Nitrogen Sorption Analysis Research Articles

Synthesis and properties of organic microporous polymers from the monomer of hexaphenylbenzene based triptycene

An expanded triptycene (hexaphenylbenzene based triptycene) monomer was synthesized from triiodotriptycene. Using this monomer, two kinds of organic microporous polymers HTPs (HTP-A and HTP-B) were prepared by Friedel–Crafts and Scholl reactions. Their structure and properties were characterized by FT-IR, solid 13C NMR, powder XRD, SEM, TEM and gas absorption. Nitrogen sorption analysis displayed that the BET surface areas are 569 and 914 m2 g−1 for HTP-A and HTP-B, respectively. For HTP-B, they can reversibly absorb 1.09 wt % H2 (1.0 bar and 77 K) and 10.3 wt% CO2 (1.0 bar and 273 K), respectively.

Effects of Porosity and Amount of Surface Hydroxyl Groups of a Porous TiO2 Layer on the Performance of a CH3NH3PbI3 Perovskite Photovoltaic Cell

The structural and physicochemcal properties of a porous titanium oxide layer (pTiO2) in CH3NH3PbI3 perovskite photovoltaic cells were systematically investigated by Raman spectroscopy, nitrogen sorption, and temperature desorption spectroscopy analyses. When the heat treatment temperature (TpTO) during the fabrication of pTiO2 was changed from 400 to 700 °C, its porosity and amount of surface hydroxyl groups were varied without alteration of the crystalline structure (anatase). Power conversion efficiencies (PCEs) of solar cells based on pTiO2 prepared at different temperatures showed a volcanic-like pattern depending on TpTO of pTiO2; the highest PCE was obtained by using pTiO2 prepared at TpTO of 550 °C. Structural analyses of the CH3NH3PbI3 perovskite part performed by X-ray diffraction indicated that formation of CH3NH3PbI3 perovskite was inhibited by the presence of a large amount of surface hydroxyl groups on pTiO2 prepared at relatively low TpTO (<550 °C). On the other hand, significant reduction of porosity of pTiO2 occurred when pTiO2 was prepared at relatively high TpTO (>550 °C) because of extinction of micropores and sintering between the TiO2 particles; such a structural alteration hindered the penetration of CH3NH3I into the pore channel of TiO2 filled by PbI2, resulting in a large amount of PbI2 remaining in the finally obtained photovoltaic cell. Hence, the optimum TpTO (550 °C) for fabrication of pTiO2 should be determined by its porous nature and sufficient removal of surface hydroxyl groups.

Origin of High Areal Capacitances of Low Apparent Surface Area Carbons

The energy storage mechanism of low apparent specific surface carbons derived from direct pyrolysis of biomass or N-rich polymers has puzzled the researchers in the supercapacitor field in recently years. In order to explore this scientific problem, such carbon materials were prepared through pyrolysis of seaweed and nitrogen-rich polymers such as melamine formaldehyde resin and polyaniline. The chemical and physical properties of these carbons were investigated intensively by nitrogen sorption analysis, CO2 sorption analysis, X-ray photoelectron spectroscopy and X-ray diffraction. Besides, the capacitive properties of these carbon materials were investigated by galvanostatic charge-discharge, cyclic voltammetry and electrochemical impedance spectroscopy. The results show that all the carbons derived from direct pyrolysis of seaweed or polymers possess low apparent specific surface areas of no more than 60 m2 g-1, and their areal capacitance could reach up to an abnormally high value of 252 μF cm-2. Combining the results of systematical pore structure analyses and electrochemical measurements, it was found that these carbons contain numerous ultramicpores which could not be detected by the adsorbate of N2 but are accessible to CO2 and electrolyte ions. These ultramicropores play dominant roles in the charge storage process for these low apparent surface area carbons. We concluded that the energy storage mechanism of these carbons is mainly electric double layer capacitance and that the contribution of pseudocapacitance to the total capacitance is less than 15 %. This finding challenges the widely accepted viewpoint that the high capacitance of O-rich or N-doped carbon is mainly attributed to the pseudocapacitance generated from the faradic reactions between oxygen or nitrogen functionalities and electrolyte.

Hydrophobicity of amorphous silica-based inorganic-organic hybrid materials derived from perhydropolysilazane chemically modified with alcohols

Perhydropolysilazane (PHPS) was chemically modified with various alcohols (ROH, RCH3, n-C3H7, n-C5H11, n-C10H21, CH3OC2H4 or C2H5OC2H4) at a PHPS (Si basis) to ROH molar ratio of 3:1. The resulting alkoxy group-functionalized PHPS materials were successfully converted to amorphous silica-based inorganic-organic hybrids by exposure to vapour from aqueous ammonia at room temperature. Nitrogen sorption analyses demonstrated that these hybrids contained a small quantity of micropores less than 0.9 nm in size along with mesopores having a relatively wide pore size distribution (PSD). The PSD plots of the CH3O, CH3OC2H4O and C2H5OC2H4O functionalized samples had especially wide distributions extending to more than 50 nm. Water sorption tests showed that the hybrid synthesized from PHPS modified with n-C10H21OH was stable and did not exhibit significant capillary condensation even at higher levels of humidity above P/Po = 0.6. As a result, the number of water molecules adsorbed per square nanometre of the sample surface area at P/Po = 0.95 was as low as 4 mol nm−2. The relatively low density of hydrophilic silanol groups (0.21), smaller average mesopore size (3.3 nm) and longer hydrophobic alkyl chain of the n-C10H21O moiety were all thought to contribute to improving the hydrophobicity of this hybrid. These results indicate that n-C10H21OH is a useful alcohol modifier for synthesizing amorphous silica-based inorganic-organic hybrid materials with improved hydrophobic properties through a polymer precursor route.

Mechanically robust aerogels derived from an amine-bridged silsesquioxane precursor

A novel bridged silsesquioxane (BSQ) monomer was synthesized from 3-(2,3-epoxypropoxy)propyltrimethoxysilane and (3-aminopropyl)trimethoxysilane based on the reaction between epoxy and amine groups. The monomer was used to fabricate aerogels with excellent mechanical properties via sol–gel processes followed by supercritical CO2 drying. The influence of the sol–gel conditions on the chemical structure, morphology and mechanical property of the aerogels was investigated by NMR, TGA, SEM, nitrogen sorption analysis and DMA. BSQ aerogels prepared from the optimal sol–gel procedure showed excellent properties with high mechanical performance (compression modulus of 20.4 MPa) and low density (0.22 g cm−3), which are of great advantage for practical applications. Further, SiO2/BSQ composite aerogels with significantly improved mechanical performance than SiO2 aerogels can be obtained by co-condensing of BSQ monomer and tetraethoxysilane. The abundant hydroxyl groups in the BSQ precursor are believed to contribute to the robustness of BSQ and SiO2/BSQ composite aerogels due to the strengthened skeleton via the intermolecular H-bonds.

Enhanced dye loading-light harvesting TiO2 photoanode with screen printed nanorod-nanoparticles assembly for highly efficient solar cell

Morphology tailored TiO2 nano assemblies consisting of nanorods with and without nanoparticle attachments were hydrothermally synthesized and their characteristics and light scattering properties were determined by x-ray diffraction (XRD), nitrogen sorption analysis, scanning electron microscopy (SEM), transmission electron microscopy (TEM), electrochemical impedance spectroscopy (EIS) and ultraviolet–visible spectroscopy (UV–Vis). The nanorod-nanoparticles (NR-NP) assemblies and smooth nanorod (NR) double layers were screen printed onto fluorine doped tin oxide coated glass underlayers to fabricate dye-sensitized solar cell (DSSC) photoanodes. The double layer heterogeneous hierarchical NR-NP decoration had wide Brunauer–Emmett–Teller (BET) area which resulted in 45.1% dye loading capacity, 18.96mAcm−2 photocurrent and average photoanode efficiency of 8.07% which was 21% greater than NRs photoanode efficiency. Distinct NR-NPs morphology indicated multiple wave trapping and strong light scattering which was as high as 89.2%. Improvements in NR-NPs DSSCs performance were obtained because of lower resistance to charge transfer (10.07Ω) and faster diffusion of electrolyte ions (1.22Mho).

Meso-Structuring of SiCN Ceramics by Polystyrene Templates.

A simple one-pot synthesis of well-defined PS-silazane nano-composites (polystyrene, PS) is described. In contrast to the, thus far, used two-step procedure ((1) assembly of a PS template bed and (2) careful filling of the voids between the PS spheres), which is restricted to macro structuring, we are able to simply mix the PS template and a commercially available silazane precursor HTT-1800 in toluene. The key is the alteration of the zeta potential of the PS template leading to a homogeneous dispersion in the silazane-toluene mixture. Removal of solvent gives rise to a highly ordered PS-silazane nano-composites and subsequent pyrolysis leads to mesoporous silicon carbonitride (SiCN) materials. The one-pot procedure has two advantages: easy upscaling and the use of PS spheres smaller than 100 nm in diameter, here 60 nm. The PS template was characterized by photon correlation spectroscopy, zeta potential measurements, scanning electron microscopy (SEM), and thermal gravimetric analysis (TGA). The resulting mesoporous SiCN materials were analyzed by SEM, transmission electron microscopy (TEM), nitrogen sorption analysis, and Fourier transform infrared measurements (FT-IR).

Tungstate Supported on Periodic Mesoporous Organosilica with Imidazolium Framework as an Efficient and Recyclable Catalyst for the Selective Oxidation of Sulfides.

A catalyst based on immobilization of tungstate ions (WO4 2- ) inside the mesochannels of periodic mesoporous organosilica comprising bridged ionic liquid (1,3-bis(3-trimethoxysilylpropyl)imidazolium chloride) has been synthesized and characterized. This catalyst was then employed for the selective oxidation of organic sulfides to the corresponding sulfoxides or sulfones. The final synthesized catalyst was characterized by various techniques such as nitrogen sorption analysis, transmission electron microscopy, and thermogravimetric analysis. The catalyst was also applied to the selective oxidation of sulfides containing readily oxidizable functional groups such as hydroxyl, allylic, and even challenging aliphatic sulfides. Interestingly, it was found that on changing the reaction medium from aqueous methanol to aqueous acetonitrile, the product selectivity was changed successfully from sulfoxide to sulfone with good to excellent yields. Moreover, the catalyst can also be recovered and reused efficiently in nine subsequent reaction cycles without any remarkable decrease in the catalyst activity and selectivity.

Novel one-pot synthesis of hierarchically porous Pd/C monoliths by a co-gelation method

Abstract

Preparation and characterization of silica aerogel-ZIF-8 hybrid materials

A novel silica aerogels hybrid material with two different proportions of Zeolitic imidazolate frameworks (ZIF-8) is prepared using a conventional sol–gel process. The ZIF-8 has tunable pores and functionalities, and usually exhibit high surface areas. The synthesized materials are denoted as SA-ZIF-8(x), were characterized by XRD, nitrogen sorption analysis, Elemental analysis and HR-TEM techniques. The textural investigations reveal that hybrid materials with a wide variation in their pore characteristics can be synthesized by varying ZIF-8 content in the sol. The BET surface area was found to be in the range of 563–540m2g−1. The potential applications of silica aerogels (SA) ZIF-8 hybrid materials covers a wide range of fields are related to pore sizes and structures.

Preparation of Nitrogen and Sulfur dual-doped Mesoporous Carbon for Supercapacitor Electrodes with Long Cycle Stability

Nitrogen and sulfur dual-doped mesoporous carbons (NSMCs) have been fabricated through a facile template-mediated pyrolyzing method using poly(ethyleneimine) (PEI) as sources of nitrogen (N) and carbon (C), ferrous sulfate(FeSO4 7H2O) as both precursor of sulfur (S) and activation reagent along with nanoscaled silica as sacrificial supports. The composition, morphology, and microstructure of the products are characterized using X-ray diffraction, scanning electron microscopy, nitrogen sorption analysis and X-ray photoelectron spectroscopy. It reveals that these NSMCs possess a BET surface area over 1064m2g−1and abundant mesoporous structure with pore size ranged from 4 to 20nm. The atomic percentages of N and S functionalities are found to be 4.00at.% N and 0.83at.% S, indication of successful incorporation of both nitrogenand sulfur into carbon network. Benefiting from the aforementioned characteristics, these NSMCs show perfect supercapacitive performances, which have been demonstrated by cyclic voltammetry and constant-current charge/discharge cycling techniques. In 0.5M H2SO4 electrolyte, the specific capacitance (SC) of the as-prepared NSMCs electrode can reach 280F/g at a current density of 1A/g. Even at a high rate capability of 100A/g, the NSMCs electrode still shows the SC value as high as 232F/g, retaining 83% of that at 1A/g. Also, the electrode exhibits excellent charge/discharge cycling stability, and no measurable capacitance losses is observed even after 5000 cycles, making them potentially promising for high-performance energy storage devices.

Direct decomposition of methane over SBA-15 supported Ni, Co and Fe based bimetallic catalysts

Thermocatalytic decomposition of methane is an alternative route for the production of COx-free hydrogen and carbon nanomaterials. In this work, a set of novel Ni, Co and Fe based bimetallic catalysts supported over mesoporous SBA-15 was synthesized by a facile wet impregnation route, characterized for their structural, textural and reduction properties and were successfully used for the methane decomposition. The fine dispersion of metal oxide particles on the surface of SBA-15, without affecting its mesoporous texture was clearly shown in the low angle X-ray diffraction patterns and the transmission electron microscopy (TEM) images. The nitrogen sorption analysis showed the reduced specific surface area and pore volume of SBA-15, after metal loading due to the partial filling of hexagonal mesopores by metal species. The results of methane decomposition experiments indicated that all of the bimetallic catalysts were highly active and stable for the reaction at 700°C even after 300min of time on stream (TOS). However, a maximum hydrogen yield of ∼56% was observed for the NiCo/SBA-15 catalyst within 30min of TOS. A high catalytic stability was shown by the CoFe/SBA-15 catalyst with 51% of hydrogen yield during the course of reaction. The catalytic stability of the bimetallic catalysts was attributed to the formation of bimetallic alloys. Moreover, the deposited carbons were found to be in the form of a new set of hollow multi-walled nanotubes with open tips, indicating a base growth mechanism, which confirm the selectivity of SBA-15 supported bimetallic catalysts for the formation of open tip carbon nanotubes. The Raman spectroscopic and thermogravimetric analysis of the deposited carbon nanotubes over the bimetallic catalysts indicated their higher graphitization degree and oxidation stability.

Synthesis of microporous amorphous silica from perhydropolysilazane chemically modified with alcohol derivatives

Perhydropolysilazane (PHPS) was chemical modified with alcohol derivative (ROH, R = CH3, i-C3H7, n-C5H11, n-C10H21) at the silicon (Si) of PHPS/ROH molar ratio of 4/1. The alkoxy group-functionalized PHPS was converted into amorphous silica powders by curing at 270°C to promote oxidative crosslinking, followed by pyrolysis at 600°C in air to complete the polymer/amorphous silica conversion. Thermogravimetric analysis in air of the 270°C-crosslinked PHPS showed an approximately 18%weight gain at 200 to 500°C. This weight gain was suppressed consistently with the number of carbon atoms of the alkoxy groups introduced to PHPS. Upon heating to 600°C, the PHPS modified with n-C5H11OH showed a total weight loss of 12%, and further weight loss of 31%was observed for the PHPS modified with n-C10H21OH. The nitrogen sorption analysis revealed that micropore volume of the polymer-derived amorphous silica increased consistently with the weight loss during the pyrolysis up to 600°C, and the amorphous silica derived from the PHPS modified with n-C10H21OH exhibited the highest micropore volume. Further increase in the micropore volume was achieved by increasing the Si/n-C10H21OH molar ratio from 4/1 to 2/1. The micropore volume and specific surface area of the resulting amorphous silica powders were 0.193 cm3/g and 370m2/g, respectively.

Pd–Ti-MCM-48 cubic mesoporous materials for solar simulated hydrogen evolution

A facile synthetic method (in as little as four hours) for simultaneously loading high amounts of titania (Si/Ti = 3) and Pd0 co-catalyst (0.1 wt.% per gram of total catalyst) in cubic mesoporous MCM-48 material was developed at room temperature. The solar simulated photocatalytic hydrogen evolution from photocatalysts containing Pd0 and TiO2 nanoclusters in periodic cubic MCM-48 and aperiodic mesoporous silica was compared. The results indicate that the periodicity of the mesoporous silica support, the oxidation state of Pd, the location and dispersion of Pd0 have a significant impact on the photocatalytic activity. Periodic cubic MCM-48 mesoporous silica containing Pd0 in close contact with titania exhibit superior hydrogen evolution rates compared to Pd0-TiO2 containing aperiodic mesoporous silica. The highly ordered and open three-dimensional mesoporous cubic MCM-48 support has high surface area and facilitate good dispersion and close contact of titania and Pd0. At very low loadings of 0.1 wt.% of Pd, hydrogen yield was found to be 560 μ mol h−1, which is among the highest reported in the literature for Pd0 containing TiO2 based materials under solar simulated conditions. The results suggest that the pore architecture of the support is also an important parameter that governs the photocatalytic activity. In addition, the Pd0-mesoporous materials in general possess higher activity than Pd2+ containing mesoporous materials. The photocatalysts were extensively characterized by a variety of techniques such as powder X-ray diffraction (XRD), nitrogen sorption analysis, transmission and scanning electron microscopic studies, photoluminescence, diffuse reflectance spectroscopy (DRS), CO Chemisorption, and X-ray photoelectron spectroscopy (XPS).

Preparation, characterization, and in vitro evaluation of antibacterial sol–gel coated cotton textiles with prolonged release of curcumin

The aim of this study was to develop a textile-based sol–gel release system with antibacterial properties intended for medical applications. Curcumin (a herbal compound extracted from Curcuma longa L.) was embedded in an acid-catalyzed silica xerogel coating on cotton textiles. The release of curcumin was found to be diffusion-controlled, as expressed by the Higuchi and the first-order models. Matrix dissolution release was ruled out by the absence of dissolved silica in the release medium. Results from nitrogen sorption analysis confirmed the presence of mesopores in the xerogel coating, and an increase in both the BET surface area from 1.95 to 2.23 m2 g−1 and in the mesopore volume from 0.003 to 0.004 cm3 g−1 after the sol–gel treatment. Thicker xerogel coatings therefore provided greater porosity for curcumin entrapment, leading to retardation of the diffusion processes and consequently extended release profiles. The treated samples showed better antibacterial properties against Staphylococcus aureus (99% reduction) compared with Escherichia coli (37% reduction). Overall, the developed sol–gel coated textiles demonstrate promising potential for use as wound dressing materials.

Effect of Pore Morphology on the Dielectric Properties of Porous Carbons for Microwave Absorption Applications

The porous carbons (PCs) with tunable morphologies and pore sizes were prepared by the sol–gel process via a freeze-drying technique for microwave absorption applications. The results of Raman spectroscopy and nitrogen sorption analysis showed that the graphitization degree was barely influenced as the ratio of tert-butanol (T) to resorcinol (R) decreased, while the pore morphologies changed from the disordered slit-shaped pores to the uniform cage-like pores. Dielectric properties of the as-prepared carbon samples were determined by a vector network analyzer in the frequency range of 8.2–12.4 GHz. Results showed that the effect of pore morphology on the dielectric loss of PCs was dominant in the case of similar graphitization. When the T/R ratio was 7.5, the sample with cage-like pores revealed the maximum values in the real part ε′ and the imaginary part ε″ of complex permittivity, which were 13.2–6.5 and 15.6–10.1, respectively, suggesting a better capacity of dielectric loss in the 8.2–12.4 GHz range. The proposed mechanism for the effect of the pore morphologies on microwave absorption performance was discussed.

Mixed-phase iron oxide nanocomposites as anode materials for lithium-ion batteries

Mixed-phase iron oxide nanocomposites (abbreviated as m-Fe2O3) of hematite (α-Fe2O3) and magnetite (γ-Fe2O3), using potassium ferricyanide (K3[Fe(CN)6]) as the precursor, are successfully synthesized via a simple two-step approach incorporating a hydrothermal reaction and the subsequent thermal annealing. The crystalline structures, specific surface areas and surface morphologies of the as-prepared m-Fe2O3 are characterized in detail by X-ray diffraction (XRD), nitrogen sorption analysis and scanning electron microscopy (SEM), respectively. The electrochemical performances of m-Fe2O3 are examined by galvanostatic cycling and cyclic voltammetry (CV). Transmission electron microscope (TEM), High resolution TEM (HRTEM), selected area electron diffraction (SAED) and Raman are used to investigate the nanocrystalline and composition of the materials. Compared to α-Fe2O3, m-Fe2O3 exhibits a much more excellent cycling stability with a typical discharge specific capacity of 982 mAh g−1 after 50 cycles at a current density of 100 mA g−1, which is attributed to α-Fe2O3 converted to γ-Fe2O3 during charge–discharge cycling. The superior performance of m-Fe2O3 to α-Fe2O3 would provide a new perspective about the effect of mixed-phase on improving the electrochemical properties of lithium-ion batteries.

Synthesis and characterization of LTA zeolite with uniform intracrystal mesopores directed by bridged polysilsesquioxane monomer

An ordered mesoporous LTA zeolites (MLTA) have been synthesized in presence of the bridged polysilsesquioxane monomer (BS-1) as mesoporogen. The relatively well-defined small-angle X-ray diffraction peaks and nitrogen sorption isotherms with narrow pore size distribution centered at around 2.2 nm both indicated the presence of uniformly mesopores in MLTA samples. The scanning electron microscopy and transmission electron microscopy observations further confirmed that the uniform and partially interconnected intracrystal mesopores were randomly distributed throughout the globular particles with rugged surfaces. Interestingly, removal of the BS-1 resulted in uniform mesopore diameters that are nearly consistent with the molecular size of BS-1 (1.8 nm). 29Si MAS NMR revealed that the BS-1 was linked to MLTA zeolite crystal surface through 2 Si–O bonds and 3 Si–O bonds before calcinations. Nitrogen sorption analysis showed that the mesoporosity in MLTA samples could be adjusted by adding different amounts of BS-1 in starting gels. Relative to conventional mesoporous materials, one obvious feature of MLTA is that the resultant mesopores were structured by the bridged polysilsesquioxane monomer instead of commercial polymers or micelles, which broad the routes in synthesizing of various mesoporous materials with controllable pore size distribution, adjustable mesopore volume, and large surface area.

Hierarchical porous carbon prepared by NaOH activation of nano-CaCO3templated carbon for high rate supercapacitors

Hierarchical porous carbon is prepared from sucrose by the nano-CaCO3 template method followed by NaOH activation for supercapacitors. As evidenced by SEM, TEM, nitrogen sorption and Hg porosimetry analysis, the carbon possesses a highly developed hierarchical porous texture containing interconnected micro-, meso-, and macropores. The surface area and pore volume of the carbon reach up to 2032 m2 g−1 and 2.602 cm3 g−1, respectively. Galvanostatic charge–discharge and cyclic voltammetry measurements indicate that the carbon shows high capacitance and excellent rate capability in both aqueous and non-aqueous electrolytes, which are attributed to its unique hierarchical porosity. In the 6 mol L−1 KOH aqueous electrolyte, it can afford a capacitance of 245 F g−1 at 0.05 A g−1, which remains at 188 F g−1 as the current density increases up to 50 A g−1, while the value reaches 144 F g−1 at 0.05 A g−1 and remains at 103 F g−1 at 10 A g−1 in the 1 mol L−1 Et4NBF4/PC non-aqueous electrolyte.

Synthesis of meso-SAPO-11 and its enhancement of isomerization in fluid catalytic cracking process

With the quality of crude oil becoming worse, the efficient Fluid catalytic cracking (FCC) conversion of heavy oil is of great challenge. The enhancement of isomerization during catalytic cracking process is a feasible approach to improve the gasoline yield and quality. In this study, meso-SAPO-11 was synthesized by citric acid modification to generate mesopores in the SAPO-11 molecular sieve. The modification temperature played an important role in the mesopore generation. Nitrogen sorption and X-ray diffraction analysis had been utilized to characterize the mesoporous structure. Meso-SAPO-11 was further used as an additive in the FCC catalyst for catalytic evaluation with atmospheric gas oil and coking gas oil. The additive showed significant improvement of heavy oil conversion, especially for the gasoline yield and quality .