Carbon sorbents and their utilization for the preconcentration of organic pollutants in environmental samples

Linking chemical surface water monitoring and pesticide regulation in selected European countries

The progress in chemical analytics and understanding of pesticide dynamics in surface waters allows establishing robust data on compounds with frequent exceedances of quality standards. The current chemical, temporal, and spatial coverage of the pesticide monitoring campaigns differs strongly between European countries. A questionnaire revealed differences in monitoring strategies in seven selected European countries; Nordic countries prioritize temporal coverage, while others focus on spatial coverage. Chemical coverage has increased, especially for non-polar classes like synthetic pyrethroids. Sweden combines monitoring data with agricultural practices for derived quantities, while the Netherlands emphasizes spatial coverage to trace contamination sources. None of the EU member states currently has established a process for linking chemical surface water monitoring data with regulatory risk assessment, while Switzerland has recently established a legally defined feedback loop. Due to their design and objectives, most strategies do not capture concentration peaks, especially 2-week composite samples, but also grab samples. Nevertheless, for substances that appear problematic in many data sets, the need for action is evident even without harmonization of monitoring programs. Harmonization would be beneficial, however, for cross-national assessment including risk reduction measures.

Hierarchical Biobased Macroporous/Mesoporous Carbon: Fabrication, Characterization and Electrochemical/Ion Exchange Properties

With the goal of improving the mechanical properties of porous hierarchical carbon, cellulosic fiber fabric was incorporated into the resorcinol/formaldehyde (RF) precursor resins. The composites were carbonized in an inert atmosphere, and the carbonization process was monitored by TGA/MS. The mechanical properties, evaluated by nanoindentation, show an increase in the elastic modulus due to the reinforcing effect of the carbonized fiber fabric. It was found that the adsorption of the RF resin precursor onto the fabric stabilizes its porosity (micro and mesopores) during drying while incorporating macropores. The textural properties are evaluated by N₂ adsorption isotherm, which shows a surface area (BET) of 558 m²g^-1. The electrochemical properties of the porous carbon are evaluated by cyclic voltammetry (CV), chronocoulometry (CC), and electrochemical impedance spectroscopy (EIS). Specific capacitances (in 1 M H₂SO₄) of up to 182 Fg^-1 (CV) and 160 Fg^-1 (EIS) are measured. The potential-driven ion exchange was evaluated using Probe Bean Deflection techniques. It is observed that ions (protons) are expulsed upon oxidation in acid media by the oxidation of hydroquinone moieties present on the carbon surface. In neutral media, when the potential is varied from values negative to positive of the potential of zero charge, cation release, followed by anion insertion, is found.

Novel Porous Carbon Material for the Detection of Traces of Volatile Organic Compounds in Indoor Air

A highly sensitive and selective silicon-based microanalytical prototype was used to identify a few ppb of volatile organic compounds (VOCs) in indoor air. Herein, a new nonactivated tannin-derived carbon synthesized by an environmentally friendly method, DM2C, a MIL-101(Cr) MOF, and a DaY zeolite were selected for the preconcentration of BTEX compounds (i.e., benzene, toluene, ethylbenzene, and xylenes). Integrating a small amount of these nanoporous solids inside a miniaturized preconcentration unit led to excellent preconcentration performance. By taking advantage of the high adsorption-desorption capacities of the DM2C adsorbent, concentrations as low as 23.5, 30.8, 16.7, 25, and 28.8 ppb of benzene, toluene, ethylbenzene, ortho- and para-xylene, respectively, were detected in a short analysis time (∼10 min) even in the presence of 60% relative humidity at 25 °C. The DM2C showed excellent stability over a period of 4 months and more than 500 tests, as well as repeatability, which makes it a very reliable adsorbent for the detection of trace VOCs in indoor air under realistic conditions in the presence of humidity.

SiO2 aerogel monolith allows ultralow amounts of TiO2 for the fast and efficient removal of gaseous pollutants

Coupled adsorption and photocatalytic oxidation brings high expectations regarding the fast and efficient removal of gaseous pollutants in air. However, to fabricate an adsorbent-photocatalyst composite, coating of a photocatalyst on adsorbent support inevitably results in loss of adsorption and light blocking on interior surfaces. In this work, we attempt to develop an adsorbent-photocatalyst monolith composite, which not only perfectly retains original high adsorption capacity, but also allows complete penetration of UV light through the whole monolith. We employ a SiO2 aerogel monolith with a diameter of 2.5 cm and thickness of 0.7 cm as adsorbent and support. After atomic layer deposition (ALD) followed by calcination, 0.32-1.25 wt% TiO2 is dispersed on the skeleton of the SiO2 aerogel. In spite of such a low level of loading, the monolith composites exhibit fast and efficient removal of gaseous acetaldehyde and NO. Therein, the best performance is achieved at a loading of 0.6 wt% TiO2. By dark adsorption, the acetaldehyde pollutant with initial concentration of 200 ppm can be adsorbed by 54% within 10 min. Moreover, the light transmittance at 387 nm can be retained as high as 6% after penetrating through the whole monolith, confirming that all loaded TiO2 nanoparticles can participate in the photocatalytic oxidation of acetaldehyde. Under UV irradiation with intensity close to natural sunlight, the preadsorbed acetaldehyde can be completely mineralized into CO2 by photocatalytic oxidation in another 60 min, benefiting from the ultradispersion of TiO2 nanoparticles inside the SiO2 aerogel. The study provides a novel three-dimensional model of an adsorbent-photocatalyst composite for the fast and efficient removal of gaseous pollutants.

Effect of the surface properties of resorcinol–formaldehyde resin/carbon nanocomposites and their carbonization products on the solid-phase extraction of explosives

This is the first application of composites containing carbon nanofillers as effective adsorbents for SPE of explosives from aqueous samples.

Synthetic Carbon Derived from Polyimide

Synthetic carbon was obtained from the porous copolymer of 4, 4'-bis(maleimidodiphenyl)methane and styrene by carbonization in inert and methane atmospheres. The samples were characterized by nitrogen adsorption and mercury intrusion using BET, αs, DR and Kelvin analysis. It was shown that carbonization in an inert atmosphere results in the formation of microporous and mesoporous carbon, while heat treatment in an atmosphere of methane decreases the porosity due to the deposition of pyrolytic carbon in small pores (R < 2–3 nm).

Determination of volatile organic compounds from biowaste and co-fermentation biogas plants by single-sorbent adsorption

Characterisation of biogases is normally dedicated to the online monitoring of the major components methane and carbon dioxide and, to a lesser extent, to the determination of ammonia and hydrogen sulphide. For the case of Volatile Organic Compounds (VOCs), much less attention is usually paid, since such compounds are normally removed during gas conditioning and with exception of sulphur compounds and siloxanes represent a rather low risk to conventional downstream devices but could be a hindrance for fuel cells. However, there is very little information in the literature about the type of substances found in biogases generated from biowaste or co-fermentation plants and their concentration fluctuations. The main aim of this study was to provide information about the time dependencies of the VOCs in three biogas plants spread out through Germany from autumn until summer, which have different process control, in order to assess their potential as biofuels. Additionally, this study was an attempt to establish a correlation between the nature of the substrates used in the biogas plants and the composition of the VOCs present in the gas phase. Significant time-dependent variations in concentration were observed for most VOCs but only small changes in composition were observed. In general, terpenes and ketones appeared as the predominant VOCs in biogas. Although for substances such as esters, sulphur-organic compounds and siloxanes the average concentrations observed were rather low, they exhibited significant concentration peaks. The second biogas plant which operates with dry fermentation was found to contain the highest levels of VOCs. The amount of total volatile organic compounds (TVOCs) for the first, second and third biogas plants ranged from 35 to 259 mg Nm(-3), 291-1731 mg Nm(-3) and 84-528 mg Nm(-3), respectively.

Application of Carbonaceous Materials in Separation Science

Porous carbons in the separation sciences occupy an important niche owing to their unique retention characteristics, chemical stability and the ability to control pore structure through template strategies. However, these same synthetic processes utilise oil-based carbonising resins and high temperature, energy-intensive pyrolysis steps to ensure the carbon product has pore-size regularity, minimal micropore content and homogeneous surface chemistry. This chapter will primarily focus on the development of porous carbons for application as chromatographic stationary phases. Discussion will cover the unique characteristics of the porous carbon retention mechanism and its application in separating a broad range of analyte classes. The chapter then moves on to describe the current disadvantages in the manufacture of commercially available carbon phase and then highlight recent efforts aimed at the development of alternative porous carbon stationary phases derived from sustainable carbon precursors.

In-line sampling with gas chromatography-mass spectrometry to monitor ambient volatile organic compounds

An existing GC-MS/FID method coupling with the cryogenic trapping was improved to perform continuous field monitoring of 106 VOCs, covering a wide range of volatilities and polarities (C(2)-C(11) NMHCs, ≥C(1) halocarbons, toxic chlorinated compounds, ethers, some esters and ketones). Cryogenic enrichment was employed from the standpoints of higher signal-to-noise ratio, less carry-over and better protection of thermally labile compounds than chemical sorbent enrichment. However, cryogen consumption is large and creates a great logistical burden for field deployment. As a result, a new in-line sampling manifold was designed and incorporated into the system to separate the sampling from trapping during enrichment of ambient VOCs, which gave rise to two major advantages: (1) the sampling is performed by a pre-evacuated flask, which does not need cryogen when filling a sample, so that the sampling time can be extended to yield better sample representation (approximately one hour was chosen for the sampling time for hourly data resolution in this study) and (2) because the cryo-trapping only takes a short time period (3 min in this study), the consumption of cryogen is greatly reduced (4 L liquid nitrogen per sample for conventional cryo-trapping vs. 0.6L for the new method). The robustness of the automated GC-MS/FID coupling with in-line sampling for the 106 target compounds was assessed with a set of quality assurance criteria of system blank, wall effect, precision, linearity, detection limit and field test to support the field applicability of the method. The configuration of the proposed in-line sampling apparatus is simple and rugged, which can be easily built and connected with any GC or GC-MS and readily deployed in the field to perform high-quality continuous measurements of more than 106 VOCs.

Proton-transfer reaction mass spectrometry (PTRMS) in combination with thermal desorption (TD) for sensitive off-line analysis of volatiles

RATIONALE

When performing trace gas analysis, it is not always possible to bring the source of volatiles and the gas analyzer together. In these cases, volatile storage containers, such as thermal desorption (TD) tubes, can be used for off-line measurement. TD is routinely combined with gas chromatography/mass spectrometry (GC/MS), but so far not with proton-transfer reaction mass spectrometry (PTRMS), which has a faster response.

METHODS

A PTR-quadrupole-MS instrument and a PTR-ion-trap-MS instrument were separately coupled to a TD unit for off-line analysis of trace volatiles in air. Carbograph 1TD/Carbopack X sorbent tubes were filled with different concentrations of a trace gas mixture containing low molecular weight volatiles (32 g/mol up to 136 g/mol) and measured with the above-mentioned combinations. The carrier gas in the TD unit was changed from helium to nitrogen to be able to combine this instrument with the mass spectrometer.

RESULTS

Good linearity and reproducibility with the amount of gas stored were obtained. The storage capacity over time (up to 14 days) showed larger variability (<11% for all compounds, except for acetone 27%). Several tubes were filled with breath of different persons, and the breath of a smoker showed increased levels of acetonitrile and benzene. The combination of the PTR ion-trap instrument with the TD unit was also investigated. Due to its higher sampling rate, the ion-trap system showed higher throughput capabilities than the quadrupole system.

CONCLUSIONS

The combination of TD with PTRMS using both a quadrupole and an ion trap for off-line volatile analysis has been validated. TD tubes can be a robust and compact volatile storage method when the mass spectrometry and the sampling cannot be performed in the same place, for example in large screening studies. In addition, a higher measurement throughput than with GC/MS could be obtained.

Application of Chemically Modified and Unmodified Waste Biological Sorbents in Treatment of Wastewater

Protein wastes (feathers, goat hair) and cellulosic wastes (corn cob, coconut husks) were collected and washed with detergent solution, thoroughly rinsed and sun dried for 2 days before drying in an oven, and then ground. One-half of ground material was carbonized at a maximum temperature of 500°C after mixing with H2SO4. The carbonized parts were pulverized; both carbonized and uncarbonized sorbents were sieved into two particle sizes of 325 and 625 μm using mechanical sieve. Sorbents of a given particle size were packed into glass column.Then, textile wastewater that had its physicochemical parameters previously determined was eluted into each glass column and a contact time of 60 and 120 mins was allowed before analysis. Results showed 48.15–99.98 percentage reduction of , EC, Cl−, BOD, COD, DO, TSS, and TDS, 34.67–99.93 percentage reduction of , EC, Cl−, BOD, COD, DO, TSS, and TDS, 52.83–97.95 percentage reduction of Pb2+, Ni2+, Cr3+and Mn2+and 34.59–94.87 percentage reduction of Pb2+, Ni2+, Cr3+and Mn2+. Carbonization, small particle, size and longer contact time enhanced the sorption capabilities of the sorbents. These show that protein and cellulosic wastes can be used to detoxify wastewater.

Odour detection methods: olfactometry and chemical sensors

The complexity of the odours issue arises from the sensory nature of smell. From the evolutionary point of view olfaction is one of the oldest senses, allowing for seeking food, recognizing danger or communication: human olfaction is a protective sense as it allows the detection of potential illnesses or infections by taking into account the odour pleasantness/unpleasantness. Odours are mixtures of light and small molecules that, coming in contact with various human sensory systems, also at very low concentrations in the inhaled air, are able to stimulate an anatomical response: the experienced perception is the odour. Odour assessment is a key point in some industrial production processes (i.e., food, beverages, etc.) and it is acquiring steady importance in unusual technological fields (i.e., indoor air quality); this issue mainly concerns the environmental impact of various industrial activities (i.e., tanneries, refineries, slaughterhouses, distilleries, civil and industrial wastewater treatment plants, landfills and composting plants) as sources of olfactory nuisances, the top air pollution complaint. Although the human olfactory system is still regarded as the most important and effective "analytical instrument" for odour evaluation, the demand for more objective analytical methods, along with the discovery of materials with chemo-electronic properties, has boosted the development of sensor-based machine olfaction potentially imitating the biological system. This review examines the state of the art of both human and instrumental sensing currently used for the detection of odours. The olfactometric techniques employing a panel of trained experts are discussed and the strong and weak points of odour assessment through human detection are highlighted. The main features and the working principles of modern electronic noses (E-Noses) are then described, focusing on their better performances for environmental analysis. Odour emission monitoring carried out through both the techniques is finally reviewed in order to show the complementary responses of human and instrumental sensing.

Development of a graphite low-temperature plasma source with dual-mode in-source fragmentation for ambient mass spectrometry

A new low-temperature plasma (LTP), based on dielectric barrier discharge (DBD), has been developed as an alternative ionization source for ambient mass spectrometry. For organic samples, the source is able to produce two different fragmentation patterns which are selectable by an electrical switch. The two source modes are different only in the second electrodes: in configuration (A), bar-plate and in configuration (B), coaxial bar-cylinder shapes are used. A disposable graphite probe is used as the first electrode, the same in both configurations, and a copper foil is used as the second electrode. The ionization source is applicable to gas and liquid samples, without any change being necessary in its design. Under optimal conditions, to take ethylbenzene as an example, a detection limit of less than 25 ng was obtained and a relative standard deviation (RSD) of 13.36% has been demonstrated for 50 ng of ethylbenzene (n = 11). We have found several interesting differences in the mass spectra of the tested volatile organic compounds (VOCs) in the two modes, which might be applicable in identification studies. We have investigated the effect of variation of the first electrode material and the second electrode length in mode B. Moreover, in this design the graphite electrode is capable of acting as a sample adsorbent, which is a new sampling method for LTP mass spectrometry (MS). This capability was investigated by adsorption of the selected VOCs onto the surface of the graphite electrode in a headspace solid-phase microextraction (SPME) system, and direct desorption and ionization of the samples by LTPMS.

Modifying the sorption properties of multi-walled carbon nanotubes via covalent functionalization

We demonstrate that the functionalization of carbon nanotubes dramatically alters their sorption characteristics. The effect of covalent functionalization of multiwalled carbon nanotubes (MWNTs) on the gas phase adsorption and desorption of polar and nonpolar organics is presented. Carboxylation and nitration led to the generation of polar functional groups on the nanotube surface. The derivatized nanotubes showed strong adsorption of polar analytes such as alcohols and relatively weaker adsorption for nonpolar and aromatic compounds. The breakthrough volume of ethanol increased by 300%, where as that of hexane decreased by 75% after functionalization. The functionalized MWNT also showed rapid desorption of the polar as well as nonpolar compounds.

Experimental choices for the determination of carbonyl compounds in air

The analysis of carbonyls in ambient air has received a great deal of scientific attention with the advancement of analytical techniques and increased demand for the build-up of its data base. In this review article, we have attempted to provide some insight into the relative performance of different instrumental approaches available for the analysis of ambient carbonyls with a major emphasis on high performance liquid chromatographic and gas chromatographic methods. Reported in several international standard procedures, derivatization of carbonyls with 2,4-dinitrophenylhydrazine (2,4-DNPH) with either an impinger or cartridges is the most commonly used method of HPLC detection. In this respect, a number of alternative hydrazine reagents have also been discussed for use with HPLC. In contrast, GC methods based on the combined application of adsorptive enrichment on solid sorbents and thermal desorption are examined with regard to their suitability for carbonyl analysis in air. Particular emphasis has been directed towards the advantages and drawbacks of these different instrumental techniques for ambient carbonyls. Based on this comparative approach, we discuss the suitability for each method for carbonyl analysis.

Volatile organic compounds: sampling methods and their worldwide profile in ambient air

The atmosphere is a particularly difficult analytical system because of the very low levels of substances to be analysed, sharp variations in pollutant levels with time and location, differences in wind, temperature and humidity. This makes the selection of an efficient sampling technique for air analysis a key step to reliable results. Generally, methods for volatile organic compounds sampling include collection of the whole air or preconcentration of samples on adsorbents. All the methods vary from each other according to the sampling technique, type of sorbent, method of extraction and identification technique. In this review paper we discuss various important aspects for sampling of volatile organic compounds by the widely used and advanced sampling methods. Characteristics of various adsorbents used for VOCs sampling are also described. Furthermore, this paper makes an effort to comprehensively review the concentration levels of volatile organic compounds along with the methodology used for analysis, in major cities of the world.

Routine determination of benzo[a]pyrene at part-per-billion in complex industrial matrices by multidimensional liquid chromatography

A rapid and selective high performance liquid chromatography (HPLC) method using a column-switching technique has been developed for the determination of benzo[a]pyrene in complex mixtures containing polycyclic aromatic hydrocarbons. The diluted sample is directly injected into the chromatographic system without pre-treatment. The purification is performed on-line using three cleaning columns filled with various stationary phases. The sample preparation, a simple dilution, and the analysis time do not exceed 45 min. The method developed was used to analyze industrial products such as oil, bitumen, etc. and was compared with an off-line method requiring treatment and extraction steps before the analysis.