Search Results (203)

Nickel–titanium (NiTi) shape memory alloys are promising materials for orthopedic implants due to their unique mechanical properties, including superelasticity and shape memory effect. However, the high nickel content in NiTi alloys raises concerns about biocompatibility and potential cytotoxic effects. This review focuses on the recent advancements in surface modification techniques aimed at enhancing the properties of NiTi alloys for biomedical applications, with particular emphasis on low-temperature glow discharge plasma oxidation methods. The review explores various surface engineering strategies, including oxidation, nitriding, ion implantation, laser treatments, and the deposition of protective coatings. Among these, low-temperature plasma oxidation stands out for its ability to produce uniform, nanocrystalline layers of titanium dioxide (TiO₂), titanium nitride (TiN), and nitrogen-doped TiO₂ layers, significantly enhancing corrosion resistance, reducing nickel ion release, and promoting osseointegration. Plasma-assisted oxynitriding processes enable the creation of multifunctional coatings with improved mechanical and biological properties. The applications of modified NiTi alloys in orthopedic implants, including spinal fixation devices, joint prostheses, and fracture fixation systems, are also discussed. Despite these promising advancements, challenges remain in achieving large-scale reproducibility, controlling process parameters, and reducing production costs. Future research directions include integrating bioactive and antibacterial coatings, enhancing surface structuring for controlled biological responses, and expanding clinical validation. Addressing these challenges can unlock the full potential of surface-modified NiTi alloys in advanced orthopedic applications for safer, longer-lasting, and more effective medical implants. Full article

The electrochemical reduction of CO₂ (CO₂RR) to value-added products has garnered significant interest as a sustainable solution to mitigate CO₂ emissions and harness renewable energy sources. Among CO₂RR products, formic acid/formate (HCOOH/HCOO⁻) is particularly attractive due to its industrial relevance, high energy density, and potential candidate as a liquid hydrogen carrier. This study investigates the influence of the initial oxidation state of tin on CO₂RR performance using nanostructured SnO_x catalysts. A simple, quick, scalable, and cost-effective synthesis strategy was employed to fabricate SnO_x catalysts with controlled oxidation states while maintaining consistent morphology and particle size. The catalysts were characterized using SEM, TEM, XRD, Raman, and XPS to correlate structure and surface properties with catalytic performance. Electrochemical measurements revealed that SnO_x catalysts annealed in air at 525 °C exhibited the highest formate selectivity and current density, attributed to the optimized oxidation state and the presence of oxygen vacancies. Flow cell tests further demonstrated enhanced performance under practical conditions, achieving stable formate production with high faradaic efficiency over prolonged operation. These findings highlight the critical role of tin oxidation states and surface defects in tuning CO₂RR performance, offering valuable insights for the design of efficient catalysts for CO₂ electroreduction to formate. Full article

Biological neural circuits are based on the interplay of excitatory and inhibitory events to achieve functionality. Axons form long-range information highways in neural circuits. Axon pruning, i.e., the removal of exuberant axonal connections, is essential in network remodeling. We propose the photocatalytic growth and chemical dissolution of gold lines as a building block for neuromorphic computing mimicking axon growth and pruning. We predefine photocatalytic growth areas on a surface by structuring titanium dioxide (TiO₂) patterns. Placing the samples in a gold chloride (HAuCl₄) precursor solution, we achieve the controlled growth of gold microstructures along the edges of the indium tin oxide (ITO)/TiO₂ patterns under ultraviolet (UV) illumination. A potassium iodide (KI) solution is employed to dissolve the gold microstructures. We introduce a real-time monitoring setup based on an optical transmission microscope. We successfully observe both the growth and dissolution processes. Additionally, scanning electron microscopy (SEM) analysis confirms the morphological changes before and after dissolution, with dissolution rates closely aligned to the growth rates. These findings demonstrate the potential of this approach to emulate dynamic biological processes, paving the way for future applications in adaptive neuromorphic systems. Full article

This study investigates the effects of varying indium tin oxide (ITO) layer thicknesses and the patterning of the ITO layer on the growth of metallic gold (Au) nano- and microstructures on titanium dioxide (TiO₂) templates. The ITO-TiO₂ heterojunction serves to collect photogenerated electrons in the ITO sublayer, facilitating their transport to the pattern edges and concentrating photocatalytic activity at these edges. Six template types were fabricated on glass substrates, with systematic variations in ITO thickness (0, 3, 6, 10, and 30 nm) and different ITO patterning methods (either continuous or patterned with the TiO₂ layer). Photocatalytic gold growth was carried out on each of the substrates, and morphological analysis was conducted using scanning electron microscopy (SEM). Results showed that a 6 nm ITO layer beneath a 70 nm TiO₂ layer yielded the most uniform gold lines, characterized by 3D flower-shaped structures and enhanced edge growth. Conductance measurements indicated a value of 23 mS, suggesting potential applications in bio-inspired electronics. These findings provide insights into optimizing gold structure growth for advanced neuromorphic devices. Full article

In this study, tin oxide (SnO₂)/polyaniline (PANI) composite nanowires (NWs) with varying amounts of PANI were synthesized for carbon dioxide (CO₂) gas sensing at room temperature (RT, 25 °C). SnO₂ NWs were fabricated via the vapor–liquid–solid (VLS) method, followed by coating with PANI. CO₂ sensing investigations revealed that the sensor with 186 μL PANI exhibited the highest response to CO₂ at RT. Additionally, the optimized sensor demonstrated excellent selectivity for CO₂, long-term stability, and reliable performance across different humidity levels. The enhanced sensing performance of the optimized sensor was attributed to the formation of SnO₂-PANI heterojunctions and the optimal PANI concentration. This study underscores the potential of SnO₂-PANI composites for CO₂ detection at RT. Full article

This study explores the surface chemistry and electrical responses of ultra-high-sensitivity SnO₂ MEMS arrays to enable a novel sequential detection methodology for detecting nitrogen dioxide (NO₂) and ethanol (C₂H₅OH) as a route to achieve selective gas sensing in electronic nose (E-nose) applications. Utilizing tin oxide (SnO₂) thin films deposited via atomic layer deposition (ALD), the array achieves the lowest reported detection limits of 8 parts per billion (ppb) for NO₂. The research delves into the detection mechanisms of NO₂ and C₂H₅OH, both individually and in subsequent exposures, assessing the sensor’s dynamic response across various operating temperatures. It demonstrates rapid response and recovery times, with averages of 48 s and 277 s for NO₂ and 40 and 48 for C₂H₅OH. Understanding the role of individual gases on the SnO₂ surface chemistry is paramount in discerning subsequent gas exposure behavior. The oxidizing behavior of C₂H₅OH following NO₂ exposure is attributed to interactions between NO₂ and oxygen vacancies on the SnO₂ surface, which leads to the formation of nitrate or nitrite species. These species subsequently influence interactions with C₂H₅OH, inducing oxidizing properties, and need to be carefully considered. Principal component analysis (PCA) was used to further improve the sensor’s capability to precisely identify and quantify gas mixtures, improving its applicability for real-time monitoring in complex scenarios. Full article

Chemical nanosensors based on nanoparticles of tin dioxide and graphene-decorated tin dioxide were developed and characterized to detect low NO₂ concentrations. Sensitive layers were prepared by the drop casting method. SEM/EDX analyses have been used to investigate the surface morphology and the elemental composition of the sensors. Photoactivation of the sensors allowed for detecting ultra-low NO₂ concentrations (100 ppb) at room temperature. The sensors showed very good sensitivity and selectivity to NO₂ with low cross-responses to the other pollutant gases tested (CO and CH₄). The effect of humidity and the presence of graphene on sensor response were studied. Comparative studies revealed that graphene incorporation improved sensor performance. Detections in complex atmosphere (CO + NO₂ or CH₄ + NO₂, in humid air) confirmed the high selectivity of the graphene sensor in near-real conditions. Thus, the responses were of 600%, 657% and 540% to NO₂ (0.5 ppm), NO₂ (0.5 ppm) + CO (5 ppm) and NO₂ (0.5 ppm) + CH₄ (10 ppm), respectively. In addition, the detection mechanisms were discussed and the possible redox equations that can change the sensor conductance were also considered. Full article

This paper presents the results of a study on the characteristics of semiconductor sensors based on thin SnO₂ films modified with antimony, dysprosium, and silver impurities and dispersed double Pt/Pd catalysts deposited on the surface to detect carbon monoxide (CO). An original technology was developed, and ceramic targets were made from powders of Sn-Sb-O, Sn–Sb-Dy–O, and Sn–Sb-Dy-Ag–O systems synthesized by the sol–gel method. Films of complex composition were obtained by RF magnetron sputtering of the corresponding targets, followed by technological annealing at various temperatures. The morphology of the films, the elemental and chemical composition, and the electrical and gas-sensitive properties were studied. Special attention was paid to the effect of the film composition on the stability of sensor parameters during long-term tests under the influence of CO. It was found that different combinations of concentrations of antimony, dysprosium, and silver had a significant effect on the size and distribution of nanocrystallites, the porosity, and the defects of films. The mechanisms of degradation under prolonged exposure to CO were examined. It was established that Pt/Pd/SnO₂:0.5 at.% Sb film with optimal crystallite sizes and reduced porosity provided increased stability of carbon monoxide sensor parameters, and the response to the action of 100 ppm carbon monoxide was G₁/G₀ = 2–2.5. Full article

For the first time, nitrogen- and carbon-present tin dioxide-supported palladium composite catalysts (denoted as Pd/N-C-SnO₂) were prepared via an HCH method (HCH is the abbreviation for the hydrothermal process–calcination–hydrothermal process preparation process). In this work, firstly, three catalyst carriers (denoted as cc) were prepared using a hydrothermal-process-aided calcination method, and catalyst carriers prepared using ammonia monohydrate (NH₃∙H₂O), N,N-dimethylformamide (C₃H₇NO) and triethanolamine (C₆H₁₅NO₃) as the nitrogen sources were nominated as cc₁, cc₂ and cc₃, respectively. Secondly, these catalyst carriers were reacted with palladium oxide monohydrate (PdO·H₂O) hydrothermally to generate catalysts c₁, c₂ and c₃. As testified by XRD and XPS, besides carbon materials and the N-containing substances, the main substances of all prepared catalysts were SnO₂ and metallic palladium (Pd). Above all things, all resultant catalysts, especially c₂, showed a prominent electrocatalytic activity towards the ethanol oxidation reaction (EOR). As indicated by the CV (cyclic voltammetry) results, all fabricated catalysts presented a clear electrocatalytic activity towards the EOR. In the CA (chronoamperometry) measurement, the faradaic current density of EOR measured on c₂ at −0.27 V vs. an SCE (saturated calomel electrode) after 7200 s was still maintained at about 5.6 mA cm⁻². Preparing a novel catalyst carrier, N-C-SnO₂, and preparing a new EOR catalyst, Pd/N-C-SnO₂, were the principal dedications of this preliminary work, which was very beneficial to the development of Pd-based EOR catalysts. Full article

This article presents the results of the formation of hierarchical micro–nano structures in nanostructured tin dioxide films obtained from the lyophilic film-forming system SnCl₄/EtOH/NH₄OH. The classification of the shape and size of the synthesized structures, in relation to the pH of the solution, is presented. Measurements were carried out on an X-ray diffractometer to study the crystal structure of the samples analyzed. It was found that SnO₂ and NH₄Cl crystallites participate in the formation of the synthesized hierarchical structures. It is shown that the mechanism of the formation of hierarchical structures depends on the amount of ammonium hydroxide added. This makes it possible to control the shape and size of the synthesized structures by changing the ratio of precursors. Full article

Graphene and MXenes have emerged as promising materials for gas sensing applications due to their unique properties and superior performance. This review focuses on the fabrication techniques, applications, and sensing mechanisms of graphene and MXene-based composites in gas sensing. Gas sensors are crucial in various fields, including healthcare, environmental monitoring, and industrial safety, for detecting and monitoring gases such as hydrogen sulfide (H₂S), nitrogen dioxide (NO₂), and ammonia (NH₃). Conventional metal oxides like tin oxide (SnO₂) and zinc oxide (ZnO) have been widely used, but graphene and MXenes offer enhanced sensitivity, selectivity, and response times. Graphene-based sensors can detect low concentrations of gases like H₂S and NH₃, while functionalization can improve their gas-specific selectivity. MXenes, a new class of two-dimensional materials, exhibit high electrical conductivity and tunable surface chemistry, making them suitable for selective and sensitive detection of various gases, including VOCs and humidity. Other materials, such as metal-organic frameworks (MOFs) and conducting polymers, have also shown potential in gas sensing applications, which may be doped into graphene and MXene layers to improve the sensitivity of the sensors. Full article

Metal oxide core–shell fibrous nanostructures are promising gas-sensitive materials for the detection of a wide variety of both reducing and oxidizing gases. In these structures, two dissimilar materials with different work functions are brought into contact to form a coaxial heterojunction. The influence of the shell material on the transportation of the electric charge carriers along these structures is still not very well understood. This is due to homo-, hetero- and metal/semiconductor junctions, which make it difficult to investigate the electric charge transfer using direct current methods. However, in order to improve the gas-sensing properties of these complex structures, it is necessary to first establish a good understanding of the electric charge transfer in ambient air. In this article, we present an impedance spectroscopy study of networked SnO₂/Ga₂O₃ core–shell nanobelts in ambient air. Tin dioxide nanobelts were grown directly on interdigitated gold electrodes, using the thermal sublimation method, via the vapor–liquid–solid (VLS) mechanism. Two forms of a gallium oxide shell of varying thickness were prepared via halide vapor-phase epitaxy (HVPE), and the impedance spectra were measured at 189–768 °C. The bulk resistance of the core–shell nanobelts was found to be reduced due to the formation of an electron accumulation layer in the SnO₂ core. At temperatures above 530 °C, the thermal reduction of SnO₂ and the associated decrease in its work function caused electrons to flow from the accumulation layer into the Ga₂O₃ shell, which resulted in an increase in bulk resistance. The junction resistance of said core–shell nanostructures was comparable to that of SnO₂ nanobelts, as both structures are likely connected through existing SnO₂/SnO₂ homojunctions comprising thin amorphous layers. Full article

Tin dioxide (SnO₂) is a low-cost and high-capacity anode material for lithium-ion batteries, but the fast capacity fading significantly limits its practical applications. Current research efforts have focused on preparing sophisticated composite structures or optimizing functional binders, both of which increase material manufacturing costs. Herein, we utilize pristine and commercially available SnO₂ nanopowders and enhance their cycling performance by simply narrowing the potential range and optimizing electrolytes. Specifically, a narrower potential range (0–1 V) mitigates the capacity fading associated with the conversion reaction, whereas an ether-based electrolyte further suppresses the volume expansion related to the alloy reaction. Consequently, this SnO₂ anode delivers a promising battery performance, with a high capacity of ~650 mAhg⁻¹ and stable cycling for 100 cycles. Our work provides an alternative approach to developing high-capacity and long-cycling metal oxide anode materials. Full article

The aim of this work was to investigate the possibility of modifying the physical properties of indium tin oxide (ITO) layers by annealing them in different atmospheres and temperatures. Samples were annealed in vacuum, air, oxygen, nitrogen, carbon dioxide and a mixture of nitrogen with hydrogen (NHM) at temperatures from 200 °C to 400 °C. Annealing impact on the crystal structure, optical, electrical, thermal and thermoelectric properties was examined. It has been found from XRD measurements that for samples annealed in air, nitrogen and NHM at 400 °C, the In₂O₃/In₄Sn₃O₁₂ share ratio decreased, resulting in a significant increase of the In₄Sn₃O₁₂ phase. The annealing at the highest temperature in air and nitrogen resulted in larger grains and the mean grain size increase, while vacuum, NHM and carbon dioxide atmospheres caused the decrease in the mean grain size. The post-processing in vacuum and oxidizing atmospheres effected in a drop in optical bandgap and poor electrical properties. The carbon dioxide seems to be an optimal atmosphere to obtain good TE generator parameters—high ZT. The general conclusion is that annealing in different atmospheres allows for controlled changes in the structure and physical properties of ITO layers. Full article

Furfural, an important biobased compound, can be synthesized through the chemocatalytic conversion of D-xylose and hemicelluloses from lignocellulose. It has widespread applications in the production of valuable furans, additives, resins, rubbers, synthetic fibers, polymers, plastics, biofuels, and pharmaceuticals. By using barley hulls (BHs) as biobased support, a heterogeneous biochar Sn-NUS-BH catalyst was created to transform corncob into furfural in cyclopentyl methyl ether–H₂O. Sn-NUS-BH had a fibrous structure with voids, a large comparative area, and a large pore volume, which resulted in more catalytic active sites. Through the characterization of the physical and chemical properties of Sn-NUS-BH, it was observed that the Sn-NUS-BH had tin dioxide (Lewis acid sites) and a sulfonic acid group (Brønsted acid sites). This chemocatalyst had good thermostability. At 170 °C for 20 min, Sn-NUS-BH (3.6 wt%) was applied to transform 75 g/L of corncob with ZnCl₂ (50 mM) to generate furfural (80.5% yield) in cyclopentyl methyl ether–H₂O (2:1, v/v). This sustainable catalytic process shows great promise in the transformation of lignocellulose to furfural using biochar-based chemical catalysts. Full article