Minyoung Yoon

Core–Shell Ferromagnetic Nanorod Based on Amine Polymer Composite (Fe3O4@DAPF) for Fast Removal of Pb(II) from Aqueous Solutions

Heavy metal ion removal from wastewater constitutes an important issue in the water treatment industry. Although a variety of nanomaterials have been developed for heavy metal removal via adsorption, the adsorption capacity, removal efficiency, and material recyclability still remain a challenge. Here, we present novel Fe3O4@DAPF core-shell ferromagnetic nanorods (CSFMNRs) for the removal of Pb(II) from aqueous solutions; they were prepared by the facile surface modification of twin-like ferromagnetic Fe3O4 nanorods using a 2,3-diaminophenol and formaldehyde (DAPF)-based polymer. The crystallinity and structure of the Fe3O4 nanorods were confirmed via X-ray diffraction (XRD). Transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) revealed the core-shell morphology and composition of the materials. Pb(II) removal using the prepared Fe3O4@DAPF CSFMNRs was assessed, and comparable adsorption capacities (83.3 mg g(-1)) to the largest value were demonstrated. A thermodynamic study of the adsorption clearly indicated that the adsorption was exothermic and spontaneous. Due to the ferromagnetic properties with a high saturation magnetization value (56.1 emu g(-1)) of the nanorods, the nanorods exhibited excellent reusability with one of the fastest recovery times (25 s) among reported materials. Therefore, the Fe3O4@DAPF CSFMNRs can serve as recyclable adsorbent materials and as an alternative to commonly used sorbent materials for the rapid removal of heavy metals from aqueous solutions.

Bioinspired 2D-Carbon Flakes and Fe3O4 Nanoparticles Composite for Arsenite Removal.

Development of carbon-based materials has received tremendous attention owing to their multifunctional properties. Biomaterials often serve as an inspiration for the preparation of new carbon materials. Herein, we present a facile synthesis of a new bioinspired graphene oxide-like 2D-carbon flake (CF) using a natural resource, waste onion sheathing (Allium cepa). The 2D-CF was further decorated with crystalline Fe3O4 nanoparticles for applications. Superparamagnetic Fe3O4 nanoparticles (7 nm) were well-dispersed on the surface of the 2D-CF, which was characterized by X-ray diffractometry, X-ray photoelectron spectroscopy, Raman spectrometry, and transmission electron microscopy. Batch As(III) adsorption experiments showed that aqueous arsenic ions strongly adsorbed to the Fe3O4@2D-CF composite. The adsorption capacity of the Fe3O4@2D-CF composite for As(III) was 57.47 mg g(-1). The synergetic effect of both graphene oxide-like 2D-CF and Fe3O4 nanoparticles aided in excellent As(III) adsorption. An As(III) ion adsorption kinetics study showed that adsorption was very fast at the initial stage, and equilibrium was reached within 60 min following a pseudo-second-order rate model. Owing to the excellent superparamagnetic properties (52.6 emu g(-1)), the Fe3O4@2D-CF composite exhibited superb reusability with the shortest recovery time (28 s) among reported materials. This study indicated that Fe3O4@2D-CF composites can be used for practical applications as a global economic material for future generations.

Charged functional group effects on a metal–organic framework for selective organic dye adsorptions

A quaternary N-alkyl ammonium salt-containing zinc-based metal–organic framework (MOF) was synthesized and tested for selective organic dye adsorption experiments. Through covalent post-synthetic modification (PSM), the tertiary amine-containing MOF was converted into a quaternary N-alkyl ammonium salt-containing MOF under solid-state methylation conditions. The positively charged MOF was found to exclusively adsorb the negatively charged organic dye, while the positively charged organic dyes were not adsorbed. This separation experiment revealed that functional group control is an important and critical factor for molecule separations using porous materials.

Rapid removal of cadmium ions using green-synthesized Fe3O4 nanoparticles capped with diethyl-4-(4 amino-5-mercapto-4H-1,2,4-triazol-3-yl)phenyl phosphonate

Water-dispersible diethyl-4-(4-amino-5-mercapto-4H-1,2,4-triazol-3-yl)phenyl phosphonate (DEAMTPP)-capped biogenic Fe3O4 magnetic nanocomposites (DEAMTPP@Fe3O4 MNP) have been successfully synthesized using Ananas comosus peel pulp extract. The size, structure, magnetic properties, and porosity of the prepared DEAMTPP@Fe3O4 MNPs were investigated. The concentration- and pH-dependence of Cd(II)-adsorption properties of the DEAMTPP@Fe3O4 MNPs was demonstrated: the adsorption efficiency maximized (96.1%) at pH 6 and at 60 mg L−1 of Cd(II) concentration. The maximum Cd(II) adsorption capacity of the DEAMTPP@Fe3O4 MNPs, calculated using a Langmuir isotherm, was 49.1 mg g−1, amongst the highest values reported for Cd(II) adsorbents. The ferromagnetic nature of the composite material allows its facile recycling without significant loss of removal efficiency. The excellent adsorption capacity of the nano-adsorbent, together with other advantages like reusability, easy separation, and environmentally-friendly composition, makes it a suitable adsorbent for removal of Cd(II) ions from environmental and industrial wastes.

Hierarchical Zeolites with Amine-Functionalized Mesoporous Domains for Carbon Dioxide Capture

To prepare materials with high CO2 adsorption, a series of hierarchical LTA zeolites possessing various mesopore spaces that are decorated with alkylamines was designed and synthesized. The highest CO2 uptake capacity was achieved when (3-aminopropyl)trimethoxysilane (APTMS) was grafted onto the hierarchical LTA zeolite having the largest mesopores. Owing to the contributions of both alkylamine groups grafted onto the mesopore surfaces and active sites in the LTA zeolites, the amount of CO2 that can be taken up on these materials is much higher than for conventional aminosilicas such SBA-15 and MCM-41. Furthermore, the adsorbent shows good CO2 uptake capacity and recyclability in dynamic flow conditions.

Facile synthesis of γ-Fe2O3@porous carbon materials using an Fe-based metal–organic framework: structure and porosity study

Metal oxide nanoparticle embedded porous carbon composite materials have various uses, including as catalyst supports and adsorbents, because of their good stability and unique porosity. Despite their importance, the synthetic strategies of metal-oxide nanoparticle-embedded porous carbon composites to control their properties have not been widely studied. Here, we present a facile synthesis method for γ-Fe2O3-embedded porous carbon materials via the pyrolysis of Fe-based metal–organic framework (MOF, MIL-100). We found that simple treatment to the starting material (MIL-100) allows control γ-Fe2O3 particle size, chemical composition, porosity, and H2 sorption property of the resulting composite materials. This work presents a synthesis of a series of porous carbon composites from a single MOF by treating further carbon source. This synthetic strategy may provide a clue for synthesis of a variety of composite materials using MOFs for battery electrode and catalyst applications.

Systematic study on preparation of copper nanoparticle embedded porous carbon by carbonization of metal–organic framework for enzymatic glucose sensor

Recently, metal–organic frameworks (MOFs) have been widely used in the preparation of metal oxide-embedded porous carbon composite materials. However, non-oxidized metal nanoparticle embedded porous carbon composites have rarely been prepared from MOFs to date. Herein, we present a systematic synthetic condition study of a Cu nanoparticle embedded porous carbon composite (Cu@C-500) by simple carbonization of a copper-based MOF (HKUST-1). The conditions for the synthesis of the pure Cu nanoparticles embedded composite were optimized by changing the reaction temperature and time. The prepared composite retained its original octahedron shape, with uniformly distributed copper nanoparticles (∼30 nm) in the carbon bed. The composite Cu@C-500 exhibited hierarchical porosity with a moderate surface area (195 m2 g−1). Due to its hierarchical porosity and unique redox activity, Cu@C-500 was examined for peroxidase-like catalytic activity, particularly for glucose sensing assays. The results indicated that this carbon composite displayed high catalytic activity similar to that of the peroxidase enzyme. Moreover, it presented one of the best detection limits (3.2 × 10−9 M) in colorimetric glucose sensing. In addition, Cu@C-500 exhibited good selectivity towards other sugars. The high sensitivity and selectivity of Cu@C-500 show great potential in the development of highly efficient glucose sensing devices.

Modeling adsorption properties of structurally deformed metal–organic frameworks using structure–property map

Significance Modeling amorphous materials using the conventional molecular simulation method is exceedingly difficult because structural information of the material is absent. Here, we present a way to indirectly model structurally deformed metal–organic frameworks using a large number of simulation data for crystalline metal–organic frameworks. Our experimental/computational results demonstrate that computed adsorption properties of crystalline metal–organic frameworks can be transferred onto those of structurally deformed, amorphous metal–organic frameworks. This opens up a way to understand adsorption properties of amorphous materials. Structural deformation and collapse in metal-organic frameworks (MOFs) can lead to loss of long-range order, making it a challenge to model these amorphous materials using conventional computational methods. In this work, we show that a structure–property map consisting of simulated data for crystalline MOFs can be used to indirectly obtain adsorption properties of structurally deformed MOFs. The structure–property map (with dimensions such as Henry coefficient, heat of adsorption, and pore volume) was constructed using a large data set of over 12000 crystalline MOFs from molecular simulations. By mapping the experimental data points of deformed SNU-200, MOF-5, and Ni-MOF-74 onto this structure–property map, we show that the experimentally deformed MOFs share similar adsorption properties with their nearest neighbor crystalline structures. Once the nearest neighbor crystalline MOFs for a deformed MOF are selected from a structure–property map at a specific condition, then the adsorption properties of these MOFs can be successfully transformed onto the degraded MOFs, leading to a new way to obtain properties of materials whose structural information is lost.

Flexibility in metal–organic frameworks derived from positional and electronic effects of functional groups

The position of identical functional groups and the subsequent electron density of structural benzene rings in a zinc-based metal–organic framework (MOF) have been controlled to reveal flexibility (or breathing behavior) differences. Both ortho- and para-positioned bi-functional benzene-1,4-dicarboxylic acid (BDC) ligands were synthesized with amino-, chloro-, methoxy-, and nitro groups. Additionally, two tri-functionalized, dimethoxy-amino and dimethoxy-nitro BDCs were prepared. All bi- and tri-functionalized BDCs were successfully incorporated into DABCO MOFs (DMOFs), except two diamino BDCs which were insoluble and thermally unstable. Among the eight bi-/tri-functionalized DMOFs, only para-dimethoxy exhibited flexibility in its framework after evacuation in preparation for N2 isotherm measurement. Since the dimethoxy combination has the most electron-rich environment in the benzene ring of the BDC in this series, this indicates that electron density plays a role in the flexibility changes of identically bi-functionalized DMOFs. However, the electron density alone could not fully explain the flexibility changes suggesting that the position of the functional groups is also important. These findings have been corroborated through the synthesis of two tri-functionalized DMOFs with identical functional group locations but opposite electronic environments.