Self-cleaning modified TiO2-cotton pretreated by UVC-light (185 nm) and RF-plasma in vacuum and also under atmospheric pressure

Two new innovative findings presented in this study are: (a) TiO2-cotton fabrics obtained by pretreatment with UVC-light (185nm) at atmospheric pressure introduced functionalities into the cotton surface enabling the chelation/binding of TiO2. This was possible since the molar absorption coefficient of O-2 and N-2 is very low at 185 nm and (b) the radiofrequency (RF-plasma) pretreatment of cotton surface lead to the formation active binding sites on the cotton at atmospheric pressure. This unexpected RF effect was due to the drastic localized heating of the cotton leading to intermolecular H-bond breaking between the cellulose surface-OH groups of adjacent molecules with the formation of functionalized groups in the cellulose fibers. The discoloration kinetics of the wine stain on the TiO2-cotton pretreated by RF at atmospheric pressure for 10 min was the most favorable. The red wine stains discoloration under Suntest simulated light was monitored by diffuse reflectance spectroscopy (DRS) and by the CO2 evolution during the stain mineralization. By X-ray photoelectron spectroscopy (XPS) it was possible to monitor the decrease of the C, N, S-species on the textile topmost layers during the discoloration process. The XPS Ti 2p(3/2) peak shifts indicating Ti4+/Ti3+ oxido-reduction taking place during the photocatalysis. X-ray diffraction showed the formation of the anatase phase on the cotton. By X-ray fluorescence the loading of TiO2 before and after the discoloration process was found to be similar to 0.8%. High-resolution electron microscopy (HRTEM) shows transparent TiO2 anatase 8-18 nm coating the cotton with layers similar to 31 nm (+/- 10%). These 3-4 TiO2 layers on the cotton did not affect the touch or handling properties of the cotton enabling the potential commercial use of the TiO2-cotton fabrics. (C) 2009 Elsevier B.V. All rights reserved.

Inactivation of bacteria under visible light and in the dark by Cu films. Advantages of Cu-HIPIMS-sputtered films

Juan Kiwi, César Pulgarin

The Cu polyester thin-sputtered layers on textile fabrics show an acceptable bacterial inactivation kinetics using sputtering methods. Direct current magnetron sputtering (DCMS) for 40 s of Cu on cotton inactivated Escherichia coli within 30 min under visible light and within 120 min in the dark. For a longer DCMS time of 180 s, the Cu content was 0.294% w/w, but the bacterial inactivation kinetics under light was observed within 30 min, as was the case for the 40-s sputtered sample. This observation suggests that Cu ionic species play a key role in the E. coli inactivation and these species were further identified by X-ray photoelectron spectroscopy (XPS). The 40-s sputtered samples present the highest amount of Cu sites held in exposed positions interacting on the cotton with E. coli. Cu DC magnetron sputtering leads to thin metallic semi-transparent gray-brown Cu coating composed by Cu nanoparticulate in the nanometer range as found by electron microscopy (EM). Cu cotton fabrics were also functionalized by bipolar asymmetric DCMSP. Sputtering by DCMS and DCMSP for longer times lead to darker and more compact Cu films as detected by diffuse reflectance spectroscopy and EM. Cu is deposited on the polyester in the form of Cu2O and CuO as quantified by XPS. The redox interfacial reactions during bacterial inactivation involve changes in the Cu oxidation states and in the oxidation intermediates and were followed by XPS. High-power impulse magnetron sputtering (HIPIMS)-sputtered films show a low rugosity indicating that the texture of the Cu nanoparticulate films were smooth. The values of R (q) and R (a) were similar before and after the E. coli inactivation providing evidence for the stability of the HIPIMS-deposited Cu films. The Cu loading percentage required in the Cu films sputtered by HIPIMS to inactivate E. coli was about three times lower compared to DCMS films. This indicates a substantial Cu metal savings within the preparation of antibacterial films.

Springer Heidelberg2012

Innovative transparent non-scattering TiO2 bactericide thin films inducing increased E. coli cell wall fluidity

Mariusz Andrzejczuk, Juan Kiwi, Andrzej Kulik, César Pulgarin, Sami Rtimi, Rosendo Sanjines

This study presents the first account for transparent, non-scattering TiO2 films on radio-frequency (RF) plasma and ultraviolet light in the C-spectral region (UVC) pretreated polyethylene (PE). These pretreatments allow the PE to bind higher amounts of TiO2 necessary to induce E. coil inactivation in the minute range under simulated sunlight irradiation. The uniform TiO2 film was sputtered by direct current magnetron sputtering (DC). These higher TiO2 loadings were necessary to obtain faster bacterial inactivation kinetics on the PE films. The peak shifts in the stretching of the symmetric and asymmetric vibrational infrared spectra of the C H groups were followed during the time of bacterial inactivation (60 min). This time was concomitant with the time required for the hydrophobic to hydrophilic transition on PE-TiO2. The production of malondialdehyde (MDA) was observed during E. coli loss of viability. PE pretreatment led to a significant increase in the TiO2 loadings on the PE surface as shown by X-ray fluorescence (XRF), X-ray-diffraction (XRD) by X-ray photoelectron spectroscopy (XPS). (C) 2014 Elsevier B.V. All rights reserved.

Elsevier Science Sa2014

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

Inactivation of bacteria under visible light and in the dark by Cu films. Advantages of Cu-HIPIMS-sputtered films

Juan Kiwi, César Pulgarin

Springer Heidelberg2012