Enhanced H2S sensing performance of TiO2-decorated α-Fe2O3 nanorod sensors

Pristine and TiO₂ nanoparticle-decorated Fe₂O₃ nanorods were synthesized via thermal oxidation of Fe thin foils, followed by the solvothermal treatment with titanium tetra isopropoxide (TTIP) and NaOH for TiO₂ nanoparticle-decoration. Subsequently, gas sensors were fabricated by connecting the nanorods with metal conductors. The structure and morphology of the pristine and TiO₂ nanoparticle-decorated Fe₂O₃ nanorods were examined via X-ray diffraction and scanning electron microscopy, respectively. The gas sensing properties of the pristine and TiO₂ nanoparticle-decorated Fe₂O₃ nanorod sensors with regard to H₂S gas were examined. The TiO₂ nanoparticle-decorated Fe₂O₃ nanorod sensor showed a stronger response to H₂S than the pristine Fe₂O₃ nanorod sensor. The responses of the pristine and TiO₂ nanoparticle-decorated Fe₂O₃ nanorod sensors were 2.6 and 7.4, respectively, when tested with 200 ppm of H₂S at 300 °C. The TiO₂ nanoparticle-decorated Fe₂O₃ nanorod sensor also showed a faster response and recovery than the sensor made from pristine Fe₂O₃ nanorods. Both sensors showed selectivity for H₂S over NO₂, SO₂, NH₃, and CO. The enhanced sensing performance of the TiO₂ nanoparticle-decorated Fe₂O₃ nanorod sensor compared to that of the pristine Fe₂O₃ nanorod sensor might be due to enhanced modulation of the conduction channel width, the decorated nanorods’ increased surface-to-volume ratios and the creation of preferential adsorption sites via TiO₂ nanoparticle decoration. The dominant sensing mechanism in the TiO₂ nanoparticle-decorated Fe₂O₃ nanorod sensor is discussed in detail.     

Effects of Sb-doped SnO2–WO3 nanocomposite on electrochromic performance

With the increase in global challenges related to energy depletion, there is significant emphasis on studies involving next-generation optoelectronic applications such as smart windows and electronic displays. In particular, electrochromic devices (ECDs) have been identified as strategic innovations for energy-saving “smart windows” to address these challenges. Despite this increased level of attentions, ECDs have not yet attained broad commercial acceptance because of their limited electrochromic (EC) properties including coloration efficiency (CE,< 30.0 cm²/C) and switching speeds (> 10.0 s). To address these limitations, critical effort is required to enhance the EC properties by tuning the film structure and electronic structure of ECDs. In this study, we demonstrated the effect of nanocomposite structure of conductive metal oxides and WO₃ EC films. Antimony-doped tin oxide nanoparticles (ATO NPs) were utilized because of their superior electrical conductivity and large band gap. To achieve the optimum addition amount of ATO NPs in EC films, we adjusted the amount as 0, 0.6, 1.2, 2.4 wt%. WO₃ EC films with the optimum addition amount (1.2 wt%) of ATO NPs exhibited improved EC performance including both the switching speeds (5.4 s for the coloration speed and 2.4 s for the bleaching speed) and CE value (48.2 cm²/C). The enhancement of EC performance was attributed to the well-dispersed ATO NPs in the WO₃ films that can effectively improve electrical conductivity via the formation of by forming preferred electron pathway. In addition, the large band gap of ATO NPs broadens the transmittance modulation of the EC layer which contributed to the increment of the CE value. Therefore, our results suggest a strategy to obtain the enhanced WO₃ films with superior EC performances using conductive metal oxides nanocomposite structure.     

Hierarchical assembly of SnO2 nanorod on spindle-like α-Fe2O3 for enhanced acetone gas-sensing performance

Preparing a heterojunction structure in different metal oxides is an efficacious method to improve the gas-sensing properties. In this article, a novelty SnO₂ nanorod/spindle-like Fe₂O₃ heterostructure was successfully fabricated through a simple two-step hydrothermal route. The morphological characterization revealed that the spindle-shaped Fe₂O₃ with length and diameter of 400 and 100 nm were firstly fabricated by a hydrothermal process, and then a large number of SnO₂ nanorods (lengths of 30 nm and diameterd of 8 nm) covered the spindle-shaped Fe₂O₃ uniformly. In order to facilitate better practical applications, the gas sensing performance of sensors based on SnO₂/Fe₂O₃ nanostructures and pure Fe₂O₃ nanospindles on volatile organic compounds were systematically studied. Gas sensing tests indicated that such hierarchical SnO₂/Fe₂O₃ heterostructures revealed improved acetone sensing performance compared to pure spindle-like Fe₂O₃, and the enhanced gas-sensitivity performance possibly be attributed to the synergistic effect and heterojunction of the interface between spindle-like Fe₂O₃ and SnO₂ nanorod. Additionally, this research on as-obtained SnO₂/Fe₂O₃ hierarchical assembly may provide a new insight and a rational strategy to upgrade the sensing performance of certain semiconductor metal oxide materials by rationally designing various novel layered nanostructures in the future.     

Mechanism of NO removal in selective catalytic reduction based on γ-Fe2O3 catalyst doped with Mg element

The doping of different elements will make the Fe₂O₃ catalyst show different catalytic characteristics and improve the activity of the Fe₂O₃ catalyst in selective catalytic reduction (SCR), mainly by increasing the types of reactive oxygen species and the specific surface area of the catalyst. In this paper, density functional theory (DFT) was used to reveal the reaction path and adsorption behaviour of the Mg-doped γ-Fe₂O₃ catalyst. The results show that the doping of Mg ions can contribute electrons and lead to electron migration on the catalyst surface, which changes the acidity of some sites on the catalyst surface. The adsorption energy of NH₃ is related to the binding sites of N atoms on the catalyst surface, and different adsorption sites will be enhanced or weakened due to Mg doping. NH₂ reacts with NO to form N₂ and H₂O, so the dehydrogenation of NH₃ to the NH₂ radical is a key step in SCR. With doping, this process becomes more likely to occur. In addition, the activation energy barrier of NH₂ formation in the aerobic environment is lower than that in the anaerobic condition, which contributes to NH₃ dehydrogenation. Therefore, doping Mg on the surface of γ-Fe₂O₃ catalyst can improve the catalytic activity of NO removal.     

Preparation of the γ-Al2O3/PANI nanocomposite via enzymatic polymerization

Peroxidase-catalyzed template-guided polymerization of aniline in the presence of γ- alumina nanosheet (NS) particles have been carried out in aqueous media and γ-Al₂O₃/PANI nanocomposite was obtained. The polymerization of aniline occurred in aqueous solution in the presence of SPS (sulfonated polystyrene) as a template and SDS (sodium dodecyl sulfate) as a surfactant. Both obtained nanocomposites were comparable by SEM images. It was demonstrated that the γ-Al₂O₃ NS/PANI-SPS nanocomposite has higher conductivity and the γ-Al₂O₃ NS/PANI-SDS nanocomposite has higher void areas. The higher conductivity of γ-Al₂O₃ NS/PANI-SPS nanocomposite is attributed to the higher coated areas of γ-Al₂O₃ NS during polymerization in comparison with γ-Al₂O₃ NS/PANI-SDS which are not coated efficiently as the former. The FT-IR studies showed that the γ-Al₂O₃ NS/PANI nanocomposite was formed by interaction of the polyaniline (PANI) and γ-Al₂O₃ NS. FTIR also showed that the amount of PANI in γ-Al₂O₃ NS/PANI-SPS is more than in γ-Al₂O₃ NS/PANI-SDS. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

The Preparation and Gas-sensing Property of Nanosize γ-Fe2O3／SiO2

Nanostructured γ-Fe2O3/SiO2 complex oxide was prepared by sol-gel method with tetraethoxysilane and iron nitrate as precursors. The particle size distribution, thermal and phase stabilities and gas sensing properties were systematically characterized by TEM, granularity distribution, TG-DTA, XRD and gas sensitivity measurements. The particle size is about 10 nm and size distribution is very narrow. The sensitivity of the sensing element to CO, H2, C2H4, C6H6 and the effects of calcination temperature on the sensitivity and conductance of gases were examined. The combination of excellent thermal stability and tunable gas sensing properties through careful control of the preparation and judicious selection of material compositions gives rise to novel nanocomposites, which is attractive for the sensitive and selective detection of reducing gases and some hydrocarbon gases.     

Photocatalytic performance of β-Ga2O3 microcubes towards efficient degradation of malachite green

In this work, the photocatalytic degradation of malachite green (MG) solutions by β-Ga₂O₃ was investigated. The latter was synthetized by reacting gallium nitrate with concentrated formic acid, which produced gallium formate. The thermal decomposition of this compound at 850 °C produced single-phase β-Ga₂O₃. The resulting morphology corresponds to non-agglomerated microcubes, with a size in the range of 0.8 and 2.3 μm. The surface chemical composition and bandgap energy of this oxide were determined by X-ray photoelectron spectroscopy (XPS) and the Tauc method, respectively. The photodegradation of MG was carried out under violet light (λ = 405 nm), at room temperature, using the as-prepared powder. The results revealed a fast degradation of the dye during the first 20 min, which attenuates over time. The rate of photodegradation depends on the amount of β-Ga₂O₃ used and can be fitted by an exponential equation. The role of free hydroxyl radicals and reactive oxygen species in photocatalysis was addressed by using analytic techniques (FTIR and XPS).     

WO3/α-Fe2O3对溴酚蓝的光催化降解性能

用复相光催化荆WO3/α-Fe2O3对含溴酚蓝的水溶液处理进行了研究.探讨了光催化剂作用机理,讨论了光催化剂的配比、试液的起始浓度、光催化剂的用量、试液的pH值、双氧水的用量、光照时间与溴酚蓝溶液脱色率的关系.实验结果表明:催化剂配比WO3/α-Fe2O3=3:1、试液起始浓度为15mg/L、催化剂用量为0.300g、pH=6.3、双氧水的用量为0.20mL、光照6h,溴酚蓝溶液的脱色率可以达到99.1%.     

Preparation of magnetic α-Fe2O3/ZnFe2O4@Ti3C2 MXene with excellent photocatalytic performance

The high conductivity Ti₃C₂ MXene with the unique lamellar nanostructure can effectively improve photoelectrocatalytic ability of composite as cocatalyst. In this paper, the magnetic α-Fe₂O₃/ZnFe₂O₄ heterojunctions were obtained using one-step hydrothermal synthesis. And α-Fe₂O₃/ZnFe₂O₄@Ti₃C₂ MXene photocatalyst can be easily obtained by ultrasonic assisted self-assembly approach for dispersing magnetic α-Fe₂O₃/ZnFe₂O₄ heterojunctions on Ti₃C₂ MXene surface. Due to the improving photoelectron ability, the α-Fe₂O₃/ZnFe₂O₄@Ti₃C₂ MXene was found to exhibit the higher photocatalytic ability than the α-Fe₂O₃/ZnFe₂O₄ heterojunctions in eliminating Rhodamine B (RhB) pollutant and toxic Cr(Ⅵ) in water. Even more important, as a magnetic composite, the 10 wt% α-Fe₂O₃/ZnFe₂O₄@Ti₃C₂ MXene photocatalyst exhibited the excellent reusability. The terrific photocatalytic ability is due to the numerous heterostructure interfaces, the increase of visible light harvesting and high conductivity.     

Separation of Arsenic from Aqueous Solutions by Amino-Functionalized γ-Fe2O3-β-Zeolite

In this research, γ-Fe₂O₃-β-zeolite nanocomposite was synthesized and functionalized by 3-amino propyl trimethoxysilane. The magnetic functionalized adsorbent was characterized by FTIR, X-ray diffraction, thermal analysis, vibrating sample magnetometry, scattering electron microscopy, and N₂ adsorption-desorption techniques. The adsorbent was then used for adsorption of arsenic from aqueous solutions. At optimized conditions the adsorption capacity of 30 mg.g^?1 was obtained, which was higher than the previously reported values. The loaded adsorbent was easily separated from the solution by applying an external magnetic field. Regeneration of the adsorbent by NaOH solution indicated that 97% of the initial capacity was remained after four adsorption-regeneration cycles.     

Efficient removal of Congo red by magnetically separable mesoporous TiO2 modified with γ-Fe2O3

Magnetically separable mesoporous TiO₂ modified with γ-Fe₂O₃ was prepared and characterized by X–ray diffraction, N₂ adsorption–desorption measurements, scanning electron microscopy, UV–vis absorption and magnetic measurements. The adsorptive removal of Congo red using the binary system was performed under various experimental conditions to examine the effects of contact time, solution pH, and initial concentration of Congo red. The results show that the removal abilities and separability of mesoporous TiO₂ adsorbent for Congo red can be significantly improved by modification with γ-Fe₂O₃. The adsorption of Congo red on the γ-Fe₂O₃–TiO₂ reaches the maximum percentage removal of ca. 97 % within 60 min, showing that most of Congo red can be removed in a short time. When the pH of solution is varied from 3.4 to 10.3, the percentage removal of Congo red decreases from ca. 97 to ca. 15 %, showing that the adsorption is strongly dependent on solution pH. The adsorption kinetics of Congo red fit well with pseudo-second-order kinetic model, and the equilibrium data is best described by Langmuir adsorption model. The maximum adsorption capacity of the γ-Fe₂O₃–TiO₂ for Congo red is estimated to be 125.0 mg/g.     

Enhanced thickness uniformity of large-scale α-Ga2O3 epilayers grown by vertical hot-wall mist chemical vapor deposition

Smooth surface morphology and high thickness uniformity heteroepitaxy of corundum-structured (α-) gallium oxide (Ga₂O₃) crystalline thin films on 100-mm diameter c-plane sapphire substrates were successfully demonstrated using vertical hot-wall mist chemical vapor deposition (CVD). The growth rate and surface morphology of the epitaxial layers were numerically and experimentally found to be dependent on the diameter of the precursor-diluted microdroplets approaching the substrate surface. Since the microdroplet is gradually evaporated while traveling through the furnace, the growth variables such as temperature, mist-flow velocity, and substrate position were tuned to obtain a suitable diameter of microdroplets approaching the substrate. In this study, the diameter of the approaching microdroplet was ≈2 μm, which was optimal for the smooth surface (root mean square roughness ≈1 nm) of α-Ga₂O₃ epitaxial layers with a growth rate of ≈230 nm/h. Due to the even flow of mist in the vertical furnace, high thickness uniformity of the α-Ga₂O₃ epitaxial layer is guaranteed on large-scale substrates, with a standard deviation of thickness as small as 28 nm, paving the way for highly reliable Ga₂O₃-based electric and optoelectronic devices.     

Polyacrylonitrile/α-Fe2O3 Hybrid Photocatalytic Composite Adsorbents for Enhanced Dye Removal

The potential of a novel α-Fe₂O₃/polyacrylonitrile (PAN) hybrid composite adsorbent to eliminate methylene blue (MB) from aqueous solution was evaluated. PAN was selected as the base composite. The presence of α-Fe₂O₃ as nanophotocatalyst on the surface of PAN introduced an efficient photocatalytic hybrid composite adsorbent for degrading MB. Effects of α-Fe₂O₃ nanopowder loading, pH, temperature, MB initial concentration, solar light, and contact time were investigated. Langmuir, Freundlich, and Temkin isotherms were applied to analyze the adsorption behavior. The Freundlich equation provided the best correlation with experimental data. Pseudo-first-order, pseudo-second-order, and intraparticle models were employed. Thermodynamic studies indicated an endotherm and spontaneous adsorption process in a defined temperature range.     

Enhanced performance of low-carbon MgO–C refractories with nano-sized ZrO2–Al2O3 composite powder

Low-carbon MgO–C refractories are facing great challenges with severe thermal shock and slag corrosion in service. Here, a new approach, based on the incorporation of nano-sized ZrO₂–Al₂O₃ composite powder, is proposed to enhance the thermal shock resistance and slag resistance of such refractories in this work. The results showed that addition of ZrO₂–Al₂O₃ composite powder was helpful for improving their comprehensive performances. Particularly, the thermal shock resistance of the specimen containing 0.5 wt% composite powder was enhanced significantly which was related to the transformation toughening of zirconia and in-situ formation of more spinel phases in the matrix; also, the slag resistance of the corresponding specimen was significantly improved, which was attributed to the optimization of pore structure and formation of much thicker MgO dense layer.     

Sintering of α-Al2O3-seeded nanocrystalline γ-Al2O3 powders

This paper demonstrates that seeding nanocrystalline transition alumina powders is a viable option for producing high quality, alumina-based ceramics. By using α-Al₂O₃ concentrations of ⩾1.25 wt.% α-Al₂O₃ seed particles (equivalent to 5 ×10¹⁴ seeds/cm³ of γ-Al₂O₃) the sintering temperature is reduced from 1600°C for unseeded γ-Al₂O₃ to 1300–1400°C in dry pressed powders. The scale of the sintered microstructure is related to N_v^−1/3 and thus a 100-nm grain size is obtained. It is apparent that seeding is necessary for producing dense, alumina-based ceramics from nanocrystalline transition alumina powders.     

Effect of Pd loading and precursor on the catalytic performance of Pd/WO3–ZrO2 catalysts for selective oxidation of ethylene

The structure and properties of Pd/WO₃–ZrO₂ (W/Zr = 0.2) catalysts with different Pd loadings and precursors were investigated. The results indicate that Pd/WO₃–ZrO₂ prepared from a PdCl₂ precursor was optimum for high activity and selectivity. Moreover, ethylene conversion increased with the Pd loading. The structure and nature of the catalysts were characterized using X-ray diffraction, BET N₂ adsorption, H₂ temperature-programmed reduction and H₂ pulse adsorption techniques. The results reveal that the higher catalytic performance of Pd/WO₃–ZrO₂ prepared from PdCl₂ could be related to the formation of polytungstate species and the existence of well-dispersed Pd particles.     

Epoxide functionalized γ-Al2O3/Fe3O4/SiO2 nanocomposite and comparative adsorption behavior of a model reactive azo dye

In this investigation, magnetic γ-Al₂O₃ nanocomposite polymer particles with epoxide functionality were prepared following a multistep process. The prepared nanocomposite polymer particle was named as γ-Al₂O₃/Fe₃O₄/SiO₂/poly(glycidyl methacrylate (PGMA). The surface property was evaluated by carrying out the adsorption study of Remazol Navy RGB (RN), a model reactive azo dye, on both γ-Al₂O₃/Fe₃O₄/SiO₂ and γ-Al₂O₃/Fe₃O₄/SiO₂/PGMA nanocomposite particles, that is, before and after epoxide functionalization. A contact time, temperature, adsorbent dose, and dye concentration dependent change in adsorption behavior was observed on both nanocomposite particles. The adsorption amount reached equilibrium (q_e) value within 5 minutes at the respective point of zero charge (PZC). The adsorption density of RN per unit specific surface area on epoxide functional γ-Al₂O₃/Fe₃O₄/SiO₂/PGMA nanocomposite polymer particles (1.30 mg/m²) was higher relative to that on γ-Al₂O₃/Fe₃O₄/SiO₂ nanocomposite particles (0.87 mg/m²). The optimum adsorbent dose for obtaining the maximum adsorption density was 0.01 g. Comparatively, Langmuir isotherm model was better to describe the adsorption process and the adsorption process was favorable at low temperature (283 K). Batch kinetic adsorption experiment suggested that a pseudo-second-order rate kinetic model is more appropriate. Nanocomposite polymer particles were used as adsorbent up to third cycle with almost 99% adsorption efficiency.