Biogenic synthesis of ZnO–TiO 2 nanocomposites using the marine macroalga Chaetomorpha crassa for sunscreen application

This study presents the biosynthesis of a ZnO-TiO2 nanocomposite using an aqueous extract of the green macroalga Chaetomorpha crassa for sunscreen application. Chaetomorpha crassa is a potential source of antioxidant and anti-inflammatory compounds. GC-MS analysis revealed bioactive compounds and phytochemical screening confirmed alkaloids and flavonoids. The extract showed a Total Phenolic Content of 5.26 ± 1.70 mg GAE/g and Total Flavonoid Content of 8.51 ± 0.75 mg QE/g, which may contribute to its antioxidant properties. The nanocomposite formed a grey suspension and was calcined to fine powder. UV-Visible spectroscopy showed a peak at 374.0 nm. FTIR identified functional groups potentially involved in nanoparticle formation, while XRD confirmed crystalline structure and phase purity. DLS showed a hydrodynamic diameter of 61.6 nm (PDI 0.43), SEM revealed rough spherical morphology and EDS confirmed Zn, Ti and O. The nanocomposite showed antioxidant (DPPH IC50 = 562.7 µg/mL) and anti-inflammatory (Egg albumin IC50 = 676.1 µg/mL) activities, while extract and nanocomposite exhibited antibacterial potential. Among four formulations, F1 was selected for its UVB protection (307.1 nm) and antibacterial activity, with an SPF of 17.35 ± 0.13. These findings suggest the potential of algae-mediated ZnO–TiO2 nanocomposites for further evaluation in cosmetic sunscreen applications.