To broaden applications, increase environmental friendliness, reduce cost, and sustainability, water is a tempting choice as a solvent for waterborne polyurethane (WPU). WPU is a revolutionary step in the reduction of volatile organic contents in the field of green polymer chemistry. In the first part of the dissertation, eco-friendly emulsifier-free biodegradable WPU elastomers were synthesized via a two-step prepolymer process by using renewable ionomer lysine and aliphatic diamines as a chain extender (CE). Different series of WPU were synthesized by changing molecular weight (Mw) of soft segment (SS), NCO/OH ratio, length of CE, and methyl methacrylate (MMA) concentration. The focus of this research was to study the dependence of mechanical properties, thermal, surface, structural, and the drug delivery applications of WPU on length of CE, size of the hard segment (HS), NCO/OH ratio (3-4), molecular weight (Mw) of polyethylene glycol (PEG, Mw varies from 650 to 2000 g/mol), and concentration of MMA (10%-40%). Biodegradable WPUs were employed as the stimuli-responsive drug release matrix, loaded by cisplatin as a model anticancer drug. Sustained-drug release was studied by changing pH (4.4-7.4), polarity of drug release medium (solvents), temperature, concentration of MMA, Mw of PEG, length of CE and NCO/OH contents (3-4). So, drug release rate was adjusted under different conditions with the help of stimuli-responsive drug release WPU matrix. Semiconductor nanocrystals are potential resources for clean energy conversion and storage. In the 2nd part of this dissertation, the author focuses on the controlled synthesis of different magnetic nanoparticles (NPs) and robust photocatalytic systems, microwave absorber, and construction of anode material for a lithium-ion battery. Several scientific research achievements attained are as follows: (1) Eco-friendly, biocompatible, water dispersible, impurity-free, single-phase, citric acid surface capped, ultrafine-superparamagnetic magnetite nanoparticles (USM NPs) were prepared. USM NPs were synthesized by modifying wet chemical facile co-precipitation green itinerary. Size of USM NPs was tuned from 11-15 nm by controlling pH of reaction media. Citric acid, polyaniline, trimethoxy silyl propyl methacrylate, polyacrylamide, and polyamine surface-modified USM NPs ferrofluid was formed for different applications. Novel self-assembled morphologies of magnetite (Fe3O4) were controlled by using a facile, template-free hydrothermal pathway under optimized conditions engaging different precursors with the best control of morphology and electrochemical properties. A detailed study of the thermal, Controlled Synthesɨs and Potentɨal Applɨcations of Eco-friendly Polyurethane & Magnetɨc Nanomaterials xiv magnetic, dielectric, optical, and biological properties of USM NPs were conducted. Excellent reflection loss values confirmed that these USM NPs are promising microwave absorber which is very useful in satellite communications and EMR pollution control. USM NPs were further investigated for potential photocatalytic applications in dye degradation under visible light with detailed mechanism. (2) In the electric energy storage technology, lithium-ion battery (LIB) is a revolutionary step for making a green environment. The anodic material for LIB was made by using graphene-magnetite-polyaniline nanocomposite (Gr-Fe3O4-PANI NC) as a high-performance electrode. Gr-Fe3O4-PANI NC based LIB has shown superior reversible current capacity of 960 mAh g−1 and high cycling stability along with more than 99% coulombic efficiency even at a high current density of 5 Ag−1, low volume expansion, and excellent power capabilities over 250 cycles. (3) For the photocatalytic water oxidation application, morphologically-controlled pseudobrookite Fe2TiO5-TiO2 yolk-shell hollow spheres were synthesized by using facile sacrificial hard template strategy. The Fe2TiO5-TiO2 yolk-shell hollow spheres have exhibited high oxygen evolution reaction (OER) rate of 148 μmolg−1h−1 under UV-Vis light. So, designed Fe2TiO5-TiO2 yolk-shell hollow spheres are beneficial for the photocatalytic water oxidation. (4) Ultrapure hexagonal BaFe12O19 nanoferrite was prepared by a facile coprecipitation route. Crystallite size was found to grow from 50 nm to 78 nm when the annealing temperature increased from 800 °C to 1000 °C, respectively. The EMR absorption was obtained at a frequency of 2-18 GHz from VNA which showed maximum absorption of -26.52 dB at a frequency of 5.79 GHz