Volatile Organic Compound Vapors Research Articles

Highly sensitive fluorescent nitrobenzene gas sensing by nitrogen-doped graphene quantum dots embedded in ZIF-8 nanocomposite

This study introduces a straightforward and highly sensitive luminescence gas sensor designed for the detection of nitrobenzene in gaseous state. The sensor utilizes an innovative composite composed of nitrogen doped graphene quantum dots (nGQDs) as luminescent materials, successfully encapsulated within the stable porous carrier zeolitic imidazolate framework-8 (ZIF-8). The resulting nGQD@ZIF-8 nanocomposite showed highly sensitive luminescence sensing towards nitrobenzene gas, with a wide linear detection range from 8 to 320 ppm, and the detection limits of sensor as low as 0.44 ppm. Moreover, the nGQD@ZIF-8 sensor demonstrated enhanced ppm-level sensitivity and long-term stability for nitrobenzene detection at room temperature, while maintaining high stability under varying humidity levels and exposure to high temperatures. This enhancement is attributed to the increased contact area provided by ZIF-8 matrix, facilitating adsorption of nitrobenzene molecules on nGQDs. The nGQD@ZIF-8 exhibited good selectivity towards nitrobenzene gas (57 %) compared to other nitro volatile organic compound (VOC) vapors (nitromethane and nitropropane), and almost no significant responses were observed for the other tested VOC vapors (methanol, acetone, formaldehyde, benzene). This can be attributed to the strong interaction between the electron-deficient nitrobenzene and the nGQD@ZIF-8 nanocomposite. Overall, the proposed gas sensor in this study showed high potential for a simple, efficient, and reliable detection of nitrobenzene gas in environmental monitoring.

Ultrathin photonic crystal based on photo-crosslinked polymer and metal–organic framework for highly sensitive detection and discrimination of benzene series vapors

Volatile organic compounds (VOCs) have always been a major concern as a global environmental problem. As a low-cost, high-efficiency and visual sensor, photonic crystals (PCs) have been actively studied in VOCs detection. Herein, a one-dimensional PC sensor for visual sensing of highly toxic benzene series VOC vapors is prepared for the first time by integrating a new photo-crosslinked polymer-poly(styrene-benzoylphenyl acrylate) P(St-BPA) and a high specific surface area metal–organic framework (MOF) MIL-101(Cr). The PC can detect VOCs quantitatively and visually, and clearly distinguish 7 benzene series vapors. The detection limit of the benzene series VOCs is as low as 0.06–3.45 g/m3. Meanwhile, owing to the ultra-thin layer and porous structure, the PC can reach a response equilibrium to the VOCs within 1–2.6 s. Moreover, the PC has a good organic vapor tolerance and can maintain stable optical performance after 1000 times of reuse in VOCs. Besides, 4 other PCs assembled with different aryl polymers and MOFs are first fabricated and their sensing performance to benzene series VOCs are studied and compared, which provides a valuable reference for the selection of materials for the preparation of such PC sensors.

Bimetallic Co-Mn catalysts for synergistic enhancement of VOC gas-sensing performance of ZnO hierarchical nanostructures.

The synergistic effect between bonding dissimilar metals is a very effective way to improve the performance of metal catalysts. In this work, we prepared a series of bimetallic co-doped ZnO hierarchical nanostructures by controlling Mn and Co contents. The gas-sensing properties of the sensors based on the bimetallic co-doped ZnO hierarchical nanostructures were studied systematically through different volatile organic compound (VOC) vapors for the temperature range from 160 to 400 °C. In the testing of normal butanol gas by the bimetallic co-doped ZnO sensor, its performance was tens of times higher than that of pure zinc oxide, and the response values to other VOCs tested were very low, which also indicates that the sensor has good selectivity. The promoted performance is attributed to the increase of adsorbed oxygen content on the surface of the sensor material due to the bimetallic synergistic enhancement effect. XPS spectra of O 1s region of the sensor show that the adsorbed oxygen content is 22.4%, which is higher than that of the pure ZnO (8.5%). The synergistic effect between bimetallic Mn and Co leads to electron enrichment on the surface of ZnO. Electron enrichment can not only promote the activation of ZnO, but also can help to improve the gas-sensing performance.

Plasma Polymerized Organosilicon Thin Films for Volatile Organic Compound (VOC) Detection

Plasma polymerized (PP) thin films deposited in a soft or intermediate plasma discharge from hexamethyldisiloxane (HMDSO) were developed as sensors for the detection of volatile organic compound (VOC) vapors. Energy dispersive X-ray spectroscopy (EDX) and X-ray reflectometry (XRR) were performed to determine the organosilicon films’ elemental composition and density. Spectroscopic ellipsometry measurements were carried out to determine the refractive index of the films. Quartz crystal microbalance (QCM) and ellipsometry coupled to vapor sorption were used to investigate the sorption mechanism of several VOC vapors into the films as a function of the plasma deposition conditions. The density and the refractive index of the PP-HMDSO films increased with the plasma energy due to a different chemical composition and different proportion of free volumes in the material network. The PP-HMDSO films showed different affinities towards the VOC vapors depending on the plasma discharge energy. The films elaborated in the lowest plasma energy revealed a good sensitivity towards the VOCs, especially toluene (one of the BTEX vapors), compared to the other films deposited under higher plasma energy. In addition, the selectivity between toluene and other non-BTEX VOCs such as heptane and ethanol decreased to become zero while increasing the plasma energy.

Low-Cost ZnO Spray-Coated Optical Fiber Sensor for Detecting VOC Biomarkers of Diabetes.

A non-invasive optical fiber sensor for detecting volatile organic compounds (VOCs) as biomarkers of diabetes is proposed and experimentally demonstrated. It offers a low-cost and straightforward fabrication approach by implementing a one-step spray coating of a ZnO colloidal solution on a glass optical fiber. The structure of the optical fiber sensor is based on a single-mode fiber-coreless silica fiber-single-mode fiber (SMF-CSF-SMF) structure, where the CSF is the sensor region spliced between two SMFs. The ZnO layer of a higher refractive index coated over the sensing region improves the light interaction with the surrounding medium, leading to sensitivity enhancement. The optical properties, morphology, and elemental composition of the ZnO layer were analyzed. The sensing mechanism of the developed sensor is based on a wavelength interrogation technique showing wavelength shifts when the sensor is exposed to various VOC vapor concentration levels. Various concentrations of the three VOCs (including acetone, isopropanol, and ethanol) ranging from 20% to 100% were tested and analyzed. The sensor noticeably shows a significant response towards acetone vapor, with a better sensitivity of 0.162 nm/% vapor than for isopropanol (0.082 nm/% vapor) and ethanol (0.075 nm/% vapor) vapors. The high sensitivity and selectivity towards acetone, a common biomarker for diabetes, offers the potential for further development of this sensor as a smart healthcare system for monitoring diabetic conditions.

Prototype for chemical analysis and process intensification that is useful for research and teaching

This work describes the design, manufacturing and testing of a detection system useful to be applied with microTAS or other compact equipment, such as those needed for Process Intensification in Chemical Engineering. The detection is carried out by a Quartz Microbalance (QCM), based on Piezoelectric Quartz Crystals (PQC) of multiple frequencies, from tens of kHz to almost GHz. With this instrument, it is possible to detect particles and droplets in a gaseous flow, as well as vapors of volatile organic compounds. The system allows simultaneous measurement at five different points, and due to its modularity, such points can be positioned several centimeters apart from each other. The use in teaching is favored not only because of its low cost and modularity, and also due to its portability, i.e., its small size.

Influence of deposition temperature and time on structural and gas sensing properties of electrochemically deposited ZrO2 layers

This research is focused on the influence of deposition temperature and time on structural and gas sensing properties of electrochemically deposited ZrO2 layers. ZrO2 layers were deposited on gold electrodes of quartz resonators by electrochemical process using a three-electrode electrochemical system. The deposition was carried out in an aqueous solution containing ZrOCl2 (5 mM) and KCl (0.1 M). The surface morphology, structure and average roughness of the layers were determined by Scanning Electron Microscopy (SEM) and 3D optical profilometry. Studies demonstrated that deposition temperature strongly influences the surface morphology of the films, especially at higher temperatures whereas weaker dependence on deposition time was observed. The layers sensitivity to volatile organic compound (VOC) vapors was determined by the quartz crystal microbalance method (QCM) method. The measurements of sensitivity were performed in an airtight box at different concentrations.

The two-stepwise luminescent switching properties of triple-stimuli-responsive platinum(II) complexes bearing 4,4′-bis(2-phenylethynyl)-2,2′-bipyridine ligand

Three new square-planar platinum(II) complexes, Pt(PhC≡CbpyC≡CPh)(C≡CC6H4-X-2)2 [PhC≡CbpyC≡CPh = 4,4′-bis(2-phenylethynyl)-2,2′-bipyridine; X = F(1), Cl(2), and Br(3)] were synthesized and characterized. Upon exposure of the ground sample to volatile organic compound (VOC) vapors, a series of metastable structures of three complexes, including yellow solvent-free species 2 and 3, orange species 1, 2·ClCH2CH2Cl and 3·ClCH2CH2Cl, red species 1·1.5(CHCl3), 2·½(CH2Cl2), 2·½(ClCH2CH2Cl), 3·½(Toluene), and 3·½(ClCH2CH2Cl) were isolated. All three complexes exhibit vapor-, thermo-, and mechanical-grinding-triggered triple-stimuli-responsive luminescent switching properties. More interestingly, upon exposure to ClCH2CH2Cl vapor, the red species 2·½(CH2Cl2) or 3·½(Toluene) undergo an unusual time-dependent two-stepwise luminescent switching process and convert to the orange species 2·ClCH2CH2Cl or 3·ClCH2CH2Cl via intermediate 2·½(ClCH2CH2Cl) or 3·½(ClCH2CH2Cl). Furthermore, 1·1.5(CHCl3) also displays a two-stepwise thermoluminescent property and is transformed into orange species 1via intermediate 1·⅛(CHCl3). Furthermore, both 2 and 3 present the irreversible vapochromic and vapoluminescent properties as the yellow and orange species could not be converted to each other or transformed to the red species by absorbing the corresponding VOC vapors. Systematic studies revealed that the vapor-, thermo-, and mechanical-grinding-triggered triple-stimuli-responsive luminescence switching properties of 1–3 are due to the structural conversion and resultant changes of the lowest-energy excited states. The crystal structure, 1H NMR, luminescence spectra and PXRD measurements demonstrate that the two-stepwise luminescent switching behavior of complexes are associated with the stacking structure of species with same kind and different amount of solvent molecule. The irreversible vapoluminescent property of 2 and 3 are most likely due to the closed stacking of species which prevent the inserting of solvent molecules into the crystal lattice. In addition, complexes 1–3 have good application prospects in the visual identification of CHCl3, CH3CN and 1,2-dichloroethane vapors.

Swellable Array Strategy Based on Designed Flexible Double Hypercross-linked Polymers for Synergistic Adsorption of Toluene and Formaldehyde.

High-capacity adsorption and removal of complex volatile organic compounds (VOCs) from real-world environments is a tough challenge for researchers. Herein, a swellable array adsorption strategy was proposed to realize the synergistic adsorption of toluene and formaldehyde on the flexible double hypercross-linked polymers (FD-HCPs). FD-HCPs exhibited multiple adsorption sites awarded by a hydrophobic benzene ring/pyrrole ring and a hydrophilic hydroxyl structural unit. The array benzene ring, hydroxyl, and pyrrole N sites in FD-HCPs effectively captured toluene and formaldehyde molecules through π-π conjugation and electrostatic interaction and weakened their mutual competitive adsorption. Interestingly, the strong binding force of toluene molecules to the skeleton deformed the pore structure of FD-HCPs and generated new adsorption microenvironments for the other adsorbate. This behavior significantly improved the adsorption capacity of FD-HCPs for toluene and formaldehyde by 20% under multiple VOCs. Moreover, the pyrrole group in FD-HCPs greatly hindered H2O molecule diffusion in the pore, thus efficiently weakening the competitive adsorption of H2O toward VOCs. These fascinating properties enabled FD-HCPs to achieve synergistic adsorption for multicomponent VOC vapor under a highly humid environment and overcame single-species VOC adsorption properties on state-of-the-art porous adsorbents. This work provides the practical feasibility of synergistic adsorption to remove complex VOCs in real-world environments.

Adsorption of a Four-Component Mixture of Volatile Organic Compound Vapors on Modified Activated Carbons

This work aimed to evaluate the effect of activated carbon modifications on the adsorption of volatile organic compound vapors. In this study, two commercial activated carbons WG-12 and DT0 (Grand Activated Sp. z o.o.) were modified by melamine and dl-malic acid and heat treatment. Then, the activated carbons were used as adsorbents in the adsorption of a gaseous mixture of four volatile organic compounds (acetone, ethyl acetate, toluene, n-butyl acetate) from the air. The properties of modified adsorbents were described using thermogravimetric analysis, elemental analysis, Boehm titration, and iodine number. Adsorption processes were characterized by breakthrough curves, velocities of the sorption front migration, and the Yoon–Nelson model. The study showed that surface modifications of activated carbons affect the adsorption properties of a mixture of acetone, ethyl acetate, toluene, and n-butyl acetate. The introduction of nitrogen on the surface of the activated carbons did not significantly improve the adsorption efficiency. It was identified that increasing the degree of carbonization of the activated carbon favored the adsorption of the tested adsorbates. The adsorption process of this mixture occurs by diffusion and depends on the diffusion velocity of the adsorbate molecules in the pores. It has been demonstrated that the velocity of the sorption front migration is inversely proportional to the boiling point of the adsorbates. In addition, it was found that competitive adsorption takes place in this process. Modified adsorbents can be thermally regenerated with almost 100% efficiency and reused in the next adsorption process. Furthermore, the Yoon–Nelson model can be successfully used to describe the kinetics of this process up to the point of displacement.

Characteristic vapochromic detection of platinum(II) 3,8-bis-(2-triisopropylsilylethynyl)-phenanthroline organometallic complexes with bis-arylethynyl derivatives

The vapochromism of square-planar platinum(II) complexes has been widely studied because of its potential as a useful chemical sensor of harmful volatile organic compounds (VOCs). We synthesized six platinum(II) organometallic complexes with 3,8-bis-(triisopropylsilyl)ethynyl-1,10-phenanthroline (PhenTIPS) and six respective arylethynyl ligands with different substituents (Pt(PhenTIPS)(-Ph-R)2: R = 4-Me (1TIPS), 4-CF3 (2TIPS), 4-t-Bu (3TIPS), 3,5-di-Me (4TIPS), 3,5-di-CF3 (5TIPS), 3,5-di-t-Bu (6TIPS)), as well as two complexes with 3,8-bis-(trimethylsilyl)ethynyl-1,10-phenanthroline (PhenTMS) and 3,8-bis-(triethylsilyl)ethynyl-1,10-phenanthroline (PhenTES) including a 3,5-dimethyl-phenylethynyl ligand: Pt(PhenTMS)(-Ph-3,5-di-Me)2 (4TMS) and Pt(PhenTES)(-Ph-3,5-di-Me)2 (4TES). These complexes were characterized by their luminescence in solution and in the solid state by photoluminescence spectroscopy and showed the phosphorescence from the mixed transition of triplet metal-to-ligand charge transfer (3MLCT)/triplet ligand-to-ligand charge transfer (3LLCT) or the transition of a triplet metal-metal-to-ligand charge transfer (3MMLCT) including the Pt-Pt interaction in the solid state. In vapoluminescence experiments, we found that three complexes (3TIPS, 4TIPS, and 4TMS) in the solid state showed unique luminescent color changes against the vapors of specific VOCs. Also, in vapoluminescence experiments, the solid-state photoluminescence spectra of 3TIPS and 4TMS showed a blue shift in phosphorescence from the 3MMLCT transition to the 3MLCT/3LLCT mixed transition against the vapors of specific VOCs. The vapoluminescence experiment with 4TIPS against 13 species of VOCs showed only the characteristic selective detection against CHCl3 with a bright green emission.

Tuning the Selectivity of Metal Oxide Gas Sensors with Vapor Phase Deposited Ultrathin Polymer Thin Films.

Metal oxide gas sensors are of great interest for applications ranging from lambda sensors to early hazard detection in explosive media and leakage detection due to their superior properties with regard to sensitivity and lifetime, as well as their low cost and portability. However, the influence of ambient gases on the gas response, energy consumption and selectivity still needs to be improved and they are thus the subject of intensive research. In this work, a simple approach is presented to modify and increase the selectivity of gas sensing structures with an ultrathin polymer thin film. The different gas sensing surfaces, CuO, Al2O3/CuO and TiO2 are coated with a conformal < 30 nm Poly(1,3,5,7-tetramethyl-tetravinyl cyclotetrasiloxane) (PV4D4) thin film via solvent-free initiated chemical vapor deposition (iCVD). The obtained structures demonstrate a change in selectivity from ethanol vapor to 2-propanol vapor and an increase in selectivity compared to other vapors of volatile organic compounds. In the case of TiO2 structures coated with a PV4D4 thin film, the increase in selectivity to 2-propanol vapors is observed even at relatively low operating temperatures, starting from >200 °C. The present study demonstrates possibilities for improving the properties of metal oxide gas sensors, which is very important in applications in fields such as medicine, security and food safety.

Real‐Time In Situ Volatile Organic Compound Sensing by a Dual‐Emissive Polynuclear Ln‐MOF with Pronounced LnIII Luminescence Response

AbstractLanthanide metal–organic frameworks (Ln‐MOFs) are promising for luminescence detection of volatile organic compound (VOC) vapors, but usually suffer from the silent or quenched Ln3+ emission. Herein, we report a new dual‐emissive Eu‐MOF composed of the coordinatively unsaturated Eu9 clusters that afford abundant open metal sites to form a confined “binding pocket” to facilitate the preconcentration and recognition of VOCs. Single‐crystal structural analyses reveal that specific analytes can replace the OH oscillators in the first coordination sphere of Eu3+ and form a unique hydrogen‐bonding second‐sphere adduct tying adjacent Eu9 clusters together to minimize their nonradiative vibrational decay. With the promoted Eu3+ luminescence, the MOF realizes real‐time in situ visual sensing of THF vapor (&lt;1 s) and shows a quantitative ratiometric response to the vapor pressure with a limit of detection down to 17.33 Pa. Also, it represents a top‐performing ratiometric luminescent thermometer.

Real-Time In Situ Volatile Organic Compound Sensing by a Dual-Emissive Polynuclear Ln-MOF with Pronounced LnIII Luminescence Response.

Lanthanide metal-organic frameworks (Ln-MOFs) are promising for luminescence detection of volatile organic compound (VOC) vapors, but usually suffer from the silent or quenched Ln3+ emission. Herein, we report a new dual-emissive Eu-MOF composed of the coordinatively unsaturated Eu9 clusters that afford abundant open metal sites to form a confined "binding pocket" to facilitate the preconcentration and recognition of VOCs. Single-crystal structural analyses reveal that specific analytes can replace the OH oscillators in the first coordination sphere of Eu3+ and form a unique hydrogen-bonding second-sphere adduct tying adjacent Eu9 clusters together to minimize their nonradiative vibrational decay. With the promoted Eu3+ luminescence, the MOF realizes real-time in situ visual sensing of THF vapor (<1 s) and shows a quantitative ratiometric response to the vapor pressure with a limit of detection down to 17.33 Pa. Also, it represents a top-performing ratiometric luminescent thermometer.

Improvement in gas sensitivity of carbon nanotube to volatile organic compounds by covering zinc oxide nanowire

Carbon nanotubes (CNTs) have been utilized in many gas sensor structures, individually or in hybrid form with other materials to enhance their gas sensing properties. CNT and CNT–ZnO nanowire structures were fabricated by plasma-enhanced chemical vapor deposition (PECVD) and hydrothermal growth methods to explore and compare their gas sensing properties. The morphologies of the fabricated samples were characterized using scanning electron microscopy and Fourier-transform infrared spectroscopy. Gas sensing properties of fabricated samples were assessed at different atmospheric and thermal conditions. Results verified CNT–ZnO has two times higher response than the CNT sample toward volatile organic compounds vapor at room temperature. A longer lifetime and more stability are other advantages of the CNT–ZnO hybrid. Moreover, it is shown that increasing the length of ZnO nanowires exhibits a higher response to examined analytes. It was found that increasing the temperature causes different sensing regimes in CNT and CNT–ZnO samples. At all ranges of temperatures, the resistance of CNT samples increased in the presence of reducing gases while CNT–ZnO samples exhibited similar behavior only below ∼90 °C. At elevated temperatures, their resistances decreased in response to the same gases.

Chemical VOC sensing mechanism of sol-gel ZnO pellets and linear discriminant analysis for instantaneous selectivity.

This work reports on the integration of ZnO pellets for use as a virtual sensor array (VSA) of volatile organic compounds (VOCs). ZnO pellets consist of nano-powder prepared using a sol-gel technique. The microstructure of the obtained samples was characterized by XRD and TEM methods. The response to VOCs at different concentrations was measured over a range of operating temperatures (250-450 °C) using DC electrical characterization. The ZnO based sensor showed a good response towards ethanol, methanol, isopropanol, acetone and toluene vapors. We note that the highest sensitivity (0.26 ppm-1) is obtained with ethanol while the lowest one (0.041 ppm-1) corresponds to methanol. Consequently, the limit of detection (LOD) estimated analytically reached 0.3 ppm for ethanol and 2.0 ppm for methanol at an operating temperature of 450 °C. The sensing mechanism of the ZnO semiconductor was developed on the basis of the reaction between the reducing VOCs with the chemisorbed oxygen. We verify through the Barsan model that mainly O- ions in the layer react with VOC vapor. Furthermore, dynamic response was investigated to construct mathematical features with distinctly different values for each vapor. Basic linear discrimination analysis (LDA) shows a good job of separating two groups by combining features. In the same way we have shown an original reason embodying the distinction between more than two volatile compounds. With relevant features and VSA formalism, the sensor is clearly selective towards individual VOCs.

Flexible TPU inverse opal fabrics for colorimetric detecting of VOCs.

Recently, responsive structure color fibers and fabrics have been designed and prepared for colorimetric detecting of volatile organic compounds (VOCs). Fabric substrates can offer greater flexibility and portability than flat and hard substrates such as glass, silicon wafers, etc. At present, one-dimensional photonic crystal (multilayer films) and three-dimensional dense photonic crystal layers are mainly constructed on fabrics to achieve the response to VOCs. However, the binding force between these structural color coatings and the fabrics was poor, and the dense structures inevitably hindered the diffusion of VOCs. Here, thermoplastic polyurethane (TPU) inverse opal (IOs) fabrics were prepared by sacrificing the SiO2 photonic crystal templates to achieve colorimetric detecting of VOCs. The IOs layer of TPU was cured directly on the fabric surface, TPU infiltrated into the fabric yarns, and bonded the fabrics and IOs layer into a whole, which greatly improved the binding force, and the porous structure and large specific surface area of IOs were conducive to the diffusion of VOCs. The results showed that the TPU IOs fabrics have large reflection peak shifts to DMF, THF, toluene and chloroform vapors, and its concentration has a good linear relationship with the maximum reflection peak value of TPU IOs fabrics. The theoretical detection limits are 1.72, 0.89, 0.78 and 1.64 g m-3, respectively. The response times are 105, 62, 75 and 66 seconds, with good stability. Finally, it was calculated that the discoloration of the TPU IOs fabrics in VOCs was due to the joint-effects of lattice spacing and effective refractive index increase.

Fabrication and application of free-standing fiber based on blue phase liquid crystal.

The application of blue phase liquid crystals (BPLCs) in optical control devices has been widely studied due to their fast response characteristics. However, the fabrication of free-standing BPLC fiber with emerging functionalities is challenging. Here, we demonstrate a free-standing fiber based on BPLC with excellent stability, flexibility, and multifunction. The multi-mode fiber (MMF) end face is etched by the etching agent of buffered oxide etch (BOE), which can be fixedly connected with the free-standing BPLC fiber after polymerization in order to overcome the problems of optical signals transmission and reception. Three types of free-standing BPLC fiber-based devices, including Volatile Organic Compound (VOC) vapor sensors, vector position sensors, and color fibers, are fabricated and investigated, to the best of our knowledge, for the first time. The free-standing BPLC fiber as a multifunctional material will provide broad application prospects in VOC sensors without power supply, smart fabrics, flexible displays, decorations fields with no dyes, as well as vector displacement sensors for robotic arm positioning.

Piezoelectric Gas Sensors with Polycomposite Coatings in Biomedical Application

When developing methods for diagnosing pathologies and diseases in humans and animals using electronic noses, one of the important trends is the miniaturization of devices, while maintaining significant information for diagnostic purposes. A combination of several sorbents that have unique sorption features of volatile organic compounds (VOCs) on one transducer is a possible option for the miniaturization of sensors for gas analysis. This paper considers the principles of creating polycomposite coatings on the electrodes of piezoelectric quartz resonators, including the choice of sorbents for the formation of sensitive layers, determining the mass and geometry of the formation of sensitive layers in a polycomposite coating, as well as an algorithm for processing the output data of sensors to obtain maximum information about the qualitative and quantitative composition of the gas phase. A comparative analysis of the efficiency and kinetics of VOC vapor sorption by sensors with polycomposite coatings and a set of sensors with relevant single coatings has been carried out. Regression equations have been obtained to predict the molar-specific sensitivity of the microbalance of VOC vapors by a sensor with a polycomposite coating of three sorbents with an error of 5-15% based on the results of the microbalance of VOC vapors on single coatings. A method for creating "visual prints" of sensor signals with polycomposite coatings is shown, with results comparable to those from an array of sensors. The parameters Aij∑ are proposed for obtaining information on the qualitative composition of the gas phase when processing the output data of sensors with polycomposite coatings. A biochemical study of exhaled breath condensate (EBC) samples, a microbiological investigation of calf tracheal washes, and a clinical examination were conducted to assess the presence of bovine respiratory disease (BRD). An analysis of the gas phase over EBC samples with an array of sensors with polycomposite coatings was also carried out. The "visual prints" of the responses of sensors with polycomposite coatings and the results of the identification of VOCs in the gas phase over EBC samples were compared to the results of bacteriological studies of tracheal washes of the studied calves. A connection was found between the parameters Aij∑ of a group of sensors with polycomposite coatings and the biochemical parameters of biosamples. The adequacy of replacing an array of piezoelectric sensors with single coatings by the sensors with polycomposite coatings is shown.

Novel reduced graphene oxide/zinc phthalocyanine and reduced graphene oxide/cobalt phthalocyanine hybrids as high sensitivity room temperature volatile organic compound gas sensors

In this work, novel 4-pyridynyl-oxadiazole tetrasubstituted zinc and cobalt phthalocyanine compounds were synthesized and characterized by UV-vis, Fluorescence spectroscopy, and SEM. Then these compounds were mixed with reduced graphene oxide. As a result of the interaction of these newly synthesized phthalocyanines with reduced graphene oxide (rGO), rGO/ZnPc and rGO/CoPc hybrids were obtained. The measurement results confirm that the prepared non-covalent rGO/ZnPc and rGO/CoPc hybrid structures are formed by strong π–π interaction. A comparative study of the sensor response of rGO and non-covalently functionalized with zinc and cobalt phthalocyanines (rGO/ZnPc, and rGO/CoPc) hybrids to five different volatile organic compound vapors, ammonia, acetone, ethanol, methanol and butanol is carried out. The response of the sensors increases with respect to ammonia concentrations ranging from 30 to 210 ppm. The response time for 120 ppm ammonia vapor were approximately 250s, 230s and 190s for rGO, rGO/ZnPc, and rGO/CoPc based sensors, respectively. Also, we have conducted selectivity experiments with the aformentioned vapors, thus, studies have indicated that functionalization of rGO with ZnPc results in a 43-fold improvement in sensor response towards ammonia vapors.