Volatile Organic Molecules Research Articles

(Invited) Ionic Liquids and Gas Sensor Applications

This presentation will discuss the notable contributions to the sensor fields using ionic liquids from our laboratory. Ionic liquids (ILs) are excellent solvents that have wide varying gas solubility for common gases and volatile organic molecules which have been demonstrated for the storage and delivery of gases that are flammable, and/or reactive. Ionic liquids also have good ionic conductivity and have been explored as nonvolatile and nonflammable electrolytes for many electrochemical device developments. In the past ten years, our laboratory has systematically investigated the redox mechanisms of common gases (i.e. CH4, NO2, SO2, H2, CO, CO2, O2) and small organic molecules (methanol, ethanol, formaldehyde, formic acid etc.) in ILs and we have identified new reaction mechanisms for ionic liquid based gas sensor development which uniquely overcome many sensor performance challenges, especially those related to sensing capability and miniaturized sensor system implementation. By synergistically utilizing the unique ionic liquid interface electrochemistry as well as molecular design and control of ionic liquid/conductive polymer composites, we have demonstrated new ionic liquid gas sensors enabling multiple gas detections with multiple modes detection principles via low cost and low power piezoelectric/QCM and electrochemical transducers that yields forward-thinking solutions to many gas sensors challenges, especially miniaturization and robustness. The simplicity of the demonstrated detection principles allows for easy integration with engineering advancements such as portable electronics, networked sensing and next-generation monolithic implementation of autonomous sensors with the performance, cost, power, and operational lifetime characteristics to suit a broad range of applications.

Luminescent MOF material based on cadmium(ii) and mixed ligands: application for sensing volatile organic solvent molecules

A luminescent MOF was constructed by employing a mixed ligands strategy and may be used as a potential luminescent probe for the detection of acetone.

A novel fluorescence probe for sensing organic amine vapors from a Eu3+β-diketonate functionalized bio-MOF-1 hybrid system

A classic anionic metal–organic framework (bio-MOF-1) for Eu3+-β-diketonate complex encapsulation has the utility of a sensory material for sensing volatile organic molecules, especially volatile amines.

A luminescent mixed-lanthanide-organic framework sensor for decoding different volatile organic molecules.

A flexible tripodal polyaromatic acid (4,4',4″-(((2,4,6-trimethylbenzene-1,3,5-triyl)-tris(methylene))-tris(oxy))tribenzoic acid, H3TCM) was used to adapt the coordination sites of lanthanide ions for the construction of microporous lanthanide-organic frameworks (LOFs) [LnTCM(H2O)2]·3DMF·H2O (Ln-TCM; Ln = La, Eu, and/or Tb). In these LOFs, the emission band of TCM matches well with the excitation energy of lanthanide ions (Eu(3+) and Tb(3+)) which results in high-efficient resonance energy transfer from TCM to lanthanide ions. Moreover, the mixed EuxTb1-x-TCM has tunable pores to adapt different induced-fit-type host-guest interactions which can modulate both the energy transfer efficiency from TCM to Ln(3+) ions and the energy allocation between Eu(3+) and Tb(3+) ions in the luminescence spectra. We demonstrate that the Eu(x)Tb(1-x)-TCM sensor has the capability of decoding different volatile organic molecules (VOMs) with a clearly differentiable and unique emission intensity ratio of (5)D0 → (7)F2 (Eu(3+), 614 nm) to (5)D4 → (7)F5 (Tb(3+), 545 nm) transitions for every different VOM. Compared with the traditional absolute emission intensity method, such a self-referencing emission intensity strategy has generated self-calibrating, highly differentiable, and very stable luminescent signals for decoding different VOMs from the unique Eu(x)Tb(1-x)-TCM platform, which has great potential for practical applications.

A Luminescent Dye@MOF Platform: Emission Fingerprint Relationships of Volatile Organic Molecules

AbstractSelf‐assembly of luminescent moieties into porous metal–organic frameworks (MOFs) has generated many luminescent platforms for probing volatile organic molecules (VOMs). However, most of those explored thus far have only been based on the luminescence intensity of one transition, which is not efficient for probing different VOMs. We have synthesized a luminescent MOF material containing 1D nanotube channels, and further developed a luminescent dye@MOF platform to realize the probing of different VOMs by tuning the energy transfer efficiency between two different emissions. The dye@MOF platform exhibits excellent fingerprint correlation between the VOM and the emission peak‐height ratio of ligand to dye moieties. The dye@MOF sensor is self‐calibrating, stable, and instantaneous, thus the approach should be a very promising strategy to develop luminescent materials with unprecedented practical applications.

A Luminescent Dye@MOF Platform: Emission Fingerprint Relationships of Volatile Organic Molecules

Self-assembly of luminescent moieties into porous metal-organic frameworks (MOFs) has generated many luminescent platforms for probing volatile organic molecules (VOMs). However, most of those explored thus far have only been based on the luminescence intensity of one transition, which is not efficient for probing different VOMs. We have synthesized a luminescent MOF material containing 1D nanotube channels, and further developed a luminescent dye@MOF platform to realize the probing of different VOMs by tuning the energy transfer efficiency between two different emissions. The dye@MOF platform exhibits excellent fingerprint correlation between the VOM and the emission peak-height ratio of ligand to dye moieties. The dye@MOF sensor is self-calibrating, stable, and instantaneous, thus the approach should be a very promising strategy to develop luminescent materials with unprecedented practical applications.

A pinch-valve interface for automated sampling and monitoring of dynamic processes by gas chromatography-mass spectrometry

Gas chromatography (GC) is frequently used in qualitative and quantitative analysis of volatile organic molecules. In its most common embodiment, samples are prepared in the laboratory, and injected into the capillary column using an autosampler. Analytes are separated, and detected by one of several available detection systems, including mass spectrometry (MS). However, this mode of operation is not convenient when monitoring dynamic chemical systems – for example, reaction mixtures. Here we present a facile approach for automated sampling, and subsequent introduction of samples to a GC apparatus in order to enable monitoring of dynamic chemical processes in real time. The proposed system incorporates two pinch valves, a peristaltic pump, a thermoshaker, and an electronic control unit (Raspberry Pi microcomputer) with several relays. The device facilitates dosing small volumes of liquid samples to the injection port of a commercial GC-MS apparatus. A program in C language controls the operation of the pump (on/off, direction of flow) and actuation of the pinch valves, and it initiates GC-MS runs. The system has been characterised with artificial samples, and successfully used in the monitoring of transesterification reactions catalysed by single microbeads containing immobilised lipase, as well as in the monitoring of the extraction of natural products from plant tissue samples. We believe that – following further improvements – this automated approach may be adapted for monitoring industrial processes and environmental analysis.

The influence of film morphology and illumination conditions on the sensitivity of porphyrins-coated ZnO nanorods

ZnO and porphyrins have complementary properties that make their combination attractive for diverse applications such as photovoltaic and chemical sensing. Among the other features, the organic layer morphology is supposed to influence both the chemical sensitivity and the charge transfer processes. In this paper, we studied the influence of the film morphology on the sensing properties by comparing porphyrins coated ZnO nanorods obtained with two different methods. In the first approach, each porphyrin unit is grafted onto preformed ZnO nanorods by a carboxylic group as linker. The second method is a one-pot procedure, where ZnO nanorods growth occurs in the presence of the water soluble tetrakis-(4-sulfonatophenyl)porphyrin. In both cases the macrocycles share the same Zn-tetraphenylporphyrin core structure, but decorated with different peripheral groups, necessary to comply with the material growth conditions.The adsorption of volatile organic molecules has been monitored measuring the contact potential difference between the sensitive surface and a gold electrode, by means of a Kelvin probe setup. Sensitive signals have been measured both in dark and under visible light. The results show that material preparation affects both the sensitivities to gases and light. A chemometric analysis of four sensors (first and second growth method, measured in dark and in light) shows two main evidences: (a) the interaction between volatile compounds and the sensing layer is largely dominated by non-specific dispersion interaction and (b) the signal of the four sensors becomes rather uncorrelated when the contribution of the dispersion interaction is removed. These results indicate that the differences due to film morphology are enough to differentiate the sensor behaviour, even when the same porphyrin nucleus is used as sensing element. This feature provides an additional degree of freedom for the development of gas sensor arrays.

Enantiomeric separation of volatile organics by gas chromatography for the in situ analysis of extraterrestrial materials: Kinetics and thermodynamics investigation of various chiral stationary phases

The performances of several commercial chiral capillary columns have been evaluated with the aim of determining the one most suitable for enantiomeric separation in a gas chromatograph onboard a space probe. We compared the GC–MS response of three capillary columns coated with different chiral stationary phases (CSP) using volatile chiral organic molecules which are potential markers of a prebiotic organic chemistry. The three different chiral capillary columns are Chirasil-Val, with an amino acid derivative CSP, ChiralDex-β-PM, with a CSP composed of dissolved permethylated β-cyclodextrins in polysiloxane, and Chirasil-Dex, with a CSP made of modified cyclodextrins chemically bonded to the polysiloxane backbone. Both kinetics and thermodynamics studies have been carried out to evaluate the chiral recognition potential in these different types of columns. The thermodynamic parameters also allow a better understanding of the driving forces affecting the retention and separation of the enantiomers. The Chirasil-Dex-CSP displays the best characteristics for an optimal resolution of the chiral compounds, without preliminary derivatization. This CSP had been chosen to be the only chiral column in the Sample Analysis at Mars (SAM) experiment onboard the current Mars Science Laboratory (MSL) mission, and is also part of the Mars Organic Molecules Analyzer (MOMA) gas chromatograph onboard the next Martian mission ExoMars. The use of this column could also be extended to all space missions aimed at studying chirality in space.

Structural descriptors for the correlation of human blood:air partition coefficient of volatile organic molecules by QSPRs

The human blood:air partition coefficients expressed as log Kblood, for a set of 91 structurally diverse molecules, were investigated using quantitative structure–property relationships (QSPRs). A successful five-descriptor model with good statistical fitting (R2 = 0.93) and predicting capability (RCV2 = 0.86) was established using multiple linear regression (MLR). The model is based on the total energy (E), octanol:water partition coefficient (log P), polarizability (α), molecular weight (M), and electrophilicity (ω), log P is found to be the most important descriptor for predicting log Kblood. The obtained QSPR model could be used for predicting the log Kblood of volatile organic molecules presented in our study, and further studies would be needed to test additional molecules for external validation.

A dynamic, luminescent and entangled MOF as a qualitative sensor for volatile organic solvents and a quantitative monitor for acetonitrile vapour

A new luminescent entangled (srs nets with two-fold interpenetration, linked via short Cu⋯Cu distances of ca. 2.8 Å) MOF, namely, [(CuCN)3L·(guest)x]n (L = 2,6-bis((3,5-dimethyl-1H-pyrazol-4-yl)methyl)pyridine; x = 1 or 2), which contains microporous channels, is synthesized. This MOF material shows structural dynamics upon adsorption of various volatile organic solvent molecules, accompanied by reversible guest responsive colour changes of the fluorescence emission that are discernible by the naked eyes. The vacuated form of this material can also exhibit qualitative solvate-optical sensing behaviours toward various mixed solvents. Moreover, a quantitative real-time monitoring device is constructed that implements the determination of acetonitrile vapour pressure through optical response, which causes a drastic emission change from blue to yellow. The detailed structural elucidation provides structure–property understanding for the host–guest responsive dynamics.

Computer screen assisted digital photography

The computer screen photo-assisted techniques (CSPT) have been developed during the last 10 years through an extensive collaboration between University of Rome “Tor Vergata” and Linköping University in Sweden. CSPT has thus evolved into a concept we now call computer screen assisted digital photography, yielding detailed information about the interaction between color indicators and (volatile) analytes. In the present paper, we give a brief summary of the CSPT concept and its connection to digital photography. We concentrate, however, on the most recent results, which were obtained by using most of the degrees of freedom offered by a computer screen as a light source and a digital (web) camera as a detector. Thus, we describe in detail recent experiments on cotton yarns impregnated with color indicators for volatile organic molecules. The interaction between the color indicators and molecules, like trimethylamine, was investigated by CSPT in high dynamic imaging together with a background noise limiting algorithm. It is shown that the simultaneous use of the last two additions to the CSPT concept considerably enhances the chemical sensing ability of CSPT. It is concluded that the collaboration between Rome and Linköping has generated a useful platform for further developments of chemical analysis with a ubiquitous instrumentation, a (computer) screen and a web camera. This technique is aimed at facilitating the assembly of opto-chemical sensors with evident benefits in the reduction of cost of sensor systems and in an increased integrability with the existent telecommunication infrastructures.

Effect of Perforation on the Sensing Properties of Monolayer-Capped Metallic Nanoparticle Films

We report on the effect of perforation within a monolayer-capped metallic nanoparticle (MCNP) film on sensing of volatile organic compounds (VOCs) and water molecules. Our results show that continu...

Volatile organic compounds decomposition using nonthermal plasma coupled with a combination of catalysts

A series of experiments were performed for toluene decomposition from a gaseous influent at normal temperature and atmospheric pressure by nonthermal plasma coupled with a combination of catalysts technology. Nonthermal plasma was generated by dielectric barrier discharge. γ-Al2O3 was used to be a sorbent and a catalyst carrier. Nanocatalysts were MnO2/γ-Al2O3 coupled with modified ferroelectric of nano-Ba0.8Sr0.2Zr0.1Ti0.9O3. γ-Al2O3 played an important role in prolonging reaction time of nonthermal plasma with volatile organic compounds molecules. MnO2/γ-Al2O3 has an advantage for ozone removal, while nano-Ba0.8Sr0.2Zr0.1Ti0.9O3 is a kind of good ferroelectric material for improving energy efficiency. Thus these packed materials were incorporated together to strengthen nonthermal plasma power for volatile organic compounds decomposition. The results showed the synergistic technology resulted in greater enhancement of toluene removal and energy efficiencies and a better inhibition for ozone formation in the gas exhaust. Based on the data analysis of the Fourier transforms infrared spectrum, the reaction process of toluene decomposition and the mechanism of synergistic effect are discussed. The results showed in a complex oxidation mechanism of toluene via several pathways, producing either ringretaining or ringopening products. The final products were carbon dioxide and water.

Carborane-Containing Poly(fluorene): Response to Solvent Vapors and Amines

Hybrid conjugated polymers containing carborane directly bonded in the aromatic backbone repeat structure have interesting electronic bonding structures and are potentially useful new materials in organic electronics. Conjugated polymers based on o-carborane are particularly interesting for applications in sensing and detection because of the cage's unique bonding scheme and its bent geometry. Poly(fluorene) containing o-carborane displays multiple emission pathways that can be modulated through interactions with small molecules. In this paper, we report that films of poly(fluorene) with o-carborane in the backbone function as vapochromatic photoluminescent sensors toward volatile organic molecules.

Interactions of Benzo[<italic>a</italic>]pyrene and Diesel Exhaust Particulate Matter with the Lung Surfactant System

One of the reasons for cellular changes in the lung tissue exposed to the diesel exhaust composed of soot particles with adsorbed volatile organic molecules is the reduction of the clearance rate in the pulmonary region of the respiratory system. The interaction of the fractal-like particles and organic substances with a surfactant monolayer limits its dynamic activity. The surface properties of Survanta, a purified extract of bovine lung surfactant (LS), which interacted with carbon particles (200 nm aggregates) and benzo[a]pyrene (BaP), molecules were measured with the oscillating bubble technique. The results showed a significant lowering of the dynamics of the surfactant monolayer compared to the control case (no exposure). Additional measurements of surface pressure during the monotonic compression of the air-water interface containing the major LS phospholipid, dipalmitoylphosphatidylcholine (DPPC), showed that the presence of BaP molecules in the system influenced its stability. The experimental results were supplemented with a theoretical molecular dynamics model of the interaction between BaP and DPPC molecules. The simulation results indicated the insertion of BaP molecules into the lipid layer, which explained the measured effects.

Synthesis and complexation of amphiphilic calix[4]arene phosphonates with organic molecules in solutions and Langmuir-Blodgett films

A family of amphiphilic alkoxycalix[4]arenes bearing phosphonyl groups directly attached to para positions of the aromatic rings is synthesized by the Arbuzov reaction of para-bromoalkoxycalix[4]arenes with alkyl esters of phosphorus (III) acid in the presence of NiBr 2. Amphiphilicity of the calixarene phosphonates is controlled by varying the quantities of the hydrophilic phosphoryl groups at the upper rim and the hydrophobic alkyl groups at the lower rim. Complexation of the calixarenes with benzene derivatives and iso-butanol in solutions is studied by RP HPLC and IR spectroscopy methods. Langmuir-Blodgett films of the calixarene phosphonates are prepared. Physical characteristics and complexation of the films with volatile organic molecules are characterized.

Heavy Metal Pollutants and Chemical Ecology: Exploring New Frontiers

Heavy metals are an important class of pollutants with both lethal and sublethal effects on organisms. The latter are receiving increased attention, as these may have harmful ecological outcomes. For example, recent explorations of heavy metals in freshwater habitats reveal that they can modify chemical communication between individuals, resulting in "info-disruption" that can impact ecological relationships within and between species. Info-disruption can affect animal behavior and social structure, which in turn can modify both intraspecies and interspecies interactions. In terrestrial habitats, info-disruption by metals is not well studied, but recent demonstrations of chemical signaling between plants via both roots and volatile organic molecules provide potential opportunities for info-disruption. Metals in terrestrial habitats also can form elemental plant defenses, in which they can defend a plant against natural enemies. For example, hyperaccumulation of metals by terrestrial plants has been shown to provide defensive benefits, although in almost all known cases the metals are not anthropogenic pollutants but are naturally present in soils inhabited by these plants. Info-disruption among microbes is another arena in which metal pollutants may have ecological effects, as recent discoveries regarding quorum sensing in bacteria provide an avenue for metals to affect interactions among bacteria or between bacteria and other organisms. Metal pollutants also may influence immune responses of organisms, and thus affect pathogen/host relationships. Immunomodulation (modification of immune system function) has been tied to some metal pollutants, although specific metals may boost or reduce immune system function depending on dose. Finally, the study of metal pollutants is complicated by their frequent occurrence as mixtures, either with other metals or with organic pollutants. Most studies of metal pollutants focus on single metals and therefore oversimplify complex field conditions. Study of pollutant impacts on chemical ecology also are difficult due to the necessity of studying effects at varying ecological scales: "dynamic scaling" of chemical ecology studies is rarely done completely. It is clear that much remains to be learned about how heavy metal pollution impacts organisms, and that exciting new research frontiers are available for experimental exploration.

Modeling permeation of volatile organic molecules through reverse osmosis spiral-wound membranes

Reverse osmosis is an interesting process to eliminate organic solutes from distillery condensates before recycling them into the fermentation step. However, organic solutes transport phenomena through reverse osmosis membranes are specific. Rejection and sorption of five compounds were studied on a brackish water membrane. Acetic acid and 2,3-butanediol were not sorbed on the membrane while furfural and 2-phenylethanol presented strong sorption following the Langmuir pattern. These sorption effects coupled with solute molecular weight (MW) led to low rejections of acetic acid and furfural (30–60%) and high rejections of 2,3-butanediol and 2-phenylethanol (80–98%). With intermediate sorption and MW, butyric acid showed rejections between 70 and 80%. A modified solution-diffusion model was developed to take into account the sorption pattern and predict the concentration profile along the membrane on the retentate and permeate sides. Equilibrium properties were determined experimentally while transport properties were identified with data obtained from a synthetic condensate. This model was validated for various operating conditions with the synthetic and the industrial condensates. It was then used to simulate the influence of the recovery rate on the retentate and permeate concentrations. It showed the behavior differences between solutes with a linear sorption and solutes with a saturating sorption.

Electric‐Field Triggered Controlled Release of Bioactive Volatiles from Imine‐Based Liquid Crystalline Phases

Application of an electric field to liquid crystalline film forming imines with negative dielectric anisotropy, such as N-(4-methoxybenzylidene)-4-butylaniline (MBBA, 1), results in the expulsion of compounds that do not participate in the formation of the liquid crystalline phase. Furthermore, amines and aromatic aldehydes undergo component exchange with the imine by generating constitutional dynamic libraries. The strength of the electric field and the duration of its application to the liquid crystalline film influence the release rate of the expelled compounds and, at the same time, modulate the equilibration of the dynamic libraries. The controlled release of volatile organic molecules with different chemical functionalities from the film was quantified by dynamic headspace analysis. In all cases, higher headspace concentrations were detected in the presence of an electric field. These results point to the possibility of using imine-based liquid crystalline films to build devices for the controlled release of a broad variety of bioactive volatiles as a direct response to an external electric signal.