RESEARCH Synergistic effects of zirconium and silver co-dopants in TiO 2 nanoparticles for photocatalytic degradation of an organic dye and antibacterial activity Pornrat Sanitnon 1,2 & Siriluk Chiarakorn 3,4 & Chamorn Chawengkijwanich 5 & Surawut Chuangchote 6 & Thirawudh Pongprayoon 7 Received: 19 June 2018 /Revised: 21 April 2019 /Accepted: 7 May 2019 # Australian Ceramic Society 2019 Abstract The objective of this research is to study the effects of zirconium and silver co-dopants on the photocatalytic reactivity of TiO 2 . Zirconium and silver co-doped titanium dioxide (Zr-Ag co-doped TiO 2 ) was synthesized by sol-gel method. The molar ratio of silver was fixed at 5% mol, while the molar ratio of zirconium was varied at 5, 10, and 15% mol. The synthesized photocatalysts were calcined at 500 °C for 5 h. The characteristics of the photocatalysts were examined by X-ray diffraction spectroscopy (XRD), ultraviolet-visible spectroscopy (UV-Vis), and field emission scanning electron microscope (FESEM). The XRD results indicated that the anatase phase of TiO 2 and metal doping did not affect the crystal phase of TiO 2 , and the FESEM confirmed the presence of silver and zirconium in co-doped TiO 2 . After doping, the band gap energy of the doped TiO 2 was significantly reduced due to the red shift effect. The photocatalytic reactivity and kinetics of the photocatalysts were investigated by photo- catalytic decolorization of methylene blue (MB) under UV and fluorescent light. Photocatalytic decolorization of MB dramat- ically improved when TiO 2 was co-doped with silver and zirconium. The antibacterial efficiency of Zr-Ag co-doped TiO 2 against Escherichia coli (E. coli) was also investigated under fluorescent light and in the dark. The synergistic effects of zirconium and silver dopants on the photocatalytic and antibacterial activity of TiO 2 were observed. The 5% mol of silver and 10% mol of zirconium co-doped TiO 2 exhibited the highest decolorization efficiency at 98.07% under fluorescent light and could completely inhibit E. coli under fluorescent light within 20 min. Keywords Titanium dioxide . Silver . Zirconium . Photocatalysis . Co-doping . Decolorization . Antibacterial Introduction In recent years, indoor air pollution has become an increas- ingly serious environmental problem, especially for people who live in urban areas. The accumulated pollutants in the indoor air cause an illness known as Sick Building Syndrome (SBS). The symptoms for SBS are headaches; nose, eye, or throat irritation; dizziness; dry cough; itching; and increased incidence of asthma [1]. Common indoor air pollutants are CO, CO 2 , NO, NO 2 , VOCs and particles, and * Siriluk Chiarakorn siriluk.chi@kmutt.ac.th 1 The Joint Graduate School of Energy and Environment, King Mongkut’ s University of Technology Thonburi, Bangkok 10140, Thailand 2 Center of Excellence on Energy Technology and Environment, PERDO, Bangkok, Thailand 3 Division of Environmental Technology, School of Energy, Environment and Materials, King Mongkut’ s University of Technology Thonburi, Bangkok 10140, Thailand 4 Nanotec-KMUTT Center of Excellence on Hybrid Nanomaterials for Alternative Energy, King Mongkut’ s University of Technology Thonburi, Bangkok 10140, Thailand 5 National Nanotechnology Center (NANOTEC), National Science and Technology Development Agency (NSTDA), Klong Luang, Pathumthani 12120, Thailand 6 Department of Tool and Materials Engineering, Faculty of Engineering, King Mongkut’ s University of Technology Thonburi, Bangkok 10140, Thailand 7 Department of Chemical Engineering, Faculty of Engineering Center of Eco-Materials and Cleaner Technology, King Mongkut’ s University of Technology North Bangkok, Bangkok 10800, Thailand Journal of the Australian Ceramic Society https://doi.org/10.1007/s41779-019-00368-w