Mechanistic study of simultaneous arsenic and fluoride removal using granular TiO 2 -La adsorbent Li Yan a,b , Haowei Tu c , Tingshan Chan c , Chuanyong Jing a,b,⇑ a State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China b University of Chinese Academy of Sciences, Beijing 100049, China c National Synchrotron Radiation Research Center, 101 Hsin-Ann Road, Hsinchu Science Park, Hsinchu 30076, Taiwan highlights  Simultaneous As(III) and F removal is achieved by using granular TiO 2 -La composite.  LaCO 3 OH showing orientated growth on TiO 2 {1 0 0} facet with matched lattice fringes.  Molecular-level coadsorption mechanism is investigated by EXAFS and DFT calculation.  The importance of crystal facet in material synthesis and adsorption is highlighted. graphical abstract article info Article history: Received 16 September 2016 Received in revised form 28 October 2016 Accepted 31 October 2016 Available online 1 November 2016 Keywords: Coexisting As and F Hybrid TiO 2 -La adsorbent Crystal facets Orientated growth Molecular-level mechanisms abstract Naturally co-occurring arsenic (As) and fluoride (F) in groundwater have caused increasing public con- cerns, and their simultaneous removal is still a challenge due to the lack of efficient adsorptive materials and their competition for adsorption sites. This study fabricated a novel TiO 2 -La granular composite adsorbent with LaCO 3 OH showing orientated growth on TiO 2 {1 0 0} facet. The material exhibited high As(III) (114 mg/g) and F (78.4 mg/g) adsorption capacities and a wide application pH, ranging 3–9, achieving a high percentage (>90%) of As(III) and F adsorption. Coadsorption experiment results demon- strated that high F concentrations inhibit As(III) adsorption, whereas the coexisting As(III) has no signif- icant effect on F removal. The molecular-level mechanisms with EXAFS and DFT studies demonstrated that As(III) adsorption is favorable only on Ti sites as evidenced by an As-Ti distance of 3.36 Å when pH < 7, while La adsorption sites can also be occupied with an As-La distance at 3.42 Å when pH > 10. The F adsorption is pH-dependent and mainly occurred on La sites. The granular TiO 2 -La with high As (III) and F adsorption capacities can be used to simultaneously remove As(III) and F. The insights gained from this study shed a new light on the interaction mechanism of As(III) and F with the TiO 2 -La composite. Ó 2016 Elsevier B.V. All rights reserved. 1. Introduction Elevated concentrations of co-existing arsenic (As) and fluoride (F) in groundwater have become a worldwide problem due to their synergistic adverse health effects [1–3]. As the World Health Orga- nization (WHO) suggests, the drinking water standards for As and F are 10 lg/L and 1.5 mg/L, respectively. However, reaching this WHO standard is still a great challenge, especially in low income and heavily contaminated areas, due to the lack of proper treat- ment [4,5]. Therefore, highly efficient simultaneous removal of As and F is of great urgency and high priority. http://dx.doi.org/10.1016/j.cej.2016.10.142 1385-8947/Ó 2016 Elsevier B.V. All rights reserved. ⇑ Corresponding author at: State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China. E-mail address: cyjing@rcees.ac.cn (C. Jing). Chemical Engineering Journal 313 (2017) 983–992 Contents lists available at ScienceDirect Chemical Engineering Journal journal homepage: www.elsevier.com/locate/cej