# The Role of Surface Texture on the Photocatalytic H\({}_{2}\) Production on TiO\({}_{2}\)
## 3 Photocatalytic Hydrogen Production from Anatase TiO\({}_{2}\)
### Effect of Exposed Surfaces
Then, treatment with  
Figure 8: Energy-level diagram and charge carriers transfer process of the “surface hetero-junction” between facets {101} and {001} of TiO\({}_{2}\) anatase under UV irradiation. Figure 9: (**a**) Mass and (**b**) surface normalized photocatalytic hydrogen evolution rate of three anatase TiO\({}_{2}\) nanocrystals with different {001} to {101} facet ratios. Reprinted with permission from [95]. Copyright © 2017 American Chemical Society. NaOH exchanged the fluorides at the surface with OH groups. The materials were then tested for H\({}_{2}\) production in the presence of methanol as sacrificial agent and photodeposited Pt as occatalyst under simulated solar light. The results showed that the samples with higher content of {101} facets were better than {001} for this particular reaction, both with and without fluorine on the surface. This clearly demonstrates the importance of the presence of the [101] to have efficient reductive processes. The photocatalytic production of hydrogen from methanol steam reforming was also investigated over a series of fluorinated Pt/TiO\({}_{2}\) samples (F for O nominal molar substitution ranging from 5 to 15%) synthesized by flame spray pyrolysis by [PERSON] et al. in a work published in 2014 [96]. A substitution lower than 10% led to an increase of surface hydroxylation which favored an indirect hydroxyl mediated mechanism, with the consequent increase of hydrogen production rate. Conversely, fluorination \(>10\%\) introduced an excess of bulk structural defects that can act as electron-hole recombination centers. Moreover, an excess of fluorination increases the F-induced surface electronegativity, inhibiting CB electron transfer. Both these effects led to lower hydrogen production rate under UV irradiation. The effect of the nanoparticles shape and the surface fluorination were investigated by [PERSON] and coworkers in 2010 [97], investigating the hydrogen production over Pt/TiO\({}_{2}\) nanosheets that largely exposed {001} facets. They prepared anatase nanosheets by acidic hydrolysis of Ti(IV) butoxide using hydrofluoric acid as capping agent. A part of the obtained nanoparticles was then cleaned with diluted 0.1 M NaOH solution in order to remove the surface fluorides. To investigate the influence of the shape, the same synthesis procedure was repeated but replacing the hydrofluoric acid with the same volume of distilled water. Pt nanoparticles were photodeposited from a 0.26 mM H\({}_{2}\)PtCl\({}_{6}\) solution in order to obtain a final weight ratio of Pt to Ti of 2%. The fluorinated TiO\({}_{2}\) material presented higher photocatalytic activity than the other two materials, due to the synergistic effect of fluorination (reduction of the charge carriers recombination rate) and exposed {001} facets. The higher reactivity of the {001} facet is in contrast compared with most of the works published in the last few years. For example, [PERSON] et al. [75] synthesized anatase microcrystals with three different morphologies and different percentages of {101}, {010} and {001} surfaces. The hydrogen evolution on the samples  
Figure 10: **Top**: TEM images of TiO\({}_{2}\) nanocrystals synthesized (**a–c**). **Bottom**: H\({}_{2}\) production rate over fluorinated and NaOH-treated materials. Adapted with permission from [49]. Copyright © 2012 American Chemical Society. was estimated from methanol (10%) photoreforming using 1 wt % Pt cocatalyst under Xe arc lamp irradiation. The authors found that the presence of fluorides (derived from synthesis conditions) is deleterious for the photoreduction of H\({}_{2}\), especially for the surfaces [101] and [010], counteracting the different facets terminations. After removal of the capping agent (2 h 600 \({}^{\circ}\)C in air), the F-free surfaces presented different behaviors, with a new photoreactivity order (\(\langle\)[010] \(>\) [101] \(>\) [001]).