Conversion of ZnO Nanowires into Nanotubes with Tailored Dimensions

Abstract

An innovative route is presented to obtain arrays of single-crystal ZnO nanotubes with tailored dimensions. The three-step process combines electrochemical and chemical approaches. The first step consists in the electrodeposition of ZnO nanowire arrays from the O 2 reduction in an aqueous solution of zinc chloride (ZnCl 2 ) and potassium chloride (KCl). In the second step the core of ZnO nanowires is selectively etched in a KCl solution, resulting in the formation of tubular structures. The influence of KCl concentration, temperature, and immersion time in the ZnO nanotube formation process is investigated, with the finding that the dissolution of the nanowire core occurs for [KCl] g 1 M and the etching rate is enhanced with the temperature. Arrays of ZnO nanotubes with tailored dimensions (200-500 nm external diameter and 1-5 µm length) are obtained by varying the conditions of nanowire array deposition and taking into account the dimensions of the nanowires to adjust the dissolution time. A precise control of the nanotube wall thickness is achieved by performing a further electrodeposition step. The whole process occurs at low temperature (80°C) in aqueous chloride solution at neutral pH, in a couple of hours. The structural properties of obtained ZnO nanotubes are analyzed by transmission electron microscopy, showing their single-crystal character.

One-dimensional ZnO nanostructures: Solution growth and functional properties

“…13. The nanotube wall thickness can be precisely controlled by controlling the electrodeposition time [179]. The nanotube could also be grown on large scale on seeded general substrates [180], with a yield approaching 100% [181].…”

Indirect optical transition due to surface band bending in ZnO nanotubes

“…1 It is obvious that 1D nanostructures of ZnO with a wide band gap ͑E g = 3.37 eV͒ and a large exciton binding energy ͑60 meV͒ have become important nanomaterials owing to their special properties and potential applications in nanoscale electric and optoelectronic devices. [1][2][3][4][5][6][7] During the past decade, different 1D ZnO nanostructures such as nanotubes, [8][9][10][11][12][13][14][15] nanowires, 1 nanorods, 16 nanobelts, 17,18 tetrapods, 19 and nanoribbons 20 have been successfully fabricated by different methods. Among these 1D structures, the tubular structures of ZnO become particularly important since numerous applications, such as dye-sensitized photovoltaic cells 21 and bio/ gas sensors, 22,23 are required their high porosity and large surface area to fulfill the demand for high efficiency and activity.…”

“…To date, ZnO nantubes has been synthesized by electrochemical method, [10][11][12] low temperature solution method, 8,9,13,14 vapor phase growth 15 and so on. As a common knowledge, the reproducibility and control of growth in synthesis of ZnO nanostructures are a major issue.…”

(Research Award of the Energy and Technology Division) (Photo)Electrochemistry in the Service of Solar Energy Conversion

“…Our work in this area has spanned over several years, with focus on different types of materials pertinent to solar energy conversion. Thus, early work in II-VI films [33][34][35][36] led to studies of related compounds such as copper containing compounds such as CuSe, related compounds and their phase transitions [37], MoS 2 [38][39][40] and finally to development of new phases of semiconductors such as δ-SnS and Bi 2 S 3 [41,42] or new morphologies of zinc oxide including vertically aligned nanowires [43][44][45][46], nanotubes [47] and arrays of urchin-like by combining electrochemistry and sphere lithography [48].…”