Biomedical subjects

Jiunn-Fwu Lee

Publications and source records attributed to Jiunn-Fwu Lee.

10 recordsLinked to original sources

PubMed2006

The structural and sorptive characteristics of high-surface-area carbonaceous material (HSACM) in soils.

The structural and sorptive characteristics of the high-surface-area carbonaceous material (HSACM) isolated from soils were investigated. The HSACM contents in soils were first identified by the organic petrology method. A novel isolation method using acid demineralization, base extraction, and ZnBr(2) floatation sequential steps was developed to extract the HSACM from soil. The differences in structural and sorptive characteristics with the HSACM and the intact soil were investigated using nitrogen adsorption isotherms and trichloroethylene (TCE) sorption isotherms at low concentrations (0 to about 2 mg/L) both with and without tetrachloroethylene (PCE) as the cosolute. It was found that HSACM possesses a much higher specific surface area and pore volume as well as a smaller pore size than the original soil. Moreover, the sorption of TCE to HSACM is noticeably more nonlinear and competitive than to the original soil. A small amount of highly adsorptive HSACM is largely responsible for the nonlinear soil sorption of a single solute at very low concentrations.

Adsorption↗

PubMed2005

Organic compound distribution between nonionic surfactant solution and natural solids: applicability of a solution property parameter.

A solution property parameter phi was defined to examine the distribution characteristics of organic compounds between the solids and four nonionic surfactant solutions. The studied compounds consisted of BTEX (benzene, toluene, ethylbenzene, and p-xylene) and chlorinated pesticides (lindane, alpha-BHC, and heptachlor epoxide), which span several orders of magnitude in terms of water solubility (Sw). The solid samples were composed of a very low organic matter clay (Ca-montmorillonite), and a high organic matter natural soil (Shamou Mountain soil). The surfactants tested included two alkyl chain surfactants and two containing aromatic group surfactants with added concentrations both below and above their critical micelle concentration (CMC). By observing the Kom or Ksf variation, the result indicates, besides the Sw of the organic compounds, the distribution coefficient is regarded as a function of the soil organic matter (SOM) constituents, and the chemical structure of the organic compounds. Also, it can be found the greater phi values represent the higher releasing ratios of the organic compounds from the contaminated soil to groundwater. For the relatively higher Sw compounds, such as BTEX, all of the phi values are close to 1. The phi values for the relatively lower Sw compounds are far greater than 1, and increase with the increasing affinity of the compounds to the surfactants.

Benzene↗

PubMed2005

The influences of solid-phase organic constituents on the partition of aliphatic and aromatic organic contaminants.

The influence of natural organic matter (NOM) constituents on contaminant distribution coefficients was evaluated by determining the Koc values of aromatic and aliphatic organic compounds (solutes) with clays modified with both aromatic- and aliphatic-rich organic constituents. The studied compounds consisted of naphthalene, phenanthrene, n-pentane, and 2,3,4-trimethylmethane; the solid samples comprised two clays with little organic content, kaolinite and Ca-montmorillonite. Two aliphatic surfactants and three aromatic dyes, sorbed to the clays, served as reference NOM constituents. For solutes of comparable water solubilities, the organic-carbon normalized distribution coefficients (Koc) of the aliphatic solutes between sorbed aliphatic organic matter and aqueous solution slightly exceed those of the aromatic solutes. By contrast, the aromatic solutes exhibited higher Koc values than did the aliphatic compounds with sorbed aromatic-rich organic matter. The difference in Koc values could be attributed to either comparable solubility parameters or the difference in the chemical structure between nonionic organic solutes and specific components of the simulated NOM. The much higher Koc values observed for the aromatic solutes indicate that the NOM composition is a major factor determining the NOC environmental distribution.

Journal Article↗

PubMed2004

An alternative method for predicting organic solute volatilization rates under gas and liquid turbulence.

A method for predicting organic compound volatilization rates under turbulent liquid and gas conditions is developed. The reference compounds are classified according to their physico-chemical properties. The mass transfer coefficient (K(OL)) ratios for organic solutes to the reference compounds are constant for a wide range of environmental conditions, including liquid or air turbulence, or both at once. The obtained results indicate that when the environmental conditions are the same the determination of the volatilization rates is strongly dependent on the solute properties and the chemical structure. The presented method can more effectively estimate the volatilization rates of the solutes than the traditional one under various environmental conditions especially for low volatility solutes. The advantages and disadvantages of the traditional method are also discussed.

Air Movements↗

PubMed2004

Effects of exchanged surfactant cations on the pore structure and adsorption characteristics of montmorillonite.

Ca-montmorillonite (Ca-Mont) was exchanged with two quaternary amines, tetramethylammonium (TMA) chloride and hexadecyltrimethylammonium (HDTMA) bromide, to study the surfactant ion exchange effect on the pore structure, surface characteristics, and adsorption properties of montmorillonite. The revolution of both the surface area and pore structure of montmorillonite was characterized based on classical and fractal analyses of the nitrogen isotherms as well as the XRD patterns. The change of surface characteristics was identified from FTIR patterns and zeta-potential plots. The adsorption isotherms of acid dye, Amido Naphthol Red G (AR1), were then measured to identify the effects of the ion-exchange process on the adsorption properties of montmorillonite. It was found that the exchange processes might induce an increase or decrease in the surface area, pore size, pore volume, and surface fractal dimension D of montmorillonite, depending on the size, the molecular arrangement, and the degree of hydration of the exchanged ion in the clay. On the other hand, it was also found that the hydrophobic bonding by conglomeration of large C(16) alkyl groups associated with HDTMA could cause positive charge development on the surface of montmorillonite, which was not observed for TMA-modified montmorillonite (TMM). The effects of the alteration of the surface characteristics of montmorillonites on their adsorption selectivity for acid dye were discussed.

Journal Article↗

PubMed2004

The effect of surfactants on the distribution of organic compounds in the soil solid/water system.

The efficiency of soil remediation by surfactant washing was evaluated via the measured distribution coefficients of a number of nonpolar compounds in several soil-water mixtures. The studied compounds (contaminants) are BTEX (benzene, toluene, ethylbenzene, and p-xylene) and three chlorinated pesticides (lindane, alpha-BHC, and heptachlor epoxide), which span several orders of magnitude in water solubility (S(w)). A peat, and two natural soils were used that comprise a wide range in soil organic matter (SOM) content. The surfactants tested included cationic, anionic and nonionic types, with concentrations up to five to six times the critical micelle concentration (CMC). The K(d)(*)/K(d), values were used to evaluate the remediation efficiency under various operation conditions. For relatively water soluble BTEX compounds, the surfactant adsorption on the soil surface is the deciding factor on contaminant desorption from soil. For the less-soluble pesticides, surfactant micelles in solution influence the contaminant desorption more. The contaminants partitioning to SOM or adsorbed surfactants lowers the desorption efficiency. Anionic surfactants are found to be a better choice on soil remediation because they do not form admicelle on soil surface that enhances the SOM content. Cationic surfactant, which adsorb onto soil surfaces, leads to poor remediation efficiency. An improper selection of surfactant would result in inefficiency in soil remediation by surfactant washing.

Absorption↗

PubMed2004

Turbulence effects on volatilization rates of liquids and solutes.

Volatilization rates of neat liquids (benzene, toluene, fluorobenzene, bromobenzene, ethylbenzene, m-xylene, o-xylene, o-dichlorobenzene, and 1-methylnaphthalene) and of solutes (phenol, m-cresol, benzene, toluene, ethylbenzene, o-xylene, and ethylene dibromide) from dilute water solutions have been measured in the laboratory over a wide range of air speeds and water-stirring rates. The overall transfer coefficients (K(L)) for individual solutes are independent of whether they are in single- or multi-solute solutions. The gas-film transfer coefficients (kG) for solutes in the two-film model, which have hitherto been estimated by extrapolation from reference coefficients, can now be determined directly from the volatilization rates of neat liquids through a new algorithm. The associated liquid-film transfer coefficients (kL) can then be obtained from measured K(L) and kG values and solute Henry law constants (H). This approach provides a novel means for checking the precision of any kL and kG estimation methods for ultimate prediction of K(L). The improved kG estimation enables accurate K(L) predictions for low-volatility (i.e., low-H) solutes where K(L) and kGH are essentially equal. In addition, the prediction of K(L) values for high-volatility (i.e., high-H) solutes, where K(L) approximately equal to kL, is also improved by using appropriate reference kL values.

Algorithms↗

PubMed2004

Adsorption of basic dyes onto montmorillonite.

Ca-montmorillonite (Ca-Mont) was exchanged with titanium cations and the adsorption equilibrium and kinetics of Basic Green 5 (BG5) and Basic Violet 10 (BV10) on these montmorillonites were measured to examine the ion-exchange effects on the basic dyes adsorption. The relationship between the dye adsorption and the alteration of pore structures of montmorillonite induced by ion-exchange processes was discussed. Moreover, the changes in the surface and pore structure of montmorillonites during adsorption were characterized based on classical and fractal analyses of the nitrogen adsorption isotherms as well as the XRD patterns. The decrease in BET surface area of montmorillonites after adsorption of dyes was interpreted in terms of both the coverage of some surface roughness (surface screening effect) and the inhibition of the movement of nitrogen molecule into some pores (pore blocking effect). The surface fractal dimension D was used to examine whether or not the surface screening effect exists and the pore blocking effect was examined with the changes of mean pore size before and after adsorbing basic dyes.

Journal Article↗

PubMed2004

Clay-catalyzed reactions of coagulant polymers during water chlorination.

The influence of suspended clay/solid particles on organic-coagulant reactions during water chlorination was investigated by analyses of total product formation potential (TPFP) and disinfection by-product (DBP) distribution as a function of exchanged clay cation, coagulant organic polymer, and reaction time. Montmorillonite clays appeared to act as a catalytic center where the reaction between adsorbed polymer and disinfectant (chlorine) was mediated closely by the exchanged clay cation. The transition-metal cations in clays catalyzed more effectively than other cations the reactions between a coagulant polymer and chlorine, forming a large number of volatile DBPs. The relative catalytic effects of clays/solids followed the order Ti-Mont > Fe-Mont > Cu-Mont > Mn-Mont > Ca-Mont > Na-Mont > quartz > talc. The effects of coagulant polymers on TPFP follow the order nonionic polymer > anionic polymer > cationic polymer. The catalytic role of the clay cation was further confirmed by the observed inhibition in DBP formation when strong chelating agents (o-phenanthroline and ethylenediamine) were added to the clay suspension. Moreover, in the presence of clays, total DBPs increased appreciably when either the reaction time or the amount of the added clay or coagulant polymer increased. For volatile DBPs, the formation of halogenated methanes was usually time-dependent, with chloroform and dichloromethane showing the greatest dependence.

Journal Article↗

PubMed2004

Effects of organic solutes properties on the volatilization processes from water solutions.

Effects of organic solutes properties, including Henry's law constant (H), molecular weight (M), molar volume at normal boiling point (Vb), and solubility (S), on the usefulness of rate estimation by reference to a reference substance (i.e., reference substance concept) and on the evaporation rate were investigated by measuring the volatilization rate constant of organic solutes under different environmental conditions, including mixing and surfactants. It was found that if benzene was used as a reference substance, the ratio of the solute rate to that of benzene (F) becomes insensitive to water mixing, whether the solute possessed high or low Henry's law constant. In the presence of surfactants, however, the F value changes sharply as the solute solubility decreases. For benzene, toluene, ethylbenzene, and xylenes (BTEX), the F values are essentially constant irrespective of the presence of other chemicals (including organic compounds, surfactants, and salinity) and of the variation in temperature. On the other hand, the volatilization rates are closely related to molecular weight (solubility) in the existence of mixing (surfactants). Three different approaches, i.e., mass-transport theory, modified Knudsen equation, and reaction rate concept, were used to evaluate the dependence of solute volatilization rates on solute properties. It was concluded that the interaction between solute properties and environmental parameters might play a key role in the volatilization process of organic solutes under different environmental conditions.

Molecular Weight↗