Visible-light-driven photocatalytic S- and C- codoped meso/nanoporous TiO 2 Pu Xu, a Tao Xu, * b Jun Lu, c Shanmin Gao, * ad Narayan S. Hosmane, b Baibiao Huang, d Ying Dai d and Yubao Wang a Received 28th January 2010, Accepted 30th April 2010 DOI: 10.1039/c001940m The first facile and efficient soft synthesis for fabricating S- and C- co-doped hierarchically meso/nanoporous TiO 2 is hereby presented. The doping of sulfur is achieved through a counter strategy, in which the precursor of TiO 2 is added to the sulfur hydrosol. The sulfur nanoparticles in the sulfur hydrosol serve as the seeds for the formation of bimodal meso/nanopores TiO 2 upon calcination treatment. The prepared anatase TiO 2 exhibited excellent thermal stability and photocatalytic activity. In comparison to commercial P25 TiO 2 , our S- and C- codoped meso/ nanoporous anatase TiO 2 exhibits remarkably enhanced visible light-driven photocatalytic activity on the decomposition of methylene blue (MB). The samples also showed excellent cyclic stability in the photocatalytic activity of degrading MB. The formation mechanism of these S-, C- codoped hierarchically meso/nanoporous TiO 2 spheres is also discussed. The high photocatalytic activity in the visible light region is attributed to numerous oxygen vacancies, acidic sites on the surface of TiO 2 , and large specific surface area. 1. Introduction With the discovery of the photocatalytic splitting of water on titania electrodes in 1972 by Fujishima and Honda, 1 a significant amount of effort has been made to understand the fundamental processes of the photocatalytic efficiency of titania. 2 Because the photogenerated holes in TiO 2 is approximately 7.4 eV vs. vacuum, below the highest occupied molecular orbitals (HOMO) of most organic molecules, it can thus aggressively oxidize (rip off electrons from) organic pollutants. Along with its biological and photochemical stability, TiO 2 has essentially proved to be one of the most efficient photocatalytic materials for environ- mental purification. However, because of its large band gap of 3.20 eV, only the UV fraction of solar light (about 2–3% of the total solar energy) can be utilized to generate electron-hole pairs. To enhance the energy efficiency, therefore, photosensitization of TiO 2 that can lead to high photocatalytic activity in visible light region has become the current topic of interest. 3 An effective approach to tackle this challenge is to dope TiO 2 with hetero elements such as carbon, 4 sulfur, 5–7 iodine 8–10 and nitrogen, 11,12 which act as electron donor or acceptor in the forbidden band of TiO 2 , thus to induce absorption in the visible region. Carbon doping, on the other hand, can significantly stabilize the photoactive anatase TiO 2 under high temperature, and inhibit the sintering of nanocrystals and improve the adsorption of organic pollutant molecules on the surface of the catalysts. 13–15 Furthermore, it was also reported that carbon doping can enhance the conductivity of TiO 2 nanostructures. 13–16 This can be an added advantage of carbon- doped TiO 2 , as it will facilitate the charge transfer from bulk of the TiO 2 structure to the surface region where the desired a School of Chemistry and Materials Science, Ludong University, Yantai, 264025, Shandong, PR China. E-mail: gaosm@ustc.edu b Department of Chemistry and Biochemistry, Northern Illinois University, DeKalb, IL, 60115, USA. E-mail: txu@niu.edu c Department of Physics, Northern Illinois University, DeKalb, IL, 60115, USA d State key labs of Crystal Materials, Shandong University, Jinan, 250100, PR China Broader context Anatase TiO 2 is envisioned as the most promising photocatalyst for environmental purification due to its excellent photochemical stability and intense photo-oxidative properties. The photogenerated holes in TiO 2 is approximately 7.4 eV vs. vacuum, below the highest occupied molecular orbitals (HOMO) of most organic molecules. Thus, it can aggressively oxidize (rip off electrons from) organic pollutants. However, because of its large band gap of 3.20 eV, only the UV fraction of solar light (about 2–3% energy of the total solar spectrum) can be utilized to generate electron-hole pairs. To enhance the energy efficiency, therefore, photosensitization of TiO 2 by doping of hetero elements that can lead to high photocatalytic activity in visible light region becomes the current topic of interest. We present here an efficient soft synthesis for fabricating S- and C- codoped hierarchically meso/nanoporous TiO 2 . The doping of sulfur is achieved through a counter strategy, in which the precursor of TiO 2 is added to the sulfur hydrosol. The sulfur nanoparticles in the sulfur hydrosol serve as the seeds for the formation of bimodal meso/nanopores TiO 2 upon calcination treatment. The prepared anatase TiO 2 exhibits excellent thermal stability and photocatalytic activity in comparison to commercial P25 TiO 2 . 1128 | Energy Environ. Sci., 2010, 3, 1128–1134 This journal is ª The Royal Society of Chemistry 2010 PAPER www.rsc.org/ees | Energy & Environmental Science