Hydrocarbons In Aqueous Solutions Research Articles

Detection of Aromatic Hydrocarbons in Aqueous Solutions Using Quartz Tuning Fork Sensors Modified with Calix[4]arene Methoxy Ester Self-Assembled Monolayers: Experimental and Density Functional Theory Study.

Quartz tuning forks (QTFs), which were coated with gold and with self-assembled monolayers (SAM) of a lower-rim functionalized calix[4]arene methoxy ester (CME), were used for the detection of benzene, toluene, and ethylbenzene in water samples. The QTF device was tested by measuring the respective frequency shifts obtained using small (100 µL) samples of aqueous benzene, toluene, and ethylbenzene at four different concentrations (10-12, 10-10, 10-8, and 10-6 M). The QTFs had lower limits of detection for all three aromatic hydrocarbons in the 10-14 M range, with the highest resonance frequency shifts (±5%) being shown for the corresponding 10-6 M solutions in the following order: benzene (199 Hz) > toluene (191 Hz) > ethylbenzene (149 Hz). The frequency shifts measured with the QTFs relative to that in deionized water were inversely proportional to the concentration/mass of the analytes. Insights into the effects of the alkyl groups of the aromatic hydrocarbons on the electronic interaction energies for their hypothetical 1:1 supramolecular host-guest binding with the CME sensing layer were obtained through density functional theory (DFT) calculations of the electronic interaction energies (ΔIEs) using B3LYP-D3/GenECP with a mixed basis set: LANL2DZ and 6-311++g(d,p), CAM-B3LYP/LANL2DZ, and PBE/LANL2DZ. The magnitudes of the ΔIEs were in the following order: [Au4-CME⊃[benzene] > [Au4-CME]⊃[toluene] > [Au4-CME]⊃[ethylbenzene]. The gas-phase BSSE-uncorrected ΔIE values for these complexes were higher, with values of -96.86, -87.80, and -79.33 kJ mol-1, respectively, and -86.39, -77.23, and -67.63 kJ mol-1, respectively, for the corresponding BSSE-corrected values using B3LYP-D3/GenECP with LANL2dZ and 6-311++g(d,p). The computational findings strongly support the experimental results, revealing the same trend in the ΔIEs for the proposed hypothetical binding modes between the tested analytes with the CME SAMs on the Au-QTF sensing surfaces.

(Digital Presentation)Cu Coordination Environment Modification Via Atomic Layer Infiltration As High Selective CO2RR Catalyst

Carbon dioxide (CO2) is the most notorious greenhouse gas, released by both natural and artificial processes. In an ideal scenario, the production and consumption of CO2 should be balanced so that the concentration of CO2 in atmosphere remains constant to maintain environmental stability. Unfortunately, with the intensification of human industrial activities, this balance has gradually been disrupted, leading to more CO2 production and making global warming a pressing issue. With carbon neutrality gaining increasing attention, electrochemical CO2 reduction reaction (CO2RR) has emerged as a research orientation which converts CO2 to value-added products while storing renewable energy. Cu-based electrocatalysts have been studied extensively for the CO2RR into hydrocarbons in aqueous solutions under environmental conditions. However, they frequently endure low Faradaic Efficiency (FE) and selectivity of specific single product. Particularly, precise construction of Cu micro-environment is of great challenge for the design and fabrication of excellent Cu-based CO2RR catalysts.Atomic layer infiltration (ALI) allows gas phase precursors to penetrate and diffuse into porous substrates through their nanoporous structures and to grow within the subsurface. Aiming at systematically regulating the Cu metal site micro-environment, porous HKUST-1 containing paddle-wheel Cu coordination nodes was chosen as a template and modified with ALI technique in this work. Various metals were introduced into HKUST-1 using ALI method to construct bimetallic sites which tended to produce CO, HCOOH and other products with high FEs. Density Functional Theory (DFT) calculations prove the modification with metals by ALI enhances the adsorption enthalpy of CO2 and alters the bonding interaction between reaction intermediates and adsorption center, thereby changing the reaction pathways. MOF conversion technique based on atomic layer deposition (ALD) will be utilized to fabricate HKUST-1 thin film in our future work, which allows nanometer precision of catalyst loading to balance active-site density with mass/charge transfer. The proposed ALI and ALD techniques elucidate the reliance of CO2RR selectivity on the Cu micro-environment and provide a platform for regulating Cu or other metal-base electrocatalyst coordination environment to facilitate high selectivity of CO2RR in the future

Aqueous Electrochemical Partial Oxidation of Hydrocarbons By a Gas Diffusion Electrode Carrying Ru-Doped Covalent Triazine Framework

The oxidative functionalization of organic substrates to valuable chemicals has attracted global interest from both fundamental and practical viewpoints. One of the promising approaches for the C-H oxidative functionalization is an aqueous electrochemical method because it can operate under mild conditions without toxic oxidants or flammable solvents. However, there are two major challenging issues for the further dissemination of electrochemical hydrocarbon oxidation in aqueous solution. The first one is the low solubility of raw organics in aqueous media. Here, we focus on gas diffusion electrodes (GDEs) that have been originally developed for hydrogen/oxygen fuel cells in an attempt to overcome this problem. The other major issue is that highly reactive species on an electrocatalyst are required for the activation of stable C−H bonds of hydrocarbons. Although high-valency ruthenium-oxo species (RuIV=O or RuV=O) are known to catalyze O-atom insertion into stable C-H bonds, Ru-based molecular electrocatalysts generally exhibit poor robustness and also catalyze the competitive oxygen evolution reaction (OER) in aqueous solutions. Our group has recently reported that singly isolated Ru-doped covalent triazine frameworks (Ru-CTF) effectively oxidize benzyl alcohol in aqueous electrolytes without the OER[1]. Besides, Ru-CTF displayed higher stability than an organometallic complex immobilized on an electrode because of the covalently cross-linked structure of CTF. In this study, we attempt to realize the electrochemical oxidation of vaporized hydrocarbons in aqueous solutions using a GDE that supports Ru-CTFs (Ru-CTF/GDE).A mixture of 1.0 g ZnCl2, 100 mg 2,6-dicyanopyridine, and 100 mg Ketjenblack was filled into a vacuum glass tube and then heated at 400 °C for 40 hours to prepare a CTF. Ru atoms were then impregnated into the CTF using 0.91 mM RuCl3 ethanol solution for 6 h at 90 °C. A catalyst ink was prepared by dispersing 4.0 mg Ru-CTF in 38 μL 5% Nafion solution and 400 μL ethanol, which was then added dropwise onto the GDE.Ethylbenzene (EB)-saturated (1.2×103 Pa) argon gas was supplied from the backside of GDE as a model substrate. Reaction products in liquid phases after electrolysis were quantitatively analyzed using high-performance liquid chromatography. When the GDE electrode carrying Ru-CTF was applied at 1.5V vs. RHE, acetophenone was generated as the product of ethylbenzene oxidation. The amount of generated acetophenone reached up to 4.7 µmol after 6 h electrolysis. In contrast, generated acetophenone was almost negligible in the absence of ethylbenzene or for bare CTF (without Ru). These results indicated that the Ru atoms in CTF served as the active center for ethylbenzene oxidation. For comparison, electrochemical measurements of Ru-CTF/GDE with 0.2 mM EB in the electrolyte instead of gaseous EB were also conducted using the same GDE electrochemical cell. In this case, the gas chamber was filled with pure argon gas. Although the EB concentration of 0.2 mM is about one-seventh lower than the saturated concentration (solubility of EB in water: 1.4 mM), the amount of acetophenone generated from gaseous EB was over 40-fold larger than that from the electrolyte. This result demonstrates that a GDE is effective for the aqueous electrochemical oxidation of hydrophobic organic compounds. The stability of Ru-CTF on GDE was investigated by the repeated tests in which an EB oxidation reaction was performed over four consecutive cycles with the replacement of the electrolyte every 12 h. Ru-CTF on GDE had negligible deactivation for both current-time profiles and acetophenone generation with repeated use. These results indicate that Ru-CTF on GDE has good stability at 1.5 V vs. RHE.In summary, gaseous EB was successfully oxidized to acetophenone in aqueous electrolytes using a GDE that supported Ru-CTF. Singly isolated Ru-atoms coordinated with nitrogen atoms in Ru-CTF were converted to high-valency Ru=O by water oxidation, and O-atom insertion into the C-H bond of EB was facilitated. Considering that Ru-CTF is highly stable during the long-term electrolysis in aqueous solution, Ru-CTF is a novel platform as a heterogeneous electrocatalyst for partial hydrocarbon oxidation reactions. This is the first demonstration of electrochemical hydrocarbon oxidation in aqueous electrolytes using GDEs. The three-dimensional microstructures in the GDE maximized the transportation of gaseous hydrocarbons, and the oxidation reaction occurred at the triple-phase boundary. The present results clearly demonstrate that GDEs are a promising approach for the electrochemical oxidative upgrading of hydrophobic organics.Reference:[1] S. Yamaguchi et al. Chem. Commun. 2017, 53, 10437-10440.Figure. (a) Schematic illustration of GDE carrying Ru-CTF (left), Molecular structure of Ru-CTF (right), (b) The amount of acetophenone generated as a function of time with gaseous EB (Black), with 0.2 mM aqueous EB (Gray). Figure 1

Fate and transport of bromide and mononuclear aromatic hydrocarbons in aqueous solutions through Berea Sandstone

A series of miscible displacement tests were performed on a 51 mm wide by 76 mm long well-laminated core of Berea Sandstone to determine the transport parameters of the anion bromide and a homologous series of seventeen mononuclear aromatic hydrocarbons (MAHs). In each test, a continuous input pulse of a single tracer was passed through the cylindrical core housed in a hydrostatic core holder at a confining pressure of 200 bar. The effluent concentration, as measured by in-line UV absorbance, versus time resulted in smooth high-resolution sinusoidal breakthrough curves (BTCs). In comparison to the near Gaussian BTCs of bromide, the transport of the MAHs was differentially retarded with minimal levels of delayed transport along the more rapid flow lines, but with progressively more along the slower flow paths. These results show that despite a lack of significant hydraulic heterogeneity, there is a high degree of heterogeneity among the sorption sites. The BTCs were aptly modeled with a one-dimensional flow model consisting of a mixture of instantaneous equilibrium and rate-limited reversible sorption sites. The relative fraction of instantaneous sites increased proportionately with the rate the subject MAH passed through the core. Potential quantitative structure-retention relationships (QSRR) between common chemical parameters of the MAHs and their overall retardation factors, sorption coefficients and the fraction of instantaneous equilibrium were evaluated. Among the compounds examined, relatively strong correlations were found with molecular weight, aqueous solubility, and octanol-water partitioning coefficient with which relative MAH transport retardation, the linear phase distribution coefficient, and the dimensionless partitioning coefficient between sorption sites.

The photocatalytic destruction of cinnamic acid and cinnamyl alcohol: Mechanism and the effect of aqueous ions

Cinnamic acid was chosen as an exemplar molecule to study the effect of potential contaminants on the kinetics and mechanism of the photocatalytic destruction of hydrocarbons in aqueous solutions. We identify the principal intermediates in the photocatalytic reaction of the acid and corresponding alcohol, and propose a mechanism that explains the presence of these species. The impact of two likely contaminants of aqueous systems, sulfate and chloride ions were also studied. Whereas sulfate ions inhibit the degradation reaction at all concentrations, chloride ions, up to a concentration of 0.5 M, accelerate the removal of cinnamic acid from solution by a factor of 1.6. However, although cinnamic acid is removed, the pathway to complete oxidation is blocked by the chloride, with the acid being converted (in the presence of oxygen) into new products including acetophenone, 2-chloroacetophenone, 1-(2-chlorophenyl)ethenone and 1,2-dibenzoylethane. We speculate that the formation of these products involves chlorine radicals formed from the reaction of chloride ions with the photoinduced holes at the catalyst surface. Interestingly, we have shown that the 1-(2-chlorophenyl)ethenone and 1,2-dibenzoylethane products form from 2-chloroacetophenone when irradiated with 365 nm light in the absence of the catalyst. The formation of potentially dangerous side products in this reaction suggest that the practical implementation of the photocatalytic purification of contaminated water needs to considered very carefully if chlorides are likely to be present.

Layer-by-layer self-assembly of a novel covalent organic frameworks microextraction coating for analyzing polycyclic aromatic hydrocarbons from aqueous solutions via gas chromatography.

In this study, a new covalent organic framework, consisting of tetra(4-aminophenyl)porphyrin and tris(4-formyl phenyl)amine, was layer-by-layer immobilized on stainless-steel wire as a coating for microextraction. The fabrication process was easy and controllable under mild conditions. The as-grown fiber was applied to extract polycyclic aromatic hydrocarbons in aqueous solution via head-space solid-phase microextraction. Furthermore, it was analyzed by gas chromatography with a flame ionization detector. A wide linear range (0.1-50µg/L), low limits of detection (0.006-0.024 µg/L, signal-to-noise ratio=3), good repeatability (intra-fiber, n=6, 3.1-8.50%), and reproducibility (fiber to fiber; n=3, 5.79-9.98%), expressed as relative standard deviations, demonstrate the applicability of the newly developed coating. This new material was successfully utilized in real sample extraction with a satisfactory result. Potential parameters affecting the extraction efficiency, including extraction temperature and extraction time, salt concentration, agitation speed, sample volume, desorption temperature, and time, were also optimized and discussed.

Kinetics of Photocatalyzed Reactions: Five Lessons Learned.

Elucidation of kinetics of photocatalyzed chemical mechanisms occurring at interfaces (gas-solid, liquid-solid) has been challenging. We summarize here five lessons learned over five decades.1. An assumed reaction network leads to a single kinetic model, but a common model, the Langmuir–Hinshelwood rate equation, r = kcat K C/ [1 +KC], arises from multiple mechanisms, hence models alone do not reveal unique mechanisms.2. The Langmuir–Hinshelwood model parameter kcat represents the slow step at a catalyst surface, and in thermal catalysis, depends upon the reactant structure. However, early photocatalysis work with light chlorinated hydrocarbons in aqueous solutions showed a single kcat value, independent of reactant structure.3. The dependence of the Langmuir-Hinshelwood parameters, kcat and K, upon intensity indicates that a pseudo-steady state approach is more fundamental than the presumed equilibrated adsorption of the LH model.4. Dyes and phenols are commonly studied, and claimed as first order reactions, despite often exhibiting rate constants which diminish with increasing contaminant concentration. We show that such studies are the result of intrinsic zero order data plotted on a semilog graph, and involve zero order rate limitation by reactant saturation, electron transfer to O2, oxygen mass transfer, or light supply.5. The apparent kinetics for contaminant removal from photocatalytic self-cleaning surfaces depends upon multiple circumstances, including the geometry of reactant deposit, catalyst porosity, and reactant light absorption. A single decision table suffices to indicate the apparent reaction order, n, to assume when fitting photocatalytic kinetic data from self-cleaning surfaces to a power law rate form, rate = k Cn.

Emissions of organic compounds from produced water ponds III: Mass-transfer coefficients, composition-emission correlations, and contributions to regional emissions

A common method for treating the aqueous phase (produced water) brought to the surface along with oil and natural gas is to discharge it into surface impoundments, also known as produced water ponds. Here we analyze data on the concentration of organic compounds in the water and on the flux of the same compounds into the atmosphere. Flux data extending from about 5 × 10−2 to 10+3 mg m−2 h−1 are consistent with mass-transfer laws given by the WATER9 semi-empirical algorithm, although empirical data display a noise level of about one order of magnitude and predictions by WATER9 are biased high. The data suggest partitioning between hydrocarbons in aqueous solution and in suspension, especially at higher overall concentrations. Salinity of the produced water does not have a detectable effect on hydrocarbon fluxes. Recently impounded waters are stronger emitters of hydrocarbons, while emissions of older waters are dominated by CO2. This aging effect can be explained by assuming, first, poor vertical mixing in the ponds, and second, gradual oxidation of hydrocarbons to CO2. Our measurements account for about 25% of the produced water ponds in the Uinta Basin, Eastern Utah, and when extrapolated to all ponds in the basin, account for about 4% to 14% of all organic compound emissions by the oil and natural gas sector of the basin, depending on the emissions inventory, and about 13% and 58%, respectively, of emissions of aromatics and alcohols.

IrO2-Ta2O5|Ti electrodes prepared by electrodeposition from different Ir:Ta ratios for the degradation of polycyclic aromatic hydrocarbons

This work investigates the feasibility of producing IrO2-Ta2O5|Ti electrodes by electrodeposition. Using precursor solutions with Ir:Ta molar ratios from 0:100 to 100:0, followed by thermal treatment, the goal was to find the optimal composition for enhancing the formation of hydroxyl radicals and providing long service lives. Scanning electron microscopy (SEM), coupled with energy dispersive X-ray spectroscopy (EDX), revealed that the production of homogeneous coatings with a good surface coverage and absence of agglomerates was only possible for electrodes with 70% or 100% Ir. The potential for O2 evolution was similar for all the electrodes containing Ir, at about 0.90 V vs Ag|AgCl. However, the ability to produce M(OH) clearly increased with increasing Ir in the Ir:Ta ratios (100:0 > 70:30 > 30:70 > 0:100). This observation was confirmed by the transformation of coumarin to 7-hydroxycoumarin as determined by spectroscopic and chromatographic techniques after treatment. Once manufactured and characterized, the electrodes were tested, as anodes, for the electro-oxidation of polycyclic aromatic hydrocarbons in aqueous solutions at natural pH (i.e., without pH adjustment). The anodes prepared from 70:30 and 100:0 ratios produced the fastest and highest removal, reaching 86% and 93% for phenanthrene and naphthalene, respectively, after 120 min at 50 mA. This was accompanied by a high degree of mineralization, as the result of direct and M(OH)-mediated oxidation, with some refractory intermediates remaining in the final solutions. The interaction between IrO2 and Ta2O5 oxides appeared to be important. The 100:0 anode provided high electrocatalytic effectiveness, whereas the anode with the 70:30 ratio provided improved long-term stability, as confirmed by its service life of about 93 h.

Nickel Phosphides as Catalysts for Direct Electrochemical CO2 Reduction to Important Renewable Polymers

Copper1 and noble-metal alloys2 have been shown to catalyze the electrochemical reduction of CO2 to hydrocarbons such as methane (C1) and ethylene (C2). C1 and C2 hydrocarbons are the simplest building blocks for the synthesis of most industrial products and are therefore common chemical feedstocks. However, the production of hydrocarbons in aqueous solution is highly energy-consuming mainly due to the over-potential needed to overcome the transition states in C1 and C2 synthesis. In addition, there are significant efficiency losses due to the concomitant H2 production that is kinetically and thermodynamically favored under these conditions. As ethylene and methane from fossil source are comparatively cheap, the high cost of electricity makes the production of these simple hydrocarbons prohibitively expensive. We have developed a noble metal free catalyst that is able to reduce carbon dioxide to hydrocarbons at lower over-potentials than copper (-0.6 V vs RHE), with significant suppression of the hydrogen production compared to the CO2 free environment. In addition, by changing the reactor configuration, CO2 may now be converted to a valuable polymer with composition akin to an aldehyde-carbonate co-polymer. This solid product can easily be de-polymerized to its parent monomers by changing pH. The resulting complex organic acids and aldehydes produced in at only -0.9 V vs RHE, have a significantly increased value to the simple hydrocarbons making this a very promising technology. Supported by the BASF Corporation Catalysis Division Fellowship.

Quantum Mechanical Screening of Single-Atom Bimetallic Alloys for the Selective Reduction of CO2 to C1 Hydrocarbons

Electrocatalytic reduction of CO2 to energy-rich hydrocarbons such as alkanes, alkenes, and alcohols is a very challenging task. So far, only copper has proven to be capable of such a conversion. We report density functional theory (DFT) calculations combined with the Poisson–Boltzmann implicit solvation model to show that single-atom alloys (SAAs) are promising electrocatalysts for CO2 reduction to C1 hydrocarbons in aqueous solution. The majority component of the SAAs studied is either gold or silver, in combination with isolated single atoms, M (M = Cu, Ni, Pd, Pt, Co, Rh, and Ir), replacing surface atoms. We envision that the SAA behaves as a one-pot tandem catalyst: first gold (or silver) reduces CO2 to CO, and the newly formed CO is then captured by M and is further reduced to C1 hydrocarbons such as methane or methanol. We studied 28 SAAs, and found about half of them selectively favor the CO2 reduction reaction over the competing hydrogen evolution reaction. Most of those promising SAAs contain M ...

Uptake of Hydrocarbons in Aqueous Solution by Encapsulation in Acyclic Cucurbit[n]uril‐Type Molecular Containers

AbstractThe ability of two water‐soluble acyclic cucurbit[n]uril (CB[n]) type containers, whose hydrophobic cavity is defined by a glycoluril tetramer backbone and terminal aromatic (benzene, naphthalene) sidewalls, to act as solubilizing agents for hydrocarbons in water is described. 1H NMR spectroscopy studies and phase‐solubility diagrams establish that the naphthalene‐walled container performs as well as, or better than, CB[7] and CB[8] in promoting the uptake of poorly soluble hydrocarbons into aqueous solution through formation of host–hydrocarbon complexes. The naphthalene‐walled acyclic CB[n] container is able to extract large hydrocarbons from crude oil into aqueous solution.

High-Sensitivity Surface-Enhanced Raman Scattering (SERS) Substrate Based on a Gold Colloid Solution with a pH Change for Detection of Trace-Level Polycyclic Aromatic Hydrocarbons in Aqueous Solution.

In this study, a gold colloid solution whose parameters were optimized, and without any surfactants, was developed as a surface-enhanced Raman scattering (SERS) substrate for the detection of trace-level polycyclic aromatic hydrocarbons (PAHs). A gold colloid solution with 57 nm gold particles and pH 13 was prepared to be the SERS substrate. It had impressive enhancement that was two orders of magnitude higher than that of a gold colloid solution with 57 nm gold particles and without pH change (pH 6). Even with a compact field-based Raman spectrometer, naphthalene, phenanthrene, anthracene, fluoranthene, and pyrene were detected, with limits of detection at 6.8 nM, 3.4 nM, 1.8 nM, 0.68 nM (680 pM), and 0.44 nM (440 pM), respectively. The significant enhancement was ascribed to an electromagnetic mechanism and a charge-transfer mechanism. Quantitative analyses for these five PAHs in water were also performed. The SERS intensities of PAHs were found to have good linear dependence relations with the concentrations in low concentration. This high-sensitivity, easily prepared substrate offers a promising technology for the quantitative detection of trace-level PAHs.

Alternative method to predict activity coefficients at infinite dilution of hydrocarbons in aqueous solutions

Activity coefficients at infinite dilution are important property in solute-solvent interactions. Experimental techniques show high costs, skilled labour and safety. To solve this, a neural network model with five different topological descriptors to implement different Artificial Neural Network has been implemented. The best Artificial Neural Network (5-11-8-1 topology) presents good fits for the training phase with an Average Percentage Deviation of 1.85%. Similar results have been obtained for the validation phase of the Artificial Neural Network (1.88%). The implemented Neural Networks techniques showed better results than other developed methods, around 30.70% and 24.60% for training and validation phase, respectively.

Cloud Point Extraction of Polycyclic Aromatic Hydrocarbons in Aqueous Solution with Nonionic Surfactants

AbstractA cloud point extraction (CPE) process using the two nonionic surfactants, Tergitol 15-S-9 and Tergitol 15-S-7, mixtures of secondary ethoxylated alcohols, to extract selected polycyclic aromatic hydrocarbons (PAHs) from aqueous solutions at 25°C was investigated. Cloud point temperatures (CPTs) of selected nonionic surfactants were studied against the effect of added electrolytes on their cloud points. Sodium iodide could increase the cloud points of selected nonionic surfactants, i.e., the salt-in effect, whereas sodium chloride, sodium phosphate and sodium sulfate could decrease the cloud point, i.e., the salt-out effect. Cloud point temperatures (CPTs) of these micellar solutions were regulated and reduced enough with addition of sodium phosphate and sodium sulfate, so that the cloud point extraction (CPE) process could be facilitated at 25°C. It was found that a higher preconcentration factor could be achieved in the micellar solution having a lower surfactant concentration. The average preconcentration factor was also discussed as a function of surfactant concentration used in the CPE process.

An improved self‐assembly gold colloid film as surface‐enhanced Raman substrate for detection of trace‐level polycyclic aromatic hydrocarbons in aqueous solution

To detect trace‐level polycyclic aromatic hydrocarbons, some investigations of an improved self‐assembly method are carried out using gold colloid films for the preparation of the surface‐enhanced Raman scattering (SERS)‐active substrate. Extinction spectra and scanning electron microscopy images reveal that controllable surface plasmonic metal substrates can be obtained by increasing the temperature of (3‐aminopropyl)trimethoxysilane solution up to 64.5 °C. The SERS‐active substrates have a high enhancement factor, and they can be both easily prepared and reproducible. With the use of these substrates, different concentrations of pyrene and anthracene in aqueous solutions were detected by SERS. A further enhancement can be supported by shifted excitation Raman difference spectroscopy. Raman signals of pyrene and anthracene adsorbed on gold colloid substrates up to limits of detection at 5 and 1 nmol/l, respectively, can be obtained. The quantitative analysis shows the possibility of in situ detection of polycyclic aromatic hydrocarbons while such gold colloid film serves as a SERS‐active substrate. Copyright © 2012 John Wiley & Sons, Ltd.

The impact of water and hydrocarbon concentration on the sensitivity of a polymer-based quartz crystal microbalance sensor for organic compounds

Long-term environmental monitoring of organic compounds in natural waters requires sensors that respond reproducibly and linearly over a wide concentration range, and do not degrade with time. Although polymer coated piezoelectric based sensors have been widely used to detect hydrocarbons in aqueous solution, very little information exists regarding their stability and suitability over extended periods in water. In this investigation, the influence of water aging on the response of various polymer membranes [polybutadiene (PB), polyisobutylene (PIB), polystyrene (PS), polystyrene-co-butadiene (PSB)] was studied using the quartz crystal microbalance (QCM). QCM measurements revealed a modest increase in sensitivity towards toluene for PB and PIB membranes at concentrations above 90 ppm after aging in water for 4 days. In contrast, the sensitivity of PS and PSB coated QCM sensors depended significantly on the toluene concentration and increased considerably at concentrations above 90 ppm after aging in water for 4 days. Attenuated total reflectance Fourier transform infrared spectroscopy (ATR–FTIR) showed that there is a change in the sorption mechanism at higher toluene levels for PS and PSB. Positron annihilation lifetime spectroscopy (PALS) studies were performed to investigate the free volume properties of all polymers and to monitor any changes in the free volume size and distribution due to water and toluene exposure. The PALS did not detect any considerable variation in the free volume properties of the polymer films as a function of solution composition and soaking time, implying that viscoelastic and/or interfacial processes (i.e. surface area changes) are probably responsible for variations in the QCM sensitivity at high hydrocarbon concentrations. The results suggest that polymer membrane conditioning in water is an issue that needs to be considered when performing QCM measurements in the aqueous phase. In addition, the study shows that the hydrocarbon response is concentration dependant for polymers with a high glass transition temperature, and this feature is often neglected when comparing sensor sensitivity in the literature.

Potentiometric Online Detection of Aromatic Hydrocarbons in Aqueous Phase Using Carbon Nanotube-Based Sensors

Surfaces made of entangled networks of single-walled carbon nanotubes (SWCNTs) display a strong adsorption affinity for aromatic hydrocarbons. Adsorption of these compounds onto the walls of SWCNTs changes the electrical characteristics of the SWCNT-solution interface. Using these features, we have developed a potentiometric sensor to detect neutral aromatic species. Specifically, we can detect online aromatic hydrocarbons in industrial coolant water. Our chromatographic results confirm the adsorption of toluene onto the walls of carbon nanotubes, and our impedance spectroscopy data show the change in the double layer capacitance of the carbon nanotube-solution interface upon addition of toluene, thus confirming the proposed sensing mechanism. The sensor showed a toluene concentration dependent EMF response that follows the shape of an adsorption isotherm and displayed an immediate response to the presence of toluene with a detection limit of 2.1 ppm. The sensor does not respond to other nonaromatic hydrocarbons that may coexist with aromatic hydrocarbons in water. It shows a qualitative sensitivity and selectivity of 100% and 83%, respectively, which confirms its ability to detect aromatic hydrocarbons in aqueous solutions. The sensor showed an excellent ability to immediately detect the presence of toluene in actual coolant water. Its operational characteristics, including its fast response, low cost, portability, and easy use in online industrial applications, improve those of current chromatographic or spectroscopic techniques.

Biosorption and biodegradation of polycyclic aromatic hydrocarbons in aqueous solutions by a consortium of white-rot fungi

Bioremediation is a popular approach used to abate polycyclic aromatic hydrocarbons (PAHs) in the environment. A consortium of white-rot fungi (CW-1) isolated from wood pieces was used for studying their potential of bioremediation of PAHs. Biosorption and biodegradation of PAHs by live and heat-killed white-rot fungi (CW-1) were investigated to elucidate the bio-dissipation mechanisms of PAHs. Sorption isotherms of naphthalene, acenaphthene, fluorene, phenanthrene and pyrene to heat-killed fungal biomass were linear and non-competitive, indicating the primary mechanism of biosorption to be by partition. The carbon-normalized partition coefficients ( K oc) were linearly correlated with octanol–water partition coefficients ( K ow), i.e., log K oc = 1.13 log K ow − 0.84 ( n = 5, r 2 = 0.996). Biosorption and biodegradation of phenanthrene and pyrene by live white-rot fungi were quantified. In 1 week, the removal efficiency of phenanthrene (70–80%) and pyrene (90%) by live fungi from aqueous solution were comparable to those by heat-killed fungi. However, approximately 40–65% of phenanthrene and 60–85% of pyrene were still stored in organismal bodies. Biosorption might restrict biodegradation while nutrient limitation and presence of a PAH mixture might stimulate biodegradation. The apparent partition coefficients ( K d * ) in live fungal systems and the K d of heat-killed fungi without biodegradation were compared, and then the K d * / K d ratios were employed to illustrate the relative contributions of biosorption and biodegradation under different nutrient conditions.

On-line adsorption—liquid-chromatographic determination of polycyclic aromatic hydrocarbons in aqueous solutions: Selection of preconcentration conditions

A method is proposed for the selection of conditions for the preconcentration of polycyclic aromatic hydrocarbons (PAH) from aqueous solutions on octadecyl silica gel in an on-line adsorption—Chromatographic system. Deterministic models of adsorption dynamics, based on partial differential equations, were used for a uniform mathematical description of all stages of adsorption preconcentration. The parameters of an adsorption system, such as dead volume, longitudinal dispersion coefficient, and distribution and mass transfer coefficients in adsorption and desorption, were calculated, and the adsorption isotherm was plotted. The conditions for the on-line determination of compounds were selected by simulation analysis, and the procedure was developed for determining PAH in natural and potable waters. The detection limits for PAH were 1–90 ng/L.