Uniform TiO2/In2O3 surface films effective in bacterial inactivation under visible light

This study shows that the surface modification of TiO2 is an effective route to increase the TiO2 absorption in the visible region up to similar to 600 nm for photocatalytic applications. The In2O3 decorated TiO2 films on polyester obtained by reactive sputtering were shown to accelerate the Escherichia coli inactivation under actinic and simulated solar light. TiO2 sputtered films for 10 min inactivated bacteria within 300 min under actinic light. The inactivation time was reduced when using a TiO2 10 min-In2O3 10 s sample to 150 min when using actinic light and 90 min by simulated sunlight with 50 mW/cm(2) (one half of AM1). Thinner TiO2-In2O3 coatings led to faster bacterial inactivation compared to thicker TiO2-In2O3 layers due to the reverse diffusion of the generated charges. The increase in the optical absorption of the green coloured TiO2-In2O3 film was a function of the In2O3 loading as detected by diffuse reflectance spectroscopy (DRS). Evidence of the lack of TiO2 lattice doping by the sputtered In2O3 was found by X-ray diffraction spectroscopy (XRD). The deconvolution of TiO2 bands detected by X-ray photoelectron spectroscopy (XPS) revealed the existence of Ti4+/Ti3+ signals suggesting redox catalysis at the surface of the TiO2-In2O3. The photo-induced interfacial charge transfer (IFCT) between TiO2 and In2O3 can be accounted for by the band position potentials of both semiconductors. The faster kinetics of TiO2-In2O3 inducing E. coli inactivation with a higher quantum efficiency compared to TiO2 takes place in spite of the low intensity of the IFCT optical absorption bands >400 nm.

Influence of gold particle size on the photocatalytic activity for acetone oxidation of Au/TiO2 catalysts prepared by dc-magnetron sputtering

Francis Lévy

Two series of Au/TiO2 materials with different gold content have been prepared by dc-magnetron sputtering on ceramic shaped pure anatase or Degussa P25 TiO2. The time of deposition was varied between 1 and 20 min in order to obtain different thickness and nanoparticle size of the gold films. For comparison samples with Au loadings in the range 0.3-0.9 wt% were prepared using the deposition-precipitation methodology. The obtained materials were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS). DR-UV-Vis and atomic force and scanning electron microscopy techniques. The photocatalytic activity was checked in the photo-oxidation of acetone under both UV and visible irradiation conditions. Several factors were found to influence the photoactivity. An optimal Au content corresponding to a maximum activity is observed and attributed to the occurrence of adequate titania surface coverage and Au particle size. The support plays an important role and it was found that pristine anatase on which gold (average particle size 7.7 nm) was deposed by dc-reactive sputtering exhibits the maximum of the activity. Samples prepared by dc-sputtering were more active than samples prepared by deposition-precipitation method. Also, the photocatalysts prepared using dc-reactive sputtering showed activity under both UV and visible light irradiation, while those prepared using the deposition-precipitation technique are active only under UV light. The most likely mechanism of gold activation of titania is that upon light absorption, gold nanoparticles inject electrons into the titania conduction band. (C) 2011 Elsevier B.V. All rights reserved.

2011

Introduction of oxygen vacancies and fluorine into TiO2 nanoparticles by co-milling with PTFE

Benjamin Bauer, Vincent Laporte

Solid-state processes of introducing oxygen vacancies and transference of fluorine to n-TiO2 nanoparticles by co-milling with poly(tetrafluoroethylene) (PTFE) powder were examined by diffuse reflectance spectroscopy (DRS) of UV, visual, near- and mid-IR regions, thermal analyses (TG-DTA), energy-dispersive X-ray spectroscopy (EDXS), X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD). The broad absorption peak at around 8800 cm(-1) (1140 nm) was attributed to the change in the electronic states, viz, electrons trapped at the oxygen vacancies (Vo) and d-d transitions of titanium ions. Incorporation of fluorine into n-TiO2 was concentrated at the near surface region and amounted to ca. 40 at% of the total fluorine in PTFE, after co-milling for 3 h, as confirmed by the F1s XPS spectrum. The overall atomic ratio, F/Ti, determined by EDXS was 0.294. By combining these analytical results, a mechanism of the present solid state processes at the boundary between PTFE and n-TiO2 was proposed. The entire process is triggered by the partial oxidative decomposition of PTFE. This is accompanied by the abstraction of oxygen atoms from the n-TiO2 lattices. Loss of the oxygen atoms results in the formation of the diverse states of locally distorted coordination units of titania, i.e. TiO(6-n)Vo(n), located at the near surface region. This leads subsequent partial ligand exchange between F and O, to incorporate fluorine preferentially to the near surface region of n-TiO2 particles, where local non-crystalline states predominate. (C) 2012 Elsevier Inc. All rights reserved.

2012

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.

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