Search Results (24)

Hydrogen (H₂) monitoring demonstrates significant practical importance for safety assurance in industrial production and daily life, driving the demand for gas-sensing devices with enhanced performance and reduced power consumption. This study developed a room-temperature (RT) hydrogen-sensing platform utilizing two-dimensional (2D) Ag-doped SnS₂ nanomaterials activated by light illumination. The Ag-SnS₂ nanosheets, synthesized through hydrothermal methods, exhibited exceptional H₂ detection capabilities under blue LED light activation. The synergistic interaction between silver dopants and photo-activation enabled remarkable gas sensitivity across a broad concentration range (5.0–2500 ppm), achieving rapid response/recovery times (4 s/18 s) at 2500 ppm under RT. Material characterization revealed that Ag doping induced S vacancies, enhancing oxygen adsorption, while simultaneously facilitating photo-induced hole transfer for surface hydrogen activation. The optimized sensor maintained good response stability after five-week ambient storage, demonstrating excellent operational durability. Experimental results further demonstrated that Ag dopants enhanced hydrogen adsorption–activation, while S vacancies improved the surface oxygen affinity. This work provides fundamental insights into defect engineering strategies for the development of optically modulated gas sensors, proposing a viable pathway for the construction of energy-efficient environmental monitoring systems. Full article

The development of state-of-the-art gas sensors based on metal oxide semiconductors (MOS) to monitor hazardous and greenhouse gas (e.g., methane, CH₄, and carbon dioxide, CO₂) has been significantly advanced. Moreover, the morphological and topographical structures of MOSs have significantly influenced the gas sensors by means of surface catalytic activities. This work examines the impact of morphological and topological networked assembly of zinc oxide (ZnO) nanostructures, including microparticles and nanoparticles (0D), nanowires and nanorods (1D), nanodisks (2D), and hierarchical networks of tetrapods (3D). Gas sensors consisting of vertically aligned ZnO nanorods (ZnO–NR) and topologically interconnected tetrapods (T–ZnO) of varying diameter and arm thickness synthesized using aqueous phase deposition and flame transport method on interdigitated Pt electrodes are evaluated for methane detection. Smaller-diameter nanorods and tetrapod arms (nanowire-like), having higher surface-to-volume ratios with reasonable porosity, exhibit improved sensing behavior. Interestingly, when the nanorods’ diameter and interconnected tetrapod arm thickness were comparable to the width of the depletion layer, a significant increase in sensitivity (from 2 to 30) and reduction in response/recovery time (from 58 s to 5.9 s) resulted, ascribed to rapid desorption of analyte species. Additionally, nanoparticles surface-catalyzed with Pd (~50 nm) accelerated gas sensing and lowered operating temperature (from 200 °C to 50 °C) when combined with UV photoactivation. We modeled the experimental findings using a modified general formula for ZnO methane sensors derived from the catalytic chemical reaction between methane molecules and oxygen ions and considered the structural surface-to-volume ratios (S/V) and electronic depletion region width (L_d) applicable to other gas sensors (e.g., SnO₂, TiO₂, MoO₃, and WO₃). Finally, the effects of UV light excitation reducing detection temperature help to break through the bottleneck of ZnO-based materials as energy-saving chemiresistors and promote applications relevant to environmental and industrial harmful gas detection. Full article

Sensors based on nanocomposites of quantum dots (QDs) and wide-gap metal oxides are of exceptional interest for photoactivated detection of toxic and pollutant gases without thermal heating. However, the class of detecting gases has been limited almost exclusively to oxidizing gases like NO₂. Here, we designed a photoactivated sensor for the selective detection of primary alcohols at room temperature using CdSe quantum dots coupled to a wide-gap SnO₂ semiconductor matrix. Our concept of the sensor operations is based on the photochemical reaction of primary alcohols via photoactivated QD-SnO₂ charge transfer and does not involve chemisorbed oxygen, which is traditional for the operation of metal oxide sensors. We demonstrated an efficient sensor response to C₁–C₄ primary alcohols of ppm concentration under photoexcitation with a yellow LED in the absence of a signal from other volatile organic compounds (VOCs). We believe that proposed sensor concept opens up new ways to design photoactivated sensors without heating for the detection of VOCs. Full article

Chemical nanosensors based on nanoparticles of tin dioxide and graphene-decorated tin dioxide were developed and characterized to detect low NO₂ concentrations. Sensitive layers were prepared by the drop casting method. SEM/EDX analyses have been used to investigate the surface morphology and the elemental composition of the sensors. Photoactivation of the sensors allowed for detecting ultra-low NO₂ concentrations (100 ppb) at room temperature. The sensors showed very good sensitivity and selectivity to NO₂ with low cross-responses to the other pollutant gases tested (CO and CH₄). The effect of humidity and the presence of graphene on sensor response were studied. Comparative studies revealed that graphene incorporation improved sensor performance. Detections in complex atmosphere (CO + NO₂ or CH₄ + NO₂, in humid air) confirmed the high selectivity of the graphene sensor in near-real conditions. Thus, the responses were of 600%, 657% and 540% to NO₂ (0.5 ppm), NO₂ (0.5 ppm) + CO (5 ppm) and NO₂ (0.5 ppm) + CH₄ (10 ppm), respectively. In addition, the detection mechanisms were discussed and the possible redox equations that can change the sensor conductance were also considered. Full article

Two-dimensional (2D) materials have emerged as a promising candidate in the chemoresistive gas sensor field to overcome the disadvantages of conventional metal-oxide semiconductors owing to their strong surface activities and high surface-to-volume ratio. This review summarizes the various approaches to enhance the 2D-material-based gas sensors and provides an overview of their progress. The distinctive attributes of semiconductor gas sensors employing 2D materials will be highlighted with their inherent advantages and associated challenges. The general operating principles of semiconductor gas sensors and the unique characteristics of 2D materials in gas-sensing mechanisms will be explored. The pros and cons of 2D materials in gas-sensing channels are discussed, and a route to overcome the current challenges will be delivered. Finally, the recent advancements to enhance the performance of 2D-material-based gas sensors including photo-activation, heteroatom doping, defect engineering, heterostructures, and nanostructures will be discussed. This review should offer a broad range of readers a new perspective toward the future development of 2D-material-based gas sensors. Full article

Chemical nanosensors based on nanoparticles (NPs) of pure tin dioxide (SnO₂) and graphene-decorated tin dioxide were developed and characterized for the detection of pollutant gases. Sensitive layers were prepared by a drop casting method. The photoactivation of the sensors allows for the detection of ultra-low NO₂ concentrations (50 ppb) at room temperature. The sensors show strong responses to NO₂ and weak ones to the other tested polluting gases (CO, CH₄ and CO₂). The effect of humidity and the presence of graphene on the sensors’ response were studied. Full article

Graphene-wrapped ZnO nanocomposites were fabricated by a simple solvothermal technology with a one-pot route. The structure and morphology of these as-fabricated samples were systematically characterized. The adding of graphene enhanced the content of the oxygen vacancy defect of the sample. All gas-sensing performances of sensors based on as-prepared samples were thoroughly studied. Sensors displayed an ultrahigh response and exceptional selectivity at room temperature under blue light irradiation. This excellent and enhanced toluene gas-sensing property was principally attributed to the synergistic impacts of the oxygen vacancy defect and the wrapped graphene in the composite sensor. The photo-activated graphene-wrapped ZnO sensor illustrated potential application in the practical detection of low concentrations of toluene under explosive environments. Full article

Nanocomposites, including nanoparticles of semiconductor metal oxide (MO) and reduced graphene oxide (rGO), are of exceptional interest for light-activated gas sensors functioning without thermal heating. In this paper, we discuss the sensor properties of electrospun ZnO nanofibers and ZnO/rGO composites. The materials were characterized by transmission and scanning electron microscopy (TEM, SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and IR spectroscopy (FTIR). The sensor characteristics were studied when detecting reducing gases CO, H₂, and NH₃ and oxidizing gases NO and NO₂ at 25–150 °C in dark conditions and under UV illumination. ZnO nanofibers and ZnO/rGO composites have no sensitivity when detecting CO, NH₃, and H₂ either in dark conditions or under UV illumination. At T = 25 °C, UV illumination is a necessary condition for the appearance of a sensor response when detecting both NO and NO₂. The increased sensitivity of ZnO/rGO composites when detecting nitrogen oxides at T = 25 °C is discussed in terms of the heterojunction formation. Observed at T = 150 °C, opposite trends in the UV illumination influence on the sensor response toward NO and NO₂ are due to the participation of chemisorbed oxygen in the processes responsible for the sensor response formation when detecting NO. Full article

Photoactivation by UV and visible radiation is a promising approach for the development of semiconductor gas sensors with reduced power consumption, high sensitivity, and stability. Although many hopeful results were achieved in this direction, the theoretical basis for the processes responsible for the photoactivated gas sensitivity still needs to be clarified. In this work, we investigated the mechanisms of UV-activated processes on the surface of nanocrystalline ZnO, In₂O₃, and SnO₂ by in situ mass spectrometry and compared the obtained results with the gas sensitivity to oxygen in the dark and at UV irradiation. The results revealed a correlation between the photoactivated oxygen isotopic exchange activity and UV-activated oxygen gas sensitivity of the studied metal oxides. To interpret the data obtained, a model was proposed based on the idea of the generation of additional oxygen vacancies under UV irradiation due to the interaction with photoexcited holes. Full article

Photoactivated gallium nitride (GaN) nanowire-based gas sensors, functionalized with either bare In₂O₃ or In₂O₃ coated with a nanolayer of evaporated Au (Au/In₂O₃), were designed and fabricated for high-sensitivity sensing of NO₂ and low-power operation. The sensors were tested at room temperature under 265 nm and 365 nm ultraviolet illumination at several power levels and in relative humidity ranging from over 20% to 80%. Under all conditions, photoconductivity was lower in the Au/In₂O₃-functionalized sensors compared to that of sensors functionalized with bare In₂O₃. However, when tested in the presence of NO₂, the Au/In₂O₃ sensors consistently outperformed In₂O₃ sensors, the measured sensitivity being greater at 265 nm compared to 365 nm. The results show significant power reduction (×12) when photoactivating at (265 nm, 5 mW) compared to (365 nm, 60 mW). Maximum sensitivities of 27% and 42% were demonstrated with the Au/In₂O₃ sensors under illumination at (265 nm, 5 mW) for 1 ppm and 10 ppm concentration, respectively. Full article

This work is devoted to the investigation of heterobimetallic Ru(II) complexes as photosensitizers for room-temperature photoactivated In₂O₃-based gas sensors. Nanocrystalline In₂O₃ was synthesized by the chemical precipitation method. The obtained In₂O₃ matrix has a single-phase bixbyite structure with an average grain size of 13–14 nm and a specific surface area of 72 ± 3 m²/g. The synthesis of new ditope ligands with different coordination centers, their ruthenium complexes, and the preparation of heterobimetallic complexes with various cations of heavy and transition metals (Ag⁺, Pb²⁺, or Cu²⁺) is reported. The heterobimetallic Ru(II) complexes were deposited onto the surface of the In₂O₃ matrix by impregnation. The obtained hybrid materials were characterized by X-ray fluorescent analysis, FTIR spectroscopy, and optical absorption spectroscopy. The elemental distribution on the hybrids was characterized by energy-dispersive X-ray spectroscopy (EDS) mapping. The gas sensor properties were investigated toward NO₂, NO, and NH₃ at room temperature under periodic blue LED irradiation. It was identified that the nature of the second binding cation in Ru(II) heterobimetallic complexes can influence the selectivity toward different gases. Thus, the maximum sensor signal for oxidizing gases (NO₂, NO) was obtained for hybrids containing Ag⁺ or Pb²⁺ cations while the presence of Cu²⁺ cation results in the highest and reversible sensor response toward ammonia. This may be due to the specific adsorption of NH₃ molecules on Cu²⁺ cations. On the other hand, Cu²⁺ ions are proposed to be active sites for the reduction of nitrogen oxides to N₂. This fact leads to a significant decrease in the sensor response toward NO₂ and NO gases. Full article

In this work, the photostimulated processes of O₂ and NO₂ molecules with the surface of ZnO under UV radiation were studied by in situ mass spectrometry in the temperature range of 30–100 ${}^{\circ }$C. Nanocrystalline needle-like ZnO was synthesized by decomposition of basic zinc carbonate at 300 ${}^{\circ }$C, and the surface concentration of oxygen vacancies in it were controlled by reductive post-annealing in an inert gas at 170 ${}^{\circ }$C. The synthesized materials were characterized by XRD, SEM, low-temperature nitrogen adsorption (BET), XPS, Raman spectroscopy, and PL spectroscopy. Irradiation of samples with UV light causes the photoabsorption of both O₂ and NO₂. The photoadsorption properties of ZnO are compared with its defective structure and gas-sensitive properties to NO₂. A model of the sensor response of ZnO to NO₂ under UV photoactivation is proposed. Full article

In this work, nitrogen dioxide (NO₂) gas sensors based on zinc oxide nanorods (ZnO NRs) decorated with gold nanoparticles (Au NPs) working under visible-light illumination with different wavelengths at room temperature are presented. The contribution of localized surface plasmon resonant (LSPR) by Au NPs attached to the ZnO NRs is demonstrated. According to our results, the presence of LSPR not only extends the functionality of ZnO NRs towards longer wavelengths (green light) but also increases the response at shorter wavelengths (blue light) by providing new inter-band gap energetic states. Finally, the sensing mechanism based on LSPR Au NPs is proposed. Full article

Because the oxides of nitrogen (NO_x) cause detrimental effects on not only the environment but humans, developing a high-performance NO₂ gas sensor is a crucial issue for real-time monitoring. To this end, metal oxide semiconductors have been employed for sensor materials. Because in general, semiconductor-type gas sensors require a high working temperature, photoactivation has emerged as an alternative method for realizing the sensor working at room temperature. In this regard, titanium dioxide (TiO₂) is a promising material for its photocatalytic ability with ultraviolet (UV) photonic energy. However, TiO₂-based sensors inevitably encounter a problem of recombination of photogenerated electron-hole pairs, which occurs in a short time. To address this challenge, in this study, TiO₂ nanorods (NRs) and Pt nanoparticles (NPs) under a UV-LED were used as an NO₂ gas sensor to utilize the Schottky barrier formed at the TiO₂-Pt junction, thereby capturing the photoactivated electrons by Pt NPs. The separation between the electron-hole pairs might be further enhanced by plasmonic effects. In addition, it is reported that annealing TiO₂ NRs can achieve noteworthy improvements in sensing performance. Elucidation of the performance enhancement is suggested with the investigation of the X-ray diffraction patterns, which implies that the crystallinity was improved by the annealing process. Full article

Prolonged exposure to NO₂ can cause lung tissue inflammation, bronchiolitis fibrosa obliterans, and silo filler’s disease. In recent years, nanostructured semiconducting metal oxides have been widely used to fabricate gas sensors because of their unique structure and surface-to-volume ratio compared to layered materials. In particular, the different morphologies of ZnO-based nanostructures significantly affect the detection property of NO₂ gas sensors. However, because of the large interaction energy of chemisorption (1–10 eV), metal oxide-based gas sensors are typically operated above 100 °C, overcoming the energy limits to attain high sensitivity and fast reaction. High operating temperature negatively affects the reliability and durability of semiconductor-based sensors; at high temperature, the diffusion and sintering effects at the metal oxide grain boundaries are major factors causing undesirable long-term drift problems and preventing stability improvements. Therefore, we demonstrate NO₂ gas sensors consisting of ZnO hemitubes (HTs) and nanotubes (NTs) covered with TiO₂ nanoparticles (NPs). To operate the gas sensor at room temperature (RT), we measured the gas-sensing properties with ultraviolet illumination onto the active region of the gas sensor for photoactivation instead of conventional thermal activation by heating. The performance of these gas sensors was enhanced by the change of barrier potential at the ZnO/TiO₂ interfaces, and their depletion layer was expanded by the NPs formation. The gas sensor based on ZnO HTs showed 1.2 times higher detection property than those consisting of ZnO NTs at the 25 ppm NO₂ gas. Full article