Template-free room temperature solution phase synthesis of Cu 2 O hollow spheres† Wenzhong Wang, * Pengcheng Zhang, Lei Peng, Wenjuan Xie, Guling Zhang, Ya Tu and Weijie Mai Received 24th June 2009, Accepted 13th October 2009 First published as an Advance Article on the web 23rd October 2009 DOI: 10.1039/b912514k A facile template-free room temperature solution phase route has been developed to large scale synthesize Cu 2 O hollow spheres with an average diameter of about 550 nm. Cuprous oxide (Cu 2 O), a p-type semiconductor with a band gap of 2.17 eV, has potential applications in the fields of solar energy conversion, catalysis, and gas sensors. 1 Many methods have therefore been developed to synthesize Cu 2 O nano- or micro-structures with well defined morphologies, such as hollow spheres, wires, cubes, cages and octahedra. 2 While the Cu 2 O hollow spheres have recently received a great deal of attention due to their unique physical and chemical properties, which mean they have potential applications in solar energy conversion, catalysis, gas sensors, carriers, and drug delivery. 3 To date, several methods have been designed to prepare Cu 2 O hollow spheres. Fore example, multi-shelled Cu 2 O spheres were successfully synthesized using CTAB multi-lamellar vesicles as templates at 60  C. 3 Sub-micrometer Cu 2 O hollow spheres were prepared by using a multiple emulsion (O/W/O) as the template. 4 The Cu 2 O hollow spheres also were synthesized under solvothermal conditions at 150–180  C by using CuO as a hard template. 5 As reviewed above, although several methods have been successfully used to prepare Cu 2 O hollow spheres, generally these methods require the template to direct the growth of hollow spheres. In addition, most of these methods require the temperature in the formation of Cu 2 O hollow spheres. Therefore, it still is a great challenge to develop a facile template-free room temperature route to synthesize Cu 2 O hollow spheres. In this communication, we report on a facile template-free room temperature solution phase route to large scale synthesize Cu 2 O hollow spheres for the first time. The synthesis of Cu 2 O hollow spheres was carried out at room temperature. In a typical procedure, 0.25 g of CuSO 4 $5H 2 O was dissolved in 100 mL deionized water under constant stirring by a magnetic stirrer, then 1 mL of N 2 H 4 $H 2 O solution with concen- tration of 8 M was added into the above solution. The color of the solution was gradually turned into red. After stirring for 10 min, the red precipitate was centrifuged, washed several times with deionized water and ethanol. The XRD pattern was recorded with a D/MAX 2250 V diffrac- tometer (Rigaku, Japan) using CuKa radiation (l ¼ 1.5406  A). The morphologies and microstructures of the as-prepared products were investigated by a transmission electron microscope (TEM, JEOL 2010) and a field-emission scanning electron microscope (FE-SEM, S 4800). The low-magnification image (Fig. 1a) clearly reveals that a large quantity of spherical particles with a narrow size distribution was achieved. The high-magnification image (Fig. 1b) demonstrates that the spherical shaped particles are micrometer-scale hollow spheres with an average diameter of about 550 nm. The broken sphere as marked by an arrow in Fig. 1b clearly indicates that the spheres prepared via our present template-free room temperature method are hollow. Fig. 1c shows the typical XRD pattern of the as-prepared Cu 2 O hollow spheres. The XRD pattern contains five peaks that are clearly distinguishable and broadened. All of the diffraction peaks can be perfectly indexed to 110, 111, 200, 220, and 311 peaks of cubic Cu 2 O (JCPDS No. 5-666, Pn  3m). The average nanocrystal size was about 10 nm calculated from XRD pattern using the Debye–Scherrer formula. The morphologies, size and microstructure of the as-prepared Cu 2 O product were further characterized by TEM and high-resolu- tion TEM (HRTEM) microscope. Fig. 2a shows a typical low- magnification TEM image of the as-prepared Cu 2 O hollow spheres, indicating that the product is composed of large quantity hollow spheres. The medium-magnification TEM miages (Fig. 2 b and c) clearly demonstrates that these hollow spheres are composed of nanoparticles through aggregating. The aggregating feature is further confirmed by HRTEM image (Fig. 2d), in which can find the shell of the hollow spheres is composed of nanocrystals with different growth direction as marked by circles in Fig. 2d. Before discussing the growth mechanism of Cu 2 O hollow spheres, we first discuss the reaction process in our present synthetic system. To obtain structure and composition of the product formed in initial Fig. 1 (a) Low- and (b) high-magnification SEM images of Cu 2 O hollow spheres. (c) XRD pattern of the as-prepared Cu 2 O hollow spheres. Center for Exploitation and Utilization of Natural Resources of Minority Regions, Minzu University of China, Beijing, 100081, P. R. China. E-mail: wzhwang@aphy.iphy.ac.cn; Fax: +86-10-68930239; Tel: +86-10-68930239 † Electronic supplementary information (ESI) available: Raman scattering measurement. See DOI: 10.1039/b912514k 700 | CrystEngComm, 2010, 12, 700–701 This journal is ª The Royal Society of Chemistry 2010 COMMUNICATION www.rsc.org/crystengcomm | CrystEngComm Published on 23 October 2009. Downloaded by University of California - Santa Cruz on 23/10/2014 10:52:40. View Article Online / Journal Homepage / Table of Contents for this issue