Showing papers on "BET theory published in 2015"

A three-dimensional porous LiFePO4 cathode material modified with a nitrogen-doped graphene aerogel for high-power lithium ion batteries

Abstract: A composite cathode material consisting of (010) facet-oriented LiFePO4 nanoplatelets wrapped in a nitrogen-doped graphene aerogel is reported. Such a composite possesses a 3D porous structure with a BET surface area as high as 199.3 m2 g−1. In this composite, the nitrogen-doped graphene aerogel combined with its interconnected porous networks provides pathways for rapid electron transfer and ion transport, while the thin LFP nanoplatelets with large (010) surface area enhance the active sites and shorten the Li+ diffusion distances. As a result, a high rate capability (78 mA h g−1 at 100 C) as well as a long life cycling stability (89% capacity retention over 1000 cycles at 10 C) are achieved.

Iron-copper bimetallic nanoparticles embedded within ordered mesoporous carbon as effective and stable heterogeneous Fenton catalyst for the degradation of organic contaminants

Abstract: Iron-copper bimetallic nanoparticles embedded within ordered mesoporous carbon composite catalyst (CuFe-MC) was synthesized via a “one-pot” block-copolymer self-assembly strategy. The catalyst was characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), etc. The results showed the catalyst was ordered 2D hexagonal mesostructure and iron-copper nanoparticles highly dispersed in the matrix of ordered mesoporous carbon. The composite was used as a heterogeneous Fenton catalyst and showed a promising application in the degradation of non-biodegradation organic contaminants. Eight organic compounds were chosen as model contaminants, such as phenol, bisphenol A (BPA), etc. Efficient total organic carbon (TOC) removal of each organic contaminant was achieved by using CuFe-MC as catalyst, which was higher than that by Fe2+ ion at the same reaction condition. BPA was selected to further investigate the high catalytic activity of CuFe-MC. CuFe-MC presented high adsorption capacity for BPA due to its high BET surface area (639 m2 g−1) and mesostructure. The results of BPA degradation showed that the catalytic activity of CuFe-MC was much higher than Fe-MC and Cu-MC. Electron spin resonance (ESR) and high performance liquid chromatography (HPLC) results indicated that the concentration of generated hydroxyl radicals (•OH) with CuFe-MC was much higher than Fe-MC and Cu-MC. The low iron leaching of CuFe-MC suggested its good stability. Moreover, it could be easily separated by using an external magnet after the reaction and remained good activity after being recycled for several times, demonstrating its promising long-term application in the treatment of wastewater.

Ultrahigh Surface Area Zirconium MOFs and Insights into the Applicability of the BET Theory

Abstract: An isoreticular series of metal–organic frameworks (MOFs) with the ftw topology based on zirconium oxoclusters and tetracarboxylate linkers with a planar core (NU-1101 through NU-1104) has been synthesized employing a linker expansion approach. In this series, NU-1103 has a pore volume of 2.91 cc g–1 and a geometrically calculated surface area of 5646 m2 g–1, which is the highest value reported to date for a zirconium-based MOF and among the largest that have been reported for any porous material. Successful activation of the MOFs was proven based on the agreement of pore volumes and BET areas obtained from simulated and experimental isotherms. Critical for practical applications, NU-1103 combines for the first time ultrahigh surface area and water stability, where this material retained complete structural integrity after soaking in water. Pressure range selection for the BET calculations on these materials was guided by the four so-called “consistency criteria”. The experimental BET area of NU-1103 was ...

Nitrogen-rich porous carbon derived from biomass as a high performance anode material for lithium ion batteries

Abstract: Nitrogen-rich porous carbon derived from ox horns has been successfully synthesized through an economically viable and an environmentally benign approach Such an ox horn derived carbon (OHC) possesses a large surface area (BET surface area is 1300 m2 g−1), a unique 3D porous nanostructure and a high inherent nitrogen content (55%) The OHC, as an anode material for lithium ion batteries (LIBs), exhibits superior electrochemical performances, such as a high reversible capacity (1181 mA h g−1 at a current density of 100 mA g−1) and a superior rate capability (304 mA h g−1 at 5 A g−1) Furthermore, this study demonstrates the exploitation of a universal material in nature, viz, ox horn, as a potential anode for the most sought after energy storage application

Synthesis of β-Cyclodextrin-Based Electrospun Nanofiber Membranes for Highly Efficient Adsorption and Separation of Methylene Blue

Abstract: Water-insoluble β-cyclodextrin-based fibers were synthesized by electrospinining followed by thermal cross-linking. The fibers were characterized by field-emission scanning electron microscopic (FE-SEM) and Fourier transformed infrared spectrometer (FT-IR). The highly insoluble fraction obtained from different pH values (3-11) indicates successful cross-linking reactions and their usability in aqueous solution. After the cross-linking reaction, the fibers' tensile strength increases significantly and the BET surface area is 19.49 m(2)/g. The cross-linked fibers exhibited high adsorption capacity for cationic dye methylene blue (MB) with good recyclability. The adsorption performance can be fitted well with pseudo-second-order model and Langmuir isotherm model. The maximum adsorption capacity is 826.45 mg/g according to Langmuir fitting. Due to electrostatic repulsion, the fibers show weak adsorption toward negatively charged anionic dye methyl orange (MO). On the basis of the selective adsorption, the fiber membrane can separate the MB/MO mixture solution by dynamic filtration at a high flow rate of 150 mL/min. The fibers can maintain good fibrous morphology and high separation efficiency even after five filtration-regeneration cycles. The obtained results suggested potential applications of β-cyclodextrin-based electrospun fibers in the dye wastewater treatment field.

Biomass-derived nitrogen self-doped porous carbon as effective metal-free catalysts for oxygen reduction reaction

Abstract: Biomass-derived nitrogen self-doped porous carbon was synthesized by a facile procedure based on simple pyrolysis of water hyacinth (eichhornia crassipes) at controlled temperatures (600-800 °C) with ZnCl2 as an activation reagent. The obtained porous carbon exhibited a BET surface area up to 950.6 m(2) g(-1), and various forms of nitrogen (pyridinic, pyrrolic and graphitic) were found to be incorporated into the carbon molecular skeleton. Electrochemical measurements showed that the nitrogen self-doped carbons possessed a high electrocatalytic activity for ORR in alkaline media that was highly comparable to that of commercial 20% Pt/C catalysts. Experimentally, the best performance was identified with the sample prepared at 700 °C, with the onset potential at ca. +0.98 V vs. RHE, that possessed the highest concentrations of pyridinic and graphitic nitrogens among the series. Moreover, the porous carbon catalysts showed excellent long-term stability and much enhanced methanol tolerance, as compared to commercial Pt/C. The performance was also markedly better than or at least comparable to the leading results in the literature based on biomass-derived carbon catalysts for ORR. The results suggested a promising route based on economical and sustainable biomass towards the development and engineering of value-added carbon materials as effective metal-free cathode catalysts for alkaline fuel cells.

Preparation and characterization of activated carbons from Paulownia wood by chemical activation with H3PO4

Abstract: High-surface area activated carbons were prepared by chemical activation of Paulownia (Paulownia elongata) wood with H3PO4 as a chemical activating agent. The chemical activation process was conducted at different impregnation ratios (1–4) and final carbonization temperatures (300–600 °C). The influences of carbonization temperature and impregnation ratio on the surface area, pore development and yield of activated carbon were investigated. The effect of the impregnation ratio on the porous structure of the activated carbon is stronger than that of the final carbonization temperature. H3PO4 was found to be more effective for developing microporous structure in the activated carbon. A final carbonization temperature of 400 °C and impregnation ratio of 4 were found to be suitable for producing high-surface-area activated carbon. The pore properties of the carbons including the BET surface area, pore volume, pore size distribution, and average pore diameter were determined by adsorption of N2 at 77 K using the BET, t-plot and density functional theory (DFT) methods. BET surface area and total pore volume values were achieved as high as 2806 m2/g and 1.746 cm3/g, respectively. Activated carbons were also examined with instrumental methods such as SEM and FTIR.

Mechanism on the sorption of heavy metals from binary-solution by a low cost montmorillonite and its desorption potential

Abstract: The potential of a low-cost Nigerian montmorillonite for the adsorption of Ni(II) and Mn(II) ions from aqueous solution was investigated by batch mode. XRD, SEM and BET analysis were used to characterize the adsorbent. The experiments were performed as a function of pH, particle size, adsorbent dose, initial metal ion concentration, contact time, ligands and temperature. The process was found to be dependent on all the parameters investigated, with a pH of 6.0 obtained for optimum removal of both metal ions. The Langmuir monolayer adsorption capacity of 166.67 and 142.86 mg/g was obtained for Ni(II) and Mn(II) ions respectively. The Freundlich isotherm gave the best fit to the experimental data than the Langmuir, Temkin and Dubinin–Radushkevich isotherms. The scatchard plot analysis indicated the existence of more than one type of active site on the montmorillonite which corroborates the good fit of the Freundlich model. The pseudo-first order, pseudo-second order and intraparticle diffusion models were applied to the kinetic data. The best fit was achieved with the pseudo-first order model and the existence of intraparticle diffusion mechanism was indicated. Thermodynamic studies showed an endothermic, dissociative, spontaneous and a physical adsorption process between the metal ions and the montmorillonite. Desorption studies revealed over 90% desorption of both metal ions from the metal loaded adsorbent.

Adsorption of Methylene Blue by ultrasonic surface modified chitin

Abstract: Hypothesis Chitin is a biopolymer which can be used as a low-cost and eco-friendly material for dyes adsorption. The use of chitin for dyes removal is little investigated, due its low surface area, porosity and high crystallinity. So, an ultrasonic surface modified chitin (USM-chitin) was prepared and used for Methylene Blue (MB) adsorption. Experiments Chitin was obtained from shrimp wastes and its surface was modified by an ultrasound-assisted treatment. USM-chitin was characterized by N2 adsorption/desorption isotherms (BET surface area, total pore volume), infrared spectroscopy, X-ray diffraction and scanning electron microscopy. The adsorption of MB on USM-chitin was studied by kinetic, equilibrium, thermodynamic, interactions analysis, desorption and mass transfer aspects. Findings USM-chitin presented surface area 25 times higher than raw chitin. The porosity was increased and the crystallinity was decreased. The general order model was suitable to represent the adsorption kinetics and the Langmuir model was adequate for the equilibrium. The maximum adsorption capacity was 26.69 mg g−1. The adsorption was spontaneous, favorable and exothermic. USM-chitin can be used seven times maintaining the same adsorption capacity.

N-doped porous carbon capsules with tunable porosity for high-performance supercapacitors

Abstract: A procedure for the fabrication of N-doped hollow carbon spheres with a high rate capability for supercapacitors has been developed. The approach is based on a nanocasting method and the use of a nitrogen-rich compound (pyrrole) as a carbon precursor. The carbon particles thus produced combine a large BET surface area (∼1500 m2 g−1) with a porosity made up of mesopores of ∼4 nm, a high nitrogen content (∼6 wt%) and a capsule morphology which entails short ion diffusion paths derived from the shell morphology (thickness ∼60 nm). The porous properties of these hollow particles can be enhanced by means of an additional activation step with KOH. The activation process does not alter the hollow structure or spherical morphology, but strongly modifies the pore structure from a mesoporous network to a microporous one. The N-doped carbon capsules were tested in aqueous and organic electrolytes. In an aqueous medium (1 M H2SO4), the mesoporous carbon capsules offer the best performance due to the pseudocapacitive contribution of the N-groups, exhibiting a specific capacitance of ∼240 F g−1 at 0.1 A g−1 and a capacitance retention as high as 72% at 80 A g−1. In contrast, in an organic electrolyte (1 M TEABF4/AN), where the charge storage mechanism is based on the formation of the electric double-layer, the microporous capsules perform better due to the larger specific surface area. Thus, the microporous carbon capsules display a specific capacitance of up to 141 F g−1 at 0.1 A g−1 and an outstanding capacitance retention of 93% for an ultra-high discharge current density of 100 A g−1.

3D flower- and 2D sheet-like CuO nanostructures: Microwave-assisted synthesis and application in gas sensors

Abstract: 3D flower- and 2D branching sheet-like CuO nanostructures have been synthesized by a microwave-assisted hydrothermal method. The samples were characterized through X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), infrared spectroscopy (IR), UV–vis diffuse reflectance spectroscopy (UV-DRS), and Brunauer–Emmett–Teller (BET) specific surface area analysis. The phase and morphology observations showed the formation of monoclinic CuO nanostructures with well-defined morphology. BET analysis displayed that the measured surface area was 15.0 m 2 g −1 for CuO flowers, and 20.8 m 2 g −1 for CuO nanosheets. Gas sensing properties of the as-synthesized CuO nanostructures were evaluated by the detection of volatile and toxic gases including ethanol, ethyl-acetate, acetone, xylene, and toluene. It was found that CuO flowers exhibited an enhanced gas response to the five gases at 260 °C, compared to CuO nanosheets. Furthermore, at 1000 ppm, the CuO flower sensor gave a higher response to ethyl-acetate ( R g / R a = 4.6) and ethanol ( R g / R a = 4.0), in comparison with toluene ( R g / R a = 2.8). In addition, the CuO flowers displayed a rapid response and recovery as well as good reproducibility.

Surface Area: Brunauer–Emmett–Teller (BET)

Abstract: The BET equation is used for determining the surface area of solids from the nitrogen sorption isotherm at liquid nitrogen temperatures, but the equation has also been used with a wide range of other gases and vapours. This chapter describes details of methods employed for measuring BET surface area of solid materials at ambient temperature and pressure.

An Azine‐Linked Covalent Organic Framework: Synthesis, Characterization and Efficient Gas Storage

Abstract: A azine-linked covalent organic framework, COF-JLU2, was designed and synthesized by condensation of hydrazine hydrate and 1,3,5-triformylphloroglucinol under solvothermal conditions for the first time. The new covalent organic framework material combines permanent micropores, high crystallinity, good thermal and chemical stability, and abundant heteroatom activated sites in the skeleton. COF-JLU2 possesses a moderate BET surface area of over 410 m(2) g(-1) with a pore volume of 0.56 cm(3) g(-1) . Specifically, COF-JLU2 displays remarkable carbon dioxide uptake (up to 217 mg g(-1) ) and methane uptake (38 mg g(-1) ) at 273 K and 1 bar, as well as high CO2 /N2 (77) selectivity. Furthermore, we further highlight that it exhibits a higher hydrogen storage capacity (16 mg g(-1) ) than those of reported COFs at 77 K and 1 bar.

Characterization and Properties of Activated Carbon Prepared from Tamarind Seeds by KOH Activation for Fe(III) Adsorption from Aqueous Solution.

Abstract: This research studies the characterization of activated carbon from tamarind seed with KOH activation. The effects of 0.5 : 1-1.5 : 1 KOH : tamarind seed charcoal ratios and 500-700°C activation temperatures were studied. FTIR, SEM-EDS, XRD, and BET were used to characterize tamarind seed and the activated carbon prepared from them. Proximate analysis, percent yield, iodine number, methylene blue number, and preliminary test of Fe(III) adsorption were also studied. Fe(III) adsorption was carried out by 30 mL column with 5-20 ppm Fe(III) initial concentrations. The percent yield of activated carbon prepared from tamarind seed with KOH activation decreased with increasing activation temperature and impregnation ratios, which were in the range from 54.09 to 82.03 wt%. The surface functional groups of activated carbon are O-H, C=O, C-O, -CO3, C-H, and Si-H. The XRD result showed high crystallinity coming from a potassium compound in the activated carbon. The main elements found in the activated carbon by EDS are C, O, Si, and K. The results of iodine and methylene blue adsorption indicate that the pore size of the activated carbon is mostly in the range of mesopore and macropore. The average BET pore size and BET surface area of activated carbon are 67.9764 A and 2.7167 m(2)/g, respectively. Finally, the tamarind seed based activated carbon produced with 500°C activation temperature and 1.0 : 1 KOH : tamarind seed charcoal ratio was used for Fe(III) adsorption test. It was shown that Fe(III) was adsorbed in alkaline conditions and adsorption increased with increasing Fe(III) initial concentration from 5 to 20 ppm with capacity adsorption of 0.0069-0.019 mg/g.

CuO nanoparticles encapsulated inside Al-MCM-41 mesoporous materials via direct synthetic route

Abstract: Highly ordered aluminum-containing mesoporous silica (Al-MCM-41) was prepared using attapulgite clay mineral as a Si and Al source. Mesoporous complexes embedded with CuO nanoparticles were subsequently prepared using various copper sources and different copper loadings in a direct synthetic route. The resulting CuO/Al-MCM-41 composite possessed p6mm hexagonally symmetry, well-developed mesoporosity, and relatively high BET surface area. In comparison to pure silica, these mesoporous materials embedded with CuO nanoparticles exhibited smaller pore diameter, thicker pore wall, and enhanced thermal stability. Long-range order in the aforementioned samples was observed for copper weight percentages as high as 30%. Furthermore, a significant blue shift of the absorption edge for the samples was observed when compared with that of bulk CuO. H2-TPR measurements showed that the direct-synthesized CuO/Al-MCM-41 exhibited remarkable redox properties compared to the post-synthesized samples, and most of the CuO nanoparticles were encapsulated within the mesoporous structures. The possible interaction between CuO and Al-MCM-41 was also investigated.

Ultralight carbon aerogel from nanocellulose as a highly selective oil absorption material

Abstract: The synthesis of a sponge-like carbon aerogel from microfibril cellulose, with high porosity (99 %), ultra-low density (0.01 g/cm3), hydrophobic properties (149° static contact angle) and reusability is reported in this paper. The physical properties, internal morphology, thermal properties, and chemical properties of carbon aerogels heat-treated at 700 and 900 °C (Samples C-700 and C-900) were examined. Stabilization and carbonization parameters were optimized in terms of residual carbon yield. The BET surface area of Sample C-700 (521 m2/g) was significantly higher than of Sample C-950 (145 m2/g). Graphitic-like domains were observed in C-950. The highest normalized sorption capacity (86 g/g) for paraffin oil was observed in sample C-700. The removal of hydrophilic function groups during carbonization causes carbon aerogel to present highly hydrophobic properties. Carbon aerogel’s ability to absorb oil is enhanced by its highly porous 3D network structure with interconnected cellulose nanofibrils.