Facile synthesis of NiTiO 3 yellow nano-pigments with enhanced solar radiation reflection efficiency by an innovative one-step method at low temperature Abdolmajid Moghtada a, ** , Ali Shahrouzianfar b , Rouholah Ashiri b, * a Department of Materials Science and Engineering, Sharif University of Technology, Tehran, Iran b Department of Materials Science and Engineering, Dezful Branch, Islamic Azad University, P.O. Box 313, Dezful, Iran article info Article history: Received 17 September 2016 Received in revised form 12 November 2016 Accepted 20 December 2016 Available online 22 December 2016 Keywords: Nano-pigment NiTiO 3 Sonochemical method Purified distilled water (PDW) Optical properties Cool colorants abstract Inorganic NiTiO 3 nano-pigments have received recent attentions as possible candidates for cool materials to be used in building roofs and facades. In this paper, we have attempted to develop an innovative low temperature pathway (processed at 50  C) for obtaining NiTiO 3 nanocrystals by an ultrasound-assisted wet chemical processing method. Different characterization techniques such as X-ray diffraction (XRD), Fourier transform infrared spectrometry (FT-IR), field emission scanning electron microscopy (FE- SEM), transmission electron microscopy (TEM), and diffuse reflectance spectroscopy (DRS) were used in order to characterize the size, morphology and optical responses of the obtained NiTiO 3 nanoparticles. The crystallite size, particle size distribution range and band gap were found to be 10 nm, in the range of 10e20 nm and 3.72 eV, respectively. UVeViseNIR diffuse reflectance spectrum of NiTiO 3 nanoparticles exhibited an intense reflection peak at around 580 nm, which is related to the brilliant yellow color of the synthesized nano-pigments. The enhanced reflectance seen in this work is much higher than that re- ported in similar works indicating these nano-pigments can be used as cool colorants for coating the building with better energy saving performance. Scanning electron microscopy studies indicated a uniform particle shape with a narrow size distribution. We believe that the methodology developed in this work provides a simple, cost-effective, and convenient route for synthesizing a variety of perovskite materials for assembling in nanotechnology. © 2016 Elsevier Ltd. All rights reserved. 1. Introduction Newly, special attention has been paid to the titanium-based ilmenites, MTiO 3 , as chemical, electrical and optical materials because of their weak magnetism and semiconductivity and consequently their excellent ferroelectric, dielectric and electro- optical properties [1]. Nickel titanate ðNiTiO 3 ; NTOÞ belongs to the ilmenite type structure with both Ni and Ti possessing octahedral coordination and the alternating cation layers occupied by Ni þ2 and Ti þ4 alone [2]. NTO has a wide range applications in various in- dustries including electrodes of solid oxide fuel cells, metaleair barriers, gas sensors, high performance catalysts [3], tribological coatings [4], corrosion inhibitors [5], pigments [6e8], electronic materials in electrochemical energy storage devices [9,10], catalysts [11e 16], and gas sensors [17]. Moreover, the properties of NTO depend on its preparation method. Nanostructured NTO powders can be obtained by different synthesis methods such as solid-state reaction [2], wet chemical processing [7,18], solution combustion [14], electrospinning [19], polymeric precursor [20,21], precipita- tion [22,23], Pechini [24,25] and sol-gel [3,26e29] methods. The main disadvantage of the conventional approaches is calcination of the powder mixture at high temperatures ranging from 1373 to 1573 K (1100e1300  C); the coarse-grained powders synthesized by these methods contain agglomerated particles of different size and impure phases due to incomplete synthesis reactions [30,31]. On the other hands, temperatures above 200  C are required to obtain NTO powders through advanced wet chemical methods. It still remains a challenge for the scientific community to obtain high quality NTO nanocrystals at a low temperature while avoiding unwanted by-products [31]. This work develops an innovative pathway, which is able to obtain carbonate-free NTO yellow nano- * Corresponding author. ** Corresponding author. E-mail addresses: majid.moghtada@hotmail.com (A. Moghtada), ro_ashiri@ yahoo.com (R. Ashiri). Contents lists available at ScienceDirect Dyes and Pigments journal homepage: www.elsevier.com/locate/dyepig http://dx.doi.org/10.1016/j.dyepig.2016.12.044 0143-7208/© 2016 Elsevier Ltd. All rights reserved. Dyes and Pigments 139 (2017) 388e396