## 3 Results
Morphologically, the formations exhibit platy and rod-like appearances, with thicknesses up to 60 nm. These structures predominantly form agglomerates due to the large specific surface area associated with their nanometric size. Figure 3: SEM micrographs (**a**,**a**,**a**,**a**,**b**,**b**,**b**,**b**,**b**,**b**,**b**), EDX spectra (**d**,**d**,**d**,**d**,**d**), and size distribution (**c**,**c**,**c**,**c**) by length and thickness for ZnO powders from Zn\({}^{2+}\) precursor concentration of 0.3488 mol/L after 15, 30, and 60 min reaction time. Figure 4: SEM micrographs (**a**,**a**,**a**,**a**,**b**,**b**,**b**,**b**) and size distribution (**c**,**c**,**c**) by length and thickness for ZnO powders from Zn\({}^{2+}\) precursor concentration of 0.1744 mol/L after 15, 30, and 60 min reaction time. The distributions of pore sizes and specific surface areas (SSAs) were estimated using the Brunauer-Emmett-Teller (BET) method and are presented in Table 2. The specific surface area is defined as the grain surface-to-volume or mass ratio and depends on the particle size and shape, generally increasing with decreasing particle size for spherical or cubical particles. Correlating the BET results from Table 2 with the size distribution mean values obtained after measuring 100 particles/platelets/rods in SEM images (presented in Table 2). Figure 5: SEM micrographs (**a**,**a**’,**a**’,**b**,**b**’,**b**’) and size distribution (**c**,**c**’,**c**’) by length and thickness for ZnO powders after 15 min reaction time with Zn\({}^{2+}\) precursor concentrations of 0.0872 mol/L, 0.0436 mol/L and 0.0218 mol/L. Figure 8), it is observed that a reduced reaction time leads to the smallest particles (in length). This consequently leads to a larger specific surface area of these ZnO powders (S1_15, S2_15, S3_15, S4_15, S5_15) and a potentially enhanced antimicrobial effect. When discussing the effect of the precursor concentration on the particle size and specific surface area, a strictly monotonic trend cannot be determined among these five samples. This might be attributed to the change in morphology observed when decreasing the Zn\({}^{2+}\) concentration, from mostly platelets and rod-like to rounded nanoparticles, with a higher tendency to agglomerate. However, the smallest SSA was registered for the S1_60 sample, associated with the longest reaction time and highest precursor concentration. These changes in shape, agglomeration, and the complexity of the pore structure can also determine the diverse values obtained for the pore size. The true density (the ratio between the dried sample's mass and the real measured volume) of the ZnO powders is shown in Figure 9. Different letters (a, b, c) were used to mark statistically significant differences between samples. For all variables with the same letter, the difference between the means is not statistically significant. If two variables have different letters, they are significantly different [29]. It is observed that the ZnO particle density increases with the decrease in Zn\({}^{2+}\) precursor concentration, with the highest value recorded for the S5_15 sample. A possible explanation might reside in the high frequency of small nanoparticles (below 50 nm in length) observed for this sample in particular (see size distribution graph in Figure 5) since the density is predicted to increase with decreasing  
Figure 6: Transmission electron microscopy (TEM) images (a,b), high-resolution transmission electron microscopy (HR-TEM) image (c), and selected area electron diffraction (SAED) pattern (d) for the S1_15 ZnO sample. size for nanoparticles [30]. When using a high concentration of precursor (S1_15, S2_15), the found values are similar to the theoretical density of ZnO, which is 5.606 g/mL.