Microwave-assisted synthesis of Nb 2 O 5 for photocatalytic application of nanopowders and thin films
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aría José López-Muñoz Department of Chemical and Environmental Technology, Rey Juan Carlos University, Móstoles 28933, Madrid, Spain
Juan Carlos Fariñas Institute of Ceramics and Glass, CSIC, Madrid 28049, Spain
João Batista Rodrigues Neto Department of Mechanical Engineering, Federal University of Santa Catarina, Florianópolis 88040-900, SC, Brazil
Rodrigo Morenoa) Institute of Ceramics and Glass, CSIC, Madrid 28049, Spain (Received 23 December 2016; accepted 3 March 2017)
A new rapid and energy saving method for the obtention of high performance nanoparticles and thin films of Nb2O5 by microwave-assisted hydrothermal synthesis is reported. The hydrothermal treatment of a sol–gel precursor solution in a microwave oven at 180 °C for 20 min was enough to obtain amorphous nanoparticles with average sizes of 40 nm. The calcination promotes the formation of different phases of Nb2O5 (TT and T) with pseudohexagonal and orthorhombic structure, respectively, that transform at higher temperatures in a mixture of orthorhombic and monoclinic phases. Crystalline phase composition was found to have a significant influence on the photocatalytic activity. The best photocatalytic performance was observed for the material mainly constituted by the TT-Nb2O5 phase. Thin films constituted by the TT phase were prepared by dip-coating. Photocatalytic experiments confirmed the high photocatalytic activity of this material, which showed a kinetic curve similar to that of a reference TiO2-P25 thin film.
I. INTRODUCTION
In recent years, the synthesis of nanomaterials based on oxides such as TiO2, MnO2, ZnO, VOx, and Nb2O5 has attracted increasing interest in different research fields due to their chemical, physical, optical, and electronic properties that make these materials promising in several technological applications, such as catalyst in various types of reactions,1,2 electronics,3,4 semiconductor elements in solar cells,5–8 or photocatalytic applications,9–11 among others. In particular, niobium pentoxide (Nb2O5) has n-type semiconductor properties with a band gap of 3.0–3.4 eV, low toxicity potential, good chemical and thermal stabilities, surface acidity, and high selectivity.12,13 Furthermore, this material has a high potential for application in Contributing Editor: Eugene Medvedovski a) Address all correspondence to this author. e-mail: [email protected] b) Current Address: Empa, Laboratory for High Performance Ceramics, 8600 Dübendorf, Switzerland. DOI: 10.1557/jmr.2017.93
different photocatalytic systems, including the photodegradation of organic dyes, and hydrogen production.14–16 It is well established that the structure and morphology of oxides strongly depend on their synthesis method and the involved experimental variables. Different preparation conditions can produce materials with different structural and morphological properties, with enhanced performance for specific applications. In this context, various studies have been proposed to optimize the properties of Nb2O5 and maximize their application efficiency.17–20 Stab
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