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

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

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

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

Innovative photo-Fenton catalysis by PE-FeOx films leading to methylene blue (MB) degradation: Kinetics, surface properties and mechanism

Huiyu Dong, Juan Kiwi, César Pulgarin, Rosendo Sanjines, Laura Victoria Suárez Murillo

This study reports an innovative preparation polyethylene-FeOx (PE-FeOx films) leading to the degradation of the methylene blue (MB) dye under low intensity sunlight/visible light (>400 nm). The intermediate highly oxidative radicals generated by PE-FeOx leading to MB discoloration/degradation in the presence of H2O2 were identified. The relative contribution to the MB discoloration by the Fe ions leached from the PE-FeOx films into solution was determined quantitatively. This allows estimating the contribution of the heterogeneous and of the homogeneous leading to MB-degradation. The shift in the peak binding energy (BE) for Fe was detected by photoelectron spectroscopy (XPS) after the MB degradation providing the evidence for redox catalysis occurring during MB-degradation at the PE-FeOx surface. The particle size and roughness of the PE-FeOx surfaces were determined by atomic force spectroscopy (AFM). The spectral properties of PE-FeOx films are reported and insight is provided for the mechanism of MB-degradation. (C) 2016 Elsevier B.V. All rights reserved.

Elsevier2016