IP: 185.251.70.37 On: Tue, 07 Aug 2018 03:25:41 Copyright: American Scientific Publishers Delivered by Ingenta Copyright © 2018 American Scientific Publishers All rights reserved Printed in the United States of America Article Journal of Nanoscience and Nanotechnology Vol. 18, 7302–7309, 2018 www.aspbs.com/jnn Effect of Metal (Mn, Co, Zn, Ni) Doping on Structural, Optical and Photocatalytic Properties of TiO 2 Nanoparticles Prepared by Sonochemical Method Prasopporn Junlabhut 1 ∗ , Chakkaphan Wattanawikkam 2 , Wanichaya Mekprasart 2 , and Wisanu Pecharapa 2 1 Department of Applied Physics, Faculty of Science and Technology, Rajabhat Rajanagarindra University, Chachoengsao 24000, Thailand 2 College of Nanotechnology, King Mongkut’s Institute of Technology Ladkrabang, Bangkok 10520, Thailand Metal-doped TiO 2 nanoparticles (Metal = Mn, Co, Zn, Ni) were synthesized by sonochemical method accompanying post calcination process using metallic nitrates of manganese, cobalt, zinc, nickel with various metal contents from 0–5 mol% and titanium isopropoxide as a starting precursors. Sodium hydroxide (NaOH) base was used as a precipitating agent. The influence of ultrasound operated at 750 W 20 kHz on the crystalline structure of metal-doped TiO 2 nanoparticles has been characterized by X-ray diffraction (XRD) while morphologies and grain size of the nanoparticles were monitored by field emission scanning electron microscope (FE-SEM). The optical absorp- tivities and corresponding band gaps were evaluated by diffuse reflectance spectroscopy (DRS). The performance of photocatalytic activities of metal-doped TiO 2 nanoparticles against aqueous organic dye Rhodamine B (RhB) under visible light was investigated. The results reveal that their crystallinity of synthesized metal doped TiO 2 nanoparticles is in mixed phase between anatase, rutile and brookite with calcination temperature at 500  C for 3 h and their crystalline of all samples are shown. The incorporation of metal dopant on the photocatalytic performance of TiO 2 exhibits a significant enhancement in its photocatalytic activities under visible light due to the decrease in band gap energy of metal doped TiO 2 nanoparticles. Keywords: Metal Doped TiO 2 , Sonochemical, Photocatalytic Activities. 1. INTRODUCTION Over decades, titanium dioxide (TiO 2  has been utilized for various applications such as pigment, 1 photocatalyst, 2 3 dye-synthesized solar cell 4 and sensor devices. 5 TiO 2 is one of the most studied photocatalysts because of its high photocatalytic efficiency, chemical stability, cheap- ness, and non-toxicity. 6–8 Typically, TiO 2 exists in three crystalline polymorphic phases including anatase, rutile, and brookite. Anatase and rutile have tetragonal struc- ture whereas brookite has an orthorhombic structure. It is recognized that anatase and brookite phase is rather metastable and easy to transform to rutile after calcination at a certain temperature. 9 In typical photocatalysis process, electron–hole pairs can be generated under illumination with light whose energy is greater than the band gap of the ∗ Author to whom correspondence should be addressed. catalyst. The photo-excited electrons and holes could fur- ther proceed oxidation and de-oxidation processes. 10 How- ever, the main drawback of TiO 2 catalyst is related to its wide band gap (∼3.2 eV) resulting in small absorption por- tion of UV spectra that is only 3–5% of solar irradiation. To overcome this limitation of TiO 2 catalyst, doping with proper metal ions such as Fe, V, Cr, Co, Mn, Ni and Zn was found to be one of effective approaches for narrow- ing its band gap leading to the enhancement in solar light harvesting of TiO 2 . 11–15 Metal-dopant incorporated into TiO 2 lattice introduce addition energy levels into the band structure. It can be used to trap electron hole to separate carriers from the band. This reasons could induce signifi- cant optical absorption in the visible range by increasing the doping ions or increasing the oxygen defect in TiO 2 . The metal doped TiO 2 is modifying its large bandgap and electronic structure to optimize optical properties. The recombination rate was reduced to improve the activity 7302 J. Nanosci. Nanotechnol. 2018, Vol. 18, No. 10 1533-4880/2018/18/7302/008 doi:10.1166/jnn.2018.15717