Pure In2O3 Research Articles

Preparation of In2O3@TiO2 core-shell spherical nanocomposites with the enhanced photocatalytic activity under solar light irradiation

In this study, we demonstrate In2O3@TiO2 core-shell spherical nanocomposites prepared by hydrothermal method and sol-gel coating method. The In2O3 particles show quite a uniform part icle size (∼200 nm in diameter) and smooth surface. Porous TiO2 polycrystalline is coated on the surface of In2O3 nanospheres as a shell. The thickness of the shell can be controlled by adjusting the molar rat ios of In to Ti. UV-Vis spectra indicate that the adsorption peaks of pure In2O3 and TiO2 nanospheres are located at 323 and 319 nm, respectively. The surface coating of TiO2 canmake the adsorption of nanocomposites shift to the long wavelength to ∼340 nm. The photocatalytic activities of the pure In2O3, TiO2, and the nanocomposites obtained with different molar rat ios of In to Ti were evaluated by measurement of the degradation concentration of 30 ppm methylene blue (MB). The results show that the nanocomposites show higher photocatalytic performance than the pure oxides. The ratio at 1:10 exhibits the highest reaction rate constant (0.0152 min−1), similar to other nanocomposites but higher than pure In2O3 nanospheres (0.0069 min−1) and TiO2 (0.0058 min−1). This can be attributed to the large surface and tuned band energy structure for enhanced visible light absorption and the effective charge separation at the heterojunction of In 2O3 and TiO2. These findings may benefits to the new developed core-shell material as photocatalysts with enhanced efficiency for environmental applications.

Preparation of Fe-doped In2O3 gas sensing semiconductor by one-step impregnation with enhanced ethanol sensing

Abstract Here we demonstrate high-performance ethanol sensors based on Fe-doped In2O3 mesoporous nanospheres. By using FDU-12 as template via a facile one-step impregnation method Fe-doped In2O3 were synthesized, which display high surface area, uniform shape, ordered mesoporous structure and small particle size. The Fe-doped In2O3 exhibited a larger response to ethanol gases than pure In2O3 under all measured concentrations. Furthermore, the effect of Fe/In molecular ratio on sensing property was investigated by comparing their response. The enhanced sensing properties could result from the unique mesoporous structure and the synergic electronic interaction between the guest Fe dopant and the host In2O3 material.

Metal-Doped In2O3 Nanosphere Arrays with Enhanced Gas-Sensing Property

In2O3 and metal-doped (Ni or Ce) In2O3 mesoporous three-dimensional (3D) nanospheres arrays were synthesized via nanocasting using mesoporous silica as hard templates. Effects of Ni or Ce doping on the structure, optical and gas-sensing properties of the In2O3 nanospheres were investigated. Both the undoped and the doped In2O3 nanospheres showed single-phase structure without any impurity. The nanospheres were about 20[Formula: see text]nm in size and they stacked closely to form rigid 3D mesoporous structure. A change in the value of optical band gap was observed upon metal doping. The room temperature photo luminescence behavior also showed some differences between pure and doped In2O3. Compared with pure In2O3 nanospheres, the metal-doped In2O3 exhibited superior response, fast recovery and good selectivity to ethanol. The enhanced gas-sensing properties might be related to the doping of metal ion and its effective contribution towards the oxygen vacancies, conductivity and crystallite size of the grains.

Discriminative detection of indoor volatile organic compounds using a sensor array based on pure and Fe-doped In2O3 nanofibers

Representative indoor volatile organic compounds (VOCs) such as benzene, xylene, toluene, formaldehyde, and ethanol need to be detected in a highly sensitive and discriminative manner because of their different impact on human health. In this study, pure and 0.05, 0.1, 0.3, and 0.5 at% Fe-doped In2O3 nanofibers were prepared by electrospinning and their gas sensing characteristics toward the aforementioned VOCs were investigated. The doping of In2O3 nanofiber sensor with 0.05 and 0.1 at% Fe shifted the temperature to show the maximum responses to benzene, xylene, and toluene, and reduced responses to ethanol and formaldehyde, thus demonstrating changed gas selectivity. The gas sensing characteristics of 0.5 at% Fe-doped In2O3 nanofiber sensor were substantially different from those of the other sensors. Significantly different gas sensing patterns of pure and Fe-doped In2O3 sensors could be used to discriminate between the five different VOCs at 375 °C and to distinguish between the aromatic and non-aromatic gases at all sensing temperatures. The mechanism underlying the Fe-induced change in gas sensing characteristics has been discussed in relation to the variation of catalytic activity, morphology, oxygen adsorption, and charge carrier concentration.

Controlled growth and characterization of In2O3 nanowires by chemical vapor deposition

The high-crystalline indium oxide (In2O3) nanowires were deposited by chemical vapor deposition (CVD) method on Si (111) substrates using C and In2O3 powders as the raw materials. The morphology, microstructures and the valences analysis of In2O3 nanowires were characterized by XRD, SEM, EDS, XPS and TEM techniques. The length and density of In2O3 nanowires can be effectively controlled by adjusting the experimental parameters. The optimal growth condition is obtained, namely the Au catalyst thickness of 12 nm, growth temperature of 1050 °C and Ar flow rate of 200 sccm. The cubic bixbyite structure as pure In2O3 (space group I a3¯) as well as large amounts of oxygen vacancies can be observed in the deposited In2O3 nanowires. The photoluminescence (PL) spectrum shows an ultraviolet emission peak located at 390.6 nm and two luminescence peaks located at 423.6 nm and 436.5 nm, which can be attributed to the near-band-edge emission and the presence of oxygen vacancy defects in the In2O3 nanowires, respectively.

ZnO-enhanced In2O3-based sensors for n-butanol gas

A series of high-response and fast-response/recovery n-butanol gas sensors was fabricated by adding ZnO to In2O3 in varying molar ratios to form ZnO-In2O3 nanocomposites via a facile co-precipitation hydrothermal method. Morphological characterizations revealed that the shape of pure In2O3 was changed from irregular cubes into irregular nanoparticles, 30–50 nm in size, with the addition of ZnO. Compared with the pure In2O3 gas sensor, the ZnO-In2O3 gas sensor exhibits superior n-butanol sensing performance. With the introduction of ZnO, the response of the sensor to n-butanol was improved from 17 to 99.5 at 180 °C for a [Zn]:[In] molar ratio of 1:1. In addition, the ZnO-In2O3 gas sensors show a reduced optimal working temperature, excellent selectivity to n-butanol, and good repeatability. The response of the ZnO-enhanced In2O3-based sensors showed a strong linear relationship with the n-butanol gas concentration, allowing for the quantitative detection of n-butanol gas.

Core-shell structured TiO2@In2O3 for highly active visible-light photocatalysis

Core-shell structured TiO2@In2O3 with high visible-light photocatalytic activity have been successfully fabricated by solvothermal method. The as-obtained products were characterized by field transmission electron microscopy (TEM), X-ray diffraction (XRD) and UV–visible diffuse reflectance spectra (UV–vis DRS). Structural characterizations demonstrated that the In2O3 layers were comprised of nanocrystallites ca. 14 nm in size and displayed rough surfaces. The UV–vis DRS data showed that In2O3 greatly expanded the visible light absorption band edge of TiO2. The results revealed that the obtained TiO2@In2O3 with core-shell structure showed enhancement of the visible-light photocatalytic activity to degrade methyl orange (MO) comparing with the pure TiO2 and In2O3 products.

Tailorable Morphology of Core–Shell Nanofibers with Surface Wrinkles for Enhanced Gas-Sensing Properties

One-dimensional core–shell nanostructures have attracted considerable attention because of their excellent carrier transport characteristics between core and shell layers. In this work, we report the preparation of surface-wrinkled In2O3@ZnO core–shell nanofibers (IZO CSNFs) in a facile way, where the as-spun polyacrylonitrile/indium nitrate (PAN/In(NO3)3) nanofibers are used as scaffolds directly in subsequent atomic layer deposition process. The thermal decomposition of the PAN can lead to the formation of the wrinkled ZnO shells. Especially, an evolvement has been observed from solid to hollow IZO CSNFs with the increase of shell thickness, where the ZnO thick shell is robust enough and may act as another type of scaffold to tailor their morphologies. Considering the different carrier transport features in various atmospheres, the IZO-x (x is the number of ALD cycles) sensors exhibit a clear shell thickness dependence on their gas-sensing properties compared to the cases of pure In2O3 and ZnO NFs. Furt...

Construction of Co3O4 nanorods/In2O3 nanocubes heterojunctions for efficient sensing of NO2 gas at low temperature

The development of NO2 gas sensor with high sensitivity, low detection limit and high selectivity is highly required. This article reports a NO2 gas sensor based on Co3O4/In2O3 heterojunction structure fabricated by a two-step hydrothermal method. Particularly, morphological and structural analysis of the Co3O4 nanorods/In2O3 nanocubes nanocomposite was examined by SEM, TEM, XRD, EDS and XPS measurements. The Co3O4/In2O3 nanocomposite sensor was tested toward NO2 gas (1–200 ppm) under different operation temperature. The sensor exhibited excellent gas sensing properties for NO2 sensing at an optimal temperature of 150 °C. The corresponding response is 27.9 to 10 ppm NO2 at 150 °C, 1.2 times higher than that of pure In2O3 and 10 times higher than that of pure Co3O4. Moreover, the Co3O4/In2O3 sensor shows sub-ppm level detection ability, good selectivity and long-term stability at low temperature. The enhanced sensing performance can be attributed to the Co3O4/In2O3 heterojunction structure formed at the interfaces of n-type In2O3 nanocubes and p-type Co3O4 nanorods.

Fabrication, characterization and excellent formaldehyde gas sensing of Tb-doped In2O3 beaded-porous nanotubes

The pure and Tb-doped In2O3 beaded-porous nanotubes (BPNTs) are fabricated by simple electrospinning method. The crystal phase, morphology and chemical composition of the obtained samples were analyzed by characteristic techniques (XRD, FE-SEM, TEM, EDS, XPS, etc.). The mechanism of forming BPNTs structure was studied, and phase separation plays a key role in the process of formation. A series of sensing tests toward formaldehyde gas showed that 6 mol% Tb-doped In2O3 BPNTs exhibited the best sensing performance: high response (75–50 ppm), shorter response and recovery times (2 s and 12 s), low limit of detection (LOD, 1.27–100 ppb), good selectivity and long-term stability, etc. The significantly improved gas sensing properties were mainly resulted from their high surface basicity, enriched defects (oxygen vacancies), small crystallite size and complex porous structures.

High response and selectivity of single crystalline ZnO nanorods modified by In2O3 nanoparticles for n-butanol gas sensing

In2O3-nanoparticle-modified single crystalline ZnO nanorods with enhanced gas-sensing performance were prepared using a facile sol-gel and chemical precipitation process. In2O3 nanoparticles obtained good dispersibility and were modified on the surface ZnO nanorods. One-dimensional ZnO nanorods served as a matrix for In2O3 nanoparticles, which effectively restrained the agglomeration of the In2O3 nanoparticles and increased the active sites for the sensing reaction. The sensing performance of as-prepared In2O3/ZnO and ZnO sensors was systematically tested using n-butanol as the probe analyte. Test results revealed the In2O3/ZnO sensor response was 104.3 at a concentration of 100 ppm, 3.5 and 5.3 times higher than that of the pure ZnO and In2O3 sensor, respectively. The influence of added In2O3 on sensing performance of the In2O3/ZnO nanocomposites was discussed. Test results showed that the optimal atomic ratio of indium was 3.3%. The response of the In2O3/ZnO sensor reached 6.1 at a concentration of 1 ppm, suggesting good detection of n-butanol. The In2O3/ZnO sensor displayed rapid response-recovery speed along with good selectivity and stability. A possible sensing mechanism for In2O3/ZnO was thus proposed based on experimental data and band structure analysis.

Facile synthesis of La-doped In2O3 hollow microspheres and enhanced hydrogen sulfide sensing characteristics

The undoped and 1.0–5.0 mol% La–doped In2O3 hollow microspheres have been successfully synthesized via a simple hydrothermal method without template and gas sensor have been fabricated basing on them. The nanostructures and morphologies of the maintained hollow spheres were characterized by various experimental techniques. The gas sensing properties of these hollow microspheres were investigated systematically. The results indicated that among all the samples (pure, 1.0, 3.0 and 5.0 mol% La–doped In2O3), 3.0 mol% La–doped In2O3 exhibited the highest response toward 10 ppm hydrogen sulfide (H2S) at 200 °C, having a response value of 17.8, approximately 4.8 times higher than pure In2O3. Furthermore, excellent selectivity, good repeatability and outstanding long-term stability were also achieved. The significantly enhanced sensing properties to H2S could be attributed to the changes in distribution of different oxygen components, crystallite size and specific surface area caused by La doping.

Highly sensitive and selective formaldehyde gas sensor based on CdO–In2O3 beaded porous nanotubes at low temperature

Pure In2O3 nanowires (PINW) and CdO–In2O3 composited beaded porous nanotubes (CIBPNT) were successfully prepared by conventional electrospinning method and followed by calcination. The peculiar surface morphological images of as-synthesized nanomaterials were observed via scanning electron microscope (SEM) and transmission electron microscopy (TEM) from which we could observe a series of irregular holes distributed on the surface of beaded nanotubes. The inner structure of the samples was investigated using X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results reveal that the element composition of the samples are in conformity with the CdO–In2O3 materials. In addition, the average crystallite size of CIBPNT (17.5 nm) can be estimated from XRD which accords with the TEM images, and XPS analysis supports the oxygen vacancy principle by proving the oxygen vacancies concentration of CIBPNT is more than in PINW. The formaldehyde sensing performances of the samples were evaluated at different temperatures. The result shows that the sensor based on CIBPNT exhibits a excellent response (72–50 ppm formaldehyde) at a low operation temperature of 132 °C, and the value is eight times that of the response of PINW (9 to 50 ppm formaldehyde).The sensor based on CIBPNT could detect 0.1 ppm formaldehyde with a response of 2. In addition, good selectivity and a short response and recovery time (6 s, 12 s) are exhibited. The enhancement of gas sensitivity is attributed to not only the unique beaded shape of hollow and porous 1D nanostructures, but also the high catalytic activity of the CdO additive.

Ultra-sensitive room-temperature H2S sensor using Ag–In2O3 nanorod composites

Ultra-sensitive H2S sensors operated at room temperature were fabricated using Ag–In2O3 nanorod composites synthesized using sol–hydrothermal method followed by NaBH4 reduction process. TEM proved that the In2O3 was nanorod structures of ~ 110 nm in length and ~ 35 nm in diameter. Ag nanoparticles with diameters from 10 to 15 nm homogeneously decorated on the surfaces of the In2O3 naonorods. XRD and XPS analysis proved that the Ag elements existed as zero-valent metallic silver on the surface of the In2O3 nanorods. Ag nanoparticles could enhance the formation of chemisorbed oxygen species and interactions between H2S molecules and oxygen species due to spillover effect, and the electron transfer between Ag and In2O3 nanorods also enhanced the sensing properties. Therefore, the H2S sensors based on the Ag–In2O3 nanorod composites showed significantly improved sensing performance than those based on the pure In2O3 nanorods. The optimized content of Ag nanoparticles is 13.6 wt%. Operated at room temperature, the H2S sensors made of 13.6 wt% Ag–In2O3 nanorod composites exhibited an ultra-high response of 93719 to 20 ppm H2S and a superior detection limit of 0.005 ppm. The sensor also showed good reversibility, good selectivity, excellent reproducibility and stability for detection of H2S gas.

High-temperature electrical and thermal transport behaviors of In2O3-based ceramics by Zn-Sn co-substitution

We report remarkably the enhanced thermoelectric performance of Sn-Zn co-doped In2O3 that were synthesized by a solid-state reaction followed by spark plasma sintering in the mid-temperature range. The X-ray diffraction study indicates that Sn and Zn were successfully co-substituted at the In site without forming any additional phase even at 8% doping concentration. The co-substitution shows a significant increase in the electrical conductivity by band structure modification resulting in a significantly enhanced power factor. The point defect engineering combined with nanostructuring using a high energy ball milling suppressed the lattice thermal conductivity, which eventually resulted in an increased ZT value of 0.32 at 973 K, that is, about 7 times higher than that of pure In2O3. Thus, this study demonstrates the important role of co-substitution in improving the thermoelectric properties of n-type oxides.

Towards high-mobility In2xGa2–2xO3 nanowire field-effect transistors

Recently, owing to the excellent electrical and optical properties, n-type In2O3 nanowires (NWs) have attracted tremendous attention for application in memory devices, solar cells, and ultra-violet photodetectors. However, the relatively low electron mobility of In2O3 NWs grown by chemical vapor deposition (CVD) has limited their further utilization. In this study, utilizing in-situ Ga alloying, highly crystalline, uniform, and thin In2xGa2−2xO3 NWs with diameters down to 30 nm were successfully prepared via ambient-pressure CVD. Introducing an optimal amount of Ga (10 at.%) into the In2O3 lattice was found to effectively enhance the crystal quality and reduce the number of oxygen vacancies in the NWs. A further increase in the Ga concentration adversely induced the formation of a resistive β-Ga2O3 phase, thereby deteriorating the electrical properties of the NWs. Importantly, when configured into global back-gated NW field-effect transistors, the optimized In1.8Ga0.2O3 NWs exhibit significantly enhanced electron mobility reaching up to 750 cm2·V–1·s–1 as compared with that of the pure In2O3 NW, which can be attributed to the reduction in the number of oxygen vacancies and ionized impurity scattering centers. Highly ordered NW parallel arrayed devices were also fabricated to demonstrate the versatility and potency of these NWs for next-generation, large-scale, and high-performance nanoelectronics, sensors, etc.

Highly discriminative and sensitive detection of volatile organic compounds for monitoring indoor air quality using pure and Au-loaded 2D In2O3 inverse opal thin films

The lack of gas selectivity in oxide semiconductor chemiresistors has long been an obstacle to realizing discriminative detection of indoor volatile organic compounds (VOCs) with different health impacts. A simple and reliable algorithm to discriminate between critically harmful aromatic VOCs (benzene, xylene, and toluene) and less harmful ethanol is suggested by the simple combination of sensor signals from pure In2O3 and Au-loaded In2O3 2D inverse opal (IO) thin films prepared by heat-treating the precursor-dipped self-assembled polystyrene templates and Au deposition. The Au-loaded In2O3 IO sensor showed unprecedentedly high responses to 5 ppm ethanol (resistance ratio = 1640.2) and comparably high responses to 5 ppm benzene, p-xylene, and toluene (resistance ratio range of 674.5–1012.9). Such high gas responses were attributed to the periodically porous and thus highly gas-accessible structures, while the clear discrimination between aromatic VOCs and ethanol was achieved by tuning gas selectivity through systematic control of the size, morphology, and loading concentration of Au nano-catalysts. The results of this study can be used for reliable and precise monitoring of indoor air pollutants.

The Fabrication of Au@C Core/Shell Nanoparticles by Laser Ablation in Solutions and Their Enhancements to a Gas Sensor.

A convenient and flexible route is presented to fabricate gold noble metal nanoparticles wrapped with a controllable ultrathin carbon layer (Au@C) in one step based on laser ablation of the noble metal targets in toluene-ethanol mixed solutions. The obtained metal nanoparticles were <20 nm in size after ablation, and the thickness of the wrapped ultrathin carbon layer was 2 nm in a typical reaction. The size of the inner noble metal nanoparticles could be controlled by adjusting the power of laser ablation, and the thickness of the ultrathin carbon layer can be controlled from 0.6 to 2 nm by laser ablation in different components of organic solution. Then the resultant Au@C core/shell nanoparticles were modified on the surface of In2O3 films through a sol-gel technique, and the hydrogen sulfide (H2S) gas-sensing characteristics of the products were examined. Compared to pure and Au-modified In2O3, the Au@C-modified In2O3 materials exhibited a revertible and reproducible performance with good sensitivity and very low response times (few seconds) for H2S gas with a concentrations of 1 to 5 ppm at room temperature. Evidence proved that the ultrathin carbon layer played an important role in the improved H2S sensor performance. Other noble metals wrapped by the homogeneous carbon shell, such as Ag@C, could also be prepared with this method.

A highly sensitive and moisture-resistant gas sensor for diabetes diagnosis with Pt@In2O3 nanowires and a molecular sieve for protection

Sensitive and selective detection of acetone in human exhaled breath plays an important role in the diagnosis of diabetes. However, obtaining a reliable response to ppb levels of acetone and avoiding cross-sensitivity due to the large amount of moisture in exhaled breath are still great challenges. In this work, a type of acetone sensor with ultrahigh sensitivity and moisture resistance is reported. Electrospun In2O3 nanowires with a controllable Pt core (Pt@In2O3 core-shell nanowires) are designed and prepared as sensitive layers. A mesoporous silica molecular sieve is further integrated as the moisture filter layer. The Pt@In2O3 core-shell nanowire-based sensor exhibits a highly improved response compared with a sensor based on pure In2O3 nanowires due to the probable increase in surface resistance and the introduction of p–n junctions after rational design of the structure. In addition, a good performance in terms of the fast dynamic process, selectivity and long-term stability is also achieved, and the detection limit can be as low as 10 ppb, which is much lower than the concentration level of 1.8 ppm in the exhaled breath of diabetic patients. The influence of the large amount of moisture is greatly weakened by using the molecular sieve as a moisture filter layer, leading to much improved sensitivity in clinical sample detection among healthy and diabetic patients. Based on the optimized composite structure of the Pt@In2O3 core-shell nanowire sensor and moisture filter layer, a simple portable sensing prototype is successfully fabricated. The reported Pt@In2O3 core-shell nanowires and the acetone sensing approach open up a new opportunity for a simple, inexpensive, and noninvasive diagnosis of diabetes.

Design of superior ethanol gas sensor based on indium oxide/molybdenum disulfide nanocomposite via hydrothermal route

This paper demonstrates an ethanol gas sensor based on indium oxide/molybdenum disulfide (In2O3/MoS2) nanocomposite via hydrothermal route. The microstructure and micromorphology of In2O3/MoS2 nanocomposite were fully characterized by various analytical techniques. The gas-sensing properties of the In2O3/MoS2 composite were investigated upon exposure to different concentrations of ethanol gas from 1 ppm to 50 ppm at the optimum temperature, and compared with the pristine In2O3 sensors. Owing to the supporting substrate of specific two-dimensional MoS2 nanosheets, the sensor based on In2O3/MoS2 composite exhibit superior gas sensing performance towards ethanol, which outstripped that of pure In2O3 sensor and have potential applications in the detection of ethanol vapors.