNi counter electrode could reach a cell efficiency of 8.6%, which is higher than that using Pt (8.4%).

Enhancing the Performance of CoO as Cathode Catalyst for Li-O2 Batteries through Confinement into Bimodal Mesoporous Carbon

Rechargeable Li-O2 batteries show great potential owing to the super high energy density. However, the poor kinetics of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) limits their practical application. The exploration of noble metals-free cathode catalysts with high catalytic activity on both ORR and OER is still a big challenge. Herein, CoO has been confined into bimodal mesoporous carbon frameworks (CoO@BMC) via a wet-chemistry impregnation approach and the performance of CoO@BMC as cathode catalyst for Li-O2 batteries has been largely improved. For comparison, CoO@CMK-3 composite has also been prepared. In comparison with bulk CoO, BMC and CoO@CMK-3, CoO@BMC based cathode shows a higher initial capacity (∼4000mAhg−1), much higher cycling stability, higher rate capability and lower overpotential,which can be largely attributed to the synergetic effect of CoO and hierarchical BMC on both ORR and OER. In addition, the formation and decomposition of Li2O2 and side products in the process of ORR and OER have also been analyzed and the results indicate that CoO@BMC nanocomposite can efficiently promote the decomposition of Li2O2 and even some side products of carbonates.

Bimodal Mesoporous Carbon-Coated MgO Nanoparticles for CO2 Capture at Moderate Temperature Conditions

Bimodal mesoporous carbon supported MgO (MgOMC) materials were prepared to provide a candidate for trapping CO2 in flue gas at high temperature by an impregnation method. Textural properties of MgOMC were characterized by X-ray diffraction, N2 adsorption/desorption isotherm, scanning electron microscopy, transmission electron microscopy and an element mapping method, and their CO2 adsorption behaviors in both pure CO2 and 10 vol % CO2 simulated flue gas were evaluated by a thermal gravimetric method at ambient temperature. Effects of MgO content in composite and calcination temperature on CO2 adsorption capacity were studied. Results showed that MgOMC samples with high content of basic MgO sites and well-developed porous structure exhibit high CO2 uptakes at 75 °C, rapid adsorption kinetics, excellent CO2 selectivity in flue gas and good regenerability under mild temperature below 300 °C, indicating their potential application in the CO2 capture from flue gas.

Synthesis of bimodal mesoporous carbon spheres from biomass starch and CBZ release

Well-dispersed bimodal mesoporous carbon spheres (BMCSs) with abundant porosity were prepared through a convenient stirring method, in which silica particles were added to improve the porosity of the products. No toxic organic solvent was involved. Thus, the procedure was green and productive. The BMCSs exhibited single or bimodal mesoporous structure, tunable mesopore volume, and specific surface area, which depended on starch concentration. Carbamazepine (CBZ), due to its poor water-solubility and low release rate, was selected as a model drug and loaded onto the as-prepared BMCSs to investigate its release behavior. The experimental results showed that the dissolution rate was significantly increased after CBZ loading onto BMCSs than the pure CBZ, which could be explained by the noncrystalline state, improved dispersibility, and nanoscale size of CBZ in the pore channels of the BMCSs.

Selective surface modification in bimodal mesoporous CMK-5 carbon

Ordered, bimodal mesoporous carbon with distinct pore modes of different hydrophobicity is prepared by selective surface modification.