Search Results (105)

Efficient detection of toxic and flammable vapors remains a major technological challenge, especially for environmental and industrial applications. This paper reports on the fabrication technology and gas-sensing properties of nanostructured Ga₂O₃/GaS_0.98Se_0.02. The β-Ga₂O₃ nanowires/nanoribbons with inclusions of Ga₂S₃ and Ga₂Se₃ microcrystallites were obtained by thermal treatment of GaS_0.98Se_0.02 slabs in air enriched with water vapors. The microstructure, crystalline quality, and elemental composition of the obtained samples were investigated using electron microscopy, X-ray diffraction, and Raman spectroscopy. The obtained structures show promising results as active elements in gas sensor applications. Vapors of methanol (CH₃OH), ethanol (C₂H₅OH), and acetone (CH₃-CO-CH₃) were successfully detected using the nanostructured samples. The electrical signal for gas detection was enhanced under UV light irradiation. The saturation time of the sensor depends on the intensity of the UV radiation beam. Full article

Electrocatalytic nitrate reduction reaction (NO₃⁻RR) to ammonia (NH₃) presents an alternative, sustainable approach to ammonia production. However, the existing catalysts suffer from poor NH₃ yield under lower concentrations of NO₃⁻, and the kinetic understanding of bimetal catalysis is lacking. In this study, a Co₃O₄–modified Cu₂₊₁O nanowire (CoCuNWs) catalyst with a high specific surface area was synthesized to effectively produce NH₃ from a 10 mM KNO₃ basic solution. CoCuNWs demonstrated a high NH₃ yield rate of 0.30 mmol h⁻¹ cm⁻² with an NH₃ Faradaic efficiency (FE) of 96.7% at −0.2 V vs. RHE, which is 1.5 times higher than the bare Cu₂₊₁O NWs. The synergistic effect between Co₃O₄ and Cu₂₊₁O significantly enhanced both the nitrate conversion and ammonia yield. Importantly, it is revealed that the surface of CoCuNWs is kinetically more easily saturated with NO₃⁻ (NO₂⁻) ions than that of Cu₂₊₁O NWs, as evidenced by both the higher current density and the plateau occurring at higher NO_x⁻ concentrations. In addition, CoCuNWs exhibit a higher diffusion coefficient of NO₃⁻, being 1.6 times higher than that of Cu₂₊₁O NWs, which also indicates that the presence of Co₃O₄ could promote the diffusion and adsorption of NO₃⁻ on CoCuNWs. Moreover, the ATR–SEIRAS analysis was applied to illustrate the reduction pathway of NO₃⁻ to NH₃ on CoCuNWs, which follows the formation of the key intermediate from *NO₂⁻, *NO, *NH₂OH to *NH₃. This work presents a strategy for constructing dual–metal catalysts for NO₃⁻RR and provides an insight to understand the catalysis from the perspective of the kinetics. Full article

Copper nanowires (Cu NWs) are considered a promising alternative to indium tin oxide (ITO) and silver nanowires (Ag NWs) due to their excellent electrical conductivity, mechanical properties, abundant reserves, and low cost. They have been widely applied in various optoelectronic devices. In this study, Cu NWs were synthesized using copper chloride (CuCl₂) as the precursor, monoethanolamine (MEA) as the complexing agent, and hydrated hydrazine (N₂H₄) as the reducing agent under strongly alkaline conditions at 60 °C. Notably, this is the first time that MEA has been employed as a complexing agent in this synthesis method for Cu NWs. Through a series of experiments, the optimal conditions for the CuCl₂–MEA–N₂H₄ system in Cu NWs synthesis were determined. This study revealed that the presence of amines plays a crucial role in nanowire formation, as the co-ordination of MEA with copper in this system provides selectivity for the nanowire growth direction. MEA prevents the excessive conversion of Cu(I) complexes into Cu₂O octahedral precipitates and exhibits an adsorption effect during Cu NWs formation. The different adsorption tendencies of MEA at the nanowire ends and lateral surfaces, depending on its concentration, influence the growth of the Cu NWs, as directly reflected by changes in their diameter and length. At an MEA concentration of 210 mM, the synthesized Cu NWs have an average diameter of approximately 101 nm and a length of about 28 μm. To fabricate transparent conductive films, the Cu NW network was transferred onto a polyethylene terephthalate (PET) substrate by applying a pressure of 20 MPa using a tablet press to ensure strong adhesion between the Cu NW-coated mixed cellulose ester (MCE) filter membrane and the PET substrate. Subsequently, the MCE membrane was dissolved by acetone and isopropanol immersion. The resulting Cu NW transparent conductive film exhibited a sheet resistance of 52 Ω sq⁻¹ with an optical transmittance of 86.7%. Full article

Supercapacitors have a better power density than batteries; however, there is room for improvement in energy density. Co₃V₂O₈ nanoparticles were synthesized using the hydrothermal approach, with the reaction duration tuned to enhance energy density. At a 10 h hydrothermal reaction time, bundles of nanowires with void spaces were obtained, demonstrating excellent areal capacitance of 4.67 F/cm², energy density of 94 μWh/cm², and power density of 573 μW/cm² at a current density of 3 mA/cm². With activated carbon (AC) and Co₃V₂O₈ nanoparticles prepared over a 10-h hydrothermal reaction period, an asymmetric supercapacitor (ASC) was assembled. The device performed admirably in terms of energy storage capacity, with an areal capacitance of 781 mF/cm² and a volumetric capacitance of 1.43 F/cm³. The ASC’s cyclic stability demonstrated capacity retention of 83.40% after 5000 cycles. The powering of red LEDs was used to show practical applications. In a 2M KOH electrolyte, the optimized Co₃V₂O₈ electrode demonstrated good electrocatalytic performance for the hydrogen evolution process, with an overpotential of 259 mV at a current density of 10 mA/cm². Overall, water splitting studies revealed a potential of 1.78 V with little potential enhancement after 8 h of Chrono potentiometric stability. As a result, Co₃V₂O₈ nanoparticles prepared at a 10 h hydrothermal reaction time offer excellent electrode materials for energy storage in supercapacitors and electrocatalytic applications for total water splitting. Full article

The development of micro glucose sensors plays a vital role in the management and monitoring of diabetes, facilitating real-time tracking of blood glucose levels. In this paper, we developed a three-layer core-sheath microwire (NW@CuO@Co₃O₄) with nickel wire as the core and copper oxide and cobalt oxide nanowires as the sheath. The unique core-sheath structure of microwire enables it to have both good conductivity and excellent electrochemical catalytic activity when used as an electrode for glucose detecting. The non-enzymatic glucose sensor base on a NW@CuO@Co₃O₄ core-sheath wire exhibits a high sensitivity of 4053.1 μA mM⁻¹ cm⁻², a low detection limit 0.89 μM, and a short response time of less than 2 s. Full article

The urea electro-oxidation reaction (UOR) is emerging as a new energy conversion technology and a promising method for alleviating water eutrophication problems. However, a rationally designed structure of the electrode materials is urgently required to achieve high UOR performance. Herein, P-doped MOF-derived Co₃O₄ nanowire arrays grown on nickel foam (P-Co₃O₄/NF) are successfully synthesized via the growth of Co-MOF and subsequent calcination followed by phosphorization treatment. Owing to the optimized electronic structure, the as-prepared P-Co₃O₄/NF composite exhibits much higher UOR electrocatalytic performance than the undoped Co₃O₄/NF sample. Beyond this, the meticulous structure of the one-dimensional nanowire arrays and the three-dimensional skeleton structure of nickel foam contribute to the enhanced electrocatalytic activity and stability toward UOR. As a result, the P-Co₃O₄/NF composite displays a low overpotential of 1.419 V vs. RHE at 50 mA cm⁻², a small Tafel slope of 82 mV dec⁻¹, as well as favorable long-term stability over 65,000 s in 1.0 M KOH with 1.0 M urea. This work opens a new avenue in designing non-precious electrocatalysts for high-performance urea electro-oxidation reactions. Full article

The development of state-of-the-art gas sensors based on metal oxide semiconductors (MOS) to monitor hazardous and greenhouse gas (e.g., methane, CH₄, and carbon dioxide, CO₂) has been significantly advanced. Moreover, the morphological and topographical structures of MOSs have significantly influenced the gas sensors by means of surface catalytic activities. This work examines the impact of morphological and topological networked assembly of zinc oxide (ZnO) nanostructures, including microparticles and nanoparticles (0D), nanowires and nanorods (1D), nanodisks (2D), and hierarchical networks of tetrapods (3D). Gas sensors consisting of vertically aligned ZnO nanorods (ZnO–NR) and topologically interconnected tetrapods (T–ZnO) of varying diameter and arm thickness synthesized using aqueous phase deposition and flame transport method on interdigitated Pt electrodes are evaluated for methane detection. Smaller-diameter nanorods and tetrapod arms (nanowire-like), having higher surface-to-volume ratios with reasonable porosity, exhibit improved sensing behavior. Interestingly, when the nanorods’ diameter and interconnected tetrapod arm thickness were comparable to the width of the depletion layer, a significant increase in sensitivity (from 2 to 30) and reduction in response/recovery time (from 58 s to 5.9 s) resulted, ascribed to rapid desorption of analyte species. Additionally, nanoparticles surface-catalyzed with Pd (~50 nm) accelerated gas sensing and lowered operating temperature (from 200 °C to 50 °C) when combined with UV photoactivation. We modeled the experimental findings using a modified general formula for ZnO methane sensors derived from the catalytic chemical reaction between methane molecules and oxygen ions and considered the structural surface-to-volume ratios (S/V) and electronic depletion region width (L_d) applicable to other gas sensors (e.g., SnO₂, TiO₂, MoO₃, and WO₃). Finally, the effects of UV light excitation reducing detection temperature help to break through the bottleneck of ZnO-based materials as energy-saving chemiresistors and promote applications relevant to environmental and industrial harmful gas detection. Full article

The photocatalytic oxidative coupling of methane (OCM) on metal-loaded one-dimensional TiO₂ nanowires (TiO₂ NWs) was performed. With metal loading, the electric and optical properties of TiO₂ NWs were adjusted, contributing to the improvement of the activity and selectivity of the OCM reaction. In the photocatalytic OCM reaction, the 1.0 Au/TiO₂ NW catalyst exhibits an outstanding C₂H₆ production rate (4901 μmol g⁻¹ h⁻¹) and selectivity (70%), alongside the minor production of C₃H₈ and C₂H₄, achieving a total C₂–C₃ hydrocarbon selectivity of 75%. In contrast, catalysts loaded with Ag, Pd, and Pt show significantly lower activity, with Pt/TiO₂ NWs producing only CO₂, indicating a propensity for the deep oxidation of methane. The O₂-TPD analyses reveal that Au facilitates mild O₂ adsorption and activation, whereas Pt triggers excessive oxidation. Spectroscopic and kinetic studies demonstrate that Au loading not only enhances the separation efficiency of photogenerated electron–hole pairs, but also promotes the generation of active oxygen species in moderate amounts, which facilitates the formation of methyl radicals and their coupling into C₂H₆ while suppressing over-oxidation to CO₂. This work provides novel insights and design strategies for developing efficient photocatalysts. 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

The structural characteristics of electrode materials play a crucial role in their potential applications. Therefore, designing the material’s structure rationally is one of the most effective methods to achieve high-performance electrodes. In this study, V−ZnCo₂O₄ nanowires were synthesized on nickel foam using a simple hydrothermal method, and the prepared V−ZnCo₂O₄−2 electrode material exhibited a specific capacitance of 1621 C g⁻¹. The potential applications of the prepared material were evaluated through device assembly, using V−ZnCo₂O₄−2 as the positive electrode and activated carbon as the negative electrode. The resulting device delivered an energy density of 127.5 Wh/kg, with a corresponding power density of 2700 W/kg. Additionally, the mechanical properties of the device were assessed, revealing that after multiple bends at different angles, the shape of the device remained well-preserved, further confirming its excellent mechanical stability. Full article

The conversion of carbon dioxide, a greenhouse gas, into valuable chemicals using sunlight is highly significant technologically and holds the promise of providing a more sustainable alternative to fossil fuels. To effectively utilize the abundant solar irradiation, it is essential to develop catalysts that can absorb a significant portion of the solar spectrum, particularly in the UV, visible, and infrared regions. Silicon nanowire arrays grown on silicon substrates meet this criterion, as they can absorb over 85% of solar irradiation and show minimal reflective losses across the UV, visible, and infrared portions of the solar spectrum. Herein, we report the deposition of various catalysts, including iron oxyhydroxides, copper, nickel, and ruthenium, on silicon nanowires using different catalyst deposition techniques. The photocatalytic reduction of carbon dioxide was evaluated using these catalysts. The results show that silicon nanowires coated with nickel and ruthenium oxide had the highest activity towards the photocatalytic reduction of carbon dioxide, with photomethanation rates reaching 546 μmolg_cat⁻¹h⁻¹ for RuO₂@SiNWs and 278 μmolg_cat⁻¹h⁻¹ for Ni/NiO@SiNWs. Continued improvement of photocatalysts using nanostructured silicon supports could enable the development of solar refineries for converting gas-phase CO₂ into value-added chemicals and fuels. Full article

Metal-assisted catalyzed etching (MACE) technology is convenient and efficient for fabricating large-area silicon nanowires at room temperature. However, the mechanism requires further exploration, particularly the dynamic effect of various ions in the acid-etching solution. This paper investigated the MACE of silicon wafers predeposited with metal nanofilms in an HF-M(NO₃)x-H₂O etching solution (where M(NO₃)x is the nitrate of the fourth-period elements of the periodic table). The oxidizing ability of Fe³⁺ and NO₃⁻ was demonstrated, and the dynamic influence of metal ions on the etching process was discussed. The results show that the MACE of silicon can be realized in various HF-M(NO₃)_x-H₂O etching solutions, such as KNO₃, Al(NO₃)₃, Cr(NO₃)₃, Mn(NO₃)₂, Ni(NO₃)₂, Co(NO₃)₂, HNO₃, and Ca(NO₃)₂. It is confirmed that the concentration and type of cations in the etching solution affect the etching rate and morphology of silicon. Fe³⁺ and NO₃⁻ act as oxidants in catalytic etching. The fastest etching rate is about 5~6 μm/h in Ni(NO₃)₂, Co(NO₃)₂, and Ca(NO₃)₂ etching solutions. However, a high concentration of K⁺ hinders silicon etching. This study expands the application of MACE etching solution systems. Full article

Needle-like CoO nanowires have been successfully synthesized by a facile hydrothermal process on an electrospun carbon nanofibers substrate. The as-prepared sample mesoporous CoO nanowires aligned vertically on the surface of carbon nanofibers and cross-linked with each other, producing loosely porous nanostructures. These hybrid composite electrodes exhibit a high specific capacitance of 1068.3 F g⁻¹ at a scan rate of 5 mV s⁻¹ and a good rate capability of 613.7 F g⁻¹ at a scan rate of 60 mV s⁻¹ in a three-electrode cell. The CoO NWs@CNF//CNT@CNF asymmetric device exhibits remarkable cycling stability and delivers a capacitance of 79.3 F/g with a capacitance retention of 92.1 % after 10,000 cycles. The asymmetric device delivers a high energy density of 37 Wh kg⁻¹ with a power density of 0.8 kW kg⁻¹ and a high power density of 16 kW kg⁻¹ with an energy density of 23 Wh kg⁻¹. This study demonstrated a promising strategy to enhance the electrochemical performance of flexible supercapacitors. Full article

The Co₃O₄ nanowire@NiCo₂O₄ nanosheet hierarchical array was constructed on Ni foam using hydrothermal and annealing approaches in turn, from which a NiCo₂O₄ nanosheet could self-assemble on the Co₃O₄ nanowire. The structure and morphology of the Co₃O₄ nanowire@NiCo₂O₄ nanosheet hierarchical array were characterized via XRD, EDS, SEM, and FESEM, respectively. The electrochemical performance of the composite array was measured via a cyclic voltammetry curve, galvanostatic current charge–discharge, charge–discharge cycle, and electrochemical impedance and then compared with the Co₃O₄ nanowire. The results show that the Co₃O₄ nanowire@NiCo₂O₄ nanosheet hierarchical array could reach a high value of 2034 F g⁻¹ at a current density of 2.5 A g⁻¹. After 5000 galvanostatic charge–discharge cycles, the specific capacitance of the Co₃O₄ nanowire@NiCo₂O₄ nanosheet hierarchical array could still maintain 94.7% of the original value. Therefore, the Co₃O₄ nanowire@NiCo₂O₄ nanosheet hierarchical array would be a desirable electrode material for a high-performance supercapacitor. Full article

The present study investigates the photocatalytic properties of hydrothermally synthesized TiO₂ nanowires (NWs) for CO₂ reduction in H₂O vapor. It has been demonstrated that TiO₂ NWs, thermally treated at 500–700 °C, demonstrate an almost tenfold higher yield of products compared to the known commercial powder TiO₂ P25. It has been found that the best material is a combination of anatase, TiO₂-B and rutile. The product yield increases with increasing heat treatment temperature of TiO₂ NWs. This is associated with an increase in the degree of crystallinity of the material. It is shown that the best product yield of the CO₂ reduction in H₂O vapor is achieved when the TiO₂ NW photocatalyst is heated to 100 °C. Full article