Wha-Seung Ahn

Amine-impregnated silica monolith with a hierarchical pore structure: enhancement of CO2 capture capacity

A polyethylenimine-impregnated hierarchical silica monolith exhibited significantly higher CO(2) capturing capacity than other silica-supported amine sorbents, and produced a reversible and durable sorption performance.

Microfluidic Approach toward Continuous and Ultrafast Synthesis of Metal-Organic Framework Crystals and Hetero Structures in Confined Microdroplets

Herein, we report a novel nanoliter droplet-based microfluidic strategy for continuous and ultrafast synthesis of metal-organic framework (MOF) crystals and MOF heterostructures. Representative MOF structures, such as HKUST-1, MOF-5, IRMOF-3, and UiO-66, were synthesized within a few minutes via solvothermal reactions with substantially faster kinetics in comparison to the conventional batch processes. The approach was successfully extended to the preparation of a demanding Ru3BTC2 structure that requires high-pressure hydrothermal synthesis conditions. Finally, three different types of core-shell MOF composites, i.e., Co3BTC2@Ni3BTC2, MOF-5@diCH3-MOF-5, and Fe3O4@ZIF-8, were synthesized by exploiting a unique two-step integrated microfluidic synthesis scheme in a continuous-flow mode. The synthesized MOF crystals were characterized by X-ray diffraction, scanning electron microscopy, and BET surface area measurements. In comparison with bare MOF-5, MOF-5@diCH3-MOF-5 showed enhanced structural stability in the presence of moisture, and the catalytic performance of Fe3O4@ZIF-8 was examined using Knoevenagel condensation as a probe reaction. The microfluidic strategy allowed continuous fabrication of high-quality MOF crystals and composites exhibiting distinct morphological characteristics in a time-efficient manner and represents a viable alternative to the time-consuming and multistep MOF synthesis processes.

Control of catenation in CuTATB-n metal–organic frameworks by sonochemical synthesis and its effect on CO2 adsorption

The metal–organic frameworks CuTATB-n (TATB = 4,4′,4″-s-triazine-2,4,6-triyltribenzoate; n = power level) having either catenated (CuTATB-60) or non-catenated (CuTATB-30) structure were synthesized in 1 h via a novel sonochemical route. The control of catenation was achieved by simple adjustment of the ultrasonic power levels. The X-ray diffraction patterns, BET surface areas (3778 and 2477 m2 g−1, respectively) and pore volumes, and TGA patterns of the individual product obtained were in agreement with the published literature data of the corresponding materials known as PCN-6 (catenated) and PCN-6′ (non-catenated). Catenation of the two identical networks within large pores resulted in both high surface area and enhanced stability of the network. Such control of catenation was additionally demonstrated by successful synthesis of IRMOF-9 (catenated) and IRMOF-10 (non-catenated) pair by the same sonochemical method. CO2 adsorption properties of the CuTATB-n were measured at 273 and 298 K, which indicated the contribution of catenation in CuTATB-n for CO2 capture. The adsorption isotherms for CO2 and N2 show high adsorption capacity for CO2 (189 mg g−1 and 156 mg g−1, respectively for CuTATB-60 and -30 at 298 K) and excellent selectivity over N2 (>20 : 1). Five consecutive adsorption–desorption runs performed using high purity CO2 in a flow system established no deterioration in the adsorption capacity of CuTATB-60, which showed reversible adsorbent regeneration at 75 °C under He flow and excellent stability for a total duration of 800 min. CuTATB-60 has also demonstrated high gas adsorption capacity (1171 mgCO2 g−1adsorbent) at 30 bar and 298 K.

Synthesis of metal-organic frameworks: A mini review

Metal organic frameworks (MOFs) are porous crystalline materials of one-, two-, or three-dimensional networks constructed from metal ions/clusters and multidentate organic linkers via coordination bonding, which are emerging as an important group of materials for energy storage, CO2 adsorption, alkane/alkene separation, and catalysis. To introduce newcomers in chemical engineering discipline to the rapidly expanding MOF research works, this review presents a brief introduction to the currently available MOFs synthesis methods. Starting from the conventional solvothermal/hydrothermal synthesis, microwave-assisted, sonochemical, electrochemical, mechanochemical, ionothermal, drygel conversion, and microfluidic synthesis methods will be presented. Examples will be limited to those representative MOF structures that can be synthesized using common organic ligands of 1,4-benzenedicarboxylic acid (and its functionalized forms) and 1,3,5-benzenetricarboxylic acid, in conjunction with metal nodes of Zn2+, Cu2+, Cr3+, Al3+, Fe3+ and Zr4+. Synthesis of widely-investigated zeolitic imidazolate framework (ZIF) structure, ZIF-8 is also included.

Post-synthetic preparations of titanium-containing mesopore molecular sieves

Abstract Titanium-substituted mesoporous molecular sieves were prepared post-synthetically by applying Ti-butoxide in ethanol solutions of different concentrations to MCM-41, MCM-48, and KIT-1. The catalysts obtained were characterized by XRD, FT-IR, UV–Vis spectroscopies, XAS, and N 2 physisorption. Incorporation of Ti seems to promote further crosslinking of the mesoporous walls of the samples, and resulted in wall thickness increases. The post-synthetically prepared Ti-mesoporous derivatives using titanium butoxide grafting were catalytically active for the selective oxidation of 2,6-di- tert -butylphenol with H 2 O 2 . Their activities depended on the Ti concentration of the catalysts. Comparison works with hydrothermally prepared Ti-MCM-41, Ti-HMS or post-synthetically prepared Ti-mesopore catalysts, either using titanocene grafting or by TiCl 4 atom planting method, are also reported.

CO2 capture by amine-functionalized nanoporous materials: A review

Amine-functionalized nanoporous materials can be prepared by the incorporation of diverse organic amine moieties into the pore structures of a range of support materials, such as mesoporous silica and alumina, zeolite, carbon and metal organic frameworks (MOFs), either by direct functionalization or post-synthesis through physical impregnation or grafting. These hybrid materials have great potential for practical applications, such as dry adsorbents for post-combustion CO2 capture, owing to their high CO2 capture capacity, high capture selectivity towards CO2 compared to other gases, and excellent stability. This paper summarizes the preparation methods and CO2 capture performance based on the equilibrium CO2 uptake of a range of amine-functionalized nanoporous materials.

Electrorheological characterization of zeolite suspensions

The rheological properties of the electrorheological (ER) fluids prepared from commercial zeolites 3A, 5A and 13X suspended in silicone oil were investigated through steady shear and oscillatory shear experiments. Dielectric spectra of the fluids were also measured to examine their possible correlation with the flow behavior of the ER fluids. Among the zeolite ER fluids investigated, the ER fluid using 13X showed the best performance and had the shortest relaxation time of an interfacial polarization. Viscoelastic behavior was observed in the dynamic test under the applied electric field. The elasticity increased with the strength of the electric fields under linear viscoelastic conditions.

Electrorheological properties of a suspension of a mesoporous molecular sieve (MCM-41)

We report on the electrorheological (ER) properties of an ER fluid made of suspensions of MCM-41 particles in silicone oil under a high electric field. The effect of the particle concentration on the ER performance was also investigated. Typical behaviors of shear stresses and apparent shear viscosities as functions of both the electric field and the shear rate were observed for the ER system with a 20 wt.% particle suspension. In addition, a water content of ca. 6 wt.% in the MCM-41 particles was found to be responsible for their ER effect.

Microporous covalent triazine polymers: efficient Friedel–Crafts synthesis and adsorption/storage of CO2 and CH4

Two kinds of microporous covalent triazine-based organic polymers (MCTPs) were synthesized from inexpensive starting materials via a simple and cost effective Friedel–Crafts reaction route, and their CO2 and CH4 gas uptake capacities were investigated. The synthesized microporous materials showed high BET surface areas of 1452 (MCTP-1) and 859 m2 g−1 (MCTP-2). MCTP-1 exhibited a significant CO2 uptake capacity (204.3 mg g−1, 273 K/1 bar) with moderate CO2/N2 selectivity (15.4), whereas MCTP-2 showed a moderate CO2 uptake capacity (160.6 mg g−1, 273 K/1 bar) but exceptional CO2/N2 selectivity (68.6). MCTP-1 also exhibited substantial CO2 (497.4 mg g−1) and CH4 (85.4 mg g−1) storage capacities at 300 K and 35 bar.

Direct synthesis and characterization of high-SiO2-content mordenites

A direct synthesis of high-SiO 2 -content mordenite without addition of organic compounds was studied. The effects of starting raw materials, substrate composition, aging time, and reaction temperature on the crystallization rates were investigated. Morphology, N 2 sorption capacity, surface area, thermal stability of crystals, and hexane-cracking property of the silica-rich mordenite are also reported.