As-prepared In2O3 Research Articles

Environmentally friendly synthesis of In2O3 nano octahedrons by cellulose nanofiber template-assisted route and their potential application for O3 gas sensing

Cellulose has recently been utilized as a green and eco-friendly substrate template for synthesizing semiconductor oxide materials. This paper introduces a novel and sustainable method for obtaining In2O3 nano octahedrons, using cellulose nanofibers (CNF) as sacrificial templates. To demonstrate the importance and advantages of the CNF template, a parallel synthesis was conducted under the same conditions, but with no CNF. The as-prepared In2O3 compounds were thoroughly characterized by XRD, SEM, and XPS techniques. The CNF template-assisted route resulted in an approximately 3000 % particle size reduction and a narrow distribution compared to the sample prepared with no CNF as a template. Notably, the sensing performance towards ozone (O3) gas was also substantially enhanced in the CNF template-assisted sample and a significantly higher response (Rg/Ra = 42 @ 70 ppb O3) was observed compared to the In2O3 sample with no CNF (Rg/Ra = 3.5 @ 70 ppb O3). Furthermore, sensors based on CNF-assisted In2O3 octahedra synthesis showed greater selectivity towards O3 than towards NO2, another oxidizing gas, and a relatively lower operation temperature (200 °C). The enhancement in gas sensing properties for O3 detection was attributed mainly to the higher concentration of chemically adsorbed oxygen species and surface defects, such as oxygen vacancies, which were promoted by the reduction in the particle size and the removal of CNF, respectively. The sustainable and CNF template-assisted approach represents a promising result for environmentally-friendly synthesis and advanced gas sensing applications.

MOFs-Derived Fusiform In2 O3 Mesoporous Nanorods Anchored with Ultrafine CdZnS Nanoparticles for Boosting Visible-Light Photocatalytic Hydrogen Evolution.

The development of efficient visible-light-driven photocatalysts is one of the critically important issues for solar hydrogen production. Herein, high-efficiency visible-light-driven In2 O3 /CdZnS hybrid photocatalysts are explored by a facile oil-bath method, in which ultrafine CdZnS nanoparticles are anchored on NH2 -MIL-68-derived fusiform In2 O3 mesoporous nanorods. It is disclosed that the as-prepared In2 O3 /CdZnS hybrid photocatalysts exhibit enhanced visible-light harvesting, improves charges transfer and separation as well as abundant active sites. Correspondingly, their visible-light-driven H2 production rate is significantly enhanced for more than 185 times to that of pristine In2 O3 nanorods, and superior to most of In2 O3 -based photocatalysts ever reported, representing their promising applications in advanced photocatalysts.

Temperature-dependent dual selectivity of hierarchical porous In2O3 nanospheres for sensing ethanol and TEA

Realizing dual gas selectivity on a sensor based on metal oxide semiconductor (MOS) is a meaningful work, but still remains a challenge. In this paper, we reported the synthesis of In2O3 hierarchical porous nanospheres (HPNSs) that showed high sensitivity and dual selectivity to ethanol and trimethylamine (TEA) by controlling the operating temperature. Uniform In(OH)3 nanospheres that assembled with solid nanocubes were prepared in advance via a facile hydrothermal route and then used as precursor for In2O3 by calcinating at different temperatures. At an optimized calcination temperature of 500 °C, In2O3 HPNSs with uniform diameter of about 100 nm, unique micro- and mesoporous structure, and high content of oxygen vacancy (Ov: 45.2 %) were successfully prepared. At the operating temperatures of 240 and 320 °C, the sensor based on as-prepared In2O3 HPNSs (IO-500) showed high sensitivity and excellent selectivity to ethanol and TEA, respectively. Moreover, when the IO-500 sensor was used to detect ethanol and TEA, it also showed some other impressive characteristics, such as fast response speed, perfect response linearity, and good repeatability and stability. The temperature-dependent dual selectivity of the In2O3 HPNSs for ethanol and TEA was discussed.

Sensitive Detection of Methane By Indium Oxide Nanoparticles for Environmental Monitoring System

Introduction and MotivationWith the development of science and technology, the process of industrialization is getting faster and faster, and people's living standards have also increased. However, the emission of gases such as methane has led to the greenhouse effect, which is 25 times [1] that of CO2 with equal molar volume. In addition, methane, as one of the main components of natural gas, is also flammable and explosive. If the gas concentration in the underground operation is too high (>5% [2]), it will be prone to explosion, resulting in casualties and property losses. Therefore, the development of high-performance methane gas sensors is particularly important.In the past few decades, sensors prepared using metal oxide semiconductors (MOS) have been widely used in various application with the advantages of low-cost, easy fabrication and integration, good safety and long service life. Up to now, many kinds of MOS have been reported to detect methane, TiO2 [3], SnO2 [4], VO2 [5] and so on. However, there is little literature on the detection of methane by using indium oxide. Indium oxide (In2O3) has been extensively applied to the field of gas sensor as a gas sensing material due to its good catalytic activity and high electric conductivity.In this paper, In2O3 NPs were prepared by co-precipitation method, and their morphology, nanostructure and sensing properties to methane gas were investigated.ExperimentIndium oxide (In2O3) NPs were prepared by the co-precipitation method. Ammonia hydroxide (NH4OH), ethanol and indium nitrate (In(NO3)2·9H2O) were used as raw materials to obtain the precursor, which was calcined in a furnace at 300°C for 2h to get yellow powder. The as-prepared In2O3 NP powder was dissolved in methanol and dropped on Pt interdigitated electrode, which was fabricated with photolithographic techniques. After that, the sensor was annealed at 600℃ for 30 minutes.Surface morphology and structural properties of In2O3 powder were investigated by field-emission scanning electron microscopy (FE-SEM), transmission electron microscopes (TEM) and X-ray diffraction (XRD). The sensing properties of In2O3 NPs toward methane gas were investigated at various operating temperatures (200-500℃). The response of the sensor was defined as R = (Ra-Rg)/Rg, where Ra and Rg represent the resistance of the sensor in air and CH4 gas, respectively.Results and ConclusionsThe SEM image shows that indium oxide is composed of the spherical nanoparticles and the TEM image (Figure 1) confirms its spherical structure with a diameter of about 20 nm. The XRD result reveals that all the diffraction peaks are in good agreement with the cubic structure In2O3 (JCPD 06-0416). No impurity peaks were found, and the diffraction peaks had high diffraction intensity, which indicated that In2O3 had high purity and crystallinity.The response of the In2O3 NP sensor increased and reached a maximum (R=6.81) at 350 ℃ and decreased with the increasing temperature (Figure 2). Therefore, this temperature is optimized and used for subsequent experiments.The higher response compared to other groups means that the prepared sensor has a good potential for the detection of methane. Limit of detection, long-term stability, repeatability and selectivity are also important parameters for a successful sensor. Therefore, we will conduct a number of follow-up experiments to further analyze the performance of In2O3 NP sensor.

Enhanced gas sensing performance based on p-NiS/n-In2O3 heterojunction nanocomposites

Heterostructured semiconductor materials, combining the collective advantages of individuals and synergistic properties, have spurred great interest as a new paradigm toward detecting of volatile organic compounds recently. Direct use of NiS as a sensing material is impractical because the structure of NiS is unstable, exhibiting an undesirable sensing performance. Herein, we firstly report its incorporation into an ethanol gas sensor with a conventional n-type sensitive material of In2O3, and the gas sensing performance of the NiS@In2O3 nanocomposites has been significantly enhanced. Nanofiber-like NiS and In2O3 were fabricated via a synergetic approach of electrospinning and calcination processes. The diameters of crystalline NiS and In2O3 are about 150 nm and 120 nm, respectively. Then, the NiS@In2O3 nanocomposites were prepared via re-calcination of as-prepared NiS and In2O3 nanofibers. The results show that the sensor based on NiS@In2O3 exhibits a detecting limit of as low as 5 ppm and a short response time of 8 s at the optimum temperature of 300 ºC, which outstripped that (13 s) of pristine In2O3 and pure NiS sensors (21 s) for the detection of ethanol gas. The remarkable improvement of sensing performance can be attributed to the p-n heterojunction in multi-component phases of NiS and In2O3.

Enhanced photocatalytic activity of porous In2O3 for reduction of CO2 with H2O

In this paper, a series of indium oxides were prepared by calcining the In(OH)3 precursors, which were synthesized by hydrothermal method using the mixed solution of ethylenediamine (En) and water as a solvent. The morphologies, particle sizes, pore structure, crystallinity and surface defect concentration of these photocatalysts were adjusted by varying the ratio of En to water during the preparation of In(OH)3 precursors. The results revealed that In2O3 photocatalysts obtained from the precursor prepared in En containing solvent exhibited much higher photocatalytic activities for CO2 reduction with H2O when compared to that derived from the precursor prepared in pure water. This result can be ascribed to several reasons as following. Firstly, the En addition with a suitable amount can improve the crystallinity of In2O3 and decrease the surface defect concentration, which obviously depressed the recombination of photogenerated electrons and holes. Also, the addition of En during the preparation of precursor can decrease the particle size, increase specific surface area and pore structure, resulting into the increase of active sites. Finally, the band gap of In2O3 can be slightly narrowed after the addition of En, resulting in enhanced light absorption in the visible region. When the ratio of ethylenediamine to water is 1:1, the as-prepared In2O3 possessing the largest specific surface area and pore volume, enhanced light absorption ability and higher hole–electron separation efficiency, exhibited the highest photocatalytic activity. Under visible light irradiation, the H2, CO and CH4 production rates of 5.3, 8.3 and 27.2 µmol/gcat/h can be achieved, respectively.

Template-free fabrication of hierarchical In2O3 hollow microspheres with superior HCHO-sensing properties

Hierarchical In2O3 hollow microspheres were successfully prepared via a facile and low-cost hydrothermal method. Their morphology and structure were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and the Brunauer-Emmett-Teller (BET) approach. The SEM and TEM results revealed that the as-obtained hollow In2O3 microspheres is composed of In2O3 nanospheres with 200–400 nm in diameter, and the size of In2O3 microspheres is about 2–4 μm. The specific surface area of the as-prepared In2O3 is about 40.94 m2/g. The sensor based on hierarchical In2O3 hollow microspheres displays excellent sensing properties to 10 ppm HCHO, and the optimum operating temperature is relatively low (200 °C). The response value of the as-fabricated sensor to 10 ppm HCHO is about 20. Due to the sensor based on hierarchical In2O3 hollow microspheres has many advantages, such as facile preparation and excellent gas-sensing properties, it has a wide range of prospects in practical applications.

Facile synthesis of In2O3 microcubes with exposed {1 0 0} facets as gas sensing material for selective detection of ethanol vapor

The rational designs of metal oxides with well exposed facets have stimulated tremendous attentions due to their vital importance for practical applications. In2O3 microcubes (In2O3 MCs) were synthesized by a simple hydro-thermal method with cubic structure and high surface area. Various techniques were employed for characterization of the structure and morphology of the as-prepared In2O3 MCs. The as-synthesized In2O3 MCs, when utilized as gas sensing material, exhibited high sensitivity and selectivity towards ethanol vapor. Such outstanding gas sensing performance of In2O3 MCs benefits from their large specific surface area and exposure of {100} facets.

Oxygen vacancies and grain boundaries potential barriers modulation facilitated formaldehyde gas sensing performances for In2O3 hierarchical architectures

The distinctive In2O3 hierarchical architectures are successfully prepared via a facile solution route at room temperature combined with a subsequent thermal treatment. Microstructural characterizations by means of SEM, TEM and XRD indicate the as-prepared In2O3 hierarchical architectures are assembled by nanoparticles and show loose porous surfaces. The room temperature PL spectra and BET surface area analyses demonstrate In2O3 hierarchical architectures possess more oxygen vacancies and larger surface area. To demonstrate potential applications of such hierarchical porous architectures, as-prepared In2O3 samples are fabricated to be gas sensors to investigate their gas sensing properties. The gas sensing tests reveal In2O3 hierarchical architectures exhibit excellent formaldehyde sensing performances with rapid response/recovery behavior (1s/8s), good selectivity and favorable stability for 100ppm formaldehyde (HCHO) at 260°C. The sensitivity of In2O3 hierarchical architectures is about 4 times higher than that of In2O3 nanoparticles. The cooperative effect between oxygen vacancies and grain boundaries potential barriers induced by hierarchical porous architecture contributes to the improvement of gas sensing performances. The favorable gas sensing properties make In2O3 hierarchical architecture becomes a promising material for formaldehyde detection.

Synthesis and photocatalytic properties of In2O3 micro/nanostructures with different morphologies

The special In(OH)3 micro/nanostructures with hollow tube-like, hollow ball-like and rod-like are successfully synthesized by some novel composite soft template methods. The morphologies and sizes of In2O3 micro/nanostructures can be completely preserved after calcinating In(OH)3 precursor. The as-prepared samples were characterized by TEM, FE-SEM, XRD, UV-vis, and BET, respectively. The photocatalytic activity of In2O3 micro/nanostructures with different morphologies was monitored by the degradation of methyl violet aqueous solution under UV-light irradiation. For three In2O3 micro/nanostructures, the hollow tube-like In2O3 exhibits the best photocatalytic activity. The experimental results also demonstrate that the morphologies of as-prepared In2O3 micro/nanostructures exert significant influence on the decolorizing efficiency for methyl violet (MV), which could be attributed to the difference in the amount of light absorption and the specific surface area.

Fabrication and formaldehyde sensing performance of Fe-doped In2O3hollow microspheres via a one-pot method

Pure and Fe-doped In2O3 hollow microspheres (HMSs) constructed from numerous nanoparticles have been successfully synthesized via a simple and efficient one-pot method combined with a subsequent thermal treatment. Various techniques were employed to acquire the crystalline and morphological information of the as-obtained samples. Structural characterization indicated that the as-prepared Fe-doped In2O3 HMSs displayed a porous structure with a coarse surface and a diameter of approximately 1 μm. The lattice constants for In2O3 in the Fe-doped product were slightly smaller than those in the pure one, which could be apparently revealed by XRD results. Furthermore, gas sensing performance of the pure In2O3, Fe-doped In2O3 and pure Fe2O3-based gas sensors to the ppm level of formaldehyde (HCHO) vapor was also systematically investigated at a low operating temperature of 260 °C. It has been demonstrated that the Fe-doped In2O3 sensor showed enhanced sensing properties compared with the pure ones with a response of about 12.9 to 100 ppm of HCHO vapor, as well as good selectivity for indoor carcinogenic gases and long-term stability. The enhanced sensing properties could result from the unique hollow structure with a porous shell and the synergic electronic interaction between the guest α-Fe2O3 dopant and the host In2O3 material.

Effective surface disorder engineering of metal oxide nanocrystals for improved photocatalysis

Metal oxide (MO) semiconductors such as titanium dioxide (TiO2) are often used in many photo-chemical processes (e.g. waste-water remediation). However, their large band gaps limit their catalytic performances. Various techniques have been developed to improve the photocatalytic activity of TiO2 nanocrystals (NCs), e.g., via chemical doping, designing hybrid electronic structures, and creating surface disorders. Unfortunately, these techniques suffered from various disadvantages including complex/expensive operations and still poor photoactivity of modified TiO2 under near-infrared (IR) light (53% of the full solar irradiation). Here, we demonstrate a simple but universal route to introducing continous internal energy levels in MO semiconductors, including TiO2, zinc oxide (ZnO) and indium oxide (In2O3) NCs. This new technique just requires simply heating a mixture of an MO NC with potassium (K). Distingctly from conventional MO NCs, NCs prepared using the present technique were all in black color and able to adsorb nearly full solar spectrum. As-prepared black TiO2 NCs performed >300 times better than their conventional counterparts in the photocatalytic degradation of methylene blue (MB) dye under visible light irradiation. Similar levels of improvements in the photocatalytic performance were also achieved with as-prepared ZnO and In2O3 NCs. In addition, we show how NCs could be changed to black ones with tailored electronic structures. Our results suggested that the improvements in the NC’s photoactivity were mainly attributed to the surface disorder induced, oxygen (O) vacancies and metallic phases likely formed during the reaction process with K.

Facile synthesis and high acetone gas sensing performances of popcorn-like In2O3 hierarchical nanostructures

In2O3 hierarchical nanostructures are successfully synthesized by a facile room temperature solution route and a subsequent annealing treatment. The morphology and structure characterizations by SEM and XRD demonstrate that the as-prepared In2O3 architectures show unique popcorn-like contour and are of similar size about 200–300nm. In addition, the room temperature photoluminescence (PL) spectrum of popcorn-like In2O3 clearly indicates the existence of abundant oxygen vacancies. The gas sensor based on In2O3 architectures exhibits a superior sensitivity, a good selectivity, a rapid response rate and a well stability towards 50ppm acetone gas. The excellent acetone gas sensing properties are predominantly attributed to the synergistic effect of unique popcorn-like hierarchical structures and the oxygen vacancies.

Facile synthesis and excellent formaldehyde gas sensing properties of novel spindle-like In2O3 porous polyhedra

Novel spindle-like In2O3 porous polyhedra are successfully fabricated by a facile solution route at room temperature combined with a subsequent thermal treatment. Such unique architectures are developed for formaldehyde (HCHO) gas detection. Morphology and structure characterizations confirm that the as-prepared nanoparticles-assembled In2O3 polyhedra are composed of two hexagonal pyramids in the form of bottom overlap and present hierarchical porous structure with novel spindle-like morphology. The gas sensors based on spindle-like In2O3 polyhedra exhibit high sensitivity to 20ppm HCHO with very fast response time (1s), recovery time (2s), good selectivity and well stability. The excellent gas sensing properties are predominantly attributed to the unique spindle-like shape and highly porous structure, thus facilitating gas adsorption/desorption and enhancing surface reaction.

Facile synthesis of In2O3 nanoparticles for sensing properties at low detection temperature

In2O3 nanoparticles are successfully prepared via a facile solvothermal method without any templates or surfactants at a rather low temperature (100°C). The results of various physical characterizations revealed that the solvothermal precursor is irregular-shaped and the as-prepared In2O3 samples are constructed from uniform nanoparticles with unique diameter (20–30nm) after calcining. Time-dependent experiment was carried out to understand morphology evolution during the calcining process. The In2O3 nanoparticles as novel gas sensors exhibit fast and high response as well as good selectivity toward NO2 gas at ppb level at a rather low operating temperature (60°C). The sensing process is tentatively explained in terms of the adsorption-desorption mechanism and chemical kinetics theories.

Facile synthesis and enhanced gas sensing properties of grain size-adjustable In2O3 micro/nanotubes

Without accurately controlling the ratio of reactants, indium oxide (In2O3) micro/nanotubes are successfully fabricated by a facile coaxial electrospinning route and a subsequent annealing treatment. The micro/nanotubes consist of In2O3 nanocrystals with primary grain sizes of 10-23nm and present rough surfaces. The grain sizes of In2O3 micro/nanotubes can be adjusted by the calcination temperature. The In2O3 micro/nanotubes present grain size-dependent gas sensing properties. The sensors based on In2O3 micro/nanotubes calcined at 400°C (NT400) show better HCHO gas sensing performances in comparison with the sensors based on In2O3 micro/nanotubes calcined at 600°C (NT600) and 800°C (NT800). The facile fabrication method and excellent gas sensing performances make as-prepared In2O3 micro/nanotubes developed for HCHO gas detection in practice.

Hierarchical nanorod-flowers indium oxide microspheres and their gas sensing properties

In this work, In2O3 microspheres with hierarchical nanostructures were successfully synthesized by solvothermal method in the presence of oleic acid and urea. The as-synthesized samples were characterized by X-ray powder diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM). The results indicate that the synthesized hierarchical In2O3 consists of irregular nanorods. Moreover, the gas sensing properties of as-prepared In2O3 hierarchical microspheres were investigated. It was found that the sensor based on such hierarchical nanostructures exhibited high response and good selectivity to NO2 at 145°C.

Effects of Particle Size on the Gas Sensitivity and Catalytic Activity of In2O3

Nanosized In2O3 powders with different particle sizes were prepared by the microemulsion synthetic method. The effects of particle size on the gas-sensing and catalytic properties of the as-prepared In2O3 were investigated. Reductions in particle size to nanometer levels improved the sensitivity and catalytic activity of In2O3 to i-C4H10 and C2H5OH. The sensitivity of nanosized In2O3 (<42 nm) sensors to i-C4H10, H2 and C2H5OH was 2-4 times higher than that of chemically precipitated In2O3 (130 nm) sensor. A nearly linear relationship was observed between the catalytic activity and specific surface area of In2O3 for the oxidation of i-C4H10 and C2H5OH at 275 °C. The relationship between gas sensitivity and catalytic activity was further discussed. The results of this work reveal that catalytic activity plays a key role in enhancing the sensitivity of gas-sensing materials.

Monodispersed In2O3 mesoporous nanospheres: One-step facile synthesis and the improved gas-sensing performance

Mesoporous In2O3 nanospheres were successfully synthesized by a simple solvothermal route, which was performed without the assistance of any additives or templates. The obtained mesoporous In2O3 nanospheres show high monodispersity with average size about 90nm and pore size about 2–4nm. The optical absorption property of the In2O3 mesoporous spheres was investigated by UV–vis spectroscopy, which indicates that the In2O3 mesoporous spheres are semiconducting with a direct band gap of 3.1eV. The gas sensing performance of the as-prepared In2O3 mesoporous nanospheres was investigated towards a series of typical organic solvents and fuels. For 100ppm of butanol and ethanol, the mesoporous In2O3 demonstrates sensing responses of 59.6 and 29.6, respectively. These values are much higher than those of the reported In2O3-based gas sensors and the In2O3 powder sample with similar size, indicating the highly enhanced gas sensing performance of In2O3 mesoporous nanospheres. The obtained In2O3 mesoporous nanospheres appear to be a promising sensing material for environmental detection application and would also find applications in catalyst, electrode, or related fields.

Vitamin C-assisted synthesis and gas sensing properties of coaxial In2O3 nanorod bundles

In2O3 nanorod bundles with well-designed morphology, hierarchical nanostructure and large specific surface area were quickly prepared via microwave hydrothermal method in the presence of vitamin C. The observations of field emission electron microscopy and transmission electron microscopy revealed that the as-prepared In2O3 samples were constructed from lots of well-aligned nanorods with average diameter of about 50nm. To demonstrate their potential application in detecting harmful gases, these bundle-like In2O3 samples were applied to fabricate gas sensor and their sensing properties were examined. It was found that the sensors based on such novel In2O3 nanorod bundles exhibited high response and excellent selectivity during detecting NO2 gas at the operating temperature of 100°C.