Chien M. Wai

Supercritical fluid extraction in herbal and natural product studies - a practical review.

Due to increasingly stringent environmental regulations, supercritical fluid extraction (SFE) has gained wide acceptance in recent years as an alternative to conventional solvent extraction for separation of organic compounds in many analytical and industrial processes. In the past decade, SFE has been applied successfully to the extraction of a variety of organic compounds from herbs and other plants. This review article presents the practical aspects of SFE applications in sample preparation, selection of modifiers, collection methods, on-line coupling techniques, means for avoiding mechanical problems, and approaches to optimization of SFE conditions. SFE can also be used to clean up pesticides from herb medicines. SFE processes can be modeled to acquire useful information for better understanding of the extraction, mechanisms and optimization of the extraction procedures. With increasing public interest in natural products, SFE may become a standard extraction technique for studying herbal, food and agricultural samples.

Arsenic species in groundwaters of the blackfoot disease area, taiwan.

The groundwaters collected from three wells in the Blackfoot disease (BFD) area in southwest Taiwan contain, on the average, 671 149 [mu]g of total dissolved arsenic/L. The arsenic contents in the well waters of Hsinchu, a city in the northwest of the island where no BFD has ever been reported, are less than 0.7 [mu]g/L. The predominant arsenic species in the well waters of the BFD area is As[sup 3+] with an average As[sup 3+]/As[sup 5+] ratio of 2.6. The methyl arsenicals, monomethylarsinic acid and dimethylarsonic acid, are below detection limits ( 300 000 Da. The results obtained from the BFD area are compared with similar arsenic studies conducted in the United States. The importance of arsenic speciation in environmental water studies and the possible cause of BFD are discussed. 21 refs., 1 fig., 3 tabs.

Supercritical fluid synthesis and characterization of catalytic metal nanoparticles on carbon nanotubes

A rapid, convenient and environmentally benign method has been developed for the fabrication of metal nanoparticle–multiwall carbon nanotube (MWCNT) composites. Nanoparticles of palladium, rhodium and ruthenium are deposited onto functionalized MWCNTs through a simple hydrogen reduction of metal–β-diketone precursors in supercritical carbon dioxide, and are characterized by transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) analyses. These highly dispersed nanoparticles, with a narrow range of size distribution and good adhesion on MWCNT surfaces, are expected to exhibit promising catalytic properties for a variety of chemical reactions. Preliminary experiments demonstrate that Pd nanoparticles supported on MWCNTs are effective catalysts for hydrogenation of olefins in carbon dioxide. The Pd nanoparticle–MWCNT composite also shows a high electrocatalytic activity in oxygen reduction for potential fuel cell application.

Supercritical fluid extraction of thorium and uranium ions from solid and liquid materials with fluorinated [beta]-diketones and tributyl phosphate

A recent report shows that trivalent lanthanide and uranyl ions can be extracted by supercritical CO[sub 2] containing the fluorinated [beta]-diketone, 2,2-dimethyl-6,6,7,7,8,8,8-hyptafluoro-3,5-octanedione (FOD). Extraction and separation of actinides by supercritical fluids are of particular interest today because of potential applications to nuclear waste analysis and management. This paper describes the conditions of extracting thorium and uranium ions from solid and liquid materials by supercritical CO[sub 2] containing different [beta]-diketones. The synergistic extraction of the actinides by mixed ligands involving [beta]-diketones and tributyl phosphate (TBP) in supercritical CO[sub 2] is also reported. Synergistic extraction is another approach to improve the efficiencies of ligands of SFE of actinides. Potential applications of this new extraction technique for the separation of actinides from environmental samples are discussed. The five [beta]-diketones tested for the extraction of uranyl and Th(IV) ions in supercritical carbon dioxide are given as follows: acetylacetone, trifluoroacetylacetone, hexafluoroacetylacetone, thienoyltrifluoroacetylacetone, and FOD. 12 refs., 5 tabs.

Supercritical fluid extraction of uranium and thorium from nitric acid solutions with organophosphorus reagents

Extraction techniques for the recovery of uranium and transuranic elements from acid waste solutions are important in nuclear waste management. This paper examines the feasibility of extracting uranyl and thorium ions from nitric acid solutions with supercritical CO{sub 2} containing the different organophosphorus reagents. In this study, an organophosphorus reagent is dissolved in supercritical CO{sub 2} by passing the fluid through a reagent vessel placed upstream of the sample vessel in the extractor. Using TBPO or TOPO in supercritical CO{sub 2}, effective extraction of uranyl and thorium ions can be achieved even in dilute HNO{sub 3} solutions, thus yielding the possibility of reducing acidic waste volumes in nuclear waste treatment. The results may form the basis of a novel extraction process for the treatment of acidified nuclear wastes, while minimizing the production of secondary wastes. 12 refs., 2 figs., 2 tabs.

Supercritical fluid extraction

Supercritical fluid extraction (SFE) is presented as an efficient, environmentally clean, and selective alternative to conventional extraction methods. In this work, the fundamentals and the most important parameters to be considered during a SFE process are presented. Moreover, recent developments of SFE in the field of bioactive compounds extraction from some interesting natural sources such as plants, marine products, and food and agricultural by-products are shown in order to make the reader aware of the last applications in these areas, in which SFE has an extraordinary impact.

Supercritical fluid extraction of organic and inorganic mercury from solid materials.

Mercuric ions (Hg(2+)) can be extracted from solid samples (cellulose matrix) using methanol modified supercritical CO(2) containing the fluorinated chelating agent lithium bis(trifluoroethyl)dithiocarbamate (LiFDDC). Methylmercuric chloride (CH(3)HgCl) and dimethylmercury [(CH(3))(2)Hg] can be extracted by supercritical CO(2) without chelating agent and modifier. The solubility of Hg(FDDC)(2) in supercritical CO(2) has been determined to be 5 x 10(-3)M at 5O degrees C and 150 atm, which is about 3 orders of magnitude greater than that of the non-fluorinated analogue Hg(DDC)(2). Use of methanol (5%)-modified CO(2) further enhances the solubility of Hg(FDDC)(2) by a factor of 2.4. A small amount of water added to the sample matrix tends to facilitate the extraction of Hg(FDDC)(2) and CH(3)HgCl. Potential applications of this in situ chelation-supercritical fluid extraction method for the preconcentration of mercury species and treatment of mercury contaminated wastes are discussed.

The rate of loss of mercury from aqueous solution when stored in various containers

Abstract Solutions of natural water and distilled water were spiked with mercury(II) (25 p.p.b.) and stored in polyethylene, polyvinyl chloride, and soft glass containers. Losses of mercury at different pH values were monitored by flameless atomic absorption for a total of 17 days. Severe losses of mercury were observed at pH 2 and 7. Mercury loss from solution followed first-order kinetics; the half-lives of mercury loss under various conditions were calculated. Acidification of the solutions to pH 0.5 with nitric acid curtailed mercury loss substantially. Possible ways of reducing the loss of mercury from environmental water samples are discussed.

One-pot synthesis of B-doped three-dimensional reduced graphene oxide via supercritical fluid for oxygen reduction reaction

There has been a great deal of interest recently in three-dimensional (3D) graphene based materials, as they exhibit large surface areas, unique electronic properties, and other attractive features. Particularly, 3D graphene doped with heteroatoms catalysts show high electrocatalytic activity toward oxygen reduction reaction (ORR), which can be used as metal-free catalysts. Most of the existing synthesis strategies of 3D graphene invariably involve multiple steps and procedures are often energy intensive and time-consuming. In this paper, we reported a one-pot and green method to synthesize boron-doped 3D reduced graphene oxide (B-3DrGO) using the supercritical carbon dioxide (ScCO2) technique. The resulting products exhibit hierarchical porous structures, leading to a high specific surface area of 541 m2 g−1. A high content of B (2.9 at%) was detected in the product, suggesting that B-doping was efficient using this technique. The B-3DrGO displays electrocatalytic activity toward ORR, which is comparable to the commercially available Pt/C (20 wt%) catalyst, in addition to their superior durability and resistance to the crossover effect. Moreover, the supercritical fluid technique, which uses non-flammable, essentially nontoxic, inexpensive, and environmentally benign CO2, is a new and green approach for the synthesis of heteroatom doped 3D graphene.

Solubility parameters and solubilities of metal dithiocarbamates in supercritical carbon dioxide.

The solubilities of Cu, Hg, and Zn complexes with seven different dithiocarbamate ligands in supercritical fluid CO(2) at 60 °C and two pressures (100 and 230 atm) are reported. In each metal chelate system, the solubility of the metal-dithiocarbamate complex shows a strong correlation with the solubility parameters of the ligands, calculated using a group contribution method. Dithiocarbamate ligands with smaller solubility parameter values form metal complexes with higher solubilities in supercritical CO(2). The solubility parameter value may provide a general guideline for selecting effective ligands for metal extraction in supercritical CO(2).