Showing papers on "BET theory published in 2011"

Influence of pyrolysis temperature on biochar property and function as a heavy metal sorbent in soil.

Abstract: While a large-scale soil amendment of biochars continues to receive interest for enhancing crop yields and to remediate contaminated sites, systematic study is lacking in how biochar properties translate into purported functions such as heavy metal sequestration. In this study, cottonseed hulls were pyrolyzed at five temperatures (200, 350, 500, 650, and 800 °C) and characterized for the yield, moisture, ash, volatile matter, and fixed carbon contents, elemental composition (CHNSO), BET surface area, pH, pHpzc, and by ATR-FTIR. The characterization results were compared with the literature values for additional source materials: grass, wood, pine needle, and broiler litter-derived biochars with and without post-treatments. At respective pyrolysis temperatures, cottonseed hull chars had ash content in between grass and wood chars, and significantly lower BET surface area in comparison to other plant source materials considered. The N:C ratio reached a maximum between 300 and 400 °C for all biomass sources ...

Enhanced carbon dioxide capture upon incorporation of N,N′-dimethylethylenediamine in the metal–organic framework CuBTTri

Abstract: High capacity, high selectivity, and low-cost regeneration conditions are the most important criteria by which new adsorbents for post-combustion carbon dioxide capture will be judged. The incorporation of N,N′-dimethylethylenediamine (mmen) into H3[(Cu4Cl)3(BTTri)8 (CuBTTri; H3BTTri = 1,3,5-tri(1H-1,2,3-triazol-4-yl)benzene), a water-stable, triazolate-bridged framework, is shown to drastically enhance CO2 adsorption, resulting in one of the best performing metal–organic frameworks for CO2 separation reported to date. High porosity was maintained despite stoichiometric attachment of mmen to the open metal sites of the framework, resulting in a BET surface area of 870 m2 g−1. At 25 °C under a 0.15 bar CO2/0.75 bar N2 mixture, mmen-CuBTTri adsorbs 2.38 mmol CO2 g−1 (9.5 wt%) with a selectivity of 327, as determined using Ideal Adsorbed Solution Theory (IAST). The high capacity and selectivity are consequences of the exceptionally large isosteric heat of CO2 adsorption, calculated to be −96 kJ mol−1 at zero coverage. Infrared spectra support chemisorption between amines and CO2 as one of the primary mechanisms of uptake. Despite the large initial heat of adsorption, the CO2 uptake was fully reversible and the framework could be easily regenerated at 60 °C, enabling a cycling time of just 27 min with no loss of capacity over the course of 72 adsorption/desorption cycles.

Well-Ordered Large-Pore Mesoporous Anatase TiO2 with Remarkably High Thermal Stability and Improved Crystallinity: Preparation, Characterization, and Photocatalytic Performance

Abstract: Thermally-stable, ordered mesoporous anatase TiO2 with large pore size and high crystallinity has been successfully synthesized through an evaporation-induced self-assembly technique, combined with encircling ethylenediamine (EN) protectors to maintain the liquid crystal mesophase structure of TiO2 primary particles, followed by calcination at higher temperature. The structures of the prepared mesoporous TiO2 are characterized in detail by small-angle and wide-angle X-ray diffraction, Raman spectra, N2 adsorption/desorption isotherms, and transmission electron microscopy. Experimental results indicate that the well-ordered mesoporous structure could be maintained up to 700 °C (M700) and also possesses large pore size (10 nm), high specific BET surface area (122 m2 g−1), and high total pore volumes (0.20 cm3 g−1), which is attributed to encircling EN protectors for maintaining the mesoporous framework against collapsing, inhibiting undesirable grain growth and phase transformation during the calcination process. A possible formation mechanism for the highly stable large-pore mesoporous anatase TiO2 is also proposed here, which could be further confirmed by TG/FT-IR in site analysis and X-ray photoelectron spectroscopy. The obtained mesoporous TiO2 of M700 exhibit better photocatalytic activity than that of Degussa P25 TiO2 for degradation of highly toxic 2,4-dichlorophenol under UV irradiation. This enhancement is attributed to the well-ordered large-pore mesoporous structure, which facilitates mass transport, the large surface area offering more active sites, and high crystallinity that favors the separation of photogenerated electron-hole pairs, confirmed by surface photovoltage spectra.

Catalytic pyrolysis of plastic wastes with two different types of catalysts: ZSM-5 zeolite and Red Mud

Abstract: The influence of ZSM-5 zeolite and Red Mud in the pyrolysis of plastic wastes has been studied. Both catalysts have been thoroughly characterized; the zeolite shows weak and strong acid sites and great BET surface area (412.0 m2 g−1), while Red Mud contains lower acidity, with also weak and strong acid sites, meso-macropores and BET surface area of 27.49 m2 g−1. Both catalysts have been tested in pyrolysis of a mixture of plastics which resembles municipal plastic wastes, at 440 and 500 °C in a 3.5 dm3 semi-batch reactor. The results have been compared with those of the thermal process. It has been proved that ZSM-5 zeolite has a strong effect in the characteristics and distribution of pyrolysis products. It generates at both temperatures a greater proportion of gases and liquids with a higher content of aromatics than without catalyst. Red Mud needs higher temperatures than ZSM-5 zeolite to exert a catalytic effect in pyrolysis, since similar results to those obtained without catalyst are obtained at 440 °C, while at 500 °C a higher yield of gases and a greater proportion of aromatics in the liquids is obtained.

Innovative visible light-activated sulfur doped TiO2 films for water treatment

Abstract: Visible light-activated sulfur doped TiO2 nanocrystalline films were synthesized by a sol–gel method based on the self-assembly technique with nonionic surfactant to control nanostructure and an inorganic sulfur source (i.e., H2SO4). The films were characterized by UV–vis diffuse reflectance, XRD, TEM, Raman, AFM, ESEM, XPS, FT-IR, EDX, EPR and porosimetry. The results showed that the physicochemical properties of the films, such as BET surface area, porosity, crystallite size and pore size distribution could be controlled by the calcination temperature. The highest surface area, smallest crystallite size and narrow pore size distribution were obtained for sulfur doped TiO2 films calcined at 350 °C, which exhibit very smooth surface with minimal roughness (

Stable polyoxometalate insertion within the mesoporous metal organic framework MIL-100(Fe)

Abstract: Successful encapsulation of polyoxometalate (POM) within the framework of a mesoporous iron trimesate MIL-100(Fe) sample has been achieved by direct hydrothermal synthesis in the absence of fluorine. XRPD, 31P MAS NMR, IR, EELS, TEM and 57Fe Mossbauer spectrometry corroborate the insertion of POM within the cavities of the MOF. The experimental Mo/Fe ratio is 0.95, in agreement with the maximum theoretical amount of POM loaded within the pores of MIL-100(Fe), based on steric hindrance considerations. The POM-MIL-100(Fe) sample exhibits a pore volume of 0.373 cm3 g−1 and a BET surface area close to 1000 m2 g−1, indicating that small gas molecules can easily diffuse inside the cavities despite the presence of heavy phosphomolybdates. These latter contribute to the decrease in the overall surface area, due to the increase in molar weight, by 65%. Moreover, the resulting Keggin containing MIL-100(Fe) solid is stable in aqueous solution with no POM leaching even after more than 2 months. In addition, no exchange of the Keggin anions by tetrabutylammonium perchlorate in organic media has been observed.

Free-Standing Mesoporous Carbon Thin Films with Highly Ordered Pore Architectures for Nanodevices

Abstract: We report for the first time the synthesis of free-standing mesoporous carbon films with highly ordered pore architecture by a simple coating-etching approach, which have an intact morphology with variable sizes as large as several square centimeters and a controllable thickness of 90 nm to ∼3 μm. The mesoporous carbon films were first synthesized by coating a resol precursors/Pluronic copolymer solution on a preoxidized silicon wafer and forming highly ordered polymeric mesostructures based on organic-organic self-assembly, followed by carbonizing at 600 °C and finally etching of the native oxide layer between the carbon film and the silicon substrate. The mesostructure of this free-standing carbon film is confirmed to be an ordered face-centered orthorhombic Fmmm structure, distorted from the (110) oriented body-centered cubic Im3m symmetry. The mesoporosity of the carbon films has been evaluated by nitrogen sorption, which shows a high specific BET surface area of 700 m(2)/g and large uniform mesopores of ∼4.3 nm. Both mesostructures and pore sizes can be tuned by changing the block copolymer templates or the ratio of resol to template. These free-standing mesoporous carbon films with cracking-free uniform morphology can be transferred or bent on different surfaces, especially with the aid of the soft polymer layer transfer technique, thus allowing for a variety of potential applications in electrochemistry and biomolecule separation. As a proof of concept, an electrochemical supercapacitor device directly made by the mesoporous carbon thin films shows a capacitance of 136 F/g at 0.5 A/g. Moreover, a nanofilter based on the carbon films has shown an excellent size-selective filtration of cytochrome c and bovine serum albumin.

Preparation of Microporous Carbon Fibers through Carbonization of Al-Based Porous Coordination Polymer (Al-PCP) with Furfuryl Alcohol

Abstract: Here, we report preparation of microporous carbon fibers through carbonization of an Al-based porous coordination polymer (Al-PCP) with furfuryl alcohol (FA) at 1000 °C under an inert gas atmosphere. During the carbonization process, the Al species are aggregated to form γ-alumina nanoparticles. After the carbonization, the γ-alumina nanoparticles (from 2 to 10 nm) are distributed over the entire area. By chemical treatment with HF, the γ-alumina nanoparticles can be easily removed to obtain pure microporous carbon. Interestingly, the fibrous morphology of the original Al-PCP is successfully retained after the carbonization process. The effect of the loading amount of FA into the porous networks of Al-PCP on properties of the obtained microporous carbon is carefully examined. From the N2 adsorption−desorption isotherms, an increase in the BET surface area upon increasing the loading amount of FA is observed. The maximum surface area and pore volume of the obtained microporous carbon reach 513 m2/g and 0.8...

Facile synthesis of mesoporous carbon nitrides using the incipient wetness method and the application as hydrogen adsorbent

Abstract: Highly nitrogen-enriched mesoporous carbon nitride materials with 2-dimensional (2-D) (2D-meso-CN) and 3-dimensional (3-D) mesostructures (3D-meso-CN) were synthesized using mesoporous silica as a hard template and cyanamide as a precursor via the incipient wetness process without using any solvent. The materials were characterized by small-angle X-ray scattering (SAXS), X-ray diffraction (XRD), and transmission electron microscopy (TEM) for the mesostructure analysis, N2 adsorption–desorption isotherms for surface area and pore size distribution, and X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared (FT-IR) spectroscopy for the composition analysis of frameworks. The mesoporous carbon nitride replicas have graphitic-like stacking of carbon nitride sheets in mesopore walls. The N/C ratio of the mesoporous carbon nitride replicas is 1.13 after the carbonization at 550 °C for 3 h. 2D-meso-CN and 3D-meso-CN have the BET surface area of 361 and 343 m2 g−1, large pore volume of 0.50 and 0.67 cm3 g−1, and pore diameter of 27.8 A (for 2D-meso-CN), 24.5 and 80.3 A (for 3D-meso-CN), respectively. It was found that the 3D-meso-CN has higher capacity of hydrogen uptake of 0.25 wt% than the pure mesoporous carbon FDU-15 (0.16 wt%) at 50 bar under room temperature (298 K).

Cinder supported K2CO3 as catalyst for biodiesel production

Abstract: This study aims to explore cheap macroporous solid base catalyst with high transesterification efficiency. Cinder, as solid waste from coal burning industry, with natural macroporous structure and alkalinity, was served as the support for K 2 CO 3 to prepare solid base catalyst for biodiesel production. In the present paper, catalysts prepared in different conditions were characterized by base strength, BET surface area, X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), and the triglyceride (TG) conversion from the transesterification catalyzed by each catalyst was determined using high performance liquid chromatography (HPLC). The effects of various parameters such as concentration of K 2 CO 3 impregnating solution, catalyst loading, molar ratio of methanol to oil and reaction time on the activity of catalysts were investigated. A maximum TG conversion of 99.5% was obtained under the optimal conditions as catalyst amount of 17.4%, methanol/oil of 12:1 and reaction time of 1 h, which was catalyzed by the catalyst prepared with 0.50 g mL −1 K 2 CO 3 impregnating solution. The results indicated that K 2 CO 3 was decomposed into K 2 O by the catalysis of metal oxides in cinder or transformed into Al–O–K compounds through reaction with cinder. The formation of K 2 O and Al–O–K compounds should be the main reason for the catalytic activity. Continuous use of the catalyst in a tubular reactor showed high TG conversion (>90%) maintained 9 h. The deactivation of the catalyst after 9 h use was mainly caused by potassium leaching to the glycerol phase.

Adsorption of Nickel Ions from Aqueous Solutions by Nano Alumina: Kinetic, Mass Transfer, and Equilibrium Studies

Abstract: The presence of nickel in aquatic systems due to discharge of industrial effluents is of concern because of its toxic and nonbiodegradable nature. Its removal from water and wastewater is mandatory. Though activated carbon has been effective in removing metallic species including nickel from water and effluents, its high cost limits its large scale application to developing nations. The present paper addresses the removal of nickel from aqueous solutions by alumina nano particles. The adsorbent, nano alumina powder, was synthesized in the laboratory and was characterized by X-ray diffractometry (XRD), Fourier transformation infrared spectroscopy (FTIR), and transmission electron microscopy (TEM). The BET surface area and porosity of nanosized alumina powder were found to be 78.79 m2 g−1 and 0.51, respectively. The initial concentration of nickel, agitation speed, and contact time were found to affect the removal of nickel from aqueous solutions. Kinetic studies were performed and pseudofirst order, second...

Development of Biochar-based Catalyst for Transesterification of Canola Oil

Abstract: Heterogeneous catalysts bearing sulfonic acid groups were prepared using biochar as the carbon support. Biochar samples were first treated with KOH before carbonization at different temperatures (450, 675, and 875 °C) then sulfonated using fuming H2SO4 at 150 °C for 15 h. The sulfonated catalysts were characterized using BET surface area and porosity, elemental analysis, total acid density, FT-IR spectroscopy, X-ray diffraction, and thermogravimetric analysis. Catalytic performance was determined via the transesterification of canola oil with methanol. The reaction yield was found to be dependent on both catalyst surface area and total acid density, suggesting that the maximum yield would be obtained for a catalyst prepared from char carbonized between 675 and 875 °C. FT-IR spectra and XRD patterns reveal that higher carbonization temperatures cause an increasing reorientation of the biochar’s carbon sheets toward a more graphite-like structure, decreasing the total acid density despite the increasing sur...

Solvent evaporation induced aggregating assembly approach to three-dimensional ordered mesoporous silica with ultralarge accessible mesopores.

Abstract: A solvent evaporation induced aggregating assembly (EIAA) method has been demonstrated for synthesis of highly ordered mesoporous silicas (OMS) in the acidic tetrahydrofuran (THF)/H(2)O mixture by using poly(ethylene oxide)-b-poly(methyl methacrylate) (PEO-b-PMMA) as the template and tetraethylorthosilicate (TEOS) as the silica precursor. During the continuous evaporation of THF (a good solvent for PEO-b-PMMA) from the reaction solution, the template molecules, together with silicate oligomers, were driven to form composite micelles in the homogeneous solution and further assemble into large particles with ordered mesostructure. The obtained ordered mesoporous silicas possess a unique crystal-like morphology with a face centered cubic (fcc) mesostructure, large pore size up to 37.0 nm, large window size (8.7 nm), high BET surface area (508 m(2)/g), and large pore volume (1.46 cm(3)/g). Because of the large accessible mesopores, uniform gold nanoparticles (ca. 4.0 nm) can be introduced into mesopores of the OMS materials using the in situ reduction method. The obtained Au/OMS materials were successfully applied to fast catalytic reduction of 4-nitrophenol in the presence of NaHB(4) as the reductant. The supported catalysts can be reused for catalytic reactions without significant decrease in catalysis performance even after 10 cycles.