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.

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.