3D nanostructures have attracted much attention because of their unique properties and potential applications. [1][2][3][4][5][6][7][8][9][10][11][12][13] The simplest synthetic route to 3D nanostructures is probably selfassembly, in which ordered aggregates are formed in a spontaneous process.[2] However, it is still a big challenge to develop simple and reliable synthetic methods for hierarchically selfassembled architectures with designed chemical components and controlled morphologies, which strongly affect the properties of nanomaterials. Iron oxides have been extensively studied in diverse fields including catalysis, [14][15][16] environment protection, [17][18][19][20][21][22][23] sensors, [24] magnetic storage media, [25] and clinical diagnosis and treatment. [26] Various iron oxide structures, such as nanocrystals, [27][28][29] particles, [30,31] cubes, [32] spindles, [33] rods, [34,35] wires, [36] tubes, [37] and flakes, [38] have been successfully fabricated by a variety of methods. However, the self-assembly of these low-dimensional building blocks into complex 3D ordered nanostructures is still considerably more difficult. In order to further understand the mechanism of self-organization and expand the applications of iron oxide nanomaterials, self-assembled iron oxide 3D nanostructures need to be explored in more detail. Herein, we report the synthesis of novel 3D flowerlike iron oxide nanostructures by an ethylene glycol (EG)-mediated self-assembly process. Such a method has been adopted previously for the preparation of V 2 O 5 hollow microspheres, [7] SnO 2 nanowires, [39,40] and cobalt alkoxide disk-shaped particles.[41] However, in these previous studies, expensive metal organic compounds including acetates, oxalates, or acetylacetonates were used as metal-ion sources; in this study we used ferric chloride, an inexpensive and nontoxic reagent, as our iron source. By calcination at an elevated temperature, the assynthesized iron oxide precursor was transformed into iron oxide. The phase of the final product could easily be controlled to be either a-Fe 2 O 3 , c-Fe 2 O 3 , or Fe 3 O 4 , three of the most common iron oxides, simply by altering the calcination conditions. All of the products maintained their original flowerlike morphology. The reaction mechanism leading to the iron oxide precursor and the self-assembly process are discussed. As an example of potential applications, the as-obtained iron oxide nanomaterials were used as adsorbent in waste-water treatment, and showed an excellent ability to remove various water pollutants. In a typical procedure, ferric chloride (FeCl 3 ·6 H 2 O), urea, and tetrabutylammonium bromide (TBAB) were dissolved in EG. The solution was refluxed at ca. 195°C for 30 min. After cooling, the as-synthesized iron oxide precursor was collected as a green precipitate by four centrifugation and ethanolwashing cycles. The morphology of the precursor was studied by scanning electron microscopy (SEM). Figure 1a shows the SEM image of a typical sample composed of many un...

Self-assembled structures with highly specific morphology and novel properties are of great interest to chemists and materials scientists. As a result of rapid advancements in synthetic strategies, highly organized building blocks of metals, [1] semiconductors, [2] copolymers, [3] organic-inorganic hybrid materials, [4] and biominerals [5] have been synthesized by using various methods. However, controlled organization into curved structures from rodlike building blocks remains a challenge. Such a capability is attractive to scientists not only because of its importance in understanding the concept of self-assembly with artifial building blocks but also for its great application potential. [6][7][8][9] Vanadium pentoxide (V 2 O 5 ) has been extensively studied as a well-known transition-metal oxide. Various nanostructures of V 2 O 5 , [10] such as nanotubes, nanowires, nanofibers, nanobelts, nanorods, and mesoporous structures have already been synthesized by a variety of methods, including reverse-micelle transition, sol-gel process, hydrothermal treatment, and electrochemical deposition. Nanostructured V 2 O 5 has potential application in the fields of lithium-ion batteries, [10c,d, 11] actuators, [10f] catalysis, [12] and sensors.[13] To our knowledge, hollow microspherical V 2 O 5 has not been reported until now although such a structure has long been a focus of research. [14] Herein, we describe a facile method to self-assemble V 2 O 5 nanorods into microspheres. A mediated polyol process was adopted to prepare hollow microspherical V 2 O 5 , in which ethylene glycol (EG) is treated with a metal salt in the presence of poly(vinylpyrrolidone) (PVP). Such a method was previously used to obtain metal nanoparticles, nanowires (EG as a reductant), [15] and oxide nanowires (EG as a ligand). [16] We now present its use, for the first time, to synthesize hollow microspheres of V 2 O 5 . Using vanadium(iii) acetylacetonate (acac) as the metal-ion source, we have synthesized hollow microspheres with nanorods on their surface; moreover, the morphologies of such nanorods are