## 7 Composite Carbonaceous-Titanium Dioxide and the Photocatalytic Activities
Functionalization of TiO\({}_{2}\)/Fe\({}_{3}\)O\({}_{4}\) with graphene stabilized the magnetic oxide complex by attracting TiO\({}_{2}\) photoelectrons toward graphene's surface instead of transferring them to Fe\({}_{3}\)O\({}_{4}\), which could lead to photodissolution of the latter compound. The study also examined the effects of initial uranium concentration, pH, ionic strength, and the presence of organic pollutants in water on the reaction [136]. The photodegradation studies of pharmaceutical pollutants were also performed with the use of reduced graphene oxide (rGO) deposited on the surface of titanium(IV) oxide. The GO-TiO\({}_{2}\) has a narrower band gap, which results in better absorption of light. With a widened absorption band, its reduced form--rGO-TiO\({}_{2}\)--was used for the degradation of diphenhydramine under visible light with promising results [137]. In other studies, magnetically recyclable GO-TiO\({}_{2}\) removed 99% of carbamazepine and caffeine after 1 h of irradiation with UV light, and the composite could be recovered fully after the experiment by magnetic separation [138], whereas the 3D porous rGO-TiO\({}_{2}\) aerogel also removed 99% of carbamazepine from the polluted solution [139]. The single-walled CNTs-TiO\({}_{2}\) hybrid system was used by [PERSON] et al. in photodegradation studies of 22 organic pollutants including pharmaceuticals such as warfarin, mefenamic acid, metoprolol, \(\beta\)-estradiol, paracetamol, carbamazepine, naproxen, trimethoprim, and sulfamethoxazole [140]. The measurements were performed in both ultrapure water and real secondary wastewater effluent under UV and solar light irradiation. The catalytic activity of SWCNTs-TiO\({}_{2}\) nanoparticles was compared with Degussa P25 TiO\({}_{2}\). The calculated degradation rates were very similar; however, the TiO\({}_{2}\) loading in the SWCNTs-TiO\({}_{2}\) system was lower than in Degussa P25. Furthermore, when the photodegradation was performed in real wastewater samples, the obtained efficiency was also lower in the case of both catalysts in comparison to measurements in ultrapure water [140]. Another system of similar catalytic activity, based on multi-walled carbon nanotubes (MWCNTs) and TiO\({}_{2}\) was used in the preparation of a nanocomposite for the degradation of tetracycline antibiotic (TCL) and some wastewater samples [141]. MWCNTs-TiO\({}_{2}\) was prepared by the surfactant wrapping sol-gel method [142]. Two UVC lamps (240 nm) with the power of 6 W were used for reactor irradiation. TCL degradation was conducted in deionized water. Effects of various parameters including MWCNTs/TiO\({}_{2}\) ratio (0.5-10), initial pH (3-11), irradiation time (0-120 min), and TCL concentration (0.5-30 mg \(\times\) dm\({}^{-3}\)) were tested. With the nanocomposite, it was possible to completely remove up to 10 mg \(\times\) dm\({}^{-3}\) of TCL concentration from the reaction environment with 0.2 g \(\times\) dm\({}^{-3}\) of 1.5 \(w\)/\(\%\) MWCNTs to the TiO\({}_{2}\) photocatalyst, at pH 5, and after 100 min of irradiation. For higher concentrations up to 30 mg \(\times\) dm\({}^{-3}\) of the substrate, the efficiency decreased to 92.8%, whereas low TCL concentrations (<0.8 mg \(\times\) dm\({}^{-3}\)) were removed after only 10 min of irradiation. For the 10 mg \(\times\) dm\({}^{-3}\) sample, TOC analysis resulted in 37% TOC removal after 100 min, reaching 83% after 5 h of irradiation. Real wastewater treatment test with 0.2 mg \(\times\) dm\({}^{-3}\) of MWCNTs-TiO\({}_{2}\), at pH equal to 5, led to the reduction in COD (Chemical Oxygen Demand) from 2267 mg \(\times\) dm\({}^{-3}\) to 342 mg \(\times\) dm\({}^{-3}\) (84.9% reduction) and TOC reduction from 1295 mg \(\times\) dm\({}^{-3}\) to 228 mg \(\times\) dm\({}^{-3}\) (82.3% reduction) after 240 min of treatment. The results obtained for MWCNTs-TiO\({}_{2}\) presented a significant improvement compared to bare TiO\({}_{2}\), where only 47% TOC removal was noted.