Superior UV Blocking, Biological and Suppressed Photocatalytic Properties of Melanoidins-Hybridized ZnO Nanocomposites

Topical sunscreens have emerged as a shield against prolonged exposure to ultraviolet (UV) radiations that have deleterious consequences on humans. To augment the UV-blocking efficiency and reduce photocatalysis, the present study reports the synthesis of hydrophilic xylose–lysine and hydrophobic xylose–valine melanoidins. The melanoidins were individually refluxed with hydroxylated ZnO nanoparticles (ZnO Nps) to produce xylose–lysine-hybridized ZnO (XL-Mel/ZnO) and xylose–valine-hybridized ZnO (XV-Mel/ZnO) through a simple hydrothermal reflux condensation reaction. The physicochemical properties of the nanocomposites were studied using UV–Vis–NIR, FT-IR, XRD, TGA, HR-TEM, EDX and DLS. The XL-Mel/ZnO and XV-Mel/ZnO exhibited tremendous sun protection factor of 123.00 and 74.80 at 25 wt%, respectively, when formulated with glycerol. This proved that melanoidins-hybridized ZnO (Mel/ZnO) exhibited a broad-spectrum protection against UVA-I, UVA-II and UVB radiations. The XL-Mel/ZnO and XV-Mel/ZnO nanocomposites displayed excellent antibacterial properties against E. coli and S. aureus with zone diameters of 24 mm and 20 mm at 10 mg/mL, respectively. Additionally, the free radical scavenging properties of XL-Mel/ZnO and XV-Mel/ZnO were outstanding with at least 50% inhibition potential. The photocatalytic behaviour of XL-Mel/ZnO and XV-Mel/ZnO was reduced by half compared to ZnO Nps due to the radical scavenging potential of hybridized melanoidins. Thus, the melanoidins-hybridized ZnO (Mel/ZnO) nanocomposites could act as a promising stand-alone constituent in sunscreens.