applied sciences  
Article  
TiO\({}_{2}\)-Fe\({}_{3}\)O\({}_{4}\) Composite Systems--Preparation, Physicochemical Characterization, and an Attempt to Explain the Limitations That Arise in Catalytic Applications  
[PERSON] \({}^{1,\bullet}\), [PERSON] \({}^{2}\), [PERSON] \({}^{3}\), [PERSON] \({}^{1}\), [PERSON] \({}^{3}\), [PERSON] \({}^{2}\) and [PERSON] \({}^{1,\bullet}\)  
Chair and Department of Chemical Technology of Drugs, Poznan University of Medical Sciences, Grunwaldzka 6, 60-780 Poznan, Poland Institute of Chemistry and Technical Electrochemistry, Poznan University of Technology, Berdychowo 4, 60-965 Poznan, Poland Medical Chemistry Research Group, Department of Biomedical & Polymer Chemistry, Faculty of Chemistry, Nicolaus Copernicus University in Torun, Gagarina 7, 87-100 Torun, Poland Correspondence: [EMAIL_ADDRESS] (f.  
water [3]. Although many of them are daily-use products and are safe for humans, such as pharmaceutical and personal care products, the effects of prolonged exposure to low concentrations of PPCPs are, for the most part, poorly documented and/or understood. Important to note that while PPCPs are safe for humans, exposure to low doses of these substances can be lethal for animals and lead to bio-accumulation in plants [4]. These substances, which are potential threats to the environment, were dubbed emerging contaminants and are now one of the most important topics in environmental chemistry [5]. In order to reduce the environmental threat, ways of remediating emerging contaminants are being sought. Photocatalysis is being investigated as one of such potential methods. Bare TiO\({}_{2}\) can be used as an efficient UV-light photocatalyst, and its efficiency has been proven in a number of studies, even in the photodegradation of chemically stable emerging contaminants [3; 6; 7; 8]. However, its broader uses in photocatalysis are limited by TiO\({}_{2}\)'s physicochemical properties, mainly its relatively high band gap of anatase at 3.2 eV. A number of approaches can be chosen to modify the behavior of the material, such as surface modification, doping, and preparation of composite systems. The modifications allow for achieving new properties such as visible light activity or enhanced filtration potential through compositing with magnetic materials or by coating solid surfaces with functionalized TiO\({}_{2}\) composites. One such modification is the preparation of TiO\({}_{2}\)-Fe\({}_{3}\)O\({}_{4}\) composite systems. Iron(II,III) oxide is a ferrimagnetic metal oxide that naturally occurs in minerals such as magnetite. Similar to TiO\({}_{2}\), Fe\({}_{3}\)O\({}_{4}\) is commonly used as a pigment and also finds applications in medicine as part of contrast agents in magnetic resonance imaging [9]. Its magnetic nature is often the reason it is used for the functionalization of other materials. Therefore, TiO\({}_{2}\)-Fe\({}_{3}\)O\({}_{4}\) composite systems have been researched in several studies in terms of photocatalytic efficiency, often revealing promising properties in the photodegradation reactions of organic dyes [10; 11]. Not only that, one of the problems hindering TiO\({}_{2}\) research is the treatment of post-degradation slurry. In water solutions, TiO\({}_{2}\) forms milky suspensions, which are problematic to separate and, if not properly treated, pose a risk of environmental exposure. While generally safe for humans, it has been proven that exposure to TiO\({}_{2}\) might have adverse effects on aquatic life [12]. The magnetic properties of Fe\({}_{3}\)O\({}_{4}\) allow for magnetic filtration of the photocatalyst after the photocatalytic process, thus reducing the above-mentioned threat. Such composite materials can be prepared through a mechanothermal method--this method is particularly popular in the production of carbon nanotubes and nanofibers [13]. The method has been implemented in industrial processes due to its simplicity. Basic mechanothermal methods are two-step processes.