**5. Concluding remarks**

The ATR-FTIR technique offers the chance to obtain novel information concerning interfacial processes *in situ*. This information can be used to explain surface reaction mechanisms. Hence, ATR-FTIR studies are becoming increasingly popular as an investigative technique and may now be considered as one tool of choice in the field of interfacial chemistry when compared to other techniques, particularly in obtaining data under ambient conditions. This is due to the major advantages of ATR-FTIR spectroscopy such as the *in situ* data collection, as well as the high sensitivity, simplicity, and rapidity of the measurements.

The use of ATR-FTIR in the area of photocatalysis is of great importance since it provides both qualitative and quantitative molecular insight into interfacial processes occurring in the dark (adsorption) and under UV illumination (adsorption/desorption and chemical reactions). The information obtained will often be the key for a deeper understanding of the mechanisms occurring in metal oxide photocatalysis.
