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A TEM image of an extruded pore on the surface of a WO3 NF, (b) a magnified high-resolution TEM image of a crystallized WO3 NF (red dotted box in (a)), (c) selected area electron diffraction (SAED) pattern of WO3 NFs, (d) TEM image of a PS (500)-WO3 NF functionalized with a 0.1 wt% NOGR flake, (e) magnified TEM image of (d), and (f) SAED pattern of a PS (500)-WO3 NF functionalized with 0.1 wt% NOGR flakes with a TEM image of an electron beam illuminating the spot shown in the inset.
Source publication
Tailoring of semiconducting metal oxide nanostructures, which possess controlled pore size and concentration, is of great value to accurately detect various volatile organic compounds in exhaled breath, which act as potential biomarkers for many health conditions. In this work, we have developed a very simple and robust route for controlling both t...
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... TEM (HRTEM) analysis was performed to invest- igate crystallographic structures (Figure 4). The analysis was per- formed on the extruded pore site at the surface of the porous WO 3 NFs (Figure 4a). ...
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... TEM (HRTEM) analysis was performed to invest- igate crystallographic structures (Figure 4). The analysis was per- formed on the extruded pore site at the surface of the porous WO 3 NFs (Figure 4a). The magnified TEM image (dotted red box) revealed that the synthesized porous WO 3 NFs exhibited highly crystallized monoclinic structure with interplanar distances of 3.85 A ˚ , 2.67 A ˚ , and 3.75 A ˚ , which correspond to the crystal planes of (002), ( 202), and (020) (Figure 4b). ...
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... analysis was per- formed on the extruded pore site at the surface of the porous WO 3 NFs (Figure 4a). The magnified TEM image (dotted red box) revealed that the synthesized porous WO 3 NFs exhibited highly crystallized monoclinic structure with interplanar distances of 3.85 A ˚ , 2.67 A ˚ , and 3.75 A ˚ , which correspond to the crystal planes of (002), ( 202), and (020) (Figure 4b). Selected area electron diffraction (SAED) pat- terns of the porous WO 3 NFs were investigated in which the (020), (022), and (411) crystal planes, which correspond to the interplanar distances of 3.75 A ˚ , 2.71 A ˚ , and 1.72 A ˚ , were observed (Figure 4c). ...
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... magnified TEM image (dotted red box) revealed that the synthesized porous WO 3 NFs exhibited highly crystallized monoclinic structure with interplanar distances of 3.85 A ˚ , 2.67 A ˚ , and 3.75 A ˚ , which correspond to the crystal planes of (002), ( 202), and (020) (Figure 4b). Selected area electron diffraction (SAED) pat- terns of the porous WO 3 NFs were investigated in which the (020), (022), and (411) crystal planes, which correspond to the interplanar distances of 3.75 A ˚ , 2.71 A ˚ , and 1.72 A ˚ , were observed (Figure 4c). ...
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... composite of PS (500)-WO 3 NFs with 0.1 wt% NOGR flakes were investigated by TEM (Figures 4d-f). The NOGR flakes, which were prepared with 1-6 layers, were attached to the porous WO 3 NF, as shown in Figure 4d. ...
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... composite of PS (500)-WO 3 NFs with 0.1 wt% NOGR flakes were investigated by TEM (Figures 4d-f). The NOGR flakes, which were prepared with 1-6 layers, were attached to the porous WO 3 NF, as shown in Figure 4d. The magnified image of Figure 4d (red solid box) revealed that the thin layer of NOGR flakes was well-decorated on the porous WO 3 NF (Figure 4e). ...
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... NOGR flakes, which were prepared with 1-6 layers, were attached to the porous WO 3 NF, as shown in Figure 4d. The magnified image of Figure 4d (red solid box) revealed that the thin layer of NOGR flakes was well-decorated on the porous WO 3 NF (Figure 4e). The physical contact by anchor- ing the two-dimensional structure of NOGR flakes on the porous WO 3 NFs can lead to the functionalization of several WO 3 NFs (Supporting Information, Figure S4). ...
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... NOGR flakes, which were prepared with 1-6 layers, were attached to the porous WO 3 NF, as shown in Figure 4d. The magnified image of Figure 4d (red solid box) revealed that the thin layer of NOGR flakes was well-decorated on the porous WO 3 NF (Figure 4e). The physical contact by anchor- ing the two-dimensional structure of NOGR flakes on the porous WO 3 NFs can lead to the functionalization of several WO 3 NFs (Supporting Information, Figure S4). ...
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... magnified image of Figure 4d (red solid box) revealed that the thin layer of NOGR flakes was well-decorated on the porous WO 3 NF (Figure 4e). The physical contact by anchor- ing the two-dimensional structure of NOGR flakes on the porous WO 3 NFs can lead to the functionalization of several WO 3 NFs (Supporting Information, Figure S4). The characteristic SAED pat- tern was obtained with the composite of PS (500)-WO 3 NFs with 0.1 wt% NOGR flakes, which showed the hexagonal pattern of a crystallite graphene structure 35 (Figure 4f). ...
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... physical contact by anchor- ing the two-dimensional structure of NOGR flakes on the porous WO 3 NFs can lead to the functionalization of several WO 3 NFs (Supporting Information, Figure S4). The characteristic SAED pat- tern was obtained with the composite of PS (500)-WO 3 NFs with 0.1 wt% NOGR flakes, which showed the hexagonal pattern of a crystallite graphene structure 35 (Figure 4f). ...
Citations
... Therefore, a H 2 S monitoring sensor with a fast response time and low operation temperature is required to prevent gas poisoning. Various semiconductor metal oxide nanomaterials including CuO [10], Fe 2 O 3 [11], In 2 O 3 [12], SnO 2 [13], WO 3 [14], and ZnO [15] have been explored for H 2 S gas sensor applications. While ZnO has been widely used as a gas sensor application due to its properties of non-toxic, low cost, excellent physical/chemical stability, and n-type Materials 2022, 15, 399 2 of 10 wide bandgap of 3.2 eV, the broad/unconfined gas sensing characteristics of the ZnO nanostructure easily tends to lose selectivity for the target gas [16]. ...
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 oxides and metal precursors generate a hollow nanostructure during calcination. The hollow structure of the ZnO-ZnFe2O4 enables an enlarged surface area and increased gas sensing sites. In addition, the interface of ZnO and ZnFe2O4 forms a p-n junction to improve gas response and to lower operation temperature. The optimized ZnO-ZnFe2O4 has shown good H2S gas sensing properties of 84.5 (S = Ra/Rg) at 10 ppm at 250 ∘C with excellent selectivity. This study shows the good potential of p-n junction ZnO-ZnFe2O4 on H2S detection and affords a promising sensor design for a high-performance gas sensor.
... Hence, having potential applications of NH 3 sensors in environmental monitoring, medical diagnosis and industrial area needs detection limit from ppb levels to 1000 ppm. In this respect, semiconducting metal oxides (SMOs) such as SnO 2 [5], WO 3 [6], ZnO [7], TiO 2 [8] etc. gain considerable attention in detecting hazardous gases such as NH 3 , CO, H 2 S, NO 2 etc. Among these SMOs, WO 3 is a n-type semiconductor that possesses wide band gap (2.6-3.3 eV) [9,10] and has stable physiochemical property. ...
Cu doped WO3 (Cu: WO3) films synthesized by chemical spray pyrolysis were explored for Ammonia (NH3) gas sensing. Obtained films were examined by X-ray diffraction technique (XRD), Scanning Electron Microscopy (SEM), UV–Visible spectroscopy (UV), Photoluminescence (PL), Raman and X-ray Photoelectron spectroscopy (XPS). XRD and Raman studies reveals the existence of monoclinic-I (γ-WO3) phase. Lower angle shift of (200) peak was noted in XRD for 3% Cu: WO3 primarily due to tensile strain developed in the WO3 lattice caused by Cu incorporation. SEM morphographs exhibited well defined grains on amalgamation of Cu in WO3 matrix. Photoluminescence studies showed enhancement in the oxygen vacancies upon Cu doping which plays crucial role in improving the sensor response. Gas sensing measurements of the films were performed at an operating temperature of 250 °C towards 1, 3 and 5 ppm concentration of NH3 gas. Incorporation of Cu into WO3 enhanced sensor response and shortened response time compared to pristine WO3 films. 3% Cu doped WO3 showed good sensor response of 1.58 for 5 ppm concentration of NH3.
... Often, the objective of this type of composite is to improve the intensity of the response by the addition of materials with a high surface area. [78][79][80][81] For instance, the composite of ZnO nanofiber and reduced graphene oxide was reported to increase the sensor response from 63.8 for pristine ZnO to 1731.6 for a ZnO-graphene composite with similar selectivity. [80] These composites can also contribute to selectivity by incorporating appropriate material. ...
The selectivity of a sensor is the ability to discriminate the target from the interference molecules and display a target-specific sensor response. It is a critical trait for gas sensors that are used in real-time air pollution control, hazardous materials detection, food quality inspection and personal health monitoring. Attaining high target selectivity ensures that sensors will exhibit accurate information about the existence and concentration of a target gas, which is essential for reliable sensor response. To obtain target selectivity, it is critical to determine the optimum modification technique and receptor materials as well as to understand how each method works and how it could be designed for a specific target. For this purpose, in this review we present the working principles of the three leading chemical modification methods including catalyst decoration, composite formation, and surface functionalization, as well as the selection criteria of various recognition materials. Throughout the report, we offer a rich apprehension of these techniques by providing mechanistic insights, application areas, advantages, disadvantages, and plausible applications for the invention of the target-specific gas sensors.
... Copyright 2009 ACS; (i) Reprinted with the permission from [28]. Copyright 2019 Elsevier; (b) Reprinted from [29]; (c-e) Reprinted from [30]. ...
Electrospun metal oxide nanofibers, due to their unique structural and electrical properties, are now being considered as materials with great potential for gas sensor applications. This critical review attempts to assess the feasibility of these perspectives. The article in Part 1 discusses the basic principles of electrospinning and the features of the formation of metal oxide nanofibers using this method. Approaches to optimization of nanofibers’ parameters important for gas sensor application are also considered.
... There have been many reports on the application of graphene in gas sensors, including pure graphene [23][24][25][26] and graphene composite materials [27][28][29][30][31]. There are many factors affecting graphene-based sensors, including: synthetic method [32-34], chemical structure [35][36][37], interlaminar structure [34,38], testing environment [39][40][41][42], and surface properties [43][44][45][46][47]. Due to the π-π accumulation and Van Der Waals force binding between graphene, the 2D graphene nanocomposites tend to agglomerate, resulting in the reduction of specific surface area [48][49][50]. ...
Air pollution is becoming an increasingly important global issue. Toxic gases such as ammonia, nitrogen dioxide, and volatile organic compounds (VOCs) like phenol are very common air pollutants. To date, various sensing methods have been proposed to detect these toxic gases. Researchers are trying their best to build sensors with the lowest detection limit, the highest sensitivity, and the best selectivity. As a 2D material, graphene is very sensitive to many gases and so can be used for gas sensors. Recent studies have shown that graphene with a 3D structure can increase the gas sensitivity of the sensors. The limit of detection (LOD) of the sensors can be upgraded from ppm level to several ppb level. In this review, the recent progress of the gas sensors based on 3D graphene frameworks in the detection of harmful gases is summarized and discussed.
... 20 Furthermore, multiple exciton generation, sensitization, and tandem approach play a significant part in concentrating the solar light and consequently improving the efficiency of PV solar cell. [21][22][23][24] Sensitizers in PV applications have achieved tremendous attention in recent years. 25,26 Depending upon unique electrochemical and photophysical properties, organic sensitizers are widely employed in PVs. ...
In this work, a new organic compound (K-Azo) was introduced to enhance the electrical and optical performance of graphene oxide (GO) and reduced GO (rGO) nanostructured films. The improved and modified chemical vapour method was employed for the synthesis of GO and rGO. The photophysical characterization of thin films was performed by applying analytical techniques including X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy, ultraviolet-visible, and Raman spectroscopy. The electrical properties (I-V characteristic) of GO and rGO thin films displayed higher conductivity which was 4.07 × 10 −7 and 1.10 × 10 −3 S/cm, respectively in the presence of organic sensitizer. However, GO and rGO thin films showed 9.91 × 10 −7 and 6.17 × 10 −4 S/cm, respectively in the absence of K-Azo sensitizer. Optical and electrical investigations indicated that the characteristics of GO and rGO were improved due to the presence of organic sensitizer. The long-range π-electron delocalization in organic sensitizer contributed to higher conductivity for potential photovoltaic solar cell applications.
... Thus, high porosity and large pore size are essential for enhancing the gas-sensing performance of mesoporous nanomaterials, which can provide efficacious pathway for gas penetration into the whole sensing layer [29,30]. For instances, Choi et al. prepared WO 3 nanofibers with spherical pores by a spherical polystyrene (PS) colloidal templating route, which showed a significantly enhanced H 2 S response [31]. Kim et al. reported porous WO 3 nanofibers with hierarchically interconnected porosity through dual sacrificial templates including spherical PS colloids and multi-walled carbon nanotubes (MWCNTs), which exhibited excellent acetone response [32]. ...
A facile electrospinning technique combined with varied heating rates was developed to tune the porosity and oxygen vacancy of mesoporous WO 3 nanofibers. The porosity of WO 3 increased as the heating rate increased gradually up to 10 C/min, but decreased after that value because of the destruction of WO 3 fiber-like structure. WO 3 nanofibers with a heating rate of 10 C/min (WO 3-10) thus exhibited the largest pore size and the highest surface area. Simultaneously, as the heating rate increased, the oxygen vacancy concentration increased visibly because of locally lower oxygen partial pressure during the rapider decomposition of organic polymer at higher heating rate. Consequently, the low-temperature NO 2 sensing performances of WO 3 were modulated by the heating rate. The best sensing performances were found for the WO 3-10 nanofibers, displaying the highest response of 101.3 and the shortest response time (125 s)/recovery time (231 s) toward 3 ppm NO 2 at 90 C. These excellent sensing characteristics were attributed to the high gas diffusion coefficient and strong absorbing capability for surface O À 2 species and NO 2 gas molecules, originating from the high porosity, high oxygen vacancy concentration, and high surface area of the WO 3-10 nanofibers.
... Metal-oxide-based semiconducting gas sensors have attracted immense interest owing to their small size, easy and low-cost fabrication, and good sensitivity [10][11][12][13][14][15][16][17][18][19]. There have been several studies on H 2 Ssensing metal oxides, which include WO 3 [20][21][22], SnO 2 [23,24], ZnO [25][26][27], Co 3 O 4 [28], CuO [29,30], and Fe 2 O 3 [31,32]. ...
In this study, the double hydrothermal method is proposed as a facile approach to the synthesis of ZnTe/ZnO core–shell nanorods. The coating thickness of the p-type ZnTe is varied to adjust the junction depth in the n-type ZnO nanorods, and the conductance measurements reveal the change in the conduction path in the heterojunction structures. Structural and chemical investigations conducted using X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy confirm the hetero-nanostructure formation of ZnTe/ZnO. The role of ZnTe in H2S-gas sensing by the ZnO nanorods is discussed. The enhanced sensing performance observed with a thin ZnTe coating confirms the importance of the base resistance of the nano-transducer in achieving high response characteristics. The composite structure also demonstrates a superior sensing performance of good repeatability, stability, linearity, and gas selectivity at temperatures greater than 200 °C.
... Semiconducting metal oxides have brought incredible attention as chemical sensors due to its characteristic resistivity and sensitivity changing features in an ambient environment [1,2]. Being an N-type semiconductor, ZnO has been extensively used as a gas-sensing material owing to its wide band gap of 3.37 eV and high exciton binding energy of 60 meV at ambient temperature [3][4][5][6][7][8][9]. ...
... To achieve this, one needs to control the porosity of sensing materials. Currently, several techniques to introduce porosity in metal oxides have been suggested: such approaches include apoferritin templating [80,81], chitosan templating [82], soft templating [83], and hard templating [84][85][86][87][88][89][90], among many others. Unfortunately, ABO 3 perovskites mainly used in gas-sensing applications are those based on solid-state reactions of precursor powders [44,50] or sputtered films [28,91]. ...
... The thickness of the film was determined to be 192 nm, whereas the thickness of the pore wall was 28 nm. Ideally, even the sizes of pores previously occupied by PS beads are expected to be 40-60% smaller due to shrinkage as PS beads decompose in the temperature range of 325-390 °C [87]. Because of numerous oxygen vacancies in LaFeO 3 , the ratio of adsorbed to lattice oxygen species (O − /O 2− ) was even higher than that of Fe 2 O 3 prepared by a similar technique. ...
Perovskite-type oxides with general stoichiometry ABO3 (A is a lanthanide or alkali earth metal, and B is transition metal) constitute a rich material playground for application as resistive-type gas-sensing layers. Immense interest is triggered by, among other factors, stability of abundant elements (≈ 90% in the periodic table) in this stoichiometry, relatively easy tunability of structure and chemical composition, and their off-stoichiometry stability upon doping. Moreover, their capability to host cationic and abundant oxygen vacancies renders them with excellent electrical and redox properties, and synergistic functions that influence their performance. Herein, we present an overview of recent development in the use of ABO3 perovskites as resistive-type gas sensors, clearly elucidating current experimental strategies, and sensing mechanisms involved in realization of enhanced sensing performance. Finally, we provide a brief overview of limitations that hamper their potential utilization in gas sensors and suggest new pathways for novel applications of ABO3 materials.
