catalysts Article Synthesis of Oxygen Deficient TiO 2 for Improved Photocatalytic Efficiency in Solar Radiation Kassim Olasunkanmi Badmus 1, *, Francois Wewers 1 , Mohammed Al-Abri 2,3 , Mohd Shahbaaz 4,5 and Leslie F. Petrik 6   Citation: Badmus, K.O.; Wewers, F.; Al-Abri, M.; Shahbaaz, M.; Petrik, L.F. Synthesis of Oxygen Deficient TiO 2 for Improved Photocatalytic Efficiency in Solar Radiation. Catalysts 2021, 11, 904. https:// doi.org/10.3390/catal11080904 Academic Editors: Paula Oulego and Ewa Kowalska Received: 23 May 2021 Accepted: 23 June 2021 Published: 26 July 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 Chemistry Department, Cape Peninsula University of Technology, Bellville, Cape Town 7535, South Africa; WewersF@cput.ac.za 2 Nanotechnology Research Center, Sultan Qaboos University, Al-Khoud 123, Oman; alabri@squ.edu.om 3 Department of Petroleum and Chemical Engineering, College of Engineering, Sultan Qaboos University, Al-Khould 123, Oman 4 South African Medical Research Council, Bioinformatics Unit, South African National Bioinformatics Institute, University of the Western Cape, Private Bag X17, Bellville, Cape Town 7535, South Africa; mohammed.shahbaaz@gmail.com 5 Laboratory of Computational Modeling of Drugs, South Ural State University, 76 Lenin Prospekt, 454080 Chelyabinsk, Russia 6 Environmental and Nano Science, Chemistry Department, University of The Western Cape, Bellville, Cape Town 7535, South Africa; lpetrik@uwc.ac.za * Correspondence: badmusk@cput.ac.za Abstract: The photocatalytic activities of TiO 2 have been limited mainly to absorbing in the ultraviolet spectrum which accounts for only 5% of solar radiation. High energy band gap and electron recombination in TiO 2 nanoparticles are responsible for its limitations as a photocatalyst. An oxygen deficient surface can be artificially created on the titanium oxide by zero valent nano iron through the donation of its excess electrons. A visible light active TiO 2 nanoparticle was synthesized in the current investigation through simple chemical reduction using sodium boro-hydride. The physical and textural properties of the synthesized oxygen deficient TiO 2 photocatalyst was measured using scanning/ transmission electron microscopy while FTIR, XRD and nitrogen sorption methods (BET) were employed for its further characterizations. Photochemical decoloration of orange II sodium dye solution in the presence of the synthesized TiO 2 was measured using an UV spectrophotometer. The resulting oxygen deficient TiO 2 has a lower energy band-gap, smaller pore sizes, and enhanced photo-catalytic properties. The decoloration (88%) of orange (II) sodium salt solution (pH 2) under simulated solar light was possible at 20 min. This study highlights the effect of surface oxygen defects, crystal size and energy band-gap on the photo-catalytical property of TiO 2 nanoparticles as impacted by nano zero valent iron. It opens a new window in the exploitation of instability in the dopant ions for creation of a visible light active TiO 2 photocatalyst. Keywords: nanoparticles; photo-catalyst; titanium (IV) oxide; energy band-gap; solar light 1. Introduction The oxides of semiconductors are capable of absorbing a substantial quantity of (UV) radiation from a sunlight source and thus generate electron/hole pairs. This forms the basis of their utilization in photocatalysis and several other applications [1]. The generated electrons are capable of using the available excess energy to gain promotion (excitation) from the valence band (VB) to the conduction band (CB) and therefore leave behind positive holes. These holes are capable of breaking down water molecules into hydrogen and hydroxyl radicals as the electrons react with oxygen to produce the superoxide anion (O -2 )[2,3]. Thereafter, both radicals and super-oxides react with persistent chemical or biological contaminants to generate more biodegradable end products [4]. Under solar radiation, the degradation of water contaminants is possible at room temperature and Catalysts 2021, 11, 904. https://doi.org/10.3390/catal11080904 https://www.mdpi.com/journal/catalysts