Go-Woon Lee

Porous three-dimensional graphene foam/Prussian blue composite for efficient removal of radioactive 137Cs

In this study, a simple one-step hydrothermal reaction is developed to prepare composite based on Prussian blue (PB)/reduced graphene oxide foam (RGOF) for efficient removal of radioactive cesium (137Cs) from contaminated water. Scanning electron microscopy and transmission electron microscopy show that cubic PB nanoparticles are decorated on the RGO surface. Owing to the combined benefits of RGOF and PB, the composite shows excellent removal efficiency (99.5%) of 137Cs from the contaminated water. The maximum adsorption capacity is calculated to be 18.67 mg/g. An adsorption isotherm fit-well the Langmuir model with a linear regression correlation value of 0.97. This type of composite is believed to hold great promise for the clean-up of 137Cs from contaminated water around nuclear plants and/or after nuclear accidents.

Aquatic ecotoxicity effect of engineered aminoclay nanoparticles

In the present study the short term aquatic ecotoxicity of water-solubilized aminoclay nanoparticles (ANPs) of ~51±31 nm average hydrodynamic diameter was characterized. An ecotoxicological evaluation was carried out utilizing standard test organisms of different phyla and trophic levels namely the eukaryotic microalga Pseudokirchneriella subcapitata, the crustacean Daphnia magna and the bioluminescent marine bacteria Vibrio fisheri. The effective inhibitory concentration (EC50) with 95% confidence limits for the microalga was 1.29 mg/L (0.72-1.82) for the average growth rate and 0.26 mg/L (0.23-0.31) for the cell yield. The entrapping of algal cells in aggregates of ANP may play a major role in the growth inhibition of algae P. subcapitata. No inhibition was observed for V. fisheri up to 25,000 mg/L (no observed effect concentration; NOEC). For D. magna no immobilization was observed in a limit test with 100 mg/L in 24 h while in 48 h a single animal was immobilized (5% inhibition). Correspondingly, the NOEC of ANP in 24 h was 100 mg/L and the lowest observed effect concentration (LOEC) for 48 h was 100 mg/L. Therefore it can be considered to use ANP as an algal-inhibition agent at concentrations <100 mg/L without affecting or only mildly affecting other organisms including zooplanktons, but further studies on the environmental fate and chronic toxicity of ANP is needed to confirm this.

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.

Synergistically strengthened 3D micro-scavenger cage adsorbent for selective removal of radioactive cesium.

A novel microporous three-dimensional pomegranate-like micro-scavenger cage (P-MSC) composite has been synthesized by immobilization of iron phyllosilicates clay onto a Prussian blue (PB)/alginate matrix and tested for the removal of radioactive cesium from aqueous solution. Experimental results show that the adsorption capacity increases with increasing the inactive cesium concentration from 1 ppm to 30 ppm, which may be attributed to greater number of adsorption sites and further increase in the inactive cesium concentration has no effect. The P-MSC composite exhibit maximum adsorption capacity of 108.06 mg of inactive cesium per gram of adsorbent. The adsorption isotherm is better fitted to the Freundlich model than the Langmuir model. In addition, kinetics studies show that the adsorption process is consistent with a pseudo second-order model. Furthermore, at equilibrium, the composite has an outstanding adsorption capacity of 99.24% for the radioactive cesium from aqueous solution. This may be ascribed to the fact that the AIP clay played a substantial role in protecting PB release from the P-MSC composite by cross-linking with alginate to improve the mechanical stability. Excellent adsorption capacity, easy separation, and good selectivity make the adsorbent suitable for the removal of radioactive cesium from seawater around nuclear plants and/or after nuclear accidents.

Efficient harvesting of wet blue-green microalgal biomass by two-aminoclay [AC]-mixture systems

Blue-green microalgal blooms have been caused concerns about environmental problems and human-health dangers. For removal of such cyanobacteria, many mechanical and chemical treatments have been trialled. Among various technologies, the flocculation-based harvesting (precipitation) method can be an alternative if the problem of the low yield of recovered biomass at low concentrations of cyanobacteria is solved. In the present study, it was utilized mixtures of magnesium aminoclay [MgAC] and cerium aminoclay [CeAC] with different particle sizes to harvest cyanobacteria feedstocks with ∼100% efficiency within 1h by ten-fold lower loading of ACs compared with single treatments of [MgAC] or [CeAC]. This success was owed to the compact networks of the different-sized-ACs mixture for efficient bridging between microalgal cells. In order to determine the usage potential of biomass harvested with AC, the mass was heat treated under the reduction condition. This system is expected to be profitably utilizable in adsorbents and catalysts.

Porous 3D Prussian blue/cellulose aerogel as a decorporation agent for removal of ingested cesium from the gastrointestinal tract

In the present study, we successfully synthesized a porous three-dimensional Prussian blue-cellulose aerogel (PB-CA) composite and used it as a decorporation agent for the selective removal of ingested cesium ions (Cs+) from the gastrointestinal (GI) tract. The safety of the PB-CA composite was evaluated through an in vitro cytotoxicity study using macrophage-like THP-1 cells and Caco-2 intestinal epithelial cells. The results revealed that the PB-CA composite was not cytotoxic. An adsorption study to examine the efficiency of the decorporation agent was conducted using a simulated intestinal fluid (SIF). The adsorption isotherm was fitted to the Langmuir model with a maximum Cs+ adsorption capacity of 13.70 mg/g in SIF that followed pseudo-second-order kinetics. The PB-CA composite showed excellent stability in SIF with a maximum Cs+ removal efficiency of 99.43%. The promising safety toxicology profile, remarkable Cs+ adsorption efficacy, and excellent stability of the composite demonstrated its great potential for use as an orally administered drug for the decorporation of Cs+ from the GI tract.

A recyclable, recoverable, and reformable hydrogel-based smart photocatalyst

We present a novel hydrogel-based photocatalyst that contains TiO2 nanoparticles (NPs) uniformly dispersed in an agarose hydrogel matrix. The preparation of the TiO2/agarose hybrid gel photocatalyst was based on the gelation of agarose in the presence of well-dispersed TiO2 NPs in hot water. TiO2 NPs were homogeneously distributed in the agarose gel as characterized by Fourier transform infrared spectroscopy (FT-IR) analysis. It was found that the size, uniformity, and concentration of the hybrid gel as well as the contents of constituent ingredients have significant effects on the photocatalytic activity. The smaller and uniform size of the hybrid gel at an appropriate concentration exhibited superior photocatalytic performance in both photodegradation of methylene blue (MB) under UV light and TiO2 leakage. In the moderate concentration range of TiO2 and agarose, the degradation rate of MB increased upon increasing the TiO2 content or decreasing the agarose concentration. Under the optimized conditions, our hybrid gel showed excellent recycling performance over repeated use. Furthermore, we demonstrate the additional excellent features of our hybrid gel, which are: i) regeneration of pure TiO2 NPs and ii) thermal reconstruction of the hybrid gel. During the recycling, the TiO2 NPs initially immobilized in the hydrogel could be recovered through the programmed heating and separation techniques. Also, our hybrid gel could be easily reshaped into a new hydrogel with a desired architecture in terms of its size and shape. These unprecedented properties make our hybrid gel a smart and cost-effective new promising material for use in practical waste/water treatment.

Adsorption of rare earth metals (Sr2+ and La3+) from aqueous solution by Mg-aminoclay–humic acid [MgAC–HA] complexes in batch mode

The recoveries of Sr2+ and La3+ as rare earth metals (REMs) were studied using Mg-aminoclay–humic acid [MgAC–HA] complexes prepared by self-assembled precipitation due to electrostatic attraction between water-solubilized [MgAC] and water-soluble [HA], and were compared with the recoveries using [MgAC] and [HA]. The influences of pH and Sr2+ and La3+ concentrations in single and binary systems were evaluated. The adsorbents before/after adsorption of Sr2+ and La3+ were characterized by (1) scanning electron microscopy (SEM) micrographs, (2) Fourier transform infrared (FT-IR), X-ray photoelectron spectroscopy (XPS), and extended X-ray absorption fine structure (EXAFS) spectra, and by (3) powder X-ray diffraction (XRD) pattern analysis. After fitting Langmuir and Freundlich isotherms, the Langmuir model was found to present better matches than the Freundlich one: the maximum adsorption capacities of Sr2+ and La3+ were 0.12 mg g−1 and 4.76 mg g−1 in the binary system at room temperature, and the optimal recovery pH was ∼8.0. In practical seawater meanwhile, the recoveries of Sr2+ and La3+ by [MgAC–HA] complexes were the highest in the binary system. However, with further recycling runs, the recoveries of Sr2+ and La3+ were critically diminished due to disassembly in [MgAC–HA] complexes under acidic conditions. Thus, for the purposes of industrial application, we are currently pursuing the enhancement of recyclability for [MgAC–HA] complexes by their encapsulation or direct hydrogel formation.

Feasibility tests of –SO3H/–SO3−-functionalized magnesium phyllosilicate [–SO3H/–SO3− MP] for environmental and bioenergy applications

We have prepared a simple water-solubilized, transparent, and anionic clay. –SH-functionalized magnesium phyllosilicate [–SH MP] was easily oxidized into –SO3H/–SO3−-functionalized magnesium phyllosilicate [–SO3H/–SO3− MP] by treatment of 5.0% H2O2 at 60 °C for 24 hours, showing a pH of ∼2.0. These water-solubilized and anionic nanoparticles (NPs) were tested with organo-building blocks of –SO3H/–SO3− MP for removal of cationic pollutant dye (methylene blue) and heavy metals (Cd2+ and Pb2+). Furthermore, interactions of ubiquitous humic acid (HA) with –SO3H/–SO3− MP were removed due to an ion exchange mechanism. For bioenergy applications, glucose conversion from cellulose was tested, focusing on Bronsted acid-rich sites in –SO3H/–SO3− MP.

Fe-aminoclay-entrapping electrospun polyacrylonitrile nanofibers (FeAC-PAN NFs) for environmental engineering applications

Electrospun polyacrylonitrile nanofibers (PAN NFs) with entrapped water-soluble Fe-aminoclay (FeAC) [FeAC-PAN NFs] were prepared. Slow dropwise addition of water-soluble FeAC into a PAN solution, less aggregated of FeAC into electrospun PAN NFs was one-pot evolved without FeAC post-decoration onto as-prepared PAN NFs. Taking into consideration both the Fe3+ source in FeAC and the improved surface hydrophilicity, the feasibility of Fentonlike reaction for decolorization of cationic model dye methylene blue (MB) under 6 hrs UV-light irradiation was established. In the case where FeAC-PAN NFs were enhanced by hydrogen peroxide (H2O2) injection, the apparent kinetic reaction rates were increased relative to those for the PAN NFs. Thus, our flexible FeAC-PAN NF mats can be effectively utilized in water/waste treatment and other environmental engineering applications.