PhD Defense by Usuma Naknikham
Usuma Naknikham, Department of Chemistry and Bioscience will defend her thesis on: "Multifunctional TiO2-graphene oxide materials for water purification"
12.04.2019 kl. 13.00 - 16.00
"Multifunctional TiO2-graphene oxide materials for water purification"
Nanocomposites of titanium dioxide (TiO2) and graphene oxide (GO) are interesting materials for applications in water purification, since they have excellent photocatalytic activity, chemical stability, and high surface area for the adsorption of water pollutants. Many of the previous studies have focused on the optimization of TiO2-GO nanocomposites to improve their photocatalytic activity under UV light for the degradation of organic dyes as model pollutants. However, the proposed synthesis procedures are often complicated and costly. Moreover, common water pollutants have electronic structure and adsorption properties much different than those of organic dyes. Therefore, this study addressed the development of environment friendly preparation procedures for TiO2-GO materials. The new materials were tested for their ability to eliminate phenol from water under simulated solar light. This study aims to give a deeper understanding of the chemical nature of TiO2-GO nanocomposites, since the rational designing of TiO2-GO relies on our ability to tailor the final chemical properties of these materials.
Enhanced TiO2-GO composites were synthesized via the sol-gel method at pH 6 in a stirred mixture solution in a glass beaker at 60-100°C or in a static vessel at 100-200°C, where TiO2 nanocrystals formed and anchored over GO sheets, due to the in-situ nucleation and growth of TiO2 on GO plans. In addition, TiO2 nanoparticles agglomeration and crystal size distribution were controlled by the GO loading. X-ray photoelectron spectroscopy (XPS) of our nanocomposites showed the presence of Ti-O-C bonding at the interface. Such type of interaction induces the stabilization of TiO2 and GO during thermal treatment, i.e., it retards both TiO2 phase transitions and GO reduction. Moreover, Ti-C bonding was observed for samples synthetized at ≥ 175°C. Both types of interface bonding are believed to influence the physical and chemical properties of TiO2-GO composite materials and hence their photocatalytic performances.
The photocatalytic activity of the new materials was tested for the degradation of 10 ppm phenol under simulated solar light for 3 hours. The TiO2-GO composite synthetized at 200°C with a GO loading of 0.05 wt% (0.05GTS-200) showed the highest photocatalytic activity: 4.6±0.1 10-3 min-1. The enhanced activity of this sample can be explained by considering its structural features. This nanocomposite combines Ti-O-C and Ti-C interface bonding, TiO2 particles are enclosed by GO single layers or thin ribbons, and the particles contain high anatase fraction (92%) and less residual oxygen functional groups on GO (AC-O/AC-C and AO-C=O/AC-C are 0.24 and 0.13, respectively). The structure of TiO2-GO composites is also strongly influenced by the synthesis temperature and it was possible to obtain GO atomic monolayers decorated with TiO2 nanoparticles or TiO2–GO core-shell structures. But the latter ones are not desirable for photocatalytic applications, because they hinder the excitation of TiO2 photocatalytic centers via visible light.
GO membranes were prepared with various thicknesses from 0.2 to 1.4 μm simply by vacuum filtering GO dispersions with defined concentration. Continuous films were obtained for nanocomposites with TiO2 (P25) loading up to 80%. Intercalation of TiO2 nanoparticles within GO reduces the thickness of GO nanoribbons in the membranes, but does not change the distance between GO monolayers. Therefore we expect that the membrane selectivity is preserved. These findings could stimulate further development of TiO2-GO photocatalytic membranes.
SUPERVISOR and co-supervisor:
- Supervisor: Professor Yuanzheng Yue, Dept. Chemistry and Bioscience, AAU, Denmark
- Co-supervisor: Associate Professor Vittorio Boffa, Dept. Chemistry and Bioscience, AAU, Denmark
- Associate Professor Peter Roslev, Dept. Chemistry and Bioscience, AAU, Denmark
- Associate Professor Fernando Sebastián García Einschlag, Faculty of Exact Sciences,
University of La Plata, Argentina
- Associate Professor Alessandra Bianco Prevot, Department of Chemistry,
University of Torino, Italy
AFTER THE DEFENSE A SMALL RECEPTION WILL BE HELD AT FREDRIK BAJERS VEJ 7H.
Department of Chemistry and Bioscience, AAU, Section of Biotechnology
Fredrik Bajers Vej 7H, 9220 Aalborg Ø, room number: 1.102-1.106