Electrostatic and Ultrasound-Assisted Deposition of ZnO on Plasma-Activated Polypropylene: Toward Stable and Reusable Photocatalytic Surfaces

Abstract

ZnO nanoparticles were deposited onto oxygen plasma–modified polypropylene (PP) from aqueous suspensions at controlled pH (electrostatic) or by ultrasound-assisted deposition (UAD) to produce photocatalytic ZnO/PP surfaces. We systematically compared adhesion, nanoparticles dispersion, and photocatalytic performance. XPS verified plasma-generated oxygen functionalities that increased wettability and enabled ZnO immobilization. TOF-SIMS revealed mixed ZnO-hydrocarbon cluster ions uniquely for UAD samples, indicating enhanced interfacial coupling. Methyl orange degradation under UV-A showed comparable initial activity for optimized electrostatic deposition (pH 7–8) and UAD, demonstrating that performance is governed not only by ZnO loading but also by dispersion and accessibility of active sites. Despite higher loading near the ZnO point of zero charge, pH 7 coatings contained larger agglomerates and does not exhibited higher activity. Reusability tests showed progressive deactivation of electrostatically deposited ZnO, consistent with insufficient long-term adhesion, whereas UAD composites maintained stable activity over repeated cycles. SEM, XPS, and FAAS corroborated differences in ZnO loading and surface organization. Overall, combining plasma activation with UAD yields robust, durable ZnO/polymer composites suitable for reusable photocatalytic surfaces.