Mesopore Size Distribution Research Articles

Experimental study on salt–metal organic framework composites for water absorption

In this article, MIL-101(Cr) powder material was successfully prepared by hydrothermal synthesis and combined with different mass fractions of CaCl2 by immersion method to obtain MIL-101(Cr)/CaCl2 composite materials. The physical properties of the adsorbent were determined by X-ray powder diffraction, N2 adsorption/desorption isotherm, TGA and FTIR. The water vapor adsorption performance of MOFs was tested by a gravimetric instrument to analyze the underlying mechanism. Results indicated that the specific surface area, total pore volume, and pore size distribution of micropores and mesopores of MIL-101(Cr)/CaCl2 composites decreased with increasing CaCl2 content. When P/P0 = 0.9, the water vapor equilibrium adsorption capacities of MIL-101(Cr), MIL-101(Cr)/CaCl2-10%, MIL-101(Cr)/CaCl2-20%, and MIL-101(Cr)/CaCl2-30% were 1.05, 0.88, 1.13, and 1.35 g/g, respectively. MIL-101(Cr)/CaCl2-30% agglomerated after water absorption, so MIL-101(Cr)/CaCl2-20% was selected as the final experimental material. The water vapor adsorption heat of MIL-101(Cr)/CaCl2-20% was 42–58 kJ/mol, which is close to the evaporation enthalpy of water (44 kJ/mol at 25 °C). The analysis of the adsorption kinetics showed the relatively uniform adsorption rate of MIL-101(Cr)/CaCl2-20%. Overall, MIL-101(Cr)/CaCl2-20% exhibited superior water vapor adsorption performance and have great potential for application to adsorption heat pumps.

Designing of Hollow ZSM-5 with Controlled Mesopore Sizes To Boost Gasoline Production from Syngas

Hollow mesoporous ZSM-5 zeolite is synthesized through a method of alkaline treatment with the TPAOH/NaOH mixed solution. The amount and pore size distribution of mesopores in the shell of hollow z...

Preparation of hydrophobic MFI zeolites containing hierarchical micro-mesopores using seeds functionalized with octyltriethoxysilane

In this work, we report the synthesis of hydrophobic MFI zeolites presenting a mesopore size distribution and high specific external area (∼288 m2 g−1), employing surface functionalization with octyltriethoxysilane (OTEOS). Previously, the MFI seeds were generated from a clear solution, followed by grafting with OTEOS and crystallization by hydrothermal treatment. The modifications of the properties of MFI synthesized with different amounts of OTEOS (0–15 mol%) were confirmed by X-ray powder diffraction, thermogravimetric, and elemental analyses. Contact angle (θ ∼140°) and 29Si NMR (T3 signals) measurements demonstrated that OTEOS was effectively grafted on the zeolite surface, resulting in powders with hydrophobic profiles. The grafting, which was mostly on the external surface, was crucial for avoiding the aggregation of MFI crystals during the synthesis, since the OTEOS chains (C8) caused steric hindrance, while allowing fine-tuning of the intercrystalline mesopore volume and increasing the external surface area. This effect was less pronounced when grafting of the MFI zeolites was carried out using organosilanes with longer carbon chain lengths (C12 and C16). This method enables the easy preparation of functionalized zeolitic materials, where the hierarchical pores and hydrophobic surface are essential characteristics for advanced technological applications.

The influence of porosity on radon emanation in alkali-activated mortars containing high volume bauxite residue

In this study the influence of porosity on radon emanation was examined when incorporating high volume bauxite residue, ranging from 30 to 90 wt%, in alkali-activated mortars. Samples were produced using the semi-dry pressing and the high-slump-casting techniques. The porosity and specific surface area were assessed by means of N2 adsorption/desorption. Upon alkali activation, part of the bauxite residue dissolved, increasing the emanation coefficient. The mesopore size distribution was strongly determined by the process followed, and higher cumulative mesopore volumes resulted generally in higher emanation rates. Low correlation was found between the specific surface area and emanation coefficient.

Hygroscopicity and dimensional stability of Populus euramericana Cv. modified by furfurylation combined with low hemicellulose pretreatment

Hygroscopicity and dimensional instability usually impair the service of wood products. To upgrade the property, fast-growing poplar wood (Populus euramericana Cv.) was treated with furfuryl alcohol at a concentration of 25% combined with low hemicellulose pretreatment. Equilibrium moisture content and dimensional changes were measured within the range of 0–96% relative humidity (RH) at 25 °C. New voids caused by hemicellulose loss suggested by the scanning electron microscope contributed to higher weight percent gain of furfural resin with more obvious bulking of cell walls. The size distribution of mesopores increased after low hemicellulose pretreatment but decreased much more after furfurylation from the analysis of nitrogen adsorption. After hemicellulose loss, moisture sorption was weakened indicated from the decrease in moisture content (MC) and hydrated MC as well as dissolved MC due to the decrement of accessible hydroxyl groups calculated by Hailwood–Horrobin theory. Furthermore, dimensional stability was improved. Furfurylation led to further reduction in moisture sorption and enhancement of dimensional stability, since water paths were blocked and less hydroxyl groups were accessible. The bulking also limited the swelling of cell walls. After the combined modification, over 45% reduction in moisture content and dimensional changes of wood at 60% RH can be achieved. Such upgraded fast-growing wood could be utilized more widely with a longer service life as a potential replacement for traditional high-quality solid wood and helpful with building a more efficient and environmentally friendly material industry.

Facile synthesis of mesoporous zeolite Y using seed gel and amphiphilic organosilane

Abstract Zeolite Y is widely used as an industrial catalyst for catalytic cracking of heavy feedstocks to lighter olefins. However, incorporation of uniform mesoporosity in zeolite Y without compromising the microporous characteristics is required to improve the catalyst efficiency and minimize catalyst deactivation. Here, we report a facile synthesis method for mesoporous zeolite Y (MPY sg ) using seed gel and amphiphilic organosilane, that results in mesoporous zeolite showing a narrow mesopore size distribution (3–4 nm) with high external surface area (110 m 2 g -1 ) and high micropore surface area (654 m 2 g -1 ). During the crystallization of MPY sg , the organosilane acted as a mesopore-generating agent, and the seed gel provided secondary nuclei that created a uniform mesoporous structure in the zeolite Y nanocrystals. Analysis of aluminosilicate precursors collected during the crystallization revealed that the crystallization process starts with a long nucleation period, followed by rapid crystal growth. Due to the highly accessible strong acid sites present on its external surface, MPY sg shows catalytic activity in the decalin cracking reaction higher than that of conventional microporous zeolite Y.

The influence of mesopore size distributions on the electrochemical activity and two-electron selectivity of the oxygen reduction reaction in nitrogen-doped and CoOx-loaded activated carbon

The electro-synthesis of hydrogen peroxide (H2O2) through the two-electron oxygen reduction reaction (ORR) is an inexpensive and environmentally friendly process. In this study, as catalysts for the ORR, two kinds of activated carbon (AC) with different mesopore size distributions are modified by nitrogen (N)-doping and cobalt oxide (CoOx)-loading treatment. It can be concluded that pyridinic-N and pyrrolic-N (48.94%) are more easily formed on the AC with narrow mesopore size distributions (AC-1, 2–5nm), however, graphite-N (63.9%) are more easily formed on the AC with broad mesopore size distributions (AC-2, 5–15nm). Furthermore, Co3O4 and CoO is the predominant crystal loaded onto the modified AC-1 and modified AC-2, respectively. The modified AC-1 has an extremely high propensity for a four-electron ORR pathway, while the modified AC-2 has an extremely high propensity for a two-electron ORR pathway. In addition, a rolling activated carbon electrode (RACE) with low-cost and high-efficiency is fabricated by modified AC-2. The H2O2 electro-synthesis rate and current efficiency for the RACE are 0.236±0.025mg/h/mA/cm2 and 63.25±6.79%, respectively.

Effect of swelling agent in the synthesis of porous nanocrystalline nickel-zirconia-ceria composite

Abstract Porous ceria-zirconia (Zr0·1Ce0·9O2−δ δ delete) powders were synthesized by a sol-gel route using inorganic chlorides (ZrCl4 and CeCl3·7H2O) as precursors, block copolymer P123 (PEO20PPO70PEO20) as the template and tri-isopropyl-benzene (TIPB) as the swelling agent. These porous materials show high surface area and gas permeability, important properties for Intermediate Temperature-Solid Oxide Fuel Cell (IT-SOFC) and catalytic applications. The samples were prepared with different P123:TIPB (w/w) % ratios (1:0, 1:1, 1:2 and 1:4), as a strategy to increase porosity. The samples were calcined at 400 °C in air to remove the template. Post-synthesis nickel impregnation was planned to obtain 3 and 10 (w/w) % of NiO after calcination. The structure and morphology of the samples were determined by X-ray diffraction (XRD), small angle X-ray scattering (SAXS), nitrogen adsorption isotherms (NAI) and transmission and scanning electron microscopies (TEM and SEM). The resulting materials have high specific surface area (≈110 m2. g-1) and a wide pore size distribution of mesopores (3–50 nm). They are formed by nanocrystals (≈15 nm) of the predominant (≈90%) F m 3 ¯ m cubic phase and by the P 4 2 / n m c tetragonal phase. The micrographs revealed that the nanocrystalline oxides have mesopores with slit shape and a secondary smaller mesoporosity with a narrow size distribution (≈4 nm). An increase of micropore volume (sizes

Sulfides/3D reduced graphene oxide composite with a large specific surface area for high-performance all-solid-state pseudocapacitors

Abstract Exploring highly efficient electrode materials is crucial for advancing clean energy storage devices such as pseudocapacitors (PCs). Transition-metal sulfides (TMSs), typically involving conventionally stoichiometric ternary components (such as NiCo2S4 and Ni2CoS4), are suggested as promising electrode nanomaterials for PCs. Herein, a large-specific-surface-area NiS2/CoS2 composite anchored on three-dimensional reduced graphene oxide (NiS2/CoS2/3DGO) is prepared by the sulfuration of a needle-like NiCo-hydroxycarbonate precursor grown on the 3DGO support. The NiS2/CoS2/3DGO composite is endowed with the following advantages: CoS2 and NiS2 composite, a large specific surface area (200.48 m2 g−1) and narrow mesoporous size distribution, as well as high conductivity. The composite electrode indeed delivers a highly attractive capacitance of 2451 F g−1 at 1 A g−1, which is comparable or superior to most TMS electrodes reported previously. Furthermore, the all-solid-state NiS2/CoS2/3DGO//activated carbon for PCs achieves a decent energy density and power density at 1 A g−1, and an attractive reversible capacitance retention of 97.2% after 5000 cycles at the high current density of 20 A g−1. Such an improvement strategy can be extended for constructing diverse transition-metal sulfides and phosphides as electrode materials for energy storage.

Carbide derived carbon obtained from SiC-based fibers by phosphating-NaOH bath process

Abstract Carbide derived carbon (CDC) are unique materials with tunable micro and mesopore size distribution. They are produced selectively removing metallic elements from carbides. Halogenation or hydrothermal treatments were, therefore, extensively studied. The study reports a new route to produce such carbon, aforementioned CDCp, applied to SiC-based fibers by reacting phosphoric acid vapors at 580–800 °C range, followed by condensed silicophosphate dissolution in tempered NaOH bath. Fibers could be, this way, fully or partially transformed. Obtained CDCp show a broad pore size distribution extending from microporosity (7–9 A) to mesoporosity (up to 60 A), specific surface area >1000 m2 g−1 and pore volume >0.7 cm3 g−1. Mesoporosity may infer from partial carbon oxidation or in-situ silicophosphate and carbon demixion at nanoscale. CDCp burn-off kinetics and tensile strength of non-etched fiber core are discussed. Depending on phosphating conditions, monolayer or concentric CDCp tubes could coat each individual fiber within complex fabric geometry.

Analytical equation for the mesopore size distribution function of open cylindrical capillaries

For the characterization of porous structures, besides the specific surface area, the pore size distribution is of special interest. In this paper, the pore size distribution of mesoporous structures is calculated from the adsorption branch of the hysteresis loop, whereby only loops of type H1 are considered. The modeling is done only for cylindrical capillaries and the calculation of the pore size distribution is done by a combination of the percolation theory and the theory of capillary condensation. By applying percolation theory to the adsorption process, the pressure dependence of pore filling during capillary condensation is described. Because of a lack of strictly theoretically based equations for the adsorption process by capillary condensation, a mathematical adaptation to measured data is done by the Bernoulli equation. This is proposed by the authors for the first time for a description of adsorption–desorption processes. Thus a new, strictly thermodynamic method to calculate the mesopore size ...

How does delignification influence the furfurylation of wood?

To investigate the influence of delignification on wood furfurylation, poplar wood (Populus euramericana Cv.) was partly delignified prior to the impregnation of furfuryl alcohol (FA) at concentration of 25%. The observation by using scanning electron microscope (SEM) and confocal laser scanning microscopy (CLSM) showed that many intercellular spaces appeared in middle lamella and cell corners in the wood with 8.86% lignin loss (LL), after further furfurylation, these spaces were filled with polymerized furfural resin, which contributed to the more uniform distribution of modifier and larger bulking of cell wall in furfurylated wood with low lignin (LF) than furfurylated control (CF). The size distribution of mesopores increased after delignification but decreased after furfurylation, and the specific surface area was reduced over 20% for LF with about 50% total pore volume decrease compared with the control from the analysis of nitrogen adsorption. Lignin loss and chemical polymerization of furfural resin were confirmed but without chemical reaction between FA and cell wall components by both results of Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (NMR). Delignification resulted in increased equilibrium moisture content (EMC) and dimensional instability, after further furfurylation, the EMC and dimensional changes of LF decreased and were lower than those of control by 16.3% on average, suggesting the availability of furfurylation in reducing moisture sorption and improving dimensional stability of low lignin content wood. The number of accessible hydroxyl groups in wood calculated by using Hailwood-Horrobin theory exhibited in the following order: LL > control > LF > CF. The results can potentially help with understanding the action of delignification in wood furfurylation, as well as providing information on the possibility of make sustainable use of wood products with degraded lignin by furfurylation.

Controlled microstructure in two dimensional Ni-Co LDH nanosheets-crosslinked network for high performance supercapacitors

Based on the electrochemical mechanism of Faraday supercapacitors (FSs), we design a microstructure configuration of electrode materials (EMs) in this work, aiming to promote the electrochemical performance of FSs. This configuration of EMs has two dimensional sheets-crosslinked network with narrow mesopore size distribution. It is reasonable to believe that the configuration is in favor of the electrochemical performance of EMs to the greatest extent. We try to build this structure configure using Ni-Co layered double hydroxide (LDH) nanosheets as building blocks by a facile sol-gel approach. Due to the Co2+ ions, we realize this structure configuration consisting of Ni-Co LDH nanosheets. Benefiting from the advantages of this configuration, the Ni-Co LDH presents high electrochemical performance. It has high specific capacity of 1170 C g−1 at low current density of 2.0A g−1, and 500 C g−1 at high current density of 39.6 A g−1. The asymmetric supercapacitors of Ni-Co LDH exhibit high energy density of 74.37 Whkg−1 at low power density of 492 Wh kg−1 and keep relatively high energy density of 15.99 Whkg−1 at high power density of 6395 Wh kg−1. These results suggest that the designed structure configuration of EMs is rational for application in FSs.

Structural Differences of Spontaneous Combustion Prone Inertinite-Rich Chinese Lignite Coals: Insights from XRD, Solid-State13C NMR, LDIMS, and HRTEM

China has a considerable lignite deposit in the Xinjiang province, but surface and underground coal seam fires pose a threat to the resources, environment, economy, and health. As the chemical and physical structure impacts coal fire propensity and behavior, two raw Xinjiang lignites were examined from the Shaerhu (SEH) and Piliqing (PLQ) Collieries. The SEH lignite is more prone to spontaneous combustion (from regional observations). These coals were of the same geological age and were both inertinite-rich 69.8 and 95.6% for SEH and PLQ, respectively (by the point counting approach). The more spontaneous combustion prone lignite had a significantly higher micropore contribution and surface area (92.4% and 195.6 m2/g), while both coals had similar micro- and mesopore size distribution ranges. Despite being classified as lignite by the mean vitrinite random reflectance (Rr, 0.30 and 0.26%) the inertinite contribution displaces some of the structural properties to be similar to the vitrinite-rich, high-vola...

Preparation and application of ordered mesoporous carbon-based solid acid catalysts for transesterification and epoxidation

Ordered mesoporous carbon (OMC) was prepared via the inverse replication method using SBA-15 as a hard template and sucrose as a carbon precursor. OMC was sulfonated to obtain the solid acid catalysts, such as OMC-SS and OMC-DS, by heating with sulfuric acid or coupling with sulfanilic acid diazonium. TEM and small-angle X-ray diffraction (XRD) results showed that OMC, OMC-SS, and OMC-DS exhibited ordered porous structures. XPS and Raman analysis showed that OMC had graphite structure. N2-BET analysis indicated that OMC, OMC-SS, and OMC-DS had average pore diameters of 3.0–3.3 nm and exhibited bimodal mesopore size distributions. Moreover, N2-BET analysis revealed that OMC, OMC-SS, and OMC-DS had surface areas of 1411, 924 and 1001 m2/g, respectively. The surface acid contents of OMC-SS and OMC-DS were 3.9–4.0 mmol H+/ g and higher than those of OCM (2.8 mmol H+/g). FTIR results demonstrated that –SO3H was present on OMC-SS and OMC-DS. OMC-SS and OMC-DS were used to catalyze the transesterification and epoxidation of waste frying oil. The transesterification reactions catalyzed using OMC-SS and OMC-DS provided the maximum yields of fatty acid methyl esters of 90.3 ± 3.3% and 89.0 ± 2.1%, respectively. The double-bond conversion rates of epoxidation reactions catalyzed using OMC-SS and OMC-DS reached 77.2 ± 1.9% and 68.5 ± 2.6%, respectively. The epoxy yields of epoxidation reactions catalyzed using OMC-SS and OMC-DS were 70.3 ± 2.4% and 65.1 ± 1.8%, respectively.

A Facile Route to Synthesize Micron Size Nearly Spherical Mesoporous Silica Particles

AbstractFor many applications as structured packing material, the micron size spherical silica particles with the bicontinuous mesoporous structures are required. Herein, we report a facile route to synthesize the micron size nearly spherical mesoporous silica (MSNSMS) particles. The chitosan is crucial in the synthesis strategy as an adjuvant agent to facilitate the formation of the micron size nearly spherical particles. The MSNSMS particles demonstrate narrow mesopore and particle size distributions with the average particle sizes at 3.6 μm (MSNSMS‐0.5) or 4.7 μm (MSNSMS‐1). The MSNSMS samples possess the large ordered domains of pure bicontinuous mesoporous structure with the interpenetrating cylindrical pores at about 8 nm in diameter. The MSNSMS particles are promising structured packing material candidate for catalyst support applications.

The processing of Pinus radiata: Pore size distribution changes in the cell wall structure studied by pressure plate technique and mercury intrusion porosimetry

The pore size distribution of cell walls in softwood pulps was studied using the pressure plate technique and mercury intrusion porosimetry, which together make it possible to cover the range from 101 to 106 nm in pore sizes (mesopores and macropores). The differences in pore size distribution between never-dried pulp from a fiber line, industrially-dried pulp, and laboratory-dried pulps were evaluated. The results showed an increase in the relative pore volume (100 to 2,000 nm) between industrial washing and bleaching stages. Also, mercury porosimetry showed a broadening of the pore size distribution of cell walls after industrial drying. Results showed that, besides the changes in micropore and mesopore size distributions, the macropore range is also affected by processing and drying.

Stability of a highly dealuminated Y-zeolite in liquid aqueous media

Abstract A dealuminated Y-zeolite with a nSi/nAl ratio of 130 is treated in pure water and aqueous solutions of NaCl at different pH values between 3 and 7 at 100 °C for up to 3 weeks. The change of specific micropore volume, the specific external surface, and the mesopore size distribution are monitored by N2-adsorption (77 K). The decrease of micropore volume proceeds due to a zero order kinetics. The zeolite loses no mass, but according to an XRD analysis the loss of micropore volume is paralleled by the formation of mainly amorphous material. The amorphization is assumed to start at the outer surface of the zeolite crystals leading to a core-shell distribution of amorphous and zeolitic material. The amorphization is coupled with the formation of mesopores and an increasing external surface area. The evolution of mesopores mainly occurs at diameters near the lower boundary region of the pore size analysis by N2 sorption (3 nm). The degradation is catalyzed by hydroxide ions present in bulk water. Both the exchange of the acidic protons with Na+-ions and the presence of NaCl in the water phase accelerate the degradation at pH 7. The zeolite is decomposed in 1 M NaCl at pH 7 and 100 °C within 40 min. However, when the pH is lowered to 3, it is stable in 1 M NaCl for more than 10 days. The protonated form in pure water is about half as stable as the Na+-form in 1 M NaCl at pH 3.

3D Graphene-based macro-mesoporous frameworks as enzymatic electrodes

An efficient method was developed to fabricate three-dimensional (3D) graphene-based nanomaterials with hierarchical macro-mesoporous structures as novel enzymatic electrode materials. The 3D continuously interconnected macropores were generated by hydrothermal self-assembly of graphene oxide sheets to form 3D graphene-based frameworks, and uniform mesopores on the surface of graphene frameworks were obtained by replicating the previously synthesized mesoporous silica. Due to the integration of macropores that can promote the efficiency of mass transfer, and mesopores that can facilitate enzyme immobilization and electron transfer, the unique 3D graphene-based macro-mesoporous frameworks with narrow mesopore size distribution, large surface area and high electrical conductivity can be applied as an excellent platform to immobilize glucose oxidase as enzymatic electrodes, displaying enhanced glucose-sensing properties. This approach can be utilized to fabricate various 3D hierarchical macro-mesoporous nanomaterials for application in a broad range of sensors, supercapacitors, batteries and catalysis.

Adsorption Analyses of Phenol from Aqueous Solutions Using Magadiite Modified with Organo-Functional Groups: Kinetic and Equilibrium Studies.

Organically-modified magadiite (MAG–CTAB–KH550) was synthesized via ion-exchange method and condensation reaction in the presence of pure magadiite (MAG), cetyltrimethylammonium bromide (CTAB) and γ-aminopropyltriethoxysilane (KH550) in aqueous solution in this research. This new adsorbent material was studied using scanning electron microscope (SEM), X-ray diffraction (XRD), Fourier transforms infrared spectroscopy (FTIR), and N2 adsorption/desorption isotherms process. It was found that the MAG–CTAB–KH550 has high Brunaur-Emmet-Teller (BET) specific surface area and mesoporous pore size distribution which enhanced its ability to remove phenol in aqueous solution; and, the value of pH has a relatively large impact on the adsorption behavior of the sorbent. Finally, the adsorptive behavior of the mesoporous material on phenol was followed pseudo-second-order kinetic adsorption model. In contrast, the adsorption equilibrium isotherm was better performed Langmuir isotherm model than the Freundlich isotherm model; in addition, the results also showed that the MAG–CTAB–KH550 had a better adsorption capacity and removal efficiency than MAG.