Ni-doped In2O3 Research Articles

Photothermal CO2 Hydrogenation to Methanol over Ni-In2O3/g-C3N4 Heterojunction Catalysts

Selective CO2 hydrogenation faces significant technical challenges, although many efforts have been made in this regard. Herein, a Ni-doped In2O3 catalyst supported by g-C3N4 was prepared using the co-precipitation method, and its composition, morphology, specific surface area, and band gap were characterized using TEM, XPS, BET, XRD, CO2-TPD, H2-TPR, UV-Vis, etc. The catalytic hydrogenation reduction of CO2 to produce methanol was tested. Under low-photothermal conditions (1.0 MPa), the hydrogenation of carbon dioxide to methanol is stable, effective, and highly selective, with a spatiotemporal yield of 86.0 gMeOHh−1 kgcat−1, which is 30.9% higher than that of Ni-In2O3 without g-C3N4 loading under the same conditions.

Metal-Organic Framework-Derived Ni-Doped Indium Oxide Nanorods for Parts per Billion-Level Nitrogen Dioxide Gas Sensing at High Humidity.

Detecting parts per billion (ppb)-level nitrogen dioxide in high-moisture environments at room temperature without reducing sensing performance is a well-recognized significant challenge for metal oxide-based gas sensors. In this study, metal-organic framework-derived nickel-doped indium oxide (Ni-doped In2O3) mesoporous nanorods were prepared by a solvothermal method combined with the calcination process. The sensors prepared using the obtained Ni-doped In2O3 nanorods showcase an ultrahigh response, low detection limit, and excellent selectivity. Moreover, the abundant active sites triggered by nickel doping and the capillary enhancement effect caused by mesopores endow the sensor with ppb-level (20 ppb) NO2 detection capability in high-moisture environments (95% RH) at room temperature. With the increase in humidity, the carrier concentration of the sensor increases, and the nitric acid generated by nitrogen dioxide dissolved in water can be completely ionized in water and has high conductivity. Therefore, the gas response of the sensors increases with the increase in humidity. This study establishes a promising approach for the development of trace nitrogen dioxide-sensing devices that are resilient in high-humidity environments.

Metal organic framework-derived porous Ni-doped In2O3 for highly sensitive and selective detection to hydrogen at low temperature

Achieving high sensitivity and selective detection at low temperature is of great significance for hydrogen leakage monitoring and early warning. As a very promising hydrogen sensitive material, In2O3 still faces great challenges in achieving high-performance hydrogen sensing at low temperatures due to inherent defects such as low specific surface area and limited active sites. Here, we prepared Ni-doped In2O3 mesoporous nanomaterials using metal organic framework (MOF) as sacrificial templates. The prepared Ni-doped In2O3 exhibited mesoporous structures with small diameters (2–3 nm), which could be used as effective molecular sieves for the selective detection of hydrogen. The high specific surface area (72.0 m²/g) provided numerous active sites for surface redox reactions, resulting in a remarkable hydrogen sensing response. Notably, gas sensitivity tests demonstrated that the Ni-doped In2O3 gas sensor achieved optimal hydrogen detection performance at 100°C. Particularly, the 3 at% Ni-doped In2O3 nanomaterials exhibited a high response of 12.5–100 ppm hydrogen, along with favorable response/recovery time and a practical limit of detection down to 5 ppm. Furthermore, the Ni-doped In2O3 sensor exhibited excellent reversibility, reproducibility, selectivity and long-term stability. In addition, simulation calculations based on molecular dynamics (MD) and density functional theory (DFT) show that molecular sieve effect is the main reason for the enhanced selectivity, and Ni doping induced oxygen vacancy (OV) defects could enhance gas adsorption. This work could provide technical support for leak detection and warning during hydrogen use, storage and transportation in the future.

NO2 sensing behavior of Ni-doped In2O3 microcubes based chemiresistive gas sensors

NO2 sensing behavior of Ni-doped In2O3 microcubes based chemiresistive gas sensors

Ni-Doped In2O3 Nanoparticles and Their Composite with rGO for Efficient Degradation of Organic Pollutants in Wastewater under Visible Light Irradiation.

The efficient degradation of organic effluent is always desirable when using advanced photocatalysts with enhanced activity under visible light. Nickel-doped indium oxide (Ni-In2O3) is synthesized via a hydrothermal route as well as its composites with reduced graphene oxide (rGO). Facile synthesis and composite formation methods lead to a well-defined morphology of fabricated nanocomposite at low temperatures. The bandgap energy of indium oxide lies in the range of 3.00-4.30 eV. Its high light absorption capacity, high stability, and non-toxicity make it a choice as a photocatalyst that is active under visible light. The transition metal Ni-doping changes the indium oxide's chemical, optical, and physicochemical properties. The Ni-In2O3 and rGO composites improved the charge transport and reduced the charge recombination. The phase analysis of the developed photocatalysts was performed using X-ray diffraction (XRD), and the morphological and structural properties were observed using advanced microscopic techniques (SEM and TEM), while UV-vis and FTIR spectroscopic techniques were used to confirm the structure and optical and chemical properties. The electrochemical properties of the photocatalysts were investigated using cyclic voltammetry (CV), linear sweep voltammetry (LSV), and electrochemical impedance spectroscopy (EIS), and the charge-transfer properties of the obtained photocatalysts and the mechanism of the photocatalytic degradation mechanism of methylene blue, a common dye used in the dyeing industry, were determined.

Fast responding and recovering of NO2 sensors based on Ni-doped In2O3 nanoparticles

In this work, Ni-doped In2O3 nanoparticles were successfully fabricated via a simple metal-organic framework-derived solvothermal method. The synthesized Ni-In2O3 exhibited as ultrafine nanoparticles with an average size of 13 nm. Gas sensing test results demonstrated that the sensor composed of Ni-doped In2O3 (2 mol%) nanoparticles showed fast response/recovery properties, and the response and recovery speeds toward 10 ppm NO2 were 2 and 2 s, respectively. Furthermore, the response value to 10 ppm NO2 was about 70 at the optimum working temperature of 200 °C exhibiting high sensitivity of the sensors. Additionally, the sensor indicated a superior low detection limit of 5 ppb. These characteristics make Ni-doped In2O3 nanoparticles a desiring candidate for rapid detection of NO2. The possible mechanism of enhanced sensing properties was discussed in detail. The Debye-scale nanoparticles furnish abundant adsorption sites. High oxygen vacancies content provides more electrons to accelerate NO2 excitation. Furthermore, the catalytic action of Ni2+ improved the response/recovery speed. The Ni-doped In2O3 nanoparticles are reasonable to be an ideal substitution for fabricating rapid NO2 detection devices in the future.

Dual functionalized Ni substitution in shuttle-like In2O3 enabling high sensitivity NH3 detection

Hetero-atom doping is an effective way to improve the sensing performance of metal oxide semiconductor gas sensors. However, the synergistic effects generated from hetero-atom substitution in In2O3 lattice and the relationship between the fine surface structure and sensing performance is still ambiguous. Here, Ni substitution in shuttle-like In2O3 nanoparticles have been successfully synthesized, and the materials are fabricated as gas sensor to detect ammonia, which is a toxic molecule that is harmful for human healthy. We find the 2 wt% Ni-doped In2O3 NPs exhibit high sensitivity (Ra/Rg = 2569.42 towards 50 ppm NH3 at 140 °C), achieving 34 folds improvement compared with pristine In2O3 NPs. The sensor also shows good long-term stability, high selectivity and fast response/recovery (23/10 s). Detail structural analysis illustrate the substitution of Ni in rh-In2O3 phase and surface O−(ad) species neighboring the substitution sites are recognized as the active sites, and the reactive oxygen species and surface Bronster acidity can be dramatically enhanced after Ni modification, which contribute to the improvement of sensing performance. Our work illustrate the synergistic effects of hetero-atom doping on the sensing performance and pave the way for design of high performance sensing materials.

Ultrahigh methane sensing properties based on Ni-doped hierarchical porous In2O3 microspheres at low temperature

Improving the methane (CH4) sensing characteristics of metal oxide semiconductors is a vital research issue. Herein, we reported the synthesis of porous Ni-doped In2O3 microspheres through an effective solvothermal strategy. The composition and structure of the as-prepared samples as well as the CH4 sensing properties were systematically characterized and investigated. The results demonstrate that Ni-doped In2O3 microspheres possess suitable pore sizes, small particle sizes and oxygen-enriched defects. Compared to bare In2O3 sensor, the sensor based on 5.0 mol% Ni-doped In2O3 (NIO-5.0) shows enhanced response (72.727) to 200 ppm CH4 at relatively low operating temperature (140 °C). Meanwhile, it also displays good selectivity, superior repeatability and long-term stability. The enhanced CH4-sensing performance could be mainly attributed to the stable porous structure and the abundant oxygen vacancy defects induced by Ni doping. Significantly, this work provides a great application prospect of Ni-doped In2O3 porous microspheres for low-temperature and high-response CH4 detection.

Ni/Au bimetal decorated In2O3 nanotubes for ultra-sensitive ethanol detection

In this work, we report on a high-performance ethanol sensor using Au decorated Ni-doped In2O3 nanotubes (NIO-Au NTs). The morphology, microstructure and surface chemistry of pristine In2O3, NIO and NIO-Au NTs have been discussed by the analysis of SEM, TEM, XRD and XPS spectra. Gas sensing test results reveal that NIO-Au NTs with optimal Au decorated concentration of 2 mol% (NIO-2 mol% Au) exhibits the highest response of 167 towards 50 ppm ethanol at lower working temperature (180 °C), which is about 18 times and 13 times higher than pristine In2O3 NTs and Ni-doped In2O3 NTs, respectively. Moreover, some other important gas sensing properties of NIO-2 mol% Au NTs, such as selectivity and stability, have been proved to be greatly improved. The approach and results proposed in this study are attributed to the catalysis of Ni, the spillover effect of Au and formation of Schottky barrier. The proposed functional hybrid nanomaterial-based sensing strategy offers an effective design for highly sensitive and efficient VOC detection devices, which can operate well at low temperatures also.

Role of nickel dopant on gas response and selectivity of electrospun indium oxide nanotubes

It has been demonstrated that the incorporation of Ni into metal oxide-based gas sensors often enhances the sensing performance by increasing the catalytic and heterojunction effects. However, it remains unclear how these two effects work either individually or synergistically in gas sensing. Herein, a series of Ni-doped In2O3 nanotubes (NIO NTs) with different doping concentrations were synthesized through a traditional electrospinning technique. The as-prepared NIO NTs were uniform, with length of micron scale, an average diameter of approximately 70 nm, and a tube wall thickness of approximately 10 nm. Following their incorporation into gas sensors, the NIO NTs often showed improved sensing properties (including excellent response and selectivity) for ethanol vapor compared to the pristine In2O3 NTs. Specifically, at 100 ppm ethanol and 220 °C, the response of NIO-7 NTs (7 mol% Ni) was approximately four-fold higher than that of pristine In2O3 NTs (49.74 vs. 13.39). The gas sensing test results indicated that the improved sensing performance was due to the formation of a heterojunction between In2O3 and NiO, as well as to the catalysis effects of Ni3+ ions. Additionally, simulation results indicated that the improved gas selectivity could be due to the Ni doping-induced change in surface adsorption energies of the tested gases.

High-Performance Thin-Film Transistors with Aqueous Solution-Processed NiInO Channel Layer

We report the aqueous-solution-processed Ni-doped In2O3 (NixIn2–xO3, NiInO) thin-film transistors (TFTs) for the first time. The effect of Ni doping on In2O3 microstructure, oxygen defects, and the electron transport properties are investigated by extensive characterization techniques. Analyses indicate that the oxygen vacancies in NiInO are suppressed as the Ni-doping concentration increases, leading to a lower off-state current and a positive shift in threshold voltage. The optimized NiInO TFTs exhibit a high mobility of 17.71 cm2/(V s), on/off current ratio > 106, threshold voltage of 4.21 V, and superior bias stress stability. The success of Ni doping could be attributed to the small ion radius of Ni, large Lewis acid value, and strong Ni–O bond strength. Therefore, the fabricated NiInO TFT provides a bright path for the development of high-performance oxide TFTs.

Designed synthesis of Ag-functionalized Ni-doped In2O3 nanorods with enhanced formaldehyde gas sensing properties

A new formaldehyde sensing material based on Ag-functionalized Ni-doped In2O3 nanorods was fabricated for easier detection of formaldehyde gas.

Structural and electron transport properties of single-crystalline In2O3 films compensated by Ni acceptors

For device applications, the ability to grow semi-insulating or p-type indium oxide (In2O3) is highly desirable. With this in focus, high quality single-crystalline Ni-doped In2O3 films have been grown by plasma-assisted molecular beam epitaxy and structurally and electrically characterized. Within a concentration range of approximately 1017–1019 cm−3, Ni is fully incorporated in the In2O3 lattice without the formation of secondary phases. At doping higher than roughly 1020 cm−3, secondary phases seem to start forming. No film exhibits p-type conductivity at room temperature. Instead, Ni is shown to be a deep compensating acceptor—confirming theoretical calculations, the effect of which only becomes apparent after annealing in oxygen. Combined Hall and Seebeck measurements reveal the compensation of bulk donors already at low Ni concentrations (∼1018 cm−3) and a residual film conductance due to mainly the interface region to the substrate. This residual conductance is gradually pinched off with increasing Ni doping, eventually resulting in semi-insulating films at excessive Ni concentrations (∼1021 cm−3).

Roles of oxygen vacancy on ferromagnetism in Ni doped In2O3: A hybrid functional study

The roles of oxygen vacancies on the electronic and magnetic properties of Ni doped In2O3 have been studied by first-principles calculations based on hybrid functional theory. Our results predict that the Ni-doped In2O3 system displays a ferromagnetic semiconducting character. However, the presence of oxygen vacancies results in antiferromagnetic coupling between the neighboring Ni pair bridged by an oxygen vacancy. The antiferromagnetic coupling is found to arise from the predominant role of superexchange due to the strong Ni 3d–O 2p hybridization. Consequently, the oxygen vacancies play a key role in the lower saturation magnetization of Ni:In2O3 polycrystalline sample, as observed in experiments.

Effects of rapid thermal annealing on electrical, optical, and structural properties of Ni-doped In2O3 anodes for bulk heterojunction organic solar cells

The authors investigated the effects of rapid thermal annealing (RTA) on the electrical, optical, and structural properties, and work functions of Ni-doped In2O3 (INO) anodes prepared by a DC/RF co-sputtering process for use in bulk heterojunction organic solar cells (OSCs). By RTA processing at 600 °C, the authors obtained the optimized INO anodes with a sheet resistance of 28 Ω/sq, an optical transmittance of 82.93%, and a work function of 5.02 eV, which are acceptable in OSC fabrication. In particular, the 600 °C annealed INO anode showed much higher optical transmittance in the near infrared wavelength region than the conventional ITO film, even though it had a low resistivity of 5.66 × 10−4 Ω cm. The OSC fabricated on the annealed INO anode showed a higher power convention efficiency of 2.65% than the OSC with as-deposited INO anodes (2.19%) because the fill factors of the OSC are critically dependent on the sheet resistance of the anode.

Synthesis, Characterization, and Gas-Sensing for Trimethylamine of Mesoporous Ni-Doped Indium Oxide

Ni-doped mesoporous indium oxide has been successfully obtained by a simple and effected in-situ nanocasting method. The results characterized indicated that powders had a good crystalline structure, and the synthesis was successfully controlled in nanoscale (meso-structure). The gas sensor based on Ni-doped mesoporous In2O3 exhibit good trimethylamine (TMA) sensing properties, and a possible mechanism was aSubscript textlso provided.

Effects of oxygen vacancy and local spin on the ferromagnetic properties of Ni-doped In2O3 powders

(In1−xNix)2O3 (x=0.03 and 0.06) powders were prepared by a solid-state reaction and a vacuum annealing process. The air-sintered samples initially showed paramagnetism, and then exhibited obvious room temperature ferromagnetism after vacuum annealing. The ferromagnetic signal almost disappeared after air annealing and reappeared after vacuum annealing. Hence, the ferromagnetism can be switched “on” and “off” by alternate air and vacuum annealing. X-ray diffraction, high-resolution transmission electron microscopy, and field-cooled/zero-field-cooled measurements were performed. These analyses confirmed that there was no detectable trace of Ni or Ni oxide secondary phase in vacuum-annealed (In1−xNix)2O3 samples, and that the Ni ions were incorporated into the indium oxide lattice (substituting the In3+ ions). No ferromagnetic signal emerged from pure In2O3 powders regardless of undergoing vacuum or air annealing. These results revealed that oxygen vacancy and local spin are two factors that indispensably affect the ferromagnetic properties of the Ni-doped In2O3 system.

Preparation and NO2 Sensing Properties of the Ni-Doped In2O3 Nanofibers

In this letter, pure and 10% (mol) Ni-doped In2O3 nanofibers were prepared by an electrospinning method and characterized by differential thermal analyse (DTA), thermal gravimetric analyse (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) etc. The fibers after calcining at 600°C for 4 h belong to cubic structure. SEM images exhibited that the nanofibers had an average diameter of about 100 nm and are several tens of microns long. The NO2 sensing properties based on these fibers at 95°C were also investigated. In the low concentration range (5–150 ppm), the Ni-doped sensor exhibited excellent linear dependence. Moreover, good selectivity was also observed in our investigations.

Synthesis, Structural and Magnetic Properties of Ni-Doped In2O3 Nanoparticles

Pure and Ni-doped In2-xNixO3 (x = 0.0, 0.01, 0.05, 0.1) nanocrystalline powders were synthesized using sol-gel process. The XRD patterns revealed the formation of nanocrystalline particles with cubic bixbyte crystal structure. The average crystal size was calculated from XRD patterns using Debye-Scherer's Equation for (222) peak and it was found to be 8 nm. This observation agrees well with the particle size estimated from the transmission electron microscope (TEM). The observed Raman peaks in the doped materials were negligibly shifted towards the lower frequency. This clearly indicates that Ni ions are incorporate into the host In2O3 structure, in agreement with the XPS measurements. The Raman spectra show that the nanoparticles are free of secondary crystalline phase. The temperature dependent magnetization showed no evidence of ferromagnetism at room temperature.

High temperature ferromagnetism in Ni-doped In2O3 and indium-tin oxide

Observation of high temperature ferromagnetism in Ni-doped In2O3 and indium-tin-oxide (ITO) samples prepared by a solid state synthesis route is reported. Both Ni-doped compounds showed a clear ferromagnetism above 300K with the magnetic moments of 0.03–0.06μB∕Ni and 0.1μB∕Ni at 300 and 10K, respectively. Ni-doped In2O3 samples showed a typical semiconducting behavior with a room temperature resistivity of ρ∼2Ωcm, while Ni-doped ITO samples were metallic with ρ∼2×10−2Ωcm. Analysis of different conduction mechanisms suggested that variable range hopping model explains our ρ-T data for the Ni-doped In2O3 sample the best.