Hydrothermal Synthesis of Core/Shell ZnO:Mn/Mn₃O₄ Nanowires

Abstract

Practical applications of ZnO are widely known, and it is one of the more prevalent wide band gap semiconductors being explored in research. It is most known for its potential as an n-type window material in solar cells. 1,2 ZnO has been thoroughly explored in many forms: as a thin film, nanowires, nanoparticles, etc. 3À5 It has also been demonstrated that Mn-doped ZnO has ferromagnetic properties at room temperature and is therefore of interest in spintronics applications. 6À8 In addition, the introduction of such impurities has been shown to red-shift the band gap of ZnO and cause other changes in its optical characteristics, such as its photoluminescence. 9 This allows the material to be potentially beneficial for solar cells, as the dopants can cause reduction of near band-edge electron-hole pair recombination as well as internal down-conversion of higher energy photons, which could be absorbed by a narrow band gap material. The ZnO/Mn 3 O 4 core-shell structures produced in this study also show promise for lithium-ion battery applications. The substrate-grown nanowires provide a large functional surface area and the manganese oxide crystallites would be a highly favorable cathode material once enriched with lithium. Based on the length and density of the structures grown in this study, an estimated 20À30-fold increase in surface area would be observed in comparison to a thin film. This would result in a corresponding increase in battery capacity. To explore the potential of this material, optimize synthesis procedures, and develop further insights about the doping mechanism, a study of growth processes and properties was implemented. Reagent concentrations were varied to establish doping and crystallite formation regimes. Upon establishment of optimal ratios, reactions were carried out for various times, and the results are presented herein.' EXPERIMENTAL METHODS Synthesis. Synthesis of nanowires was carried out by a seeded chemical bath method. The seed solution was prepared as 0.750 M Zn(CH 3 COO) 2 and 0.750 M methenamine in deionized (DI) H 2 O. To assist in dissolution of the zinc acetate, the solution was heated to 60°C for 30 min under agitation. SnO 2 :F-coated SiO 2 substrates were cleaned for use by a two-part washing process: a 10 min isopropyl alcohol bath followed by a 10 min DI-H 2 O bath, both involving sonication. The substrates were allowed to air-dry. The seed was transferred to the substrates via pipet and distributed via spin coating at 1500 rpm for 90 s. To ensure a uniform seed layer, the substrates were then annealed for 1 h at 400°C. To reduce thermal strain on substrates, the samples were inserted after the furnace was preheated to 100°C; the furnace was subsequently ramped to the target temperature at an average rate of 20°C/min. The samples were permitted to cool in the furnace after it was turned off until they had reached room temperature. Growth of ZnO nanowires was carried out by use of a growth solution of 27.8 mM Zn(NO 3 ) 2 and 27.8 mM methenamine in DI-H 2 O. The samples w...

Recent Progress in Hydrothermal Synthesis of Zinc Oxide Nanomaterials

“…Hydrothermal or solution treatment after growth can be used for various purposes, such as improvement of the material quality, as well as doping [54]. Hydrothermal or solution treatment after growth can be used for various purposes, such as improvement of the material quality, as well as doping [54].…”

Anticorrosion Performance and Application of a Mixed-Valence Mn0xMn2+0.05–xZn0.95O Solid Solution Induced by Magnetic Doping

“…The introduction of mixed-valence Mn ions can change the oxidation state, growth kinetics, amount of oxygen vacancies, and electronic properties of the materials. Most research studies have focused on the preparation, origin of magnetism, and crystal structure. , The studies of mixed-valence Mn-doping materials in the field of supercapacitors, spintronic devices, batteries, and gas sensors remain in the phase of theoretical analysis. Further exploration of pragmatic applications and mechanisms is demanded.…”

“…Most research studies have focused on the preparation, 20 origin of magnetism, and crystal structure. 21,22 The studies of mixed-valence Mn-doping materials in the field of supercapacitors, 23 spintronic devices, 24 batteries, 25 and gas sensors 26 remain in the phase of theoretical analysis. Further exploration of pragmatic applications and mechanisms is demanded.…”

Electrodeposition of a Mn–Cu–ZnO Hybrid Material for Supercapacitors: A Soft X‐ray Fluorescence and Absorption Microspectroscopy Study

“…Other metal oxides have been considered as possible candidates for electrochemical supercapacitor devices, among which zinc, manganese, and copper-oxide systems have received great attention because of their high theoretical pseudocapacitance, wide voltage windows, low cost, and environmental compatibilities. [5][6][7][8][9][10][11] ZnO, possessing several, extensively investigated physical properties that have led to a wide range of applications in optoelectronics and catalysis, has recently been considered as a candidate for use in supercapacitors as a pure oxide, [12][13][14] as a Mn-doped oxide, [15,16] and as a dopant of Mn oxide. [17] ZnO for supercapacitor applications has been prepared by using sol-gel techniques, [17] precipitation, [12] microwave assisted synthesis, [13] seeded [14] and wet [16] chemical methods, and by spray pyrolysis.…”