# Surface fluorination of TiO2 for visible light photocatalysis

T.K. Le, Delphine Flahaut, Sylvie Blanc, H. K. Hung Nguyen, T.K. Xuan Huynh, Hervé Martinez

► To cite this version:

T.K. Le, Delphine Flahaut, Sylvie Blanc, H. K. Hung Nguyen, T.K. Xuan Huynh, et al. Surface fluorination of TiO2 for visible light photocatalysis. 2nd European Symposium on Photocatalysis, Sep 2011, Bordeaux, France. [hal-05367792](https://hal-05367792v1)

HAL Id: hal-05367792

https://univ-pau.hal.science/hal-05367792v1

Submitted on 16 Nov 2025

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Distributed under a Creative Commons Attribution 4.0 International License
# Surface fluorination of TiO₂ for visible light photocatalysis

T. Khoa Le, D. Flahaut, S. Blanc, H. K. Hung Nguyen, T. K. Xuan Huynh and H. Martinez

IPREM – UMR 5254 ECP – University of Pau et des Pays de l'Adour – France
Department of Inorganic Chem. – University of Science – Ho Chi Minh city – Vietnam

<figure><img src="image_2.png" /></figure>

## Problematic

### Photocatalytic technology based on TiO₂

promising means for the treatment and the destruction of non-biodegradable organic pollutants in wastewater

* ✓ Activity of TiO₂ is not high enough for practical applications

* ✓ TiO₂ almost operates under UV irradiation which occupies 3 – 5% of solar energy

<figure><img src="image_3.png" /></figure>

Improvement of photocatalytic activity in UV and Vis by surface modification

### Surface fluorination of TiO₂ (P25) by thermal shock method

Increase

Activity of fluorinated catalysts in UV and Vis irradiation

Better understanding

Crystallite structure, light absorption, surface characterization

Adsorption and photocatalytic tests

XRD, SEM, XPS, UV-Vis diffuse reflectance

## Catalysts preparation

formed by ligand exchange between :
F⁻ and surface OH⁻

$$ \equiv \text{Ti} - \text{OH} + \text{F}^{-} \leftrightarrow \equiv \text{Ti} - \text{F} + \text{OH}^{-} $$

<figure><img src="image_4.png" /></figure>

<figure><img src="image_5.png" /></figure>

FTO-400

FTO-500

FTO-600

FTO-700

FTO-800

FTO-950

## Photocatalytic test: Degradation of methylene blue (MB)

0.125 g catalyst + 200 mL of 10⁻⁵ mol/l MB solution

<figure><img src="image_6.png" /></figure>

* ■ Ultrabatch during 15 min

→ disperse large aggregates

* ■ Stirring in the dark during 30 min

→ ads/desorption equilibrium

* ■ Irradiation: UV 350 nm or Vis 420 nm

* ■ Sampling every 30 min

* ■ [BM] = f(t) with SP-300 Optima spectrometer at 645 nm

## XRD and SEM

<figure><img src="image_7.png" /></figure>

* indicates K₂Ti₆O₁₃ phase

* ✓ TiO₂ P25: 90% anatase, 10% rutile

* ✓ Stability of anatase and rutile for fluorination up to 500°C

<figure><img src="image_8.png" /></figure>

* ✓ From 600°C: formation of K₂Ti₆O₁₃ phase

<figure><img src="image_9.png" /></figure>

<table><thead><tr><th></th><th>anatase</th><th>rutile</th><th>K₂Ti₆O₁₃</th></tr></thead><tbody><tr><td>P25</td><td>90</td><td>10</td><td></td></tr><tr><td>FTO-600</td><td>63</td><td>19</td><td>18</td></tr><tr><td>FTO-800</td><td>13</td><td>15</td><td>72</td></tr><tr><td>FTO-950</td><td></td><td>6</td><td>94</td></tr></tbody></table>

## Characterization

### XPS

* ✓ Unique fluorine environment up to 700°C

F 1s at 685 eV: F chemisorbed on the surface

<figure><img src="image_10.png" /></figure>

Successful surface fluorination

* ✓ From 800°C

F 1s at 687 eV: F in TiO₂-xFₓ environment

<figure><img src="image_11.png" /></figure>

F-doping in lattice

<figure><img src="image_12.png" /></figure>

## Photocatalytic properties

### UV-Vis diffuse reflectance

<figure><img src="image_13.png" /></figure>

* ✓ Red shift for fluorinated samples up to 600°C

* ✓ Blue shift for samples fluorinated from 700-950°C

<table><thead><tr><th>Band gap (eV)</th><th>P25</th><th>FTO-400</th><th>FTO-500</th><th>FTO-600</th><th>FTO-700</th><th>FTO-800</th><th>FTO-950</th></tr></thead><tbody><tr><td>3.2</td><td>2.8</td><td>2.9</td><td>3.1</td><td>3.1</td><td>3.2</td><td>3.7</td></tr></tbody></table>

### MB adsorption

<figure><img src="image_14.png" /></figure>

* → methylene blue :

positively charged dye

* → F-TiO₂:

negatively charged surface

<figure><img src="image_15.png" /></figure>

stronger MB adsorption on the

surface for fluorinated samples

### Degradation of MB under

#### UV irradiation

<figure><img src="image_16.png" /></figure>

* ✓ Kinetics: Pseudo – first order formula

TS at 400 & 500°C: activity ↗

<figure><img src="image_17.png" /></figure>

* ✓ From 600°C: activity ↗

#### Visible irradiation

<figure><img src="image_18.png" /></figure>

Best photocatalyst: FTO-500

Surface fluorination by TS

Structure TiO₂ of anatase and rutile

<figure><img src="image_19.png" /></figure>

Activity in UV and Vis

## Conclusion and perspectives:

* ✓ Thermal shock: new and simple method to fluorinate TiO₂ and increase its photoactivity under UV and Vis light

* ✓ Using thermal shock for surface halogenation of TiO₂