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.

New evidence for TiO2 uniform surfaces leading to complete bacterial reduction in the dark: Critical issues

Juan Kiwi, Danièle Laub, Jelena Nesic, César Pulgarin, Sami Rtimi

This study presents new evidence for the events leading to Escherichia coil reduction in the absence of light irradiation on TiO2-polyester (from now on TiO2-PES. By transmission electron microscopy (TEM) the diffusion of TiO2 NP's aggregates with the E. coil outer lipo-polyssacharide (LPS) layer is shown to be a prerequisite for the loss of bacterial cultivability. Within 30 min in the dark the TiO2 aggregates interact with E. coil cell wall leading within 120 min to the complete loss of bacterial cultivability on a TiO2-PES 5% TiO2 sample. The bacterial reduction was observed to increase with a higher TiO2 loading on the PES up to 5%. Bacterial disinfection on TiO2-PES in the dark was slower compared to the runs under low intensity simulated sunlight light irradiation. The interaction between the TiO2 aggregates and the E. coil cell wall is discussed in terms of the competition between the TiO2 units collapsing to form TiO2-aggregates at a physiologic pH-value followed by the electrostatic interaction with the bacteria surface. TiO2-PES samples were able to carry repetitive bacterial inactivation. This presents a potential for practical applications. X-ray photoelectron spectroscopy (XPS) evidence was found for the reduction of Ti4+ to Ti3+ contributing to redox interactions between TiO2-PES and the bacterial cell wall. Insight is provided into the mechanism of interaction between the E. coil cell wall and TiO2 NP's. The properties of the TiO2-PES surface like percentage atomic concentration, TiO2-loading, optical absorption, surface charge and crystallographic phases are reported in this study. (C) 2014 Elsevier B.V. All rights reserved.

Elsevier Science Bv2014

Preparation, kinetics, mechanism and properties of semi-transparent photocatalytic stable films active in dye degradation

Juan Kiwi, César Pulgarin, Christophe Roussel, Laura Victoria Suárez Murillo

The photocatalytic activity, mechanism and characterization of polyethylene-TiO2 films (PE-TiO2) during the discoloration/degradation of methylene blue (MB) are reported in this study. PE-TiO2 films were prepared at moderate temperatures (similar to 90 degrees C). TiO2 did not leach out during discoloration/degradation of MB. This is a significant finding for a low temperature catalyst-polymer preparation leading to a stable repetitive MB degradation kinetics. MB discoloration on PE-TiO2 films proceeded showing a quantum yield of 0.25%. Band-gap irradiation of TiO2 was applied by way of a mercury medium pressure lamp to excite only TiO2 and avoid MB photosensitization. The nature of the oxidative radicals intervening in MB discoloration was investigated by scavenging experiments. The relative importance of the oxidative species during MB discoloration is: TiO(2)vbh(+) > HO2 center dot/O-2(center dot-) > O-1(2) > OH center dot. Evidence is presented for the superoxide anion-radical O-2(center dot-) at pH 6, as the main radical species leading to MB-discoloration. The MB-discoloration kinetic trend on PE-TiO2 followed the behavior observed for diffusion-controlled reactions. The diffusion distance of the HO2 center dot and OH center dot radicals during the discoloration of a solution MB 1 x 10(-5) mol L-1 were estimated as 71 and 2.2 mu m respectively. The OH center dot formation was assessed quantitatively during MB degradation by fluorescence measurements. The PE-TiO2 film at time zero presented a contact angle (CA) of similar to 92 degrees, decreasing within the five hour MB discoloration period to

Elsevier2016

Cu-decorated Raschig-TiO2 rings inducing MB repetitive discoloration without release of Cu-ions under solar light

Juan Kiwi, César Pulgarin, Rosendo Sanjines, Laura Victoria Suárez Murillo, Helena Luisa Teixido Pedarros

The methylene blue (MB) discoloration on innovative photocatalysts made up of Raschig-rings coated by pre-formed TiO2 nanoparticles decorated with CuOx (RR@TiO2-Cu) is presented. The MB-discoloration was drastically accelerated by the subsequent addition of 0.004% Cu. This Cu-content being similar to 3000 times below the TiO2 present in the RR@TiO2 samples led to MB-discoloration in shorter times. The Cu-ions released from the RR@TiO2-Cu 0.004% were determined 0.018% decreased the MB-discoloration kinetics due to the Cu acting as recombination sites for the photogenerated charges. The total organic carbon (TOC) reduction concomitant with the MB-discoloration is reported as well as the effect of the initial MB-concentration and pH on the discoloration kinetics. The Cu-addition shifted significantly the TiO2 absorption into the visible region even when added in sub-microgram quantities (0.004%) to RR@TiO2 as detected by diffuse reflectance spectroscopy (DRS). The Cu level added to RR@TiO2 was too low to be detected by X-ray diffraction (XRD). The roughness of the RR@TiO2-Cu (0.018%-0.081% Cu) presented Rg-values between 11.8 nm and 23.9 nm. The RR@TiO2Cu presented agglomerate sizes of similar to 200 nm for TiO2 and for the Cu aggregates sizes of similar to 20 nm. The MB discoloration kinetics and reuse of the RR@TiO2-Cu suggest the potential as a supported catalyst in environmental cleaning process. A reaction mechanism is suggested taking into consideration the role of the Cu1+/2+ intra-gap states involving redox catalysis as detected by X-ray photoelectron-spectroscopy (XPS). (C) 2016 Elsevier Ltd. All rights reserved.

Elsevier Sci Ltd2017