• Journal of the Mineralogical Society of Korea
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• v.32 no.3
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• pp.151-162
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• 2019

Todorokite, a tunnel-structured manganese oxide, can contain cations within the relatively large nanopores created by the $3{\times}3$ Mn octahedra. Because todorokite is poorly crystalline and found as aggregates mixed with other phases of Mn oxides in nature, the coordination structure of cations in the nanopores is challenging to fully characterize in experiment. In the current article, we report the atomistic coordination structures of $Mg^{2+}$ ions in todorokite tunnel nanopores using the classical molecular dynamics (MD) simulations. In experiment, $Mg^{2+}$ is known to occupy the center of the nanopores. In our MD simulations, 60 % of $Mg^{2+}$ ions were located at the center of the nanopores; 40 % of the ions were found at the corners. All $Mg^{2+}$ located at the center formed the six-fold coordination with water molecules, just as the ion in bulk aqueous solution. $Mg^{2+}$ ions at the corners also formed the six-fold coordination with not only water molecules but also Mn octahedral surface oxygens. The mean squared displacements were calculated to examine the dynamic features of $Mg^{2+}$ ions in the one-dimensional (1D) nanopores. Our MD simulations indicate that the dynamic features of water molecules and the cations observed in bulk aqueous solution are lost in the 1D nanopores of todorokite.

• Korean Journal of Mineralogy and Petrology
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• v.36 no.4
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• pp.221-232
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• 2023

Carbon neutrality requires carbon dioxide reduction technology and alternative green energy sources. Palygorskite is a clay mineral with a ribbon structure and possess a large surface area due to the nanoscale pore size. The clay mineral has been proposed as a potential material to capture carbon dioxide (CO₂) and possibly to store eco-friendly hydrogen gas (H2). We report our preliminary results of grand canonical Monte Carlo (GCMC) simulations that investigated the adsorption isotherms and mechanisms of CO₂ and H₂ into palygorskite nanopores at room temperature. As the chemical potential of gas increased, the adsorbed amount of CO₂ or H₂ within the palygorskite nanopores increased. Compared to CO₂, injection of H₂ into palygorskite required higher energy. The mean squared displacement within palygorskite nanopores was much higher for H₂ than for CO₂, which is consistent with experiments. Our simulations found that CO₂ molecules were arranged in a row in the nanopores, while H₂ molecules showed highly disordered arrangement. This simulation method is promising for finding Earth materials suitable for CO₂ capture and H₂ storage and also expected to contribute to fundamental understanding of fluid-mineral interactions in the geological underground.

• Journal of the Korean Recycled Construction Resources Institute
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• v.7 no.2
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• pp.166-173
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• 2019

In this paper, the reaction properties of silica source in the accelerated curing conditions using autoclave and the fundamental properties of inorganic Micro Defect Free(MiDF) concrete using silica source are studied. Studies show that Si ions elution rate from silica source in autoclave curing is higher in amorphous source. In tap water conditions, solids which is source after autoclaved curing show a higher mass reduction in amorphous materials, which is attributed to the higher elution rate of ion. In $Ca(OH)_2$ solution conditions, amorphous materials show higher mass increase, due to increase in C-S-H minerals. From experiment for influence on the properties of MiDF concrete by using nano silica materials, the specimen with silica fume shows an increase in compressive strength and a decrease in absorption depending on replacement rate up to 5.5%, while nano silica with amorphous phase and high-fineness shows a decrease in compressive strength and decrease in the water absorption. The specimen with nano silica increases the pore below 10,000nm, but reduces pore between 10,000 and 100,000nm. The above results show that the porosity and absorption rate of MiDF concrete can be reduced by using amorphous nano-size silica. However, to reduce the pore of 50 to 10,000nm, better dispersion of nano material in the cement matrix will be necessary. We will focus on the this item in the next research.

• Journal of the Korea institute for structural maintenance and inspection
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• v.20 no.1
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• pp.56-63
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• 2016

This experiment was compared and analyzed between the original surface paint through chloride penetration, neutralization, freeze-thaw and chemical corrosion resistance measuring internal structure and volume of voids in order to evaluate the effect of increase in durability of the newly modeled nano synthesized polymer paint painted on concrete surface which results improvement on air permeability to increase the durability of concrete structures. The test result of measuring volume of void and inner structure, concrete, spreaded with nano synthesized polymer paint, showed decreasing trend of pore volume in the range of less than $0.1{\mu}m$ and more than $0.3{\mu}m$. Also, using an electron microscope inside showed tightness of hydration texture. Chloride penetration depth of concrete, painted with nano synthesized polymer paint, was decreased more than 92% compared to non-painted concrete and 70% with water-based epoxy painted concrete. Especially, chemical corrosion resistance test set with aqueous solution of 5% sulfuric acid, non-painted concrete and water-based epoxy painted concrete showed weight loss of 4% after dipping for 12 days. On the other hand, concrete painted with nano synthesized polymer paint showed 1.7% weight loss under the same condition. Also, it showed great result of appearance under the criteria of Tsivilis et al.

• Journal of the Korean Recycled Construction Resources Institute
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• v.11 no.2
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• pp.97-104
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• 2023

In order to maximize the utilization of recycled fine aggregate, high strength mortar made of 100 % recycled fine aggregate was prepared, and its physical properties were evaluated to determine the possibility of using recycled fine aggregate as structural aggregate. The effect caused by the amount of nanosilica on the physical properties of w/b 0.2 recycled fine aggregate mortar consisting of cement, silica fume, and blast furnace slag. To improve the dispersion of nanosilica inside mortar, an aqueously dispersed nanosilica solution by ultrasonic tip sonication was prepared, and incorporated into the mortar to evaluate changes in mortar flow, porosity and compressive strength depending on nanosilica content. According to the experimental results, mortar flow decreased as the replacement ratio of nano-silica increased. As the replacement ratio of nanosilica increased up to 0.75 %, the porosity decreased and the compressive strength increased, but, at a replacement ratio of 1 %, the porosity increased and the compressive strength decreased. It was confirmed that the nano-silica replacement ratio of 0.75 % was optimum proportion to maximize the mechanical performance of high-strength recycled fine aggregate mortar.

• Journal of IKEEE
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• v.10 no.2 s.19
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• pp.161-167
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• 2006

The effect of aging on the optoelectronic properties of a single ZnO nanowire is investigated in this study. The photoluminescence (PL), photocurrent spectrum, current-voltage characteristics, and photoresponse were measured for the as-grown ZnO nanowire and for the same nanowire exposed to air for three months. For the aged nanowire, the broad PL band is weaker, the intensity of the photocurrent is strengthened, and the photoresponse is slower, compared with the as-grown nanowire. It Is suggested in this paper that the observed aging effect on the PL is due to the reduction in the number of oxygen vacancies within the nanowire and that the aging effect on the photocurrent and photoresponse originates from the formation of oxygen vacancies near the surface.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.1
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• pp.41-48
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• 2017

Fine polymeric fibers have been gaining interest from the energy harvesting/storage, tissue, and bioengineering industries because of advantages such as the small diameter, high porosity, permeability, and similarities to a natural extracellular matrix. Electrospinning is one of the most popular methods used to fabricate polymeric fibers because it is not as limited in regards to the materials selection, and it does not require expensive or complex equipment. However, electrospun fibers have a severe aerodynamic instability because the small diameter fibers are able to pass through the atmospheric layer when there is a high electric field. As a result, electrospun fibrous mats have serious difficulties with controlling its shape and geometric properties. In this study, a hybrid nano/microfibrous mat is presented that is fabricated using electrospinning with two different solvent-based PCL solutions. This provides control of the fiber diameter, mat porosity, and mechanical properties. Various hybrid fibrous mats were fabricated after an experimental investigation of the effects of solvent on fiber diameter. It was then demonstrated that the mechanical properties and porosity of the fabricated various hybrid mats could be successfully controlled.

• Journal of the Korea Institute of Building Construction
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• v.20 no.1
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• pp.11-18
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• 2020

Carbon nanotubes are used in various industries with their excellent mechanical properties and electrical conductivity. In the construction industry, research is being conducted to give self-sensing capabilities to structures, but the results of experiments vary among researchers, and the analysis is insufficient. Therefore, in this study, the hydration and electrical properties of MWCNT-added cement pastes were measured. The electrical resistance values of hydration heat, porosity, Rietveld quantitative analysis, compressive strength, and distance were measured.. The heat resistance, porosity, Rietvelt quantitative analysis, compressive strength and distance were measured according to electrical resistance. Experimental results showed that the heat of hydration decreased with increasing MWCNT. XRD Rietveld quantitative analysis showed that there was no significant difference in the amount of hydration products with increasing addition rate of MWCNT. As a result of SEM analysis, the MWCNT is agglomerated by van der Waals forces, and this area is considered to be caused by voids and weak areas. The electrical resistance value decreases as the addition rate is increased, and thus may play a role for magnetic sensing in the future.

• Economic and Environmental Geology
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• v.46 no.1
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• pp.51-61
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• 2013

Researches on the oil recovery enhancement using the nanotechnology has recently been studied in the United States. The previous researches has focused mainly on the flow characteristics of nanoparticles in porous media, and the stability of the nano-emulsion itself. However, the analysis did not deal with the size effects between a nano-emulsion and the pore size which has an important role when nano-emulsion flows in the porous media. In this research, nano-based emulsion was fabricated which is able to be applied for the enhanced oil recovery techniques and its characteristics was analyzed. In addition, in order to identify the characteristics of nano-emulsions flowing through the porous media, the size effect was analysed by filtering test. According to the results, when the emulsion was fabricated, SCA(Silane Coupling Agent) or PVA(Poly Vinyl Alcohol) are added to improve the stability of emulsion. As the ratio of the decane to water increased, the viscosity of emulsion and the droplet size also increased. For the filtering test at the atmospheric conditions, the droplet did not go through the filter; only the separated water from the emulsion was able to be filtered. This phenomenon occurred because the droplet was not able to overcome the capillary pressure. At the filtering test by suction pressure, most of the emulsion was filtered over the filter size of $60{\mu}m$. However, the ratio of filtration was rapidly degraded at less than $45{\mu}m$ filters. This is caused due to deformation and destruction of the droplet by strong shear stress when passing through the pore. The results from the study on the basic characteristic of nano-emulsion and filtering test will be expected to play as the important role for the fabrication of the stable nano-emulsion or the research on the recovery of residual oil in porous media.

• Journal of Soil and Groundwater Environment
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• v.14 no.6
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• pp.101-107
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• 2009

Carboxymethyl cellulose (CMC) as stabilizer is expected to facilitate in-situ delivery of zero-valent iron (ZVI) nanoparticles in a contaminated aquifer because it increases dispersity of ZVI nanoparticles. This work investigated the transport of CMC-stabilized ZVI nanoparticles (CMC-Fe) using column breakthrough experiments. The ZVI nanoparticles (100 mg/L Fe) were transportable through sand porous media. In contrast, non-stabilized ZVI nanoparticles rapidly agglomerate in solution and are stopped in sand porous media. At pH 7 of solution approximately 80% CMC-Fe were eluted. When the pH of solution is below 5, 100% CMC-Fe were eluted. These results suggest that the mobility of CMCFe was increased as pH decreases. In the mobility test under different ionic strengths using $Na^+$ and $Ca^{2+}$ ions, there was no signigficant difference in the mobility of CMC-Fe. Also, in the experiments of effect of clay and natural organic mater (NOM) on the mobility of ZVI, there was no significant difference in the mobility of CMC-Fe not only between 1 and 5% clay, but 100 and 1000 mg/L NOM. The results from this work suggests that the CMC-Fe nanoparticles could be easily delivered into the subsurface over a broad range of ionic strength, clay and NOM.