2D-Titanium dioxide nanosheets modified with Nd, Ag and Au: Preparation, characterization and photocatalytic activity

• Published in: Catalysis today 2017-03, Vol.281, p.165-180
• Main Authors: Pližingrová, Eva, Klementová, Mariana, Bezdička, Petr, Boháček, Jaroslav, Barbieriková, Zuzana, Dvoranová, Dana, Mazúr, Milan, Krýsa, Josef, Šubrt, Jan, Brezová, Vlasta
• Format: Article
• Language: English
• Subjects: EPR spectroscopy; Lyophilization; Modified titanium dioxide; Photocatalysis; Plasmonic effect; Spin trapping
• ISSN: 0920-5861; 1873-4308
• DOI: 10.1016/j.cattod.2016.08.013

[Display omitted] •Nd-, Au- and Ag-modified 2D-TiO2 were synthesized by lyophilization and annealing.•TiO2 nanosheets reveal foiled morphology (lateral size ∼100μm, thickness ∼20nm).•Anatase nanocrystals dominate in 2D-TiO2 nanosheets annealed at 500, 650 or 800°C.•Nd is built into anatase structure, Au and Ag form nanoparticles on TiO2 surface.•Modified 2D-TiO2 show lower UV-activity and minimal visible-light activity. 2D-Titanium dioxide nanosheets modified by the addition of Nd, Au and Ag dopant in the first reaction step were synthesized from the lyophilized aqueous colloids of peroxo titanic acid by high-temperature treatment. The concentration of the dopant in the sample was 1at.% towards Ti. The results of their detailed morphological and phase characterization (SEM, TEM with EDX, XRD) evidenced that annealing temperatures 500, 650 and 800°C caused the formation of 2D-foils composed of packed anatase nanocrystals; samples annealed at 950°C represent anatase/rutile mixture. While neodymium dopant is built into the structure of anatase causing the changes in the parameters of anatase crystal lattice, such alterations were not found for Au- and Ag-modified samples, with gold or silver nanoparticles dispersed on surface detected by TEM/ED/EDX. Q-band EPR spectra of modified 2D-TiO2 annealed at 800°C measured at room temperature or 100 K revealed the presence of paramagnetic signals corresponding to Ti(III) centers inside the anatase lattice, along with signals associated with medium-polarized conduction electrons, already before exposure. The photoinduced generation of paramagnetic species (e.g., Ti(III), O−, O2−) upon UVA exposure of modified 2D-TiO2 was confirmed by X-band EPR spectroscopy. Moreover, EPR spectra evidenced that Au- or Ag-modified samples annealed at 500°C contained nitrogen paramagnetic species (Nb• and NO) coming from the aqueous ammonia used in synthesis, which are responsible for the visible-light activity of these samples. The tests of photocatalytic activity of modified 2D-TiO2 dispersed in water or dimethylsulfoxide performed using EPR spin trapping technique or via the decomposition of 4-chlorophenol showed a decline in UVA photoactivity for all modified titania samples in comparison to the unmodified 2D-TiO2; visible-light activity of modified 2D-TiO2 nanosheets annealed at 800°C was almost negligible.