Green Synthesis of ZnO/SnO₂ Hybrid Nanocomposite for Degradation of Cationic and Anionic Dyes under Sunlight Radiation

The aim of this work was to biosynthesize SnO₂-decorated ZnO (ZT) nanocomposites (NCs) of different Sn content (10, 20, and 30 mol%), namely, ZT10, ZT20, and ZT30, using Olea europaea leaf aqueous extract-based phytocompounds as nanoparticle facilitating agents for application as effective photocatalyst in the removal of dyes from polluted water. The obtained ZT NCs were characterized using various techniques, including FTIR, XRD, TGA, TEM, EDS, UV-Vis, PL, and BET surface area. X-ray diffraction patterns show that rutile SnO₂ and hexagonal ZnO coexist in the composites, and their crystallite size (D) is affected by the SnO₂ ratio; the obtained D-values were 17.24, 19.07, 13.99, 6.45, and 12.30 nm for ZnO, SnO₂, ZT10, ZT20, and ZT30, respectively. The direct band gaps of the ZT heterostructure increase with increasing SnO₂ ratio (band gap = 3.10, 3.45, 3.14, 3.17, and 3.21 eV, respectively). TEM spectroscopy revealed nanorod and spherical grain morphologies of the composites, while EDS confirmed the elemental composition, the element ratio, and the composite's purity. All catalysts exhibit type III isotherm with macropore structure. The photocatalytic efficiency against cationic (methylene blue (MB), rhodamine B (RB)), and anionic (methyl orange (MO)) dyes, under sunlight, was optimal with ZT20. The results revealed almost complete degradation at 55, 65, and 55 min, respectively. Hence, it is evident that incorporating SnO₂ improves the photocatalyst's performance, with an apparent optimal enhancement at 20 mol% Sn decorating ZT NCs. More interestingly, the catalyst stability and activity remained unaffected even after four activating cycles.