Stabilization mechanism of TiO2 on flexible fluorocarbon films as a functional photocatalyst

The repetitive discoloration kinetics of the azo-dye Methyl Orange (taken as a model organic compound) was followed under solar simulated radiation (90 mW/cm2) to assess the performance of the TiO2/Tedlar® composite photocatalyst. The influence of solution parameters on the photo-discoloration process: pH, dye concentration, applied light intensity and concentration of H2O2 were systematically investigated. During the photocatalysis a modification occurs in the TiO2/Tedlar® composite due to the TiO2 interaction with the Tedlar® film. Physical insight is given for the stabilization mechanism of the TiO2 particles in the Tedlar matrix based on the data obtained by X-ray photoelectron spectroscopy (XPS). The F 1s peak of the Tedlar film indicates that the TiO2 is loaded on the Tedlar fluoro-groups. The loading of TiO2 on the 75 μm thick Tedlar® film was 0.9% (w/w) as determined by atomic absorption spectrophotometry (AAS). Attenuated total reflection infrared spectroscopy (ATRIR) shows no formation of additional bands within the photodiscoloration reaction. This shows that an efficient catalysis taking place on the TiO2/Tedlar® surface. The rugosity (mean square roughness, rms) of the TiO2/Tedlar® film was determined by atomic force microscopy (AFM) to be 19.7 nm. This value remained constant during long-term operation. Transmission electron microscopy (TEM) reports the thickness and coverage of TiO2 Degussa P-25 on the Tedlar® surface before and after photocatalysis.

Highly dispersed PTFE/Co3O4 flexible films as photocatalyst showing fast kinetic performance for the discoloration of azo-dyes under solar irradiation

Michaël Bensimon, Juan Kiwi, Lioubov Kiwi, Danièle Laub, Albert Renken

Small nanosized clusters of Co3O4 coated on PTFE (polytetrafluoroethylene) flexible film is reported as a novel supported photocatalyst effective in the fast discoloration of the azo-dye Orange II under simulated solar radiation in the presence of oxone (2KHSO5·KHSO4·K2SO4). The photocatalytic discoloration of Orange II on the PTFE/Co3O4 films proceeds within minutes and the process could be repeated many times without a loss in photocatalyst stability. The photodiscoloration proceeds with a photonic efficiency of ∼1. The PTFE seems to act as a structure forming matrix for the colloidal Co3O4 coated on it surface leading to nanosized clusters of Co3O4. Monitoring the amount of Co2+-ions shows the Co2+-ions from the PTFE/Co3O4 during the photocatalysis enter the solution and at a later are stage re-adsorbed the Co3O4 crystallographic network (∼8 min). By elemental analysis (EA) the loading of Co-loading per cm2 PTFE film was found to vary between 1% and 2%. Transmission electron microscopy (TEM) shows the size of the Co3O4 clusters to vary between 3 and 10 nm. Electron dispersive spectrometry (EDS) confirms the presence of Co on the PTFE. X-ray photoelectron spectroscopy (XPS) of the PTFE/Co3O4 films reveal a partial reduction of the Co3O4 after Orange II discoloration leading to a substantial increase of the amount of Co(II) species in the Co3O4. Physical insight is provided into the catalyst film surface by carrying out Ar-sputtering of the PTFE/Co3O4 surface to remove the catalyst overlayers up to ∼20 nm.

2007

TiON and TiON-Ag sputtered surfaces leading to bacterial inactivation under indoor actinic light

Oualid Baghriche, Michaël Bensimon, Juan Kiwi, César Pulgarin, Sami Rtimi, Rosendo Sanjines

This study reports the details Escherichia coli inactivation kinetics on TiON and TiON-Ag films sputtered on polyester by direct current reactive magnetron sputtering (DC) and pulsed magnetron sputtering (DCP) in an Ar/N2 /O2 atmosphere. The use of TiON leads to bacterial inactivation avoiding leaching of Ag. The surface of TiON and TiON-Ag was characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), electron microscopy (EM), X-ray fluorescence (XRF) and contact angle (CA) measurements. Evidence for the photocatalyst self-cleaning after the bacterial inactivation was shown by XPS, contact angle (CA) and the Zetasizer zeta-potential of the proteins. The photo-induced charge transfer from Ag2 O and TiO2 is discussed considering the relative positions of the electronic bands of the two oxides. An interfacial charge transfer mechanism (IFCT) for the photo-induced electron injection is suggested. The most suitable TiON coating sputtered on polyester was 70 nm thick and inactivated E. coli within 120 min under low intensity visible/actinic light (400–700 nm, 4 mW/cm2 ). TiON-Ag sputtered catalysts shortened E. coli inactivation to ∼55 min, since Ag accelerated bacterial inactivation due to its disinfecting properties. Evidence is presented for the repetitive performance within short times of the TiON and TiON-Ag polyester under low intensity visible light.

2013

Thermal stability of size-selected copper nanoparticles: Effect of size, support and CO2 hydrogenation atmosphere

Alexandre Borsay, Mostapha Dakhchoune, Mo Li, Wen Luo, Kun Zhao, Andreas Züttel

Metal nanoparticles with a precisely controlled particle size distribution are ideal model catalysts for fundamental studies in catalysis. In this work, the thermal stability of size-selected Cu nanoparticles (Cu NPs) were deposited by magnetron sputtering, and their thermal stability was investigated using transmission electron microscopy and X-ray photoelectron spectroscopy. The influence of particle size, support, temperature, as well as CO2 hydrogenation atmosphere was systematically studied. We found that at 220 °C in ultra-high vacuum (UHV), carbon-supported 4 nm Cu NPs sintered through particle migration while the 8 nm Cu NPs were relatively stable. As the temperature increased to 320 and 460 °C, both samples sintered severely, and Ostwald ripening was suggested to be the dominant mechanism. In addition, we observed that SiO2 support can better stabilize Cu NPs upon heat treatment under both UHV and CO2 hydrogenation atmosphere (1 mbar of 1:1 CO2/H2 mixture), due to the stronger interaction between SiO2 and Cu compared to that between carbon and Cu. Furthermore, under a CO2 hydrogenation atmosphere, the stability of Cu NPs is suggested to be influenced by the interplay of redispersion, agglomeration, and volatilization. These findings from model systems can offer new insights for understanding the deactivation of Cu-based catalysts.

2020