**2. TiO2 photocatalytic applications in environmental remediation**

The potentials of applying photocatalysis in environmental management technology, particularly on pollution remediation, with prime focus on TiO2 have been proven with spectacular results and reported in a number of research reviewed articles [12, 26–28]. The science of remediation involves removal, separation,

containment and destruction of pollutants or contaminants from host environmental media such as surface-and-ground water and soil. With respect to destruction, unlike the other remediation options that not only transfer pollutants from one medium to another, destruction converts contaminants to innocuous products, such as CO2 and H2O. In view of that, the photocatalytic destruction of contaminants in the environment, especially the application of irradiated TiO2-containing materials for the remediation of contaminants from environmental media has been applied successfully for a wide variety of compound [29, 30] such as alkanes, aliphatic alcohols, aliphatic carboxylic acids, alkenes, phenols, aromatic carboxylic acids, dyes, PCB's, simple aromatics, halogenated alkanes and alkenes, surfactants, and pesticides as well as for the reduction of heavy metals (Cr, U, As, Pb, Hg, Cd) from aqueous environments to soil surfaces [31–33]. In many cases, complete mineralisation of organic compounds has been reported [34, 35]. It is in records that in the overall field of semiconductor photocatalysis, both in fundamental research and practical environmental applications, TiO2 has so far been shown to be the most promising material used for both circumstances because it is highly photo-reactive, cheap, non-toxic, chemically and biologically inert, and photo-stable [26, 27]. The major advantages of TiO2 photocatalysis are that its process is not an energyintensive pollution management method and is photo-responsive to renewable and pollution-free solar energy. Also, unlike the conventional environmental pollution treatment methods, TiO2 photocatalysis does not transform parent pollutants to more refractory types, instead converts pollutants to innocuous products, such as CO2 and H2O. Besides, the reaction conditions are mild accompanied with modest reaction time and can be applied in gaseous, aqueous and solid phase pollution remediation techniques [30, 36–43]. Therefore, TiO2 photocatalysis has the advantage of not only minimising pollution remediation project costs, but also resulted in the remediation reactions with the desired products in the most environmentally harmonious and safe ecologically.

The TiO2 photocatalytic remediation processes exploits the high reactivity of oxygen superoxide (O2 •–) and hydroxyl (OH• ) radicals as the oxidation driving forces resulting in the formation of benign by-products (i.e., H2O and CO2) of photo-mineralisation of toxic organic pollutants. Similarly, if a suitable scavenger or surface defect state is available to trap photogenerated electrons and holes and recombination is halted, a reductive pathway by a conduction-band electron(s) is also initiated. However, in very small TiO2 nanoparticle suspensions both species are present on the surface. Therefore, simultaneous consideration of both the oxidative and the reductive pathways is required. In the remediation of organic pollutants of which spilled oil inclusive, TiO2 utilises the oxidising power of the holes either directly or indirectly. On the other hand, to prevent a build-up of electrons, oxygen in the reaction environment serves as an electron acceptor that reacts with the electrons. The oxygen used in the process is atmospheric oxygen, and therefore, in general, there is no need for additional oxidising agents. Accordingly, TiO2 has taken a highly prominent position of usage in solving environmental pollution problems both in aquatic and terrestrial environments. Similarly, it has taken centre stage in the campaign for solar-driven photocatalytic remediation of oil spills, as TiO2 demonstrated the capability to develop such a green system that utilises renewal energy source and converts organic contaminants to innocuous products, such as CO2 and H2O that are environment friendly (**Figure 1**). From this perspective, as the most promising solar responsive semiconductor, TiO2-based materials are therefore expected to play a major role to curb serious environmental and pollution challenges through the utilisation of renewable solar energy. Therefore, oxidation of organic compounds by TiO2-based materials is of considerable interest *Titanium Dioxide – A Missing Photo-Responsive Material for Solar-Driven Oil Spill… DOI: http://dx.doi.org/10.5772/intechopen.98631*

**Figure 1.**

*Photoremediation of spilled oil into innocuous compound by TiO2 photocatalysis. (Sourced from Nyankson et al. [44] oil photocat itself) but modified.*

for environmental applications, particularly for the control and eventual destruction or elimination of hazardous wastes such as spilled oils in aquatic and/or terrestrial environmental compartments. Accordingly, the oxidation process of TiO2 is indiscriminate and therefore, leading to the mineralisation of almost all-organic pollutants in surface waters and soils.
