Green emission of indium oxide via hydrogen treatment

Unraveling the molecular and growth mechanism of colloidal black In2O3-x

Black metal oxides with varying concentrations of O-vacancies display enhanced optical and catalytic properties. However, direct solution syntheses of this class of materials have been limited despite being highly advantageous given the different synthetic handles that can be leveraged towards control of the targeted material. Herein, we present an alternate colloidal synthesis of black In2O3-x nanoparticles from the simple reaction between In(acac)3 and oleyl alcohol. Growth studies by PXRD, TEM, and STEM-EDS coupled to mechanistic insights from 1H, 13C NMR revealed the particles form via two paths, one of which involves In0. We also show that variations in the synthesis atmosphere, ligand environment, and indium precursor can inhibit formation of the black In2O3-x. The optical spectrum for the black nanoparticles displayed a significant redshift when compared to pristine In2O3, consistent with the presence of O-vacancies. Raman spectra and surface analysis also supported the presence of surface oxygen vacancies in the as-synthesized black In2O3-x.

Engineering of Mesoporous Cube-like In2O3 Products as Ethanol Detection Platform at Low Operating Temperature: Effects of Different Transition Metals as Dopant Ions

Although most semiconductor metal oxides including In2O3 show acceptable sensitivity to volatile organic compounds, it is difficult to detect ethanol effectively at low operating temperatures and detection levels. In this study, pure and Co-, Ni-, and Cu-doped In2O3 products with their doping content maintained at 1 mol % were successfully produced using a hydrothermal approach. Explicit contrast on the structural, microstructural, and textural properties of the synthesized In2O3 products was examined to determine their gas sensing performance. The Cu-doped In2O3 sensor demonstrated improved response of 15.3 to 50 ppm ethanol and has satisfactory selectivity, stability, low detection limit of 0.2, humidity resistance, and decreased working temperature of 80 °C compared to 150 °C of the pure In2O3 sensor. This optimal gas sensing performance is derived from the cube-like morphology assembled with interlinked nanoparticles, which favors trapping more target gas molecules and exposing more active sites, thereby greatly improving its sensing ability. This study showed that the Cu-doped In2O3 sensor with 1 mol % is suitable for monitoring ethanol gas for food safety applications.

Enhanced Solar Fuel Production over In2 O3 @Co2 VO4 Hierarchical Nanofibers with S-Scheme Charge Separation Mechanism

The conversion of CO2 into valuable solar fuels via photocatalysis is a promising strategy for addressing energy shortages and environmental crises. Here, novel In2 O3 @Co2 VO4 hierarchical heterostructures are fabricated by in situ growing Co2 VO4 nanorods onto In2 O3 nanofibers. First-principle calculations and X-ray photoelectron spectroscopy (XPS) measurements reveal the electron transfer between In2 O3 and Co2 VO4 driven by the difference in work functions, thus creating an interfacial electric field and bending the bands at the interfaces. In this case, the photogenerated electrons in In2 O3 transport to Co2 VO4 and recombine with its holes, indicating the formation of In2 O3 @Co2 VO4 S-scheme heterojunctions and resulting in effective separation of charge carriers, as confirmed by in situ irradiation XPS. The unique S-scheme mechanism, along with the enhanced optical absorption and the lower Gibbs free energy change for the production of * CHO, significantly contributes to the efficient CO2 photoreduction into CO and CH4 in the absence of any molecule cocatalyst or scavenger. Density functional theory simulation and in situ diffuse reflectance infrared Fourier transform spectroscopy are employed to elucidate the reaction mechanism in detail.

rh-In2O3 Nanoparticles for Efficient Photocatalytic Degradation of Rifampin

Photodegradation, a widely accepted and promising technology, has gained significant attention for addressing the escalating concerns of environmental deterioration. In this article, rhombohedral corundum-type In2O3 nanocrystals were obtained from the transformation of InOOH via a simple calcining process. Under ultraviolet light irradiation, they showed higher photocatalytic activity in the decomposition of rifampin compared to that of the cubic phase In2O3 and P25-TiO2. Furthermore, the probable pathway and the feasible mechanism for the degradation of rifampin were also deeply explored and discussed.

Transducer-Aware Hydroxy-Rich-Surface Indium Oxide Gas Sensor for Low-Power and High-Sensitivity NO2 Gas Sensing

Low-power metal oxide (MOX)-based gas sensors are widely applied in edge devices. To reduce power consumption, nanostructured MOX-based sensors that detect gas at low temperatures have been reported. However, the fabrication process of these sensors is difficult for mass production, and these sensors are lack uniformity and reliability. On the other hand, MOX film-based gas sensors have been commercialized but operate at high temperatures and exhibit low sensitivity. Herein, commercially advantageous highly sensitive, film-based indium oxide sensors operating at low temperatures are reported. Ar and O₂ gases are simultaneously injected during the sputtering process to form a hydroxy-rich-surface In₂O₃ film. Conventional indium oxide (In₂O₃) films (A0) and hydroxy-rich indium oxide films (A1) are compared using several analytical techniques. A1 exhibits a work function of 4.92 eV, larger than that of A0 (4.42 eV). A1 exhibits a Debye length 3.7 times longer than that of A0. A1 is advantageous for gas sensing when using field effect transistors (FETs) and resistors as transducers. Because of the hydroxy groups present on the surface of A1, A1 can react with NO₂ gas at a lower temperature (∼100 °C) than A0 (180 °C). Operando diffuse reflectance infrared Fourier transform spectrometry (DRIFTS) shows that NO₂ gas is adsorbed to A1 as nitrite (NO₂^-) at 100 °C and nitrite and nitrate (NO₃^-) at 200 °C. After NO₂ is adsorbed as nitrate, the sensitivity of the A1 sensor decreases and its low-temperature operability is compromised. On the other hand, when NO₂ is adsorbed only as nitrite, the performance of the sensor is maintained. The reliable hydroxy-rich FET-type gas sensor shows the best performance compared to that of the existing film-based NO₂ gas sensors, with a 2460% response to 500 ppb NO₂ gas at a power consumption of 1.03 mW.

Fabrication and Photocatalytic Properties of Zinc Tin Oxide Nanowires Decorated with Silver Nanoparticles

With the continuous advancement of high-tech industries, how to properly handle pollutants has become urgent. Photocatalysis is a solution that may effectively degrade pollutants into harmless molecules. In this study, we synthesized single crystalline Zn2SnO4 (ZTO) nanowires through chemical vapor deposition and selective etching. The chemical bath redox method was used to modify the ZTO nanowires with Ag nanoparticles to explore the photocatalytic properties of the nanoheterostructures. The combination of the materials here is rare. Optical measurements by photoluminescence (PL) and UV-Vis show that the PL spectrum of ZTO nanowires was mainly in the visible light region and attributed to oxygen vacancies. The luminescence intensity of the nanowires was significantly reduced after modification, demonstrating that the heterojunction could effectively reduce the electron-hole pair recombination. The reduction increased with the increase in Ag decoration. The conversion from the UV-Vis absorption spectrum to the Tauc Plot shows that the band gap of the nanowire was 4.05 eV. With 10 ppm methylene blue (MB) as the degradation solution, ZTO nanowires exhibit excellent photodegradation efficiency. Reusability and stability in photodegradation of the nanowires were demonstrated. Photocatalytic efficiency increases with the number of Ag nanoparticles. The main reaction mechanism was confirmed by photocatalytic inhibitors. This study enriches our understanding of ZTO-based nanostructures and facilitates their applications in water splitting, sewage treatment and air purification.

Synthesis and Characterization of Indium Tin Oxide Nanowires with Surface Modification of Silver Nanoparticles by Electrochemical Method

In this study, indium tin oxide nanowires (ITO NWs) with high density and crystallinity were synthesized by chemical vapor deposition (CVD) via a vapor-liquid-solid (VLS) route; the NWs were decorated with 1 at% and 3 at% silver nanoparticles on the surface by a unique electrochemical method. The ITO NWs possessed great morphologies with lengths of 5~10 μm and an average diameter of 58.1 nm. Characterization was conducted through transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and X-ray photoelectron spectroscope (XPS) to identify the structure and composition of the ITO NWs. The room temperature photoluminescence (PL) studies show that the ITO NWs were of visible light-emitting properties, and there were a large number of oxygen vacancies on the surface. The successful modification of Ag was confirmed by TEM, XRD and XPS. PL analysis reveals that there was an extra Ag signal at around 1.895 eV, indicating the potential application of Ag-ITO NWs as nanoscale optical materials. Electrical measurements show that more Ag nanoparticles on the surface of ITO NWs contributed to higher resistivity, demonstrating the change in the electron transmission channel of the Ag-ITO NWs. ITO NWs and Ag-ITO NWs are expected to enhance the performance of electronic and optoelectronic devices.

Synthesis of High-Density Indium Oxide Nanowires with Low Electrical Resistivity

In this study, indium oxide nanowires of high-density were synthesized by chemical vapor deposition (CVD) through a vapor-liquid-solid (VLS) mechanism without carrier gas. The indium oxide nanowires possess great morphology with an aspect ratio of over 400 and an average diameter of 50 nm; the length of the nanowires could be over 30 μm, confirmed by field-emission scanning electron microscopy (SEM). Characterization was conducted with X-ray diffraction (XRD), transmission electron microscopy (TEM), photoluminescence spectrum (PL). High-resolution TEM studies confirm that the grown nanowires were single crystalline c-In2O3 nanowires of body-centered cubic structures. The room temperature PL spectrum shows a strong peak around 2.22 eV, originating from the defects in the crystal structure. The electrical resistivity of a single indium oxide nanowire was measured to be 1.0 × 10-4 Ω⋅cm, relatively low as compared with previous works, which may result from the abundant oxygen vacancies in the nanowires, acting as unintentional doping.

Black indium oxide a photothermal CO2 hydrogenation catalyst

Nanostructured forms of stoichiometric In₂O₃ are proving to be efficacious catalysts for the gas-phase hydrogenation of CO₂. These conversions can be facilitated using either heat or light; however, until now, the limited optical absorption intensity evidenced by the pale-yellow color of In₂O₃ has prevented the use of both together. To take advantage of the heat and light content of solar energy, it would be advantageous to make indium oxide black. Herein, we present a synthetic route to tune the color of In₂O₃ to pitch black by controlling its degree of non-stoichiometry. Black indium oxide comprises amorphous non-stoichiometric domains of In₂O_3-x on a core of crystalline stoichiometric In₂O₃, and has 100% selectivity towards the hydrogenation of CO₂ to CO with a turnover frequency of 2.44 s^-1.

Electron injection effect in In2O3 and SnO2 nanocrystals modified by ruthenium heteroleptic complexes

In this work, the optical characteristics and conductivity under photoactivation with visible light of hybrids based on nanocrystalline SnO2 or In2O3 semiconductor matrixes and heteroleptic Ru(ii) complexes were studied. The heteroleptic Ru(ii) complexes were prepared based on 1H-imidazo[4,5-f][1,10]phenanthroline and 2,2'-bipyridine ligands. Nanocrystalline semiconductor oxides were obtained by chemical precipitation with subsequent thermal annealing and characterized by XRD, SEM and single-point BET methods. The heteroleptic Ru(ii) complexes as well as hybrid materials were characterized by time-resolved luminescence and X-ray photoelectron spectroscopy. The results showed that the surface modification of SnO2 nanoparticles with heteroleptic ruthenium complexes led to an increase in conductivity upon irradiation with light appropriate for absorption by organometallic complexes. In the case of In2O3, the deposition of Ru(ii) complexes resulted in a decrease in conductivity, apparently due to the special structure of the surface layer of the semiconductor.

Organic-Inorganic Hybrid Materials for Room Temperature Light-Activated Sub-ppm NO Detection

Nitric oxide (NO) is one of the main environmental pollutants and one of the biomarkers noninvasive diagnosis of respiratory diseases. Organic-inorganic hybrids based on heterocyclic Ru (II) complex and nanocrystalline semiconductor oxides SnO2 and In2O3 were studied as sensitive materials for NO detection at room temperature under periodic blue light (λmax = 470 nm) illumination. The semiconductor matrixes were obtained by chemical precipitation with subsequent thermal annealing and characterized by XRD, Raman spectroscopy, and single-point BET methods. The heterocyclic Ru (II) complex was synthesized for the first time and characterized by 1H NMR, 13C NMR, MALDI-TOF mass spectrometry and elemental analysis. The HOMO and LUMO energies of the Ru (II) complex are calculated from cyclic voltammetry data. The thermal stability of hybrids was investigated by thermogravimetric analysis (TGA)-MS analysis. The optical properties of Ru (II) complex, nanocrystalline oxides and hybrids were studied by UV-Vis spectroscopy in transmission and diffuse reflectance modes. DRIFT spectroscopy was performed to investigate the interaction between NO and the surface of the synthesized materials. Sensor measurements demonstrate that hybrid materials are able to detect NO at room temperature in the concentration range of 0.25-4.0 ppm with the detection limit of 69-88 ppb.

In Situ Electronic Probing of Photoconductive Trap States for the Catalytic Reduction of CO2 by In2O3- xOH y Nanorods

We use photoconductivity time, optical absorption, and electron quantum efficiency measurements under in situ reactant CO₂ + H₂ atmospheres to determine the role of surface trap states during photoreduction of CO₂ to CO using In₂O_{3- x}OH _y nanorods of varied annealing times. Photocurrent decay trends show an asymmetric energy distribution of surface barrier potentials with increased asymmetry from vacuum to CO₂ + H₂. Urbach analysis shows crystalline disorder parameters of 0.35-0.40 under vacuum and 0.45-0.6 under CO₂ + H₂. Quantum efficiency spectra show that under H₂ + CO₂ average tail state energies are similar to those under vacuum but with increased densities of photoconductive gap states. Photoelectro-paramagnetic-resonance measurements show the creation of new paramagnetic centers. Overall, enhanced activity is associated with a lower maximum barrier potential of 0.39 eV than that of 0.41 eV, lower average trap energies of 2.58 eV compared to 2.69 eV, with higher disorder due to increased surface state densities. These techniques pave the way for facile in situ probing of gas-phase photocatalysts, providing simple macrolevel understanding of adsorbed reactants on surface band bending, thus correlating to catalytic efficacy.