Adsorbent Trap Research Articles

UIO-66-NH2 Packed Needle Trap for Accurate and Reliable Sampling and Analysis of the Halogenated Volatile Organic Compounds in Air

ABSTRACT This paper introduces a novel inside needle adsorption trap device based on UiO-66-NH2 adsorbent for the sampling and analysis of halogenated volatile organic compounds (HVOCs), including chloroform, carbon tetrachloride, and perchloroethylene in air. In this study, the UiO-66-NH2 adsorbent was first synthesized and then packed into spinal needles (22 Gauge). This study was conducted both in the laboratory and in the field. Scanning Electron Microscope (SEM), Fourier Transform Infrared Spectroscopy (FT-IR) and X-Ray Diffraction (XRD) were used to investigate the sorbent characteristics. In this study, Response Surface Methodology (RSM) and Central Composite Design (CCD) were utilized to optimize the effects of sampling parameters and desorption parameters on needle trap device (NTD) performance. In this regard, a constant concentration of the compounds of interest was injected into a standard chamber, and then the packed NTD was used for the sampling of HVOCs under a given condition. According to the results, the maximum peak area response was obtained at 280 ˚C of desorption temperature and 4 min of desorption time. The results showed that increased sampling humidity and temperature interfered with the NTD performance and decreased the peak area responses of the analytes. The proposed NTD had a high sensitivity for the sampling and analysis of the desired compounds. Limit of Detection (LOD) and the Limit of Quantitation (LOQ) of the NTD for the analytes were in the range 0.01-0.03 and 0.02-0.05 ng.mL-1, respectively. Moreover, the repeatability of the proposed NTD was obtained to be in the range of 2.3-9.1%. Therefore, the NTD packed with UiO-66-NH2 adsorbent can be used as a suitable and robust method for the active sampling and analysis of occupational/environmental pollutants in the air.

Bacterial volatiles from mealybug honeydew exhibit kairomonal activity toward solitary endoparasitoid Anagyrus dactylopii

Anagyrus dactylopii (Howard) (Hymenoptera: Encyrtidae) is a solitary koinobiont endoparasitoid of grapevine mealybugs and has been reported to parasitize 70% of mealybug populations naturally. In the present study, we have isolated and identified by employing a 16S rRNA technique, a total of ten cultivable bacteria from the honeydew of two species of grapevine mealybugs, Maconellicoccus hirsutus and Nipaecoccus viridis. In the honeydew of M. hirsutus, seven bacteria were found, which included Micrococcus luteus, Kocuria rosea, Bacillus aquimaris, Exiguobacterium aquaticum, Staphylococcus pasteuri, Bacillus oceanisediminis and Bacillus flexus. From the honeydew of N. viridis, three bacteria, viz. Bacillus firmus, Microbacterium testaceum and Pesudomonas oryzihabitans, could be recovered. Further, we have collected the headspace from 72 h active cultures of these honeydew-associated bacteria by sorption over adsorbent trap made up of 0.2 g porapak using dynamic headspace sampling technique with pull and push system and tested the behavioral responses of mated females of A. dactylopii to these volatiles in a Y-tube olfactometer. The mated females positively responded to volatiles from five bacteria, which included only two bacteria associated with the honeydew of M. hirsutus, i.e., K. rosea, and S. pasteuri and all the three bacteria from honeydew of N. viridis. This indicates an ability of A. dactylopii to exploit cues associated with the mealybug honeydew for host location. The GC–MS analysis of bacterial headspace revealed six volatile organic compounds (VOCs), viz. propanoic acid, 2-methyl-2,2-dimethyl-1-(2-hydroxy-1-methylethyl) propyl ester; tetradecane; dodecane; 10-heptadecen-8-ynoic acid, methyl ester; 10,13-octadecadiynoic acid, methyl ester and limonen-6-ol, pivalate. Interestingly, limonen-6-ol, pivalate has been found as a common constituent of volatiles from all the three bacteria that were isolated from honeydew of N. viridis. The possible exploitation of bacterial VOCs in enhancing populations of A. dactylopii and promoting conservation biological control of mealybugs in grape vineyards is discussed.

Radon removal trap design and coefficient testing for the development of an effective radioxenon sampling, separation and measurement system

To monitor low-level radioxenon isotopes activity concentrations in the bulk gases, a radioxenon sampling, separation and measurement system has been developed. The xenon enrichment factor of this system is more than 105 after the separation of impurities, including N2, O2, CO2and H2O, as well as radon and its progenies, such as 214Pb and 214Bi. Since radon and its progenies interfere with radioxenon measurement, they have to be removed before radioxenon counting. To separate radon from xenon, different dynamic adsorption coefficients of xenon and radon are used to design small radon removal trap to retain radon after eluting xenon, and the ratio between radon and xenon dynamic adsorption coefficient gives the adsorbent weight relationship between the xenon adsorption trap and its related radon removal trap. To test the effectiveness of radon removal, the relative measuring method is used by measuring γ-rays energies of radon progenies in canister filling with either the measuring sample prepared by the system or the original gas. The results show that the radon removal coefficient and the stable xenon recovery, which are two important parameters in the radioxenon system, are at the order of 10−6 and >70% respectively. These meet the specifications proposed by the Comprehensive Nuclear-Test-Ban Treaty Organization.

A Study on the Improvement Repeatability and Accuracy of the Analysis Method for SF6 of Trace Level

Kyoto Protocol, adopted in 1997, set the obligation to reduce CO2, CH4, N2O, HFCs, PFCs, and SF6 in developed countries during 1st promised period. SF6 has been drawing a lot of attention since the Kyoto Protocol because once it is released into the atmosphere, it not only stays in the atmosphere for more than 3,200 years but also emits 22,800 times stronger global warming potential at the same concentrations as CO2 if remains in the atmosphere for 100 years. This study introduces 12 methods for SF6 of measuring trace. SF6 of trace level in the atmosphere correctly, the measurement method was changed and as a result, when the back flush method was applied to the pre-concentration system that used low-temperature concentration and high-temperature desorption system, which used Carboxen-1000 adsorption trap, the effect was the best.

Influence of shale‐total organic content on CO2 geo‐storage potential

AbstractShale CO2 wettability is a key factor which determines the structural trapping capacity of a caprock. However, the influence of shale‐total organic content (TOC) on wettability (and thus on storage potential) has not been evaluated despite the fact that naturally occurring shale formations can vary dramatically in TOC, and that even minute TOC strongly affects storage capacities and containment security. Thus, there is a serious lack of understanding in terms of how shale, with varying organic content, performs in a CO2 geo‐storage context. We demonstrate here that CO2‐wettability scales with shale‐TOC at storage conditions, and we propose that if TOC is low, shale is suitable as a caprock in conventional structural trapping scenarios, while if TOC is ultrahigh to medium, the shale itself is suitable as a storage medium (via adsorption trapping after CO2 injection through fractured horizontal wells).

The Effectiveness of Moringa oleifera Seed Flour and Chitosan as Coagulant‐Flocculants for Water Treatment

The aim of this contribution is to provide a comprehensive comparison between chitosan and Moringa oleifera seed flour (MOSF) as coagulant‐flocculants. MOSF was obtained as a byproduct in a biodiesel process. Turbidity and heavy metal ion removal, using both eco‐friendly materials, was assessed. Jar tests were performed on samples taken from river water, agricultural wastewater, and mixed wastewater (contaminated with agricultural and urban residues). Bioflocculant dosages within the range of 0.005–20 mg L−1 were tested. Irrespective of the initial turbidity, the optimal dosage of chitosan and MOSF for decreasing turbidity in river water was 1 and 5 mg L−1, respectively. Furthermore, from river water, Pb removal up to 95% was achieved irrespective of the bioflocculant; for Mn removal, MOSF performed better than chitosan, with the adsorbent trapping close to 90% of this metal. MOSF decreased turbidity levels and heavy metal content (Mn and Pb) to under the permissible limits (Mexican environmental regulation for potable water, NOM‐127‐SSA1‐1994). Additionally, kinetic data were fitted to kinetic models of adsorption for the pollutants. For agricultural wastewater, a chitosan dosage of 10 mg L−1 reduced turbidity to 5–10 nephelometric turbidity units (NTU), and a MOSF dosage of 10 mg L−1 decreased the turbidity to values lower than 5 NTU. For the mixed wastewater, chitosan achieved a high turbidity removal, while MOSF was not suitable.

Single-step reinforced microextraction of polycyclic aromatic hydrocarbons from soil samples using an inside needle capillary adsorption trap with electropolymerized aniline/multi-walled carbon nanotube sorbent

A polyaniline/multi-wall carbon nanotubes (PANI/MWCNT) composite was electrodeposited on the interior surface of a platinized stainless steel capillary needle and used to prepare an inside needle capillary adsorption trap (INCAT) device. The platinization expanded the interior adsorbing surface of the needle and made it more porous and cohesive for nanocomposite film. The nanocomposite was characterized using scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR). The fabricated INCAT was fixed into a cooling capsule to fabricate a cooling-assisted INCAT (CA-INCAT) system. The CA-INCAT device was used to extract polycyclic aromatic hydrocarbons (PAHs) from solid samples followed by gas chromatography-flame ionization detection (GC-FID) determination. To obtain the best extraction efficiency, the important experimental variables were studied and optimized. Under the optimal conditions, the limits of detection (LODs) for the studied PAHs were in the range of 0.002–0.02ngg−1. Linear dynamic ranges (LDRs) for the calibration curves were found to be 0.1–30,000ngg−1. Relative standard deviations (RSDs%) for six replicated analysis of 1ngg−1 PAHs were obtained 7.7–11%. The CA-INCAT-GC-FID method was successfully applied for the extraction and determination of PAHs in contaminated soil samples. The results were in agreement with those obtained by a validated ultrasound-assisted solvent extraction (UA-SE) method.

Preparation of gold- and chlorine-impregnated bead-type activated carbon for a mercury sorbent trap

This study aimed to develop a mercury (Hg) adsorption trap, which can be used to measure the concentration of elemental Hg in emissions from a Hg discharge facility, and evaluate its adsorption efficiency. The Hg spiking efficiency was compared by impregnating metallic and halogen materials that have high affinity for Hg into activated carbon (AC) to determine an accurate spiking method for Hg on AC. The Hg spiking efficiency was compared according to the type and content of the impregnated substances. AC impregnated with Cl and Au had a 15–20% higher Hg spiking efficiency compared to virgin AC. For Au impregnation at weight ratios of 0–20 wt% of adsorbent, spiking efficiencies of over 97% were observed under certain conditions. The Hg adsorption properties of the above adsorbent were determined experimentally, and the results were used to test the adsorption performance of Hg adsorption traps.

CO2-wettability of low to high rank coal seams: Implications for carbon sequestration and enhanced methane recovery

Coal seams offer tremendous potential for carbon geo-sequestration with the dual benefit of enhanced methane recovery. In this context, it is essential to characterize the wettability of the coal–CO2–water system as it significantly impacts CO2 storage capacity and methane recovery efficiency. Technically, wettability is influenced by reservoir pressure, coal seam temperature, water salinity and coal rank. Thus a comprehensive investigation of the impact of the aforementioned parameters on CO2-wettability is crucial in terms of storage site selection and predicting the injectivity behaviour and associated fluid dynamics. To accomplish this, we measured advancing and receding water contact angles using the pendent drop tilted plate technique for coals of low, medium and high ranks as a function of pressure, temperature and salinity and systematically investigated the associated trends. We found that high rank coals are strongly CO2-wet, medium rank coals are weakly CO2-wet, and low rank coals are intermediate-wet at typical storage conditions. Further, we found that CO2-wettability of coal increased with pressure and salinity and decreased with temperature irrespective of coal rank. We conclude that at a given reservoir pressure, high rank coal seams existing at low temperature are potentially more efficient with respect to CO2-storage and enhanced methane recovery due to increased CO2-wettability and thus increased adsorption trapping.

Development of INCAT-GC-MS for analysis of metabolites in urine

This paper aims to develop a non-solvent microextraction technique using INCAT (Inside Needle Capillary Adsorption Trap) for GC-MS analysis of volatile metabolites in urine. INCATs with different sorbents were tested, resulting in an INCAT with 3 sorbent layers Chromosorb W+ 20% SE-54, Carbopack X and Carboxen 1000 (1 : 1 : 1), which proved to be the most suitable for differentiating and identifying volatile metabolites in urine samples of patients from those of healthy people.

Extension of a dynamic headspace multi-volatile method to milliliter injection volumes with full sample evaporation: Application to green tea

An extension of multi-volatile method (MVM) technology using the combination of a standard dynamic headspace (DHS) configuration, and a modified DHS configuration incorporating an additional vacuum module, was developed for milliliter injection volume of aqueous sample with full sample evaporation. A prior step involved investigation of water management by weighing of the water residue in the adsorbent trap. The extended MVM for 1mL aqueous sample consists of five different DHS method parameter sets including choice of the replaceable adsorbent trap. An initial two DHS sampling sets at 25°C with the standard DHS configuration using a carbon-based adsorbent trap target very volatile solutes with high vapor pressure (>10kPa) and volatile solutes with moderate vapor pressure (1–10kPa). Subsequent three DHS sampling sets at 80°C with the modified DHS configuration using a Tenax TA trap target solutes with low vapor pressure (<1kPa) and/or hydrophilic characteristics. After the five sequential DHS samplings using the same HS vial, the five traps are sequentially desorbed with thermal desorption in reverse order of the DHS sampling and the desorbed compounds are trapped and concentrated in a programmed temperature vaporizing (PTV) inlet and subsequently analyzed in a single GC–MS run. Recoveries of 21 test aroma compounds in 1mL water for each separate DHS sampling and the combined MVM procedure were evaluated as a function of vapor pressure in the range of 0.000088–120kPa. The MVM procedure provided high recoveries (>88%) for 17 test aroma compounds and moderate recoveries (44–71%) for 4 test compounds. The method showed good linearity (r2>0.9913) and high sensitivity (limit of detection: 0.1–0.5ngmL−1) even with MS scan mode. The improved sensitivity of the method was demonstrated with analysis of a wide variety of aroma compounds in brewed green tea. Compared to the original 100μL MVM procedure, this extension to 1mL MVM allowed detection of nearly twice the number of aroma compounds, including 18 potent aroma compounds from top-note to base-note (e.g. 2,3-butanedione, coumarin, furaneol, guaiacol, cis-3-hexenol, linalool, maltol, methional, 3-methyl butanal, 2,3,5-trimethyl pyrazine, and vanillin). Sensitivity for 23 compounds improved by a factor of 3.4–15 under 1mL MVM conditions.

The analysis of linear and monomethylalkanes in exhaled breath samples by GC×GC-FID and GC-MS/MS.

A new arrangement of the INCAT (inside needle capillary adsorption trap) device with Carbopack X and Carboxen 1000 as sorbent materials was applied for sampling, preconcentration and injection of C6C19n-alkanes and their monomethyl analogs in exhaled breath samples. For the analysis both GC-MS/MS and GC×GC-FID techniques were used. Identification of the analytes was based on standards, measured retention indices and selective SRM transitions of the individual isomers. The GC-MS/MS detection limits were in the range from 2.1 pg for n-tetradecane to 86 pg for 5-methyloctadecane. The GC×GC-FID detection limits ranged from 19 pg for n-dodecane to 110 pg for 3-methyloctane.

Multi-volatile method for aroma analysis using sequential dynamic headspace sampling with an application to brewed coffee

A novel multi-volatile method (MVM) using sequential dynamic headspace (DHS) sampling for analysis of aroma compounds in aqueous sample was developed. The MVM consists of three different DHS method parameters sets including choice of the replaceable adsorbent trap. The first DHS sampling at 25°C using a carbon-based adsorbent trap targets very volatile solutes with high vapor pressure (>20kPa). The second DHS sampling at 25°C using the same type of carbon-based adsorbent trap targets volatile solutes with moderate vapor pressure (1–20kPa). The third DHS sampling using a Tenax TA trap at 80°C targets solutes with low vapor pressure (<1kPa) and/or hydrophilic characteristics. After the 3 sequential DHS samplings using the same HS vial, the three traps are sequentially desorbed with thermal desorption in reverse order of the DHS sampling and the desorbed compounds are trapped and concentrated in a programmed temperature vaporizing (PTV) inlet and subsequently analyzed in a single GC-MS run. Recoveries of the 21 test aroma compounds for each DHS sampling and the combined MVM procedure were evaluated as a function of vapor pressure in the range of 0.000088–120kPa. The MVM provided very good recoveries in the range of 91–111%. The method showed good linearity (r2>0.9910) and high sensitivity (limit of detection: 1.0–7.5ngmL−1) even with MS scan mode. The feasibility and benefit of the method was demonstrated with analysis of a wide variety of aroma compounds in brewed coffee. Ten potent aroma compounds from top-note to base-note (acetaldehyde, 2,3-butanedione, 4-ethyl guaiacol, furaneol, guaiacol, 3-methyl butanal, 2,3-pentanedione, 2,3,5-trimethyl pyrazine, vanillin, and 4-vinyl guaiacol) could be identified together with an additional 72 aroma compounds. Thirty compounds including 9 potent aroma compounds were quantified in the range of 74–4300ngmL−1 (RSD<10%, n=5).

Metabolomics Pilot Study to Identify Volatile Organic Compound Markers of Childhood Asthma in Exhaled Breath

In-community non-invasive identification of asthma-specific volatile organic compounds (VOCs) in exhaled breath presents opportunities to characterize phenotypes, and monitor disease state and therapies. The feasibility of breath sampling with children and the preliminary identification of childhood asthma markers were studied. End-tidal exhaled breath was sampled (2.5 dm³) from 11 children with asthma and 12 healthy children with an adaptive breath sampler. VOCs were collected onto a Tenax®/Carbotrap hydrophobic adsorbent trap, and analyzed by GC-MS. Classification was by retention-index and mass spectra in a 'breath matrix' followed by multivariate analysis. A panel of eight candidate markers (1-(methylsulfanyl)propane, ethylbenzene, 1,4-dichlorobenzene, 4-isopropenyl-1-methylcyclohexene, 2-octenal, octadecyne, 1-isopropyl-3-methylbenzene and 1,7-dimethylnaphtalene) were found to differentiate between the asthmatic and healthy children in the test cohort with complete separation by 2D principal components analysis (2D PCA). Furthermore, the breath sampling protocol was found to be acceptable to children and young people. This method was found to be acceptable for children, and healthy and asthmatic individuals were distinguished on the basis of eight VOCs at elevated levels in the breath of asthmatic children.

Inhibitory Influence of Enterococcus faecium on the Propagation of Swine Influenza A Virus In Vitro

The control of infectious diseases such as swine influenza viruses (SwIV) plays an important role in food production both from the animal health and from the public health point of view. Probiotic microorganisms and other health improving food supplements have been given increasing attention in recent years, but, no information on the effects of probiotics on swine influenza virus is available. Here we address this question by assessing the inhibitory potential of the probiotic Enterococcus faecium NCIMB 10415 (E. faecium) on the replication of two porcine strains of influenza virus (H1N1 and H3N2 strain) in a continuous porcine macrophage cell line (3D4/21) and in MDBK cells. Cell cultures were treated with E. faecium at the non-toxic concentration of 1×106 CFU/ml in growth medium for 60 to 90 min before, during and after SwIV infection. After further incubation of cultures in probiotic-free growth medium, cell viability and virus propagation were determined at 48 h or 96 h post infection. The results obtained reveal an almost complete recovery of viability of SwIV infected cells and an inhibition of virus multiplication by up to four log units in the E. faecium treated cells. In both 3D4/21- and MDBK-cells a 60 min treatment with E. faecium stimulated nitric oxide (NO) release which is in line with published evidence for an antiviral function of NO. Furthermore, E. faecium caused a modified cellular expression of selected mediators of defence in 3D4-cells: while the expression of TNF-α, TLR-3 and IL-6 were decreased in the SwIV-infected and probiotic treated cells, IL-10 was found to be increased. Since we obtained experimental evidence for the direct adsorptive trapping of SwIV through E. faecium, this probiotic microorganism inhibits influenza viruses by at least two mechanisms, direct physical interaction and strengthening of innate defence at the cellular level.

Development of a Simplified, Cost Effective GC-ECD Methodology for the Sensitive Detection of Bromoform in the Troposphere

Wherever measurements have been made bromoform was found to be ubiquitous in the surface ocean in pmolar-nmolar concentrations. These measurements show concentrations in coastal regions orders of magnitude higher than in the pelagic oceans. Its atmospheric presence is primarily due to its release from algae and rapid transport to the marine boundary troposphere where it is known to participate in ozone chemistry via photochemical and catalytic pathways. Until quite recently, a limited number of studies existed (compared to other marine volatile organic compounds (VOCs)), mainly due to the analytical challenge(s) presented by the low environmental mixing ratios. In this work we detail the development of a simplified, cost effective method to detect and quantify bromoform in environmental air samples. Air samples (1.5 L) were preconcentrated onto a precooled adsorbent (Carbopack X/Carboxen 1016) trap. These samples were injected by means of rapid thermal desorption for separation and detection by GC-ECD. The system was calibrated by means of a custom-built permeation oven. A linear system response was achieved, having a detection limit of 0.73 ± 0.09 ppt. A range of environmental samples was analysed to demonstrate the ability of the technique to separate and identify bromoform from air samples. The results showed that bromoform concentrations typically averaged 24.7 ± 17.3 ppt in marine air samples, 68.5 ± 26.3 ppt in Cape Town urban air samples and 33.9 ± 40.5 ppt in simulated biomass burning plumes (SBBP).

Determination of methamphetamine, amphetamine and ecstasy by inside-needle adsorption trap based on molecularly imprinted polymer followed by GC-FID determination

We have developed a solvent-free and sensitive method for the identification and quantification of methamphetamine (MAMP), amphetamine (AMP) and ecstasy (MDMA) in human urine. It is based on the use of an inside-needle adsorption trap (INAT) and a molecularly imprinted polymer (MIP). The MAMP-MIP layer was coated on the internal surface of a hollow stainless steel needle, which was oxidized and silylated. It was used as the extraction needle. A model solution containing the drugs was slowly passed through the extraction needle. After adsorption of the analytes, the needle was directly transferred to the injector of a gas chromatograph, where the analytes were thermally desorbed, separated by GC, and detected with a flame ionization detector. The method does not require an extraction solvent, is fast and simple. The linear range of the calibration graphs are rather wide, and the limit of detection and the limit of quantification (LOQ) for MAMP are 12 and 40 ng mL−1, respectively. The relative standard deviations (RSD%) for six repeated experiments (at 500 ng mL−1 of MAMP) is 4.9 %. The relative recoveries obtained for MAMP in spiked human urine samples are in the range of 81–93 %.

Inside needle capillary adsorption trap device for headspace solid‐phase dynamic extraction based on polyaniline/hexagonally ordered silica nanocomposite

Highly porous polyaniline/hexagonally ordered silica sorbent was used for fabrication of the inside needle capillary adsorption trap (INCAT) device. Polyaniline/SBA-15 nanocomposite was synthesized via chemical polymerization technique. The fabricated INCAT device was evaluated to the extraction of some polycyclic aromatic hydrocarbons (PAHs) from aqueous sample solutions in combination with gas chromatography (GC)-mass spectrometry (MS). A one at-the-time optimization strategy was applied for optimizing the important extraction parameters such as extraction temperature, extraction time, ionic strength, sampling flow rate, desorption time, and desorption temperature. In optimum conditions (extraction temperature 55 °C, extraction time 20 min, ionic strength 20% (w/v), flow rate 4.5 mL min(-1), desorption temperature 270 °C, desorption time 3 min) the repeatability for one INCAT device (n = 4), expressed as relative standard deviation, was between 4.2 and 10.2% for the tested compounds. The quantitation limits for the studied compounds were between 1 and 5 pg mL(-1). The developed method was successfully applied to spring water sample which was spiked with PAHs with the relative recovery percentages of 87.3-109.1%. The developed method offers the advantage of being simple to use, with shorter analysis times, lower cost of equipment, and thermal stability.

Adsorption and mineral trapping dominate CO2 storage in coal systems

High-CO2 coal seams occur in many sedimentary basins world-wide and provide natural analogues of the processes likely to occur as a result of CO2 injection and storage in coal systems. CO2 is stored in coal predominantly as adsorbed molecules on micropore surfaces (adsorption trapping) that allow higher densities and greater volumes of CO2 at shallower depths than in sandstone and carbonate reservoirs. In the longer term CO2 will dissolve in formation water and react with minerals in the host formation (solubility/ionic trapping) and may be precipitated as carbonate minerals (mineral trapping). A recent study suggests that solubility trapping is the predominant CO2 sink in natural gas fields (Gilfillan et al., 2009), whereas our natural analogue studies in the Bowen and Gunnedah Basins, eastern Australia, indicate that CO2 has been stored in coal and sandstone formations since the Mesozoic through a combination of adsorption and mineral carbonation reactions. These differences reflect the different mineralogies and hydrogeology of the CO2-rich natural gas fields studied by Gilfillan et al. (2009) and coal systems. Our work shows that natural analogue studies of sites that have stored CO2 over geological time scales are essential to determine the mechanisms of CO2 storage and the level of characterisation required for storage site equivalents. (C) 2011 Published by Elsevier Ltd.

Doping PbSe nanocrystals: Predictions based on a trapped-dopant model

We recently proposed that impurity doping in colloidally grown semiconductor nanocrystals is often controlled primarily by kinetics rather than by thermodynamics. In this ``trapped-dopant'' model the diffusion of an impurity through a nanocrystal is negligible at colloidal growth temperatures. Consequently, an impurity can only be incorporated as a dopant into a growing nanocrystal if it first adsorbs on the surface and is then overgrown. This surface adsorption can be complicated by a competing process: the binding of the impurity by surfactant molecules and other agents added to the growth solution to passivate the nanocrystal and control its growth. Here we use density-functional theory to study the interplay and outcome of these processes for the doping of PbSe nanocrystals by a number of candidate dopants (Mn, Co, Cl, In, Cd, Tl, etc.) in the presence of two widely used growth additives (oleic acid and hexadecylamine). The results suggest that successful doping requires making a trade-off between surface adsorption (which favors small dopants) and interior trapping (which favors large dopants). Moreover, the widely used growth agent oleic acid binds strongly to almost all dopants, suggesting that the standard growth procedure may require modification for successful doping to be realized.