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Transition metal oxides are a great alternative to less expensive hydrogen evolution reaction (HER) catalysts. However, the lack of conductivity of these materials requires a conductor material to support them and improve the activity toward HER. On the other hand, carbon paste electrodes result in a versatile and cheap electrode with good activity and conductivity in electrocatalytic hydrogen production, especially when the carbonaceous material is agglomerated with ionic liquids. In the present work, an electrode composed of multi-walled carbon nanotubes (MWCNTs) and cobalt ferrite oxide (CoFe2O4) was prepared. These compounds were included on an electrode agglomerated with the ionic liquid N-octylpyridinium hexafluorophosphate (IL) to obtain the modified CoFe2O4/MWCNTs/IL nanocomposite electrode. To evaluate the behavior of each metal of the bimetallic oxide, this compound was compared to the behavior of MWCNTs/IL where a single monometallic iron or cobalt oxides were included (i.e., α-Fe2O3/MWCNTs/IL and Co3O4/MWCNTs/IL). The synthesis of the oxides has been characterized by X-ray diffraction (XRD), RAMAN spectroscopy, and field emission scanning electronic microscopy (FE-SEM), corroborating the nanometric character and the structure of the compounds. The CoFe2O4/MWCNTs/IL nanocomposite system presents excellent electrocatalytic activity toward HER with an onset potential of -270 mV vs. RHE, evidencing an increase in activity compared to monometallic oxides and exhibiting onset potentials of -530 mV and -540 mV for α-Fe2O3/MWCNTs/IL and Co3O4/MWCNTs/IL, respectively. Finally, the system studied presents excellent stability during the 5 h of electrolysis, producing 132 µmol cm-2 h-1 of hydrogen gas.

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This study focuses on the synthesis of mixed metal oxide anodes (MMOs) with the composition Ti/RuO2Sb2O4Ptx (where x = 0, 5, 10 mol) using hybrid microwave irradiation heating. The synthesized electrodes were characterized using scanning electron microscopy, X-ray energy-dispersive analysis, X-ray diffraction, cyclic voltammetry, and electrochemical impedance spectroscopy. These electrodes were then evaluated in both bulk electrolytic and fuel cell tests within a reversible chloralkaline electrochemical cell. The configurations using the electrodes Ti/(RuO2)0.7-(Sb2O4)0.3 and Ti/(RuO2)66.5-(Sb2O4)28.5-Pt5 presented lower onset potential for oxygen and chlorine evolution reactions and reduced resistance to charge transfer compared to the Ti/(RuO2)63-(Sb2O4)27-Pt10 variant. These electrodes demonstrated notable performance in reversible electrochemical cells, achieving Coulombic efficiencies of up to 60% when operating in the electrolytic mode at current densities of 150 mA cm-2. They also reached maximum power densities of 1.2 mW cm-2 in the fuel cell. In both scenarios, the presence of platinum in the MMO coating positively influenced the process. Furthermore, a significant challenge encountered was crossover through the membranes, primarily associated with gaseous Cl2. This study advances our understanding of reversible electrochemical cells and presents possibilities for further exploration and refinement. It demonstrated that the synergy of innovative electrode synthesis strategies and electrochemical engineering can lead to promising and sustainable technologies for energy conversion.

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In a changing environmental scenario, acid rain can have a significant impact on aquatic ecosystems. Acidification is known to produce corrosion in metals, hence increasing their harmful effects on the environment, organisms and human health. The prevalent use of metallic nanoparticles (NPs) in everyday products raises concerns regarding exposure and nanotoxicity even in these acidified conditions. We thus report on the cytotoxic and genotoxic potential of nickel oxide (NiO-NP) and zinc oxide (ZnO-NP) NPs when suspended in aqueous media in light of pH variations (7.5 and 5). A modified microsuspension method of the Salmonella/microsome assay was adopted, and strains (TA97a, TA98, TA100, TA102) were exposed to NPs (10-1280 µg/plate) with and without a metabolization fraction. The acidic condition favored disaggregation and caused a decrease in NPs size. Mutagenicity was observed in all samples and different strains, with greater DNA base pair substitution damage (TA100 and TA102), but extrinsic conditions (pH) suggest different action mechanisms of NiO-NP and ZnO-NP on genetic content. Mutagenic activity was found to increase upon metabolic activation (TA98, TA100, and TA102) demonstrating the bioactivity of NiO-NP and ZnO-NP in relation to metabolites generated by the mammalian p450 system in vitro. Modifications in the Salmonella assay methodology increased cell exposure time. The observed responses recommend this modified assay as one of the methodologies of choice for nanoecotoxicological evaluation. These findings emphasize the significance of incorporating the environmental context when evaluating the toxicity of metal-based NPs.

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The development of technologies capable of producing efficient and economically viable anodes is essential for the electrochemical treatment of water contaminated with complex organic pollutants. In this context, the use of ionic liquids as solvents to prepare mixed metal oxide (MMO) anodes has proven to be an up-and-coming alternative. Here, we analyze the influence of the temperature of calcination (300, 350, and 400 ºC) on the production of Ti(RuO2)0.8-(Sb2O4)0.2 anodes made using the thermal decomposition method using three ionic liquids (IL) as solvents: dipropyl ammonium acetate (DPA-Ac), dipropyl ammonium propionate (DPA-Pr), and dipropyl ammonium butyrate (DPA-Bu). The decomposition temperature for all IL, accessed by thermogravimetry, is below 200 ºC. Physical and electrochemical analyses demonstrate that the calcination temperature of the anodes is decisive for their durability and electrochemical properties. Anodes prepared with DPA-Bu at 350 ºC show higher stability (around 35 h) than those made with other ILs at temperatures of 300 and 400 ºC and improved results in terms of 4-NP mineralization, where 97% of TOC removal was achieved in 120 min. It could be verified that the calcination temperature and IL employed had a decisive influence on the characteristics of the presented anodes. Therefore, the anode prepared with DPA-Bu at 350 ºC is promising for application in the degradation of organic compounds.

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The improper disposal of toxic and carcinogenic organic substances resulting from the manufacture of dyes, drugs and pesticides can contaminate aquatic environments and potable water resources and cause serious damage to animal and human health and to the ecosystem. In this sense, heterogeneous photocatalysis stand out as one effective and cost-effective water depollution technique. The use of metal oxide nanocomposites (MON), from the mixture of two or more oxides or between these oxides and other functional semiconductor materials, have gained increasing attention from researchers and industrial developers as a potential alternative to produce efficient and environmentally friendly photocatalysts for the remediation of water contamination by organic compounds. Thus, this work presents an updated review of the main advances in the use of metal oxide nanocomposites-based photocatalysts for decontamination of water polluted by these substances. A bibliometric analysis allowed to show the evolution of the importance of this research topic in the literature over the last decade. The results of the study also showed that hierarchical and heterogeneous nanostructures of metal oxides, as well as conducting polymers and carbon materials, currently stand out as the main materials for the synthesis of MON, with better photocatalysis performance in the degradation of dyes, pharmaceuticals and pesticides.

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This work presents an innovative application of Frequency Response Analysis (FRA) in order to detect early degradation of Metal Oxide Surge Arresters (MOSAs). This technique has been widely used in power transformers, but has never been applied to MOSAs. It consists in comparisons of spectra, measured at different instants of the lifetime of the arrester. Differences between these spectra are an indicator that some electrical properties of the arrester have changed. An incremental deterioration test has been performed on arrester samples (with controlled circulation of leakage current, which increases the energy dissipation over the device), and the FRA spectra correctly identified the progression of damage. Although preliminary, the FRA results seemed promising, and it is expected that this technology could be used as another diagnostic tool for arresters.

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The development of new materials for the construction sector is a global trend, and products that use by-products in their composition and have also incorporated technology are commercially competitive. Microparticles have large surface areas and can modify the microstructure of materials, positively affecting their physical and mechanical properties. In this context, this study aims to investigate the effect of incorporating aluminium oxide (Al2O3) microparticles on the physical and mechanical properties of oriented strand boards (OSBs) made from reforested residual balsa and castor oil polyurethane resin and to evaluate their durability performance under accelerated aging conditions. The OSBs were produced on a laboratory scale with a density of 650 kg/m3, strand-type particles measuring 90 × 25 × 1 mm3, using castor oil-based polyurethane resin (13%) and Al2O3 microparticle content ranging from 1% to 3% of the resin mass. The physical and mechanical properties of the OSBs were determined following the EN-300:2002 recommendations. The results obtained indicated that the OSBs with 2% Al2O3 presented thickness swelling significantly lower (at the 5% significance level) after being subjected to accelerated aging and internal bonding of the particles higher than the values obtained for the references, evidencing the positive effect of including Al2O3 microparticles in balsa OSBs.

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BACKGROUND: The biogenic synthesis of metallic nanoparticles is a green alternative that reduces the toxicity of this nanomaterials and may enable a synergy between the metallic core and the biomolecules employed in the process enhancing biological activity. The aim of this study was to synthesize biogenic titanium nanoparticles using the filtrate of the fungus Trichoderma harzianum as a stabilizing agent, to obtain a potential biological activity against phytopathogens and mainly stimulate the growth of T. harzianum, enhancing its efficacy for biological control. RESULTS: The synthesis was successful and reproductive structures remained in the suspension, showing faster and larger mycelial growth compared to commercial T. harzianum and filtrate. The nanoparticles with residual T. harzianum growth showed inhibitory potential against Sclerotinia sclerotiorum mycelial growth and the formation of new resistant structures. A great chitinolytic activity of the nanoparticles was observed in comparison with T. harzianum. In regard to toxicity evaluation, an absence of cytotoxicity and a protective effect of the nanoparticles was observed through MTT and Trypan blue assay. No genotoxicity was observed on V79-4 and 3T3 cell lines while HaCat showed higher sensitivity. Microorganisms of agricultural importance were not affected by the exposure to the nanoparticles, however a decrease in the number of nitrogen cycling bacteria was observed. In regard to phytotoxicity, the nanoparticles did not cause morphological and biochemical changes on soybean plants. CONCLUSION: The production of biogenic nanoparticles was an essential factor in stimulating or maintaining structures that are important for biological control, showing that this may be an essential strategy to stimulate the growth of biocontrol organisms to promote more sustainable agriculture.

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In the last decade, TiO2 nanotubes have attracted the attention of the scientific community and industry due to their exceptional photocatalytic properties, opening a wide range of additional applications in the fields of renewable energy, sensors, supercapacitors, and the pharmaceutical industry. However, their use is limited because their band gap is tied to the visible light spectrum. Therefore, it is essential to dope them with metals to extend their physicochemical advantages. In this review, we provide a brief overview of the preparation of metal-doped TiO2 nanotubes. We address hydrothermal and alteration methods that have been used to study the effects of different metal dopants on the structural, morphological, and optoelectrical properties of anatase and rutile nanotubes. The progress of DFT studies on the metal doping of TiO2 nanoparticles is discussed. In addition, the traditional models and their confirmation of the results of the experiment with TiO2 nanotubes are reviewed, as well as the use of TNT in various applications and the future prospects for its development in other fields. We focus on the comprehensive analysis and practical significance of the development of TiO2 hybrid materials and the need for a better understanding of the structural-chemical properties of anatase TiO2 nanotubes with metal doping for ion storage devices such as batteries.

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There is a recognized need for the development of cost-effective, stable, fast, and optimized novel materials for technological applications. Substantial research has been undertaken on the role of polymeric nanocomposites in sensing applications. However, the use of PANI-based nanocomposites in impedimetric and capacitive electrochemical sensors has yet to be understood. The present study aimed to explore the relationship between the sensitivity and linearity of electrochemical pH sensors and the composition of nanocomposites. Thin films of PANI/CeO2 and PANI/WO3 were deposited via spin coating for characterization and application during the electrochemical impedance and capacitance spectroscopy (EIS and ECS) transduction stages. The findings showed that the optimized performance of the devices was extended not only to the sensitivity but also to the linearity. An increase of 213% in the ECS sensitivity of the PANI/CeO2 compared to the metal oxide and an increase of 64% in the ECS linearity of the PANI/WO3 compared to the polymeric sensitivity were reported. This study identified the structure-property relationship of nanocomposite thin films of PANI with metal oxides for use in electrochemical sensors. The developed materials could be applied in devices to be used in different fields, such as food, environment, and biomedical monitoring.

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Metal oxide (MOx) gas sensors have attracted considerable attention from both scientific and practical standpoints. Due to their promising characteristics for detecting toxic gases and volatile organic compounds (VOCs) compared with conventional techniques, these devices are expected to play a key role in home and public security, environmental monitoring, chemical quality control, and medicine in the near future. VOCs (e.g., acetone) are blood-borne and found in exhaled human breath as a result of certain diseases or metabolic disorders. Their measurement is considered a promising tool for noninvasive medical diagnosis, for example in diabetic patients. The conventional method for the detection of acetone vapors as a potential biomarker is based on spectrometry. However, the development of MOx-type sensors has made them increasingly attractive from a medical point of view. The objectives of this review are to assess the state of the art of the main MOx-type sensors in the detection of acetone vapors to propose future perspectives and directions that should be carried out to implement this type of sensor in the field of medicine.

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This paper presents a literature review on the subject of Condition-Based Maintenance of surge arresters. Both a bibliometric analysis and traditional comprehensive research are presented. The bibliometric analysis is useful for obtaining insights about the literature. It quantitatively highlights relationships between journals, authors and keywords (related to the monitoring methods) and reveals future trends for research based on the timeline of the keywords. The traditional comprehensive literature review is also presented. It summarizes the methods, their advantages and disadvantages and also points to some known measurement issues of the methods. Both online (leakage current, harmonic components, temperature, partial discharges, power loss and the counting of discharges) and offline (reference voltage, residual voltage, insulation resistance, polarization/depolarization, return voltage, microscopy, spectrometry, X-ray, RUS and the recent application of FRA) methods have been qualitatively analyzed.

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Memristors are expected to be one of the key building blocks for the development of new bio-inspired nanoelectronics. Memristive effects in transition metal oxides are usually linked to the electromigration at the nanoscale of charged oxygen vacancies (OV). In this paper we address, for Pt/TiOx/TaOy/Pt devices, the exchange of OV between the device and the environment upon the application of electrical stress. From a combination of experiments and theoretical simulations we determine that both TiOxand TaOylayers oxidize, via environmental oxygen uptake, during the electroforming process. Once the memristive effect is stabilized (post-forming behavior) our results suggest that oxygen exchange with the environment is suppressed and the OV dynamics that drives the memristive behavior is restricted to an internal electromigration between TiOxand TaOylayers. Our work provides relevant information for the design of reliable binary oxide memristive devices.

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The capacity to generate a constant signal response from an enzyme on an electrode surface has been a fascinating topic of research from the past three decades. To nourish the enzymatic activity during electrochemical reactions, the immobilization of dual enzymes on the electrode surface could prevent the enzymatic loss without denaturation and thus long-term stability can be achieved. For effective immobilization of dual enzymes, mesoporous materials are the ideal choice because of its numerous advantages such as 1. The presence of porous structure facilitates high loading of enzymes 2. The formation of protective environment can withstand the enzymatic activity even at acidic or basic pH values and even at elevated temperatures. Herein, we develop bienzymatic immobilization of horseradish peroxidase (HRP) and cholesterol oxidase (ChOx) on mesoporous V2O5-TiO2 based binary nanocomposite for effective sensing of hydrogen peroxide (H2O2) in presence of redox mediator hydroquinone (HQ). The utilization of redox mediator in second-generation biosensing of H2O2 can eliminate the interference species and reduces the operating potential with higher current density for electrochemical reduction reaction. Using this mediator transfer process approach at HRP/ChOx/V2O5-TiO2 modified GC, the H2O2 can be determined at operating potential (-0.2 V) with good linear range (0.05-3.5 mM) higher sensitivity (1040 µAµM-1 cm-2) and lower detection limit of about 20 µM can be attained, which is due to higher mediation of electrons were transferred to the enzyme cofactors. These interesting characteristics could be due to mesoporous structure of V2O5-TiO2 can induce large immobilization and facilitate higher interaction with enzymes for wide range of biosensing applications.

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Biomaterials with adequate properties to direct a biological response are essential for orthopedic and dental implants. The surface properties are responsible for the biological response; thus, coatings with biologically relevant properties such as osteoinduction are exciting options to tailor the surface of different bulk materials. Metal oxide coatings such as TiO2, ZrO2, Nb2O5 and Ta2O5 have been suggested as promising for orthopedic and dental implants. However, a comparative study among them is still missing to select the most promising for bone-growth-related applications. In this work, using magnetron sputtering, TiO2, ZrO2, Ta2O5, and Nb2O5 thin films were deposited on Si (100) substrates. The coatings were characterized by Optical Profilometry, Scanning Electron Microscopy, Energy-Dispersive X-ray Spectroscopy, X-ray Photoelectron Spectroscopy, X-ray Diffraction, Water Contact Angle measurements, and Surface Free Energy calculations. The cell adhesion, viability, proliferation, and differentiation toward the osteoblastic phenotype of mesenchymal stem cells plated on the coatings were measured to define the biological response. Results confirmed that all coatings were biocompatible. However, a more significant number of cells and proliferative cells were observed on Nb2O5 and Ta2O5 compared to TiO2 and ZrO2. Nevertheless, Nb2O5 and Ta2O5 seemed to induce cell differentiation toward the osteoblastic phenotype in a longer cell culture time than TiO2 and ZrO2.

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Enhancing the current signal response for semiconductors is the key factor for designing and fabrication of efficient electrode in electrochemical sensors. By the aid of doping with binary metal oxides, the conductivity of the resultant titanium oxide (TiO2) based nanocomposite will deliver fast electron transfer rate at the heterojunction interface. Herein, by taking advantage of mesoporous structure in TiO2, cubic shaped multivalent cerium oxide (CeO2) was incorporated into the porous cavity by simple ground assisted solvothermal process, which resulted in enormous enhancement in the current response towards detection of 2-aminophenol. The advantage of CeO2 on TiO2 not only involves the loading of binary metal oxide on its mesoporous sites, but also facilitates the formation of CeO2 nanocrystals which induce larger surface area and high electroactive sites with rapid diffusion of target species through pores. As a result, CeO2-TiO2 on modified GC electrode exhibits drastic enhancement in the current response for oxidation of 2-aminophenol with large decrease in the onset potential than TiO2/GC electrode. Furthermore, the CeO2-TiO2 modified electrode shows significant behavior for sensing of 2-aminophenol with wide linear range of 0.01-500 µM. The sensitivity and detection limit were calculated to be 0.603 µA µM cm-2 and 3.5 nM respectively. This work establishes the facile strategy for decoration of binary metal oxide-based nanocomposites as effective electrode and also possible to create new opportunities in the designing and fabrication of variety of efficient electrode in various electrochemical applications.

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Over the last two decades, oxide nanostructures have been continuously evaluated and used in many technological applications. The advancement of the controlled synthesis approach to design desired morphology is a fundamental key to the discipline of material science and nanotechnology. These nanostructures can be prepared via different physical and chemical methods; however, a green and ecofriendly synthesis approach is a promising way to produce these nanostructures with desired properties with less risk of hazardous chemicals. In this regard, ZnO and TiO2 nanostructures are prominent candidates for various applications. Moreover, they are more efficient, non-toxic, and cost-effective. This review mainly focuses on the recent state-of-the-art advancements in the green synthesis approach for ZnO and TiO2 nanostructures and their applications. The first section summarizes the green synthesis approach to synthesize ZnO and TiO2 nanostructures via different routes such as solvothermal, hydrothermal, co-precipitation, and sol-gel using biological systems that are based on the principles of green chemistry. The second section demonstrates the application of ZnO and TiO2 nanostructures. The review also discusses the problems and future perspectives of green synthesis methods and the related issues posed and overlooked by the scientific community on the green approach to nanostructure oxides.

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The production and demand of nanoparticles in the manufacturing sector and personal care products, release a large number of engineered nanoparticles (ENPs) into the atmosphere, aquatic ecosystems, and terrestrial environments. The intentional or involuntary incorporation of ENPs into the environment is carried out through different processes. The ENPs are combined with other compounds and release into the atmosphere, settling on the ground due to the water cycle or other atmospheric phenomena. In the case of aquatic ecosystems, the ENPs undergo hetero-aggregation and sedimentation, reaching different living organisms and flora, as well as groundwater. Accordingly, the high mobility of ENPs in diverse ecosystems is strongly related to physical, chemical, and biological processes. Recent studies have been focused on the toxicological effects of a wide variety of ENPs using different validated biological models. This literature review emphasizes the study of toxicological effects related to using the most common ENPs, specifically metal and metal/oxides-based nanoparticles, addressing different synthesis methodologies, applications, and toxicological evaluations. The results suggest negative impacts on biological models, such as oxidative stress, metabolic and locomotive toxicity, DNA replication dysfunction, and bioaccumulation. Finally, it was consulted the protocols for the control of risks, following the assessment and management process, as well as the classification system for technological alternatives and risk management measures of ENPs, which are useful for the transfer of technology and nanoparticles commercialization.

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Gas sensors are fundamental for continuous online monitoring of volatile organic compounds. Gas sensors based on semiconductor materials have demonstrated to be highly competitive, but are generally made of expensive materials and operate at high temperatures, which are drawbacks of these technologies. Herein is described a novel ethanol sensor for room temperature (25 °C) measurements based on hematite (α­Fe2O3)/silver nanoparticles. The AgNPs were shown to increase the oxide semiconductor charge carrier density, but especially to enhance the ethanol adsorption rate boosting the selectivity and sensitivity, thus allowing quantification of ethanol vapor in 2-35 mg L-1 range with an excellent linear relationship. In addition, the α-Fe2O3/Ag 3.0 wt% nanocomposite is cheap, and easy to make and process, imparting high perspectives for real applications in breath analyzers and/or sensors in food and beverage industries. This work contributes to the advance of gas sensing at ambient temperature as a competitive alternative for quantification of conventional volatile organic compounds.

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In this study, binary and ternary mixed metal oxide anodes of Ti/RuO2-Sb2O4 and Ti/RuO2-Sb2O4-TiO2 were prepared using two different heating methods: conventional furnace and alternative CO2 laser heating. The produced anodes were physically and electrochemically characterized by using different techniques. The main difference found in the laser-made anodes was their more compact morphology, without the common deep cracks found in anodes made by typical thermal decomposition, which showed an important correlation with the prolonged accelerated service life. The correlation between the physicochemical properties of the anodes with their performance towards the 4-nitrophenol oxidations is discussed. The results demonstrated that the ternary anode (Ti/RuO2-Sb2O4-TiO2) is very promising, presenting a kinetic 5.7 times faster than the respective binary anode and the highest removal efficiency when compared with conventionally made anodes. Also, the lowest energy consumption per unit of mass of contaminant removed is seen for the laser-made Ti/RuO2-Sb2O4-TiO2 anode, which evidences the excellent cost-benefit of this anode material. Finally, some by-products were identified, and a degradation route is proposed. Graphical abstract.

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