Contents lists available at ScienceDirect Corrosion Science journal homepage: www.elsevier.com/locate/corsci Anomalous enhancement of corrosion resistance and antibacterial property of commercially pure Titanium (CP-Ti) with nanoscale rutile titania film Nanda Gopala Krishna, R.P. George, John Philip* Corrosion Science and Technology Division, Metallurgy and Materials Group, Indira Gandhi Centre for Atomic Research, Kalpakkam & Homi Bhabha National Institute, Tamil Nadu, 603102, India ARTICLE INFO Keywords: Titanium Oxidation Passive film Polarization XPS ABSTRACT We report an anomalous enhancement of corrosion resistance and antibacterial property of CP-Ti surface in the presence of a uniform defect-free nanoscale (∼15 nm) rutile titania film. Selective absorption of blue light (∼410 nm) due to matching photon energy with the film band gap, drastically enhanced the electron-hole pair generation, recombination time and the photocatalytic activity. The corrosion resistance of the rutile phase titania films is found to be better than the amorphous films and strongly dependent on the film thickness and surface morphology. The impedance data accounts well for the dual layer structure with an outer barrier titania and inner substochiometric oxide layer. 1. Introduction Titanium (Ti) and its alloys exhibit exceptional corrosion resistance in a wide range of environments and are known for their high specific strength, biocompatibility and non toxicity [1]. The chemical inertness of these materials is attributed to the continuous titania (TiO 2 ) film formed on the surface that acts as a barrier between the metal and the electrolyte medium thus preventing corrosion. TiO 2 films formed by thermal oxidation have a higher corrosion resistance and hardness (thus better wear resistance) because of dense, uniform, compact and crys- talline nature than the films formed by anodization, which are porous, rough and amorphous [2,3]. Yet, anodization is a preferred choice due to its simplicity and ability to fine-tune the surface morphology and phase composition of oxide layers by process parameters. Even though higher roughness and porosity of TiO 2 films are beneficial for os- seointegration in bone implant applications, it suffers from lower wear resistance against bone tissue, which limits their use in implant appli- cations [4]. More often, thermal annealing treatment at tempera- tures > 400 °C, is followed by anodization to improve the film prop- erties to overcome some of the inherent limitations of the anodized films [5]. Also, safer alloying elements have been attempted for over- coming some of the drawbacks of CP-Ti [6,7]. For biomedical implants, especially for dental and orthopaedic, CP- Ti and its alloys are preferred over stainless steel due to their superior material properties. The corrosion resistance of an implanting material is the prime factor that determines its service life in the host body. The corrosion resistance of CP-Ti and its alloys is an order of magnitude greater than that of stainless steel [8]. However, CP-Ti is not inherently antibacterial and hence the risk of infection leading to the implant failure gives rise to health complications. To improve the antibacterial property of Ti based implants, other alternatives are being actively considered, which include coating of the implant surfaces with anti- microbial agents such as Ag, antibiotics and disinfectants [9,10]. Although there are studies on corrosion and antimicrobial proper- ties of CP-Ti with titania film grown on their surface by anodization, there are no systematic studies to understand the role of surface mor- phology, crystallinity and thickness of the film, especially when the film thickness is in nanoscale and grown by thermal oxidation. This study was aimed at bridging the gap in the above aspects and at developing CP-Ti metal with better antibacterial properties for biomedical implant applications. We show here a facile and novel approach for enhancing the antibacterial property of CP-Ti by using thermal air oxidation. We exploit the thickness dependent selective absorption of TiO 2 film and the resultant enhanced photocatalytic action. The corrosion perfor- mance of the different oxidized CP-Ti is studied in simulated body fluid and the underlying mechanism of improved corrosion and antibacterial property are obtained. https://doi.org/10.1016/j.corsci.2020.108678 Received 13 January 2020; Received in revised form 18 March 2020; Accepted 13 April 2020 ⁎ Corresponding author. E-mail address: philip@igcar.gov.in (J. Philip). Corrosion Science 172 (2020) 108678 Available online 26 April 2020 0010-938X/ © 2020 Elsevier Ltd. All rights reserved. T