Showing papers on "BET theory published in 2013"

Comparative study of methylene blue dye adsorption onto activated carbon, graphene oxide, and carbon nanotubes

Abstract: Three different carbonaceous materials, activated carbon, graphene oxide, and multi-walled carbon nanotubes, were modified by nitric acid and used as adsorbents for the removal of methylene blue dye from aqueous solution. The adsorbents were characterized by N2 adsorption/desorption isotherms, infrared spectroscopy, particle size, and zeta potential measurements. Batch adsorption experiments were carried out to study the effect of solution pH and contact time on dye adsorption properties. The kinetic studies showed that the adsorption data followed a pseudo second-order kinetic model. The isotherm analysis indicated that the adsorption data can be represented by Langmuir isotherm model. The remarkably strong adsorption capacity normalized by the BET surface area of graphene oxide and carbon nanotubes can be attributed to π–π electron donor acceptor interaction and electrostatic attraction.

Facile synthesis of nitrogen-doped porous carbon for supercapacitors

Abstract: A very simple, activation-free method for preparing nitrogen-doped porous carbon with high surface area for supercapacitors by direct pyrolysis of a nitrogen-containing organic salt, ethylenediamine tetraacetic acid (EDTA) disodium magnesium salt, in an inert atmosphere is presented. As the pyrolysis temperature increases from 500 to 900 °C, both the BET surface area and pore volume of the disodium magnesium EDTA-derived carbons increase and reach up to 1811 m2 g−1 and 1.16 cm3 g−1, respectively, while the nitrogen content decreases from 11.14 at.% to 1.13 at.%. The carbon obtained at a moderate pyrolysis temperature of 700 °C possesses a balanced surface area (1258 m2 g−1) and nitrogen content (5.43 at.%), exhibits high capacitance (281 F g−1), good rate capability (196 F g−1 at 20 A g−1) and cycle durability in 6 mol L−1 KOH aqueous electrolytes.

Size- and morphology-controlled NH2-MIL-53(Al) prepared in DMF–water mixed solvents

Abstract: We present here a simple solvothermal method to fabricate metal–organic framework NH2-MIL-53(Al) crystals with controllable size and morphology just by altering the ratio of water in the DMF–water mixed solvent system without the addition of any surfactants or capping agents. With increasing the volume ratio of water in the mixed solvents, a series of NH2-MIL-53(Al) crystals with different sizes and morphologies were synthesized. The average size of the smallest crystal is 76 ± 20 nm, which provides us a simple and environmentally friendly way to prepare nanoscale MOFs. The largest BET surface area of these samples is 1882 m2 g−1 that is mainly contributed by its micropore surface area, and its corresponding micropore volume is 0.83 cm3 g−1, which have greatly extended its application in the fields of gas adsorption and postsynthetic modification. All these samples were characterized by SEM, XRD, N2 adsorption/desorption, TGA and FT-IR. Then a mechanism for the impact of the water ratio on the crystal size and morphology is presented and discussed.

Highly stable nanoporous covalent triazine-based frameworks with an adamantane core for carbon dioxide sorption and separation

Abstract: Adamantane substituted with two to four 4-cyanophenyl groups was used for preparation of a new series of robust Porous Covalent Triazine-based Framework (PCTF) materials. Novel adamantane PCTFs were synthesized in good yields (>80%) by the trimerization reaction of 1,3-bis-, 1,3,5-tris- and 1,3,5,7-tetrakis(4-cyanophenyl)adamantane, respectively, in the presence of ZnCl2 (Lewis acid condition) and CF3SO3H (strong Bronsted acid condition). From N2 adsorption isotherms, the Lewis acid condition gives higher surface areas than the strong Bronsted acid condition. The amorphous nano- to microporous frameworks (>50% micropore fraction) exhibit excellent thermal stabilities (>450 °C) with BET surface areas up to 1180 m2 g−1. A very similar ultramicropore size distribution between 4 and 10 A was derived from CO2 adsorption isotherms with a “CO2 on carbon based slit-pore model”. At 1 bar the gases H2 (at 77 K), CO2 (at 273 and 293 K) and CH4 (at 273 K) are adsorbed up to 1.24 wt%, 58 cm3 g−1 and 20 cm3 g−1, respectively. Gas uptake increases with BET surface area and micropore volume which in turn increase with the number of cyano groups in the monomer. From single component adsorption isotherms, IAST-derived ideal CO2:N2, CO2:CH4 and CH4:N2 selectivity values of up to 41 : 1, 7 : 1 and 6 : 1, respectively, are calculated for p → 0 at 273 K. The adamantane PCTFs have isosteric heats of adsorption for CO2 of 25–28 kJ mol−1 at zero loading and most of them also >25 kJ mol−1 over the entire adsorption range which is well above the heat of liquefaction of bulk CO2 or the isosteric enthalpy of adsorption for CO2 on activated carbons.

Enhancement of CO2 Adsorption and CO2/N2 Selectivity on ZIF‐8 via Postsynthetic Modification

Abstract: Imidazolate framework ZIF-8 is modified via postsynthetic method using etheylenediamine to improve its adsorption performance toward CO2. Results show that the BET surface area of the modified ZIF-8 (ED-ZIF-8) increases by 39%, and its adsorption capacity of CO2 per surface area is almost two times of that on ZIF-8 at 298 K and 25 bar. H2O uptake on the ED-ZIF-8 become obviously lower compared to the ZIF-8. The ED-ZIF-8 selectivity for CO2/N2 adsorption gets significantly improved, and is up to 23 and 13.9 separately at 0.1 and 0.5 bar, being almost twice of those of the ZIF-8. The isosteric heat of CO2 adsorption (Qst) on the ED-ZIF-8 becomes higher, while Qst of N2 gets slightly lower compared to those on the ZIF-8 Furthermore, it suggests that the postsynthetic modification of the ZIF-8 not only improves its adsorption capacity of CO2 greatly, but also enhances its adsorption selectivity for CO2/N2/H2O significantly. ©2013 American Institute of Chemical Engineers AIChE J, 59: 2195–2206, 2013

Zeolitic imidazolate framework (ZIF)-derived, hollow-core, nitrogen-doped carbon nanostructures for oxygen-reduction reactions in PEFCs

Abstract: The facile synthesis of a porous carbon material that is doped with iron-coordinated nitrogen active sites (FeNC-70) is demonstrated by following an inexpensive synthetic pathway with a zeolitic imidazolate framework (ZIF-70) as a template. To emphasize the possibility of tuning the porosity and surface area of the resulting carbon materials based on the structure of the parent ZIF, two other ZIFs, that is, ZIF-68 and ZIF-69, are also synthesized. The resulting active carbon material that is derived from ZIF-70, that is, FeNC-70, exhibits the highest BET surface area of 262 m(2) g(-1) compared to the active carbon materials that are derived from ZIF-68 and ZIF-69. The HR-TEM images of FeNC-70 show that the carbon particles have a bimodal structure that is composed of a spherical macroscopic pore (about 200 nm) and a mesoporous shell. X-ray photoelectron spectroscopy (XPS) reveals the presence of Fe-N-C moieties, which are the primary active sites for the oxygen-reduction reaction (ORR). Quantitative estimation by using EDAX analysis reveals a nitrogen content of 14.5 wt.%, along with trace amounts of iron (0.1 wt.%), in the active FeNC-70 catalyst. This active porous carbon material, which is enriched with Fe-N-C moieties, reduces the oxygen molecule with an onset potential at 0.80 V versus NHE through a pathway that involves 3.3-3.8 e(-) under acidic conditions, which is much closer to the favored 4 e(-) pathway for the ORR. The onset potential of FeNC-70 is significantly higher than those of its counterparts (FeNC-68 and FeNC-69) and of other reported systems. The FeNC-based systems also exhibit much-higher tolerance towards MeOH oxidation and electrochemical stability during an accelerated durability test (ADT). Electrochemical analysis and structural characterizations predict that the active sites for the ORR are most likely to be the in situ generated N-FeN(2+2)/C moieties, which are distributed along the carbon framework.

Surfactant assisted Ce–Fe mixed oxide decorated multiwalled carbon nanotubes and their arsenic adsorption performance

Abstract: In this study, a novel mixed Ce–Fe oxide decorated multiwalled carbon nanotubes (CF-CNTs) material was prepared through a surfactant assisted method. The CF-CNTs material was characterized by various methods, including BET surface area analysis, transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). It was found that the Ce–Fe oxide was uniformly dispersed on the surface of CNTs with a mean size of 7.0 nm. The obtained CF-CNTs material was used as an adsorbent to remove arsenic from aqueous solutions. The adsorption experimental results showed that this CF-CNTs material had an excellent adsorption performance for As(V) and As(III). The adsorption processes of As(V) and As(III) could be well described by the pseudo-second-order model. The mechanistic study showed that different interactions were involved in As(V) adsorption, including electrostatic attraction and surface complexation. For As(III) adsorption, partial As(III) was oxidized to As(V) followed by the simultaneous adsorption of As(V) and As(III). It was also found that intra-particle diffusion existed in the process of adsorption on CF-CNTs, but that it was not the only rate-limiting step. The resulting CF-CNTs material can be used in a broad pH range, which suggests its great potential for the decontamination of arsenic-polluted water.

Energy Storage Studies on InVO4 as High Performance Anode Material for Li-Ion Batteries

Abstract: InVO4 has attracted much attention as an anode material due to its high theoretical capacity. However, the effect of preparation methods and conditions on morphology and energy storage characteristic has not been extensively investigated and will be explored in this project. InVO4 anode material was prepared using five different preparation methods: solid state, urea combustion, precipitation, ball-milling, and polymer precursor methods. Morphology and physical properties of InVO4 were then analyzed using X-ray diffraction (XRD), scanning electron microscope (SEM), and Brunauer–Emmett–Teller (BET) surface area method. XRD patterns showed that orthorhombic phased InVO4 was synthesized. Small amounts of impurities were observed in methods II, III, and V using XRD patterns. BET surface area ranged from 0.49 to 9.28 m2 g–1. SEM images showed slight differences in the InVO4 nanosized crystalline structures with respect to preparation methods and conditions. Energy storage studies showed that, among all the pre...

Preparation of activated carbon from cotton stalk and its application in supercapacitor

Abstract: High specific capacitance and low cost are the critical requirements for a practical supercapacitor. In this paper, a new activated carbon with high specific capacitance and low cost was prepared, employing cotton stalk as the raw material, by using the phosphoric acid (H3PO4) chemical activation method. The optimized conditions were as follows: the cotton stalk and activating agent with a mass ratio of 1:4 at an activation temperature of 800 °C for 2 h. The samples were characterized by nitrogen adsorption isotherms at 77 K. The specific surface area and pore volume of activated carbon were calculated by Brunauer–Emmett–Teller (BET) and t-plot methods. With these experimental conditions, an activated carbon with a BET surface area of 1,481 cm2 g−1 and micropore volume of 0.0377 cm3 g−1 was obtained. The capacitance of the prepared activated carbon was as high as 114 F g−1.The results indicate that cotton stalk can produce activated carbon electrode materials with low cost and high performance for electric double-layer capacitor.

Biobased chitosan hybrid aerogels with superior adsorption: Role of graphene oxide in CO2 capture

Abstract: Currently extensive research is focused on developing and designing novel porous materials for clean energy and environmental applications such as reducing the emission of carbon dioxide (CO2). In this work, hybrid monolith aerogels of chitosan (CTS), an environmentally-benign biopolymer, with different amounts of graphene oxide (GO) are prepared using freeze-drying. The sorption performance of the developed aerogels for CO2 capture is studied. The aerogels are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and nitrogen adsorption–desorption measurements. Homogeneous dispersion of GO in CTS is studied beyond the particle concentration where agglomeration takes place. The effects of GO on the specific surface area of the aerogels and CO2 capture are investigated and shown to increase with GO content. The BET surface area is dramatically increased from 153 to 415 m2 g−1 by loading 20 wt% GO into the CTS adsorbent. The amount of CO2 adsorbed at 25 °C increases from 1.92 to 4.15 mol kg−1 with the addition of 20 wt% GO. Adsorption–desorption cycles exhibit the stability of the hybrid aerogels during prolonged cyclic operations, suggesting excellent potential for CO2 capture technology.

Gelatin-derived nitrogen-doped porous carbon via a dual-template carbonization method for high performance supercapacitors

Abstract: High performance nitrogen-doped porous carbon for supercapacitors, named as Gelatin–Mg–Zn-1 : 5 : 3, has been successfully prepared via a dual-template carbonization method, without any physical/chemical activation process, in which gelatin serves as both carbon/nitrogen source, and low cost Mg(NO3)2·6H2O and Zn(NO3)2·6H2O as dual templates. It is revealed that the carbonization temperature, and the mass ratio of gelatin–Mg(NO3)2·6H2O–Zn(NO3)2·6H2O plays a crucial role in the determination of surface area, pore structure and the correlative capacitive behavior of the Gelatin–Mg–Zn-1 : 5 : 3 sample. It displays a high BET surface area of 1518 m2 g−1, large total pore volume of 4.27 cm3 g−1, and large average pore width of 11.3 nm. In a three electrode system, using 6 mol L−1 KOH solution as electrolyte, we can achieve a high specific capacitance of ca. 284.1 F g−1 at a current density of 1 A g−1 and high capacitance retention of ca. 31.2% is obtained at 150 A g−1, indicating high rate capability. It also possesses a high capacitance retention of ca. 96.1% even after charging/discharging for 10 000 cycles. More importantly, a two electrode system, using [EMIm]BF4/AN (weight ratio of 1 : 1) as electrolyte, has been adopted for the Gelatin–Mg–Zn-1 : 5 : 3 sample with different operation temperatures of 25/50/80 °C. As a result, wide voltage windows, broad operation temperatures, and high cycling stability achieved in the two electrode system make it possible for practical application under extreme conditions.

Synthesis of nano-sized spherical Mg3Al–CO3 layered double hydroxide as a high-temperature CO2 adsorbent

Abstract: Due to its layered structure, layered double hydroxides (LDHs) generally prefer to form either “sand rose” or platelet-like morphologies. To the best of our knowledge, nano-sized spherical LDHs have not been previously reported. In this work, we present the first successful synthesis of nano-sized spherical Mg3Al–CO3 LDH using a facile isoelectric point (IEP) method. SEM and TEM analyses confirmed that the size of the nanospheres is very uniform, with an average value of ca. 20 nm. Furthermore, a mesoporous LDH sample composed of the above synthesized uniform nano-spheres can be prepared, and this material showed a H1 type hysteresis loop in the N2 BET analysis. Such mesoporous LDH possesses large mesopores (18 nm) and a high surface area (103 m2 g−1), which we believe make it a promising adsorbent, catalyst, or support material. We demonstrated that its CO2 capture capacity is 0.83 mmol g−1 at 200 °C and 1 atm and it can be further increased up to 1.21 mmol g−1 by doping with 20 wt% K2CO3.