Titanium Dioxide – A Missing Photo-Responsive Material for Solar-Driven Oil Spill Remediation

*Haruna Adamu*

### **Abstract**

TiO2 nanoparticles have been extensively investigated for environmental applications, particularly in the photocatalytic decomposition of organic pollutants using solar energy. The TiO2-derived photocatalysts attract attention because of their photocatalytic efficiency and activity under a wide range of environmental conditions in response to superior structural and electronic properties. Consequently, TiO2 compares with other common semiconductors used for environmental photocatalytic applications, TiO2 is widely being considered close to an ideal semiconductor for photocatalysis. However, despite the impressive photocatalytic and material properties of titanium dioxide, TiO2 has not to this point been incorporated within commercial hub of oil spill remediation products. Therefore, this chapter covers the description of inevitable technical details required for unveiling the full potential of solar-driven photooxidation potency of TiO2, which have been the major challenges that halt its translation to commercial use in oil spill remediation. This at the end would underpin and make TiO2-derived materials a substitute ready to be commercially accepted as a promising method for remediation of oil-polluted aquatic and soil environments.

**Keywords:** Photo-remediation, oil-spill, solar-radiation, pollution

#### **1. Introduction**

The aquatic and terrestrial environments are undergoing constant compositional change due to the continuous introduction of chemicals initiating pollution problems, which considered as part of the dominant threats to living systems surviving on the earth. Crude oil is a focal commodity upon which the economy of the world relies on and thus, its production is the largest and most profitable business in the world. This has, however, created burden and disturbances in ecosystems with attendant environmental quality imbalances. From its development phase to a production phase, many disasters occur in oil industries. An Oil spill is the most important type of disaster which usually occurs and causes a lot of environmental distress. Oil spill mishaps often happen during drilling, production, transportation, transfer, and storage [1]. Besides, the extensive utilisation of crude oil products and the discharges of oily wastewater have also caused increasingly serious oil spills pollution in the harbour and riverine areas as well as other water bodies [2, 3]. In effect, oil spills not only cause loss of energy source but also have long-term

damaging impacts on the ecological environment upon which our society relies [3–6]. And so, the negative impacts of oil spills to aquatic and terrestrial ecosystems can be significantly tremendous and unimaginable [7].

It is, therefore, in recent years, the problems of oil spills worldwide have attracted constant concern because of their ecological damage and environmental pollution. Oil spills in an aquatic environment is generally much more damaging since can spread to a distance of hundreds of miles in a thin oil slick layer covering the water surface. This eventually causes the chemical components and elements of the spilled oil to impact negatively on marine life, birds, photosynthesis in plants and as a result, disrupts the normal ecosystem services and structural food chain [1, 3, 4]. Similarly, oil spills pollution could also potentially impose disastrous effects on land [8]. The damage is hard to measure and contain since it involves complex ecosystems. Moreover, low-density spilled oils have an insufficient viscosity to pull together and can therefore speedily spread and damage unimaginable portions of land. On the other hand, high-density spilled oils are too viscous to be dispersed sufficiently well in the soil environment and thus, cause agglomeration that can give rise to stronger adhesive forces of attraction between oil and soil constituents. In either of the two scenarios, it may take land years to recover, during which spilled oils are able to destroy soils, its ecosystems, and biodiversity [9]. This is because oil contamination on land reduces plants' and the soil's ability to pull water from the ground and hold oxygen for plants' growth and micro-creatures survival, respectively. Thus, existing vegetation and fauna-diversity are prone to suffocation due to oil saturation and acts as a barrier, preventing water and oxygen getting to flora and micro-fauna, correspondingly [10]. Accordingly, transporting oil from production sources to consumption locations entails risks, most notably, the risk of accidental oil spills, which causes severe damage to ecosystems and loss to human society [11]. In addition, oil spill is a serious environmental problem not only because of its ability to pollute large areas with associated consequences, but also the longest period of management that usually leads to a heavy financial burden to industries and socio-economic afflictions to society in the immediate vicinity of the affected areas [12]. This is quite challenging because the consequences are not conditional upon the particular geographic, ecological and societal settings in which the disaster occurs, rather viewed as a global problem since crude oil is obviously traded inter-regionally and continently [3, 11]. As such, the damaging impact and compositional alteration of the environment due to oil spills is one of the major concerns of today's world. For example, the tropical Gulf of Mexico oil spill reminds the world again of the importance of oil spill clean-up and environmental remediation [3]. Therefore, an efficient, economical and environmental friendly remedial action is urgently needed as a solution to oil spills pollution problems for the extermination of threats to plants, animals and human life on the gulf coasts and terrestrial environment.

Current remediation techniques for oil spills are typically classified as physical, biological, and chemical. These are the three primary remediation technologies that have widely been applied for addressing or decontamination of oil spills floating and/or dispersing in water and soil environments [13, 14]. The physical method has been considered as one of the most resourceful and inexpensive strategies for oil spills management [15], which is used to remove oil slicks from affected areas by functional materials. However, the process mainly involves the transfer of spilled oil from one environmental phase to another where disposal of oil-soaked agglomerates could also be another source or cause of environmental pollution. On the other hand, the biological method would have been the most attractive option, the hydrophobicity of weathered oil contributes to its low bioavailability to microbial actions, which increases the time for biodegradation and natural attenuation [16].

*Titanium Dioxide – A Missing Photo-Responsive Material for Solar-Driven Oil Spill… DOI: http://dx.doi.org/10.5772/intechopen.98631*

Although it can degrade oil without any recontamination [17, 18], but high-cost and a long period of action limit its practical application in emergency oil spill incidents that demand an economical and efficient approach [19]. The chemical method mostly involves the use of surfactants, dispersants, and solidifiers. Amongst the three, surfactants only break up oil into tiny droplets directing to help natural oileating microbes further break down the hydrocarbons. In contrast, dispersant perhaps do more harm than good. Dispersants hide the oil spills problem. It is used to accelerate the dispersion of the volume of oil into the water column, to reduce the visibility of oil pollution and of the potential impact on the biodiversity of the affected environment [20]. For the solidifiers, are mainly applied to immobilise oil to curtail further spread from concentrated and chunks of floating spilled oil on water or infiltrate into the soil when it occurs on the land surface. Unfortunately, solidified oil always requires to be removed and otherwise, the natural attenuation process of dispersion and volatilisation/evaporation will be inhibited leaving residues of solidified oil to be persistent due to slow weathering processes [13, 21].

It is believed that an oil spill spreads quickly and escalates rapidly and therefore, high speed of action is crucial. For this reason, the real short-time removal process of spilled oil from the environment, including water-bound systems, is imperatively needed for environmental sustainability. Although the application of TiO2 in the clean-up of oil spills is a chemical method of environmental pollution remediation, in recent years, TiO2 amongst the metal oxide semiconductors, has been considered as the most widely and well-studied material for the degradation of recalcitrant organic pollutants including spilled oil [22–24]. This is directly connected to its high photocatalytic efficiency, physicochemical stability, high photonic efficiency, and an absence of biological toxicity in bulk form. It also blends under a wide range of environmental conditions for its activity, including stability in acidic and basic aqueous media and activity under ambient temperatures, and most importantly widely available at low cost [25]. Despite these impressive photocatalytic and material properties, TiO2 solar-driven remediation, as an *in-situ* self-remediation technique and a sustainable solution due to availability of the material and abundance of solar radiation, has not been fully developed. Moreover, it has not been, to this point, adequately incorporated within commercial oil spills remediation products. Thus, the question here that requires a wide spectrum of discursive clarification is that 'will TiO2 sunlight-driven photocatalytic remediation ever be fit for oil spills pollution tragedy in water and soil environments'? Or, is TiO2 a missing materialbased novel technique for solar-driven oil spill remediation?

Therefore, in this chapter, the properties of TiO2 that whether or not make it fit to be considered as an ideal material for *in-situ* solar-driven photocatalytic remediation of oil spills, particularly in regions with high sunlight exposition and intensity, as well as the challenges that greatly restrict its application and the ability to translate and incorporate TiO2-containing materials to commercial use in oil spills remediation are discussed. This is aimed at providing research directions that can be skewed to work on facts rather than an impression in the design and development of TiO2-containing materials primarily for the solar-driven photocatalytic remediation of oil spills for environmental sustainability.
