**3.4 The oil-TiO2 nanocomposite binding strength in turbulent flow**

Turbulent motions due to strong tide and wind in surface water and soil environments can disturb oil-TiO2 nanocomposite binding strength and stability. These turbulent motions can produce an external breaking force that destroys binding between two bodies. The binding strength can be related to the inter-particle bonds between aggregate components which involves surface interaction between oil and TiO2 nanocomposite. Therefore, an oil-TiO2 nanocomposite binding force will be broken when the shear force applied to their surface of contact is larger than the bonding strength within the cohesion. As such, it is important to architecturally design TiO2-containing nanocomposite with capacity to resist shear force in a situation of turbulent condition be it in water or soil environment. This will play an important role in determining performance and general acceptance of TiO2 containing nanocomposite in real oil spill remediation application. The strength of surface interaction between oil and TiO2-containing nanocomposite will be controlled by two counteracting forces under a given turbulent condition, namely, the oil-TiO2-containing nanocomposite binding force and the turbulent breaking force of the fluid-material surface contact. The binding force is related to the material's morphological characteristics, and the breakage of binding is to be governed by turbulence kinetic parameters [84]. In this part, the oil-material's binding force and the turbulent breaking force of fluid can be deduced from morphological characteristics of material and the force of attraction between oil and the material under application. However, a method for quantitative evaluating the strength of oil-material's binding force can also be developed based on the binding and the breaking forces of the surface contact between oil and TiO2 containing nanocomposite. For easy comprehension, under a given turbulent condition, it will be deduced that the critical condition of the breakage of surface interaction between oil and TiO2-containing nanocomposite is considered to be the binding force equal to the breaking force, which can be written in the following form.

$$\mathbf{B}\_f = \mathbf{F} \tag{6}$$

When TiO2-containing nanocomposite is architecturally designed with given pore size, an increase in effective adsorption that bring spilled oils much closer to the material can facilitate an increase in oil density that would be larger enough to be stored in the macropores of the nanocomposites. This in effect can result in enhancement of adherence of the oils to the TiO2-containing nanacomposites, which is beneficial for the improvement in oil retention capacity of the material that can allow adsorbed oil to resist turbulent motion either cause by tide or wind in water or soil environment. In addition, in response on the problem of turbulent motion particularly in surface water environment, TiO2-containing nanocomposite can be engineered to a strong magnetic response to an external magnetic field according to the magnetization curve. In effect, it is expected that an architecturally designed TiO2-containing nanocomposite can be easily controlled by an external magnetic field, and then oils can be made to be strongly attracted to the magnetic component of the nanocomposite with which the adsorbed oils are to be retained structural stable. This can provide high contacting rate between spilled oils and the material as well as additional kinetic energy that could enhance the overall degradation and mineralisation rate of spilled oils in surface waters and soils. Hence, removal of spilled oils from the surface of ocean and soil environments can also be achieved in large scale through strategic TiO2 photoremediation process.
