Pure and co-doped Zno/Sno2 nanostructured thin films: analysis of doping on methylene blue decolorization

In this work, ZnO–SnO₂ (ZS) thin films—undoped, Al-doped, Ag-doped, and Ag–Al co-doped—were deposited on glass substrates using nebulized spray pyrolysis (NSP). XRD confirmed the coexistence of wurtzite ZnO and rutile SnO₂ phases, with dopant incorporation, inducing lattice strain (7.1–8.2 µm/m) and crystallite size variations (14.5–16.2 nm). SEM revealed a change from dense dual-phase aggregates in undoped films to porous microstructures in Ag–Al co-doped samples. Methylene blue (MB) decoloration followed pseudo–first-order kinetics with rate constants (k) ranging from 0.022 to 0.026 min⁻¹. The Ag–Al co-doped ZS film achieved ~99 % MB decolorization within 120 min, outperforming other samples. The enhanced performance is attributed to the combined effects of electron trapping by Ag, oxygen-vacancy generation by Al, and the synergistic morphological changes, which together promote efficient charge separation and surface reactivity. NSP reliably produces tunable, efficient, and scalable ZnO–SnO₂ photocatalysts.