In this paper, MgO nanoparticles (MNPs) were synthesized using simple wet chemical precipitation technique from evaporative brine as Mg ions precursor. The effect of NaOH concentration on morpho-structural and optical properties of as-synthesized nanoparticles was studied. The obtained nanoparticles were characterized by X-ray Diffraction (XRD), transmission electron microscopy (TEM), field emission scanning electron microscope (FESEM), energy dispersive X-ray (EDS), fourier transform infrared spectroscopy and UV–Vis absorption spectroscopy. The obtained structural properties (from XRD analysis) indicated that MNPs had pure cubic phase, high crystallinity, and average crystallite size and were in good agreement with TEM and FESEM characteristics. Also, increasing the concentration of the precipitator resulted in reduced crystallites size (from 37.09 to 17.61 nm), nanoparticles size (from 35–88 nm to 22–75 nm), and strain value (from 1.23 × 10^–3 to 0.57 × 10^–3). The optical properties of MNPs including absorption (A), transmittance (T), absorption coefficient (α), optical band gap energy (E_g), Extinction coefficient (k), and refractive index (n) were investigated using UV–Vis spectroscopy and examined in details.

In this work, synthesis and formation of porous magnesium hydroxide (MH) nanostructures were investigated by chemical precipitation and sonochemical method using hypersaline brine containing large amounts of CaCl ₂ , MgCl ₂ , NaCl and KCl. The effect of ultrasound waves was investigated on the morpho‐structural, surface and thermal properties were investigated by means of X‐ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, energy dispersive X‐ray spectrometer, Brunauer–Emmett–Teller and thermogravimetry‐differential thermal analysis techniques. It was indicated that ultrasound waves decreased grain and particle sizes of the sample which synthesised by sonochemical route (MH‐U). The MH‐U sample had a higher surface area, lower particle size, better particle distribution and lower transition temperature of MH to MgO.