Volatile Organic Compounds Sensor Research Articles

Aluminium phosphide (Al12P12) nanocage as a potential sensor for volatile organic compounds: A DFT study.

The efficacy of aluminium phosphide (Al12P12) nanocage toward sensing methanol (MeOH) and ethanol (EtOH) volatile organic compounds (VOCs) was herein thoroughly elucidated utilizing various density functional theory (DFT) computations. In this perspective, MeOH⋯ and EtOH⋯Al12P12 complexes were investigated within all plausible configurations. According to the energetic features, the EtOH⋯Al12P12 complexes exhibited larger negative values of adsorption and interaction energies with values up to -27.23 and -32.84 kcal mol-1, respectively, in comparison to the MeOH⋯Al12P12 complexes. Based on the symmetry-adapted perturbation theory (SAPT) results, the electrostatic forces were pinpointed as the predominant component beyond the adsorption process within the preferable MeOH⋯ and EtOH⋯Al12P12 complexes. The findings of the noncovalent interaction (NCI) index and quantum theory of atoms in molecules (QTAIM) outlined the closed-shell nature of the interactions within the studied complexes. Substantial variations were found in the molecular orbitals distribution patterns of MeOH/EtOH molecules and Al12P12 nanocage, outlining the occurrence of the adsorption process within the complexes under investigation. Thermodynamic parameters were denoted with negative values, demonstrating the spontaneous exothermic nature of the most favorable complexes. New energy states were observed within the extracted density of states plots, confirming the impact of adsorbing MeOH and EtOH molecules on the electronic properties of the Al12P12 nanocage. The appearance of additional peaks in Infrared Radiation (IR) and Raman spectra revealed the apparent effect of the adsorption process on the features of the utilized sensor. The emerging results declared the potential uses of Al12P12 nanocage as a promising candidate for sensing VOCs, particularly MeOH and EtOH.

Comprehensive Qualitative and Quantitative Colorimetric Sensing of Volatile Organic Compounds Using Monolayered Metal-Organic Framework Films.

Cross-responsive chemical sensors are in high demand owing to their ability to distinguish a broad range of analytes. In this study, a vapochromic sensor array based on metal-organic frameworks (MOFs), which exhibits distinct patterns when exposed to volatile organic compounds (VOCs) and humidity, is developed. Conventional sensor arrays consist of various receptors that produce different responses. The vapochromic MOF-based sensor comprises dicopper paddlewheel clusters and dimethylamine azobenzene as binary colorimetric sensing moieties. Upon exposure to VOCs, the constructed sensor encompasses a broad spectrum of colors, ranging from green to red. Furthermore, the color of the MOF is influenced by the solvent used during the pretreatment. Consequently, monolayered MOF thin films can be adapted to multicomponent array systems by immersing the MOF in different solvents. This system provides both qualitative and quantitative sensing, generating unique color patterns corresponding to specific VOC types. Notably, the sensor successfully discriminates each of 14 common VOCs and water and accurately categorizes unknown samples. Moreover, the system undergoes reversible color changes in response to humidity, obviating the need for high-temperature regeneration steps. This novel approach offers insights into the versatile applications of MOFs by creating a colorimetric sensor array capable of detecting various analytes.

Fruit Freshness Monitoring Employing Chemiresistive Volatile Organic Compound Sensor and Machine Learning

Fruit Freshness Monitoring Employing Chemiresistive Volatile Organic Compound Sensor and Machine Learning

Impedimetric Early Sensing of Volatile Organic Compounds Released from Li-Ion Batteries at Elevated Temperatures

Lithium-ion batteries prove to be a promising technology for achieving present and future goals regarding energy resources. However, a few cases of lithium-ion battery fires and failures caused by thermal runaway have been reported in various news articles; therefore, it is important to enhance the safety of the batteries and their end users. The early detection of thermal runaway by detecting gases/volatile organic compounds (VOCs) released at the initial stages of thermal runaway can be used as a warning to end users. An interdigitated platinum electrode spin-coated with a sub-micron thick layer of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT: PSS) showed sensitivity for two VOCs (ethyl-methyl carbonate and methyl formate) released from Li-ion batteries during thermal runaway, as well as their binary mixtures at elevated temperatures, which were measured using impedance spectroscopy over a frequency range of 1 MHz to 1 Hz. The sensor response was tested at three different high temperatures (40 °C, 55 °C, and 70 °C) for single analytes and binary mixtures of two VOCs at 5 ppm, 15 ppm, and 30 ppm concentrations. Equivalent electrical parameters were derived from impedance data. A machine learning approach was used to classify the sensor’s response. Classification algorithms classify the sensor’s response at elevated temperatures for different analytes with an accuracy greater than 70%. The success of the reported sensors will enhance battery safety via the early detection of thermal runaway.

Selective flexible sensor for monitoring volatile organic compounds in museum display cases

Aim of this work is the development of a new kind of corrosion sensors, based on low-cost flexible substrates, specifically designed to detect Volatile Organic Compounds (VOCs) producing significant degradation of artifacts in museum display cases. Sensors have been fabricated and tested in relevant environment with three of the most relevant VOCs (acetic acid, formic acid and formaldehyde) to the artifacts preservation. Sensitivity has been measured to be lower than 1 ppm, which is several times better than what reported in the literature on corrosion sensors for the same VOCs. In addition, different sensors, arranged with different active materials, have been implemented for the first time into a so-called multi-sensor architecture, aimed at demonstrating VOC specificity: in particular, we report here on a preliminary test in which the multi-sensor has been able to be selective between acetic acid and formaldehyde.

Disposable, strain-insensitive, and room-temperature-operated flexible humidity and VOC sensor with enhanced sensitivity and selectivity through interface control

As people are paying more attention to the health and comfort of the indoor environment, the sensors detecting the relative humidity (RH) and volatile organic compounds (VOCs) have attracted widely research interests. However, how to improve the sensitivity and selectivity remains a challenge, especially for flexible sensors working at room temperature (around 25 ℃). In this work, the controlling of solid-gas interface was found to be able to enhance the sensitivity and the manipulation of solid-solid interface increased the selectivity of the sensor for VOC detection. The flexible sensor based on electrospinning cellulose (EC) show high sensitivity for humidity detection due to its large solid-gas interface, which can be used for real-time monitoring of human breathing and speech recognition, simultaneously, it can also detect a variety of VOCs. By introducing silver nanowires (AgNWs) to establish solid-solid interface between silver and expanded graphite (EG), the selectivity of the sensor for VOCs detection was improved, which shown higher sensitivity for EtOH with faster response/recovery time, as well as long-term cycle stability and bending insensitivity. Furthermore, the sensor also can be decomposed by burning, offering a sustainable disposal method. This versatile, low-cost and environmentally friendly flexible electronic device may be used for wearable air monitoring and environmental controlling.

A turn-on type vapofluorochromic methoxybenzylidene methanone Schiff base applied to wearable VOC sensor and smartphone-based detection

This study presents the synthesis, crystallographic data and photophysical properties of a donor-acceptor (D-A) compound, methoxybenzylidene methanone Schiff base (HMPPM). It shows remarkable vapofluorochromism, embodied as turn-on red fluorescence in response to volatile organic compounds (VOCs), with fast response and high signal contrast. HMPPM is further developed into a cellulose sensor via dip-dying method for VOCs detection. We further use RGB and CIELAB color spaces to quantify the vapofluorochromic fluorescence. The limits of detection (LOD) of the sensor reach ppm level. Furthermore, it was fabricated into a wearable VOC sensor, with the introduction of an endogenous/exogenous reference, which conduces to high accuracy and visual identification. The cellulose sensor can be tailored into diversified patterns, with controllable shape and size, which facilitated the encapsulation into various wearables, including shoes, hat and smart band, etc., succeeding in scenario-based VOCs detection. In addition, we built a smartphone-based sensing platform based on HMPPM, which achieves a ppm-level LOD in VOCs monitoring.

Peptide-Functionalized Carbon Nanotube Chemiresistors: The Effect of Nanotube Density on Gas Sensing.

Biorecognition element (BRE)-based carbon nanotube (CNT) chemiresistors have tremendous potential to serve as highly sensitive, selective, and power-efficient volatile organic compound (VOC) sensors. While many research groups have studied BRE-functionalized CNTs in material science and device development, little attention has been paid to optimizing CNT density to improve chemiresistor performance. To probe the effect of CNT density on VOC detection, we present the chemiresistor-based sensing results from two peptide-based CNT devices counting more than 60 different individual measurements. We find that a lower CNT density shows a significantly higher noise level and device-to-device variation while exhibiting mildly better sensitivity. Further investigation with SEM images suggests that moderately high CNT density with a stable connection of the nanotube network is desirable to achieve the best signal-to-noise ratio. Our results show an essential design guideline for tuning the nanotube density to provide sensitive and stable chemiresistors.

Microwave-assisted solvothermal synthesis of In-MIL-68 derived hollow In2O3 microrods for enhanced 1-pentanol sensing performance

The development of microbial volatile organic compounds (MVOCs) sensors is helpful due to the detection of toxic contaminants in foods, non-invasive disease diagnosis, and monitoring of contamination in industrial processes. Materials that are typically applied in the sensors field are semiconductor metal oxides (SMOx) since they have shown efficiency in identifying gases. Using metal-organic frameworks (MOFs) as precursors is an exciting approach to producing well-structured SMOx. Therefore, we report the preparation and characterization of In-MIL-68 (a MOF composed of terephthalic acid) derived hollow In2O3 microrods. The sensor material was obtained by the microwave-assisted solvothermal (MAS) method and subsequent calcination. We also show the application of the hollow In2O3 microrods as a 1-pentanol sensor for the first time. The sensor demonstrated exceptional sensitivity to this MVOC compared to other sensors reported in the literature, achieving a great response of 390 for 100 ppm of this compound at 350 °C.

Wearable Device for Cumulative Chlorobenzene Detection and Accessible Mitigation Strategies.

Chronic exposure to low concentrations of volatile organic compounds (VOCs), such as chlorobenzene, is not being monitored in industrializing countries, although VOC exposure is associated with carcinogenic, organ-toxic, and endocrine-disrupting effects. Current VOC-sensing technologies are inaccessible due to high cost, size, and maintenance or are ineffective due to poor sensitivity or reliability. In particular, marginalized individuals face barriers to traditional prescription VOC treatments due to cost, lack of transportation, and limited access to physicians; thus, alternative treatments are needed. Here, we created a novel cumulative wearable color-changing VOC sensor with a paper-based polydiacetylene sensor array for chlorobenzene. With a single smartphone picture, the sensor displays 14 days of logged chlorobenzene exposure data, interpreted by machine-learning (ML) techniques, including principal component analysis. Further, we explored the efficacy of affordable and accessible treatment options to mitigate a VOC's toxic effects. Vitamin D and sulforaphane are naturally found in cruciferous vegetables, like broccoli, and can be used to treat chlorobenzene-mediated bone degradation. Our platform combines these components into a smartphone app that photographs the sensor's colorimetric data, analyzes the data via ML techniques, and offers accessible treatments based on exposure data.

Block Copolymer-Templated, Single-Step Synthesis of Transition Metal Oxide Nanostructures for Sensing Applications.

The synthesis of transition metal oxide nanostructures, thanks to their high surface-to-volume ratio and the resulting large fraction of surface atoms with high catalytic activity, is of prime importance for the development of new sensors and catalytic materials. Here, we report an economical, time-efficient, and easily scalable method of fabricating nanowires composed of vanadium, chromium, manganese, iron, and cobalt oxides by employing simultaneous block copolymer (BCP) self-assembly and selective sequestration of metal-organic acetylacetonate complexes within one of the BCP blocks. We discuss the mechanism and the primary factors that are responsible for the sequestration and conformal replication of the BCP template by the inorganic material that is obtained after the polymer template is removed. X-ray photoelectron spectroscopy (XPS) and powder X-ray diffraction (PXRD) studies indicate that the metal oxidation state in the nanowires produced by plasma ashing the BCP template closely matches that of the precursor complex and that their structure is amorphous, thus requiring high-temperature annealing in order to sinter them into a crystalline form. Finally, we demonstrate how the developed nanowire array fabrication scheme can be used to rapidly pattern a multilayered iron oxide nanomesh, which we then used to construct a prototype volatile organic compound sensor.

Gold Nanoparticles-Functionalized Cotton as Promising Flexible and Green Substrate for Impedometric VOC Detection.

This work focuses on the possible application of gold nanoparticles on flexible cotton fabric as acetone- and ethanol-sensitive substrates by means of impedance measurements. Specifically, citrate- and polyvinylpyrrolidone (PVP)-functionalized gold nanoparticles (Au NPs) were synthesized using green and well-established procedures and deposited on cotton fabric. A complete structural and morphological characterization was conducted using UV-VIS and Fourier transform infrared (FT-IR) spectroscopy, atomic force microscopy (AFM), and scanning electron microscopy (SEM). A detailed dielectric characterization of the blank substrate revealed interfacial polarization effects related to both Au NPs and their specific surface functionalization. For instance, by entirely coating the cotton fabric (i.e., by creating a more insulating matrix), PVP was found to increase the sample resistance, i.e., to decrease the electrical interconnection of Au NPs with respect to citrate functionalized sample. However, it was observed that citrate functionalization provided a uniform distribution of Au NPs, which reduced their spacing and, therefore, facilitated electron transport. Regarding the detection of volatile organic compounds (VOCs), electrochemical impedance spectroscopy (EIS) measurements showed that hydrogen bonding and the resulting proton migration impedance are instrumental in distinguishing ethanol and acetone. Such findings can pave the way for the development of VOC sensors integrated into personal protective equipment and wearable telemedicine devices. This approach may be crucial for early disease diagnosis based on nanomaterials to attain low-cost/low-end and easy-to-use detectors of breath volatiles as disease markers.

Synthesis of hydrogen bonded copper(II) coordination polymer: Photocatalytic degradation of Rose Bengal dye and luminescent sensing of Hg+2, Cr2O72−, and nitrofurantoin

A new helical coordination polymer, [Cu(Or)(H2O)3]n (KA@CP-ARS) has been synthesized at room temperature and examined using single-crystal X-ray diffraction (SC-XRD) and other analytical techniques. KA@CP-ARS formed 1D helical type structure via coordination bonding as well as a 3D supramolecular network through hydrogen bonding interactions. KA@CP-ARS manifested as a remarkable luminescent sensor for volatile organic compounds (VOCs), 3-Nitrophenol, Cr2O72−, Hg2+, creatinine, nitrofurantoin and sucrose (200 mg/dl) in particular along with the remarkable photocatalytic degradation of Rose Bengal (RB) dye with 96.54% efficiency. Overall this study demonstrates that the synthesized Cu-orotate coordination polymer has good luminescent sensing and catalytic degradation activity, therefore could be employed for a range of applications such as sensing of biomolecules like sucrose and photocatalysis of toxic dyes.

Photothermal-assisted for ultrafast response acetone sensing with ZIF-90/GO coated microfiber long period gratings

Volatile organic compound (VOC) sensors have recently been developed with sensitive coating layers to improve their performance. However, there are inevitable trade-offs in the performance of the VOC sensors with sensitive layers. It remains challenge to achieve higher sensitivity, faster response time, working at room temperature and better selectivity at the same time for real-world applications. In this work, we demonstrated a novel photothermal-assisted gas sensor using a microfiber long period grating (LPG) modified with zeolitic imidazolate framework-90 (ZIF-90)/graphene oxide (GO) for enhanced VOC acetone sensing. The GO-isolated ZIF-90 exhibited ultralow conductivity and high porosity, which significantly promoted light-to-heat energy conversion by trapping thermal and minimizing heat loss. Besides, the natural porosity and ultrahigh surface area of the ZIF-90 showed superior molecular adsorption making it a good choice for the acetone-sensitive layer. Based on the porous ZIF-90/GO nanohybrid and photothermal effects, the proposed sensor showed improved performance compared without adding laser towards acetone, with the sensitivity of 26.1 pm/ppm and low limit of detection of 760 ppb. Moreover, the proposed photothermal technology enhanced the response time down to 410 ms without sacrificing sensitivity. Thus, our proposed sensor constitutes a promising platform for effective acetone sensing systems that can be used for environmental monitoring and industry.

Application of Cluster Analysis to Examine the Performance of Low-Cost Volatile Organic Compound Sensors

Airtight energy-efficient buildings of today need efficient ventilation to secure high indoor air quality. There is a need for affordable and reliable sensors to make demand control available in a broad range of ventilation systems. Low-cost metal oxide semiconductor (MOS) volatile organic compound (VOC) sensors offer such a possibility, but they are usually non-selective and react to broad range of compounds. The objective of the present paper was to use cluster analysis to assess the ability of five commercially available MOS VOC sensors to detect pollutants in a residential setting. We studied three scenarios: emissions from people (human bioeffluents), furnishing materials (linoleum), and human activity (surface cleaning with spray detergent). We monitored each scenario with five MOS VOC sensors and a proton-transfer-reaction–time-of-flight mass spectrometer (PTR-ToF-MS). We applied an agglomerative hierarchical clustering algorithm to evaluate the dissimilarity between clusters. Four of the five tested sensors produced signals in agreement with the concentration patterns measured with the PTR-ToF-MS; one sensor underperformed in all cases. Three sensors showed a very similar performance under all emission scenarios. The results showed that the clustering could help in understanding whether a particular sensor matched the intended emission scenario.

Defect engineering of two-dimensional ultrathin Co3O4 nanosheets for wireless and high-performance monitoring of the sensing properties of volatile organic compounds

Volatile organic compounds (VOCs) as serious outdoor and indoor air pollutants have attracted great attention. Many detection technologies of VOCs have been investigated. However, it is challenging to develop an efficient and portable wireless sensor for monitoring VOCs. Here, we proposed a new strategy to obtain a high-performance VOC sensor based on two-dimensional Co3O4 nanosheets (NSs) with numerous oxygen vacancy defects. The Co3O4 NS-30 W sensor detected 200 ppm ethanol and exhibited a high response value (10.70) and fast response and recovery behavior (20 s and 17 s, respectively). The effect of oxygen vacancy defects on the sensitive properties was studied by theoretical calculations on the (110) plane of Co3O4. Furthermore, a unique VOC wireless sensor was fabricated in order to enable wireless early warning from multiple terminals and monitoring of alcohol in exhaled gas. The VOC sensor exhibited a promising potential for precisely monitoring the alcohol consumption of drivers.

Sniffing out a better electronic nose

Recent research on metal halide perovskites points to their promise as sensors for gases and volatile organic compounds in food, healthcare, and other industries.

Metal halide perovskites: A rising platform for gas sensing?

Sensing gases and volatile organic compounds is a highly requested ability in large economic fields, such as the food industry, agriculture, and health care. Depending on the foreseen specific application, electronic noses have to be sensitive, selective, highly reliable, and also robust and cheap. However, it is undoubted that rarely all these characteristics are met simultaneously and for every analyte. The current technology makes large use of metal oxide semiconductors, which exhibit many limitations, for example, in their selectivity and the need for very high temperatures to lower activation energies and reach high sensitivity [A. Dey, Mater. Sci. Eng., B 229, 206 (2018)]. This opens to investigations of further material platforms that may provide enhanced performance. Metal halide perovskites have shown a high sensitivity toward their environment, and the first gas-sensing behavior at room temperature was already demonstrated in 2016 [Fang et al., Sci. Adv. 2(7), e1600534 (2016)]. Recent reports show the huge potential of metal halide perovskites sensors for multiple gases and volatile organic compounds. Here, we will summarize what has been demonstrated until now with a metal halide perovskite and related system. We will discuss the physical mechanisms, which is the basis of sensing, and if these mechanisms have the potential to allow the development of sensors that are highly sensitive, selective, and efficient. Furthermore, we will conclude by giving a prospect for the future of gas sensors based on metal halide perovskites.

Monolayer fullerene network: A promising material for VOCs sensor

Carbon materials hold a great promise for gas sensors due to their diversified dimensionality, tunable structures and easy doping functionalization. Two dimensional polymeric fullerene (2DC60), which was experimentally synthesized recently (Hou et al. Nature 2022, 606, 507), offers a new candidate for gas sensors due to its moderate bandgap and high carrier mobility. Remarkably, the challenging aggregation and restacking issue of conventional 2D materials can be avoided for 2DC60 because of its unique topological structure. In this work, we deliver the first attempt to study the volatile organic compounds (VOCs) sensing capability of 2DC60 by density functional theory (DFT) calculations. Compared with pure C60 nanoclusters, 2DC60 exhibits stronger gas sensing due to formed pore center between C60 nanocages. The quasi-hexagonal 2DC60 (qHP 2DC60) possesses relatively high acetone selectivity while quasi-tetragonal 2DC60 (qTP 2DC60) possesses relatively high ethanol selectivity. B-doping for qHP 2DC60 can significantly facilitate electron transfer and sharply enhance its acetone selectivity. Our theoretical results suggest that 2DC60 is a promising candidate for VOCs sensors, which offers a fresh perspective and opportunity on the application of novel 2DC6.

Si-Doped Nitrogenated Holey Graphene (C2N) as a Promising Gas Sensor for O-Containing Volatile Organic Compounds (VOCs) and Ammonia

Two-dimensional (2D) crystalline materials have been regarded as promising sensor materials due to their large specific surface area, high sensitivity, and low cost. In the present work, based on the density functional theory (DFT) method, the sensor performance of novel silicon (Si)-doped nitrogenated holey graphene (SiC2N) toward five typical VOCs (HCHO, CH3OH, C3H6O, C6H6, and C2HCl3) and ammonia were systematically investigated. The results demonstrated that Si doping could effectively decrease the band gap of C2N and simultaneously provide active sites for gas adsorption. Through comprehensive analyses of adsorption energies and electronic properties, the SiC2N was found to exhibit high selectivity for O-containing VOCs (HCHO, CH3OH, and C3H6O) and NH3 via a covalent bond. Moreover, after the HCHO, CH3OH, C3H6O, and NH3 adsorption, the band gap of SiC2N greatly decreases from 1.07 eV to 0.29, 0.13, 0.25, and 0.12 eV, respectively, which indicated the enhancement the conductivity and enabled the SiC2N to be a highly sensitive resistive-type sensor. In addition, the SiC2N possesses a short recovery time. For instance, the recovery time of HCHO desorbed from SiC2N is 29.2 s at room temperature. Our work anticipates a wide range of potential applications of Si-doped C2N for the detection of toxic VOCs and ammonia, and supplies a valuable reference for the development of C2N-based gas sensors.