High Specific Surface Area Values Research Articles

Carbon foams from sucrose employing different metallic nitrates as blowing agents: Application in CO2 capture

Carbon foams were prepared employing sucrose as the carbon source. The porosity of the materials as well as the morphology was controlled using different metallic nitrates during the synthesis, such as aluminum (obtaining EsAl foam), iron (obtaining EsFe foam) and silver (obtaining EsAg foam) nitrate. The samples have interconnecting pores with a turbostratic structure, where the EsFe foam shows a more ordered structure. The addition of the chemical agents promotes improvements in the porosity of the foams, highlighting those obtained with the aluminum nitrate nonahydrate - EsAl (98%) and iron nitrate nonahydrate - EsFe (90%), as well as a greater control of pore growth avoiding collapse. All carbon foams presented a microporous nature, but EsFe foam also present mesoporosity (with pore sizes between 2.2 to 3.5 nm). The high specific surface area values for EsAl and EsFe carbons (600 and 380 m2/g) were attributed to in situ activation during carbonization of the foams. All carbon foams present ultramicropores with pore sizes less than 0.6 nm. The synthesized carbon foams have interesting CO2 adsorption capacities, mainly the EsAl foam that reach CO2 adsorption capacities (at 1000 kPa) of 4 and 4.4 mmol/g at 50 °C and at 35 °C, respectively. These capacities of the carbon foams obtained were similar to those reported in the bibliography for other carbon materials, shows their great potential as CO2 adsorbents. The isosteric heat of CO2 adsorption show that the CO2 capture with the carbon foams synthesized is associated with a physisorption process.

Zn-doped Nb2O5 photocatalysts driven by visible-light: An experimental and theoretical study

Abstract Zn-doped Nb2O5 are prospective photocatalysts since they can be activated by visible-light. In this context, undoped and Zn-doped Nb2O5 (0.1 and 0.2% mol of Zn) were synthesized by the oxidant peroxide method with crystallization under hydrothermal conditions. All the synthesized materials presented the diffraction pattern of the Nb2O5 orthorhombic-type phase and part of the structure was amorphous. The doped samples presented better crystallinity, high specific surface area and low band gap values, i.e., low content of zinc were able to considerably improve the photocatalytic activity of Nb2O5 under visible irradiation. Furthermore, the as-synthesized samples were versatile photocatalysts since they presented great photoactivity in rhodamine B and caffeic acid degradation. The materials with 0.1% and 0.2% mol of Zn remained degrading about 80% and 87%, respectively of caffeic acid after three consecutive use cycles, proving that the organic compounds were really degraded not just adsorbed. In addition, the computational calculations showed that the presence of Zn leads to a significant decrease of band gap, decreasing the energy required to activate the photocatalyst.

Hierarchical WO3/ZnWO4 1D fibrous heterostructures with tunable in-situ growth of WO3 nanoparticles on surface for efficient low concentration HCHO detection

Hierarchical WO3/ZnWO4 1D fibrous heterostructures with tunable in-situ growth of WO3 nanoparticles on surface have been fabricated by the original one-step electrospinning technology combined with subsequent calcination process. Phase composition and morphology can be transformed from bead-like WO3 fibers to hierarchical WO3/ZnWO4 1D composites with the introduction of ZIF-8 into the precursor solution, which was mainly attributed to the combination of nucleation competition and crystal planes matching mechanisms during heat treatment. Compared with pure WO3 and WO3/ZnWO4-10%, WO3/ZnWO4-5% displayed the highest specific surface area value evaluated to be 268.57, indicating the prominent enhanced absorption behavior for targeted organic species. It is found that WO3/ZnWO4-5% composites have a response about 44.5 for 5 ppm HCHO, which was almost 8 times higher than that of sensor based on pure WO3 nanofibers at the optimal operating temperature. Meanwhile, the fast response/recovery time (12/14 s) and excellent stability characteristics (recycling, long-term, and humidity stability) towards HCHO can be also observed for WO3/ZnWO4-5% samples. The enhanced gas-sensing mechanism based on WO3/ZnWO4 composites can be ascribed to the synergistic effect of effective heterojunctions, large specific surface area, multiple reaction sites, and unique surface/interface electron transmission. The design and construction of hierarchical WO3/ZnWO4 1D materials attest to the significant potential of their use as novel gas sensors for detecting low concentration HCHO.

Novel hypercrosslinking approach toward high surface area functional 2-hydroxyethyl methacrylate-based polyHIPEs

Highly porous poly(2-hydroxyethyl methacrylate-co-N,N′-methylenebisacrylamide) (poly(HEMA-co-MBAA)) frameworks were prepared from oil-in-water high internal phase emulsions (HIPEs). After subsequent functionalization through a two-step synthetic pathway involving i) activation of the hydroxyl functions exposed at the pore surface and ii) functionalization with allylamine or propargylamine, two different functionalized porous polymers were obtained and characterized in terms of porosity and chemical composition through mercury intrusion porosimetry, nitrogen adsorption-desorption porosimetry, and Raman spectroscopy, respectively. A final step relying on radical thiol-ene/yne “click” additions with di- or tetrathiols was further investigated so as to hypercrosslink the resulting porous materials and eventually decorate the pore surface with thiol functions. Very high specific surface area values as determined by nitrogen sorption porosimetry were found, namely up to 1500 m2.g−1 for HEMA-based material functionalized with allylamine after hypercrosslinking with pentaerythritol. In-situ generated gold nanoparticles were immobilized at the pore surface, and one such strategy allowed for the preparation of hybrid materials that were successfully applied for the supported heterogeneous catalytic reduction of a nitroaromatic compound, i.e.p-nitrophenol, and of a pollutant dye used in textile industry, i.e. Eosin Y.

Tin dioxide coated carbon materials as an alternative catalyst support for PEMFCs: Impacts of the intrinsic carbon properties and the synthesis parameters on the coating characteristics

Several carbon materials (one carbon nanotubes, two carbon blacks and one home-made carbon aerogel) were covered by thin tin dioxide (SnO2) nanoparticles coatings to improve their resistance against oxidation under the working conditions of Proton Exchange Membrane Fuel Cells. A pretreatment for the nanotubes in acidic media was also performed to improve their dispersion in the reactive medium. The coating was done by a chemical route. Samples were analysed by Scanning Electronic Microscopy (SEM), nitrogen sorption, X-ray diffraction (XRD), Raman spectroscopy, Fourier Transformed InfraRed (FTIR) and X-ray Photoelectron Spectroscopy (XPS). Their electrical conductivities were also measured. Using a reactive medium with a pH value exceeding the point of zero charge of the carbon materials is mandatory to favour electrostatic attractions, and to obtain covering and homogeneous coatings. In this condition, it is possible to reduce the quantity of precursor and to optimise the coating. The intrinsic properties of the carbon materials also influence the characteristics of the coatings. In fact, the least organised carbon materials with high specific surface area and porosity values exhibit homogeneous and covering coatings. On the contrary, organised carbon materials, with few oxygen-containing groups, lead to a smaller quantity and heterogeneous coatings (with some areas of carbon surface uncovered). The pretreatment performed on the nanotubes improves the characteristics of the coatings, even if using significant amounts of precursor remains necessary to obtain a covering and a homogeneous coating. The transformation mechanisms of the precursor into tin dioxide, depending on the pH, value are also discussed.

Characterization of Microwave and Conventional Heating on the Pyrolysis of Pistachio Shells for the Adsorption of Methylene Blue and Iodine

ABSTRACTThe production of activated carbon was investigated using the sequential combination of microwave and conventional heating of pistachio shells as the raw precursor with zinc chloride. Several techniques such as thermogravimetric and differential thermal analyses, infrared spectroscopy, scanning electron microscopy, and specific surface area analyses were performed to characterize the samples. The highest specific surface area value for the activated carbon prepared at a microwave power of 200 W with microwave time of 20 min, and flow rate of 50 mL min−1 was 1468 m2 g−1. The methylene blue and iodine adsorption capacities were 331 and 1276 mg g−1, respectively. The results were compared to those obtained using physical and chemical activation methods and showed that the sequential combination of microwave and conventional heating reasonably influenced the micropore surface area of the samples as well as the specific surface area.

Nitrogen-doped carbon aerogels with high surface area for supercapacitors and gas adsorption

Doping of nitrogen atoms has been considered to be a common strategy for improving the performance of carbon aerogels. In this work, two kinds of nitrogen-doped carbon aerogels with high porosity (NCA-800 and NCA-900) are prepared through polymerization of pyrrole and formaldehyde monomers under a hypersaline condition and subsequent carbonization at different temperatures (800 and 900 °C). In the whole preparation process, zinc chloride is not only used to provide a hypersaline environment for the polymerization of pyrrole and formaldehyde, but also applied as a catalyst and an activating agent. The as-prepared aerogels possess high specific surface area values (1450 m2 g–1 for NCA-800 and 1670 m2 g–1 for NCA-900) and moderate nitrogen contents (10.86 atom% for NCA-800 and 4.09 atom% for NCA-900). As gas adsorbents, they show high uptake capacities for carbon dioxide (∼16 wt%) at 273 K under 1.0 bar on the basis of high porosity and nitrogen contents. When applied as electrodes for supercapacitors, the as-prepared aerogels exhibit good electrochemical performances.

Novel multifunctional strontium-copper co-substituted mesoporous bioactive particles

Sr-Cu co-substituted mesoporous bioactive glasses were synthesized by two different sol-gel approaches: an ultrasound-assisted base-catalyzed sol-gel procedure and an aerosol-assisted spray-drying method. The produced spherical shaped particles showed high specific surface area values and tunable pore size. The two different routes allowed obtaining samples with different morphology and size, characterized by the ability to induce hydroxyapatite deposition, to incorporate a specific amount of therapeutic ions (strontium with the aim to improve bone formation and copper for its antibacterial and pro-angiogenic properties) and to release them. The obtained multifunctional biomaterials synergistically combine the ability to promote bone formation and angiogenesis and to impart an antibacterial effect.

Analysis of Adsorption and Desorption of Ethylene on Hard Coals

Ethylene is an unsaturated hydrocarbon that is released into the atmosphere of a mine as a result of an increase in the temperature of coal caused by the self-heating process. The content of ethylene in mine air is one of the indicators for assessing the degree of the coal self-heating process. Sorption capacities of hard coals with respect to ethylene may be the reason for the decrease in its concentration in mine air, which may affect the accuracy of self-heating process assessment. This phenomenon may be particularly important in the case of coals with significant sorption capacities. This paper presents the results of ethylene sorption studies carried out on six samples of bituminous coals collected from currently operational coal seams in Polish mines. The coals under analysis are characterized by varying sorption capacity with regard to ethylene. The highest sorption capacities were reported for low rank, high-porosity coals with easily accessible pore structure, high specific surface area values, a...

Structural, surface and magnetic properties of chalcogenide Co9S8 nanoparticles prepared by mechanochemical synthesis

In this study, the mechanochemical synthesis of Co9S8 nanoparticles from cobalt and sulphur by high-energy milling in a planetary mill in an argon atmosphere is reported. Structural characterization of the synthesized nanoparticles by XRD was performed. Co9S8 nanoparticles crystallize in the cubic structure with the crystallite size of about 16 nm. The microstructure of the Co9S8 nanoparticles was further studied using TEM, HRTEM and EDS-HAADF-STEM techniques. Co9S8 nanoparticles consist of nanocrystals exhibiting size in the range of 10–30 nm that are densely aggregated into spherical-like objects. The highest specific surface area value observed was 4 m2g-1 and the pore properties of this sample are quite poor. The magnetic properties of mechanochemically synthesized nanoparticles were investigated using SQUID magnetometer. The room temperature magnetic data supported the paramagnetic spin structure of Co9S8 nanoparticles. The transition from paramagnetic to weak ferromagnetic or ferrimagnetic behaviour was indicated from temperature dependence of magnetization at cryogenic temperatures. It is demonstrated that mechanochemical synthesis can be successfully employed in the one-step solid-state preparation of Co9S8 nanoparticles.

Properties of mesostructured silica coated CoFe2O4 versus Fe3O4-silica composites

Abstract Ferrite-based composite materials have many applications in biomedicine, catalysis, magnetic separations etc. Cobalt ferrite and magnetite were synthesized by co-precipitation method using oleic acid as capping agent. The crystalline CoFe 2 O 4 nanoparticles with an average size of 12 nm were obtained at 90 °C. The magnetic composite materials were prepared by coating the magnetic nanoparticles with MCM-41 mesoporous silica. Fe 3 O 4 nanoparticles and magnetite-based composites presented superparamagnetic behavior, while CoFe 2 O 4 and silica coated cobalt ferrite material exhibited ferrimagnetic properties. The obtained composites had high specific surface area values in the range of 612–784 m 2 /g and no significant in vitro toxicity on adherent epithelial opossum kidney cells that recommend them as platform for drug delivery systems.

Elaboration of an Easy Aqueous Sol-Gel Method for the Synthesis of Micro- and Mesoporous <i>γ</i>-Al<sub>2</sub>O<sub>3</sub> Supports

An aqueous sol-gel method for the synthesis of γ-Al2O3 supports has been developed for the use in tar reforming applications. It was determined the influences of two different aluminum precursors (aluminum sec-butoxide (Al[OCH(CH3)CH2CH3]3) and aluminum nitrate (Al(NO3)3)) on the textural and crystallographic properties of Al2O3 supports. Only the formation of γ-Al2O3 is aimed in order to use these alumina materials as catalytic supports, because it presents high specific surface area and pore volume values. Additionally, the synthesis of γ-Al2O3 was realized with the use of a functionalized silicon precursor, [3-(2-aminoethylamino)propyl]trimethoxysilane, called EDAS. By the presence of an ethylenediamine group in this molecule, it is possible to chelate metallic ions and to highly increase their dispersion at a molecular level during the synthesis of metallic catalysts supported on alumina, which is an asset for catalytic applications. So it was developed a synthesis sol-gel procedure for the cogelation between the functionalized silicon alkoxide EDAS and alumina precursor. The alumina supports synthesized with Al(NO3)3 as precursor presented higher porous values than the ones obtained with aluminium sec-butoxide precursor. Since nitrate salts are much easier to handle than alkoxides, these observations allowed validating Al(NO3)3 as aluminum source for the future synthesis procedures for metallic catalysts supported on alumina.

Li2O–ZnO–Co3O4–TiO2 composite thin-film electrocatalyst for efficient water oxidation catalysis

ABSTRACTThin films of different Li2O–ZnO–Co3O4–TiO2 (LZCT) compositions were prepared and employed as electrocatalysts (i.e., anodes) to perform water oxidation reaction (WOR). The electrocatalytic activities of these thin films were compared with those exhibited by the sodium salt of cobalt phosphate (Na2CoP2O7) (CP) thin-film electrocatalyst, which is a well-known water oxidation catalyst (WOC). These results suggest that the 10Li2O–10ZnO–40Co3O4–40TiO2 composition exhibits a better catalytic activity in terms of higher faradaic efficiency (>98%), lower over potentials (<400 mV), higher reaction stability (up to 30 continuous cyclic voltammetry (CV) cycles), and the rate of O2 and H2 gas evolution in terms of current density (about 1 mA/cm2) in comparison with those exhibited by CP thin-film electrocatalyst. Furthermore, these LZCT thin films exhibited very high specific surface area values and due to the unique microstructure of ZnCo2O4 phase evolved out of these LZCT compositions at a calcination temperature of 550°C for 30 min it has been found to be responsible for the higher specific surface area values measured for these thin-film compositions.

Formation of graphene flowers during high temperature activation of mesocarbon microbeads with KOH

Graphene flowers on porous activated carbon was successfully obtained by activation of mesocarbon microbeads (MCMB) with KOH at high temperature. By investigation of structure evolution with temperature from 800 to 1100 °C, it was found the coarse surface of activated carbon with cracks and small particles became to be graphene flowers when the activation temperature reached 1000 °C. The activated carbon with graphene flowers had high specific surface area value (1855 m2/g) and pore volume (1.18 cm3/g), which was ascribed to the chemical reactions, K intercalation and existence of graphene flowers. From the microstructural analysis, it was deduced that graphene flowers on the activated carbon was obtained from the high ordered layers in the small building units of MCMB, which processed the removal of disordered carbon, remaining the high ordered layers left under high temperature activation.

Evaluation of growth age for the diverse conversion of Ficus carica L. cut branches using steam explosion

Growth age determines the composition and structure of woody biomass and hence its conversion performance. Effects of growth age of seasonal Ficus carica L. cut branches (FCBs) on the diverse conversion efficiency by steam explosion (SE) were evaluated. Results showed that sugar contents increased with the growth age of FCBs (0.5-, 1- and 3-year-old). Sugar conversions increased dramatically after SE for all FCBs, and the highest sugar conversion was observed at 1-year-old FCB, reaching 48.4% for glucan. SE decreased number- and weight-average molecular weight and increased polydispersity of lignin. 1-year-old FCB obtained the highest specific surface area value (0.439m2/g) after SE, 64.0% and 28.8% higher than that of 0.5- and 3-year-old FCBs. Morphology observation of single fibers showed the homogeneous fiber size distribution for 1-year-old FCB after SE, which should be helpful to increase the adsorptivity of enzymes during hydrolysis. Through SE, 1-year-old FCB obtained higher sugar contents, bigger specific surface area, homogeneous fiber size distribution, and hence higher sugar conversion during enzymatic hydrolysis. Therefore, the analysis of physicochemical property and the hydrolysis performance suggested that 1-year-old FCB would be a desirable substrate for the conversion process using SE.

Experimental Study on Sorption and Desorption of Propylene on Polish Hard Coals

Propylene is the unsaturated hydrocarbon emitted to the atmosphere of a coal mine in the process of coal self-heating. Its concentration in mine air is one of the indicators for the assessment of the development of the process of coal self-heating. Coal sorption capacities with respect to propylene may be the reason for the decrease in its concentration in mine air. This may affect the accuracy of the assessment of the self-heating process development, in particular, in the case of coals of considerable sorption capacities. The paper presents the results of coal sorption capacities with respect to propylene performed on 10 samples of bituminous coals acquired from operated coal seams. The sorption capacities of tested coal samples varied depending upon level of metamorphism, porosity, and chemical characteristics of a coal surface. The highest sorption capacities were reported for high-porosity coals of easily accessible pore structure, high specific surface area values, low level of metamorphism, and hig...

Cell Wall Disruption of Rape Bee Pollen Treated with Combination of Protamex Hydrolysis and Ultrasonication

Bee pollen possesses a broad range of potential biological activities, but nutrient absorption and biological activities of bee pollen may be restricted due to complex pollen wall. This study aimed to investigate wall-disruption variations of Brassica campestris L. (rape) bee pollen treated with protamex hydrolysis, ultrasonication, and combination of protamex hydrolysis and ultrasonication. Pollen sample treated with these three treatments had higher specific surface area values and smaller particle sizes than the untreated sample. Protamex hydrolysis degraded the pollen coat and disintegrated the intine at the germinal apertures. Ultrasonication treatment cracked the pollen exine into fragments, but seemed to have little effect on the intine. The combination of protamex hydrolysis and ultrasonication can degrade pollen coat and entirely disrupt both the exine and the intine. The exine of rape bee pollen was disrupted into three fragments along germinal apertures.

Facile solvo-combustion synthesis of crystalline NaTaO3 and its photocatalytic performance for hydrogen production

Significant attention has been paid on the photocatalytic production of hydrogen from water splitting by using semiconductor materials. The NaTaO3 phase has been studied for this purpose due to its high potential to generate charge carriers by absorbing the photons energy. This work reports for the first time the synthesis of NaTaO3 powder through an innovative solvo-combustion reaction using the acetyl acetone as template and fuel. It can be mention some advantages of this method such as compounds with high crystallinity, large surface area and specific morphology at nanometer level under low temperature, 180°C. In order to remove organic material and increase phase crystallinity, this powder was annealed at different temperatures up to 700°C. All the reaction products were characterized and its photophysical and textural properties were determined. The XRD analysis results showed that crystalline phase of NaTaO3 is obtained from the as-prepared material at 180°C. At higher temperature, the presence of a second phase, Na2Ta4O11, was observed. The TEM micrographs revealed that NaTaO3 has hierarchical cubic morphology in the nanometer level with the formation of nanosteps between NaTaO3 particles. The materials presented high specific surface area values around 30–120m2g−1, which are twice at 180 and 600°C larger than other reported works. The UV–visible analysis shows a band gap value (Eg) around 4.0eV. It was found that there is a synergy effect between crystallinity of the phase and specific surface area that is the responsible to improve the hydrogen production around three times compared with the results obtained when the pure phase of NaTaO3 was employed. Also the presence of the second crystalline phase, Na2Ta4O11, in small concentration and the formation of nanosteps between NaTaO3 nanoparticles contributed to enhance of photoactivity of NaTaO3. Finally, when RuO2 (1wt.%) was added as co-catalyst, the efficiency of hydrogen production was increased considerably, reaching around 50mmol of H2 after 5h of reaction, which is higher than other reports in literature for this material.

서천화력발전소 매립 석탄재에서 분리한 미연탄소의 재활용 방안

Abstract Feasibility of utilizing unburned carbon residue in coal ash as a potential precursor for the production of activated carbon wasassessed to seek for solution to recycle unburned carbon residue. The unburned carbon concentrate generated from the 4 stagesof cleaner flotation has a grade of 87% carbon. The crystalline impurities in the concentrate included quartz and mullite.Unburned carbon had a low specific surface area of 10m 2 /g, which might be related to a high degree of coalification of domesticanthracite coal. Carbon particles were mostly porous and have a turbostratic structure. When 1g of carbon was activated with6g of KOH powder, the highest specific surface area value of 670m 2 /g was achieved. Low wettability of unburned carbon par-ticles, which was resulted from high temperature combustion in a boiler, might cause poor pore formation when they were acti-vated by KOH solution. The activated carbon produced in this study developed micropores, with an equivalent quality of * Received : November 5, 2013 · Revised : December 12, 2013 · Accepted : December 24, 2013Corresponding Author : Sujeong Lee (E-mail : crystal2@kigam.re.kr)Mineral Resources Research Division, Korea Institute of Geoscience & Mineral Resources, 124 Gwahang-no, Yuseong-gu, Daejeon,305-350 KoreaTel : +82-42-868-3125 / Fax : +82-42-868-3418ⓒThe Korean Institute of Resources Recycling. All rights reserved. This is an open-access article distributed under the termsof the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/), which permitsunrestricted non-commercial use, distribution and reproduction in any medium, provided the original work is properly cited.

A novel hybrid sol–gel method for the synthesis of highly porous silica employing hyperbranched poly(ethyleneimine) as a reactive template

A novel hybrid sol–gel templating route employing hyperbranched polymers for the production of nanostructured silica with tailored porosity and high specific surface area values is proposed based on the use of hyperbranched poly(ethyleneimine) both as a reactive template and as a macromolecular “porogen”. The procedure developed involves dissolution of hyperbranched poly(ethyleneimine), PEI, of two different molecular weights (5,000 and 25,000), in N,N-dimethylformamide or chloroform serving as solvents of different polarity and addition of 3-(triethoxysilyl)propyl isocyanate as a silica precursor which is also reactive towards PEI’s amino groups. The obtained triethoxysilyl functionalized macromolecules after hydrolysis and subsequent polycondensation reactions lead to the formation of a novel silica network architecture. By firing this hybrid material a silica powder of nanoporous structure and advanced textural properties is obtained. Synthetic reactions are monitored by FTIR spectroscopy, while the silica network formed after firing is characterized by TGA, low and wide-angle XRD, TEM and N2 adsorption techniques. The influence of several parameters, i.e., molecular weight of PEI, PEI/silica precursor molar ratio and solvent polarity on silica’s porosity is studied. Depending on the synthesis conditions, this novel templating route proved effective for the successful imprinting of mesoporous cavities into silica structure. In this way, nanostructures with tailor-made properties were obtained exhibiting specific surface area values varying from ∼600 to 1100m2/g and pore diameters up to around 5nm.