Solvent influence on the formation of ZnO nanoparticles by sonochemical technique and evaluation of UV-blocking efficiency

•ZnO nanoparticles were ultrasonically synthesised using [Zn(acac)2·H2O] without any additives.•Solvent (EtOH:H2O) plays a vital role in forming ZnO nanoparticles without the need for calcination.•Optical studies confirm the semiconducting nature of ZnO nanoparticles.•ZnO nanoparticles exhibit excellent UVA (98.1%), UVB (99.0%) blocking efficiency.•Mechanism reveals that water is responsible for the single step formation of ZnO nanoparticles. A highly efficient UV-shielding (>98.0%) ZnO nanoparticles (ZnO-A) have been synthesised sonochemically from [Zn(acac)2·H2O] and NaOH in ethanol-water mixture without any stabiliser or capping agent in a one-step process. In contrast, a combination of ultrasonic irradiation and calcination afforded pure ZnO nanoparticles (ZnO-B) with poor UV-blocking efficiency using ethanol as a solvent. A mechanism has been proposed indicating that water is the driving force to yield ZnO nanoparticles in a single step. X-ray diffraction (XRD) confirms hexagonal wurtzite structure for both products. UV–Visible (UV–Vis) spectra exhibit a broad peak at 355 nm and 360 nm corresponding to a bandgap of ∼3.49 eV and ∼3.44 eV for ZnO-A and ZnO-B. ZnO-A displays photoluminescence (PL) with violet (426 nm), blue (456 nm), and green (561 nm) emissions, while ZnO-B shows violet (428 nm) and blue (458 nm) emissions only. The field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) analysis reveal petal-like morphology for ZnO-A, whilst FESEM of ZnO-B shows aggregated nanostructures.