## 7 Composite Carbonaceous-Titanium Dioxide and the Photocatalytic Activities
Graphene was found to be an another attractive carbonaceous material to functionalize the surface of TiO\({}_{2}\) due to its unique two-dimensional structure, high surface area, electron mobility, high thermal conductivity, and mechanical strength [129]. Graphene can improve photocatalytic efficiency by promoting electron-hole recombination process [53]. Compared to CNTs-TiO\({}_{2}\), G-TiO\({}_{2}\) has a higher density of adsorption sites as a result of its open structure. In the study performed by [PERSON] et al., TiO\({}_{2}\) was functionalized with graphene oxide (GO) and used for photocatalytic degradation of atenol (ATL) under UV and visible light irradiation [134]. Atenolol belongs to the \(\beta\)-blocker family of drugs that are commonly used in the treatment of cardiovascular diseases. Atenolol cannot be fully metabolized in the human body, thus the unchanged drug, along with its metabolites, is excreted into sewage and eventually permeates into surface water, resulting in the contamination of the environment. ATL has been proven to be ecotoxic and phytotoxic, and for this reason, an effective way of its removal from the environment is necessary. GO was obtained from graphite powder by modified Hummers' method [135]. Next, graphene-TiO\({}_{2}\) was obtained by pouring 2 mg of GO to a 2:1 solution of waterethanol, treated in the ultrasonic bath for 1 h. To that solution, 200 mg of Aeroxide P25 TiO\({}_{2}\) was added and stirred for an additional 2 h. Then, the mixture was placed into an autoclave for 3 h at 120 \({}^{\circ}\)C in order to reduce GO to graphene and deposit it on the TiO\({}_{2}\) surface. Photocatalytic experiments were conducted with 0.5-2.0 g \(\times\) dm\({}^{-3}\) concentrations of the photocatalyst and 25 mg \(\times\) dm\({}^{-3}\) of ATL in an aqueous solution under constant stirring. Visible light was simulated by a solar simulator with a 1000 W Xe arc lamp. The influence of pH and light intensity on the reaction was also assessed. The pH value at 6 seemed to be the most optimal, whereas the photodegradation rate was increased with rising light intensity and peaked at the highest intensity chosen (1000 mW \(\times\) cm\({}^{-2}\)). G-TiO\({}_{2}\) exhibited significantly enhanced photocatalytic activity compared to regular TiO\({}_{2}\). The most efficient concentration was 1.5 g \(\times\) dm\({}^{-3}\), in which it degraded 72% of ATL in 1 h under solar irradiation. After 7 h of irradiation, complete removal was achieved. An interesting approach in TiO\({}_{2}\) photocatalysis was demonstrated in a study where TiO\({}_{2}\)/G/Fe\({}_{3}\)O\({}_{4}\) complex was used for magnetic removal of uranium(VI) from radioactive  
Figure 10: The applicability of carbonaceous-TiO\({}_{2}\) nanomaterials as catalysts in the photodegradation studies of various pharmaceutically active ingredients; carbon nanotube (CNT), activated carbon (AC). wastewaters [136]. Although efforts are made in developed countries to switch to more ec-friendly energy sources, nuclear energy still remains a popular choice in the energy industry due to its efficiency and despite the threats associated with the use of radioactive fuels. A material that would allow efficient removal of uranium from a polluted environment, with the possibility of potential reuse, is very much desired. The mechanism of radioactive wastewater treatment is based on the reduction of U(VI) to U(IV) due to its lower solubility compared to its hexavalent form. In the study, TiO\({}_{2}\)/Fe\({}_{3}\)O\({}_{4}\) demonstrated a 19.3 times higher photo-induced reduction rate of U(VI) in comparison to bare TiO\({}_{2}\). The reduction of U(VI) allowed deposition of insoluble U(IV) in contaminated water reservoirs, followed by magnetic separation. In further conclusion, both the radioactive pollutant and the photocatalyst were then filtered due to the presence of Fe\({}_{3}\)O\({}_{4}\), which also introduces the magnetic properties to the composite.