## 4 Conclusions and Future Perspectives  
The synergy between carbon nanostructures and titania has been extensively investigated over the years and allowed great progress in a variety of fields; in particular, for tailored applications to address urgent societal needs such as clean energy, medicine, and environmental remediation, which is now being extended to the issue of microplastics [229]. It has been undoubtedly demonstrated that the inclusion of nanocarbon into titania-based functional materials leads to the significant enhancement of the materials' properties. In photocatalysis, for example, depending on the efficiency of the titania/carbon contact, a clear reduction in the electron-hole recombination rate has been observed, as the nanocarbon scaffold is able to scavenge the photoexcited electrons. On the other hand, in electrocatalysis, the carbon conductivity has been exploited to facilitate the electron transfer processes occurring at the TiO\({}_{2}\)-based catalytic sites, resulting in enhanced performances. Regardless of the application, it appears that the suitable interface between the carbon and the TiO\({}_{2}\) phases is in most cases an essential parameter to gain definite advantages in performance. For this reason, we have seen that efforts have focused on the development of synthetic protocols that could guarantee adequate phase contact, giving rise to the desired synergistic effects. As an example, the production of co-axial CNT-titania nanostructures, with an intimate contact between the two phases, could be attained through the careful selection of CNT functionalization, so that the support displays suitable oxygen-bearing functional groups to effectively anchor titania, and the optimization of the thermal annealing step to seal the CNT-titania interface [230]. The main limitation of titania for use in photochemical applications, namely its relatively wide bandgap that makes it unresponsive to visible light, has been linked in recent times to a predicted slow decline in the popularity of titania-based materials for photochemical sustainable processes, paving the way for the exploration of new semiconductor  
Figure 10: Schematic representation of (**A**) potential titanium–implant surface modification to attain antibacterial activity, and (**B**) in particular, the use of electrochemically anodized titania nanotube arrays for the local release of antibiotics. Reprinted from [223], Copyright © 2021, with permission from Elsevier. materials with a more profitable exploitation of sunlight. However, we foresee that TiO\({}_{2}\) will still have a long life as the leading semiconductor as many authors have shown avenues for expanding its use to incorporate the exploitation of visible light. For example, defect engineering in TiO\({}_{2}\) polymorphs has reached a deep level of understanding, and the controlled alteration of the TiO\({}_{2}\) structure at atomic level can lead to considerable advantages. Black titania, obtained in 2011 by an intensive H\({}_{2}\) treatment that causes reduced Ti states by means of oxygen atom removal, is a symbolic case of a visible-light active TiO\({}_{2}\) material [231]. As the activity under visible light is caused by intragap states, it is frequently hypothesized that combined nanocarbon-TiO\({}_{2}\) could cause a C-doping of the titania at the phase interface, creating new midgap states. TiO\({}_{2}\) is being revisited in modern times as a component in more complex composites, and the interfacing with carbon nanostructures certainly brings many advantages (some of them illustrated above), in concomitance with a confinement at the nanoscale level of the material, with the expected benefits of nanomaterials. However, TiO\({}_{2}\) junctions with other semiconductors bearing suitable electronic features could make further amends for the intrinsic shortcoming of self-standing TiO\({}_{2}\). Z-schemes or _p-n_ heterojunctions are the two best known examples to improve photochemical properties.