The presented thesis comprises of 6 major chapters, clarifying synthesis of high quality nanoparticles (NPs) under microwave irradiation, presence of any kind of so-called “specific” or “non-thermal” microwave effects, continuous flow synthesis of NPs and exploration of their catalytic activity in organic reactions. In chapter A microwave assisted synthesis of CdSe quantum dots (QDs) with a narrow size distribution and high quantum yield was performed and the presence of non-thermal microwave effects was carefully investigated. Chapter B reports the continuous flow synthesis of CdSe QDs using an experimentally simple protocol. As a main part of this study, size tunability of the presented protocole was examined by varying different parameters like time, temperature, and flow rate. Additionally, the stability and reproducibility of the presented flow set-up was checked in an experiment involving an extended time period. Chapter C inspects the existence of selective microwave heating in the synthesis of CdSe NPs using SiC technology. In chapter D an environmentally friendly synthesis of silver nanocomposite on cellulose fibers under conventional and microwave assisted heating utilizing 6-O chitosan sulphate as reducing and stabilizing agent is presented. Chapters E and F elucidate the role of iron oxide NPs as an eco-friendly and relatively non-toxic catalyst in the reduction of nitro compounds. In chapter E an efficient and chemoselective method for the reduction of nitroarenes with hydrazine hydrate based on the in-situ generation of highly active Fe3O4 NPs is described. Following this study in chapter F supported iron oxide NPs on basic alumina was employed as a heterogeneous catalyst in a continuous flow reactor to produce functionalized aniline from corresponding nitroarenes. In addition, as one of the most important features of immobilized catalysts in continuous applications the ability of the nano-Fe3O4@Al2O3 to use over a prolonged time period was examined.