Anca Peter

Morphology, structure, and photoactivity of two types of graphene oxide-TiO2 composites

Two types of graphene oxide-TiO2 composites were prepared: one by including graphene oxide flakes in the TiO2 sol, followed by thermal treatment (GI composite) at 300°C, and the second by including graphene oxide flakes in the calcined (at 500°C) TiO2 xerogel (GII composite). The composites were characterized by SEM, TEM-EDS, TEM-SADP, STEM-HAADF, HRTEM coupled with FT, XRD, and XPS. Photocatalysis results were fitted to different kinetic models (pseudo-first and pseudo-second kinetics, intraparticle Weber-Morris diffusion, film diffusion, and external mass transfer). The results showed that by introducing graphene oxide flakes in the TiO2 sol, followed by thermal treatment at 300°C (GI composite), an efficient graphene oxide-TiO2 catalyst with high specific surface area, heterogeneity, and many graphitized areas can be obtained. Complete crystallization of the composite is not the key issue for the best photoactivity achievement. The rate limiting step in the photocatalytic process is the photooxidation of SA molecules on the TiO2 surface.

Changes in the microbiological and chemical characteristics of white bread during storage in paper packages modified with Ag/TiO2-SiO2, Ag/N-TiO2 or Au/TiO2.

Microbiological and chemical characteristics of white bread during storage in paper-packages modified with Ag/TiO2-SiO2, Ag/N-TiO2 or Au/TiO2 were investigated. The whiteness and the water retention of the modified packages were slightly superior to those exhibited by the reference sample, as the color of the composite was lighter. The water retention was very good especially for the Ag/TiO2-SiO2-paper. These improvements can be associated with the high specific surface area and with the low agglomeration tendency of Ag nanoparticles in comparison with the Au ones. The preservation activity of the composites for the bread storage is positively influenced by photoactivity and presence of nano-Ag. Packages Ag/TiO2-SiO2-paper and Ag/N-TiO2-paper can find their applicability for extending the shelf life of bread by 2 days as compared with the unmodified paper-package. No influence of the Au/TiO2 on the extending the shelf life of bread was observed.

Efficiency of Cu/TiO2 to remove salicylic acid by photocatalytic decomposition: kinetic modelling

Abstract Titanium dioxide has waste applications as photocatalyst, as antimicrobial material and in biomedical field. By modifying the surface of TiO2 with noble metals its photoactivity will be enhanced. This paper aims to explain the role of the copper particles deposited on titania surface during the photodecomposition of salicylic acid and to provide evidence about which kinetic model describes best the photocatalysis. The research explains why the photodecomposition rate of salicylic acid is higher in Cu/TiO2 composite as compared to in TiO2. It consists in kinetic approach of the photocatalytic behaviour of Cu–TiO2 and TiO2, thus being possible to discuss the photodecomposition mechanism. This research will allow improvement of the techniques to remove salicylic acid from synthetic solution. This could be extended to other organic pollutants.

UV Light-Assisted Degradation of Methyl Orange, Methylene Blue, Phenol, Salicylic Acid, and Rhodamine B: Photolysis Versus Photocatalyis

Methyl orange (MO), methylene blue (MB), phenol (F), salicylic acid (SA), and rhodamine B (ROD) were used as substrates during the photodegradation experiments in the absence and in the presence of nanostructured Ag/titania-silica. The catalyst was characterized by scanning electron microscopy (SEM), scanning transmission electron microscope high-angle annular dark field (STEM-HAADF), stereological analysis, nitrogen adsorption-desorption, and X-ray photoelectron spectroscopy (XPS) measurements. The results were fitted on pseudo-first and pseudo-second kinetic order models. The film diffusion was also determined. The photolysis degrades MO and F to a greater extent than the photocatalysis. The degradation of SA occurred at the same rate either by photolysis or by photocatalysis. MB was best removed by photocatalysis. With regard to the photocatalysis, the highest rates of film diffusion were obtained for MB, F, and ROD, meaning that these molecules crossed the film to arrive at the catalyst surface more rapidly than the others. For MO and MB, the results followed the pseudo-first-order kinetic model while for SA, F, and ROD, the pseudo-second-order kinetic model was more appropriate.

Structural characterisation of binary SiO2/TiO2 nanoparticle aerogels by X-ray scattering

The effect of SiO2 to TiO2 aerogels content on their local structure is evidenced from X-ray scattering measurements. TiO2-SiO2 aerogels were prepared by sol-gel method followed by supercritical drying with liquid CO2 and heat treatment. The local structure of TiO2-SiO2 system was investigated by analysing the atomic pair distribution function PDF, G(r), obtained from X ray scattering data The modified coordination radius values obtained for the first coordination spheres by addition of SiO2 denotes a diminution of the atom packing in this system. The PDF of the 300°C heat treated TiO2 aerogel sample shows well-defined features allowing an unambiguous structure search and refinement. In particular, the first peak in the PDF of the precursor phase is quite narrow and centered at about 1.9 A, which is the Ti-O distance in Ti-O6 octahedra. This observation shows that well-defined Ti-O6 octahedra are already formed during the homogeneous precipitation stage of the chemical process. Inspecting the data from the analysis of the atomic pair distribution function G(r) one remarks the occurrence of Si-O pair as a first coordination formation at a distance of 1.49 A and the interatomic distances at 2.18 A for the first Si—Si and 3.58 A for the second Si—Si bond.