**3. Results**

### *3.1. Morphological Properties*

Figure 1 shows SEM analysis of AC (activated carbon), AC-OH (OH-enriched activated carbon), and AC-TiO2 (activated carbon over titanium dioxide) samples. A smooth and nonuniform surface is registered for AC and its modified counterpart. The average particle size is around 50 μm. The presence of many cavities on the material's surface designs the morphology of AC. However, the addition of TiO2 nanoparticles is confirmed by the high distribution of TiO2 particles on the AC surface. A visible change is observed by the cavity displayed in Figure 1g, explaining the successful coating of TiO2 particles onto the AC surface. The TiO2 particles are spherical and distributed uniformly at the AC surface. It should be noted that the in situ synthesis of metallic particles presents a weak aggregation. Herein, immobilizing a high amount of TiO2 over AC could be baneful for surface reactivity and the adsorption of pollutants. The morphology changes of AC and AC-TiO2 are shown by the fewer cavities than AC, which suppose that TiO2 occupied the majority of the surface.

**Figure 1.** SEM images of AC (**a**–**c**), AC-OH (**d**–**f**), and AC-TiO2 (**g**–**i**).

#### *3.2. Surface Properties*

Figures 2 and 3 show the FTIR analysis for all samples to investigate the surface properties and the stability of synthesized samples in liquid media. Starting by measuring the ZP values of all samples, it was found that the ZP of AC-OH is less than 20 mV, suggesting the good stability of the materials. Although, ZP results confirmed the successful addition of hydroxyl groups at the AC surface, as supported by noticeable decreases in ZP. The surface charge of the particles has a potential effect on catalytic activity, as it could involve such interaction with pharmaceutical pollutants. The results on the AC-TiO2

surface displayed a marked decrease in the zeta potential from 8 mV for AC to −14 mV for AC-TiO2. The negative surface charge could play a key role in the adsorption of pollutants from the water.

**Figure 2.** FTIR spectra of AC and AC-OH.

**Figure 3.** FTIR spectra of AC and AC-TiO2.

According to the Fourier transform infrared spectrum shown in Figure 2, the peaks of the AC surface before and after hydroxylation treatment are different from one sample to another. For AC, the peak located at 1579 cm−<sup>1</sup> is assigned to the stretching vibration of C=C, whereas the band observed at 1259 cm−<sup>1</sup> is attributed to the bending vibration of C-H in the methylene group. At the same time, the spectrum of AC-OH displayed a visible change due to the hydroxylation steps. The new band that appeared at 3415 cm−<sup>1</sup> is associated with hydroxyl groups' stretching vibration (-OH). Accordingly, the chemical structure of the synthesized samples, the bands centered at around 1720 cm−<sup>1</sup> and 1105 cm<sup>−</sup>1, are attributed to the presence of the C=O and C-O groups, respectively.

A comparison between the FTIR spectra of AC and AC-TiO2 is shown in Figure 3. The stretching vibration of the hydroxyl group registered at 3400 cm−<sup>1</sup> is assigned to the

physisorbed surface water [34]. A slight shift to a lower wavenumber is observed and explained by the presence of TiO2 on the AC surface. According to Loo et al., the peak that appeared at 768 cm−<sup>1</sup> is assigned to the stretching vibration of Ti-O [34].
