Chemical Engineering Journal 166 (2011) 906–915 Contents lists available at ScienceDirect Chemical Eng ineeri ng Jour nal j o u r nal home p a g e : www.elsevier.com/locate/cej WO 3 /TiO 2 composite with morphology change via hydrothermal template-free route as an efficient visible light photocatalyst Sajjad Ahmed Khan Leghari, Shamaila Sajjad, Feng Chen, Jinlong Zhang ∗ Key Lab for Advanced Materials and Institute of Fine Chemicals, East China University of Science and Technology, 130 Meilong Road, Shanghai, 200237, PR China a r t i c l e i n f o Article history: Received 13 October 2010 Received in revised form 17 November 2010 Accepted 17 November 2010 Keywords: Template-fre e route Hydrothermal method WO3/TiO2 composite Ammonium sulfate Visible photocatalyst a b s t r a c t The WO3/TiO2 composites are prepared by a template-free synthetic approach based on hydrothermal react ion thatleads to theformation of nano parti cles andmicrosphe res withthe chan ge inconcentrations of ammonium tungstate used as a dopant precursor. 5.0% composite generally exists in loose aggregate nanoparticles. These particles are aggregated to form the peculiar morphology of microspheres at 10.0% WO3/TiO2 due to the in situ formation of ammonium sulfate in supersaturated state. 5.0% composite exhibits the best photoactivity as compared to pure TiO 2 , P-25 and pure WO 3 in the degradation of met hylorang e and 2, 4-d ichlor oph eno l in UV andvisib le light.10.0%WO3/TiO2 composi te conta ins more dopant contents but exhibits comparable higher activity due to its specific morphology of spheres. Mor- phological variations of a photocatalyst also influence the photocatalytic efficiencies. Catalysts exhibit high activity owing to the combined effects of both the unique structural characteristics and the tung- sten doping. The doped tungsten (W) inhibits the electron–hole recombination rate. The kinetics of the organics degradation is found to follow the Langmuir–Hinshelwood model. © 2010 Elsevier B.V. All rights reserved. 1. Intro ducti on The spont aneous assembly and trans formation of inorga nic matter into complex higher-order architectures is a key challenge in materials chemistry. In general, template-directed approaches have been used extensively to control the spatial patterning of inorganic materials. For example, inorganic spheres which have numerous potential applications as catalysts, lightweight fillers, low-dielectric materials, drug-release vectors and photonic crys- tals [1] have been fabr icate d using confin ed react ion enviro nments suc h as emulsions [2] and spra y-dri ed dropl ets [3] or pol y- mer/surfactant micellar templates [4] or by surface depo sitio n onto monodisperse latex particles followed by template removal [5]. Alte rnati vely, higher -ord er architectu res can be spont aneou sly assembled by mesos cale trans formation processes that invol ve metastabl e inorga nic-based colloidal aggre gates [6]. Typically nucleation and growth occur within the aggregates of amorphous inorga nic parti cles that are part ially stabilized by surfa ce-ad sorbed polymers/block copolymers [7] or surfactant molecules [8]. Under such conditions, crystallization of the precursor phase results in complex forms that bear little resemblance to the initial mor- pholo gy of the colloida l aggreg ates due to emergent processe s that radically transform the systems [9]. I n some cases, the aggre- gated precursor particles undergo self-transformation such that ∗ Correspondin g author. Tel.: +86 21 64252062; fax: +86 21 64252062. E-mail address: jlzhang@e cust.edu.cn (J. Zhang). new forms are produced by a redistribution of matter essentially within the same morphological boundary. In particular, interior structures canbe obt ain ed by the loc ali zedOstwald rip eni ng or dif - ferential diffusion (the Kirkendall effect) within metastable solid microspheres [10]. However, all of the aforementioned methods generally require the use of surfactants or polymers that must be remov ed. Moreo ver, thesematerial s are usual ly unsta ble and hence are limited in their potential applications. Coupling titania (TiO 2 ) with metal oxides and non metals is an approach which has received much attention for improving the photo catal ytic prop ertie s of TiO 2 [11–18]. Mic ro arc oxi dat ion pro - cesses have also been employed to grow WO 3 –TiO 2 composites [19,20]. In case of tungsten, this cation tends to migrate toward the surface in comparison to pristine TiO 2 by shifting the isoelec- tric poi nt to lower val ues [21,22]. Bul k pro per ties are als o mod ifie d because of the iso mor phi c sub stitution wit hin the lat tice; theelec- tronic properties of the doped material are notably different when compared with the pristine oxide [23]. The tungsten surface clus- ters work as electron traps which lead to photochromic materials with energy storage capacity [24,25]. In principle, the presence of tungs ten couldimprovethe phot odegr adat ion abili ty of TiO 2 insev- eral ways [26]. I t prevents the recombination of the electron–hole pairs [27] as well as expands the range of useful excitation light to thevisibl e spectra. In add iti on, the chemic al changes of thesurface result in enhanced acidity [28]. Taking into account the aforemen- tioned factors, the photodegradation mechanism can be affected when tungsten is incorporated into the catalyst [29]. The addition of tungsten oxide (WO 3 ) to TiO 2 has been observed to improve the 1385-8947/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.cej.2010.11.065