Easy stabilization of Evonik Aeroxide P25 colloidal suspension by 4-hydroxybenzoic acid functionalization

A new functionalization method was developed with the aim of producing stable TiO2-based colloids starting from commercial Evonik Aeroxide P25 powder. The stability of P25 colloids was efficiently increased by grafting 4-hydroxybenzoic acid (4-HBA) on the P25 surface. Results highlighted that 4-HBA interacted with the surface of P25 through its carboxylic group. The key parameter for an optimized stability is the 4-HBA/P25 ratio. If the amount of 4-HBA is too high compared to the TiO2 available surface, 4-HBA molecules preferentially interact with each other, therefore reducing their adsorption on P25. Eight different amounts of 4-HBA were grafted on P25, producing stable colloids in both ethanol and water medium. In both media, the optimal properties and highest stability were obtained for a 4-HBA/TiO2 mass ratio equal to 0.333. This optimal sample was further tested and compared to pure P25 (used as reference material) for p-nitro-phenol (PNP) degradation under UV-visible light without any stirring to highlight the beneficial effect of the powder stability. The photocatalytic results showed that the grafted sample reached a degradation up to 8 times higher than pure P25. This functionalization method is easy to implement and stabilizes colloids starting from any pre-synthesized powder. This versatility widens the field of applications, and opens the door for further developments in areas such as coatings.