DOI: 10.1021/cg900161w
Facile Synthesis, Growth Mechanism, and UV-Vis Spectroscopy of Novel Urchin-like TiO2/TiB2 Heterostructures
2009, Vol. 9 4017–4022
Fei Huang,† Zhengyi Fu,*,† Aihua Yan,‡ Weimin Wang,† Hao Wang,† Yucheng Wang,† Jinyong Zhang,† Yibing Cheng,§ and Qingjie Zhang† †
State Key Lab of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Wuhan 430070, People’s Republic of China, ‡Nanomaterial and Smart Sensor Research Laboratory, Department of Materials Science and Technology, Huazhong University of Science and Technology, Wuhan 430074, People’s Republic of China, and § Department of Materials Engineering, Monash University, Victoria 3800, Australia Received February 11, 2009; Revised Manuscript Received June 22, 2009
ABSTRACT: A TiO2/TiB2 heterostructure with a sea-urchin shape, as a new material system, was successfully synthesized by a facile hydrothermal approach in an aqueous solution of ethylenediamine (EDA). This complex architecture is a core/shell urchin structure composed of high-density anatase TiO2 (A-TiO2) nanorod-built networks (shell part) that stand on a TiB2 microcrystal (core part). The microstructure can be controlled by the temperature, time, reactants, and additives. A three-step sequential “oriented attachment growth” model is proposed based on the observations from a time-dependent and temperature-dependent morphology evolution process. Importantly, UV-vis absorption spectra show that the absorption peak and absorption edge has an obvious shift to a lower energy because of the nanometric effect and N-doping.
1. Introduction Titanium dioxide (TiO2), as the most common and prominent compound of titanium, has unique electronic and optical properties and is often used in many fields ranging from photocatalysts,1 heterogeneous catalysis,2 chemical sensors,3 and solar energy conversion devices.4 Nanostructured TiO2 materials, with the enhancement of surface area and chemical activity, show different physical and chemical properties. In the past decade, tremendous efforts have been made to synthesize different nanometer-scaled TiO2 materials. Such materials include spherical nanocrystallites5 and nanoparticles,6 together with elongated nanotubes,7 nanorods,8 nanosheets,9 and nanowires.10 One-dimensional (1D)/twodimensional (2D) nanomaterials exhibit many special properties in the optical, electrochemical, mechanical, thermal facets, etc. However, hierarchical and complex micro-/nanoarchitectures have stimulated much attention since such architectures combine the features of micrometer- and nanometer-scaled building blocks and provide a great deal of opportunity to explore their novel properties.11-14 However, fabrication of more complex TiO2 micro-/nanoarchitectures and controlling the shape of nanostructures at the microscopic level are still a significant challenging issue for material scientists. An important application of TiO2 is as a photocatalyst in environmental protection. It is well-known that the intrinsic properties of titania are strongly dependent on the choice of morphology and selection of crystallite size, as well as the method of synthesis. TiO2 exists in three types of crystalline structures: rutile, anatase, and brookite. It is reported that anatase is more active photocatalytically.15 With its band gap near 3.3 eV, undoped A-TiO2 has a photothreshold that extends from the ultraviolet region into the solar spectrum (about 367 nm). This active region of the solar spectrum only comprises
