###### Abstract  
Titanium oxide semiconductors are considered effective photocatalysts for the degradation of organic pollutants. The photocatalytic activity of titanium dioxide is influenced by several factors, one of which is its phase composition, with anatase being considered the phase with the highest photocatalytic activity. In this work, a simple acid-assisted sol-gel process was used to synthesize a pure anatase phase by varying the synthesis and calcination temperature. The synthesized materials were characterized using various techniques and tested under simulated sunlight irradiation for the photocatalytic degradation of the drug diclofenac sodium (DCF), for which the pseudo-first-order apparent degradation rate constant and mineralization efficiency were determined. A pure anatase phase with high photocatalytic activity (up to 97% TOC removal) was obtained when TiO\({}_{2}\) was synthesized at between 70 \({}^{\circ}\)C and 100 \({}^{\circ}\)C and calcined at between 400 \({}^{\circ}\)C and 500 \({}^{\circ}\)C. Furthermore, the obtained data were used to predict the optimal anatase synthesis and calcination temperatures for DCF removal using a response surface methodology (RSM) method. The model predicted a synthesis temperature of 71 \({}^{\circ}\)C and a calcination temperature of 440 \({}^{\circ}\)C, which should result in a pseudo-first-order DCF decay rate constant of 0.055 min\({}^{-1}\) and a TOC removal rate of 100%. The experimentally determined values for the degradation rate (0.063 min\({}^{-1}\)) and TOC removal (97%) were in good agreement with the model's predicted values. titania; anatase; photocatalysis; diclofenac; degradation; response surface methodology +
Footnote †: journal: Applied sciences  
0000-0001-5002-4882][PERSON]  
1 Leibniz Institute for Catalysis (LIKAT), Albert-Einstein-Str. There are several methods for the removal of pharmaceutical residuals from fresh- and wastewater. Some of these include coagulation, flocculation, adsorption, precipitation, membrane separation, and aerobic and anaerobic processes [5]. The disadvantages of the currently used removal methods include the formation of hazardous byproducts (chemicals), the use of expensive chemicals, high operation and raw material costs, long process times, complex sludge production, and separation problems [6]. In general, these treatment methods are still unsatisfactory in terms of their sustainability and environmental impact. Advanced oxidation processes (AOPs) are currently considered as an alternative method for the removal of pharmaceutical compounds from fresh- and wastewater [7]. These methods rely on the formation of highly active species through, e.g., the photolysis of H\({}_{2}\)O\({}_{2}\) and O\({}_{3}\) under UV irradiation, which can degrade even relatively inert molecules [8]. Heterogenous photocatalysis is another AOP method. Using this technique, complex organic and inorganic substances can be converted into small molecules like CO\({}_{2}\) and H\({}_{2}\)O [9] using a semiconductor and light energy [10; 11]. In a photocatalytic process, electrons and holes are generated via the irradiation of the photocatalyst with light, which can react directly with the pollutant or generate further reactive species like hydroxyl radicals and superoxide radicals [11]. Metal oxide semiconductors such as TiO\({}_{2}\), ZnO, WO\({}_{3}\), and Fe\({}_{2}\)O\({}_{3}\) are of great interest for the photocatalytic degradation of drugs, as they can harness energy in the UV-Vis range and generate reactive charge carriers when irradiated with light [12; 13]. The energetic position of their valance band and/or conduction band enables the formation of superoxide radicals via the reaction of dissolved oxygen molecules with electrons from the conduction band and/or the formation of hydroxyl radicals via the reaction of holes in the valence band with water or surface hydroxyl groups.