3D interconnected macroporous carbon monoliths prepared by ultrasonic irradiation

A new method in preparation of 3D interconnected macroporous carbon monolith has been introduced. Ultrasonic irradiation (ultrasonic intensity 78 W/cm²) and low catalyst concentration (C/W = 10 mol/m³) of RF solution are used as an interesting and unique preparation method for 3D interconnected macroporous sonogel (gel irradiated by ultrasound at gelation stage) and/or 3D interconnected macroporous carbon monolith without using templates.     

Hierarchical porous carbons with controlled micropores and mesopores for supercapacitor electrode materials

Various porous carbons were prepared by CO₂ activation of ordered mesoporous carbons and used as electrode materials for supercapacitor. The structures were characterized by using X-ray diffraction, transmission electron microscopy and nitrogen sorption at 77 K. The effects of CO₂ treatment on their pore structures were discussed. Compared to the pristine mesoporous carbons, the samples subjected to CO₂ treatment exhibited remarkable improvement in textural properties. The electrochemical measurement in 6 M KOH electrolyte showed that CO₂ activation leads to better capacitive performances. The carbon CS15A6, which was obtained after CO₂ treatment for 6 h at 950 °C using CMK-3 as the precursor, showed the best electrochemical behavior with a specific gravimetric capacitance of 223 F/g and volumetric capacitance of 54 F/cm³ at a scan rate of 2 mV/s and 73% retained ratio at 50 mV/s. The good capacitive behavior of CS15A6 may be attributed to the hierarchical pore structure (abundant micropores and interconnected mesopores with the size of 3-4 nm), high surface area (2749 m²/g), large pore volume (2.09 cm³/g), as well as well-balanced microporosity and mesoporosity.     

HEMP-derived activated carbon fibers by chemical activation with phosphoric acid

Activated carbon fibers were prepared by chemical activation of hemp fibers with phosphoric acid at different carbonization temperatures and impregnation ratios. Surface properties of the activated carbons fibers were significantly influenced by the activation temperature and the impregnation ratio. An increase of either of these parameters produced a high development of the porous structure of the fibers. Activated carbon fibers with apparent surface area of 1350 m²/g and mesopore volume of 1.25 cm³/g were obtained at 550 °C with an impregnation ratio of 3. The activated carbon fibers presented a high oxidation resistance, due to the presence of phosphorus compounds on the carbon surface. The oxidation resistance results suggest that C-O-PO₃ and mainly C-PO₃ and C-P groups act as a physical barrier, blocking the active carbon sites for the oxidation reaction.     

Synthesis of monolithic 3D ordered macroporous carbon/nano-silicon composites by diiodosilane decomposition

Monolithic carbon/nano-silicon composites with a three-dimensionally ordered macroporous (3DOM) structure were synthesized via a nanocasting route using a macro- and mesoporous silica monolith as a hard template for carbon with similar hierarchical porosity, followed by chemical vapor deposition to infiltrate mesopores with silicon nanoparticles. Diiodosilane was used as the silicon precursor to produce nano-silicon upon thermal decomposition. X-ray photoelectron spectroscopy revealed the presence of both elemental silicon and oxidized silicon in the porous carbon. Silicon was dispersed uniformly inside 3DOM carbon without forming large agglomerates. The as-synthesized material was X-ray amorphous. A lithiation experiment showed an initial charge capacity of 920 mAh g⁻¹ and a reversible Li⁺ capacity of 332 mAh g⁻¹ for the carbon/nano-silicon composite. The lower-than-expected capacity is attributed to partial oxidation of nanosized silicon in the composite structure. A mechanism for decomposition of diiodosilane in this system is proposed.     

The co-micelle/emulsion templating route to tailor nano-engineered hierarchically porous macrospheres

Here we present a new class of nano-engineered hierarchically porous materials in which the entire framework is mesoporous. This material is engineered into macrospheres of controllable size with a highly interconnected macropore network to facilitate molecular diffusion access. To achieve this, a new co-micelle/emulsion templating (co-MET) technique was developed. In this technique a block copolymer plays the dual roles of emulsion stabilization and micelle formation within the aqueous phase of that emulsion to produce the hierarchical structures. The emulsion templating provides the macroporous structure while the mesoporous structure is formed by hydrolyzation of silica around block copolymer micelles. Increasing the copolymer concentration improves the mesoporosity up to a certain concentration where the emulsion phase behavior changes and the macroporosity is affected. Unlike other hierarchically porous materials, the walls of the co-MET macrospheres are entirely mesoporous, which provides high surface areas (>500 m² g⁻¹) and pore volumes (>1 cm³ g⁻¹) and narrow mesopore size distributions (∼10 nm). This interconnected hierarchical meso/macroporous structure combined with the controlled particle size makes this new class of materials promising for applications requiring high diffusion and throughput rates, alleviating the problems of using typical fine particle mesoporous materials.     

Facile synthesis of bimodal porous silica and multimodal porous carbon as an anode catalyst support in proton exchange membrane fuel cell

A simple and easy sol-gel approach has been developed to directly synthesize in situ three-dimensionally interconnected uniform ordered bimodal porous silica (BPS) incorporating both the macroporosity and mesoporosity in the lattice without extra synthesis process performed in previous work. Multimodal porous carbon (MPC) was fabricated through the inverse replication of the BPS. The unique structural characteristics such as well-developed 3-D interconnected ordered macropore framework with open mesopores embedded in the macropore walls, large surface area (1120 m² g⁻¹) and mesopore volume (1.95 cm³ g⁻¹) make MPC very attractive as an anode catalyst support in polymer exchange membrane fuel cell. The MPC-supported Pt-Ru alloy catalyst has demonstrated much higher power density toward hydrogen oxidation than the commercial carbon black Vulcan XC-72-supported ones.     

Preparation of activated carbon derived from Jatropha curcas fruit shell by simple thermo-chemical activation and characterization of their physico-chemical properties

High surface area activated carbons were prepared by simple thermo-chemical activation of Jatropha curcas fruit shell with NaOH as a chemical activating agent. The effects of the preparation variables, which were impregnation ratio (NaOH:char), activation temperature and activation time, on the adsorption capacity of iodine and methylene blue solution were investigated. The activated carbon which had the highest iodine and methylene blue numbers was obtained by these conditions as follows: 4:1 (w/w) NaOH to char ratio, 800 °C activation temperature and 120 min activation time. Characterization of the activated carbon obtained was performed by using scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and nitrogen adsorption isotherm as BET. The results present that the activated carbon possesses a large apparent surface area (S_BET = 1873 m²/g) and high total pore volume (1.312 cm³/g) with average pore size diameter of 28.0 Å.     

Preparation of granular activated carbon from oil palm shell by microwave-induced chemical activation: Optimisation using surface response methodology

In this study, waste palm shell was used to produce activated carbon (AC) using microwave radiation and zinc chloride as a chemical agent. The operating parameters of the preparation process were optimised by a combination of response surface methodology (RSM) and central composite design (CCD). The influence of the four major parameters, namely, microwave power, activation time, chemical impregnation ratio and particle size, on methylene blue (MB) adsorption capacity and AC yield were investigated. Based on the analysis of variance, microwave power and microwave radiation time were identified as the most influential factors for AC yield and MB adsorption capacity, respectively. The optimum preparation conditions are a microwave power of 1200 W, an activation time of 15 min, a ZnCl₂ impregnation ratio of 1.65 (g Zn/g precursor) and a particle size of 2 mm. The prepared AC under the optimised condition had a BET surface area (S_BET) of 1253.5 m²/g with a total pore volume (V_tot) of 0.83 cm³/g, which 56% of it was contributed to the micropore volume (V_mic).     

Porous carbonaceous materials from hydrothermal carbonization and KOH activation of corn stover for highly efficient CO2 capture

Sustainable biomass-derived carbon materials were produced by hydrothermal carbonization of corn stover that was followed by chemical activation with KOH. The prepared carbon materials were used for CO₂ adsorption and had a CO₂ uptake of 7.14?mmol/g at a pressure of 1?bar and at 0°C that was much higher than CO₂ uptake by activated carbon that was prepared from direct activation of corn stover (2.78?mmol/g). The porous corn stover-derived carbonaceous material had high surface area (2442?m²/g) and large pore volume (1.55?cm³/g). Product yields obtained by the activation of hydrothermally carbonized corn stover were significantly higher than those obtained by the direct activation of corn stover (36–75?vs. 8%). The prepared corn stover-derived porous carbon had a high CO₂/N₂ selectivity of 15.5 and exhibited constant CO₂ uptake for five successive reuse cycles. The hydrothermal carbonization step plays an important role for producing porous carbons from biomass that have high and specific adsorption properties.     

Cellulose-based aerogels

New organic aerogels were prepared using cellulose derivatives as precursors. The elaboration process and the structural characterisations of these porous cellulose-based materials are described in the present study. Series of monolithic gels were synthesised in acetone by crosslinking cellulose acetate with a non-toxic isocyanate via sol-gel route, using tin-based catalyst. Gelation times (ranging from 15 to 150 min) were significantly dependent on reagents' nature and concentration. Low-density materials (from 0.25 cm³/g to 0.85 cm³/g) were obtained after supercritical carbon dioxide drying. These newly developed nanostructured materials were characterised using mercury porosimetry, nitrogen adsorption and scanning electron microscopy. All the prepared materials have shown both a nanostructured solid network (specific surface areas between 140 and 250 m²/g) and a nanoporous network (characteristic pore sizes between 13 and 25 nm) together with specific porous volumes as large as 3.30 cm³/g.Influence of sol-gel synthesis parameters as crosslinker content and cellulose degree of polymerisation or concentration was investigated. First empirical correlations between synthesis parameters and final material properties were obtained. A special attention was dedicated to the different shrinkages occurring during the elaboration process. In particular, the important shrinkage occurring during the supercritical drying step was studied in terms of affinity between the crosslinked polymeric network and carbon dioxide. In parallel, first thermo-mechanical properties were presented in terms of bulk modulus and effective thermal conductivity.     

An activation-free method for preparing microporous carbon by the pyrolysis of poly(vinylidene fluoride)

A simple method for the preparation of microporous carbon was presented by pyrolyzing poly(vinylidene fluoride) (PVDF) at high temperature under N₂ atmosphere without activation or any other additional processes. The yield of PVDF-derived carbon is 35.0%. Its specific surface area reaches 1012 m² g with a pore volume of 0.41 cm³ g⁻¹. The carbon is microporous with unimodal pore size distribution at 0.55 nm.     

Preparation of a highly microporous carbon from a carpet material and its application as CO2 sorbent

In order to increase the use of carpet wastes (pre- and/or post-consumer wastes), this work studies for the first time the preparation and characterisation of a microporous material from a commercial carpet (pile fiber content: 80% wool/20% nylon; primary and secondary backings: woven polypropylene; binder: polyethylene) and its application for CO₂ capture. The porous material was prepared from an entire carpet material using a standard chemical activation with KOH and then, characterised in terms of their porous structure and surface functional groups. Adsorption of CO₂ was studied using a thermogravimetric analyser at several temperatures (25-100 °C) and under different CO₂ partial pressures (i.e. pure CO₂ flow and a ternary mixture of 15% CO₂, 5% O₂ and 80% N₂). In order to examine the adsorbent regenerability, multiple CO₂ adsorption/desorption cycles were also carried out. The surface area and micropore volume of the porous adsorbent were found to be 1910.17 m² g^− 1 and 0.85 cm³ g^− 1, respectively. The CO₂ adsorption profiles illustrate that the maximum CO₂ capture on the sample was reached in less than 10 min. CO₂ adsorption capacities up to 8.41 wt.% and 3.37 wt.% were achieved at 25 and 70 °C, respectively. Thermal swing regeneration studies showed that the prepared adsorbent has good cyclic regeneration capacities.     

Impregnation of vitamin E acetate on silica mesoporous phases using supercritical carbon dioxide

Impregnation of a drug model (α-tocopheryl acetate) into mesoporous host matrices has been carried out using supercritical carbon dioxide (SC CO₂) as impregnation solvent at 15 MPa and 313 K with a flow rate of 500 g h⁻¹. The operating conditions were defined following the solute concentration in the fluid phase as a function of pressure and carbon dioxide flow rate. Solubility measurements of α-tocopheryl acetate were first performed at 313 K for pressures ranging 10-20 MPa. High values of solubility in SC CO₂ were measured: 6 wt% at 10 MPa and 14 wt% at 20 MPa. Measurements of the concentration of the solute in SC CO₂ in the experimental conditions of impregnation in dynamic mode showed than it was ten times lower than the solubility. The variations of this concentration have been studied at 313 K, for a pressure varying from 8 to 15 MPa, and for a carbon dioxide flow rate varying from 120 to 600 g h⁻¹. Two different host matrices were used: a commercial chromatographic silica support and a MCM-41-type mesoporous organized silica synthetized at the laboratory. This latter showed the best drug loading of 1.14 g per gram of adsorbent. The drug loadings obtained in supercritical media were similar to the ones obtained in liquid media using hexane as impregnation solvent. Nevertheless, the maximum loading was obtained after 1 h of impregnation in SC media while 4 h were needed in liquid media.     

Modification of Al current collector surface by sol-gel deposit for carbon-carbon supercapacitor applications

Four square centimeter carbon-carbon supercapacitor cells were assembled with Al current collectors in organic electrolyte. Different treatments of the Al current collectors were made in order to increase the supercapacitor performances. A sol-gel deposit of a conducting carbonaceous material led to the best results. On the basis of electrochemical impedance spectroscopy measurements, the differences observed with the previous treatments were assumed to be linked to the modification of the Al/active material interface. The cell using sol-gel treated current collector presented an activated carbon specific capacitance of 100 F/g and a series resistance of 0.8 Ω cm² in acetonitrile 1 M NEt₄BF₄, that are characteristics compatible with high power applications.     

Hierarchical porous nitrogen-doped carbon materials derived from one-step carbonization of polyimide for efficient CO<Subscript>2</Subscript> adsorption and separation

Hierarchical porous nitrogen-doped carbon (HPNC) materials are synthesized through one-step carbonization of polyimide using triblock copolymer P123 as mesoporous template. The microstructure, chemical composition and CO₂ adsorption behaviors are investigated in detail. The results show that HPNC materials have hierarchical micro-/mesopore structures, high specific surface area of 579 m²/g, large pore volume of 0.34 cm³/g, and nitrogen functional groups (5.2 %). HPNC materials exhibit high CO₂ uptake of 5.56 mmol/g at 25 °C and 1 bar, which is higher than those of previously reported nitrogen-doped porous carbon materials. After 5 cycles the value of CO₂ adsorption uptakes is 5.28 mmol/g, which is approximately 95 % of the original adsorption capacity. The estimated CO₂/N₂ selectivity of HPNC materials is 17, revealing great promise for practical CO₂ adsorption and separation applications. The efficient CO₂ uptake and enhanced CO₂/N₂ selectivity are due to the combination of nitrogen-doped and hierarchical porous structures of HPNC materials.     

Carbon aerogel spheres prepared via alcohol supercritical drying

We have developed a method that would allow for the fabrication of carbon aerogel (CA) spheres. The inverse phase suspension polymerization of resorcinol and formaldehyde monomers with Na₂CO₃ as a catalyst followed by supercritical drying was explored. The effects of the chemical formulation and processing procedures and the conditions of the structures of organic and related carbon aerogels were studied. The experimental results indicated that it was easy to avoid the accumulation of polymerization heat during gelation, and easy to take out the products from the reaction container, through this fabrication method. Sol-gel microspheres with diameters ranging from about 30-1000μm could be obtained. After drying the sol-gel spheres under alcohol supercritical drying conditions, aerogel spheres with a bulk density of 0.8-1.0 g/cm³were prepared, and by subsequently pyrolyzing them, CA spheres with surface areas of 250-650 m²/g were obtained. The resultant CA spheres could be used as the electrode materials of supercapacitors. The specific capacitance of the CA spheres was as high as 215 F/g, and the equivalent series resistance at 48 Hz was about 1 Ω.     

Micro and nano cellular amorphous polymers (PMMA, PS) in supercritical CO2 assisted by nanostructured CO2-philic block copolymers - One step foaming process

Microcellular foaming of commodity amorphous polymers, poly(methyl methacrylate) (PMMA), and poly(styrene) (PS) was studied in supercritical CO₂ via a batch one-step process in the presence of block copolymers able to change their foaming behaviour and therefore the porous structures. Triblock (styrene-co-butadiene-co-methylmethacrylate SBM, methylmethacrylate-co-butylacrylate-co-methylmethacrylate MAM) terpolymers were blended to PS or PMMA by extrusion. They showed advantages compared to classical PS-PMMA polymer blends in terms of cell size control and reduction of cell size. Foaming is carried out on bulk injection molded samples which were saturated under high pressures of CO₂ (300 bars) at different temperatures (25° C to 80 °C) and different depressurization rates (pressure drop rates from 150 bar/min to 12 bar/min). Very distinct cellular structures and densities were controlled by varying either the copolymer type or the foaming conditions (T,P). Cell sizes ranged from 0.2 μm to 200 μm, and densities from 0.30 g/cm³ to 1 g/cm³ in the polymers considered. Particularly, when triblock copolymers were able to self organize (nanostructuring) in a polymer matrix, they became phase separated at a nanometer level, presenting nanostructured polymers matrixes. To conclude the study, a possible nanostructuring mechanism is suggested based on the interplay between rubbery and highly CO₂-philic blocks/rigid and less CO₂-philic blocks. It is demonstrated that block copolymer additives are a good pathway towards micro and ultra microcellular supercritical CO₂ foaming of amorphous polymers.     

Activation of coal tar derived needle coke with K2CO3 into an active carbon of low surface area and its performance as unique electrode of electric double-layer capacitor

Raw needle coke from coal tar pitch was activated with K₂CO₃ at a coke:carbonate weight ratio of 1:4, to prepare an electrode for an electric double-layer capacitor (EDLC). Although the surface area of the coke activated at 900 °C for 3 h was as small as 20 m²/g, with a very high yield, the coke achieved capacitances per weight and volume of 20 F/g and 20 F/ml, respectively, in the two-electrode system, by charging at 2.7 V. The surface area of KOH-activated coke with a similar ratio (coke:hydroxide = 1:4, wt:wt) was over 2300 m²/g, and it exhibited capacitance per weight and volume values of 42 F/g and 17 F/ml, respectively. The coke activated by K₂CO₃ was found to be further activated by the charging. This electrochemical activation, which has been reported as activation in an electric field, was investigated by cyclic voltammetry in order to clarify it. The graphitic and pore structures of the coke after the electrochemical activation were analyzed by XRD to confirm retention of the graphene structure. Xe-NMR showed that the formation of small new pores was induced in the cathode material, increasing the surface area from 6 m²/g to 18 m²/g before use, although the pore volume was around 0.015-0.017 m³/g both before and after the charging. This activation with K₂CO₃ and a deeper understanding of the activation on charging suggest future directions for the preparation of electrode carbon for EDLCs.     

A simple approach for fabrication of interconnected graphitized macroporous carbon foam with uniform mesopore walls by using hydrothermal method

Three-dimensional (3D) highly interconnected graphitized macroporous carbon foam with uniform mesopore walls has been successfully fabricated by a simple and efficient hydrothermal approach using resorcinol and formaldehyde as carbon precursors. The commercially available cheap polyurethane (PU) foam and Pluronic F127 were used as a sacrificial polymer and mesoporous structure-directing templates, respectively. The graphitic structure of carbon foam was obtained by catalytic graphitization method using iron as catalyst. Three different carbon foams such as graphitized macro-mesoporous carbon (GMMC) foam, amorphous macro-mesoporous carbon (AMMC) foam and graphitized macroporous carbon (GMC) foam were fabricated and their physicochemical and mechanical properties were systematically measured and compared. It was found that GMMC possess well interconnected macroporous structure with uniform mesopores located in the macroporous skeletal walls of continuous framework. Besides, GMMC foam possesses a well-defined graphitic framework with high surface area (445 m²/g), high pore volume (0.35 cm³/g), uniform mesopores (3.87 nm), high open porosity (90%), low density (0.30 g/cm³) with good mechanical strength (1.25 MPa) and high electrical conductivity (11 S/cm) which makes it a promising material for many potential applications.     

Enhanced electrochromic performance of macroporous WO3 films formed by anodic oxidation of DC-sputtered tungsten layers

Self-organized macroporous tungsten trioxide (WO₃) films are obtained by anodic oxidation of DC-sputtered tungsten (W) layers on 10 mm × 25 mm indium tin oxide (ITO)-coated glass. Under optimized experimental conditions, uniformly macroporous WO₃ films with a thickness of ca. 350 nm are formed. The film shows a connected network with average pore size of 100 nm and a pore wall thickness of approximately 30 nm. The anodized film becomes transparent after annealing without significant change in macroporous structure. In 0.1 M H₂SO₄, the macroporous WO₃ films show enhanced electrochromic properties with a coloration efficiency of 58 cm² C⁻¹. Large modulation of transmittance (∼50% at 632.8 nm) and a switching speed of about 8 s are also achieved with this macroporous film.