This study presents the green synthesis and characterization of aluminum-doped tin oxide (SnOx:Al) nanostructures for application in carbon dioxide (CO2) sensing. Using lemon peel extract as a bio-reducing agent, SnOx nanoparticles doped with 4 wt% Al were fabricated through a wet-chemical precipitation method and processed into porous thin films. Comprehensive characterization using FTIR, XRD, DLS, SEM, and EDS confirmed successful doping, crystalline tetragonal rutile (cassiterite) phase formation, uniform nanostructure distribution, and porous morphology. The resulting SnOx:Al sensor demonstrated enhanced sensitivity, fast response, and effective recovery across a range of CO2 concentrations (20-100 ppm) at 300 °C. Aluminum doping was shown to improve electronic conductivity, reduce particle size, and increase oxygen vacancies, thereby boosting gas adsorption and sensor performance. The green synthesis route not only supports sustainable material development but also validates the potential of Al-doped SnOx nanostructures as efficient and eco-friendly CO2 sensors.
