Hern Kim

An efficient and heterogeneous recyclable silicotungstic acid with modified acid sites as a catalyst for conversion of fructose and sucrose into 5-hydroxymethylfurfural in superheated water

Acidity modified silver exchanged silicotungstic acid (AgSTA) catalyst was prepared and characterized by X-ray diffraction, FT-IR spectroscopy, Raman spectroscopy, FT-IR pyridine adsorption, SEM imaging, EDX mapping, and antimicrobial activity was also tested. The catalytic activity was evaluated for the dehydration of fructose and sucrose in superheated water. As a result, 98% conversion of fructose with 85.7% HMF yield and 87.4% HMF selectivity in 120 min reaction time at 120 °C reaction temperature using 10 wt.% of AgSTA catalyst was achieved. While, 92% sucrose conversion with 62.5% of HMF yield was obtained from sucrose at uniform condition in 160 min. The effect of reaction parameters, such as reaction temperature, time, catalyst dosage, and effect acidity on HMF yield was also investigated. The AgSTA catalyst was separated from the reaction mixture by filtration process at end of the reaction and reused eight times without loss of catalytic activity.

Characterization of structure, physico-chemical properties and diffusion behavior of Ca-Alginate gel beads prepared by different gelation methods.

Ca-Alginate beads were prepared with either external or internal calcium sources by dripping technique. It was found that beads synthesized with internal calcium source had a looser structure and bigger pore size than those produced with external calcium source. Consequently, a faster diffusion rate of Vitamin B12 (VB12) within the beads with an internal calcium source was observed. Furthermore, the concentration of calcium ion, ionic strength and pH of the external gel beads formation solution were investigated. Results showed that (a) the concentration of the calcium ion was found to be the determining factor in the gel formation phenomenon; (b) the weight and volume losses are in effect due to water removal; (c) NaCl acts as a competitor with calcium and a screen in the electrostatic repulsion; and (d) the pH controls the gel formation process by regulating the dissociation of alginate and the complexation of the calcium cations. These results are keys to understanding the behavior and performance of beads in their utilization medium.

Fabrication of Poly(vinylidene fluoride) (PVDF) Nanofibers Containing Nickel Nanoparticles as Future Energy Server Materials.

In the present study, we introduce Poly(vinylidene fluoride) (PVDF) nanofibers containing nickel (Ni) nanoparticles (NPs) as a result of an electrospinning. Typically, a colloidal solution consisting of PVDF/Ni NPs was prepared to produce nanofibers embedded with solid NPs by electrospinning process. The resultant nanostructures were studied by SEM analyses, which confirmed well oriented nanofibers and good dispersion of Ni NPs over them. The XRD results demonstrated well crystalline feature of PVDF and Ni in the obtained nanostructures. Physiochemical aspects of prepared nano-structures were characterized for TEM which confirmed nanofibers were well-oriented and had good dispersion of Ni NPs. Furthermore, the prepared nano-structures were studied for hydrogen production applications. Due to high surface to volume ratio of nanofibers form than the thin film ones, there was tremendous increase in the rate of hydrogen production. Overall, results satisfactorily confirmed the use of these materials in hydrogen production.

Biomass into chemicals: green chemical conversion of carbohydrates into 5-hydroxymethylfurfural in ionic liquids

Biomass is one of the few resources that have the potential to meet the challenges of sustainable and green energy systems. Already numerous valuable chemicals are derived from renewable resources; among these, 5-hydroxymethylfurfural (HMF), plays a vital role, because it can be obtained from carbohydrates. HMF is a versatile platform chemical for the synthesis of a wide range of industrially important materials, including biofuels. HMF is the key intermediate to bridge the gap between biomass resources and biochemicals. Recent studies have shown that all of the components of biomass are soluble in ionic liquids. Ionic liquids have undergone a remarkable process of evolution for carbohydrate conversion and several new ionic liquids have been reported. This review mainly focuses on the production of HMF from carbohydrates by using ionic liquids as solvents as well as catalysts and their reuse.

Imaging, spectroscopy, mechanical, alignment and biocompatibility studies of electrospun medical grade polyurethane (Carbothane™ 3575A) nanofibers and composite nanofibers containing multiwalled carbon nanotubes

In the present study, we discuss the electrospinning of medical grade polyurethane (Carbothane™ 3575A) nanofibers containing multi-walled-carbon-nanotubes (MWCNTs). A simple method that does not depend on additional foreign chemicals has been employed to disperse MWCNTs through high intensity sonication. Typically, a polymer solution consisting of polymer/MWCNTs has been electrospun to form nanofibers. Physiochemical aspects of prepared nanofibers were evaluated by SEM, TEM, FT-IR and Raman spectroscopy, confirming nanofibers containing MWCNTs. The biocompatibility and cell attachment of the produced nanofiber mats were investigated while culturing them in the presence of NIH 3T3 fibroblasts. The results from these tests indicated non-toxic behavior of the prepared nanofiber mats and had a significant attachment of cells towards nanofibers. The incorporation of MWCNTs into polymeric nanofibers led to an improvement in tensile stress from 11.40 ± 0.9 to 51.25 ± 5.5 MPa. Furthermore, complete alignment of the nanofibers resulted in an enhancement on tensile stress to 72.78 ± 5.5 MPa. Displaying these attributes of high mechanical properties and non-toxic nature of nanofibers are recommended for an ideal candidate for future tendon and ligament grafts.

Transition metal based ionic liquid (bulk and nanofiber composites) used as catalyst for reduction of aromatic nitro compounds under mild conditions

Ionic liquid (1,1′-hexane-1,6-diylbis (3-methylpyridinium) tetrachloronickelate (II)) and PVDF-IL ([C6(mpy)2][NiCl4]2−) nanofiber composites are synthesized and used as catalysts for the reduction of nitroarenes with NaBH4/H2O system at ambient temperature. Ionic liquid containing nickel halide anion well dispersed on the PVDF nanofibers. It efficiently catalyzes the reduction of functionalized nitroarenes to the corresponding substituted anilines, avoiding the need for inert atmosphere, and additional base or other additives. The catalytic system gives good yields with other functional groups remaining intact.

Carbon nanotube hybrid nanostructures: future generation conducting materials

The present electronic age has seen rapid advancements in the performance and versatility of electronic devices along with a simultaneous decrease in their dimensions. Miniaturising electronic devices increases their portability and ease of handling, making them ubiquitous in the modern world. Likely developments awaiting the science and technology of next-generation conducting materials are based on CNT hybrid nanomaterials. In recent times, carbon nanotubes based hybrid nanomaterials have attracted significant attention due to their unique electronic, optical, thermal, mechanical, and chemical properties. CNT powders are incorporated in diverse commercial products ranging from rechargeable batteries, automotive parts, and sporting goods to boat hulls and many more. In this review we focus on CNT based nanocomposite materials and their applications.

A highly selective SBA-15 supported fluorescent “turn-on” sensor for the fluoride anion

In an effort to improve the performance of organic-based F− receptors, organo-silica receptors are being developed taking advantage of the large surface area that mesoporous silica offers. In this work, we investigated the possibility of using a simple “piece-wise” assembly method to immobilize silyl-ether protected fluorescein isothiocyanate (FITC) molecules (receptor 1) on the surface of 3-aminopropyltrimethoxysilane (APTES) and 3-[2-(2-aminoethylamino)ethylamino] propyltrimethoxysilane (APAEAETMS) modified SBA-15 to form sensors ASBA and TSBA, respectively. We showed that aqueous solutions of TSBA (or ASBA) produce distinct changes in absorption and emission spectra upon F− addition due to the F− directed cleavage of Si–O bonds on receptor 1. TSBA (or ASBA) remained stable upon prolonged exposure to UV light (losing ∼0.12% of its fluorescence intensity), and was highly selective towards F− over other common anions (Cl−, Br−, I−, HPO42−, ACO−, and NO3−). Furthermore, the sensitivity of this type of sensor architecture followed a dependence on the kind of amino-silane compound used, which opens up the possibility of synthesizing sensors with tailored detection limits. The detection limit of TSBA and ASBA was 0.02 μM and 0.5 μM, respectively.

Titanium Dioxide Nanofibers and Microparticles Containing Nickel Nanoparticles

The present study reports on the introduction of various nanocatalysts containing nickel (Ni) nanoparticles (NPs) embedded within TiO2 nanofibers and TiO2 microparticles. Typically, a sol-gel consisting of titanium isopropoxide and Ni NPs was prepared to produce TiO2 nanofibers by the electrospinning process. Similarly, TiO2 microparticles containing Ni were prepared using a sol-gel syntheses process. The resultant structures were studied by SEM analyses, which confirmed well-obtained nanofibers and microparticles. Further, the XRD results demonstrated the crystalline feature of both TiO2 and Ni in the obtained composites. Internal morphology of prepared nanofibers and microparticles containing Ni NPs was characterized by TEM, which demonstrated characteristic structures with good dispersion of Ni NPs. In addition, the prepared structures were studied as a model for hydrogen production applications. The catalytic activity of the prepared materials was studied by in situ hydrolysis of NaBH4, which indicated that the nanofibers containing Ni NPs can lead to produce higher amounts of hydrogen when compared to other microparticles, also reported in this paper. Overall, these results confirm the potential use of these materials in hydrogen production systems.

Hypercross-linked microporous polymeric ionic liquid membranes: synthesis, properties and their application in H2 generation

This work focuses on hydrogen (H2) generation from the hydrolysis of sodium borohydride (NaBH4) by using high performance microporous polymeric ionic liquid membranes. Microporous organic polymers are broadly recognized for gas separation and gas storage. In this study, we synthesized hypercross-linked microporous polystyrene (PS) ionic liquid (IL) membranes via in situ cross-linking by the Friedel–Crafts alkylation method. The BET surface area of microporous PS/IL membranes after cross-linking is as high as 852 m2 g−1 compared to non-porous PS/IL membranes before cross-linking (2.7 m2 g−1) and pure PS membranes (2.5 m2 g−1). The as-prepared microporous membranes are tested for H2 generation. The results show that the microporous PS/IL membranes increase the H2 rate as compared to non-porous membranes. This is due to the dominant factor of hierarchical porosity and high surface area of the membranes. There is no leach or loss of the ionic liquid; it is well attached to the cross-linked membranes. The highest rate of H2 generation (3621 mL H2 g−1 min−1) was observed for 8 wt% of NaBH4 solution, which is comparable to that of noble metal-based catalysts reported in the literature for a similar kind of this reaction. The catalyst provided 17 290 total turnovers before they are deactivated.