The effect of calcination temperature on structure and photocatalytic properties of Au/Pd nanoparticles supported on TiO2

• Published in: Applied catalysis. B, Environmental Environmental, 2014-06, Vol.152-153, p.202-211
• Main Authors: Cybula, Anna, Priebe, Jacqueline B., Pohl, Marga-Martina, Sobczak, Janusz W., Schneider, Matthias, Zielińska-Jurek, Anna, Brückner, Angelika, Zaleska, Adriana
• Format: Article
• Language: English
• Subjects: Au/Pd–TiO2 nanoparticles; Catalysis; Chemistry; Colloidal state and disperse state; Exact sciences and technology; General and physical chemistry; In-situ EPR; Metal re-distribution; Photocatalysis; Photochemistry; Physical and chemical studies. Granulometry. Electrokinetic phenomena; Physical chemistry of induced reactions (with radiations, particles and ultrasonics); Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry
• ISSN: 0926-3373; 1873-3883
• DOI: 10.1016/j.apcatb.2014.01.042

•Temperature rise from 350 to 700°C causes gold-enrichment in the surface region of Au/Pd particles.•Au/Pd–TiO2 calcined at 350 and 400°C have higher activity than those calcined from 450 to 700°C.•For all Au/Pd–TiO2 samples, O•− radical are mainly responsible for phenol degradation under UV.•Visible light irradiation led to the formation of carbon radical at the Au/Pd–TiO2 surface. TiO2 modified with Au/Pd nanoparticles have been prepared using a water-in-oil microemulsion system of water/AOT/cyclohexane followed by calcination from 350 to 700°C. The photocatalysts were characterized by scanning transmission electron microscopy (STEM), X-ray powder diffraction analysis (XRD), UV–vis diffuse-reflectance spectroscopy (DRS), BET surface area measurements and X-ray photoelectron spectroscopy (XPS). In-situ EPR spectroscopy was used to examine the relevance of paramagnetic species formation at the surface of Au/Pd–TiO2 photocatalysts under visible (vis) and UV–vis light excitation. The results show that enhancement of calcination temperature from 350 to 700°C resulted in a slight drop of Au/Pd–TiO2 photoactivity under UV and quite rapid drop under visible light. The Au/Pd–TiO2 samples calcinated at 350 and 400°C possess the highest photocatalytic activity when degrading phenol under visible light, which is more than 4 times of that of calcinated at 450°C. It was observed that increasing temperature from 350 to 700°C during calcination step, caused to segregation of metals and gold-enrichment in the shell region of Au/Pd bimetallic nanoparticles formed at the TiO2 surface and finally resulted in photoactivity drop. The Pd to Au ratio in the surface layer of Au/Pd nanoparticles decreased from 5:1 to 1:4 with temperature enhancement from 350 to 700°C, respectively. Based on EPR spectra, it seems that formation of O•− radicals is mainly responsible for phenol degradation under UV light for all Au/Pd–TiO2 samples, since organic radicals could be related to phenol degradation under visible light.