Preparation of black sand-based magnetic photocatalysts for photocatalytic oxidation of aqueous phenol Mingliang Luo a,b, *, Derek Bowden b , Peter Brimblecombe b a School of Chemistry, Sichuan University, Chengdu, Sichuan, 610064, PR China b School of Environmental Sciences, University of East Anglia, Norwich, Norfolk, NR4 7TJ, United Kingdom 1. Introduction Titanium dioxide (TiO 2 ) has become the most successful photocatalyst and intensively investigated [1] since Fujishima and Honda’s discovery of the photolysis of water by titanium compounds in 1972 [2]. In the field of environmental remediation, the TiO 2 photocatalytic process is economically favorable since it is able to exploit sunlight and air to destroy pollutants. The TiO 2 photocatalyst is often used in slurry form, composed of ultra-fine particles, such as the commercial product Degussa P25. However ultra-fine particles often cause recycling problems, after use in water, because they do not easily sediment. Hence developing an appropriate form of TiO 2 that favours recovery has become an objective in this field. A popular method is to immobilize TiO 2 in film form on some inert substances [3–6]. However, this is suggested as less accessible to reactants in water and thus less efficient than a dispersed TiO 2 slurry [7]. Recently photocatalysts on a magnetic support have become prominent to address this issue [8–16]. They are a composite comprising a TiO 2 shell and a magnetic core that makes them recoverable using an external magnetic field. Additionally, their particle form circumvents the drawback of the lack of accessibility of TiO 2 films to the reactants. A simple method of preparing a magnetic TiO 2 photocatalyst involves depositing TiO 2 on magnetic iron oxide cores. However, such arrangement will bring about photo-dissolution of iron during photoreaction [13,14], as a result of the charge transfer between TiO 2 and iron oxide. Therefore it is necessary to have an insulating layer, typically a silica layer, between the magnetic core and the surface TiO 2 to prevent this charge transfer. The development of such titania– silica–magnetite composites begins with the preparation of the core materials, which are often nanosized iron oxide particles made in the laboratory through hydrolysis and precipitation of iron salts [8,10–14,17]. The core particles are then coated with a silica layer usually through a sol–gel scheme involving the Sto ¨ ber process. Afterwards TiO 2 is deposited on the silica–magnetite composite to obtain the magnetic photocatalyst. In terms of the magnetic recoverability, it is believed that the finer the magnetic particles, the weaker the interaction with the external magnetic field and the more difficult it becomes to recover the catalyst from water [18]. With few exceptions [9,16], most magnetic photocatalysts that comprise fine magnetic core parti- cles are recovered by centrifugation in the laboratory despite the assumption that they are magnetically recoverable [8,10–15]. Thus, it is of practical interest to investigate the use of coarse materials as magnetic cores. Here, black sand (BS), a natural magnetic material collected on New Zealand beach, was used as the magnetic core. The size of black sand ranges from 100 to 200 mm and can easily be tailored by grinding process to meet Applied Catalysis B: Environmental 87 (2009) 1–8 ARTICLE INFO Article history: Received 10 May 2008 Received in revised form 29 August 2008 Accepted 8 September 2008 Available online 16 September 2008 Keywords: Magnetic photocatalyst Black sand Titanium dioxide Phenol Silica coating ABSTRACT A natural magnetic material, black sand, was used as cores to prepare a magnetic photocatalyst, which can be recovered using an external magnetic field. A surfactant-involved scheme was proposed to deposit a rough silica layer on the surface of black sand, which otherwise could not be coated with silica through a conventional scheme involving Sto ¨ ber process. Titanium dioxide (TiO 2 ) was deposited on the surface of the silica–black sand (Si/BS) through an impregnation process and a direct deposition process. The catalytic property of the resultant photocatalyst (Ti/Si/BS) was evaluated using the oxidation of aqueous phenol and exhibited less reactivity than Degussa P25 TiO 2 . The phenol removal efficiency showed a pH dependence, which was ascribed to pH effect on (a) the formation of * OH and (b) the electrostatic interaction between the photocatalyst and the substrate. The prepared photocatalyst is reusable despite slight deactivation caused by the mechanical loss of TiO 2 . ß 2008 Elsevier B.V. All rights reserved. * Corresponding author. E-mail address: luoml@163.com (M. Luo). Contents lists available at ScienceDirect Applied Catalysis B: Environmental journal homepage: www.elsevier.com/locate/apcatb 0926-3373/$ – see front matter ß 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.apcatb.2008.09.002