EDTA mediated microwave hydrothermal synthesis of WO 3 hierarchical structure and its photoactivity under simulated solar light Rajesh Adhikari a , Gobinda Gyawali a , Tae Ho kim a , Tohru Sekino b , Soo Wohn Lee c, * a Research Center for Eco-multifunctional Nano Materials, Sun Moon University, Republic of Korea b Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Japan c Department of Environmental Engineering, Sun Moon University, Republic of Korea A R T I C L E I N F O Article history: Received 22 August 2013 Received in revised form 2 February 2014 Accepted 27 February 2014 Keywords: Hierarchical Complexing agent EDTA Rhodamine B A B S T R A C T In this paper, we report a facile microwave hydrothermal synthesis of WO 3 hierarchical structure in presence of disodium salt of ethylenediaminetetraacetic acid (EDTA) as a complexing agent and its photoactivity for the degradation of rhodamine B (Rh B) under simulated solar light irradiation. The synthesized WO 3 samples were structurally, morphologically and optically characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV–vis diffuse reflectance spectroscopy (UV–vis DRS) and Brunauer–Emmett–Teller (BET) surface area analysis. The result revealed that the addition of EDTA leads to the controlled aggregation of WO 3 nanoparticles having high crystallinity with monoclinic structure and creates oxygen vacancy in the WO 3 lattice. Moreover, at high concentration of EDTA, cauliflower like hierarchical structure was formed when the optimum concentration of EDTA reaches to 0.5 mol% at pH 6 and exhibited best photoactivity for the Rh B degradation. These results indicate that the WO 3 hierarchical structures with oxygen vacancies are potential materials for effective mineralization of Rh B, one of the hazardous pollutants. ã 2014 Elsevier Ltd. All rights reserved. Introduction Organic dyes such as rhodamine B (Rh B), methyl orange (MO) and indigo carmine (IC) are some of the hazardous contaminants in aquatic environment as a result of their huge production from various industries. Their elimination from wastewater effluents is now a subject of considerable concern of environmental remedia- tion and has drawn the attention in recent years. Most textile dyes are photolytically stable and refractory towards chemical oxidation [1] and these characteristics render them resistant towards decomposition by conventional biochemical and physico-chemical methods. Generally, adsorption on activated carbon, coagulation by a chemical agent or reverse osmosis was applied to such effluents [2,3]. Nevertheless, they are non-destructive methods, and merely transfer contaminants from water to sludge. Therefore, an effective monitoring of such hazardous pollutants should be the prime focus of research in scientific communities. Solar light driven photocatalysis has gained great attention over the past two decades, since it offers excellent prospects to control environmental pollution. TiO 2 is the most popular and well studied photocatalyst due to its high photo-efficiency, high oxidizing power, good stability, low cost and nontoxic properties [4–7]. However, it suffers from inefficient utilization of solar light due to its wide band gap and its optical response limited only to the UV component of the solar spectrum. The development of photo- catalysts active under visible light is an essential requirement for efficient solar light driven applications. Extensive research has been done to extend optical response of TiO 2 into the visible light range by doping with anions or cations and or by creating composites with other semiconductors [8,9]. Some progress in visible light sensitization has been made by doping; however, this process also tends to introduce recombination centers into the crystalline lattice, which typically suppresses UV-driven photo- activity [10]. The organization of nanomaterials through assembly is an important example of the order-disorder evolution of nanoscaled systems [11]. These hierarchical and repetitive super-structures provide promising complex functions and direct bridges between nanoscale objects and macro scale world [12]. Ordered assembly of nanoscale building blocks, such as nanoparticles, nanorods and others, into various single-crystalline architectures has become an important topic in recent materials research fields. Therefore, precise architectural manipulation of nano- or microcrystals and their assemblies with well controlled morphologies remains a * Corresponding author. E-mail address: swlee@sunmoon.ac.kr (S.W. Lee). http://dx.doi.org/10.1016/j.jece.2014.02.019 2213-3437/ ã 2014 Elsevier Ltd. All rights reserved. Journal of Environmental Chemical Engineering 2 (2014) 1365–1370 Contents lists available at ScienceDirect Journal of Environmental Chemical Engineering journal homepage: www.else vie r.com/locat e/jece