γ-Radiation Induced Synthesis of Metal oxides
Control of Particle Size, Composition, and Morphology
Time: Fri 2021-09-17 10.00
Doctoral student: Zhuofeng Li , Tillämpad fysikalisk kemi, Mats Jonsson's group
Opponent: Professor Hynd Remita, Université Paris-Sud 11, Paris, France
Supervisor: Professor Mats Jonsson, Kemi, Tillämpad fysikalisk kemi
Nanomaterials show a significant difference in chemical, mechanical, electronic, magnetic and optical properties compared with bulk counterparts. The synthesis is a key-step to achieve the unique properties of nanomaterials. As an efficient, clean and straightforward approach, the γ-radiation induced synthesis has been extensively applied to fabricate metal nanoparticles. However, with regard to production of metal oxide nanoparticles via γ-radiation induced synthesis, the knowledge is still insufficient. The following metal oxides have been selected as synthesis substances in this thesis: Cu2O, MnO2, Mn3O4 and CeO2.
A prerequisite for utilization of the radiation-induced approach to engineer metal oxide nanomaterials is to optimize the reaction conditions for each specific nanofabrication case. The current study aims to understand the effects of different reaction conditions, i.e., pH, scavenger concentration, precursors, dose, and support materials, on the structural, and physico-chemical properties of the fabricated metal oxide nanomaterials.
The pH of the reaction plays an important role in determining the thermodynamically stable metal oxide products in radiation-induced synthesis. (Paper I). When using high concentration of solutes, i.e., isopropanol (used as a hydroxyl radical scavenger), the solvent effects must be considered (Paper I). It is found that different metal cation precursors (same element but different oxidation state) can result in metal oxides differing in composition and morphology under different radiation-induced redox conditions (Paper II). By gradually increasing the dose, ceria nanoparticles in different growth stages can be captured, and their morphological development is studied by TEM (Paper IV). Based on this, a mechanism for nucleation of ceria nanoparticles and mesocrystal growth is proposed as a function of the dose. Support materials, i.e., carbon black and PVP nanogel, are used to engineer supported metal oxides. The reactivity of carbon black towards water radiolysis products (Paper III), and the size-controlling effect of nanogel on produced metal/metal oxide nanoparticles (Paper V) are investigated in this thesis. In addition, for the view of application, the primary electrochemical properties of radiation-induced synthesized carbon black supported samples are studied (Paper II).