Regular Article Ceria and titania incorporated silica based catalyst prepared from rice husk: Adsorption and photocatalytic studies of methylene blue Farook Adam a,⇑ , Lingeswarran Muniandy a , Radhika Thankappan b a School of Chemical Sciences, Universiti Sains Malaysia, 11800 Penang, Malaysia b Centre for Materials for Electronics Technology [C-MET], M.G. Kavu P.O., Athani, 680 581 Thrissur, Kerala, India article info Article history: Received 7 March 2013 Accepted 19 May 2013 Available online 4 June 2013 Keywords: Methylene blue Adsorption Photocatalyst Titania Ceria Rice husk silica abstract Titania and ceria incorporated rice husk silica based catalyst was synthesized via sol–gel method using CTAB and glycerol as surface directing agents at room temperature and labeled as RHS-50Ti10Ce. The cat- alyst was used to study the adsorption and photodegradation of methylene blue (MB) under UV irradia- tion. The powder XRD pattern of RHS-50Ti10Ce was much broader (2h = 25–30°) than that of the parent RHS (2h = 22°). The catalyst exhibited type IV isotherm with H3 hysteresis loop, and the TEM images showed partially ordered pore arrangements. The TGA–DTG thermograms confirmed the complete removal of the templates after calcination at 500 °C. RHS-50Ti10Ce exhibited excellent adsorption capa- bility with more than 99% removal of MB from a 40 mg L 1 solution in just 15 min. It also decolorized an 80 mg L 1 MB solution under UV irradiation in 210 min, which was comparable with the commercialized pure anatase TiO 2 . Ó 2013 Elsevier Inc. All rights reserved. 1. Introduction One of the most prominent contaminants that could be found in the water systems are azo dyes. Azo dyes are characterized by the presence of one or more azo groups (AN@NA) in the molecular chain [1]. 3,7-bis(dimethylamino)phenazathionium chloride or more commonly known as methylene blue (MB) is a famous color- ant and azo dye that is frequently used in the textile industry. MB is a cationic dye and would dissociate into a chloride anion and MB cation in aqueous solution. It was discovered in 1876 by Caro, and the powder has a distinctive dark green coloration [2]. Acute expo- sure to MB could result in severe medical complications such as quadriplegia, cyanosis, and tissue necrosis [3]. The presence of the azo dyes in wastewaters generated from the industries poses serious problems to the environment. MB for example is believed to be one of the major causes of aquatic pollution, and it is estimated that 1000 tonnes or more of dyes are released annually into water streams [4]. These pollutants are hazardous toward the environment and have the potential to be carcinogenic. This is largely due to the use of dangerous chemicals such as benzidine and heavy metals to synthesize them [5]. Conventional water treatment methods such as biodegradation of azo dyes in aerobic conditions have been described to be inef- fective and difficult [6]. Membrane filtration processes, however, are efficient for wastewater treatment, yet they remain unpopular due to the high operating costs [7]. Therefore, recent studies have been focusing more on advanced oxidation processes (AOPs) using semiconductor catalysts for the removal of organic pollu- tants from water sources. The generation of radicals (HO Å and O Å 2 ) through irradiation with UV light would initiate the degrada- tion process of the pollutants [8]. Titanium dioxide, TiO 2 , is widely used for the photocatalytic degradation of organic pollu- tants due to its low cost, non-toxicity, and high chemical stability [9]. However, there are some disadvantages of using TiO 2 due to its large band gap energy (3.2 eV) [10] and high electron–hole recombination ratio. In addition, TiO 2 nanoparticles are very fine, and this would result in difficulties during the separation process [11]. Incorporation of lanthanides into TiO 2 matrices is on the rise now, due to their unique physical, chemical, and electronic prop- erties. It was reported that incorporation of lanthanides was capa- ble of reducing the recombination of electron–hole pairs, thus increasing the photocatalytic efficiency of TiO 2 -lanthanide hybrid complex [12]. Furthermore, lanthanides could form complexes with various Lewis bases, which would result in better adsorption of organic pollutants onto the surface of the modified TiO 2 cata- lyst [13]. In the present work, however, titania and ceria incorporated rice husk silica (RHS) heterogeneous catalyst was synthesized via sol–gel method at room temperature. The catalyst was used for the simultaneous adsorption and photodegradation of MB under UV irradiation. The catalyst’s performance was compared with that of commercial TiO 2 (99% anatase) powder. 0021-9797/$ - see front matter Ó 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.jcis.2013.05.066 ⇑ Corresponding author. Fax: +60 46574854. E-mail addresses: farook@usm.my, farookdr@gmail.com (F. Adam). Journal of Colloid and Interface Science 406 (2013) 209–216 Contents lists available at SciVerse ScienceDirect Journal of Colloid and Interface Science www.elsevier.com/locate/jcis