Applied Catalysis B: Environmental 199 (2016) 187–198 Contents lists available at ScienceDirect Applied Catalysis B: Environmental journal homepage: www.elsevier.com/locate/apcatb ZnO quantum dots decorated 3DOM TiO 2 nanocomposites: Symbiose of quantum size effects and photonic structure for highly enhanced photocatalytic degradation of organic pollutants Meryam Zalfani a,b , Benoit van der Schueren a , Mounira Mahdouani b , Ramzi Bourguiga b , Wen-Bei Yu c , Min Wu c,∗∗ , Olivier Deparis d , Yu Li c,∗∗ , Bao-Lian Su a,c,e,∗ a Laboratory of Inorganic Materials Chemistry (CMI), University of Namur, 61 rue de Bruxelles, B-5000 Namur, Belgium b Laboratoire de Physique des Matériaux: Structure et Propriétés, Groupe Physique des Composants et Dispositifs Nanométriques, Faculté des Sciences de Bizerte, University of Carthage, 7021 Jarzouna-Bizerte, Tunisia c State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Luoshi Road 122, 430070, Wuhan, Hubei, China d Departement of Physics, University of Namur, Rue de Bruxelles 61, B-5000 Namur, Belgium e Clare Hall, University of Cambridge, Cambridge, United Kingdom a r t i c l e i n f o Article history: Received 18 March 2016 Received in revised form 1 June 2016 Accepted 4 June 2016 Keywords: ZnO quantum dots 3DOM TiO2 Quantum size effect Light sensitizor Photonic effect a b s t r a c t Three dimensionally ordered macroporous inverse opal TiO 2 nanocomposites decorated by ZnO quantum dots (ZnO QDs@3DOM TiO 2 ) with an intimate contact were successfully synthesized using the sol-gel technique and characterized in terms of structure, porosity, chemical composition and optical properties. The photocatalytic activity of ZnO QDs@3DOM TiO 2 nanocomposites with different ZnO QDs amounts was evaluated in the aqueous phase of dye pollutant molecules and compared with the state-of-the-art 3DOM TiO 2 and P25 photocatalysts. The symbiotic effect of ZnO QDs and 3DOM photonic structure on the light absorption and further on the photocatalytic activity of the nanocomposites was observed. The sample with the highest ZnO QDs amount exhibits extraordinarily high photocatalytic activity, which is attributed to firstly, the formation of an intimate junction between the two semiconductors, hence favoring the separation of photo-introduced electron–hole pairs in ZnO-TiO 2 photocatalyst, and, secondly, to the quantum size effect (QSE). The QSE results in an increase in the width of the forbidden electronic band, which increases the energy of electrons (holes) in the conduction (valence) and particularly leads to the displacement of the conduction band potentials of ZnO to more negative energy values compared to TiO 2 . Thanks to the heterojuction formed between ZnO QDs and 3DOM TiO 2 , the energy difference between conduction bands of both semiconductors acts as a driving force for rapid electron/hole transfer between the coupled materials. Due to the extremely short diffusion time, the lifetime of photogenerated charge carriers is extended and the effectiveness of reduction and oxidation process is increased with faster reaction kinetics. Increasing the amount of ZnO QDs can boost the photocatalytic activity. On the other hand, 3DOM photonic structure of TiO 2 with its open meso-macroporosity can facilite the diffusion of dye molecules and light propagation. This first successful example of symbiose of a series of physical effects can open a new window for solar energy conversion by the synergitic association of QSEs, photonic effect and other effects such as plasmonic effects, in one solid material to develop highly efficient solar light havesting system to enhance solar energy conversion effeciency for photocatalysis and photovoltaics. © 2016 Elsevier B.V. All rights reserved. ∗ Corresponding author at: Laboratory of Inorganic Materials Chemistry, Univer- sity of Namur, Namur, Belgium and State Key Laboraory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Wuhan, China. ∗∗ Corresponding authors. E-mail addresses: minwu@whut.edu.cn (M. Wu), yu.li@whut.edu.cn (Y. Li), bao-lian.su@unamur.be, baoliansu@whut.edu.cn, bls26@cam.ac.uk (B.-L. Su). 1. Introduction Photocatalytic degradation of organic pollutants and water splitting process using semiconductors such as TiO 2 and ZnO have been extensively investigated in order to solve environmental and energy problems [1–3]. ZnO is a direct band gap semiconduc- tor with an energy gap of 3.37 eV while TiO 2 is an indirect band http://dx.doi.org/10.1016/j.apcatb.2016.06.016 0926-3373/© 2016 Elsevier B.V. All rights reserved.