Preparation and gases storage capacities of N-doped porous activated carbon materials derived from mesoporous polymer

In this report, the chemical activation of mesoporous carbon derived from mesoporous polymer is used to prepare N-doped carbon materials with high surface area and narrow pores size distribution. The porous carbons derived from the activation of mesoporous carbon generally possess high surface area up to 2400 m² g⁻¹ and narrow micropores/super-micropore size distribution and exhibit H₂ uptake capacity of up to 4.8 wt% at −196 °C and 20 bar and CO₂ sorption capacity of up to 3.7 mmol g⁻¹ at 25 °C and 1 bar. The measured isosteric heat of adsorption for H₂ sorption is 10 kJ mol⁻¹ and 58 kJ mol⁻¹ for CO₂ sorption, indicating a strong interaction between the carbon surface and adsorbed hydrogen and carbon dioxide respectively.     

One-pot synthetic method to prepare highly N-doped nanoporous carbons for CO2 adsorption

A one-pot synthetic method was used for the preparation of nanoporous carbon containing nitrogen from polypyrrole (PPY) using NaOH as the activated agent. The activation process was carried out under set conditions (NaOH/PPY = 2 and NaOH/PPY = 4) at different temperatures in 600–900 °C for 2 h. The effect of the activation conditions on the pore structure, surface functional groups and CO₂ adsorption capacities of the prepared N-doped activated carbons was examined. The carbon was analyzed by X-ray photoelectron spectroscopy (XPS), N2/77 K full isotherms, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The CO₂ adsorption capacity of the N-doped activated carbon was measured at 298 K and 1 bar. By dissolving the activation agents, the N-doped activated carbon exhibited high specific surface areas (755–2169 m² g⁻¹) and high pore volumes (0.394–1.591 cm³ g⁻¹). In addition, the N-doped activated carbons contained a high N content at lower activation temperatures (7.05 wt.%). The N-doped activated carbons showed a very high CO₂ adsorption capacity of 177 mg g⁻¹ at 298 K and 1 bar. The CO₂ adsorption capacity was found to be dependent on the microporosity and N contents.     

High pressure carbon dioxide adsorption on nanoporous carbons prepared by Zeolite Y templating

Nanoporous carbons were synthesized by chemical vapor deposition using furfuryl alcohol/butylene as a carbon source and zeolite Y as a hard template (ZYC). The ZYC were characterized by PXRD, N₂ sorption, and SEM. The carbon materials exhibited predominant microporosity, and the specific surface area increased from 2563 to 3010 m² g⁻¹ as the pyrolysis temperature was raised from 800 to 1000 °C. ZYC prepared at 1000 °C showed a CO₂ adsorption capacity of 986 mg g⁻¹_adsorbent at 40 bar 298 K, which surpasses the capacities of commercial carbons and mesoporous carbon CMK-3, and closely approaches the best performance of the metal organic framework MOF-177. The CO₂ adsorption capacities of the adsorbents were found to be closely correlated with the BET surface areas of the materials tested.     

Effect of temperature and α-irradiation on gas permeability for polymeric membrane

In the present study the polyethersulphone (PES) membranes of thickness (35 ±2) μm were prepared by solution cast method. The permeability of these membranes was calculated by varying the temperature and by irradiation of α ions. For the variation of temperature, the gas permeation cell was dipped in a constant temperature water bath in the temperature range from 303–373 K, which is well below the glass transition temperature (498 K). The permeability of H₂ and CO₂ increased with increasing temperature. The PES membrane was exposed by a-source (₉₅Am₂₄₁) of strength (1 μ Ci) in vacuum of the order of 10⁻⁶ torr, with fluence 2.7 × 10⁷ ions/cm². The permeability of H₂ and CO₂ has been observed for irradiated membrane with increasing etching time. The permeability increases with increasing etching time for both gases. There was a sudden change in permeability for both the gases when observed at 18 min etching. At this stage the tracks are visible with optical instrument, which confirms that the pores are generated. Most of pores seen in the micrograph are circular cross-section ones.     

Thermal behaviour of NaBH4-sodalites with alumosilicate framework: Influence of cage water content and the surrounding conditions

Sodalites Na₈[AlSiO₄]₆(BH₄)_1.8(H₃O₂)_0.2 and Na₈[AlSiO₄]₆(BH₄)(H₃O₂)_0.5(CO₃)_0.25(H₂O) were examined to characterize the influence of the mixed cage fillings and the surroundings on the thermal behaviour of enclathrated BH₄⁻ and the stability of the alumosilicate framework. The samples were investigated in a NaCl matrix during temperature dependent IR-measurements (TIR) and by thermal analysis in inert atmosphere (helium) and in synthetic air. The thermal products were further characterized by XRD and SEM/EDS.It could be shown that the extent of the BH₄⁻ decomposition strongly depends on the cage-fillings of the individual sodalite phase and on the environmental experimental conditions. At low to medium temperatures hydrolysis of BH₄⁻ by water molecules from decomposition of H₃O₂⁻ and H₂O/CO₃²⁻ templates leads to B(OH)₄⁻/BH₃OH⁻ and via subsequent dehydration to BO(OH)₂⁻ and finally BO₂⁻. At elevated temperatures direct oxidation of BH₄⁻ to BO₂⁻ occurs inside the sodalite cages.Further heating results in sodalite framework destruction and finally formation of nepheline with some boron in its structure besides some unknown polymeric borates outside the alumosilicate phase. Framework stability of the sodalites was found to decrease in the direction → heating in NaCl → heating in He-atmosphere → heating in air.     

A Chemically Stable Hofmann-Type Metal−Organic Framework with Sandwich-Like Binding Sites for Benchmark Acetylene Capture

The realization of porous materials for highly selective separation of acetylene (C₂H₂) from various other gases (e.g., carbon dioxide and ethylene) by adsorption is of prime importance but challenging in the petrochemical industry. Herein, a chemically stable Hofmann-type metal−organic framework (MOF), Co(pyz)[Ni(CN)₄] (termed as ZJU-74a), that features sandwich-like binding sites for benchmark C₂H₂ capture and separation is reported. Gas sorption isotherms reveal that ZJU-74a exhibits by far the record C₂H₂ capture capacity (49 cm³ g⁻¹ at 0.01 bar and 296 K) and thus ultrahigh selectivity for C₂H₂/CO₂ (36.5), C₂H₂/C₂H₄ (24.2), and C₂H₂/CH₄ (1312.9) separation at ambient conditions, respectively, of which the C₂H₂/CO₂ selectivity is the highest among all the robust MOFs reported so far. Theoretical calculations indicate that the oppositely adjacent nickel(II) centers together with cyanide groups from different layers in ZJU-74a can construct a sandwich-type adsorption site to offer dually strong and cooperative interactions for the C₂H₂ molecule, thus leading to its ultrahigh C₂H₂ capture capacity and selectivities. The exceptional separation performance of ZJU-74a is confirmed by both simulated and experimental breakthrough curves for 50/50 (v/v) C₂H₂/CO₂, 1/99 C₂H₂/C₂H₄, and 50/50 C₂H₂/CH₄ mixtures under ambient conditions.     

The influence of O2 and N2 on the hall and field effect mobilities in CdSe and PbTe thin films

Thin films of CdSe and PbTe were evaporated onto SiO in a vacuum system in which a pressure of less than 5 × 10⁻¹⁰ torr was available. The Hall and field effect measurements were made directly after producing the sample. Furthermore, these measurements were repeated under various partial pressures of O₂ and N₂ up to nearly 10⁺² torr. A remarkable influence of these gases on the mobilities was observed. One can understand this effect by considering that p-type regions are formed at the surface of the n-type semiconductors and thus a diminution of the measured mobilities occurs.     

A Robust Molecular Porous Material for C2H2/CO2 Separation

A molecular porous material, MPM-2, comprised of cationic [Ni₂(AlF₆)(pzH)₈(H₂O)₂] and anionic [Ni₂Al₂F₁₁(pzH)₈(H₂O)₂] complexes that generate a charge-assisted hydrogen-bonded network with pcu topology is reported. The packing in MPM-2 is sustained by multiple interionic hydrogen bonding interactions that afford ultramicroporous channels between dense layers of anionic units. MPM-2 is found to exhibit excellent stability in water (>1 year). Unlike most hydrogen-bonded organic frameworks which typically show poor stability in organic solvents, MPM-2 exhibited excellent stability with respect to various organic solvents for at least two days. MPM-2 is found to be permanently porous with gas sorption isotherms at 298 K revealing a strong affinity for C₂H₂ over CO₂ thanks to a high (ΔQ_st)_AC [Q_st (C₂H₂) − Q_st (CO₂)] of 13.7 kJ mol⁻¹ at low coverage. Dynamic column breakthrough experiments on MPM-2 demonstrated the separation of C₂H₂ from a 1:1 C₂H₂/CO₂ mixture at 298 K with effluent CO₂ purity of 99.995% and C₂H₂ purity of >95% after temperature-programmed desorption. C-H···F interactions between C₂H₂ molecules and F atoms of AlF₆³⁻ are found to enable high selectivity toward C₂H₂, as determined by density functional theory simulations.     

Hydrothermal synthesis attempts of dawsonite-type hydroxymetalocarbonate precursor compounds for catalytic Ho, Sm, and La oxides

Chemical interactions in mixed, aqueous solutions of NH₄HCO₃ and M(NO₃)₃·9H₂O, where M stands for Ho, Sm, or La, were facilitated under various hydrothermal treatment conditions (pH 8-12 and temperature = 75-135 °C). The solution chemistry established did not make available necessary concentrations of soluble HCO₃⁻ and MO(OH)₂⁻ species for the formation of dawsonite-type ammonium hydroxymetalocarbonates, NH₄M(CO₃)(OH)₂, but, alternatively, high concentrations of soluble CO₃²⁻, and M(H₂O)_n³⁺ or M(H₂O)_n−1(OH)²⁺ facilitating, respectively, precipitation of corresponding hydrated carbonate, M₂(CO₃)₂·2H₂O, or carbonate hydroxide, MCO₃(OH). X-ray powder diffractometry, infrared spectroscopy, and thermal analyses proved alternative formation of Ho₂(CO₃)₃·2H₂O or LaCO₃(OH) under the whole set of hydrothermal treatment conditions probed, and Sm₂(CO₃)₃·2H₂O at pH < 10 or SmCO₃(OH) at pH ≥ 10, thus implying dependence of the composition of the product carbonate compound on the hydrolysability of the initial M(H₂O)_n³⁺ species and, hence, the metal ionic size (La > Sm > Ho). Calcination of the various hydrothermal treatment products at ≥600 °C resulted in the thermal genesis of the corresponding sesqui-oxides (M₂O₃). Bulk and surface characterization studies of the product oxides, employing N₂ sorptiometry and scanning electron microscopy, in addition to the above analytical techniques, revealed overall strong crystallinity, large average crystallite size, and well-defined particle morphology. They revealed, moreover, surfaces, though of limited accessibilities (≤13 m²/g), exposing OH groups of various coordination symmetries and, hence, acid-base properties, thus furnishing promising surface catalytic attributes.     

Design and performance characteristics of sorption pumps

This paper describes the design and performance characteristics of two types of refrigerated Molecular Sieve Sorption pump that produces and maintains a pressure of the order of 10⁻³ torr in volume of 10–50 l. in case of evacuation of air from atmospheric pressure. The main feature of this method of pumping is its freedom from pumping fluids. Some of its applications along with its limitations are discussed. Applications to multistage sorption pumping and the use of sorption pumps in combination with mechanical dry pump are illustrated.     

Liquid-in-Aerogel Porous Composite Allows Efficient CO2 Capture and CO2/N2 Separation

The pursuit of efficient CO₂ capture materials remains an unmet challenge. Especially, meeting both high sorption capacity and fast uptake kinetics is an ongoing effort in the development of CO₂ sorbents. Here, a strategy to exploit liquid-in-aerogel porous composites (LIAPCs) that allow for highly effective CO₂ capture and selective CO₂/N₂ separation, is reported. Interestingly, the functional liquid tetraethylenepentamine (TEPA) is partially filled into the air pockets of SiO₂ aerogel with left permanent porosity. Notably, the confined liquid thickness is 10.9–19.5 nm, which can be vividly probed by the atomic force microscope and rationalized by tailoring the liquid composition and amount. LIAPCs achieve high affinity between the functional liquid and solid porous counterpart, good structure integrity, and robust thermal stability. LIAPCs exhibit superb CO₂ uptake capacity (5.44 mmol g⁻¹, 75 °C, and 15 vol% CO₂), fast sorption kinetics, and high amine efficiency. Furthermore, LIAPCs ensure long-term adsorption–desorption cycle stability and offer exceptional CO₂/N₂ selectivity both in dry and humid conditions, with a separation factor up to 1182.68 at a humidity of 1%. This approach offers the prospect of efficient CO₂ capture and gas separation, shedding light on new possibilities to make the next-generation sorption materials for CO₂ utilization.     

Removal of trivalent chromium from water using low-cost natural diatomite

Trivalent chromium was removed from the artificial wastewater using low-cost diatomite in batch and continuous systems. In batch system, four different sizes and five different amount of sorbent were used. The effect of the temperature on sorption was evaluated with using three different temperatures. As a result of the experiments, 85% of the trivalent chromium was removed from the wastewater in conditions of using 1.29 mm grain material at 30 °C temperature for 60 min in batch system but chromium removal was 82% at 30 °C temperature for 22 min and 97% from the wastewater at 30 °C temperature for 80 min in continuous system. Also, the equilibrium adsorption isotherms have been analyzed by Langmuir and Freundlich models. The Langmuir isotherms have the highest correlation coefficients. Langmuir adsorption isotherm constants corresponding to adsorption capacity, q₀, were found to be 28.1, 26.5 and 21.8 mg Cr³⁺/g diatomite at 15, 30 and 45 °C, respectively. Adsorption process was an exothermic process as a result of thermodynamic parameters calculations. The kinetic data of the sorption showed that the pseudo second-order equation was the more appropriate, which indicate that the intraparticle diffusion is the rate-limiting factor.     

Equations of state valid continuously from zero to extreme pressures with H2O and CO2 as examples

A new form of equation of state is proposed for use over extremely wide ranges of pressure where conventional equations fail, In particular, fluids, including H₂O and CO₂ as well as argon, etc., remain more compressible at very high densities than can be represented by typical equations with van der Waals or Carnahan and Starling repulsive terms, The new equation is fitted to the data for H₂O and CO₂ over the entire range from the vapor and liquid below the critical temperature to at least 2000 K and from zero pressure to more than 10⁵ bar (10 GPa ) with good agreement, The extension of the equation for mixed fluids is discussed.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994, Boulder, Colorado, U.S.A.     

Techniques of vacuum pumping in multi-layer insulated cryogenic vessels

The improvement in heat transfer properties obtained by use of Multi-Layer Insulation (MLI) is reviewed. The introduction of many closely spaced layers of material increases considerably the surface exposed to vacuum and flow restrictions. Experiments have been made to demonstrate that by using correct pump-down procedures the inherent difficulties can be dealt with and the improved insulation properties of MLI can be used to full advantage in laboratory cryostats which are vented and re-pumped frequently. The test apparatus, procedure and calculation are shown in detail. Test results show that the heat losses of MLI at 10⁻⁴ torr are about 10 per cent of the losses of vacuum insulation only at 10⁻⁶ torr. Heat transfer of MLI remains constant at pressures below 10⁻³ … 10⁻⁴ torr. Recommended pump down procedures are given for equipment which is occasionally vented. The importance of cleanliness during installation of MLI, of the use of heating and getter materials is demonstrated. Pump down times to 10⁻⁴ torr of 5 … 6 h after venting were easily obtained in the test system.     

Point defect chemistry of YBa2Cu3O6.5+δ

A novel mathematical approach for defect concentration calculations proposed by Poulsen [F.W. Poulsen, Solid State Ionics, 129 (2000) 145] for oxides with rather small deviations from stoichiometry also applies to perovskite-type oxides with large ranges of oxygen nonstoichiometry. Point defect chemistry calculations have been performed for YBa₂Cu₃O_6.5+δ for which experimental equilibrium oxygen partial pressure isotherms are well known. The model applied in this work describes experimental results very well in the p_O2 range of 10⁻⁵ to 10 bar and for temperatures between 450 and 800 °C.     

Electrochromic properties of nickel oxide based thin films sputter deposited in the presence of water vapor

Electrochromic nickel oxide based thin films were prepared by reactive RF magnetron sputtering from metallic nickel in the presence of Ar, O₂ and H₂O. The water vapor led to enhanced optical modulation and charge capacity. At a wavelength of 550 nm the bleached state transmittance was 0.73 and the transmittance for the colored state was 0.28 and 0.15 for water partial pressures of p_H2O < 10⁻³ Pa and p_H2O ~ 7 × 10⁻² Pa, respectively. The charge densities were 14 and 25 mC/cm² for p_H2O < 10⁻³ Pa and p_H2O ~ 7 × 10⁻² Pa, respectively. The coloration efficiency was decreased with increased water partial pressure, from about 0.07 to 0.06 cm²/mC. Preliminary results show that the H₂O promotes an amorphous structure and makes the films increasingly hydrous.     

Investigation of a basic dye removal from aqueous solution onto chemically modified Unye bentonite

The adsorption behavior of crystal violet (CV⁺) from aqueous solution onto magnesium-oxide coated bentonite (MCB) sample was investigated as a function of parameters such as initial CV⁺ concentration, contact time and temperature. The Langmuir, and Freundlich adsorption models were applied to describe the equilibrium isotherms. The Langmuir monolayer adsorption capacity of MCB were estimated as 496 mg/g. The pseudo-first-order, pseudo-second-order kinetic and the intra-particle diffusion models were used to describe the kinetic data and rate constants were evaluated. The values of the energy (E_a), enthalpy (ΔH^≠) and entropy of activation (ΔS^≠) were 56.45 kJ/mol, 53.90 kJ/mol and −117.26 J/mol K, respectively, at pH 6.5.     

Sorption of Np(V) on kaolinite from solutions of MgCl2 and CaCl2

The Np(V) distribution coefficients between kaolinite and solutions of MgCl₂ and CaCl₂ were determined experimentally at various concentrations of the electrolytes and Np. The Np sorption decreases with increasing concentration of the supporting electrolyte. The sorption is completely reversible. The sorption equilibrium is attained in approximately one week after the start of the sorption-desorption experiments. The constants of NpO₂ ⁺-Mg²⁺ and NpO₂ ⁺-Ca²⁺ binary ion exchange on kaolinite were determined by fitting the experimental results with an ion-exchange equation for the restricted sorption capacity: $\log K_{NpO_2^ + - Mg^{2 + } } = 1.26 \pm 0.08$ and $\log K_{NpO_2^ + - Ca^{2 + } } = 0.96 \pm 0.10$ . These constants describe well the experimental data at low Np concentrations (≤1×10^?6 M). The ion-exchange capacity of kaolinite, calculated from the experimental data on Np sorption from solutions (3.03×10^?4 g-equiv kg^?1 MgCl₂), somewhat differs from that in CaCl₂ solutions (2.15×10^?4 g-equiv kg^?1).     

Calibration of ultrahigh vacuum gauge from 10 Pa to 10 Pa by the two-stage flow-dividing system

A new two-stage flow-dividing system has been developed for the calibration of ultrahigh vacuum gauges from 10⁻⁹ Pa to 10⁻⁵ Pa for N₂, Ar, and H₂. This system is designed based on the techniques for our previously developed calibration system in the range from 10⁻⁷ Pa to 10⁻² Pa. Three modifications were performed to extend the calibration pressure to a lower range. The relative standard uncertainty of the generated pressure (k = 1) is in the range from 2.3% to 2.6%, from 10⁻⁹ Pa to 10⁻⁵ Pa. The characteristics of ultrahigh vacuum gauges were also examined by using this system. The stabilities of the pressure reading, the linearity, the temperature dependence, and the long-term stability were examined. These results show that the calibration of ultrahigh vacuum gauges is possible in the range from 10⁻⁹ Pa to 10⁻⁵ Pa for N₂, Ar, and H₂ with the uncertainty of about 6.0% (k = 2) by this new system.     

Water sorption and dielectric relaxation spectroscopy studies in hydrated Nafion® (-SO3K) membranes

Dynamic and equilibrium sorption isotherm measurements were carried out on hydrated perfluorosulfonate polymer membranes in potassium salt form (Nafion^®-SO₃K, 1190 EW), at 22 and 40 °C respectively. Despite the glassy state of the membrane the diffusion process is Fickian with an average diffusion coefficient D in the range 2.8–30 × 10^–9 cm²/s. The equilibrium sorption isotherms may be quantitatively analyzed according to the GAB equation for multilayer sorption processes up to the activity value of = 0.79, which corresponds to 1.0 site-bound water molecules per (-SO₃K) group. The analysis of the equilibrium sorption isotherm, using the method of Zimm and Lundberg, suggests clustering of the water molecules for activities 0.79. The apparent polymer-water interaction parameter (Flory parameter), was found to have a maximum at = 0.79 (1.07 1.95). Also, dielectric relaxation studies of the same hydrated Nafion^® membranes have been carried out in the frequency range of 10^–2 – 5 × 10⁶ Hz and in the temperature range of 223–295 K. Two relaxation mechanisms were observed which both sift to higher frequencies by increasing the water content. The low frequency relaxation mechanism is due to interfacial polarization which takes place in the hydrated ionic regions. The high frequency relaxation mechanism, is a dipolar mechanism which may be attributed to the rotation of (-SO₃ ^–) group-water complexes at the end of the side chains.