For efficient and successful mechanical energy harvesting, a configuration that has garnered much focus in recent research is the piezoelectric nanogenerator. The concept of the nanogenerator has shown potential for harvesting energy from the ambient environment to power systems. Kinetic energy harvesting nanogenrators based on the piezoelectric properties of ZnO nanowires have attracted much interest. The aim of this work is to fabricate hydrothermally synthesized ZnO nanowire-based nanogenerators in order to control the average diameter of wires and also the quality of wire alignment. Intrinsic point defects as well as extrinsic defects introduced via doping of transition metal ions by no doubt play a crucial role not only the amplitude of generated voltage signal from nanogenerators but also the conductivity of ZnO. Despite its advantages, the lack of fundamental knowledge about intrinsic defects and doping ions presents an obstacle to the development of practical devices such as nanogenerators which requires high conductivity for high performance. The difficulty to make reliable ZnO nanowire based nanogenerators is closely related to the intrinsic and extrinsic defects specifically interstitials, vacancies and metal ions (i.e., Mn, Fe). This research provides a fundamental understanding of defects in ZnO that could lead to reliable devices using the peculiarity of nanogenerator. The results of electronic (electron paramagnetic resonance spectroscopy), optical (photoluminescence spectroscopy) and electrical (impedance spectroscopy) characterization investigations could give the basis for the industrial and economic manufacturing of ZnO nanowires. This work provides physical understanding of the defect structures in nanoscale wire form of ZnO.
Novel cost-efficient Fenton-like catalysts were prepared for the degradation of organic molecules in aqueous solutions. Porous activated carbons (ACs) were directly impregnated with Fe2+ solutions of different concentrations using the wet impregnation method. Their efficiency, as Fenton-like catalysts, was studied. Photo-Fenton tests were performed to establish the performance of the prepared Fe-impregnated ACs in relation to the degradation of organic micropollutants in aqueous solution, under different conditions. Photo-catalytic tests were carried out by means of a laboratory photo-reactor. The influence of several parameters such as solution pH value, initial concentration of the model pollutant, and hydrogen peroxide dose on the process performance was investigated. The ACs and prepared catalysts were characterized by nitrogen adsorption-desorption isotherms at 77K, FTIR, SEM, and thermogravimetric analyses. The total Fe content of the synthesized composites was estimated by the phenanthroline method using UV-Vis spectrophotometry. Photo-catalytic tests were performed in monosolute or mix solutions of MPs in order to compare the efficiency of various conventional AOPs with that of photo-Fenton-peroxone process. The results show an increase in the degradation rate in case of the heterogeneous photo-Fenton-peroxone process.