## 7 Composite Carbonaceous-Titanium Dioxide and the Photocatalytic Activities  
Graphene (G), carbon nanotubes (CNTs), and activated carbon (AC) belong to the most common carbonaceous materials used together with TiO\({}_{2}\). All of them were evaluated in their free form for water treatment and photodegradation of pharmaceuticals and personal care products [128] (Figure 10). Carbonaceous-TiO\({}_{2}\) materials present overall better properties than bare TiO\({}_{2}\), considering adsorption capacity, photocatalytic activity, and better visible light absorption rate [129]. Enhanced catalytic features of carbonaceous-TiO\({}_{2}\) mainly result from four mechanisms: (a) better interaction between waste and the catalyst as a result of high mobility, affinity, and specificity of titanium(IV) oxide surface areas toward APIs; (b) large electron storage capacity, which prevents unwanted electron recombination, promoting hole (\(lt^{+}\)) creation that takes part in redox reactions; (c) facilitating the transfer of electrons from carbonaceous materials to TiO\({}_{2}\), which allows them to act as a sensitizer, and helps in the creation of ROS after irradiation; and (d) the presence of carbon-oxygen-titanium bonding in the system, which reduces the band gap of TiO\({}_{2}\) and extends the absorption band into the low energy visible light spectrum [129]. Within the group, CNTs-TiO\({}_{2}\) and G-TiO\({}_{2}\) have better responses toward visible light irradiation than AC-TiO\({}_{2}\). Moreover, AC-TiO\({}_{2}\) tends to aggregate in comparison to more hydrophobic CNTs-TiO\({}_{2}\)[129]. However, AC-TiO\({}_{2}\) composites have a unique pore structure that improves their photocatalytic activity. The large surface area of AC in the composite system leads to a very high adsorption ability toward various substances [130]. Below, we discuss several examples of photodegradation studies with the carbonaceous-TiO\({}_{2}\) as catalysts and diverse common chemical and pharmaceutical pollutants (see summary in Figure 10). In 2007, AC-TiO\({}_{2}\) was tested by [PERSON] et al. as a potential photocatalyst in the removal of phenol, methyl orange, and inorganic pollutants like Cr(VI) salts with good results [131]. In a more recent study, the activities of bare TiO\({}_{2}\) and activated carbon-functionalized TiO\({}_{2}\) have been compared in the photodegradation experiment of amoxicillin (AMX), ampicillin (AMP), diclofenac (DIC), and paracetamol (PCT) under solar irradiation [132]. AC was deposited on TiO\({}_{2}\) by a high-temperature impregnation method. Photocatalysis experiments were carried out in a closed cycle solar reactor for 210 min. The pH influence on the reaction was studied and varied in the range between 3-10. The value of pH equal 10 was found to be the optimal one. The following concentrations of reagents were used: 50 mg \(\times\) dm\({}^{-3}\) of proper pharmaceuticals and 0.2-1.6 g \(\times\) dm\({}^{-3}\) of AC-TiO\({}_{2}\) photocatalyst. According to the results, AC-TiO\({}_{2}\) completely degraded AMX after 2 h of irradiation and AMP after 3 h, which was in contrast to bare TiO\({}_{2}\), which degraded substrates in 89% and 83% yields, respectively. Degradation rates for DIC and PCT were also higher, 85% and 70% in comparison to 68% and 57% achieved by bare TiO\({}_{2}\), respectively. In the study, the economic factor of the implemented system was also estimated. The operational costs of a reactor with AC-TiO\({}_{2}\) were more favorable than those of running a reactor with bare TiO\({}_{2}\)[132]. Of note, AC-TiO\({}_{2}\) can also be used in ozonized form to improve its activity and reusability. The ozonized AC-TiO\({}_{2}\) was used in the degradation study of metoprolol, in which the substrate was mineralized in 80% within 5 h. The ozonized AC-TiO\({}_{2}\) retained 75-85% of its initial activity after 10 consecutive cycles of photocatalysis [133].