Water defluoridation using a nanostructured diatom–ZrO 2 composite synthesized from algal Biomass Megha Thakkar, Zheqiong Wu, Liping Wei, Somenath Mitra ⇑ Department of Chemistry and Environmental Science, New Jersey Institute of Technology, Newark, NJ 07102, United States graphical abstract article info Article history: Received 13 December 2014 Accepted 7 March 2015 Available online 17 March 2015 Keywords: Diatom ZrO 2 Composite Defluoridation Adsorption abstract Frustules or the rigid amorphous silica cell wall of unicellular, photosynthetic microalgae with unique porous architecture has been used to synthesize a composite by immobilizing ZrO 2 on its surface and in the pores. This was effective in water defluoridation. The average diameter of the composite was 80 ± 2 nm and surface area was 140 m 2 /g. The adsorption isotherms followed both Langmuir and Freundlich models, and the composite was regenerable. Adsorption kinetics followed second order model and the adsorption capacity was as high as 11.32 mg/g, while the Langmuir maximum adsorption capac- ity (q m ) reached 15.53 mg/g. The research findings highlight the potential of diatoms as hosts for nano- materials for use in water treatment. Ó 2015 Elsevier Inc. All rights reserved. 1. Introduction Fluoride is widely distributed in the geological environment and is generally released into groundwater by slow dissolution of fluoride containing rocks [1]. Anthropogenic activities including ceramic/semiconductor manufacturing, electroplating, power generation and phosphate fertilizers also add to the high fluoride concentration in ground and surface water. Fluoride is unique because a dosage within 1.0 mg/L improves dental health while exposure to higher levels causes fluorosis that affects teeth and bones. Although fluoride is frequently added to municipal water supplies in some places, high fluoride content is a problem in many parts of the world with millions affected adversely [2,3]. Conventional approaches to defluoridation include ion exchange and reverse osmosis [4], use of manganese oxide and aluminium salts as precipitating agents [5], while alum, lime and activated alumina have been used as sorbents for fluoride [6]. As the http://dx.doi.org/10.1016/j.jcis.2015.03.017 0021-9797/Ó 2015 Elsevier Inc. All rights reserved. ⇑ Corresponding author. E-mail address: somenath.mitra@njit.edu (S. Mitra). Journal of Colloid and Interface Science 450 (2015) 239–245 Contents lists available at ScienceDirect Journal of Colloid and Interface Science www.elsevier.com/locate/jcis