Shape-controlled Synthesis of Porous SnO2 Nanostructures via Morphologically Conserved Transformation from SnC2O4 Precursor Approach

www.nmletters.org Shape-controlled Synthesis of Porous SnO2 Nanostructures via Morphologically Conserved Precursor Transformation from SnC2O4 Approach Qihua Wang1 , Dewei Wang∗,1,2 , Tingmei Wang1 (Received 18 Feb 2011; accepted 08 April 2011; published online 19 April 2011.) Abstract: Porous SnO2 nanostructures with controlled shapes were synthesized by a facile morphologically conserved transformation from SnC2 O4 precursor approach. Well-defined SnC2 O4 nanostructures can be obtained through a solution-based precipitation process at ambient conditions without any surfactant. The formation mechanism of such microstructures was tentatively proposed on the basis of intrinsic crystal structure and the reaction conditions. We found that the morphologies of precursor were well maintained while numerous pores were formed during the annealing process. The combined techniques of X-ray diffraction, nitrogen absorption–desorption, field emission scanning electron microscopy, and (high-resolution) transmission electron microscopy were used to characterize the as-prepared SnO2 products. Moreover, cyclic voltammetry (CV) study shows that the shape of CV presents a current response like roughly rectangular mirror images with respect to the zero-current line without obvious redox peaks, which indicating an ideal capacitive behavior of the SnO2 electrodes. The photoluminescence (PL) spectrum study suggests that the as-obtained porous SnO2 nanostructures might have a large number of defects, vacancies of oxygen, and local lattice disorder at the interface, interior and exterior surfaces. Keywords: Shape-controlled; SnO2; Solution chemistry. Citation: Qihua Wang, Dewei Wang, Tingmei Wang, “Shape-controlled Synthesis of Porous SnO2 Nanostructures via Morphologically Conserved Transformation from SnC2 O4 Precursor Approach”, Nano-Micro Lett. 3 (1), 34-42 (2011). http://dx.doi.org/10.3786/nml.v3i1.p34-42 Introduction As one of the versatile functional materials with a stable wide band gap of 3.6 eV, SnO2 has drawn immense attention to its fascinating physicochemical properties and potential applications in numerous fields, such as transparent conductive electrodes, anodes for lithium ion batteries, dye-sensitized solar cells, and chemical gas sensors [1-4]. Recent studies show that the performance of SnO2 in these applications mainly depend on its morphology and structural features. Accordingly, considerable effort has recently been devoted to synthesizing SnO2 nanostructures with different morphologies, including SnO2 octahedra, nanorods, nanowires, nanobelts, nanotubes, hollow spheres, and mesoporous structures [5-15]. Particularly, nanoporous structures have attracted considerable attention due to their improved performance compared with their solid counterpart, such as large surface area, efficient catalytic activity, and structural stability [16]. It is believed that 1 State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou, 730000, People’s Republic of China. 2 Graduate School of Chinese Academy of Sciences, Beijing, 10039, People’s Republic of China. *Corresponding author. Fax: +86-931-8277088; Tel: +86-931-4968180; E-mail: , . Nano-Micro Lett. 3 (1), 34-42 (2011)/ http://dx.doi.org/10.3786/nml.v3i1.p34-42 Nano-Micro Lett. 3 (1), 34-42 (2011)/ http://dx.doi.org/10.3786/nml.v3i1.p34-42 bundles and sheaflike shape, have been successfully synthesized via a solution-based precipitation process in a selective manner. We found that the shapes of the tin oxalate could be tuning just through simply altering the solvents used. During heating at 350℃ in air, SnC2 O4 undergoes a transformation to SnO2 without altering the morphology of their respective precursors. This facile efficient and economic work provides a new route to synthesize mesoporous SnO2 nanostructures with controllable shape. nanoporous structures with controllable shapes might allow us to harvest advantages of both morphology and porous structure, which could widen their applications. Typically, the template-assisted approach has been demonstrated to be an effective route that can be employed to produce porous SnO2 nanostructures. For example, mesoporous SnO2 has been synthesized through structure replication (nanocasting) from ordered mesoporous KIT-6 silica by Tiemann and co-workers [17]. Qi and co-workers employed 1D silica mesostructures as sacrificial templates to synthesize SnO2 nanotubes with preserved morphologies via a simple hydrothermal route [18]. Highly ordered mesostructures of SnO2 have been obtained via an evaporation-induced self-assembly process [19]. However, to obtain pure porous materials, these template strategies encompass the need to remove the template through calcinations at elevated temperatures or wet chemical etching with an appropriate solvent. In some cases, the pore structure would be destroyed or the wall has poor mechanical strength during the template removal process. Moreover, template contamination mostly decreases the activity of synthesized materials and the removal of residues is difficult, which limit their performance [20]. Furthermore, the morphologies of the porous structures are limited due to the difficulty in fabricating templates with diverse morphologies. Therefore, the development of cost-effective methods, suitable for the large-scale synthesis of SnO2 nanoporous structures with adjustable morphologies, remains to be a huge challenge. Recently, morphology conversion transformed from precursor route has been explored to generate other nanostructures that might be difficult to synthesize directly. For instance, Xia and co-workers have demonstrated that the porous SnO2 nanowires can be obtained by calcination nanowires precursor, which has been prepared by reflux in the polyalcohol medium at a high temperatures [21]. SnS2 also could be serving as a precursor to generating porous SnO2 nanostructures with preserved morphologies via a simple calcination process [22]. Tin oxalate can be used as an alternatively precursor which can be producing SnO2 due to their easy synthesis, low cost, good structure stability, and relatively low decomposition temperature in air [23]. For example, tin oxalate submicrotubes, nanorods, and flowers-like structures can be obtained in the presence or absence of the surfactant. Porous SnO2 nanostructures can be obtained after calcination tin oxalate precursor at the relatively high temperatures (typically 500℃) in air [24-27]. Despite these advantages, it is still a great challenge to synthesize tin oxalate nanostructures in high quality in terms of well-defined shape and ease of fabrication. Herein, we report a simple but effective approach for producing mesoporous SnO2 nanostructures via a two step process. SnC2 O4 with three distinct morphologies, i.e., microfibers, nanorod- Experimental Synthesis of SnC2 O4 microfibers: In a typical procedure, 1 mmol of oxalic acid (H2 C2 O4 ) and an equal mole rati (...truncated)