Physisorption Isotherms Research Articles

Fabrication of CdS/BiOI heterostructure with enhanced photocatalytic performance under visible-light irradiation

A series of CdS/BiOI (Cd-Bi) heterojunction photocatalysts with different CdS loading were prepared by a simple ultrasonic-assisted calcination method. All samples were characterized by XRD (X-ray powder diffraction), N2 physisorption isotherms and other techniques to investigate the impact of heterostructure. Among them, Cd-Bi-0.30 (0.30 represents the mass ratio of CdS to BiOI) shows a significantly improved photocatalytic oxidation capacity under LED lamp irradiation due to heterojunction construction and a suitable additive amount, leading to photogenerated electron-hole pairs separation promoting, so that more charge carriers can participate in the photoreaction. Finally, the mechanism of photocatalytic oxidation of Hg0 by the as-prepared CdS/BiOI photocatalyst was discussed in detail.

Copper promoter effect on acid–base and redox sites of Fe/Al2O3 catalysts and their role in ethanol–acetone mixture conversion

The redox site properties favours the hydride transfer.

Study of physisorption isotherm of water on technical nickel surface with a wide pressure range

During the pumping process of unbaked all-metal vacuum systems after air exposure, water dominates in a time of ∼105 s (>10−6 Pa). The pumping rates of vacuum systems are difficult to be calculated because of the term of the re-adsorption rates. Under the assumption of quasi-equilibrium state between the adsorption and the gas phases, theoretically, the isotherms of water can be used to solve the pumping equation without the re-adsorption term. Thus, it is important to measure the isotherms of water on technical metal surfaces. In this work, the physisorption isotherm of water on the nickel surface with a wide pressure range (from 1.59 Pa to saturated vapor pressure Ps) is measured using an all-metal apparatus. The results show that the experimental data agree quite well with the empirical isotherm of Redhead within 0.16 ≤ ψ ≤ 0.95 (ψ = P/Ps, P is the pressure; 1.0 ≤ θ ≤ 4.4, and θ is the surface coverage), and the BET isotherm within 0.04 ≤ ψ ≤ 0.40 (0.7 ≤ θ ≤ 1.5). When 1.59 ≤ P ≤ 250 Pa (θ ≤ 0.85), there is a linear relationship between θ and ln(P). This follows the Temkin isotherm, and it confirms the common experimental phenomenon that parts of the outgassing curves of vacuum systems are approximately P = constant × t−1. The results also indicate that some water is weakly trapped in the pores and the grain boundaries of technical metals, and it diffuses and desorbs very slowly.

Catalytic reduction of 4-nitrophenol over porous g-C<sub>3</sub>N<sub>4</sub> confinement Ag and Au nanoparticles catalysts

Ag@pg-C3N4 and Au@pg-C3N4 catalysts were synthesized based on the confinement effect of porous g-C3N4. X-ray diffraction, N2 physisorption isotherms, transmission electron microscopy, X-ray photoelectron spectroscopy were used to characterize the nanomaterials. All the catalysts presented high catalytic activity in the reduction of 4-nitrophenol. The 10 wt% Au@pg-C3N4 displayed a pseudo-first order kinetics of 2.2601 min−1, which was proved to be the most prominent one among all the obtained catalysts.

Multilevel‐layer‐structured polyamide 6/poly(trimethylene terephthalate) nanofibrous membranes for low‐pressure air filtration

ABSTRACTMultilevel‐layer‐structured polyamide 6 (PA6) and poly(trimethylene terephthalate) (PTT) nanofibrous membranes were fabricated by an electrospinning method. The morphology of the multileveled layers membranes were characterized by scanning electron microscopy. The tensile strength of the PA6–PTT membranes were controlled by the regulation of the layer structure. Additionally, the surface area of the multilevel‐layer‐structured membranes was also investigated with the nitrogen physisorption isotherms. Furthermore, the multilevel‐layered membranes, with a tensile strength of 9.8 MPa and a surface area of 5.1601 m2/g on 300‐nm dioctylphthalate (DOP) aerosol particles, showed a higher efficiency (95.825%) and a lower pressure drop (55 Pa) than the pure PA6 membranes (with values of 94.634% and 467 Pa, respectively). This suggested a new method for high‐efficiency and low‐pressure‐drop filtration applications. Correlations between the filtration pressure drop and filtration efficiency with the structure of the membranes, particle size, and surface velocity were proposed, and the advantage of the multilevel‐layered structure is also discussed. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44716.

The modulator driven polymorphism of Zr(IV) based metal-organic frameworks.

The reaction of ZrCl4 and 2,5-thiophenedicarboxylic acid (H2tdc) in the presence of trifluoroacetic acid (Htfa) as modulator results in the formation of the new metal-organic framework (MOF) named DUT-126 (DUT = Dresden University of Technology). The nature and concentration of modulators are found to be decisive synthetic parameters affecting the topology of the formed product. DUT-126 ( HBR: ) extends the series of polymorphs differing in topology, namely DUT-67 ( REO: ), DUT-68 ( BON: ) and DUT-69 ( BCT: ) to four, where DUT-67 and DUT-68 show the same eight-connected secondary building units as in DUT-126. In DUT-126, linker molecules have a peculiar orientation, resulting in HBR: topology, which is described for the first time in this work for MOFs. DUT-126 contains three pore types, including two micropores surrounding mesoporous channels. DUT-126 is stable against hydrolysis and features permanent porosity with a specific surface area of 1297 m2 g-1 and a total pore volume of 0.48 cm3 g-1, calculated from the nitrogen physisorption isotherm measured at 77 K.This article is part of the themed issue 'Coordination polymers and metal-organic frameworks: materials by design'.

Water vapour sorption on mudrocks

Abstract High-resolution water sorption isotherms were measured on 13 representative mudrock samples in order to assess the mechanisms of water vapour sorption and their relationship to the pore structure of mudrocks. The isotherm measurements were performed at 303 K on a gravimetric, dynamic vapour sorption device. Experimental data were interpreted by traditional physisorption models for which the validity was evaluated by relating model parameters to those obtained from nitrogen physisorption measurements. No direct relationships with the pore structure were observed, except for the Gurvich total pore volumes and the corresponding porosity data. Specific surface areas from Brunauer–Emmett–Teller theory are ambiguous and do not relate to nitrogen data, suggesting that water molecules do not adsorb as (multi-) layers covering pore walls. The volume filling theory (Dubinin–Astakhov equation) fits the water sorption data well but no relationship to the nitrogen data was observed in the studied sample set. A lower affinity of water for micropores was evident from the higher filling pressures of N 2 -based micropore volumes. The Barret–Joyner–Hallenda theory combined with N 2 physisorption measurements on moist mudrocks revealed that capillary condensation prevails close to saturation but not below about 0.94 relative pressure ( p / p 0 ). A distinct low-pressure hysteresis was observed from hysteresis scanning that was attributed to surface chemistry since capillary condensation occurs only at very high relative pressures. Analysis of mineralogical composition, total organic content (TOC) and organic maturity in relation to water sorption revealed only a weak correlation with the total clay content. In contrast, cation-exchange capacity (CEC) strongly correlates with water uptake, which evidences a surface-chemistry-controlled sorption mechanism. Tests of the influence of the exchangeable cation were inconclusive because pore system alteration due to cation-exchange probably superimposed the effect. To further assess the sorption mechanisms of water, nitrogen physisorption isotherms were measured on moisture-equilibrated mudrocks (11, 52, 75, 94% relative humidity at 298 K). Micropore analysis and cumulative pore-size distributions denote that water blocks pore throats rather than fills pore volumes at lower relative humidities. Over the entire humidity range, no direct relationship between water sorption and pore size was observed. These findings imply that water adsorption does not sequentially fill pores with increasing radii in mudrocks as relative humidity increases, as would be expected from water sorption by capillary condensation. This conclusion has important implications for the interpretation and measurement of geomechanical and petrophysical properties of mudrocks. Capillary pressures, particularly at low water saturations, are often calculated from water saturation using a concept based on the Kelvin equation for capillary condensation. Since water sorption in mudrocks seems to be controlled by surface chemistry rather than pore size, this approach is questionable. The observations reported here suggest that the water distribution in mudrock pore systems resulting from vapour equilibration differs from that obtained by fluid displacement (i.e. capillary drainage or imbibitions). A further consequence is that water vapour equilibration is a convenient, but not necessarily representative, method to obtain partially water-saturated mudrock samples for laboratory measurement of saturation-dependent geomechanical or petrophysical properties.

Study of Deactivation of Pd(OH)2/C Catalyst in Reductive Debenzylation of Hexabenzylhexaazaisowurtzitane

AbstractThe conversion of hexabenzylhexaazaisowurtzitane (HBIW) to 2,6,8,12‐tetraacetyl‐4,10‐dibenzyl‐2,4,6,8,10,12‐hexaazaisowurtzitane (TADB) is the major challenge in the production of hexanitrohexaazaisowurtzitane (HNIW) which only proceeds over supported palladium catalyst in a reductive debenzylation reaction. The catalyst is quickly deactivated during the debenzylation reaction. In this study, the change in Pd content in the catalyst during the reaction was measured. It was demonstrated that a portion of the palladium particles in the catalyst was leached during the reaction. The H2 chemisorption isotherm on the catalyst at 303 K showed that the volume of chemisorbed H2 on spent catalyst was significantly less than that on fresh catalyst. The N2 physisorption isotherm on the catalyst at 77 K revealed that the surface area of spent catalyst was less than that of fresh catalyst. Moreover, the FESEM‐EDS and TEM images and also wide‐angle XRD patterns demonstrated that the mean sizes of palladium crystallites and particles in spent catalyst were larger than those in the fresh catalyst. These results demonstrated that the leaching of palladium particles and the aggregation of palladium particles in catalyst play active roles in the deactivation of catalyst in the debenzylation of HBIW.

Successful application of a commercial cationic surfactant mixture (benzalkonium chloride) as porosity stabilizer in porous carbons fabrication

Porous carbons (BSPCs) were obtained by carbonization of resorcinol-formaldehyde gels in the presence of cationic surfactants mixture (benzalkonium chloride) which act as porosity stabilizer. The application of an inexpensive industrial grade surfactant mixture as porosity stabilizer permits obtaining porous carbons with well-developed micro and mesoporosity at low cost. The stabilizing effect on the sol–gel nanostructure allows maintaining the gels porosity during conventional air drying, simplifying the production of porous carbon by making unnecessary complex drying procedures (e.g. supercritical drying), cumbersome solvent exchanges, and long curing times. The carbonization process of BSPCs studied by TGA shows that the stabilizer and non-carbon elements (hydrogen and oxygen) are only eliminated during pyrolysis at temperature above 600°C. The BSPCs morphological and textural properties were studied by scanning electron microscopy and nitrogen physisorption isotherms. The BSPCs present large specific surface areas (up to 645m2/g) containing mesopores and micropores. Furthermore, the pore distribution and morphology depend on the monomer (resorcinol) to stabilizer (benzalkonium chloride) ratio. Cyclic voltammetry and electrochemical impedance spectroscopy were employed to study the electrochemical properties of the carbon materials. The BSPCs exhibit a large specific capacitance (up to 179F/g at 2.8mHz in 1M H2SO4) The results suggest that porosity stabilization of resorcinol/formaldehyde gels could be performed using different cationic surfactants, even commercial mixtures like benzalkonium chloride.

Multifunctional catalysts based on carbon nanotubes and titanate nanotubes for oxidation of organic compounds in biphasic systems

Amphiphilic catalysts composed of carbon nanotubes (CNTs) and titanate nanotubes (TiNTs) have been successfully synthesized by refluxing anatase TiO2 and functionalised CNTs in concentrated NaOH solution. The prepared materials were characterized by transmission electron microscopy, scanning electron microscopy, X-ray diffraction, thermogravimetric analysis (TGA), and N2 physisorption isotherms. The catalytic activity of the synthesized composites was first evaluated in the oxidation of methyl yellow (MY) using H2O2 as oxidant in a single liquid phase system and in a biphasic water/oil mixture. The results of these experiments indicated that the catalytic activities of nanocomposites were very similar in the single liquid-phase oxidation. However, the modification of TiNTs with CNTs led to a substantially enhanced MY oxidation in the biphasic system. The nanocomposites show excellent interaction with both hydrophilic and hydrophobic compounds and thus stabilise emulsions. Under biphasic conditions, the catalysts can be easily separated and recycled, retaining catalytic activity even after eight runs. Additionally, the hybrid materials show superior catalytic activity and selectivity in the biphasic oxidation of benzyl alcohol with H2O2, as compared to pure TiNTs.

Nanopore structure characterization for organic-rich shale using the non-local-density functional theory by a combination of N2 and CO2 adsorption

Low-pressure gas adsorption is widely used for pore size analysis of porous materials, and has been employed to characterize pore systems in shale. However, the complexity of shale pore structures means that different methods and models may lead to distinct interprets for adsorption data. Non-local-density functional theory (NLDFT) analysis based on N2 and CO2 composited adsorption isotherms is used here to investigate the pore structure of nanopores in marine organic-rich shale and compare with the results from some conventional methods in this paper. The results indicate that (1) The N2 adsorption isotherms of organic-rich shale are a composite of Types I(b), II, and IV(a), according to the IUPAC (2015) classification of physisorption isotherms. The hysteresis loops show similar shapes to Type H2(a). Delayed capillary condensation is observed in the adsorption isotherms, and the desorption step is shifted to the lower relative pressure of ∼0.45 characteristic of the cavitation mechanism, indicating ink-bottle pores with narrow necks. The CO2 adsorption isotherms are similar to Type I(b), but appear to increase without limit when p/p0 = 0.03 because of the occurrence of meso- and macropores in the shales. (2) NLDFT method based on N2 and CO2 composited adsorption isotherms is the most suitable and accurate method for using gas physisorption when considering the entire size distribution of nanopores, which allows a suitable range of critical pore sizes (∼0.33–100 nm) to be explored.

Bioethanol dehydrogenation over copper supported on functionalized graphene materials and a high surface area graphite

A high surface area graphite and three functionalized graphene materials (one undoped and two N-doped prepared by different methods) synthesized by thermal treatment of a graphitic oxide were used to support copper catalysts, which were comparatively evaluated in the bioethanol dehydrogenation reaction. The characterization of the carbon supports by nitrogen physisorption isotherms, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) allowed us to stablish differences in the structure and chemical nature of the surface properties generated by the different synthesis procedures. Furthermore, reduced copper catalysts were characterized by XRD, transmission electron microscopy to determine the Cu nanoparticle sizes and their morphologies and XPS to obtain information on the Cu surface species. It was found that catalytic properties depended on the nature of each support, because it induced significant differences on metal nanoparticles, i.e. modifications of structural properties, as consequence of specific metal-graphite or metal-graphene interactions. Comparative studies with copper supported on a commercial silica gel highlighted the application of these carbon supported Cu catalysts as a promising alternative in terms of activity, selectivity and stability for the dehydrogenation of bioethanol into acetaldehyde. Also these Cu/graphite or Cu/graphene materials displayed high stability even when water is co-fed with ethanol.

Structural, optical and electrical properties of nanocrystalline TiO2, SnO2 and their composites obtained by the sol–gel method

In this paper we describe structural, optical and electrical properties of nanocrystalline TiO2, SnO2 and their composites obtained by the sol–gel method. The materials were characterized by X-ray diffraction (XRD), surface area estimated from the N2 physisorption isotherm (BET), high-resolution transmission electron microscopy (HRTEM) and scanning transmission electron microscopy (STEM). Moreover, the paper examines optical and electrical properties of nanocomposites. In fact attention is particularly focused on the properties of the composites with various chemical compositions. An abrupt change in the optical and electrical properties has been observed, passing from the sample with the maximum amount of TiO2 to a maximum amount of SnO2. The sensor made of composite containing 58.5% of SnO2 exhibited the best NH3 sensing features.

NON-CRYSTALLINE COPPER OXIDE HIGHLY DISPERSED ON MESOPOROUS ALUMINA: SYNTHESIS, CHARACTERIZATION AND CATALYTIC ACTIVITY IN GLYCEROL CONVERSION TO ACETOL

Polymeric precursor method and wet impregnation route were applied to synthesize copper and aluminium-based catalysts in order to obtain a material with interesting properties in catalytic reactions. The changes in the structural, morphological and textural properties due to the choice of preparation method were characterized by different techniques, such as XRD, N2 physisorption isotherms and SEM. The XRD results of the solids present the formation of γ-Al2O3 or CuO and β-Al(OH)3, depending on the preparation method. The average crystallite diameters of the alumina were estimated by the Scherrer's formula with a particle size of 5.2 nm. N2 physisorption isotherms analysis shows that the alumina is a mesoporous material with a high specific surface area. An excessive increase in surface area was observed after Cu2+ insertion by wet impregnation from β-Al(OH)3 support, which is explained by the redissolution and recrystallization of bayerite to γ-Al2O3 during the impregnation of Cu2+ and recalcination process, respectively. The SEM images confirmed this phenomenon. Catalytic tests explain that the combination of the two methods improves the activity, selectivity and the stability in the conversion of glycerol to acetol. The results indicate that the way of catalyst preparation affects its structural, textural and morphological properties and consequently the catalytic performance

Tolerance of Flexible MOFs toward Repeated Adsorption Stress.

The adsorption/desorption cyclability of four flexible MOFs, namely, MIL-53(Al), ELM-11, DUT-8(Ni), and SNU-9, was studied at 298 K using n-butane as adsorptive. The detailed analysis of thermal response curves, physisorption isotherm data, powder X-ray diffraction patterns, as well as SEM images revealed the highly stable switching performance of MIL-53(Al) and ELM-11 materials during 100 adsorption/desorption cycles. In contrast, for DUT-8(Ni) and SNU-9, the multiple adsorption/desorption stress leads to the reduction of crystallite size, causing changes in the switching behavior in the initial 10 physisorption runs, and a characteristic shift of the "gate-opening" pressure to higher values is observed.

On the mechanism of oxidative degradation of rhodamine B over LaFeO3 catalysts supported on silica materials: Role of support

This work aims to investigate the role of silica support in the catalytic oxidation of rhodamine B (RhB) over LaFeO3-Silica composites. Four LaFeO3-Silica composites using mesoporous silica (SBA-15, SBA-16, MCF) and nano-sized silica powder (NSP) as supports are prepared. XRD, N2 physisorption isotherms and TEM results show that pure LaFeO3 phase, with particle size of 15–20 nm, is prepared and the texture of supports remains unchanged after the deposition of LaFeO3. Catalytic results show that, besides the function to disperse LaFeO3 on the surface, the support plays two important roles in the reaction: one is to absorb RhB from solution to its pores, and the other is to transport RhB from the pores to the active site, both influence the catalytic efficiency. Thus the non-porous NSP with negligible capacity for RhB adsorption is the worst, and the porous MCF with considerable capacity for RhB adsorption and the strongest ability for RhB transportation is the best support of LaFeO3 for RhB oxidation. SBA-15 and SBA-16, although show considerable or even higher capacity for RhB adsorption relative to MCF, their contribution to the reaction is less due to the low efficiency of transporting RhB from the pores to the active site. On these bases, the role of silica support in RhB oxidation conducted over LaFeO3-Silica composite is proposed.

A new one-pot strategy to LaF3:Ce,Tb@SiO2 core-shell nanostructures

Abstract LaF3:Ce,Tb@SiO2 core-shell nanostructures were synthesized using a new one-pot reverse microemulsion strategy. One-pot method facilitates the synthetic process of this kind of core-shell nanostructures. The crystalline phase, size, morphology, pore structure and luminescence properties were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), nitrogen physisorption isotherm, photoluminescence (PL) excitation and emission spectra. The results revealed that the core-shell nanostructures have an average diameter of about 27 nm and cores of about 3 nm, and that these nanostructures contain micropores with an average pore diameter of 0.43 nm. The characteristic emissions of Tb3+ were observed under the excitation of Ce3+ 4f–5d transition due to the energy transfer from Ce3+ to Tb3+. LaF3:Ce,Tb@SiO2 nanostructures can disperse well in water and the colloid can emit bright green light under ultraviolet (UV) irradiation.

Facile electrospun Polyacrylonitrile/poly(acrylic acid) nanofibrous membranes for high efficiency particulate air filtration

Polyacrylonitrile/poly(acrylic acid) (PAN/PAA with weight radios of 3/7, 4/6, 5/5, 6/4, 7/3 and 10/0) nanofibers (NFs) were prepared as filter medium by electrospinning. The tensile strength of blended nanofibrous mats increased as increasing PAA content, from 3.8 to 6.6 MPa, higher than pristine PAN. The mesoporous effect of nanofibrous mats was also investigated from the nitrogen physisorption isotherms, average pore size in the range of 17–44 nm. Air filtration efficiency and pressure drop of nanofibrous mats were evaluated. PAN/PAA (6/4) NFs showed high filtration efficiency (99.994 %) with lowest pressure drop (160 Pa) for 300–500 nm sodium chloride aerosol particles at a 5.3 cm/s airflow velocity, which suggested this material was appropriate as a promising candidate for high performance filters.

CO and soot oxidation over macroporous perovskite LaFeO3

Bulk, supported and macroporous perovskite LaFeO3 are synthesized and investigated as catalysts for CO and soot oxidation. The structure and physicochemical properties of LaFeO3 are characterized by XRD patterns, N2 physisorption isotherms, TEM, XPS, O2-TPD and H2-TPR measurements. Pure LaFeO3 with desired textural structures are successfully prepared, and the porous sample exhibits the best activity to both reactions, pointing out the importance of fabrication of porous perovskite for the reactions. By correlating with the catalytic activities and the physicochemical properties, it is inferred that the best activity obtained from the porous LaFeO3 is attributed to its large surface area, rich active lattice oxygen and strong surface reducibility. A decrease in the activity of porous LaFeO3 is observed for both reactions when vapor is added, but the activity is sustainable even the vapor percentage increases up to 13.5%, and moreover, the activity can be recovered after vapor is removed.

Evaluation of the physi- and chemisorption of hydrogen in alkali (Na, Li) doped fullerenes

In this study, alkali doped fullerenes synthesized by two different solvent assisted mixing techniques are compared for their hydrogen uptake activity. In particular, we investigated the interaction of hydrogen with lithium and sodium doped fullerenes via physisorption. In addition, we present the first mass spectrometric evidence for the formation of C60H60 via chemisorption. Hydrogen physisorption isotherms up to 1 atm at temperatures ranging from 77 K to 303 K were measured demonstrating an increase in hydrogen uptake versus pure C60 and increased isosteric heats of adsorption for the lithium doped fullerene Li12C60. The hydrogen uptake in Na6C60, Li6C60, and Li12C60 was enhanced compared to pure C60. However, despite these improvements the low amount of physisorbed hydrogen at 1 atm and 77 K in these materials suggests that fullerenes do not possess enough accessible surface area to effectively store hydrogen due to their close packed crystalline nature.