Sputtered Cu-polyethylene films inducing bacteria inactivation in the dark and under low intensity sunlight
This study addresses the preparation of uniform, adhesive and robust thin Cu-polyethylene films (PE-CuOx) by direct current magnetron sputtering (DCMS). Cu-coatings of 25 nm sputtered with 60W deposited 0.16% weight Cu/weight PE leading to the fastest bacterial inactivation under low intensity simulated sunlight irradiation equivalent to 20% AM1. These films were able to induce complete bacterial inactivation in the dark within 90 min and at a faster rate within 15 min under low intensity sunlight. Repetitive photo-induced bacterial inactivation was observed on the CuOx-PE. The Cu-released during the catalyst recycling in the ppb-range was determined by inductively coupled plasma mass spectrometry (ICP-MS) and showed the electrostatic interaction between bacteria and the CuOx-PE film. An increase in the applied light intensity accelerated the bacterial inactivation kinetics providing evidence for the semiconductor behavior of the CuOx film. By X-ray photoelectron spectroscopy (XPS), the binding energy (BE) of the Cu-species, were seen to shift after bacterial inactivation concomitantly with the variation in the atomic surface concentration percentage of Cu, O, C, N and S. Insight is provided for the reasons leading to the variation in the surface composition during the bacterial inactivation period. (C) 2016 Elsevier B.V. All rights reserved.