Desorption Of Hydrophobic Organic Compounds Research Articles

Development of a polyethyleneimine/poly(N-isopropylacrylamide) semi-IPN hydrogel for use in the temperature-swing adsorption and selective desorption of hydrophobic organic compounds

BackgroundA novel polyethyleneimine/poly(N-isopropylacrylamide) semi-interpenetrating polymer network (PEI/poly(NIPA) semi-IPN) hydrogel was developed as a high-performance adsorbent for use in purifying wastewater containing multiple organic compounds and recovering each organic compound. Thermosensitive poly(NIPA) with a lower critical solution temperature (LCST) of ∼33 °C in water can perform the temperature-swing adsorption, i.e., reversibly adsorb/desorb adsorbates as the temperature varies across the LCST owing to its hydrophilic/hydrophobic transition. In addition, PEI, which is a branched polymer with primary, secondary, and tertiary amine groups, can adsorb acidic adsorbates via acid-base interactions. Thus, the developed hydrogel can adsorb adsorbates via hydrophobic and/or acid-base interactions. MethodsThe PEI/poly(NIPA) semi-IPN hydrogel was prepared by free radical polymerization of NIPA and a cross-linking monomer in an aqueous solution dissolving PEI, and characterized as an adsorbent for hydrophobic organic compounds in aqueous media. FindingsThe removal (water purification) and mutual separation (recovery) of binary components (p-nitrophenol and 4-iodoaniline as model adsorbates) were demonstrated via adsorption at 50°C, followed by two-step desorption at 20°C in water and an aqueous HCl solution. This process was based on the presence or absence of hydrophobic and acid-base interactions.

Enhanced remediation of a real HCH-polluted soil by the synergetic alkaline and ultrasonic activation of persulfate

The desorption of hydrophobic organic compounds (HOCs) and limited mass transfer in soil systems is a significant challenge for efficient soil remediation by oxidation treatments. The utilization of sonochemistry is a promising technology to enhance the decontamination of HOCs-polluted soils. In this work, ultrasound (US) was coupled to NaOH for activating persulfate (PS) to enhance the remediation of a real soil polluted with hexachlorocyclohexanes (HCHs) (ΣHCHs = 404 mg kg−1).Batch experiments (mass aqueous/soil ratio, VL/WS = 2) were performed to evaluate the effect of US on HOCs desorption and oxidation. Moreover, the influence of US power (0–245 W, corresponding to 0–91 W L-1 of US power density) and the initial oxidant concentration (CPS = 10–60 g L-1) on pollutants abatement, dechlorination degree, and oxidant consumption have been studied. Scanning electron microscopy (SEM) images verified that the US facilitates the breakdown of soil aggregates, enhancing the desorption of trichlorobenzenes (TCBs) (generated from HCHs alkaline hydrolysis) from the soil. Moreover, their subsequent oxidation is favouring because of higher radical species concentrations and the temperature rise. An increase in the US power up to 165 W accelerates the production rate of radicals, improving the pollutants’ degradation. The difference between pollutant oxidation and dechlorination decreases with increasing US power, associated with a lower concentration of intermediate chlorinated compounds. In the same way, the initial oxidant concentration plays a fundamental role in the remediation treatment. At the selected operating conditions (CPS = 60 g L-1, NaOH/PS = 2, 165 W), a pollutants degradation and dechlorination of 0.94 and 0.74, respectively, were achieved in just 3 h of reaction time.

Effects of type and quantity of organic carbon on the bioaccessibility of polychlorinated biphenyls in contaminated sediments.

Organic carbon principally controls sorption and desorption of hydrophobic organic compounds in sediments. We investigated the effects of organic carbon type and quantity on compound bioaccessibility. The desorption of 21 polychlorinated biphenyl (PCB) congeners was determined in spiked sediments amended with black carbon, humic acid, and sawdust at either 3 or 6% organic carbon. Desorption parameters were determined using Tenax sequential extractions and then modeled as operationally defined rapid, slow, and very slow fractions and rate constants. The effects of the amendments on PCB bioaccumulation were also evaluated using Lumbriculus variegatus. The lowest and highest PCB bioaccessibilities were observed in the black carbon and sawdust amendments, respectively. The total amount of PCBs desorbed ranged from 3 to 27% for the black carbon amendments, 12 to 55% for humic acid amendments, 16 to 80% for sawdust amendments, and 35 to 89% for controls. The results also showed that desorption of PCBs was slower in 6% amendments than 3% amendments, and this finding was most evident in humic acid and black carbon amendments. Overall, the trend in PCB bioaccumulation was similar to what was found for compound desorption in that the highest PCB bioaccumulation was observed in controls and sawdust amendments, whereas humic acid and black carbon amendments showed lower bioaccumulation. Finally, the 24-h single-point Tenax and bioaccumulation data were fit to a Tenax regression model. The PCB bioaccumulation was effectively predicted by the model, with 80% of the data falling within the 95% confidence intervals. Environ Toxicol Chem 2018;37:1280-1290. © 2018 SETAC.

Investigation of the kinetic process of solid phase microextraction in complex sample

The presence of complex matrix in the aquatic system affects the environmental behavior of hydrophobic organic compounds (HOCs). In the current study, an automated solid-phase microextraction (SPME) desorption method was employed to study the effect of 2-hydroxypropyl-β-cyclodextrin (β-HPCD) on the kinetic process of 5 selected polyaromatic hydrocarbons (PAHs) desorbing from the fiber in aqueous sample. The results showed that the added β-HPCD facilitated the desorption rates of PAHs from SPME fiber coating, and the enhancement effect can be predicted by a proposed theoretical model. Based on this model, the kinetic parameters of organic compounds desorbing from the SPME fiber can be determined, and the calculated results showed good agreement with the experimental data. In addition, the effect of temperature on the desorption kinetic was investigated. The results found that the SPME desorption time constant increased as the sampling temperature elevated, and followed the Arrhenius equation. Also, the temperature facilitated the desorption of HOCs from the bound matrix so that increased the lability degrees of the bound compounds. Finally, a calibration method based on the proposed theoretical model was developed and applied for the analysis of unknown sample.

In-line gas chromatographic apparatus for measuring the hydrophobic micropore volume (HMV) and contaminant transformation in mineral micropores

Desorption of hydrophobic organic compounds from micropores is characteristically slow compared to surface adsorption and partitioning. The slow-desorbing mass of a hydrophobic probe molecule can be used to calculate the hydrophobic micropore volume (HMV) of microporous solids. A gas chromatographic apparatus is described that allows characterization of the sorbed mass with respect to the desorption rate. The method is demonstrated using a dealuminated zeolite and an aquifer sand as the model and reference sorbents, respectively, and trichloroethylene (TCE) as the probe molecule. A glass column packed with the microporous sorbent is coupled directly to a gas chromatograph that is equipped with flame ionization and electron capture detectors. Sorption and desorption of TCE on the sorbent was measured by sampling the influent and effluent of the column using a combination of switching and injection valves. For geosorbents, the HMV is quantified based on Gurvitsch's rule from the mass of TCE desorbed at a rate that is characteristic for micropores. Instrumental requirements, design considerations, hardware details, detector calibration, performance, and data analysis are discussed along with applications. The method is novel and complements traditional vacuum gravimetric and piezometric techniques, which quantify the total pore volume under vacuum conditions. The HMV is more relevant than the total micropore volume for predicting the fate and transport of organic contaminants in the subsurface. Sorption in hydrophobic micropores strongly impacts the mobility of organic contaminants, and their chemical and biological transformations. The apparatus can serve as a tool for characterizing microprous solids and investigating contaminant-solid interactions.

Study of desorption kinetics of polycyclic aromatic hydrocarbons (PAHs) from solid matrices using internally cooled coated fiber

The kinetics of desorption of hydrophobic organic compounds (HOCs) from soil and sediment particles is important both from environmental and analytical chemistry points of view. Reliable techniques are required for prediction of desorption behaviour of HOCs from contaminated soils and sediments. In this study internally cooled coated fiber device, in which a PDMS hollow fiber extraction phase is cooled with liquid CO 2, was used as an exhaustive extraction sorbent phase for extraction of desorbed organic compounds (e.g. polycyclic aromatic hydrocarbons, PAHs) from both laboratory-spiked and naturally contaminated solid sample into the gaseous headspace in a batch system. The extraction time profiles were obtained at two different elevated temperatures (above 100 °C) for spiked sand and silica gel matrices. The slow desorption rate constants at each temperature were determined from desorption plots and the apparent activation energies of desorption were obtained from Arrhenius equations. The apparent activation energies of desorption of naphthalene, acenaphthylene and acenaphthene, from spiked silica gel, were approximately 60 kJ mol −1, and were higher, 70 and 100 kJ mol −1 for fluoranthene and anthracene, respectively. The fast and slow desorption rates and apparent activation energies of desorption for PAHs were obtained by spiking a naturally contaminated sediment sample with deuterated PAHs (PAHs-d 10). The activation energies of native PAHs were higher than those of spiked deuterated PAHs, suggesting that the native compounds were more affected by retarded pore diffusion or slow mass transfer through glassy sorbent organic matter (SOM). The proposed technique in the present study is fully automated, and can extract the contaminants from the solid matrix fast and exhaustively, which makes it more time efficient and versatile compared to the commonly used technique for desorption studies, i.e. vial desorption.

Release of adsorbed polycyclic aromatic hydrocarbons under cosolvent treatment: Implications for availability and fate

During laboratory and field studies, a fraction of contaminants in soils or sediments often is observed to be highly resistant to desorption. This desorption-resistant fraction may have significant effects on long-term fate and exposure of soil/ sediment-bound contaminants in particular, causing much reduced availability and contaminant persistence. Previous work by many research groups has indicated that this nonideal desorption behavior could be better predicted with biphasic desorption models. The present study further investigated the release of naphthalene and phenanthrene from sediments during and after cosolvent treatment. Experimental results indicate that release of these two compounds under cosolvent conditions can be accurately predicted with a previously developed, biphasic desorption model when the solubility enhancement effect of cosolvent is accounted for using standard activity coefficient ratios. In addition, desorption of the residual contaminants after cosolvent treatment follows the original biphasic desorption model very well, suggesting that cosolvent treatment increases only the aqueous solubility and has little effect on the nature of the desorption-resistant fraction and that cosolvent desorption is a valuable analytical tool for quickly measuring the magnitude of the desorption-resistant fraction. The present findings might have important implications for the mechanisms controlling resistant desorption of hydrophobic organic compounds and for predicting the availability and long-term fate of contaminants in soils and sediments.

Modeling biphasic sorption and desorption of hydrophobic organic contaminants in sediments

A model was developed to predict biphasic sorption and desorption of hydrophobic organic compounds in contaminated sediments. The model was based on relatively rapid porous diffusion in amorphous organic carbon and slow solid-phase diffusion in condensed-phase organic carbon. The model was used to simulate measured solid-fluid phase desorption (rates and pore-water concentrations) for four polycyclic aromatic hydrocarbons exhibiting a range of hydrophobicities (phenanthrene, anthracene, pyrene, and benzo[a]pyrene) in two field-contaminated sediments from Utica Harbor (Utica, NY, USA) and Rouge River (Detroit, MI, USA). Pore-water concentrations have been related to bioavailability, indicating the potential usefulness of the model to predict bioavailability. Key model parameters included the fraction of condensed-phase carbon (estimated by combustion at 375 degrees C), partition coefficient to the condensed-phase carbon (estimated by desorption measurements on coal-like particles physically separated from Utica Harbor sediments), and diffusivity and ratio of volume to surface area of the condensed-phase organic matter (fitted to measured desorption data on both sediments and for the measured polycyclic aromatic hydrocarbons). Best fit for the diffusion coefficient in the condensed-phase organic matter was 8.5 x 10(-20) m2/s, and ratio of volume to surface area was 2 microm. These parameters estimated measured pore-water concentrations of all polycyclic aromatic hydrocarbons in both sediments with an average error of 46% and a correlation coefficient of 0.76 and the fast-desorbing fractions (as measured by the fraction removed with a nonpolar polymeric sorbent XAD-2) with an average error of approximately 30% and a correlation coefficient of 0.54 (14% and 0.76, respectively, for all but benzo[a]pyrene). Modeling results were relatively insensitive to the two fitted parameters, with changes of an order of magnitude or more being required to affect the correlation between the model and observations significantly.

Enhanced Soil Washing of Phenanthrene by Mixed Solutions of TX100 and SDBS

Increased desorption of hydrophobic organic compounds (HOCs) from soils and sediments is a key to the remediation of contaminated soils and groundwater. In this study, phenanthrene desorption from a contaminated soil by mixed solutions of a nonionic surfactant(octylphenol polyethoxylate, TX100) and an anionic surfactant (sodium dodecylbenzenesulfonate, SDBS) was investigated. Phenanthrene desorption depended on not only aqueous surfactant concentrations and phenanthrene solubility enhancement but also the soil-sorbed surfactant amount and the corresponding sorption capacity of sorbed surfactants. The added surfactant critical desorption concentrations (CDCs) for phenanthrene from soil depended on both sorbed concentrations of surfactants and their critical micelle concentrations (CMCs). Phenanthrene desorption by mixed solutions was more efficient than individual surfactants due to the low sorption loss of mixed surfactants to soil. Among the tested surfactant systems, mixed TX100 and SDBS with a 1:9 mass ratio exhibited the highest phenanthrene desorption. Mixed micelle formation, showing negative deviation of CMCs from the ones predicted by the ideal mixing theory, was primarily responsible for the significant reduction of soil-sorbed amounts of TX100 and SDBS in their mixed systems. Therefore, mixed anionic-nonionic surfactants had great potential in the area of enhanced soil and groundwater remediation.

Investigation of Mechanisms Contributing to Slow Desorption of Hydrophobic Organic Compounds from Mineral Solids

This research investigates the mechanisms contributing to the slow desorption of hydrophobic organic compounds from water-saturated mineral solids. The mechanisms investigated were adsorption-retarded aqueous diffusion, micropore diffusion, high-energy micropore adsorption, and micropore blockage by precipitated minerals. To reduce the potential confounding effects of adsorbent heterogeneity, a set of homogeneous silica gel and glass bead adsorbents were used in the investigation. Desorption rates for the slow-desorbing fractions of chloroform (CF), trichloroethylene (TCE), and perchloroethylene (PCE) from silica gel did not conform to the pore-diffusion model for adsorption-retarded aqueous diffusion. This indicated that diffusion through adsorbent mesopores was not responsible for slow desorption from silica gel. Micropore-diffusion modeling of TCE desorption from three silica gels and microporous glass beads indicated that pores less than 2 nm in diameter were responsible for slow desorption. Desorptio...

Compost extract enhances desorption of α-naphthol and naphthalene from pristine and contaminated soils

Enhancing desorption of hydrophobic organic compounds (HOCs) may be necessary to achieve bioremediation of soils. We measured desorption of added α-naphthol and naphthalene in compost extract (200 mg C in 10 mmol l −1 CaCl 2) and in 10 mmol l −1 CaCl 2 alone from (i) soils varying in age, diagenesis, and quantity and quality of organic matter, and (ii) wettable and non-wettable soil samples from a 20-y-old oil spill. Compost extract increased desorption of α-naphthol and naphthalene from all soils compared to desorption in CaCl 2 alone, despite the wide range of values among the soils for linear partition coefficients ( K d varied 40-fold for α-naphthol and 50-fold for naphthalene) and partition coefficients normalized for organic C content ( K oc varied 3-fold for α-naphthol and 2.5-fold for naphthalene). The proportional enhancement of desorption tended to be higher for α-naphthol than for naphthalene. No consistent relationship, however, was detected between the character of the soil organic matter, as measured by CPMAS- 13C NMR, and the magnitude of enhanced desorption. Furthermore, enhanced desorption could not be attributed to surfactant-like activity of the compost extract as measured by a Du Noüy tensiometer. Sorption of the compost extract on soil, however, was substantial ( f oc = 0.047, K d = 0.42) and may have contributed to enhanced desorption of HOCs. Our results reinforce previous reports that dissolved organic C can enhance desorption of HOCs from soils. Our study identified sorption of compost extract C and displacement of sorbed HOCs as a possible mechanism of desorption enhancement meriting further investigation. Furthermore, the enhanced desorption of HOCs in the presence of co-sorbed organic contaminants needs to be addressed.

Effect of clay minerals present in aquifer soils on the adsorption and desorption of hydrophobic organic compounds

Adsorption of hydrophobic organic compounds (HOCs) onto clay minerals and organic matter present in soils results in retarding their mobility. To study the impact of clay minerals on HOC sorption, kinetic and equilibrium studies were performed using naphthalene as a test surrogate contaminant. The results of these studies indicated that expandable clay minerals (clays that expand and expose large internal surface area on wetting), such as montmorillonite and vermiculite, had a significant impact on naphthalene partitioning. A mathematical model was developed from the equilibrium data which related clay mineral concentrations with the naphthalene partition coefficient. Equilibrium desorption studies were also performed by adding a micellar solution of a surfactant mixture (50:50) of Tween 20 and Aerosol AY-65 to mobilize the adsorbed naphthalene. The surfactant mixture was generally unable to mobilize the sorbed contaminant due to sorption irreversibility and adsorption hysteresis.

Effect of clay minerals present in aquifer soils on the adsorption and desorption of hydrophobic organic compounds

Effect of clay minerals present in aquifer soils on the adsorption and desorption of hydrophobic organic compounds