*2.1.1. Electrophoretic deposition*

This is the most favored method due to several reasons, which include effectiveness in the fabrication of coatings and films from suspensions [14], a short period of time is required for deposition, the ability to deposit a film on a non-uniform surface, it is cost effective, it is easy to control the thickness of the films, ability to utilize suspensions of low solids loadings, homogeneity of resultant coatings, simple apparatus requirements, binder-free process and it is possible to prepare homogeneous coated layers or deposited films [15, 16].

The process involves the movement of charged particles in a suspension medium followed by deposition on a substrate under an applied DC voltage [17, 18] as shown in **Figure 2**. When the voltage is applied to the electrodes, an electric field is created that interacts with the surface charge of the nanoparticles, producing a force that makes the particle move toward the electrode of the opposite charge and their accumulation on this electrode leads to the formation of a homogeneous layer.

Different thickness of the films can be achieved by changing the deposition parameters such as voltage, deposition time, solvent type, zeta potential particle and loading in the suspension [17]. Some researchers have used different combinations in titanium dioxide thin film

**Figure 2.** Schematic setup of the electrophoretic deposition cell [16].

deposition for different applications such as biomedical applications [19], ceramic coatings [20] and dye-sensitized solar cells [21–23]. Nyongesa and Aduda used electrophoretic deposition technique to deposit titanium dioxide thin films on conducting glass substrates for application in water purification [16]. In the study, they found out that ethanol was a better solvent to use compared to toluene, propanol or water, which they believed was due to its high dielectric constant (ε) of 24.3. Water is not a suitable suspension medium due to water electrolysis which takes place during the deposition and this can cause gas bubbles to accumulate at the electrode surfaces, which is detrimental to the electrophoretically deposited coating. The best parameters for good adherence of the nanoparticles were: pH value of 3, solid loading of 4.0 wt% and a voltage of 20 V [16]. In a similar study by Nguu et al. [24], to achieve a uniform film of 5 μm, the best voltage and time were 35 V and 90 s, respectively, and they discovered that extended deposition times (>90.0 s) resulted in formation of agglomeration [24]. In another study by Dhiflaoui et al., it was found that the coatings deposited at 20 V for 4 min were the most homogeneous [25]. They also discovered that transformation of anatase to rutile depends on the electric current in the electrochemical cell. When the voltage is increased, the modulus of elasticity and hardness of the films also increase.
