Nitrogen Sorption-desorption Research Articles

Adsorption of volatile organic compounds in composite zeolites pellets for space decontamination

FAU–*BEA-types zeolites pellets were elaborated with a hydraulic press in the presence of a small amount (5 wt%) of binder [methylcellulose (MC) or anhydrous sodium metasilicate (Na2SiO3)] for molecular decontamination, in particular for the space field. Nitrogen sorption–desorption revealed a small loss of micropore volume (10%) with a compression load of 6 tons (0.24 cm3/g instead of 0.27 cm3/g for the mixture of FAU and *BEA-types zeolites powders), which can be attributed to a partial amorphization. Adsorption kinetics of n-hexane, and cyclohexane showed that the optimum pellets can adsorb volatile organic compounds. For example, FAU–*BEA-type zeolite powder mixture (50 wt% of each zeolite) adsorb 130 mg of n-hexane per g of anhydrous zeolite whereas the pellets made with 5 wt% of MC or Na2SiO3 adsorb about 117–118 mg of n-hexane per g of anhydrous zeolite. These results are coherent with the ones obtained with the cyclohexane and nitrogen adsorption where a small loss of the adsorption capacities was observed.

In English

The aim of our work was to prepare nanoscale composites based on TiO 2 and carbon photocatalytically active under UV and visible irradiation in the destruction of safranin T. The samples were characterized by XRD, BET, SEM, UV-Vis and IR spectroscopy. X-ray analysis revealed photocatalytically active phase of anatase in all the composites. The powders consist of roundish agglomerates, crystallite size in agglomerates is 15 nm. Analysis of nitrogen sorption–desorption isotherms for the samples show the presence of a hysteresis loop which is the evidence for mesoporous structure. Vibrational spectra of the composites reveal the following bands: near 700 cm −1 corresponding to the Ti–O stretching vibration; around 3407 cm –1 attributed to the surface-adsorbed H 2 O; at 1628 cm –1 which is referred to deformational vibrations in adsorbed water, and around 1300–1500 cm –1 corresponding to carbon–oxygen bonds. Absorption spectra of nanocomposites show a bathochromic shift as compared with those of TiO 2 . Modification of TiO 2 with carbon leads to band gap narrowing of composites, as well as to emerging of additional energy levels in the band gap of TiO 2 with energies of 3.12–3.14 eV under valence band; that leads to sensitizing of C/TiO 2 composites to visible irradiation. Nanocomposites show higher photocatalytic activity compared to pure TiO 2 . It may be connected with the participation of carbon in the inhibition of electron–hole recombination, prolongation of charge lifetime, increasing of efficiency of interfacial charge separation from TiO 2 to carbon and formation of doping electronic states inside the TiO 2 band gap.

Co/ZIF-8 Heterometallic Nanoparticles: Control of Nanocrystal Size and Properties by a Mixed-Metal Approach

A mixed-metal approach has been used to control the size and physicochemical properties of heterometallic Co/ZIF-8 nanomaterials. Intentional substitution of zinc with cobalt in a broad concentration range (from 0 to 100 molar percent with a 10% step) provided a series of Co/ZIF-8 nanoparticles, whose sizes could be tuned in the range from 20 to over 500 nm in diameter. Zinc ions from the ZIF-8 matrix were found to be uniformly substituted with the cobalt ions. The increase of nanoparticles size resulted in a change of their nitrogen sorption–desorption characteristics due to decreasing participation of the external surface area in the total surface area. Insights from UV–vis-NIR and IR spectroscopies, as well as remarks on nonlinear optical properties are also provided.

Capture and Reversible Storage of Volatile Iodine by Novel Conjugated Microporous Polymers Containing Thiophene Units.

Conjugated microporous polymers having thiophene building blocks (SCMPs), which originated from ethynylbenzene monomers with 2,3,5-tribromothiophene, were designedly synthesized through Pd(0)/CuI catalyzed Sonogashira-Hagihara cross-coupling polymerization. The morphologies, structure and physicochemical properties of the as-synthesized products were characterized through scanning electron microscope (SEM), thermogravimeter analysis (TGA), (13)C CP/MAS solid state NMR and Fourier transform infrared spectroscope (FTIR) spectra. Nitrogen sorption-desorption analysis shows that the as-synthesized SCMPs possesses a high specific surface area of 855 m(2) g(-1). Because of their abundant porosity, π-conjugated network structure, as well as electron-rich thiophene building units, the SCMPs show better adsorption ability for iodine and a high uptake value of 222 wt % was obtained, which can compete with those nanoporous materials such as silver-containing zeolite, metal-organic frameworks (MOFs) and conjugated microporous polymers (CMPs), etc. Our study might provide a new possibility for the design and synthesis of functional CMPs containing electron-rich building units for effective capture and reversible storage of volatile iodine to address environmental issues.

A new generation of MFI-type zeolite pellets with very high mechanical performance for space decontamination

MFI-type zeolite pellets were elaborated with a hydraulic press in the presence of a small amount of binder (methylcellulose (MC) or anhydrous sodium metasilicate (Na2SiO3)) for molecular decontamination, in particular for the space field. The influence of the compression load and the amount of binder was investigated to determine the optimum conditions to get pellets with high mechanical performances and high adsorption capacities. The compression load varied from 2 to 8 tons and the amount of binder varied from 5 to 20 wt% of the total pellet weight. Nitrogen sorption–desorption revealed a small loss of micropore volume (17%) with a compression load of 8 tons (0.15 cm3/g instead of 0.18 cm3/g for the MFI-type zeolite powder), which can be attributed to a partial amorphization. Adsorption kinetics of n-hexane showed that the optimum pellets can adsorb volatile organic compounds. Indeed, MFI-type zeolite adsorbs 7.6 molecules of n-hexane per cell whereas the pellets made with 5 wt% of MC or Na2SiO3 adsorb about 7 molecules of n-hexane per unit-cell, respectively. These results are coherent with the ones obtained with nitrogen sorption–desorption. Uniaxial compression tests showed that the addition of small amount of binder in the mixture really improved the mechanical performances: the ultimate compressive strength was multiplied by 8 (10 MPa for the pellets without binder) when only 5 wt% of MC are used (80 MPa), with a compression load of 4 tons.

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.

Synthesis and characterization of magnetic porous Fe3O4/poly(methylmethacrylate-co-divinylbenzene) microspheres and their use in removal of Rhodamine B

Porous polymers are very suitable materials for the adsorption of organic pollutants due to their abundant pores and organic frameworks in aqueous solution. However, their recovery from treated pollutant is difficult, and thus, their application is limited. A facile strategy to synthesize reusable magnetic porous microspheres (MPMS) of Fe3O4/poly(methylmethacrylate (MMA)-co-divinylbenzene (DVB)) is described in this paper. The magnetic microspheres were synthesized by suspension copolymerization. MMA was used as a monomer, DVB was used as a crosslinker, and the magnetic fluid was added to the organic phase. The morphology of MPMS was observed by scanning electron microscope (SEM) and other properties were tested by superconducting quantum interference device, Fourier transform infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA), X-ray powder diffraction (XRD), and nitrogen sorption-desorption techniques. The synthesized MPMS possessed a high specific surface area using toluene as a porogen. It was further found that the ratio of DVB to MMA, the ratio of porogen to monomer, and the type of porogen all affected the specific surface area and the morphology of the microspheres. Furthermore, the microspheres were applied to remove Rhodamine B from its aqueous solution. The results showed that the microspheres possessed good adsorption capacity for Rhodamine B. This result was due to the porous structure, polar groups, and superparamagnetic characteristic of the synthesized microspheres.

Synthesis of Carbon-Base Materials by Microwave Irradiation of Peat

The production of carbon adsorbents by carbonization of peat under the effect of microwave irradiation within the environment of own gases was studied. The optimization of conditions and parameters for carbonization of peat was conducted. By means of FTIP-spectroscopy, elemental analysis, thermographic analysis, nitrogen sorption-desorption and model indicators’ occlusion it was found that in consequence of carbonization the content of loaded surface sites is reduced due to the destruction of functional organic compounds, dispersion is decreased, adsorption properties of carbon-base materials are increased.

Synthesis of organic–inorganic hybrid microspheres and the corresponding mesoporous silica nanoparticles

Poly(methacrylic acid-co-3-(methacryloxy)propyltrimethoxysilane) (P(MAA-co-MPS)) organic–inorganic hybrid microspheres were prepared by distillation–precipitation copolymerization of MAA and MPS in acetonitrile in absence of any surfactant and additive. The resultant hybrids had a spherical shape when the MPS inorganic precursor was varied from 0% to 60% in the comonomers during the polymerization. The hybrid microspheres can be facilely cross-linked via the hydrolysis of methoxy groups of polyMPS network and further self-condensation of the hydroxyl groups of silanols. As a result, the hybrid microspheres were facilely converted to mesoporous silica particles via the removal of the organic component through calcination. The narrow dispersed mesoporous silica had a high surface area of 554.2m2/g as well as the average pore size of 8nm and pore volume of 0.24cm3/g. The corresponding microspheres were characterized by TEM, FT-IR, TGA, and nitrogen sorption–desorption.

Hierarchically porous hybrids of polyaniline nanoparticles anchored on reduced graphene oxide sheets as counter electrodes for dye-sensitized solar cells

Hierarchically porous polyaniline–reduced graphene oxide hybrids have been developed via oxidative polymerization of aniline by MnO2 on reduced graphene sheets under acidic conditions (named M-PANI@rGO). The formation mechanism of the above hybrids indicates that the MnO2 undergoes oxidative disintegration and results in the porous structure of polyaniline (PANI) nanoparticle formation on the reduced graphene oxide (rGO) surface. The scanning electron microscopy (SEM) images and Brunauer–Emmett–Teller (BET) nitrogen sorption–desorption measurement clearly showed the nanoporous nature of the M-PANI@rGO hybrids. TEM-EDX confirmed the complete removal/degradation of MnO2 during the oxidative polymerization of aniline. Just for comparison, PANI–rGO hybrids have also been prepared via conventional polymerization using (NH4)2S2O8 as the oxidant (named C-PANI@rGO). When these different architectural PANI@rGO hybrids were applied as the counter electrode for dye-sensitized solar cells (DSSCs), the short-circuit current density (Jsc) and power-conversion efficiency (η) of the DSSCs with C-PANI@rGO hybrids are measured to be 11.64 mA cm−2 and 5.62%, respectively, while the corresponding values are 12.88 mA cm−2 and 6.15% for the DSSCs with M-PANI@rGO hybrids, which is comparable to 6.73% for the cell with a Pt counter electrode under the same experimental conditions. The hierarchically porous M-PANI@rGO hybrid is thus a promising candidate to replace platinum as a counter electrode for DSSCs.

Direct tri-constituent co-assembly of highly ordered mesoporous carbon counter electrode for dye-sensitized solar cells

Controlling over ordered porosity by self-assembly is challenging in the area of materials science. Materials with highly ordered aperture are favorable candidates in catalysis and energy conversion device. Here we describe a facile process to synthesize highly ordered mesoporous carbon (OMC) by direct tri-constituent co-assembly method, which uses resols as the carbon precursor, tri-block copolymer F127 as the soft template and tetraethoxysilane (TEOS) as the inorganic precursor. The obtained products are characterized by small-angle X-ray diffraction (SAXD), Brunauer-Emmett-Teller (BET) nitrogen sorption-desorption measurement and transmission electron microscope (TEM). The results indicate that the OMC possesses high surface areas of 1209 m(2) g(-1), homogeneous pore size of 4.6 nm and a large pore volume of 1.65 cm(3) g(-1). The advantages of high electrochemical active surface area and favorable accessible porosity of OMC benefit the catalysis of I(3)(-) to I(-). As a result, the OMC counter electrode displays a remarkable property when it was applied in dye-sensitized solar cells (DSSCs). For comparison, carbon black (CB) counter electrode and Pt counter electrode have also been prepared. When these different counter electrodes were applied for dye-sensitized solar cells (DSSCs), the power-conversion efficiency (η) of the DSSCs with CB counter electrode are measured to be 5.10%, whereas the corresponding values is 6.39% for the DSSC with OMC counter electrode, which is comparable to 6.84% of the cell with Pt counter electrode under the same experimental conditions.

Selectively reduction of tobacco specific nitrosamines in cigarette smoke by use of nanostructural titanates

In this study, titanate nanosheets, nanotubes, and nanowires, were synthesized by hydrothermal treatment anatase TiO2 in different temperatures. The obtained products are characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron micrograph (TEM) and Brunauer-Emmett-Teller (BET) nitrogen sorption-desorption measurement. Then, the nanostructural titanates were used as additives for selectively reducing tobacco-specific nitrosamines (TNSAs) in mainstream cigarette smoke (CS) for the first time. These nanomaterials exhibited high reduction ability of TSNAs which was related to their intrinsic properties. The N-NO functional group of TSNAs with a negative charge would react with H(+) on the surface of nanomaterials via chemical absorption and can be retained on the surface of the titanates. Among these materials, titanate nanowires (TNW) captured more TNSAs owing to their network structure, which resulted in the selective reduction ratio of TSNAs being improved significantly. Thus, TNW is a useful additive for selectively reducing the TSNAs in CS without changing the cigarette flavor.

Effect of PEG with different M W as template direction reagent on preparation of porous TiO2/SiO2 with assistance of supercritical CO2

Titania–silica composite have been prepared using polyethylene glycol (PEG) with different molecular weights (M w), PEG20000, PEG10000, and PEG2000, as template in supercritical carbon dioxide (SC CO2). The composite precursors were dissolved in SC CO2 and impregnated into PEG templates using SC CO2 as swelling agent and carrier. After removing the template by calcination at suitable temperature, the titania–silica composite were obtained. The composite were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, and nitrogen sorption–desorption experiment. Photocatalytic activity of the samples has been investigated by photodegradation of methyl orange. Results indicate that there are many Si–O–Ti linkages in the TiO2/SiO2 composite; the PEG template has a significant influence on the structure of TiO2/SiO2. In addition, the TiO2/SiO2 prepared with PEG10000 exhibited high photocatalytic efficiency. So this work supplies a clue to control and obtain the TiO2/SiO2 composite with different photocatalytic reactivity with the aid of suitable PEG template in supercritical CO2.

Morphology control of mesoporous silicas and their template synthesis in silica gel pores

Structure-related adsorption characteristics of ordered mesoporous silicas with spherical particles were studied depending on the conditions of their synthesis, including pH of the medium, the type of the alcohol, and the concentrations of the initial components of micelle solutions. The special features of the template synthesis of mesoporous silica in large silica gel pores were studied. The synthesized silicas were characterized by low-temperature nitrogen sorption-desorption, X-ray diffraction, and scanning electron microscopy measurements.

Porous TiO 2/SiO 2 composite prepared using PEG as template direction reagent with assistance of supercritical CO 2

Titania–silica mesoporous composites have been prepared using polyethylene glycol (PEG) 20,000 as a template direction reagent with the assistance of supercritical carbon dioxide (SC CO 2). For this preparation method, the composite precursors of tetrabutyl titanate (TBTT) and tetraethyl orthosilicate (TEOS) were dissolved in supercritical CO 2 and impregnated into PEG 20,000 using SC CO 2 as swelling agent and carrier. After removal of the PEG template by calcination in air at suitable temperatures, porous titania–silica composites were obtained. Effects of CO 2 pressure and temperature have been studied on the impregnation ratio during the supercritical fluid condition. The composite products were characterized by thermogravimetric analysis (TGA), X-ray diffraction (XRD), FTIR spectroscopy, nitrogen sorption–desorption experiments, scanning electronic microscope (SEM), and transmission electron microscope (TEM). XRD and nitrogen sorption–desorption experimental results indicate that the titania–silica composite crystallized in anatase phase and has a preferable BET surface area up to 301.98 m 2/g. It was also demonstrated that the microstructure and macroproperty of TiO 2/SiO 2 composites depend strongly on the experimental pressure during the impregnation process in SC CO 2. At suitable CO 2 pressure, silica even can be found in a single crystalline structure in nature by observation of TEM. At the same time, SEM indicates that the composite product existed in a spheric form or a cubic form inserted with many holes. So this work provides a new route to control and obtain the special micrography of TiO 2/SiO 2 composites with the aid of suitable polymer templates in supercritical CO 2.