In2O3 nanosheets array directly grown on Al2O3 ceramic tube and their gas sensing performance

Arrayed In₂O₃ nanosheets were synthesized directly via a two-step solution approach on an Al₂O₃ ceramic tube. Their morphology and structure were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV–Vis absorption spectroscopy, and scanning electron microscopy (SEM). The results reveal that the length of each nanosheet is about 1 µm, the width of the bottom of nanosheet is about 200 nm. Importantly, the In₂O₃ nanosheets with large specific surface area possess highly sensing performance for ethanol detection. The response value to 100 ppm ethanol is about 45 at an operating temperature of 280 °C, and the response and recovery time are extremely short. It is expected that the directly grown In₂O₃ nanosheets with large specific surface area and excellent sensing properties will become a promising functional material in monitoring and detecting ethanol.     

Gold Sensitized In2O3 nanocubes for ppb level NO2 gas sensing

Hydrothermally synthesized In₂O₃ nanocubes were sensitized with Au and gas sensing performance is analyzed. The Au sensitization was done using sputtering and gas sensing performance is studied as function of different sputtering time. The catalytic activity of Au particles on In₂O₃ films increases with the sputtering time but acquires saturation at high sputtering time. The Au sensitization with sputtering time of 5 s was found to show improved sensor response (R_g/R_a) of 8435 than the sensor response of 6876 for pure In₂O₃ film. The improved sensor response was attributed to the catalytic activity of Au particles on the In₂O₃ film surface. In addition, Au sensitized In₂O₃ also demonstrates the sensor response at 60 ppb.     

Ethanol sensing properties of networked In2O3 nanorods decorated with Cr2O3-nanoparticles

In₂O₃ nanorods decorated with Cr₂O₃ nanoparticles were synthesized by thermal evaporation of In₂S₃ powder in an oxidizing atmosphere followed by solvothermal deposition of Cr₂O₃ and their ethanol gas sensing properties were examined. The pristine and Cr₂O₃-decorated In₂O₃ nanorods exhibited responses of ~524% and ~1053%, respectively, to 500-ppm ethanol at 200 °C. The Cr₂O₃-decorated In₂O₃ nanorod sensor showed stronger electrical response to ethanol gas at 200 °C than the pristine In₂O₃ nanorod counterpart. The former also showed faster response and recovery than the latter. The pristine and Cr₂O₃-decorated In₂O₃ nanorod sensors showed the strongest response to ethanol gas at 250 and 200 °C, respectively. The Cr₂O₃-decorated In₂O₃ nanorod sensor showed selectivity for ethanol gas over other reducing gases. The underlying mechanism for the enhanced response, sensing speed and selectivity of the Cr₂O₃-decorated In₂O₃ nanorod sensor for ethanol gas is discussed.     

Cu2O quantum dots modified by RGO nanosheets for ultrasensitive and selective NO2 gas detection

Real-time monitoring of trace NO₂ emission has been an emerging challenge in environment and health sectors lately. Aiming to overcome this challenge, NO₂ gas sensors based on cuprous oxide quantum dots (Cu₂O QDs) anchored onto reduced graphene oxide (RGO) nanosheets serving as a sensitive layer were prepared in this report. Apart from a series of purposive measurements, various characterization techniques such as XRD, Raman, XPS and TEM were employed as well to assist the exploration of sensors performance to NO₂ gas. The experimental results revealed a 580% response enhancement for prepared RGO/Cu₂O sensors compared with pure RGO counterparts, as well as an excellent selectivity. In a specific experiment, the sensing response attained 4.8% and 29.3% toward 20 ppb and 100 ppb NO₂ respectively at 60 °C, which was larger than most Cu₂O based resistive gas sensors. Moreover, further subtle modulation of this RGO/Cu₂O nanocomposites led to a preferable room-temperature response of 37.8% toward 100 ppb NO₂, which also offered a favorable stability of 98.1% response retention after four exposures within ten days. The obtained results imply that the prepared RGO/Cu₂O QDs sensors possess a competitive capability of trace NO₂ detection.     

Enhanced NO2 gas sensor device based on supramolecularly assembled polyaniline/silver oxide/graphene oxide composites

Herein, we report a successful synthesis of supramolecularly assembled polyaniline/silver oxide/graphene oxide composite (PANI/Ag₂O/GO) for enhanced NO₂ gas sensing application. The PANI/Ag₂O/GO composite was synthesized by facile stirring followed by an ultrasonication process. The prepared material was characterized by different techniques such as x-ray diffraction, field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy and Raman-scattering spectroscopy. The detailed analysis revealed that the average crystallite sizes of PANI/Ag₂O and PANI/Ag₂O/GO composites were found to be 37.37 nm and 41.55 nm, respectively. FESEM and TEM analysis showed coral-like rough-surfaced and extensively agglomerated morphology for PANI and ultrathin flexible sheet-like morphology for GO. Ag₂O nanoparticles with diameters 20–30 nm were well incorporated in the GO sheets and PANI matrix in the case of PANI/Ag₂O/GO composites. The synthesized materials were used to make resistive sensor devices that had a high response to NO₂ gas. The fabricated sensors were examined at various temperatures to obtain the optimal sensing temperature. The fabricated NO₂ gas sensor device based on PANI/Ag₂O/GO composite exhibited a highest sensitivity of 5.85 for 25 ppm at an optimized temperature (100 °C) as compared to the pure PANI (2.5) and PANI/Ag₂O composite (3.25). Further, the fabricated sensor device based on PANI/Ag₂O/GO composite was also examined at different NO₂ gas concentrations.     

NO2 gas sensing properties of Au-functionalized porous ZnO nanosheets enhanced by UV irradiation

Porous ZnO nanosheets were synthesized by thermal evaporation. The morphology, crystal structure, and sensing properties of the ZnO nanosheets to NO₂ gas at room temperature under UV illumination were examined. Au nanoparticles with diameters of a few tens of nanometers were distributed over the ZnO nanosheets. The responses of the multiple networked nanosheet gas sensors were improved 1.8–3.3 fold by Au functionalization at NO₂ concentrations ranging from 1 to 5 ppm. Furthermore, the Au-functionalized ZnO nanosheet gas sensors showed a considerably enhanced response at room temperature under ultraviolet (UV) illumination. In addition, the mechanisms through which the gas sensing properties of ZnO nanosheets are enhanced by Au functionalization and UV irradiation are discussed.     

Fabrication of Ti3C2Tx/In2O3 nanocomposites for enhanced ammonia sensing at room temperature

Ti₃C₂T_x, as a novel two-dimensional material, displays promising prospects in NH₃ detection at room temperature. However, the NH₃ detection limit of pristine Ti₃C₂T_x is still a major research concern. Therefore, it is important to explore new Ti₃C₂T_x-based nanocomposites for better NH₃-sensing performance. In the present experiment, Ti₃C₂T_x/In₂O₃ nanocomposites were successfully synthesized by ultrasonication and characterized by XRD, FESEM, TEM, XPS, and BET. The optimal Ti₃C₂T_x/In₂O₃-based sensor had a high response of 63.8% (30.4 times higher than that of pristine Ti₃C₂T_x) to 30 ppm NH₃ at room temperature. In addition, the optimal Ti₃C₂T_x/In₂O₃-based sensor had stable repeatability, excellent selectivity, and long-term stability, while exhibiting excellent potential for NH₃ detection at room temperature.     

Ultrasensitive NO2 gas sensing performance of two dimensional ZnO nanomaterials: Nanosheets and nanoplates

Highly sensitive NO₂ gas sensors with low detection limit are vital for practical application in air pollution monitoring. Here, the NO₂ gas sensing performance of porous ZnO nanosheets and nanoplates were investigated, with different shape and thickness. It was found that ultra-thin ZnO nanoplates had a higher sensitivity than coral-like ZnO nanosheets. The results were attributed to the high specific surface and very small thickness of the ultrathin nanoplates. The nanoplates have indeed a thickness of 15 nm compared to that of the nanosheets which is 100 nm, and a BET surface area of 75 m²/g, while that of the nanosheets is 6 m²/g. The chemosensor based on ultra-thin ZnO nanoplates shows a response (calculated as the ratio between the resistance of the sensor in the presence of the gas and in its absence) of 76 to 0.5 ppm of NO₂ at 200 °C, with a theoretical detection limit of 3 parts per trillion and a selectivity higher than 760 towards acetone, ethanol, isopropyl alcohol, triethylamine, SO₂ and CO. The specific surface and the small thickness of the ultra-thin nanoplates contribute to its highly improved sensing performance, making it ideal for NO₂ gas sensing.     

Investigation on structural and H2 gas sensing response of AlCdZnNiFe2O4 sensor material

Synthesis of mixed spinel ferrite nanocomposites Al_zCd_yZn_x@Ni_1-x-y-zFe₂O₄ through sol-gel method provides an excellent opportunity to develop a new generation of gas sensors. The single-phase cubic structure was confirmed and the crystallite size increases with increasing the substitution ratios due to the successful integration of the cations into the cubic system without changing the original structure. FTIR analysis was used to identify the stretching bending vibration of NiFe₂O₄ and its functional groups. The replacement of Ni²⁺ ions by Zn²⁺, Cd²⁺, and Al³⁺ ions play a major role in the occupation of Ni²⁺ and Fe³⁺ ions between octahedral B and tetrahedral A sites and it leads to enhance response and recovery times. The FESEM images show an increase in the particle size with polyhedral shape of nanocomposites in the range of 135–342 nm and it is strongly affecting the sensibility of the sensor materials. The nanoparticles were pressed into cylindrical pellets to measure the H₂ gas detection of the novel sensor material. The hydrogen (H₂) gas sensing behavior of sensor material (x + y + z = 0.45) shows the remarkable response times such as 35, 76, and 20 s to the lower concentrations 25, 50, and 100 ppm, respectively at 250 °C.     

Realization of low-temperature and selective NO2 sensing of SnO2 nanowires via synergistic effects of Pt decoration and Bi2O3 branching

Metal oxide semiconductors with branched structures, such as branched nanowires (b-NWs), have promising properties for being used in gas sensors. In this work, we synthesized Pt-decorated Bi₂O₃-branched SnO₂ nanowires (NWs). NO₂ sensing studies revealed the superior capacity of a Pt-decorated Bi₂O₃-branched SnO₂ NWs gas sensor relative to pristine and branched SnO₂ gas sensors, and it worked at near room temperature (50 °C). The increased sensing capacity was related to the synergistic effects of Pt decoration and Bi₂O₃ branching, particularly the morphology of the gas sensor with branched structures, the promising effects of Pt as a noble metal with good catalytic activity, and the generation of homo- and heterojunctions in the Pt-decorated Bi₂O₃-branched SnO₂ NWs gas sensor. The results obtained in this work are useful for design and development of NO₂ gas sensors using a simple strategy, which can be easily extended to various metal oxides.     

In_2O_3纳米陶瓷纤维无纺布的静电纺丝制备及气敏特性研究

采用溶胶-凝胶法结合静电纺丝技术制备了直径20~60 nm的超细氧化铟(In2O3)纳米陶瓷纤维及纳米陶瓷纤维无纺布。采用XRD,IR,SEM,HR-TEM,TGA等分析方法对纳米纤维的形貌和显微结构进行了表征,并研究了其气敏特性。由700℃下煅烧的该超细In2O3纳米纤维所制备的气敏元件具有较好的反应和选择性,对甲醛气体表现出较快的响应和恢复速度。     

Enhanced performance of Zn and Co co-doped MoO3 nanosheets as gas sensor for n-butylamine

High operating temperature of metal oxide sensor devices hinders their practical applications. In order to reduce operating temperature, molybdenum trioxide (MoO₃) nanosheets co-doped with zinc (Zn) and cobalt (Co) were successfully prepared by simple one-step hydrothermal method and characterized by X-ray diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy, and by using WS-30A gas sensor measurement system. The sensor exhibited high response to n-butylamine gas at low temperature. In particular, the response of Zn and Co co-doped MoO₃ sensor was higher than that of pure MoO₃ and retained excellent selectivity of MoO₃ to n-butylamine. Optimum operating temperature gradually decreased with increasing Co and Zn doping amount. Multi-doping system shows great potential for the development and application of sensors,and provides feasible method for reducing their operating temperature of the sensor.     

In2O3 nanocubes/Ti3C2Tx MXene composites for enhanced methanol gas sensing properties at room temperature

Highly active two-dimensional (2D) nanocomposites, integrating the unique merits of individual components and synergistic effects of composites, have been recently receiving attention for gas sensing. In this work, In₂O₃ nanocubes/Ti₃C₂T_x MXene nanocomposites were synthesized using In₂O₃ nanocubes and layered Ti₃C₂T_x MXene via a facile hydrothermal self-assembly method. Characterization results indicated that the In₂O₃ nanocubes with sizes approximately 20–130 nm in width were well dispersed on the surface of layered Ti₃C₂T_x MXene to form numerous heterostructure interfaces. Based on the synergistic effects of electronic properties and gas-adsorption capabilities, In₂O₃ nanocubes/Ti₃C₂Tx MXene nanocomposites exhibited high response (29.6%–5 ppm) and prominent selectivity to methanol at room temperature. Meanwhile, the low detection concentration could be reduced to ppm-level, the response/recovery times are shortened to 6.5/3.5 s, excellent linearity and outstanding repeatability. The strategy of compositing layered MXene with metal oxide semiconductor provides a novel pathway for the future development of room temperature gas sensors.     

Evaluation of GO nanosheets decorated by CuFe2O4 and CdS nanoparticles as photocatalyst for the degradation of dinoseb and imidacloprid pesticides

Pesticides are generally utilized one after another for crop conservation, and this pesticide utilization oftentimes resulting in combined pollution of their residues in the environment. An experimental study was performed on the degradation of dinoseb and imidacloprid. In this research, GO/CuFe₂O₄–CdS nanocomposite was synthesized as a high-efficiency photocatalyst for the process of pesticides pollutants from water. Field Emission Scanning Electron Microscopy with Energy Dispersive X-ray (FESEM-EDX), X-Ray Diffraction (XRD), Vibrating-sample Magnetometer (VSM), and Fourier Transform Infrared spectroscopy (FTIR) analyses are applied to study the properties of this nanocomposite. Dinoseb and imidacloprid as pesticide materials have been utilized as water contaminants and their degradation performance using the synthesized photocatalyst is considered. The effect of initial pH, photocatalyst amount, initial pesticide concentration and degradation time are investigated in this research. The optimum values for both pesticides were as follows: pollutant concentration was 10 ppm, the nanocatalyst amount was 100 mg, irradiation time was 100 min and the pH of pesticide solution equaled to 8. The results showed that the GO/CuFe₂O₄–CdS nanocomposite is the efficient nanocatalyst for degradation of these pesticides.     

Hydrothermally grown ZnO nanorods arrays for selective NO2 gas sensing: Effect of anion generating agents

Vertically aligned ZnO nanorods (ZNRs) arrays with various aspect ratios were deposited by using a simple and inexpensive hydrothermal route at relatively low temperature of 90 °C. The influence of hydroxide anion generating agents in the solution on the growth of ZNRs arrays was studied. Hexamethylenetetramine (HMTA) and ammonia were used as hydroxide anion generating agents while polyethyleneimine (PEI) as structure directing agent. The combined effect of these three agents plays a crucial role in the growth of ZNRs arrays with respect to their rod length and diameter, which controls the aspect ratio. The deposited ZNRs exhibited hexagonal wurtize crystal structure with preferred orientation along (002) plane. The highly crystalline nature and pure phase formation of ZNRs was confirmed from FT-Raman studies. The maximum gas response (R_g/R_a) of 67.5 was observed for high aspect ratio ZNRs, deposited with combination of HMTA, ammonia as well as PEI. The enhancement in gas response can be attributed to high surface area (45 cm²/g) and desirable surface accessibility in high aspect ratio ZNRs. Fast response–recovery characteristics, especially a much quicker gas response time of 32 s and recovery time of 530 s were observed at 100 ppm NO₂ gas concentration.     

Effect of dispersant on chain formation capability of TiO2 nanoparticles under low frequency electric fields for NO2 gas sensing applications

In this study, the effect of Dolapix CE64 as dispersant on the deposition mechanism and chain formation of TiO₂ nanoparticles in the different frequencies under non-uniform AC electric field was investigated. The optical microscope (OM) images of the deposition patterns obtained at the frequency of 1 Hz and 100 Hz in non-aqueous media one containing dispersant and the other being dispersant free revealed that the addition of charge inducing agents (dispersant) has drastically changed deposition mechanism enabling particles to enter the gap leaving the electrodes surfaces uncoated. At 10 kHz, it was observed that by the introduction of Dolapix CE64 the TiO₂ nanoparticles were able to form chain-like patterns along the electric field lines bridging the interelectrode gap. The obtained pearl chain formation (PCF) was employed to fabricate an NO₂ gas sensor which showed a good response to the target gas at 450, 500 and 550 ˚C.     

Thermal annealing induced mazy structure on MoO3 thin films and their high sensing performance to NO gas at room temperature

MoS₂ thin films were prepared by radio frequency (RF) magnetron sputtering and then annealed in air. X-ray diffraction (XRD), field-emission electron scanning microscopy (FESEM) and transmission electron microscopy (TEM) were adopted to characterize the phase structure and surface morphology. Interestingly, upon thermal annealing in air, MoS₂ thin films changed into α-MoO₃ with mazy morphology, and the thin films were covered by MoO₃ nano-sheets with a length of 30–50 nm and a width of 10 nm. α-MoO₃ thin films with mazy morphology showed excellent response to NO gas at room temperature. The response of 5% and 92% was obtained at 5 ppm and 200 ppm, respectively, and the response and recovery times were 30 s and 1500 s. Moreover, the mazy structure of MoO₃ exhibited good selectivity to NO gas with respect to SO₂, NH₃ and H₂ gases. The high surface-to-volume ratio was the dominant factor for high sensing performance.     

Synthesis of porous CeO2-SnO2 nanosheets gas sensors with enhanced sensitivity

Two-dimension (2D) CeO₂-SnO₂ nanosheets with uniform size and small rhombus nanopores were synthesized by the hydrothermal method. The structure of CeO₂-SnO₂ nanosheets was confirmed by X-ray diffraction (XRD), energy dispersive spectrometer (EDS), scanning electron microscopy (SEM), transmission electron microscopy (TEM). The gas sensing behaviors of the fabricated sensors were systematically investigated. Under optimum operating temperature (340 °C), the response to 100 ppm ethanol of the CeO₂-SnO₂ sensor was 44, which was 2 times larger than that of the SnO₂ sensor (about 19). The response and recovery time of the CeO₂-SnO₂ sensor were 25 s and 6 s, while that of the SnO₂ sensor were 29 s and 7 s, respectively. The results revealed that porous CeO₂-SnO₂ nanosheets enhanced the gas sensing properties and shortened the response/recovery time, which were attributed to the porous structure and the effect of the CeO₂-doping. In addition, the ethanol sensing mechanism was carefully discussed.     

2D/2D SnO2 nanosheets/Ti3C2Tx MXene nanocomposites for detection of triethylamine at low temperature

Highly active two-dimensional (2D) nanocomposites have been widely concerned in the field of gas sensors because of their unique advantages and synergistic effects. 2D/2D SnO₂ nanosheets/Ti₃C₂T_x MXene nanocomposites were synthesized by using layered Ti₃C₂T_x MXene and uniform SnO₂ nanosheets by hydrothermal method. Characterization results show that the SnO₂ nanosheets are well dispersed and vertically anchored on the layered Ti₃C₂T_x MXene surface, forming heterogeneous interfaces. Based on the gas-adsorption capabilities and synergistic effects of electronic properties, SnO₂ nanosheets/Ti₃C₂T_x MXene nanocomposites show high triethylamine (TEA) gas-sensing performance at low temperature (140 °C). The sensor responses of the nanocomposites and pure SnO₂ nanosheets to 50 ppm of TEA are 33.9 and 3.4, respectively. An enhancement mechanism for SnO₂ nanosheets/Ti₃C₂T_x MXene nanocomposites is proposed for highly sensitive and selective detection of TEA at low temperature. The combination strategy of two-dimensional metal oxide semiconductor and multilayer MXene provides a new way for the development of cryogenic gas sensors in the future.