Continuous Photocatalytic Antibacterial Activity of AgNPs doped TiO2 Digital Printed on Commercial Porcelain-grès Tiles

Photocatalytic finishing materials, such as tiles or paints, are a productive as well as scientific reality. One of the most interesting photocatalytic material currently on the market is the porcelain stoneware which combines the beauty of a design product with hardness and absence of porosity and thus used for both floors and walls. The Ag- micrometric TiO2 allowed active ceramic slabs to be active under LED lights, bypassing the problem of the UVA radiation. SEM/TEM images in Fig. 1 indicate the full coverage of the porcelain surface (left image), besides a nanometric though heterogenous spreading of the AgNPs on top of the TiO2 matrix (right image). Figure 1. HR-SEM of the Active ceramic surface (left), TEM image of 8% AgNPs-TiO2(center); possible photocatalytic mechanistic pathways in Ag doped TiO2 system (right) An important question concerns the antibacterial action: in fact, today the role of silver is unknown when the metal is physically blocked on a surface and cannot penetrate and therefore interfere at the DNA level in the cellular barrier. The prepared porcelain Ag-TiO2 printed surfaces were tested against E. coli under solar and visible illumination and in the dark. To differenciate the semicondutor behavior and the ions mediated bacterial inactivation mechanism, porinless E. coli were used under band-gap irradiation. Stereomicroscopy analysis showed dead bacteria within 180 and 240 min respectively for normal E. coli and porinless E. coli. Using appropriate quenchers, the bacterial inactivation mechanisms under solar and visible light are proposed

Polystyrene CuO/Cu2O uniform films inducing MB-degradation under sunlight

This study reports on a Cu-sputtered film on polystyrene (PS) leading to the discoloration/degradation of methylene blue (MB) under low intensity solar simulated irradiation. Direct current magnetron sputtering (DCMS) was used to graft uniform, adhesive Cu/Cu oxides on the polystyrene substrate. The kinetics of Cu-PS mediated MB-discoloration adding H2O2 was observed to take place within 90-120 min. The surface potential and pH variation was followed on the Cu-PS surface during MB-discoloration. Insight is provided for the observed changes relating them to the dye discoloration mechanism. The concentration, mean-free path and lifetime of the oxidative radical leading to MB-degradation were estimated. The Cu/Cu-oxides on the PS were characterized by X-ray diffraction (XRD). X-ray photoelectron spectroscopy (XPS) evidence for redox catalysis involving Cu(I)/Cu(II)-species was detected during MB-discoloration. Also by XPS the surface atomic percentage concentration was determined for the topmost Cu-PS layers. The Cu-PS coatings were also investigated for their optical and crystallographic properties. (C) 2016 Elsevier B.V. All rights reserved

Accelerated self-cleaning by Cu promoted semiconductor binary-oxides under low intensity sunlight irradiation

Uniform adhesive TiO2–ZrO2 films co-sputtered on polyester (PES) under low intensity sunlight irradiation discolored methylene blue (MB) within 120 min. The discoloration kinetics was seen to be accelerated by a factor four by TiO2–ZrO2–Cu containing ∼0.01% Cu, as determined by X-ray fluorescence (XRF). TiO2–ZrO2–Cu also increased also accelerated by a factor the discoloration of MB compared to TiO2/Cu(PES). MB discoloration was also monitored under visible light in the solar cavity by using a 400 nm cutoff filter. Photocatalyst surfaces were characterized by spectroscopic methods showing the film optical absorption and by X-ray photoelectron spectroscopy (XPS), the surface atomic percentage concentration up to 120 nm (∼600 layers). The band-gaps of TiO2–ZrO2 and TiO2–ZrO2–Cu were estimated for films co-sputtered for different times. By Fourier transform attenuated infrared spectroscopy (ATR-FTIR), the systematic shift of the predominating νs(CH2) vibration-rotational MB bands was monitored up to complete MB discoloration under low intensity solar simulated light. Evidence is presented for the OHradical dot generation by TiO2–ZrO2–Cu participating in the self-cleaning mechanism. The photo-induced interfacial charge transfer (IFCT) on the TiO2–ZrO2–Cu is discussed in terms of the electronic band positions of the binary oxides and Cu intra-gap states. This study presents the first evidence for a Cu-promoted composed of two binary oxide semiconductors accelerating the self-cleaning performance

Innovative semi-transparent nanocomposite films presenting photo-switchable behavior and leading to a reduction of the risk of infection under sunlight

Novel sputtered polyethylene-TiO2 (PE-TiO2) thin films induce fast bacterial inactivation with concomitant photo-switchable hydrophobic to hydrophilic transition under light. RF-plasma pretreatments allowed an increased TiO2 loading on PE, favorably affecting the photocatalyst performance. ATR-FTIR spectroscopy shows that the increase in the cell lipid-layer fluidity leads to cell wall scission/bacterial inactivation

Deciphering the mechanisms of bacterial inactivation on HiPIMS sputtered CuxO-FeOx-PET surfaces : from light absorption to catalytic bacterial death

The production of nontoxic, affordable, and efficient antibacterial surfaces is key to the well-being of our societies. In this aim, antibacterial thin films have been prepared using earth-abundant metals deposited using high-power impulse magnetron sputtering (HiPIMS). The sputtered FeOx, CuxO, and mixed CuxO-FeOx films exhibited fast bacterial inactivation properties under exposure to indoor light (340–720 nm) showing total bacterial inactivation within 180, 120, and 60 min, respectively. The photocatalytic mechanisms of these films were investigated, from the absorption of photons up to the bacteria’s fate, by means of ultrafast transient spectroscopy, flow cytometry, and malondialdehyde (MDA) quantification justifying the cell wall disruption. The primary driving force leading to bacterial inactivation was found to be the oxidative stress at the interface between the sputtered thin films and the microorganism. This was justified by using engineered porinless bacteria disabling the possible ion diffusion leading to internal bacterial inactivation. Such stress is a direct consequence of the photogenerated electron–hole pairs at the interface of the sputtered layers. By diffuse reflectance spectroscopy, we found that both FeOx and CuxO present a band gap of ∼2.9 eV (>425 nm), while the mixed CuxO-FeOx thin film has a band gap below 2.3 eV (>540 nm). The structure and atomic composition of the films were characterized by energy-dispersive X-ray, X-ray photoelectron, and optical spectroscopy. While the composition and metal oxidation states are distinct in all three films, the difference in photocatalytic efficiency can, at first sight, be explained as the direct consequence of their absorbance and the unique interaction between Fe and Cu oxides in the composite film

Design, testing and characterization of innovative TiN–TiO2 surfaces inactivating bacteria under low intensity visible light

Ti was sputtered in a plasma chamber under a N2 atmosphere, depositing TiN films on polyester fibers. These films show a significant adsorption in the visible spectral region. A TiN layer 50 nm thick sputtered for 3 min under low intensity/actinic visible light led to the fastest bacterial inactivation (120 min). These innovative TiN nanoparticulate films were characterized by XPS, DRS and TEM

Adsorption of emerging pollutants on lignin-based activated carbon: Analysis of adsorption mechanism via characterization, kinetics and equilibrium studies

Lignin has been employed as a precursor to synthesize activated carbons with the aim of lignin-biomass revalorization. The properties of these activated carbons were compared, and the best adsorbent was employed to remove two emerging pollutants from water, acetaminophen and acetamiprid. The adsorption mechanisms of pharmaceutical and pesticide compounds were analyzed, modeled and interpreted via statistical physics models. In particular, adsorption kinetics and isotherms of acetaminophen and acetamiprid at temperatures between 20 and 60 ◦C were quantified experimentally. Equilibrium data were fitted to different statistical physics-based isotherm models to establish the corresponding adsorption mechanism. A double layer adsorption model with one type of functional group was the best to correlate and explain the removal of these organic molecules. Steric parameters for the adsorption of these organic compounds were also calculated thus determining that their adsorption was multi-molecular. At tested operating conditions, acetaminophen adsorption was endothermic, while acetamiprid removal was exothermic. Physical adsorption forces were expected to be responsible for the removal of both compounds. This study reports new insights on the adsorption mechanisms of relevant emerging pollutants commonly found in water worldwid

Grafted semiconductors on PE-films leading to bacterial inactivation: Synthesis, characterization and mechanism

This study reports the colloidal preparation FeOx, TiO2 and FeOx-TiO2 grafted on polyethylene (PE) films leading to bacterial inactivation. A fast bacterial inactivation was attained by the FeOx-TiO2 compared to the FeOx-PE film due to the interfacial charge transfer (IFCT) FeOx to the lower-lying TiO2 trapped states. A pH-decrease was observed during bacterial inactivation due to the formation of carboxylic acids on the grafted films and the recovery to the initial pH 7 after elimination of the intermediates was followed quantitatively during bacterial inactivation. The potential on the TiO2-PE, FeOx-PE and FeOx-TiO2-PE film surfaces decreased during the bacterial inactivation concomitant with the loss of the cell wall permeability. Different mechanisms for the photo-induced E. coil inactivation for random nanoparticulate FeOx-PE and FeOx-TiO2-PE films are suggested based on the experimental observations reported in this study. During the inactivation of E. coli, the Fe-ions were seen to leach out in amounts <= 0.45 ppm. This is within the EU sanitary allowed limits for industrial/drinking water. The wettability of the films was followed by contact angle measurements (CA) within the time of bacterial inactivation. By diffuse reflectance spectroscopy (DRS), the conversion of the Fe(III)-oxide to Fe(II)-oxide is reported during film recycling. The change in the Fe-oxidation states within the bacterial inactivation was further confirmed by X-ray photoelectron spectroscopy (XPS). (C) 2016 Elsevier B.V. All rights reserved

Coupling of narrow and wide band-gap semiconductors on uniform films active in bacterial disinfection under low intensity visible light: Implications of the interfacial charge transfer (IFCT)

This study reports the design, preparation, testing and surface characterization of uniform films deposited by sputtering Ag and Ta on non-heat resistant polyester to evaluate the Escherichia coil inactivation by TaON, TaN/Ag, Ag and TaON/Ag polyester. Co-sputtering for 120 s Ta and Ag in the presence of N-2 and O-2 led to the faster E. coil inactivation by a TaON/Ag sample within similar to 40 min under visible light irradiation. The deconvolution of TaON/Ag peaks obtained by X-ray photoelectron spectroscopy (XPS) allowed the assignment of the Ta2O5 and Ag-species. The shifts observed for the XPS peaks have been assigned to Ago to Ag2O and Ag-0, and are a function of the applied sputtering times. The mechanism of interfacial charge transfer (IFCT) from the Ag2O conduction band (cb) to the lower laying Ta2O5 (cb) is discussed suggesting a reaction mechanism. The optical absorption of the TaON and TaON/Ag samples found by diffuse reflectance spectroscopy (DRS) correlated well with the kinetics of E. coli inactivation. The TaON/Ag sample microstructure was characterized by contact angle (CA) and by atomic force microscopy (AFM). Self-cleaning of the TaON/Ag polyester after each disinfection cycle enabled repetitive E. coil inactivation. (C) 2013 Elsevier B.V. All rights reserved