Oxide Research Articles

Synthesis of defect-rich La2O2CO3 supports for enhanced CO2-to-methanol conversion efficiency.

Converting CO2 to methanol is crucial for addressing fuel scarcity and mitigating the greenhouse effect. Cu-based catalysts, with their diverse surface states, offer the potential to control reaction pathways and generate reactive H* species. However, a major challenge lies in oxidizing active Cu0 species by water generated during the catalytic process. While nonreducible metal oxides are beneficial in stabilizing metallic states, their limited capability to generate surface oxygen vacancies (OV) hinders CO2 activation. Herein, we present a strategy by doping Nd into a La2O2CO3 (LOC) support, enhancing OV formation by disrupting its lattice dyadicity. This leads to higher Cu0 concentration and improved CO2 activation. The resulting Cu/LOC:Nd catalyst notably outperforms Cu/LOC and CuZnAl catalysts, achieving a methanol yield of 9.9 moles of methanol per hour per mole of Cu. Our approach opens up possibilities for enhancing Cu-based catalysts in CO2 conversion.

Low-Temperature Borylation of C(sp3)-O Bonds of Alkyl Ethers by Gold-Metal Oxide Cooperative Catalysis.

Since ether moieties are often found not only in petrochemical products but also in natural organic molecules, the development of methods for manipulating C-O bonds of ethers is important for expanding the range of compound libraries synthesized from biomass resources, which should contribute to the goal of carbon neutrality. We report herein that gold nanoparticles supported on Lewis acidic metal oxides, namely α-Fe2O3, showed excellent catalytic activity for the reaction of dialkyl ethers and diborons, which enables the conversion of unactivated C(sp3)-O bonds to C(sp3)-B bonds at around room temperature. Various acyclic and cyclic ethers as well as a series of diborons participated in the heterogeneous gold-catalyzed borylation of unactivated C(sp3)-O bonds, to give a series of alkylboronates in high yields. Mechanistic studies corroborated that the present borylation of C(sp3)-O bonds of dialkyl ethers proceeded at the interface between gold nanoparticles and Lewis acidic metal oxides. Furthermore, adsorption IR measurements supported the notion that strong Lewis acid sites were generated at the boron atom of diborons adsorbed at the interface between Lewis acidic metal oxides and gold nanoparticles, which enabled us to ensure that the cooperation of gold nanoparticles and Lewis acidic metal oxides was responsible for the efficient transformation of unactivated C(sp3)-O bonds in ethers under mild conditions. This novel reaction technology which is specific to heterogeneous catalysts enables the activation of stable C(sp3)-O bonds of oxygenated chemical feedstock, which is beneficial for the sustainable synthesis of value-added organoboron compounds.

Mixed metal oxide and boron-doped diamond anodes for the treatment of 1-butyl-3-methylimidazolium chloride in single- and dual-flow configuration

Mixed metal oxide and boron-doped diamond anodes for the treatment of 1-butyl-3-methylimidazolium chloride in single- and dual-flow configuration

Using Support Effects to Increase the Productivity of Immobilized Ruthenium Hydride Catalysts for the Hydrogenation of CO2.

Interfaces between catalytically active metal surfaces/sites and metal oxides (such as those formed by metal oxides covering metal nanoparticles by strong metal-support interactions) allow both the metal and metal oxide to react with substrates simultaneously and are important for the activity of many heterogeneously catalyzed reactions. However, similar interactions for well-defined immobilized catalysts have not been investigated, despite their potential for increasing catalytic activity. We test the reactivity of a ruthenium hydride [H2Ru(PPh3)2(Ph2P)2NC3H6Si(OEt)3 (1)] in the amine-promoted hydrogenation of CO2 as both a homogeneous catalyst and anchored on SiO2, Al2O3, ZnO, and SBA-15. Anchoring 1 on the surfaces resulted in varying degrees of surface collapse (formation of H-Ru-O linkages to the surface), with ZnO and confinement in SBA-15 pores giving the least surface collapse. Immobilization of 1 on ZnO gave a 6-fold improvement of the catalytic rate over the corresponding homogeneous catalyst. This increase in the catalytic productivity was only possible when the complex was in close contact with ZnO and is most likely due to a combination of increased catalytic activity and slower deactivation. These results demonstrate the ability of surface effects to vastly improve the productivity of even mediocre catalysts upon surface immobilization.

Spray Black Coating for High‐Efficiency Light Absorption

AbstractBlack coatings have emerged as a research focus due to their excellent light absorption performance over a wide wavelength range. They play a crucial role in precision optical devices and solar thermal applications. Among various preparation methods, spray coating has attracted great attention due to its simple preparation process, low cost, scalability, and applicability to complex structures. Herein, the recent progress in spray black coatings is comprehensively presented. Various spray coating methods employed in the preparation of black coatings, including air spraying, ultrasonic spraying, electrostatic spraying, spray pyrolysis, and thermal spraying are summarized and compared. Black spray coatings based on metal sulfide, metal oxide, cermet, polymer, and carbon are then reviewed. In addition to the intrinsic absorption properties of the black coatings, light‐trapping structures are key to achieving high‐efficiency light absorption. Typical structural design strategies for enhancing absorption are highlighted. Moreover, the trade‐off between absorptance and adhesion in the design of robust spray black coatings is indicated. The remaining challenges and outlook for the spray black coatings are discussed. This review is expected to provide valuable guidelines for the future development of spray black coatings.

Porous Materials for the Heterogeneously Catalyzed Synthesis of High Value-Added Products: Latest Trends and Future Prospects.

Heterogeneous catalysis currently stands as a foundational area in materials synthesis and applied chemistry. In this context, emphasizing the significance of heterogeneous catalysis in expediting chemical reactions and controlling the formation of desired products using porous materials represents an intriguing approach in the current technological landscape. This work delves into the synthesis and design of a variety of porous materials, encompassing microporous, mesoporous and macroporous materials (e. g. carbonaceous materials, metal oxides, MOFs, zeolites and functionalized analogues), alongside their properties and characteristics pivotal in heterogeneous catalysis. among others, and their subsequent modification, underscoring the significance of tailoring porous materials for specific catalytic applications.

Unconventional quantum oscillations and evidence of nonparabolic electronic states in quasi-two-dimensional electron system at complex oxide interfaces

The simultaneous occurrence of electric-field controlled superconductivity and spin-orbit interaction makes two-dimensional electron systems (2DES) constructed from perovskite transition metal oxides promising candidates for the next generation of spintronics and quantum computing. It is, however, essential to understand the electronic bands thoroughly and verify the predicted electronic states experimentally in these 2DES to advance technological applications. Here, we present insights into the electronic states of the 2DES at oxide interfaces through comprehensive investigations of Shubnikov–de Haas oscillations in three different systems: EuO/KTaO3, LaAlO3/SrTiO3, and amorphous-LaAlO3/KTaO3. To accurately resolve these oscillations, we conducted transport measurements in high magnetic fields up to 60 T and low temperatures down to 100 mK. For 2D confined electrons at these interfaces, we observed a progressive increase of oscillations frequency and cyclotron mass with the magnetic field. We interpret these universal and intriguing findings by considering the existence of nontrivial electronic bands, for which the E−k dispersion incorporates both linear and parabolic relations. In addition to providing experimental evidence for nonparabolic electronic states in KTaO3 and SrTiO3 2DES, the unconventional oscillations presented in this study establish a paradigm for quantum oscillations in 2DES based on perovskite transition metal oxides, where the oscillation frequencies in 1/B exhibit quadratic dependence on the magnetic field. Published by the American Physical Society 2024

Non-monotonically changes in double Schottky barrier of MnCO3–doped ZnO varistors during DC aging

Abstract ZnO varistors play a crucial role as core component in metal oxide arresters due to their excellent nonlinear current density-electrical field (J–E) characteristics. After long-term operation under DC stress (DC aging), the J–E curves of ZnO varistors invented in the last decade cross with the original curve. Unexpectedly, the ‘crossover’ phenomenon cannot be explained by the vastly-accepted ion migration mechanism by which the barrier height monotonically declines after DC aging. In the present study, aging and recovery experiments were carried out on MnCO3-doped ZnO varistors. The symmetry of J–E characteristics in the same direction as and the opposite direction to the DC stress was compared, parameters of double Schottky barrier were analyzed, and evolution of point defects was deduced using dielectric spectra. It was found that, in addition to ion migrations, there are electrons ionized by zinc interstitials filling the interface states in the early stage of aging. Because these processes are dominant in different stages, the barrier height changes non-monotonically. MnCO3 can suppress the formation of zinc interstitials, so it simultaneously inhibits ion migrations and filling of the interface states by electrons. When 0.38 mol% MnCO3 is doped, J–E characteristics and the Schottky barrier of ZnO varistors show the smallest deviations during aging and recovery. The findings are helpful in updating criteria for the long-term stability of ZnO varistors and suggest that modifications to their formulae targeting the suppression of the filling the interface states by electrons are also expected to bolster the stability.

Synthesis of biochar and its metal oxide composites and application on next sustainable electrodes for energy storage devices

Biochar materials have been applied in energy storage due to their unique properties, such as high storage of ions, high conductivity, chemical stability and ease of production. Combining it with the high specific capacitance could be a promising strategy to develop devices and improve the properties. Through a hydrothermal technique the biochar powders were synthesized from sugarcane biomass. An acid pretreatment was carried out before and after the graphitization process aiming to obtain carbon materials with high surface area and porosity. The morphological characterization reveals powders with pores of submicrometer diameter. For the pure biochar it was determined a superficial area of 477.66 m2.g−1 with a median pore size of 42.92 Å and a pore volume of 0.21 cm3.g−1. A carbon-based paste was then prepared to deposit on nickel foam and obtain the electrodes. In a 3-electrode system characterization, biochar has showed higher specific capacitance than the metal oxide composites due to higher surface area and higher medium pore diameter. It was calculated a resistance of 2.7 Ω, a capacitance of 446 mF.g−1, a power density of 46.2 W.kg−1 and an energy density of 1.8 W.h.kg−1. These results indicate the potential use of biochar-based electrodes with high electrical conductivity and improved surface area to obtain higher capacitance properties for development of advanced devices.

Electrochemical lithium extraction from hectorite ore

Electrochemical technologies add a unique dimension for ore refinement, representing tunable methods that can integrate with renewable energy sources and existing downstream process flows. However, the development of electrochemical extraction technologies has been impeded by the technological maturity of hydro- and pyro-metallurgy, as well as the electrical insulating properties of many metal oxide ores. The fabrication and use of carbon/insulating material composite electrodes has been a longstanding method to enable electrochemical activation. Here, using real hectorite ore, we employ this technical approach to fabricate hectorite-carbon black composite electrodes (HCCEs) and achieve electrochemical activation of hectorite. Anodic polarization results in lithium-ion release through a multi-step chemical and electrochemical mechanism that results in 50.7 ± 4.4% removal of lithium from HCCE, alongside other alkaline ions. This technical proof-of-concept study underscores that electrochemical activation of ores can facilitate lattice deterioration and ion removal from ores.

Surface Structure Dependent Activation of Hydrogen over Metal Oxides during Syngas Conversion.

Despite the extensive studies on the adsorption and activation of hydrogen over metal oxides, it remains a challenge to investigate the structure-dependent activation of hydrogen and its selectivity mechanism in hydrogenation reactions. Herein we take spinel and solid solution MnGaOx with a similar bulk chemical composition and study the hydrogen activation mechanism and reactivity in syngas conversion. The results show that MnGaOx-Solid Solution (MnGaOx-SS) is a typical Mn-doped hexagonal close-packed (HCP) Ga2O3 with a Ga-rich surface. Upon exposure to hydrogen, Ga-H and O-H species are simultaneously generated. Ga-H species are highly active but unselective in CO activation, forming CHxO, and ethylene hydrogenation, forming ethane. In contrast, MnGaOx-Spinel is a face-centered-cubic (FCC) spinel phase featuring a Mn-rich surface, thus effectively suppressing the formation of Ga-H species. Interestingly, only part of the O-H species are active for CO activation while the O-H species are inert for olefin hydrogenation over MnGaOx-Spinel. Therefore, MnGaOx-Spinel exhibits a higher activity and higher light-olefin selectivity than MnGaOx-SS in combination with SAPO-18 during syngas conversion. These fundamental understandings are essential to guide the design and further optimization of metal oxide catalysts for selectivity control in hydrogenations.

Effect of the Chemical Structure of a Self-Assembled Monolayer on the Gas-Sensing Behavior of SnO2 Nanowires.

In this study, detailed investigations of the selective sensing capability of semiconducting metal oxide (SMO)-based gas sensors with self-assembled monolayer (SAM) functionalization were conducted. The selective gas-sensing behavior was improved by employing a simple and straightforward postmodification technique using functional SAM molecules. The chemical structure of the SAM molecules promoted interaction between the gas and SAM molecules, providing a gas selective sensing of SnO2 nanowires (NWs). In addition, a bundle of SnO2 NWs provided a large surface area that could act as a sensing site. SAM functionalization was confirmed by infrared spectroscopy and thermogravimetric analysis, and the selective gas-sensing behaviors were investigated under different sensing conditions. With variations in the chemical structures of the SAM molecules, the selective gas-sensing behaviors also changed as the corresponding intermolecular interaction forces were different. This integration of selective gas sensing and passivation of a sensing surface provides a straightforward approach for the preferred gas sensing of SnO2 NWs. Furthermore, owing to the universal binding characteristics of SAM molecules to the metal oxide surface, this approach can be expanded to other SMO-based gas-sensing platforms.

Electrochemical immunosensor for the predictive cancer biomarker SLFN11 using reduced graphene oxide/MIL-101(Cr)-NH2 composite

SLFN11 is a predictive cancer biomarker essential for identifying tumors that are sensitive to DNA-damaging agents, facilitating more personalized and effective treatment approaches. Detecting this biomarker can guide therapeutic decisions and improve outcomes for cancer patients. However, existing detection methods for SLFN11 are complex and require advanced techniques. In this study, we introduce the first immunosensor designed for on-site detection of SLFN11. An advanced electrochemical immunosensor platform utilizing a composite of graphene oxide (GO) and chromium-based metal organic framework (MIL-101 (Cr)-NH2) was developed. The integration of GO and MIL-101(Cr)-NH2 was characterized through FT-IR, XRD, SEM, and XPS, affirming the formation of the composite. The subsequent electrochemical reduction to rGO/MIL-101(Cr)-NH2 significantly improved the electrochemical performance and stability. A glutaraldehyde cross-linker was then utilized to attach the SLFN11-specific antibody to the amine groups of the MOF-modified electrodes. This led to the development of rapid, sensitive, portable, and cost-effective immunosensor for SLFN11 at concentrations as low as 8.9 pg/mL which holds promise for early cancer diagnosis. High specificity was achieved, with minimal cross-reactivity observed with other cancer biomarkers such as pepsinogen I, claudin 18.2 and Programmed cell death protein 1. Demonstrating practical applicability, the electrochemical immunosensor validated by commercial ELISA kit showed successful detection in serum samples with high recovery rates and reproducibility. This research highlights the potential of rGO/MOFs composites in electrochemical biosensors developments for early cancer diagnostics and personalized medicine.

A Universal Strategy for Synthesis of Large-Area and Ultrathin Metal Oxide/rGO Film Towards Scalable Fabrication of High-Performance Wearable Microsupercapacitors.

High-performance wearable microsupercapacitor (MSC) as energy storage components is highly desirable for developing self-powering wearable electronics. However, synthesis of MSC electrode film concurrently possessing large area, ultrathin thickness, and high areal energy storage capability is still challenging. Herein, a universal strategy is reported to synthesize large-area and ultrathin metal oxide nanoparticles (MONPs)/reduced graphene oxide (rGO) hybrid-structured films by attaching self-assembled film of a wide range of MONPs onto self-assembled rGO film and subsequent carbonization. Combining a template-assisted patterning strategy and a floating film salvaging process, flexible symmetric and asymmetric MSCs based on MONPs@C/rGO films can be easily prepared in large areas. MONP agglomeration is avoided and its pseudocapacitive behavior is well utilized, thereby realizing a high areal specific capacitance of 9.32 mF cm-2 in Fe3O4@C/rGO-based symmetric MSC at a film thickness of only 275 nm, corresponding to a high volumetric specific capacitance of 338.9 F cm-3. Moreover, the MnO@C/rGO‖Fe3O4@C/rGO-based asymmetric MSC delivers a high volumetric energy density of 69.8 mWh cm-3. The MSCs also demonstrate their efficient power supply in wearable self-powering systems. This work provides a new route for scalable preparation of high-performance wearable MSCs, and also enables customizable fabrication and performance tuning of MSCs.

Application of MOS gas sensors for detecting mechanical damage of tea plants

Mechanical damage of tea plant is a serious problem in tea production. This work employed metal oxide semiconductor (MOS) gas sensors and gas chromatography-mass spectrometer (GC-MS), as an auxiliary technique, to detect tea plants with different types of mechanical damage in different severities. Various algorithms were applied. The results showed the uniformity of the results of gas sensors and GC-MS. While, it was hard for gas sensors to discriminate among tea plants with different types of mechanical damage. However, the feasibility of gas sensors for predicting the damage severity in different damaged types based on gas sensors was proven, which was more meaningful. Finally, multi-layer perceptron neural networks (MLPNN) was employed and the results showed that the correct discrimination accuracy rate for damage severity was 99.07% for the training set and 95.83% for the testing set, which indicated that MLPNN was an excellent algorithm for damage severity determination. This study provided a new technique for mechanical damage of tea plant detection and was very meaningful for tea plant protection.

Evolutionary trends and photothermal catalytic reduction performance of carbon dioxide by MOF-derived MnOx

Metal oxide catalysts derived from MOFs can inherit the excellent performance from their parent MOFs, possess abundant surface defects and high stability, and have attracted widespread interest in multiphase catalysis. In this study, we used Mn-MOF as a precursor and systematically investigated the evolution of MnOx catalysts by setting different calcination temperatures and times. XRD, SEM, TEM, Fourier transform infrared spectroscopy (FTIR), N2 adsorption–desorption analysis, XPS, H2-TPR, CO2-TPD, electrochemical characterization, and other methods were used to investigate the structural characteristics, microstructure, surface properties, and photoelectric properties of the catalysts. The catalytic performance of the catalysts was also investigated through photocatalytic carbon dioxide hydrogenation reduction tests. Research has shown that calcination temperature and time have a significant impact on the phase structure and surface properties of MnOx, and the physicochemical properties of derived MnOx can be controlled by controlling calcination temperature and time. Among them, MnOx-500 has a wider light absorption range, better electron transfer performance, richer oxygen vacancies, and excellent separation performance of photo generated charge carriers, resulting in higher photocatalytic CO2 hydrogenation and reduction performance. Its CO yield and selectivity reached 7420 μmol/g/h and above 99 %, respectively. This study provides valuable references for the preparation, optimization, and utilization in CO2 photothermal catalytic conversion of MnOx catalysts derived from MOFs.

Influence of radio-frequency magnetron sputtering power on electrical characteristics and positive bias stress stability of indium tin zinc oxide thin-film transistors

Abstract As the pursuit of high-quality display panels intensifies, the importance of high-performance thin-film transistors (TFTs) becomes increasingly prominent. Indium tin zinc oxide (ITZO) TFTs, as one of the promising directions for high-performance metal oxide TFTs, impose high demands on their performance and reliability. In this study, the performance and stability of ITZO TFTs fabricated under different radio-frequency magnetron sputtering power conditions were systematically tested and investigated. After sputtering power optimization, the field effect mobility of ITZO TFTs reaches 29.68 cm²/V·s, with a steep sub-threshold swing of 0.17 V/decade, near-zero threshold voltage, and good stability. Using atomic force microscopy and X-ray photoelectron spectroscopy characterization techniques, the thin films were analyzed to elucidate the relationship between sputtering power variations and oxygen vacancies.

Rare earth doped CeO2 uniformly enwraps graphite felt as high current density electrode for all vanadium redox flow battery

Although the introduction of metal oxides can solve the problem of poor electrochemical activity of graphite felt electrode, their low conductivity, poor dispersibility, and difficulty in nanocrystallization restrict their application development. Herein, a uniform distributed Gd or Sm doped CeO2 nanoparticle decorated graphite felt electrode is successfully prepared by hydrothermal method. The incorporation of Gd3+ or Sm3+ into the lattice of CeO2 results in the formation of numerous oxygen vacancies, acting not only as reaction sites for redox reactions but also enhancing the charge transfer rate. Compared to CeO2/GF, Ce0.8Gd0.2O2/GF and Ce0.8Sm0.2O2/GF exhibits superior electrochemical activity and lower charge transfer resistance. Correspondingly, the energy efficiency of Ce0.8Gd0.2O2/GF and Ce0.8Sm0.2O2/GF increases 4.5 % and 7.8 % at 160 mA cm−2, respectively. The maximum operating current density of Ce0.8Sm0.2O2/GF is 200 mA cm−2, while Ce0.8Gd0.2O2/GF is 160 mA cm−2. Ce0.8Sm0.2O2/GF achieves an energy efficiency of 69.3 % using a flow-by flow field at 200 mA cm−2. The optimal doping concentration for Sm is 20 %. The Ce0.8Sm0.2O2/GF stably operate for 500 cycles at 100 mA cm−2 and the Ce0.8Sm0.2O2 nanoparticles adhere firmly to the GF without observed detachment. These results demonstrate that Ce0.8Sm0.2O2/GF with high activity and stability is a promising electrode for VRFB.

Experimental and artificial neural network (ANN) study on the impact of three different metal oxide nanoparticle combustion enhancers enriched on mahua biodiesel-diesel fuelled CI engine

Abstract The prediction of CI engine parameters has acquired significant attention and is regarded as a crucial tool for engine research and diagnosis studies. This contribution compares two different approaches for diesel engine viz. experimental and artificial neural networks (ANNs) predictions of performance and emission outputs. The base fuel M30 blend consist of mahua biodiesel 30 (% v) and 70 (% v) of diesel. The M30 blend and 50 ppm concentration of NPs (CeO2, CuO, and TiO2) were chosen for basic experimentation. The findings indicate an increase in BTE by 9.1%, peak CP by 11.3%, and HRR by 10.2%, with a decrease in BSFC by 13.7%, CO by 30.4%, HC by 30.1%, smoke by 34.7%, and NOx by 7.1%, resulting from the addition of 50 ppm CeO2 NP to D70M30 blend. The widely used backpropagation technique for ANN is implemented in multilayered feedforward design. To forecast the engine characteristics of a CI engine, a network structures including two inputs and one output is used. The given ANN model examined D100, M30, M30CeNP50, M30CuNP50, and M30TNP50 blends, using engine load and biodiesel with nanoparticle blend as the two input factors. A data-driven ANN model was created to forecast the optimised engine characteristics. The lowest and highest value of correlation coefficient (R2) and mean square errors (MSE), mean relative error (MRE) were found to for peak CP, HRR, BTE, BSFC, CO, CO2, HC, NOx and smoke. Using ANN one can choose right blend ratio among the variety of fuels blends for an appropriate requirement without much experimentation.

A gallium oxide MESFET transistor with potential barrier layers for high-power and high-frequency applications

Abstract In this article, a novel gallium oxide metal semiconductor field effect transistor (MESFET) is presented. This device is designed for high-power and high-frequency usage and features embedded potential barrier layers on each side of the gate metal within the channel. The gallium oxide semiconductor (Ga2O3) is highly valued in semiconductor technologies because of its large band gap (4.9–4.8 eV) and high breakdown field (6–8 MV cm−1). These properties make it suitable for high-power and high-frequency operations. We call the proposed structure; the potential barrier layers in Gallium Oxide MESFET (PBL-GO-MESFET). The key idea in the PBL-GO-MESFET transistor is embedding the PB layers to control the electric field distribution. Because of the PB layers, an increased breakdown voltage is observed in the PBL-GO-MESFET device, which is in contrast to conventional GO-MESFET (C-GO-MESFET) devices. The simulation findings indicate that the PBL-GO-MESFET transistor surpasses the C-GO-MESFET transistor in terms of breakdown voltage and radio frequency (RF) traits.