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Controllable preparation of fl ower-like brookite TiO 2 nanostructuresvia one-step hydrothermal methodYunling Zou a,b , Xin Tan c , Tao Yu a,*, Yan Li b , Yimei Li b , Ru Wang b , Lingqian Xue ba School of Chemical Engineering, Tianjin University, Tianjin 300072, PR Chinab College of Science, Civil Aviation University of China, Tianjin 300300, PR Chinac School of Science, Tibet University, Lhasa 850000, PR ChinaA R T I C L E I N F OArticle history:Received 5 November 2015Received in revised form 18 March 2016Accepted 4 April 2016Available online 5 April 2016Keywords:A. NanostructuresB. Chemical synthesisC. X-ray diffractionC. Electron microscopyC. Raman spectroscopyA B S T R A C TFlower-like brookite TiO 2 nanostructures were controllable prepared by a one-step hydrothermalmethod by changing experimental conditions, such as hydrothermal temperature, reaction time and theamount of polyvinylpyrrolidone. The photocatalytic activities of the samples were investigated bydegradation of methylene blue (MB) in aqueous solution under UV light irradiation. It was found that theformation of brookite TiO 2 nanostructures with various morphologies could be well controlled by theadjustment of hydrothermal temperature, reaction time and the amount of surfactant, and themorphology of the products changed from spindle-like structures to fl ower-like structures with theincrease of hydrothermal temperature, reaction time and the amount of surfactant. The photocatalytictests indicate that the fl ower-like brookite TiO 2 nanostructures shows high photocatalytic activity indegradation of methylene blue (MB) under UV light irradiation. The formation mechanism of fl ower-likebrookite TiO 2 nanostructures was also discussed in detail based on the above investigations.ã 2016 Elsevier Ltd. All rights reserved.1. IntroductionBrookite, as the least studied of crystalline TiO 2 , has attractedconsiderable interesting recent years due to its unique optical andelectronic properties [1,2]. Brookite TiO 2 with orthorhombiccrystalline structure was reported to have better photocatalyticand/or photoelectrical properties than anatase and rutile phase intheory [3–7]. Therefore, brookite has been considered as acandidate material to develop more eff i cient photocatalysts withthe deep research on TiO 2 photocatalyst resent years [8–13]. Manydifferent approaches have been used to prepare pure-phasebrookite and various morphologies of brookite TiO 2 have beenprepared, such as nanorobs [14], nanotubes [15], nanospindles[16], nanosheets [17], nanospheres [18,19], nanof l owers [20,21],and so on. Based on these studies, researchers have achieved a newunderstanding on the preparation and performance of brookiteTiO 2 . Particle size, crystal structure, and the morphology playimportant roles on photocatalytic activity of TiO 2 , which aremainly depended on synthetic method and reaction conditionsincluding titanium salt, pH value, reaction temperature and time,additive and so on [22–27]. Kuznetsova et al. [25] synthesizedbrookite TiO 2 f i lm by a new modif i ed sol–gel method and pointedout that the nature of complexation, the concentration of theprecursors, the polymer additive, solution media and the substrateplayed important roles on the formation of the brookite TiO 2 f i lms.Brookite TiO 2 -based solar cells with low cost and high conversioneff i ciency (7.57%) were achieved by Li et al. [26] by a hydrothermalprocess using Ti(SO 4 ) 2 as a titanium source and NaOH solution asthe regulating agent.Nanomaterials with hierarchical structure are reported toexhibit unique structural characteristics and size conf i nementeffects along with novel physical properties. Such materials haveattracted a def i nite interest for their current and possibleapplications in catalysis, gas sensors, and lithium batteries [28].Flower-like nanostructure, as a type hierarchical structure ofbrookite TiO 2 , has been studied by some researchers [20,21,29,30].López-Mu?noz et al. [29] reported that brookite TiO 2 with fl ower-type morphology exhibited higher activity than brookite consist-ing of an aggregation of nanoparticles in micrometric-size units.Flower-like brookite TiO 2 was also reported to show excellentelectric properties [20]. It is well known that hierarchicalnanostructure can be obtained by controlling preparation methodsand experimental conditions. Therefore, in order to better* Corresponding author.E-mail addresses: yutao@tju.edu.cn, lisat.yu@gmail.com, lisat0001yu@163.com(T. Yu).http://dx.doi.org/10.1016/j.materresbull.2016.04.0070025-5408/ã 2016 Elsevier Ltd. All rights reserved.Materials Research Bulletin 80 (2016) 237–242Contents lists available at ScienceDirectMaterials Research Bulletinjournal homepage: www.else vie r.com/locat e/mat resbu