Modification of TiO2 nanoparticles by heteropolyoxometallates leads to visible light absorption, photocatalytic and photosensitized processes under UV and visible light irradiation respectively

J. RENGIFO-HERRERA; M. BLANCO; L. PIZZIO

Washington D.C.

Conferencia; NanoTech 2015, Advanced Materials & Applications, TechConnect World Innovation Conference; 2015

TechConnect

TiO2 nano-spherical particles prepared by sol-gel method were modified with tungstophosphoric (TPA) and tungstosilicic acid (TSA) at 30% (w/w) and then annealed at 500 ºC during 2 h. Materials were characterized by multi-techniques such as: scanning electron microscopy with energy dispersive x-ray spectroscopy (SEM-EDS), FT-Raman spectroscopy, X-ray photo-electron spectroscopy (XPS), X-ray diffraction (XRD), diffuse reflective spectroscopy (DRS), 31P magic angle spinning-nuclear magnetic resonance (31P MAS-NMR), and N2 adsorption-desorption isotherms at the liquid-nitrogen temperature to estimate the specific surface area using the Brunauer-Emmett-Teller (BET) method. Acidity and isoelectric point measurements were also done. DRS results show evidence about the visible light absorption of TiO2-TPA and TiO2-TSA. MAS NMR, XPS and FT-Raman characterization revealed evidence about a strong interaction between Keggin anion of TPA, TSA and TiO2 surfaces perhaps promoted by the formation of surface heteropolyacids-TiO2 complexes; this latter should be responsible of its visible light absorption. Photocatalytic activity was evaluated in degradation of malachite green, a cationic triphenylmethane dye and 4-chlorophenol aqueous solutions under UV-A and visible light irradiation. Under UV-A light, TPA and TSA-TiO2 materials showed high photocatalytic activity towards malachite green degradation even higher than TiO2 P-25. Under visible light irradiation, malachite green oxidation was achieved while 4-chlorophenol underwent only 20-30% of degradation. Mechanisms of photocatalytic oxidation either under UV-A and visible irradiation are discussed.