Young-Chul Lee

Synthesis and electrorheological characteristics of microencapsulated polyaniline particles with melamine–formaldehyde resins

Abstract Polyaniline particles with low pH cannot be directly used in the electrorheological (ER) systems, since their emerald base form has a conductivity that is too high. Therefore, the pH of the polyaniline has been controlled to yield a lower conductivity. To improve the particle preparation method for polyaniline, which generates ER fluids with its semi-conducting characteristics, we synthesized microencapsulated polyaniline particles with melamine–formaldehyde (MF) resins. Microcapsules, containing polyaniline with a low pH as the core material, were prepared by polymerization of MF resin, which play the role of an insulator between the polyaniline particles. From rheological measurements, the yield stress of the ER fluid decreased with the increase of MF resin, and this effect enhanced as the applied electric field strength increased.

Microencapsulated polyaniline particles for electrorheological materials

Electrorheological (ER) fluids are a class of materials whose rheological characteristics are controllable through the application of an electric field. ER fluids are usually made of particle suspensions with a large dielectric constant mismatch between the particles and the fluid [1]. Upon application of an electric field, the suspended dielectric particles in an ER fluid align themselves into chains and columns parallel to the field, thereby inducing yield phenomenon, viscoelasticity, and a drastic increase in viscosity. Because of their controllable viscosity and fast response, ER fluids are regarded as a smart material for active devices, which can transform electric energy to mechanical energy [2]. Recently, much attention has been put on dry-base, nearly anhydrous ER fluids. Examples include carboneous particle [3], zeolite [4] and various polymer semi-conductors, such as acene quinone radical polymers [5, 6], poly (p-phenylene) [7], polyaniline [8, 9], and copolyaniline [10, 11]. Among these ER fluids, polyaniline in its emeraldine base form has advantages with respect to density, conductivity control and thermal stability. Polyaniline is also easy to polymerize by oxidation polymerization at relatively low temperatures [12]. Despite these merits, only the semi-conducting emeraldine base form of polyaniline can be used due to the high conductivity of the hydrochloride form and the resulting high current density causing breakdown in the structure of the fluid. In this note, we microencapsulated homopolyaniline particles with melamine-formaldehyde resin and then investigated their ER characteristics. Because microencapsulation entraps core liquid materials by circulating them with certain polymeric materials, we used this method to modify the polyaniline particles. Based on the finding that melamine-formaldehyde resin is better than urea-formaldehyde resin in hardness and resistance to heat and moisture [13], we adopted the melamine-formaldehyde resin for our microencapsulation process of homopolyaniline particles. At first, the polyaniline particles were polymerized by oxidation polymerization [14]. 1.2 mol of aniline monomer was added to 800 ml of 1 M HCl, and was chilled and stirred for 2 h. A pre-chilled solution of ammonium peroxysulfate (0.72 mol in 400 ml of

Lipid extractions from docosahexaenoic acid (DHA)-rich and oleaginous Chlorella sp. biomasses by organic-nanoclays

Microalgae biorefinement has attracted in intensive academic and industrial interest worldwide for its potential to replace petrol biofuels as economically and environmentally advantageous alternatives. However, harvesting and lipid extraction remain as critical and difficult issues to be resolved. In the present study, four amino-groups functionalized organic-nano clays were prepared. Specifically, Mg or Al or Ca backboned and covalently linked with 3-aminopropyltriethoxysilane or 3-[2-(2-aminoethylamino)ethylamino]propyltrimethoxysilane by sol-gel reaction under ambient conditions, resulted in Mg-APTES clay, Al-APTES clay, Ca-APTES clay, and Mg-N3 clay, respectively. Each organic-nanoclay was utilized for lipid extraction from wet microalgae biomass. As a result, the lipid-extraction efficiency of paste docosahexaenoic acid (DHA)-rich Chlorella sp. with low lipid content was high, while one of paste oleaginous Chlorella sp. with high lipid content was relatively low. Despite the low lipid-extraction efficiencies in all of the wet microalgae biomass, the conversion of the extracted lipids fatty acids to biodiesel was nearly 100%.

Oil extraction by aminoparticle-based H2O2 activation via wet microalgae harvesting

In this study, we demonstrated the synthesis of novel aminoparticles with Fe3+, Mn2+, and Cu2+ placed in active metal centers by means of a sol–gel reaction with 3-aminopropyltriethoxysilane (APTES) as a precursor, thereby forming –O(CH2)3NH2 organo-functionalities on cationic metals. The protonated amine groups led to the efficient flocculation of microalgae which occurred within as little as 5 min. To our surprise, the aminoparticles exhibited a Fenton-like activity when 1% hydrogen peroxide (H2O2) was introduced. Just like any Fenton-like reaction, it is plausible that •OH radicals are produced through the activation of H2O2 by the metal atoms embedded in the aminoparticles, bringing about cell damage and effectively releasing internal lipids from wet microalgae biomass. The efficiency of lipid extraction with the Fe-aminoparticle in the presence of 1% H2O2 was 26.70% and nearly 100% of the extracted oil was converted to biodiesel. It is believed that our multiple-functionality aminoparticles represent a promising means of substantially reducing the unit cost of microalgal biorefineries in general and microalgae-based biodiesel production in particular.

Sea-urchin-like iron oxide nanostructures for water treatment

To obtain adsorbents with high capacities for removing heavy metals and organic pollutants capable of quick magnetic separation, we fabricated unique sea-urchin-like magnetic iron oxide (mixed γ-Fe2O3/Fe3O4 phase) nanostructures (called u-MFN) with large surface areas (94.1m(2) g(-1)) and strong magnetic properties (57.9 emu g(-1)) using a simple growth process and investigated their potential applications in water treatment. The u-MFN had excellent removal capabilities for the heavy metals As(V) (39.6 mg g(-1)) and Cr(VI) (35.0 mg g(-1)) and the organic pollutant Congo red (109.2 mg g(-1)). The u-MFN also displays excellent adsorption of Congo red after recycling. Because of its high adsorption capacity, fast adsorption rate, and quick magnetic separation from treated water, the u-MFN developed in the present study is expected to be an efficient magnetic adsorbent for heavy metals and organic pollutants in aqueous solutions.

Self-assembled graphene oxide with organo-building blocks of Fe-aminoclay for heterogeneous Fenton-like reaction at near-neutral pH: A batch experiment

Respective water-soluble graphene oxide (GO) and Fe-aminoclay were investigated for decoloration of recalcitrant organic dyes with different charges in the presence of hydrogen peroxide (H2O2). This oxidation process was updated in order to enable development of heterogeneous catalysts by self-assembled (precipitated) GO with organo-building blocks of Fe-aminoclay in aqueous solution. Due to electrostatic attraction between the negatively charged GO and the positively charged Fe-aminoclay, the obtained catalysts decomposed H2O2 at pH 6.0 to generate •OH radicals capable of breaking aromatic carbon raphene oxide (GO) e-aminoclay elf-assembly enton-like reaction eutral pH structures. These novel catalysts were tested for cationic methylene blue (MB) and anionic orange II (OII) as model pollutants. At 1.0 wt% of H2O2 treatment, the apparent rate constants of MB and OII by the optimal loading of catalyst (0.61 mg/mL) were 0.35288 h−1 (r2 = 0.9721) and 0.57930 (r2 = 0.9581), respectively. Furthermore, in the two-dye mixture system, simultaneous decoloration of both dyes, to near-complete ∼100% removal, was achieved after 5 h. Thus, it can be concluded that our developed catalysts for heterogeneous Fenton-like reaction at neutral pH are suitable for practical application.

All solid type ISFET glucose sensor with fast response and high sensitivity characteristics

Abstract An all solid type ISFET glucose sensor using the electrolysis of hydrogen peroxide has been fabricated and the characteristics investigated. By forming thin-film type three electrodes on the ISFET chip for amperometric actuation, miniaturized solid-type sensor could be achieved. The sensor with a specially designed ladder-type working electrode showed improved operation in response time and response magnitude.

Aminoclay-induced humic acid flocculation for efficient harvesting of oleaginous Chlorella sp.

Biofuels (biodiesel) production from oleaginous microalgae has been intensively studied for its practical applications within the microalgae-based biorefinement process. For scaled-up cultivation of microalgae in open ponds or, for further cost reduction, using wastewater, humic acids present in water-treatment systems can positively and significantly affect the harvesting of microalgae biomass. Flocculation, because of its simplicity and inexpensiveness, is considered to be an efficient approach to microalgae harvesting. Based on the reported cationic aminoclay usages for a broad spectrum of microalgae species in wide-pH regimes, aminoclay-induced humic acid flocculation at the 5g/L aminoclay loading showed fast floc formation, approximately 100% harvesting efficiency, which was comparable to the only-aminoclay treatment at 5g/L, indicating that the humic acid did not significantly inhibit the microalgae harvesting behavior. As for the microalgae flocculation mechanism, it is suggested that cationic nanoparticles decorated on macromolecular matters function as a type of network in capturing microalgae.

A simple bacterial transformation method using magnesium- and calcium-aminoclays

An efficient and user-friendly bacterial transformation method by simple spreading cells with aminoclays was demonstrated. Compared to the reported transformation approaches using DNA adsorption or wrapping onto (in)organic fibers, the spontaneously generated clay-coated DNA suprastructures by mixing DNA with aminoclay resulted in transformants in both Gram-negative (Escherichia coli) and Gram-positive cells (Streptococcus mutans). Notably, the wild type S. mutans showed comparable transformation efficiency to that of the E. coli host for recombinant DNA cloning. This is a potentially promising result because other trials such as heat-shock, electroporation, and treatment with sepiolite for introducing DNA into the wild type S. mutans failed. Under defined conditions, the transformation efficiency of E. coli XL1-Blue and S. mutans exhibited ~2 × 10(5) and ~6 × 10(3)CFU/μg of plasmid DNA using magnesium-aminoclay. In contrast, transformation efficiency was higher in S. mutans than that in E. coli XL1-Blue for calcium-aminoclay. It was also confirmed that each plasmid transformed into E. coli and S. mutans was stably maintained and that they expressed the inserted gene encoding the green fluorescent protein during prolonged growth of up to 80 generations.

A ISFET cartridge for electrolyte measurement by micromachinery

Abstract A small size cartridge is designed and fabricated for ISFET-based electrolyte sensor applications. The designed cartridge is fabricated by using micromachining techniques including silicon etching and glass bonding. Photosensitive polymer (THB 30) is used both to define a micropool and to encapsulate the sensor surface. A differential amplification method utilizing REFET (reference electrode field-effect transistor) and QRE (quasi-reference-electrode) are introduced in order to substitute the conventional Ag/AgCl reference electrode, which is unsuitable to be applied in this cartridge because of its large size. Total size of the fabricated cartridge is 2.4 cm×2.5 cm, and the dead volume of a micro flow-channel inside the cartridge is only 8.5 μl. The pH-ISFET inserted into the cartridge showed stable operation and reasonable nernstian characteristics [55 mV/pH].