Pore-filling Effect Research Articles

BiOBr@SiO2 flower-like nanospheres chemically-bonded on cement-based materials for photocatalysis

Endowment of photocatalytic property on the surface of concrete structure can contribute to the self-cleaning of the structure and purification of the polluted environment. We developed a nano-structured BiOBr@SiO2 photocatalyst and innovatively used for surface-treatment of cement-based materials with the hope of attaining the photocatalytic property in visible-light region and surface modification/densification performances. The SiO2 layer on the flower-like BiOBr@SiO2 helps to maintain a stable distribution of the photocatalyst, as well as achieving a chemical bonding between the coating and the cement matrix. Results showed that the color fading rate of during the degradation of Rhodamine B dye of the BiOBr-cem sample is 2 times higher compared with the commonly studied C, N-TiO2-cem sample. The photo-degradation rates of samples BiOBr-cem and BiOBr@SiO2-cem are 93 and 81% within 150min, respectively, while sample BiOBr@SiO2-cem reveals a denser and smoother surface after curing for 28days and pore-filling effect at size within 0.01–0.2μm when compared with untreated samples. Moreover, additional C-S-H gel can be formed due to the pozzolanic reaction between BiOBr@SiO2 and the hardened cement matrix. Both advantages of the BiOBr@SiO2 favor its application for surface-treatment of hardened cement-based material to acquire an improved surface quality, as well as durable photocatalytic functionality.

Adsorptive removal of pharmaceutical antibiotics from aqueous solution by porous covalent triazine frameworks

The exposures of pharmaceutical antibiotics in water solution caused potential risks for ecological environment and human health. In the present study, porous covalent triazine frameworks (CTFs) were synthesized and the adsorption behavior of sulfamethoxazole (SMX) and tylosin (TL) was investigated. The CTFs were characterized by X-ray diffraction, transform infrared and N2 adsorption/desorption. Sulfamethoxazole displayed much stronger adsorption than tylosin on microporous CTF-1 adsorbent due to the pore-filling effect. While the adsorption of bulky tylosin on microporous CTF-1 was suppressed because of the size exclusion effect. Additionally, the porous CTFDCBP showed stronger adsorption affinity and faster adsorption kinetics than other porous adsorbents, which was attributed to wide pore size distribution and open pore structure. Findings in this study highlight the potential of using porous CTFs as a potential adsorbent to eliminate antibiotics from water, especially for selective adsorption of bulky molecular pollutant.

Effect of Friedel’s salt on strength enhancement of stabilized chloride saline soil

In the field of soil stabilization, only calcium silicate hydrate (CSH) and ettringite (AFt) as hydration products have been reported to directly contribute to the strength enhancement of the soil. A chloride dredger fill, an artificial chloride saline soil, and a non-saline soil were stabilized by Portland cement (PC) and PC with Ca(OH)2 (CH) with different contents. A series of unconfined compressive strength (UCS) tests of stabilized soil specimen after curing for 7 d and 28 d were carried out, and the hydration products and microstructure of the specimens were observed by X-ray diffractometry (XRD), scanning electronic microscopy (SEM), and energy-dispersive X-ray analysis (EDXA). The results showed that the strengths of PC+CH-stabilized chloride saline soils were much higher than those of PC-stabilized soils. A new hydration product of calcium aluminate chloride hydrate, also known as Friedel’s salt, appeared in the PC+CH-stabilized chloride saline soils. The solid-phase volume of Friedel’s salt expanded during the formation of the hydrate; this volume filled the pores in the stabilized soil. This pore-filling effect was the most important contribution to the significantly enhanced strength of the PC+CH-stabilized chloride saline soils. On the basis of this understanding, a new optimized stabilizer was designed according to the concept that the chloride in saline soil could be utilized as a component of the stabilizer. The strength of the chloride saline soils stabilized by the optimized stabilizer was even further increased compared with that of the PC+CH-stabilized soils.

Assessing the Surface Area of Porous Solids: Limitations, Probe Molecules, and Methods.

In this modeling study, the uses of nitrogen (77.3 K), probe molecule of choice for decades, and argon, opted as alternative in the 2015 IUPAC report on adsorptive characterization, as probe molecules for geometric surface area determination are compared. Graphene sheets possessing slit-shaped pores with varying size (width) are chosen as model porous solids, and different methods for the determination of specific surface areas are investigated. The BET method, which is the most commonly applied analysis, is compared to the Langmuir and relatively recently proposed ESW (excess sorption work) method. We show that either using argon or nitrogen as adsorptive, the physical meaningfulness of adsorption-derived surface areas highly depends on the pore size. When less than two full layers of adsorbate molecules can be formed within slitlike pores of a graphitic material (Dpore < 5.8 Å for Ar/N2), adsorption-derived surface areas are about half that of the geometric surface area. Between two and four layers (6.8 < Dpore < 12.8 Å), adsorption surface areas can be significantly larger (up to 75%) than the geometric surface area because monolayer-multilayer formation and pore filling cannot be distinguished. For four or more layers of adsorbate molecules (Dpore > 12.8 Å), adsorption-derived surface areas are comparable to their geometrically accessible counterparts. Note that for the Langmuir method this only holds if pore-filling effects are excluded during determination. This occurs in activated carbon materials as well. In the literature, this indistinguishability issue has been largely overlooked, and erroneous claims of materials with extremely large surface areas have been made. Both the BET and Langmuir areas, for Dpore > 12.8 Å, correspond to geometric surface areas, whereas the ESW method yields significantly lower values. For the 6.8 Å < Dpore < 12.8 Å range, all methods erroneously overestimate the specific surface area. For the energetically homogeneous graphene sheets, differences between argon and nitrogen for the assessment of surface areas are minor.

Effects of recycled glass on properties of architectural mortar before and after exposure to elevated temperatures

When put into practical uses, self-compacting architectural mortars (SCAM) containing recycled glass (RG) may face the risk of exposure to fire. It is of great interest to investigate the effect and the roles of RG acting in the SCAM after exposing to high temperatures. In this study, RG was used to replace river sand at ratios of 0%, 25%, 50%, 75% and 100% by weight. The results showed that at room temperature, the increase in RG content slightly reduced the thermal conductivity, compressive strength and elastic modulus of the SCAM samples, but had a negligible influence on the chloride-ion penetration rate. Although increasing the exposure temperatures resulted in reductions in compressive strength and elastic modulus of the SCAM samples, when the temperature was increased to 800 °C, the incurred melting and re-solidification process of the RG enabled a pore-filling effect to fill up micro-cracks and pores in the mortar matrix. Such beneficial effects were more obvious for elastic modulus than for compressive strength. It was also found that the 100% RG incorporated SCAM was able to maintain a pleasant appearance (negligible changes were induced in its appearance) after undergoing 800 °C exposure. This study demonstrated that the introduction of 100% RG in the SCAM allowed an attractive combination of high strength (45.7 MPa) and aesthetically pleasing appearance even after exposure to 800 °C. This paved way for further and broader applications of RG based SCAM products in the market. However, the melting properties of RG may incur adverse effects on the mechanical properties of the SCAM sample under loading conditions, which necessitate further studies to clarify such a potential limit.

Enhanced pore filling of spiro-OMeTAD by enlarging the porosity of TiO2 films and its effects on the photovoltaic performance of ss-DSCs

Four kinds of TiO2 electrodes with different porosities were prepared by adding different ratios of ethyl cellulous into a Dyesol 18-NRT paste. Higher polymer ratios contributed to the higher porosity of TiO2 films. All electrodes were spin-coated with spiro-OMeTAD and fabricated into solid-state dye-sensitized solar cells (ss-DSCs). This simple method allowed more spiro-OMeTAD penetrated into the more porous TiO2 films. This result demonstrated the pore-filling effect of hole transport materials on the photovoltaic performance of ss-DSCs. Photoluminescence and electrical impedance spectra measurements were introduced to investigate the dye regeneration, charge transport, and recombination kinetics of the solar cells. The increased pore filling of spiro-OMeTAD could enhance hole injection, hole transport, and recombination retardation, thus providing good charge collection efficiency and long recombination lifetime and resulting in the high short-circuit current density, open-circuit voltage, fill factor, and energy conversion efficiency of the solar cells. An efficiency enhancement of 34 % was obtained by using this method. However, further increasing the TiO2 porosity decreased the electron transport, thus causing a low charge collection and reducing cell performance.

시멘트계 제품의 CO2양생 활용을 위한 기초 연구

As global warming is higher by <TEX>$CO_2$</TEX>, most of countries have an effort to develop <TEX>$CO_2$</TEX> reducing technology like a <TEX>$CO_2$</TEX> sequestration and a <TEX>$CO_2$</TEX> curing method using cement based materials. In this study, <TEX>$CO_2$</TEX> uptake rate, compressive strength and length were investigated when <TEX>$CO_2$</TEX> curing method was applied in cement mortar. The <TEX>$CO_2$</TEX> uptake rates were ranged from 10.1 % to 11.6 %, average 10.5 % by mass measurement method. On the early compressive strength, 1 hour <TEX>$CO_2$</TEX> curing specimens were higher than 1 hour atmospheric curing specimens but lower than 5 hours steam curing specimens. As time was elapsed until 28 days, the compressive strengths of specimens by atmospheric curing and steam curing were similarly increased both. But the compressive strengths of 1 hour <TEX>$CO_2$</TEX> curing specimens were lower than other two curing methods. The dry shrinkage rates of 1 hour <TEX>$CO_2$</TEX> curing specimens were lower than those of other two curing methods by pore-filling effect of carbonation.

Effect of sodium silicate- and ethyl silicate-based nano-silica on pore structure of cement composites

This study proposes using sodium silicate-based nano-silica (SS) in cement composites. The effect of the addition of the proposed nano-silica on cement composites was compared to that of conventional ethyl silicate-based nano-silica (ES) and silica fume (SF). This study found that the inclusion of SS in cement composites has mainly two effects on their properties: one is a fast pozzolanic reaction, and the other is a pore-filling effect in a cement matrix. As a result, SS dramatically improves the early-age strength of cement composites by up to 184% and 152%, compared to a control specimen and the specimen with ES inclusion, respectively. Calorimetry, X-ray diffraction (XRD), scanning electron microscope (SEM) and mercury intrusion porosimetry (MIP) tests were conducted to monitor the effects of these nano-silicas.

Adsorption of natural organic matter analogues by multi-walled carbon nanotubes: Comparison with powdered activated carbon

With increasing production and application of carbon nanotubes (CNTs), the interaction between CNTs and natural organic matter (NOM) in water has been attracting more and more concerns. In this study, adsorption of three NOM analogues including salicylic acid (SA), phthalic acid (PA) and catechol (CA) on multi-walled carbon nanotubes (MWCNTs) as well as commercial powdered activated carbon (PAC) were investigated. All adsorption isotherms were fitted well by Freundlich isotherm model (Radj2>0.99), which was supported by the site energy distribution analysis. PAC possessed 2–10 times higher adsorption capacities towards the three compounds than MWCNTs, indicating the presence of pore-filling effect. Hydrophobic interaction, electrostatic interaction, hydrogen bond and π–π interaction acted simultaneously but had different contributions in the adsorption of the three NOM analogues on PAC and MWCNTs. Thermodynamic analysis revealed that SA and PA adsorption on the two adsorbents were exothermic while CA endothermic. Variation of the thermodynamic parameters including ΔG0, ΔH0 and ΔS0 depended on the adsorbate loadings. These findings are expected to promote the understanding of the interaction between NOM and CNTs for further evaluating the environmental risks of nanomaterials.

Adsorption of Natural Organic Matter Surrogates from Aqueous Solution by Multiwalled Carbon Nanotubes

Adsorption of two natural organic matter (NOM) surrogates (tannic acid and gallic acid) by powdered activated carbon (PAC) and four kinds of multiwalled carbon nanotubes (MWCNTs) with different diameters was investigated in aqueous solution. The tannic acid (TA) adsorption isotherm fit the Langmuir model best, while adsorption of gallic acid (GA) fit the Freundlich model. PAC has a higher adsorption capacity for GA due to the pore-filling effect, while TA adsorption on PAC was lower than that on MWCNTs because of the molecule sieving effect. Adsorption of GA and TA on MWCNTs decreased with increasing MWCNT diameter, but neither surface area nor total pore volume alone can fully explain adsorption of the two NOM surrogates on MWCNTs. Adsorption mechanisms including electrostatic interaction, hydrophobic interaction, hydrogen bond, and π–π interaction play roles in the adsorption process. This study implies that NOM properties have a great effect on their adsorption on MWCNTs, and these properties should be further considered when evaluating the risks of NOM-coated nanomaterials.

Adsorptive removal of hydrophobic organic compounds by carbonaceous adsorbents: A comparative study of waste-polymer-based, coal-based activated carbon, and carbon nanotubes

Adsorption of the hydrophobic organic compounds (HOCs) trichloroethylene (TCE), 1,3-dichlorobenzene (DCB), 1,3-dinitrobenzene (DNB) and γ-hexachlorocyclohexane (HCH) on five different carbonaceous materials was compared. The adsorbents included three polymer-based activated carbons, one coal-based activated carbon (F400) and multiwalled carbon nanotubes (MWNT). The polymer-based activated carbons were prepared using KOH activation from waste polymers: polyvinyl chloride (PVC), polyethyleneterephthalate (PET) and tire rubber (TR). Compared with F400 and MWNT, activated carbons derived from PVC and PET exhibited fast adsorption kinetics and high adsorption capacity toward the HOCs, attributed to their extremely large hydrophobic surface area (2700 m2/g) and highly mesoporous structures. Adsorption of small-sized TCE was stronger on the tire-rubber-based carbon and F400 resulting from the pore-filling effect. In contrast, due to the molecular sieving effect, their adsorption on HCH was lower. MWNT exhibited the lowest adsorption capacity toward HOCs because of its low surface area and characteristic of aggregating in aqueous solution.

Investigation on positron annihilation characteristics of CO 2-exposed zeolite

In this study, the lifetime spectra of positron annihilation for CO 2-exposed zeolite 4A at different conditions were measured. The effects of subjecting zeolite 4A to baking treatment and exposing it to CO 2 at different pressures on the positronium (Ps) annihilation characteristics was investigated using positron annihilation lifetime spectroscopy (PALS). Zeolite 4A was chosen as the medium because of its rigidity, stability, and well-understood structure. Its structure consists of cavities that can be classified into two types: α-cage and β-cage. Zeolite 4A at vacuum (or dehydrated) conditions gave the longest lifetime, whereas that at ambient (or hydrated) conditions, at which water molecules are sorbed in the cavities of zeolite 4A, gave the shortest lifetime. The water molecules in zeolite 4A cavities would inhibit the ortho-positronium (o-Ps) formation probability. At lower gas sorption, the CO 2 gas molecules exhibited the pore-filling effect, resulting in a decrease in the o-Ps lifetime. However, at higher CO 2 sorption, the shielding effect in the α-cage increased with CO 2 pressure and led to an increase in the o-Ps lifetime. When the α-cage cavity was filled with the CO 2 gas molecules at pressures greater than 5 atm, o-Ps tended to migrate from the α-cage to the β-cage.

Adsorption of Pharmaceutical Antibiotics on Template-Synthesized Ordered Micro- and Mesoporous Carbons

The presence of pharmaceutical antibiotics in aquatic environments poses potential human health and ecological risks. We synthesized ordered micro- and mesoporous carbons, and further conducted batch experiments to systematically examine their adsorption properties toward three antibiotics, sulfamethoxazole, tetracycline, and tylosin, in aqueous solution. In comparison, nonporous graphite, single-walled carbon nanotubes, and two commercial microporous activated carbons were included as additional adsorbents. Adsorption of low-sized sulfamethoxazole was stronger on the activated carbons than on other carbonaceous adsorbents resulting from the pore-filling effect; in contrast, due to the size-exclusion effect adsorption of bulky tetracycline and tylosin was much lower on the activated carbons, especially for the more microporous one, than on the synthesized carbons. After normalizing for adsorbent surface area, adsorption of tetracycline and tylosin on the synthesized carbons was similar to that on nonporous graphite, reflecting complete accessibility of the adsorbent surface area in adsorption. Additionally, compared with other porous adsorbents the synthesized carbons showed faster adsorption kinetics of tetracycline and tylosin, which was attributed to their regular-shaped, open and interconnected three-dimensional pore structure. The findings indicate that template-synthesized micro- and mesoporous carbons are promising adsorbents for the removal of antibiotics, particularly, the bulky and flexible-structured compounds, from aqueous solution.

The Inconsistency in Adsorption Properties and Powder XRD Data of MOF-5 Is Rationalized by Framework Interpenetration and the Presence of Organic and Inorganic Species in the Nanocavities

MOF-5 is the archetype metal-organic framework and has been subjected to numerous studies the past few years. The focal point of this report is the pitfalls related to the MOF-5 phase identification based on powder XRD data. A broad set of conditions and procedures have been reported for MOF-5 synthesis. These variations have led to materials with substantially different adsorption properties (specific surface areas in the range 700 to 3400 m(2)/g). The relatively low weight loss observed for some as synthesized samples upon solvent removal is also indicative of a low pore volume. Regrettably, these materials have all been described as MOF-5 without any further comments. Furthermore, the reported powder XRD patterns hint at structural differences: The variations in surface area are accompanied by peak splitting phenomena and rather pronounced changes in the relative peak intensities in the powder XRD patterns. In this work, we use single-crystal XRD to investigate structural differences between low and high surface area MOF-5. The low surface area MOF-5 sample had two different classes of crystals. For the dominant phase, Zn(OH)2 species partly occupied the cavities. The presence of Zn species makes the hosting cavity and possibly also adjacent cavities inaccessible and thus efficiently reduces the pore volume of the material. Furthermore, the minor phase consisted of doubly interpenetrated MOF-5 networks, which lowers the adsorption capacity. The presence of Zn species and lattice interpenetration changes the symmetry from cubic to trigonal and explains the peak splitting observed in the powder XRD patterns. Pore-filling effects from the Zn species (and partly the solvent molecules) are also responsible for the pronounced variations in powder XRD peak intensities. This latter conclusion is particularly useful for predicting the adsorption properties of a MOF-5-type material from powder XRD.

The synthesis of ZSM-5 and Theta-1 in the presence of diethanolamine: Theoretical modeling of ZSM-5

The synthesis of zeolites from gels comprising silica, alumina, potassium and/or sodium hydroxide or chloride, diethanolamine, and water has been studied previously, and several zeolites including Theta-1 and ZSM-5 were synthesized. Diethanolamine was considered to have both a pore-filling role and charge-compensatory role (if the amine group was protonated), and hence its overall effectiveness as a stabilizer depends upon the type of zeolite structure and the aluminum content. From these considerations, a model has been proposed which has been used to provide information on the stabilizing effect of diethanolamine within Theta-1 and ZSM-5. For a range of framework aluminum contents and distributions, the model was used to calculate the fraction of diethanolamine which was protonated and the ratio of metal cations to aluminum. A good agreement was observed between calculated and experimentally obtained data. The importance of the SiO 2 Al 2O 3 ratio on the formation of ZSM-5 and Theta-1 may be explained in terms of the relative stability afforded by the pore-filling effect of diethanolamine and its charge-compensating role. From these considerations, the model may be used to predict the gel SiO 2 Al 2O 3 ratio required to produce the two zeolites. The SiO 2 Al 2O 3 ratios calculated using the model are in good agreement with the values obtained from experiments.