Tailoring multifunctional properties of sol–gel derived Al-doped ZnO-films for environmental applications: structural, electrical, and photocatalytic insights

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Abstract Zinc oxide (ZnO) films are promising materials for photocatalysis and transparent electronics due to their wide band gap and chemical stability. This study investigates the influence of aluminum (Al) doping (0–5 wt%) on the structural, optical, electrical, and photocatalytic properties of sol–gel dip-coated ZnO films. Structural analysis confirmed that all samples preserved the wurtzite phase, with 3 wt% Al (AZ3) exhibiting the smallest crystallite size (27.4 nm) and high surface roughness ( R q = 21.2 nm). SEM observations showed enhanced grain aggregation and increased surface heterogeneity at this doping level, contributing to a maximum specific surface area of 0.262 km 2 kg −1 . These features led to improved optical transmittance (97%) and the lowest water contact angle (66.53°), indicating enhanced hydrophilicity. Under natural sunlight irradiation, AZ3 achieved the highest photocatalytic degradation efficiency of methylene blue (99.34%) and high adsorption capacity (8.26 mg g −1 ), with the process well described by the Langmuir adsorption isotherm model. These results confirm that moderate Al doping significantly improves ZnO-films’ multifunctionality for environmental and optoelectronic applications.