Innovative self-sterilizing transparent Fe–phosphate polyethylene films under visible light

Abstract

An account of stable, uniform and adhesive high-density polyethylene terephthalate Fe–phosphate (FeOx–POx–HDPET) sputtered thin films showing absorption in the visible region up to 700 nm compared to POx presenting absorption below 300 nm. These film were seen to induce bacterial inactivation in the minute range leading to repetitive E. coli inactivation without leaching Fe- and P- as determined by inductively coupled plasma mass-spectrometry (ICP-MS). By time-of-flight mass spectrometry (ToF-SIMS), the positive-ions (FeOOH, FeO⁺ and Fe₂P₃⁺) and of the negative-ions like PO₃⁻ were identified. The positive surface charge of the FeOx–POx–HDPET films (+60 mV) was determined and seems to favour the adhesion/interaction with the negative E. coli bacteria. Furthermore, the electrostatic positively and negatively charged species on the HDPET surface are reported in detail. The FeOx-clusters on HDPET presented sizes of 2–10 nm and a roughness, R_g, of 12 nm as determined by atomic force microscopy (AFM). The FeOx–POx–HDPET film under sunlight irradiation became super-hydrophilic within 30 min, a time shorter compared to the time needed for the complete bacterial inactivation (60 min). Evidence is provided by X-ray photoelectron spectroscopy (XPS) comprising the Fe₂O₃ reduction to FeO and Fe₃O₄ during the redox processes induced by the films during the bacterial inactivation time.