Enhancement of the photocatalytic activity and white emission of CaIn 2 O 4 nanocrystals M.T.S. Tavares a , M.M. Melo b , V.D. Araújo c , R.L. Tranquilin d , C.R.R. Almeida d , C.A. Paskocimas d , M.R.D. Bomio d , E. Longo e, * , F.V. Motta d a IFBA, Campus Feira de Santana, CEP 44096-486 Bahia, BA, Brazil b IFRN, Campus Santa Cruz, CEP 59200-000 Santa Cruz, RN, Brazil c UACSA e UFRPE, Recife, CEP 52171-900 Recife, PE, Brazil d LSQM- Laborat orio de Síntese Química de Materiais, DEMAT, UFRN, Natal, Campus Lagoa Nova, CEP 59078-900 Natal, RN, Brazil e LIEC- Laborat orio interdisciplinar de eletroquímica e cer^ amica e DQ, UFSCar, CEP 13565-905 S~ ao Carlos, SP, Brazil article info Article history: Received 21 August 2015 Received in revised form 3 October 2015 Accepted 18 October 2015 Available online 27 October 2015 Keywords: CaIn 2 O 4 Ultrasonic spray pyrolysis Nanocrystals Photocatalysis Photoluminescence White-light abstract CaIn 2 O 4 (CIO) nanocrystals (NCs) were prepared by ultrasonic spray pyrolysis at 1223 K without the use of surfactants to investigate the influences of the nanostructure on the photoluminescence and photo- catalytic properties of this white-light emitter. The optical properties were analyzed by ultraviolet evisible (UVevis) absorption spectroscopy, which indicated a band gap energy of 3.83 eV, and photo- luminescence (PL) measurements at room temperature that showed a broad and intense emission band. X-ray diffraction (XRD) analysis confirmed that the CIO NCs adopted the orthorhombic crystalline phase. Field-emission gun scanning electron microscopy (FEG-SEM) micrographs demonstrated the spherical morphology of the CIO NCs, comprising aggregates of several CIO NCs. Furthermore, the as-synthesized CIO NCs exhibited enhanced activity for the photodegradation of methylene blue (MB) under UVevis irradiation. The chromaticity coordinates were calculated for the sample based on the PL spectrum; the CIO NCs had values of x ¼ 0.31 and y ¼ 0.38, and this point is located on the white region of the CIE diagram. Ultrasonic spray pyrolysis provides a feasible approach for preparing shape- and size-controlled CIO nanocrystals that hold great potential for photocatalytic applications and as photoluminescent white emitters. © 2015 Elsevier B.V. All rights reserved. 1. Introduction Recently, the design and production of new materials with controlled optical properties, such as semiconductor nanocrystals, have been intensively studied [1e3]. Indium-based oxides have attracted increasing attention in the last few years because their properties are potentially exploitable in optoelectronic devices, biological applications, catalysis, and other technologies [4e9]. CaIn 2 O 4 (CIO) is a compound belonging to the AB 2 X 4 family. Ac- cording to the literature, CaIn 2 O 4 shows potential for the degra- dation of organic pollutants and is an eco-friendly material [8,10]. Conventionally, the synthesis of CIO particles requires high temperatures and long synthesis or calcination times. Zeng et al. [11] synthesized CaIn 2 O 4 by calcination at high temperatures of 1073 and 1323 Kover long periods of 1 and 12 h, respectively. CIO photocatalysts have been obtained by solidestate reaction [12e16] and solution-combustion methods [17] that involved high tem- peratures and calcination times varying from 12 to 24 h. In order to minimize these inconveniences, other synthetic routes have been developed to obtain CIO, such as solvothermal [8], co-precipitation [18,19], solegel [20e22], and an optimized solidestate reaction [7]. It is known that the key factors controlling photocatalytic re- actions are the efficiency of (1) adsorption of the reactant on the surface of the material and (2) light absorption by the material, as well as migration of the light-induced electrons and holes. The former is strongly dependent on the surface area of the material and the latter is related to the electronic structure characteristics of the material [16]. Based on these trends, the development of new strategies to obtain CIO NC photocatalysts with high surface area and optimum electronic properties geared toward photocatalysis is of great importance. Ultrasonic spray pyrolysis is deemed an effective technique for * Corresponding author. E-mail address: elson.liec@gmail.com (E. Longo). Contents lists available at ScienceDirect Journal of Alloys and Compounds journal homepage: http://www.elsevier.com/locate/jalcom http://dx.doi.org/10.1016/j.jallcom.2015.10.155 0925-8388/© 2015 Elsevier B.V. All rights reserved. Journal of Alloys and Compounds 658 (2016) 316e323