Applied Catalysis B: Environmental 188 (2016) 65–76 Contents lists available at ScienceDirect Applied Catalysis B: Environmental j ourna l h om epage: www.elsevier.com/locate/apcatb Correlating the properties of hydrogenated titania to reaction kinetics and mechanism for the photocatalytic degradation of bisphenol A under solar irradiation Evangelia Ioannidou a , Alexandra Ioannidi a , Zacharias Frontistis a , Maria Antonopoulou b , Charalampos Tselios a , Dimitris Tsikritzis a , Ioannis Konstantinou b , Stella Kennou a , Dimitris I. Kondarides a , Dionissios Mantzavinos a,∗ a Department of Chemical Engineering, University of Patras, Caratheodory 1, University Campus, GR-26504 Patras, Greece b Department of Environmental & Natural Resources Management, University of Patras, 2 Seferi St., GR-30100 Agrinio, Greece a r t i c l e i n f o Article history: Received 18 November 2015 Received in revised form 19 January 2016 Accepted 25 January 2016 Available online 28 January 2016 Keywords: Activity Annealing temperature Catalyst characterization Pathways Sodium a b s t r a c t Hydrogenation of a commercially available TiO 2 anatase catalyst was carried out at several annealing tem- peratures in the range 400–800 ◦ C to improve its photocatalytic activity for the degradation of endocrine disruptor bisphenol A (BPA) under simulated solar irradiation. The prepared hydrogenated catalysts, as well as their counterparts calcined in air were characterized with respect to their morphological, opti- cal and electronic properties by means of BET, XRD, XPS, DRS and UPS analyses. Thermal treatment under flowing hydrogen resulted in increased absorption at wavelengths below 400 nm, as well as in the appearance of a broad and almost uniform absorption band in the visible region, the intensity of which increased with increase of annealing temperature. The latter was attributed to the creation of gap states in the hydrogenated samples, which was not observed for the samples calcined in air. Interestingly, sodium inherently present in the bulk of the pristine catalyst was found to diffuse at the surface and this was more pronounced for the hydrogenated samples prepared at temperatures above 700 ◦ C. The relative catalytic activity was tested to degrade 240 g/L BPA in pure water and it was found that the hydrogenated catalysts were more active than those calcined in air at the same temperatures. The maximum rate (0.0647 min -1 ) was observed for the catalyst hydrogenated at 600 ◦ C, i.e. three times greater than the respective calcined catalyst. Higher annealing temperatures had a detrimental effect on photocatalytic activity and this may be associated with a collapse of the specific surface area. Other than the annealing temperature, the rate was also strongly dependent on the water matrix (slower for more complex matrices), BPA and catalyst concentration and the presence of electron acceptors. LC–MS/TOF analysis was employed to identify transformation by-products (TBPs) and elucidate reac- tion pathways. BPA degradation by hydrogenated catalysts seems to occur mainly through consecutive hydroxylation/oxidation reactions, as evidenced by the various oxygenated TBPs formed; conversely, scis- sion of BPA through the isopropylidene group and further oxidation, yielding different para-substituted phenolic intermediates seems to be the main degradation route in the presence of calcined catalysts. © 2016 Elsevier B.V. All rights reserved. 1. Introduction Titanium dioxide has attracted significant interest in recent years due to its potential use in a variety of photo-induced processes, including photocatalytic production of hydrogen, decomposition of pollutants in air and water, and production of electricity with solar cells [1–3]. However, the efficiency of TiO 2 for solar-driven applications is limited, because, owing to its relatively ∗ Corresponding author. E-mail address: mantzavinos@chemeng.upatras.gr (D. Mantzavinos). large band gap energy (3.0–3.3 eV) [1], it can only absorb UV pho- tons, which account for less than 5% of the total solar radiation that reaches the earth’s surface. Therefore, much effort has been made to extend the working spectrum of TiO 2 toward the visible spec- tral region. This can be achieved by modifying the valence band of the semiconductor via non-metal ion doping [4] or by forming new donor states below the conduction band of TiO 2 with incor- poration of metal ions into its crystal matrix [5]. An alternative method for improving the optical and photocatalytic properties of TiO 2 has been demonstrated recently by Chen et al. [6], who pre- pared disordered nanophase TiO 2 through hydrogenation of TiO 2 nanocrystals at 20 bar H 2 for 5 days. The so formed hydrogenated http://dx.doi.org/10.1016/j.apcatb.2016.01.060 0926-3373/© 2016 Elsevier B.V. All rights reserved.