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Atomic layer deposition of ZnO and Al2O3 on cellulose for photocatalytic antibacterial performance

In the last 20 years, photocatalysis has become an important strategy for wastewater treatment. Various types of semiconductor-based photocatalysts, such as nano-sized metal oxides (TiO2, Fe2O3, ZnO, etc.), are used in water purification [1]. Among them, zinc oxide (ZnO) has attracted much attention as a promising candidate for environmental applications due to its important properties, such as the ability to generate strong oxidants like hydroxyl and superoxide radicals, low toxicity and high chemical and thermal stability, wide band gap (E = 3, 37 eV) and low cost. Many studies have shown that ZnO efficiently degrades organic and biological pollutants in addition to its antibacterial property [2]. Recently, atomic layer deposition (ALD) proved to be a suitable technique for the preparation of highly uniform and conformal inorganic layers with defined composition and structure on thermally sensitive polymer substrates. In this work, conformal coatings of ZnO and Al2O3 on cellulose fibers were prepared by atomic layer deposition (ALD) at low temperature. The antibacterial activity of cellulose, cellulose coated with a monolayer of Al2O3, and cellulose coated with Al2O3 and ZnO was tested against two bacterial species: gram- positive Staphyloccocus aureus and gram-negative Escherichia coli at UVA and in the dark. Surface morphology, conformity, composition and film thickness were studied using a field emission scanning electron microscope (FE-SEM) and SEM in transmission mode (TSEM). We also used X-ray photoelectron spectroscopy (XPS) to study composition and chemical bonding, and secondary ion mass spectrometry (SIMS) to study film uniformity and approximate thickness in detail. Cellulose samples coated with both Al2O3 and ZnO achieved higher photoinhibition for Escherichia coli and Staphyloccocus aureus within only 15 and 60 min, respectively, after UV irradiation compared with cellulose coated with a monolayer of Al2O3. Cell damage was assessed by analysis of FE- SEM and TSEM images. Our results show that cellulose fibers coated with Al2O3 and ZnO are a suitable material for efficient photocatalytic disinfection of water.

Photocatalytic antibacterial activity ; Atomic layer deposition ; Zinc oxide ; Thin films ; Cellulose

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