Preparation of photocatalytic films from recycled high-density polyethylene using black-TiO₂ and black-TiO₂/Ag nanoparticles towards NOx abatement

Novel films from recycled high-density polyethylene (HDPEr) were decorated with two photocatalysts: black TiO₂ (B-TiO₂) and Ag-loaded black TiO₂ (B-TiO₂-Ag). B-TiO₂ synthesis and Ag deposition were achieved through chemical reduction of their respective precursors. The films were prepared via extrusion and compression molding, with two photocatalyst incorporation methods evaluated: direct addition during extrusion and film immersion into aqueous photocatalyst suspensions, including plasma pre-treatment. The latter introduced polar functional groups, enhancing nanoparticle adhesion to the film surface. Results confirmed successful Ag deposition on B-TiO₂ via chemical reduction, with anatase reduction using NaBH₄ increasing Ti³⁺ sites. Interestingly, two oxidation states of Ag were detected in B-TiO₂-Ag. However, nanoparticle aggregation occurred during extrusion, likely due to poor compatibility between the polymer matrix and nanoparticles in terms of hydrophilicity, which plasma treatment mitigated. Regarding mechanical properties, nanoparticle incorporation via extrusion improved the Young’s modulus. Moreover, plasma-treated films exhibited significantly enhanced photocatalytic activity, leading to NO_x abatement. In standardized tests, films with B-TiO₂ and B-TiO₂-Ag achieved NO_X removal rates of 30.17 % and 40.80 %, respectively. This innovative approach valorizes HDPEr, offering a sustainable strategy for developing building materials that contribute to atmospheric pollution reduction.