Search Results (6)

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

As a toxic pollutant, carbon monoxide (CO) usually causes harmful effects on human health. Therefore, the thermally catalytic oxidation of CO has received extensive attention in recent years. The CuO-based catalysts have been widely investigated due to their availability. In this study, a series of transition metal oxides (Fe₂O₃, Co₃O₄ and NiO) promoted CuO-based catalysts supported on the α-MnO₂ nanowire catalysts were prepared by the deposition precipitation method for catalytic CO oxidation reactions. The effects of the loaded transition metal type, the loading amount, and the calcination temperature on the catalytic performances were systematically investigated. Further catalyst characterization showed that the CuO/α-MnO₂ catalyst modified with 3 wt% Co₃O₄ and calcined at 400 °C performed the highest CO catalytic activity (T₉₀ = 75 °C) among the investigated catalysts. It was supposed that the loading of the Co₃O₄ dopant not only increased the content of oxygen vacancies in the catalyst but also increased the specific surface area and pore volume of the CuO/α-MnO₂ nanowire catalyst, which would further enhance the catalytic activity. The CuO/α-MnO₂ catalyst modified with 3 wt% NiO and calcined at 400 °C exhibited the highest surface adsorbed oxygen content and the best normalized reaction rate, but the specific surface area limited its activity. Therefore, the appropriate loading of the Co₃O₄ modifier could greatly enhance the activity of CuO/α-MnO₂. This research could provide a reference method for constructing efficient low-temperature CO oxidation catalysts. Full article

In this study, Fe₃O₄ magnetic nanoparticles (MNPs) were loaded on α-MnO₂ nanowires using an improved hydrothermal synthesis method combined with an ultrasonic coprecipitation method, the loading ratio was optimized, the efficiency of the prepared Fe₃O₄/α-MnO₂-activated persulfate (PS) system for the degradation of 2,4-dichlorophenol (2,4-DCP) was investigated, and the effects of PS concentration, Fe₃O₄/α-MnO₂ magnetic nanocomposites (MNCs) dosage, pH value and initial pollutant concentration on the degradation of 2,4-DCP were investigated. The results showed that when the initial concentrations of 2,4-DCP, PS, and Fe₃O₄/α-MnO₂ MNCs were 100 mg/L, 30 mmol/L, and 0.4 g/L, the degradation rate of 2,4-DCP reached 96.3% after 180 min of reaction at 30 °C under a neutral condition, and the fitting results showed that the degradation of 2,4-DCP by the Fe₃O₄/α-MnO₂-activated PS system conformed to quasi-first-order kinetics. The degradation of 2,4-DCP by different Fe₃O₄/α-MnO₂-activated PS systems was compared, and a possible PS activation mechanism was proposed. The Fe₃O₄/α-MnO₂ MNCs exhibited excellent reusability, and by introducing Fe₃O₄/α-MnO₂ MNCs as the PS activator into the advanced oxidation process (AOP) system, the electron transfer of Mn(III/IV) and Fe(III/II) on the surface of MNCs was realized, thus greatly improving the reaction efficiency. Full article

In this study, CoFe₂O₄ is selected for the first time to synthesize CoFe₂O₄/Al nanothermite films via an integration of nano-Al with CoFe₂O₄ nanowires (NWs), which can be prepared through a facile hydrothermal-annealing route. The resulting nanothermite film demonstrates a homogeneous structure and an intense contact between the Al and CoFe₂O₄ NWs at the nanoscale. In addition, both thermal analysis and laser ignition test reveal the superb energetic performances of the prepared CoFe₂O₄/Al NWs nanothermite film. Within different thicknesses of nano-Al for the CoFe₂O₄/Al NWs nanothermite films investigated here, the maximum heat output has reached as great as 2100 J·g⁻¹ at the optimal thickness of 400 nm for deposited Al. Moreover, the fabrication strategy for CoFe₂O₄/Al NWs is also easy and suitable for diverse thermite systems based upon other composite metal oxides, such as MnCo₂O₄ and NiCo₂O₄. Importantly, this method has the featured advantages of simple operation and compatibility with microsystems, both of which may further facilitate potential applications for functional energetic chips. Full article

Bimetallic oxides have been considered as potential candidates for supercapacitors due to their relatively high electric conductivity, abundant redox reactions and cheapness. However, nanoparticle aggregation and huge volume variation during charging-discharging procedures make it hard for them to be applied widely. In this work, one-dimensional (1D) MnFe₂O₄@C nanowires were in-situ synthesized via a simply modified micro-emulsion technique, followed by thermal treatment. The novel 1D and core-shell architecture, and in-situ carbon coating promote its electric conductivity and porous feature. Due to these advantages, the MnFe₂O₄@C electrode exhibits a high specific capacitance of 824 F·g⁻¹ at 0.1 A·g⁻¹ and remains 476 F·g⁻¹ at 5 A·g⁻¹. After 10,000 cycles, the capacitance retention of the MnFe₂O₄@C electrode is up to 93.9%, suggesting its excellent long-term cycling stability. After assembling with activated carbon (AC) to form a MnFe₂O₄@C//AC device, the energy density of this MnFe₂O₄@C//AC device is 27 W·h·kg⁻¹ at a power density of 290 W·kg⁻¹, and remains at a 10 W·h·kg⁻¹ energy density at a high power density of 9300 W·kg⁻¹. Full article

Porous α-Fe₂O₃ nanowire arrays coated with a layer of carbon shell have been prepared by a simple hydrothermal route. The as-synthesized products show an excellent electrochemical performance with high specific capacitance and good cycling life after 9000 cycles. A solid state asymmetric supercapacitor (ASC) with a 2 V operation voltage window has been assembled by porous α-Fe₂O₃/C nanowire arrays as the anode materials, and MnO₂ nanosheets as the cathode materials, which gives rise to a maximum energy density of 30.625 Wh kg⁻¹and a maximum power density of 5000 W kg⁻¹ with an excellent cycling performance of 82% retention after 10,000 cycles. Full article