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The response curves of (a) neat PANI polymer matrix, (b) 2.5 wt% PANI/h nanofiber, (c) 5 wt% PANI/hollow In2O3 nanofiber, (d) 10 wt% PANI/hollow In2O3 nan wt% PANI/hollow In2O3 nanofiber, (f) 20 wt% PANI/hollow In2O3 nanofiber, and PANI/hollow In2O3 nanofiber composites with exposure of 1 ppm NH3 at room temper The response curves of (a) neat PANI polymer matrix, (b) 2.5 wt% PANI/hollow In 2 O 3 nanofiber, (c) 5 wt% PANI/hollow In 2 O 3 nanofiber, (d) 10 wt% PANI/hollow In 2 O 3 nanofiber, (e) 15 wt% PANI/hollow In 2 O 3 nanofiber, (f) 20 wt% PANI/hollow In 2 O 3 nanofiber, and (g) 25 wt% PANI/hollow In 2 O 3 nanofiber composites with exposure of 1 ppm NH 3 at room temperature. Polymers 2021, 13, x FOR PEER REVIEW 11 of 19
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Hollow indium trioxide (In2O3) nanofibers fabricated via an effectively combined method of electrospinning and high-temperature calcination were coated with nitrogen-doped graphene quantum dots (N-GQDs) prepared by a hydrothermal process through electrostatic interaction. The N-GQD-coated hollow In2O3 nanofibers served as a core for the synthesis o...
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Herein, a facile fabrication process of ZnO-ZnFe2O4 hollow nanofibers through one-needle syringe electrospinning and the following calcination process is presented. The various compositions of the ZnO-ZnFe2O4 nanofibers are simply created by controlling the metal precursor ratios of Zn and Fe. Moreover, the different diffusion rates of the metal ox...
Citations
... Especially for ammonia sensors, much work has been done in recent years, and LOD values have decreased to 4 ppm [94][95][96][97][98][99]. In a recent study, the PANI/N-GQD/hollow In 2 O 3 nanofiber sensor exhibited superior selectivity and reproducibility when subjected to NH 3 concentrations of 1.0 and 2.0 ppm at ambient temperature [100]. This research has successfully obtained outstanding results in detecting 1.0 and 2.0 ppm NH 3 at room temperature, highlighting the potential utilization of the PANI/N-GQD/ hollow In 2 O 3 nanofiber composite sensor as a gas detection material [100]. ...
... In a recent study, the PANI/N-GQD/hollow In 2 O 3 nanofiber sensor exhibited superior selectivity and reproducibility when subjected to NH 3 concentrations of 1.0 and 2.0 ppm at ambient temperature [100]. This research has successfully obtained outstanding results in detecting 1.0 and 2.0 ppm NH 3 at room temperature, highlighting the potential utilization of the PANI/N-GQD/ hollow In 2 O 3 nanofiber composite sensor as a gas detection material [100]. ...
... Indium et al. fabricated a new ternary nanocomposite based on the conducting polymer PANI, hollow In 2 O 3 nanofiber, and N-GQD as a NH 3 gas sensor using in situ chemical oxidative polymerization [124]. The response of the PANI/N-GQD/hollow In 2 O 3 nanofiber sensor, with a 20 wt% loading of N-GQD-coated hollow In 2 O 3 nanofiber, reached 15.2 when exposed to 1 ppm NH 3 , marking an increase of over 4.4 times as compared to the PANI sensor ( Figure 12e). ...
... This superior performance can be attributed to the presence of oxygen-containing defects and the extensive special surface area of N-GQDs, which enhance the contact sites with PANI and provide a considerable number of adsorption sites for NH3 gas. [123]; (e) the response curves of the PANI polymer matrix, 20 wt% PANI/hollow In2O3 nanofiber, and 20 wt% PANI/GQD/hollow In2O3 nanofiber composites with an exposure of 1 ppm NH3 at room temperature [124]. ...
... This enhancement is primarily contributed to the strong synergistic effect and p-n heterojunction between the p-type GQD and the n-type SnO2 and ZnO, effectively amplifying the resistance variation due to the change in oxygen adsorption. [123]; (e) the response curves of the PANI polymer matrix, 20 wt% PANI/hollow In 2 O 3 nanofiber, and 20 wt% PANI/GQD/hollow In 2 O 3 nanofiber composites with an exposure of 1 ppm NH 3 at room temperature [124]. ...
Gas-sensing technology has witnessed significant advancements that have been driven by the emergence of graphene quantum dots (GQDs) and their tailored nanocomposites. This comprehensive review surveys the recent progress made in the construction methods and applications of functionalized GQDs and GQD-based nanocomposites for gas sensing. The gas-sensing mechanisms, based on the Fermi-level control and charge carrier depletion layer theory, are briefly explained through the formation of heterojunctions and the adsorption/desorption principle. Furthermore, this review explores the enhancements achieved through the incorporation of GQDs into nanocomposites with diverse matrices, including polymers, metal oxides, and 2D materials. We also provide an overview of the key progress in various hazardous gas sensing applications using functionalized GQDs and GQD-based nanocomposites, focusing on key detection parameters such as sensitivity, selectivity, stability, response and recovery time, repeatability, and limit of detection (LOD). According to the most recent data, the normally reported values for the LOD of various toxic gases using GQD-based sensors are in the range of 1–10 ppm. Remarkably, some GQD-based sensors exhibit extremely low detection limits, such as N-GQDs/SnO2 (0.01 ppb for formaldehyde) and GQD@SnO2 (0.10 ppb for NO2). This review provides an up-to-date perspective on the evolving landscape of functionalized GQDs and their nanocomposites as pivotal components in the development of advanced gas sensors.
... Figure 12 represents the conduction band (Ec) and the valence band (Ev) energies in N-QGD, the highest occupied (HOMO) and lowest unoccupied (LUMO) molecular orbitals for PANI, as well as the Fermi level energies (Ef) concerning the vacuum in the energetic bandgap structure of PANI/N-GQD nanocomposites. p-type PANI is strongly bonded to n-type N-GQD, providing a p-n junction [159], as seen in Figure 12. In the depletion region, the PANI/N-GQD hetero-junctions form an electronic environment. ...
... Schematic illustration of the p-n hetero-junction and energy band gap structure diagram of PANI/N-GQD (adapted from reference[159]). ...
... The PANI/N-GQDs-based NH3 gas sensor with Ag contact had the highest response with 110.9%, whereas the Al electrode sensor demonstrated a response of 86.9% at a concentration of 1500 ppm at RT[161]. In a recent work reported by Hong et al.[159], PANI/N-GQD/ hollow In2O3 nanofiber composites have been synthesized using in-situ chemical oxidative polymerization. It was used as an electrode material for gas sensors to detect NH3 at concentrations between 0.6 and 2.0 ppm at 25 ℃. ...
This review presents a brief overview of the electrical and gas-sensor properties of polyaniline (PANI) and graphene-based nanocomposites with their application as gas detection materials along with underlying sensing mechanisms. Several studies have shown that graphene-based PANI gas sensors perform remarkably well at ambient temperature, energy efficient, and are inexpensive. The electrical and gas sensing properties of PANI/graphene nanocomposites offer improved responsiveness, durability, and other detection capabilities in sensor-based devices at room temperature. Moreover, the electrical conductivity and gas sensor properties may be controlled by the synthesis methods, and the form and type of graphene. This review provides a new framework for the development of new nanomaterials based on PANI/graphene, which will advance their development and industrialization in the environment.
... In addition, raising the working temperature may impair the gas sensors' appropriateness and dependability, as has been previously noted [6]. Incorporating n-type metal oxide semiconductors, such as In2O3, SnO2, CeO2, and CoFe2O4, into carbon-based materials and CPs (conducting polymers) may increase the sensing capabilities of manufactured nanocomposites [7]. Carbon materials such as CNOs have been identified as possible candidates for gas sensing at room temperature [8]. ...
... Considerable research has been dedicated to developing nanostructured materials that exhibit exceptional gas-sensing properties at low temperatures. Quantum dots are at the forefront of this research due to their small grain size, large surface area-to-volume ratio, and abundant active surface sites [9][10][11][12]. Lead sulfide (PbS) colloidal quantum dots (CQDs), in particular, have been recognized as an excellent material for room temperature NO 2 detection [13][14][15][16], a gas species of great importance in both industrial and biological settings [17]. ...
Colloidal quantum dots (CQDs) are gaining increasing attention for gas sensing applications due to their large surface area and abundant active sites. However, traditional resistor-type gas sensors using CQDs to realize molecule recognition and signal transduction at the same time are associated with the trade-off between sensitivity and conductivity. This limitation has restricted their range of practical applications. In this study, we propose and demonstrate a monolithically integrated field-effect transistor (FET) gas sensor. This novel FET-type gas sensor utilizes the capacitance coupling effect of the CQD sensing film based on a floating gate, and the quantum capacitance plays a role in the capacitance response of the CQD sensing film. By effectively separating the gate sensing film from the two-dimensional electron gas (2DEG) conduction channel, the lead sulfide (PbS) CQD gate-sensitized FET gas sensor offers high sensitivity, a high signal-to-noise ratio, and a wide range, with a real-time response of sub-ppb NO2. This work highlights the potential of quantum dot-sensitized FET gas sensors as a practical solution for integrated gas sensor chip applications using CQDs.
... Hollow indium trioxide nanofibers were fabricated by Hong et al. (2021) via a combination of electrospinning and high-temperature calcinations. Then these were coated with nitrogen-doped graphene QDs (N-GQDs). ...
Quantum dots (QDs) are potential agents for solar energy conversion due to their size-dependent optoelectronic properties. QD-sensitized solar cells (QDSSCs) are potential candidates to meet the growing demand for clean energy due to facile and low-cost fabrication techniques. High performance is expected in this type of solar cell architecture due to multiple exciton production and energy bandgap tuning in QDs. Various types of QDs have been explored, such as CdS/CdSe, CuInS2, PbS, Zn-Cu-In-Se and perovskite QDs (PQDs). Among all QDs, Cd chalcogenide-based sensitizers, especially CdS and CdSe (CdTe) are the preferred choices for solar cell devices due to easy fabrication, low cost, and performance. This chapter focuses on advances in QDSSCs like cosensitization of CdS/CdSe, introduction of passivation layer (ZnS), annealing temperature, counter electrode modification (Cu2S, CoS, and composites of Cu2S/rGO), polysulfide electrolyte modification, doping of QDs (e.g., Mn), and use of a wide bandgap semiconductor (TiO2/ZnO) to enhance the photon conversion efficiency (PCE). Additionally, PQDs and silicon tandem solar cells exhibit potential characteristics such as low production cost, high PCE (29.5%), and suitable architecture for large-scale production. Here, QDs sensitized solar cells, mechanism, working principle, unique properties, Cd chalcogenide-based, perovskite-based, and other QDs-based solar cells and recent modifications to enhance the PCE are reported.
... When the sensor was exposed to NH 3 , NH 3 capture the proton from PANIH + , converting PANI from conductive emeraldine salt to non-conductive emeraldine base [70]. Thus, from above discussions, it can be observed that work function of the material, porosity, morphology, composition of the material, specific surface area and heterojunction properties etc. are responsible for ultrasensitive toxic gas sensing and response-recovery properties at RT. PANI/Nitrogen doped-Graphene Quantum Dots (GQD)/hollow In 2 O 3 nanofiber ternary composites showed high sensitivity towards NH 3 due to the increased surface area and heterojunction effects [72]. ...
Nanocrystalline metal oxide thin films offer toxic gas sensing with higher sensitivity at lower temperature compared to their bulk counter parts leading to miniaturization of the sensors, making them wearable and easily portable for field trials without compromising on the sensitivity, but aided with improved selectivity. Nanomaterial of different size, morphology, geometry, preparation methods and composition play an important role in sensitivity, selectivity, response time and stability of the sensor. Although there are many reports about nanostructured materials for toxic gas sensing, they lack commercialization due to reliability issues. While some reviews have focused on toxic gas sensors based on macro and nanostructured materials which work at elevated temperatures and/or for a specific gas species, this review presents the systematic advances of room temperature operating sensors and their toxic gas sensing mechanism based on design of nanostructured metal oxide semiconductors and heterostructures, with insights into their high sensitivity, selectivity and reliability. Recent studies on room temperature operating trace gas sensors (for NH3, H2S, H2, NO2 and SO2) based on nanostructured semiconducting materials and their composites in the chemiresistive mode are discussed. The roles of nanocrystallite size, morphology, surface adsorbed species, surface charge depletion layers and heterostructure interfaces of metal oxide semiconductors and their composite materials for reliable room temperature gas sensing are discussed. The article concludes with current status and future scope for optimizing the nanostructures and their heterostructure interfaces for specific gas sensing at room temperature with an understanding of the various physicochemical properties involved in enhancing the sensitivity, selectivity, stability and commercial viability.
... The sensors developed on ZnO: GQDs were found to have the best NH 3 vapour selectivity. Hong et al. [148] described the production of N-doped graphene quantum dots (N-GQDs) by a hydrothermal procedure by electrostatic interaction and were coated on hollow indium trioxide (In 2 O 3 ) nanofibers made via an efficient combination of electrospinning and high-temperature calcination. Figure 5 [148] shows the schematic diagram of the sensing mechanism of these prototypes. ...
... Hong et al. [148] described the production of N-doped graphene quantum dots (N-GQDs) by a hydrothermal procedure by electrostatic interaction and were coated on hollow indium trioxide (In 2 O 3 ) nanofibers made via an efficient combination of electrospinning and high-temperature calcination. Figure 5 [148] shows the schematic diagram of the sensing mechanism of these prototypes. The nanofiber sensor was designed to find NH3 gas in a concentration range from 0.6 ppm to 2.0 ppm at ambient temperature to determine the sensing performance of the composite sensor fabricated for the analysis of human breath and kidney diseases. ...
... The room temperature highly sensitive ammonia gas sensor is based on polyaniline and nitrogen-doped graphene quantum dot-coated hollow indium oxide nanofiber composite. Polymers, 13 (21), p. 3676 [148]. ...
The employment of graphene for multifunctional uses has been a cornerstone in sensing technology. Due to its excellent electrochemical properties, graphene has been used in its pure and composite forms to detect target molecules over a wide range of surfaces. The adsorption process on the graphene-based sensors has been studied in terms of the change in resistance and capacitance values for various industrial and environmental applications. This paper highlights the performance of graphene-based sensors for detecting different kinds of domestic and industrial gases. These graphene-based gas sensors have achieved enhanced output in terms of sensitivity and working range due to specific experimental parameters, such as elevated temperature, presence of particular gas-specific layers and integration with specific nanomaterials that assist with the adsorption of gases. The presented research work has been classified based on the physical nature of graphene used in conjugation with other processed materials. The detection of five different types of gases, including carbon dioxide (CO2), ammonia (NH3), hydrogen sulphide (H2S), nitrogen dioxide (NO2) and ethanol (C2H5OH) has been shown in the paper. The challenges of the current graphene-based gas sensors and their possible remedies have also been showcased in the paper.
... Polyaniline (PANI)/N-doped GQD/hollow In 2 O 3 NF composites are new ternarysensing compounds synthesized for NH 3 gas sensing [97]. Figure 9 shows the characterization of N-doped GQD. ...
... (a) TEM image; (b) particle size distribution; (c) Raman spectrum of N-GQD[97]. ...
... Schematic representation of the sensing mechanism of PANI/GQD/hollow In2O3 NF composite to NH3 gas[97]. ...
Quantum dots (QDs) are used progressively in sensing areas because of their special electrical properties due to their extremely small size. This paper discusses the gas sensing features of QD-based resistive sensors. Different types of pristine, doped, composite, and noble metal decorated QDs are discussed. In particular, the review focus primarily on the sensing mechanisms suggested for these gas sensors. QDs show a high sensing performance at generally low temperatures owing to their extremely small sizes, making them promising materials for the realization of reliable and high-output gas-sensing devices.
... These results revealed that the sensing properties at room temperature were considerably greater than those of pure PANI and PANI/GNR composite sensor. Recently, Wu et al. [16] applied a high special surface area hollow In 2 O 3 nanofiber, nitrogen-doped graphene quantum dot (N-GQD), and PANI to synthesize a ternary composite. Their results revealed that the sensing properties of composite sensor at room temperature were greater than those of PANI/hollow In 2 O 3 nanofiber composites. ...
... The response values of pure PANI, PANI/hollow In 2 O 3 nanofiber, and PANI/hollow C#In 2 O 3 nanofiber sensors were about 3.6, 11.2, and 18.2, respectively. The response value of the previous investigation using PANI/N-GQD/hollow In 2 O 3 nanofiber was 15.6 [16]. It is clear that the surface coated by a thin carbon layer showed a better gas sensing property. ...
Hollow carbon-coated In2O3 (C#In2O3) nanofibers were prepared using an efficiently combined approach of electrospinning, high-temperature calcination, and hydrothermal process. The polyaniline (PANI)/hollow C#In2O3 nanofiber composites were synthesized used hollow C#In2O3 nanofibers worked as a core through the in situ chemical oxidative polymerization. The morphology and crystalline structure of the PANI/hollow C#In2O3 nanofiber composite were identified using wide-angle X-ray diffraction and transmission electron microscopy. The gas-sensing performances of the fabricated PANI/hollow C#In2O3 nanofiber composite sensor were estimated at room temperature, and the response value of the composite sensor with an exposure of 1 ppm NH3 was 18.2, which was about 5.74 times larger than that of the pure PANI sensor. The PANI/hollow C#In2O3 nanofiber composite sensor was demonstrated to be highly sensitive to the detection of NH3 in the concentration range of 0.6~2.0 ppm, which is critical for kidney or hepatic disease detection from the human breath. This composite sensor also displayed superior repeatability and selectivity at room temperature with exposures of 1.0 and 2.0 ppm NH3. Because of the outstanding repeatability and selectivity to the detection of NH3 at 1.0 and 2.0 ppm confirmed in this investigation, the PANI/hollow C#In2O3 nanofiber composite sensor will be considered as a favorable gas-sensing material for kidney or hepatic disease detection from human breath.
