Green Synthesis of N/Zr Co-Doped TiO₂ for Photocatalytic Degradation of <i>p</i>-Nitrophenol in Wastewater

• Main Authors: Hayette Benkhennouche-Bouchene, Julien G. Mahy, Cédric Wolfs, Bénédicte Vertruyen, Dirk Poelman, Pierre Eloy, Sophie Hermans, Mekki Bouhali, Abdelhafid Souici, Saliha Bourouina-Bacha, Stéphanie D. Lambert
• Format: Article
• Language: English
• Published: MDPI AG 2021-02-01
• Series: Catalysts
• Subjects: ambient crystallization; photocatalysis; Zr/N doping; titania; aqueous sol-gel process; <i>p</i>-nitrophenol degradation
• Online Access: https://www.mdpi.com/2073-4344/11/2/235

TiO₂ prepared by a green aqueous sol–gel peptization process is co-doped with nitrogen and zirconium to improve and extend its photoactivity to the visible region. Two nitrogen precursors are used: urea and triethylamine; zirconium (IV) tert-butoxide is added as a source of zirconia. The N/Ti molar ratio is fixed regardless of the chosen nitrogen precursor while the quantity of zirconia is set to 0.7, 1.4, 2, or 2.8 mol%. The performance and physico-chemical properties of these materials are compared with the commercial Evonik P25 photocatalyst. For all doped and co-doped samples, TiO₂ nanoparticles of 4 to 8 nm of size are formed of anatase-brookite phases, with a specific surface area between 125 and 280 m² g⁻¹ vs. 50 m² g⁻¹ for the commercial P25 photocatalyst. X-ray photoelectron (XPS) measurements show that nitrogen is incorporated into the TiO₂ materials through Ti-O-N bonds allowing light absorption in the visible region. The XPS spectra of the Zr-(co)doped powders show the presence of TiO₂-ZrO₂ mixed oxide materials. Under visible light, the best co-doped sample gives a degradation of <i>p</i>-nitrophenol (PNP) equal to 70% instead of 25% with pure TiO₂ and 10% with P25 under the same conditions. Similarly, the photocatalytic activity improved under UV/visible reaching 95% with the best sample compared to 50% with pure TiO₂. This study suggests that N/Zr co-doped TiO₂ nanoparticles can be produced in a safe and energy-efficient way while being markedly more active than state-of-the-art photocatalytic materials under visible light.