AACVD system and protocol to fabricate CuO and Co3O4 nanostructured coatings for application as selective absorbent materials.

In the present work, an aerosol-assisted CVD (AACVD) system is described, together with a representative example of the synthesis of nanostructured coatings, which is an attractive alternative to being implemented at the industrial level. The semi-automated AACVD system synthesizes thin films or coatings of nanostructured materials, mainly metal oxides, and noble metals. Its main components, as well as its operation, are presented here. This simple AACVD method makes it possible to produce the coatings at relatively low temperatures and in a single step. Finally, the synthesis of CuO and Co3O4 nanostructured coatings deposited on stainless steel substrates is reported, which are excellent candidates for use as selective absorbent materials. The CuO and Co3O4 coatings present high quality and purity; no further thermal treatments are required to obtain the pure and crystalline phases. The main highlights of the proposed method are as follows: a)An AACVD System for depositing thin films and coatings designed and entirely fabricated at the Centro de Investigación en Materiales Avanzados, S.C.b)A low temperature (350 °C) synthesis protocol to obtain CuO and Co3O4 nanostructured coatings on stainless steel substrates.c)The CuO and Co3O4 coatings presented the optimum characteristics to be considered selective absorbent materials.

Aerosol-assisted CVD method for the synthesis of solid particles of t-YSZ-Fe3O4.

This work details the production of solid composite particles by the aerosol-assisted chemical vapor deposition method. With this method it is feasible to produce at low temperature (450 °C) the tetragonal phase of zirconium oxide stabilizing it with yttrium oxide (YSZ) and cubic iron oxide (Fe3O4) at the same time. The particles have a solid morphology in which both metal oxides coexist without mixing. The average size of the obtained particles is 329 ± 81 nm, moreover, each particle is formed by thousands of crystallites of size 2 ± 0.5 nm. The formation of solid structures is due to the amount of Zr and Y found in each particle. These particles can be applied as reinforcements of metallic structures. •A simple and low-cost method for producing composite particles to be applied as reinforcing agents for metal structures.•The particles are formed by two phases of tetragonal yttria-stabilized zirconia (t-YSZ) and cubic Fe3O4, which was synthesized following a one-step process via the aerosol-assisted chemical vapor deposition method (AACVD).•The tetragonal phase of ZrO2 is obtained at 450 °C stabilizing it with ∼3.8% of yttrium oxide.

On the Discoloration of Methylene Blue by Visible Light.

The discoloration of methylene blue in aqueous solution was studied under illumination by a fluorescent lamp, LEDs of red, green, and blue light, and a UV-A black light bulb. Overall results showed that methylene blue was discolored with and without the presence of any photoactive semiconductor. Outcomes depended on the combination substrate-light source employed. Photosensitization was assumed as the discoloration mechanism followed upon visible light irradiation. Fluorescence spectroscopy and high-performance liquid chromatography were used to investigate the possible intermediates formed in the irradiated solutions. The detailed nature of formed species was not stablished, but it was proved that the dye molecule photo-bleached and partially defragmented in several intermediates including leuco dyes, demethylated phenothiazine dyes, and probably humic substances. Since the fluorescence intermediates found were similar for most of the irradiated solutions, it was assumed that comparable reactive species were responsible for the discoloration of the molecule in solution. Results proved the misconception of discoloration experiments found in the literature when employing visible light near the absorption region of the dye.

Simplified route to multi-walled carbon nanotube synthesis by aerosol assisted chemical vapor deposition.

Uniform multi-walled carbon nanotubes (MWCNTs) were obtained decomposing toluene inside of fused silica tubing previously covered with Co oxide thin film. The two-step process, ruled successively in the same aerosol assisted chemical vapor deposition (AACVD) set up, constitutes a simplified route to the synthesis of MWCNTs. First, Co oxide thin film was deposited inside of fused silica tubing at 723 K, using a precursor solution of Co acetate in absolute methanol. After Co oxide deposition, the covered tubing was heated up to 1173 K under Ar flow, then a mist of toluene was injected inside the tubing, using also Ar as carrier gas, consequently MWCNTs were obtained in the internal wall of the tubing. The Co oxide film and the MWCNTs were analyzed by scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM) and atomic force microscopy (AFM). Uniform and very long MWCNTs (several tens of microm) with diameters around 20 to 100 nm were observed, with the advantage that the content of Co particles inside the nanotube was very low.

TEM evidence of ultrastructural alteration on Pseudomonas aeruginosa by photocatalytic TiO2 thin films.

The antibacterial efficiency of longwave UV-irradiated TiO(2) thin films as well as the ultrastructural damage on bacterial cells was evaluated using Pseudomonas aeruginosa as a model. The quantitative antibacterial efficiency assays showed a bacterial inhibition in the range of 32-72% at different times of irradiation. Transmission electron microscopy (TEM) was used to detect the effect of irradiation of TiO(2) thin films on the ultrastructure of the bacterial cell in order to reveal possible cellular damage. After 40 min irradiation, an abnormal cellular division was observed: instead of a normal septum, an 'elongated bridge' was formed. At a longer irradiation time, wavy structures all around the outer cell membrane were observed, and also some bubble-like protuberances, which expelled inner material. The mechanism of irreversible bacterial cell damage caused by the photocatalytic effect of TiO(2) could be related to abnormal cell division, aside from the reported physicochemical alteration of the cell membrane.

Photoinduced bactericidal activity against Pseudomonas aeruginosa by TiO(2) based thin films.

The photoinduced bactericidal capacity of TiO(2) based films was evaluated, using as model organism Pseudomonas aeruginosa. Thin films were obtained by spray pyrolysis; they included undoped, Cu doped, and Al doped TiO(2). Scanning electron microscopy was used to observe the final effect of the irradiated films upon the bacteria. Depending on the composition and characteristics of the films, quantitative experiments show that bacterial inhibition varies between 28 and 96%. The order of magnitude of the average quantum yield of the films was determined between 10(-9) and 10(-11) inhibited bacterial per photon.