The role of fuel to oxidizer ratio in solution combustion synthesis of TiO 2 and its influence on photocatalysis
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Recently, solution combustion synthetic approach has emerged as a potential route to synthesize a wide range of catalytic oxides. Nano TiO2 was synthesized by solution combustion methods using glycine, urea, and oxalyldihydrazide as fuels. X-ray diffraction and field emission scanning electron microscopy analyses revealed the structural and morphological differences of TiO2 synthesized with different fuels. The oxidizer to fuel ratio from lean to rich conditions also played a crucial role in determining the polymorphic percentage concentration in the synthesized TiO2 powders. However, diffuse reflectance spectroscopy and photoluminescence spectroscopy studies did not show any significant differences in the electronic properties of the synthesized TiO2. As the polymorphic composite phases synergistically influence the catalytic performances, photodegradation of methylene blue (MB) and photo hydrogen production were studied with the synthesized catalysts. The synergistic role crucially depended on the specific reaction. The presence of different TiO2 polymorphs due to difference in fuels during combustion controlled the photocatalytic efficiency of the catalysts toward MB degradation and hydrogen production.
I. INTRODUCTION
Solution combustion synthesis (SCS) is a lowtemperature initiated, energy efficient single step quick synthesis process and is widely used for the synthesis of a variety of nanomaterials. The SCS method uses watersoluble metal nitrate precursors along with the desired fuel-like urea or hydrazides [carbo hydrazide, oxalyldihydrazide (ODH), malonic acid dihydrazide, tetra formal trisazine] etc. The two primary purposes of the fuels are as follows: (i) They form complexes with the metal ions and assist in homogeneous mixing of the cations in the solution, and (ii) they help combustion and liberate heat. Nature of the fuel and fuel to oxidizer ratio play important roles in combustion synthesis since they can influence the morphology, phase, and particulate properties of the final combusted product.1–6 The fuels differ in their reducing power, the combustion temperature, and the amount of gases they generate, and these affect the characteristics of the final product.7–10 Also, fuels having lower decomposition temperatures with the evolution of larger amounts of gases (CO2 and H2O) are important. These help to generate sufficient local heating for the completion of combustion reactions during the synthesis and at the same time create materials of high porosity, good crystallinity and also prevent particle agglomeration.11–13 Contributing Editor: Scott T. Misture a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2017.244
SCS approach has shown promising results in synthesizing TiO2, which is the most widely used photocatalyst because of its chemically stable and biologically benign nature.14–25 Among the three different polymorphic structures, anatase and rutile are commonly used in photocatalysis, while brookite is rarely used. The photocatalytic efficien
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