RESEARCH ARTICLE Synthesis of mesoporous Mn/TiO 2 nanocomposites and investigating the photocatalytic properties in aqueous systems Ekemena Oghenovoh Oseghe & Patrick Gathura Ndungu & Sreekanth Babu Jonnalagadda Received: 16 May 2014 /Accepted: 17 July 2014 # Springer-Verlag Berlin Heidelberg 2014 Abstract Mesoporous 20 wt% Mn/TiO 2 nanocomposites were synthesized adopting modified sol–gel method at differ- ent pH (pH=2, 7 and 11) conditions and calcined at 400 °C. Based on the characteristics of the 20 wt% Mn/TiO 2 nano- composites synthesized at pH 11, same procedure was adopted for the synthesis of different wt% Mn/TiO 2 . The nanocomposite samples and their surface properties were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microsco- py (TEM), high resolution transmission electron microscopy (HRTEM), mapping, inductively coupled plasma optical emission spectrometry (ICP-OES), Fourier transform infrared (FTIR), and fluorescence spectrometry. The nanocomposites existed in the anatase phase of TiO 2 with no peak assigned to Mn on the diffractogram. The photocatalytic activities of the materials were evaluated by monitoring degradation of a model dye (methylene blue (MB)) in presence of visible light and ozone. The nanocomposite synthesized under neutral condition (pH=7) exhibited the best photocatalytic activity resulting from its relatively smaller crystal size (5.98 nm) and larger pore volume (0.30 cm 3 /g). One percentage of weight Mn/TiO 2 showed 100 % decolouration of MB in the presence of O 3 after 100 min. Keywords Mn/TiO 2 nanocomposite . pH water . Mesoporous . Photocatalytic ozonation . Visible light Introduction In recent times, water as a subset of the environment has been of serious concern. It stems from the fact that industries such as textile, plastics, and paper, and pulp, to name a few, gener- ate streams of waste effluents containing significant amounts of organic pollutants such as organic dyes (Jiang et al.2012; Rauf et al. 2010; Wu et al. 2013). When these compounds are discharged to the larger aquatic system without prior treat- ment, they can alter the ecological balance in the environment as these molecules have carcinogenic and mutagenic proper- ties towards aquatic organisms and humans as they bioaccumulate and biomagnifies up the food chain (Xu et al.2011). Currently, conventional methods such as adsorp- tion and coagulation are being supplemented by advanced oxidation processes (AOPs) (photocatalysis, Fenton method, ozonalysis, sonolysis, photolysis) (Rivas et al. 2011). Of all these processes, photocatalysis seems to be most versatile and promising since UV or visible light source in the presence of the catalyst, would favour the oxidation of organic pollutants present in waste effluents (Rauf et al. 2011). Mesoporous TiO 2 as a semiconductor, is known to have high surface area, excellent stability, can be regarded as non- toxic, and has a highly porous (2–50 nm in diameter) frame- work characteristics, and as such it is ideally suited as a photocatalytic material. This continuity in structure has some interesting physical–chemical implications, such as ease in the transfer of electrons within the material and from a practical viewpoint, it can aide in the recovery of catalyst material when compared to separate individual nanoparticles (Ismail and Bahnemann 2011). The photocatalytic activity of TiO 2 is mainly dependent on the incident electromagnetic radiation having equal or higher photon energy than its band gap energy (3.2 eV). In general, the photocatalytic mechanism is built around the excitation of electrons from the valence band (VB) to the conduction band (CB) of the TiO 2 , leaving holes in the Responsible editor: Philippe Garrigues E. O. Oseghe : P. G. Ndungu : S. B. Jonnalagadda (*) School of Chemistry and Physics, University of Kwa-Zulu Natal, Westville Campus, Private Bag X 54001, Durban 4000, South Africa e-mail: jonnalagaddas@ukzn.ac.za Environ Sci Pollut Res DOI 10.1007/s11356-014-3356-z