Abstract In this work, we describe the application of a micro-spatial thermal lens spectroscopy setup (thermal lens microscope, TLM) with coaxial counter-propagating pump, and probe laser beams, and an integrated passive optical Fabry-Perot, to quantify the Cr-VI concentration in water during a photocatalytic reaction in-situ. A series of test samples was analyzed using the 1.5 diphenil carbazide colorimetric method. A calibration curve was obtained by plotting of the TLM signal as a function of the concentration of Cr(VI) in a range between 0 and 10 μg/L (1 𝜇g/L = 1 ppb, part per billion), with a detection limit of 53 ng/L (1 ng/L = 1 ppt, part per trillion). A solution of 10 𝜇g/L Cr(VI) in distillated water was placed into a cell in contact with an iron-incorporated titanium dioxide film, which was previously grown onto a 1 mm thick glass microscope slide by the sol-gel dip-coating technique. The TLM signal was registered as a function of the photocatalysis time measured from the beginning of the process, radiating the film with UV-violet light. The Cr(VI) concentration was determined with the calibration curve and after the first 50 minutes a reduction of 95 % of Cr(VI) was observed, being the chemical reaction kinetic described by a potential time decreasing function.

Guadua angustifolia-Kunth is a forest resource with special physical and mechanical characteristics, which is used mainly in houses building, laminates manufacture, and decorative items. Also it plays an important role in watershed protection, in the CO2 capture and soil conservation. The thermal and mechanical characterization of this type of biological materials is very important for optimizing the industrial transformation processes and improving the final product quality. In this work, thermal diffusivity, thermal effusivity and Brinell hardness (DB) of bottom, middle and top culm areas along the Guadua were considered. These thermo-physical parameters were measured using photoacoustic technique, while DB values were calculated according to the international standards. Results show that heat transport and surface deformation magnitudes are homogeneous along this bamboo. It was found that this behavior is highly correlated with the morpho-anatomical characteristics of the plant, which were determined through photo-micrographs.

La Guadua angustifolia-Kunth es un recurso forestal que debido a sus características físicas y mecánicas ha sido utilizado principalmente en la construcción de viviendas, en la fabricación de laminados y de artículos decorativos. Además es una planta que desempeña un importante papel como protectora de cuencas hidrográficas, en la captura de CO2 y en la conservación de suelos. La caracterización térmica y mecánica de este tipo de materiales de origen biológico es de mucha importancia ya que permiten optimizar los procesos de transformación industrial para mejorar la calidad del producto final. En este trabajo se reportan mediciones de difusividad térmica, efusividad térmica y dureza Brinell (DB) que fueron hechas a muestras tomadas a lo largo del culmo de la guadua, considerando las zonas conocidas como cepa, basa y sobrebasa. Los parámetros termofísicos fueron medidos haciendo uso de la técnica fotoacústica mientras que los valores de DB fueron calculados de acuerdo con estándares internacionales. Los resultados muestran que las magnitudes asociadas al transporte de calor y a la deformación superficial en la guadua son homogéneas a lo largo de ella. Se comprobó que este comportamiento presenta alta correlación con las características morfoanatómicas de la planta, que fueron determinadas a través de la observación de micrografías.

When Titanium dioxide in contact with a polluted water sample is irradiated with ultraviolet light, electron-hole pairs can be generated, which can react with oxygen and water producing free radicals that can degrade the pollutants, changing them into harmless compounds for the environment. The ultraviolet component of the solar radiation is around 7%. Therefore, it is convenient to modify the TiO2 films crystalline structure for obtaining photocatalytical processes with visible light. In this work we report on the growth of TiO2 thin films by the Sol-gel technique considering the incorporation of AgNO3 in the initial solution containing the precursor. The concentration of the AgNO3 saline solution was changed between 5 and 30% to control the grain size of the grown TiO2 nanocrystals, impregnating 6 layers over glass slide substrates and using a sintering temperature of 600 °C. The obtained films were characterized structurally by means of X-ray diffraction. The shift in the forbidden energy bandwidth value to the red part of the optical absorption spectrum was evidenced by Photoacoustic Spectroscopy. The photocatalytic activity was tested on a solution of methylene blue using also the Photoacoustic technique.