ZnO nanoparticles (NPs) with size less than 100 nm were successfully prepared by a hybrid electrochemical-thermal method using metallic zinc and NaHCO 3 without the use of any zinc salt, template or surfactant. The NPs were characterized by Fourier transform infra-red (FT-IR) spectroscopy, UV-visible spectroscopy, photoluminescence spectroscopy (PL), thermo-gravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) spectroscopy. UV-visible spectral analysis indicated that the particle size increased with increasing calcination temperature. The band gap (3.91-3.83 eV) was higher for synthesized ZnO NPs than their bulk counterparts (3.37 eV). The FT-IR spectra at different calcination temperatures showed the characteristic band for ZnO at 450 cm -1 to be prominent with increasing temperature due to the conversion of precursor into ZnO. The wurtzite hexagonal phase was confirmed by XRD analyses for ZnO NPs calcined at 700 o C. The green photoluminescent emission from ZnO NPs at different calcination temperatures is considered to be originated from the oxygen vacancy or interstitial related defects in ZnO. SEM images clearly showed that the NPs are granular and of almost uniform size when calcined at higher temperatures. EDX spectra further confirmed the elemental composition and purity of ZnO obtained on calcination at 700 o C. The NPs are well dispersed near or above calcination temperature of 700 o C.

Nanocrystalline Fe3O4 and Fe2O3 particles were successfully synthesized by an innovative hybrid electrochemical-thermal method. The as-prepared compound was calcined for an hour from 100 to 600oC temperatures. The crystallinity, morphology and chemical state of the synthesized powders were characterized by XRD, TG-DTA, SEM/EDS, FT-IR, and UV–Vis spectral techniques after calcinations. The Brunauer–Emmett–Teller (BET) plots confirmed that iron oxide nanoparticles (NPs) calcined at 400oC has a surface area of 18.28 m2 g-1 with a total pore volume of 0.2064 cc g-1. From XRD pattern it is revealed that the precursor calcined at lower temperature (100-400oC) correspond to Fe3O4,while the ones calcined at higher temperature follow Fe2O3 pattern. The morphology of iron oxide NPs calcined at different temperatures were studied with scanning electron microscope (SEM) and exhibits spherical shaped geometries with average diameters of 80-150nm. Bangladesh J. Sci. Ind. Res.55(3), 221-228, 2020