José Solís

Characterization and butanol/ethanol sensing properties of mixed tungsten oxide and copper tungstate films obtained by spray-sol-gel

Abstract Mixed WO3–CuWO4 films have been prepared from an aqueous solution of copper sulfate and polytungsten gel with a molar ratio of Cu/W from 0 to 100%. These solutions were sprayed on to alumina substrates at 220 °C. The obtained films were amorphous and crystallized after annealing at 300 °C in air for 3 h. The annealed films were composed of a mixture of CuWO4 and WO3 phases. The film obtained from a solution with an equimolar ratio of Cu/W was pure CuWO4. The pure WO3 films obtained have high surface ‘irregularities’, such as porosity. These surface ‘irregularities’ in the films were maintained or even increased as Cu/W molar ratio augments in the starting solution up to 10%. The gas sensitivity to butanol and ethanol vapors is also enhanced when the CuWO4 phase increases in the film by up to 7–10%; with further increments to this proportion the detection sensitivity decreases, so compromises are approximately 7–10%. The gas sensitivity of pure CuWO4 was lower than that of pure WO3.

The Influence of the Ethanol-water Molar Ratio in the Precursor Solution on Morphology and Photocatalytic Activity of Pyrolytic ZnO Films¶

Abstract Zinc oxide films were fabricated by a homemade spray pyrolysis system equipped with an optical setup ensuring the in situ control of the film growth. Zinc acetate (0.1 M) diluted in a mixture of ethanol and water was used as the precursor solution. The ethanol–water molar ratio, Γ, in the precursor solution was varied from 0 to 0.92. The deposition temperature and the pH of the precursor solution were kept at 350°C and 4.5, respectively. X-ray diffraction patterns revealed that films were zincitelike with a grain size depending on the ethanol–water molar ratio in the precursor solution. The interference pattern obtained during film deposition was used to monitor the film roughness; it was found that this is related with those results of surfaces and optical analysis obtained by scanning electron microscopy and spectrophotometric measurements, respectively. The morphology of the ZnO films obtained from Γ equal to either 0 or 0.92 are dense with agglomerates uniformly distributed, whereas the films obtained from Γ equal to either 0.03 or 0.06 are very rough with irregular agglomerates. The films obtained from Γ equal to 0.12, 0.18 and 0.31 are rough. Photoelectrocatalytic results indicated that there is a correlation of the partial molar volume of ethanol with respect to water in the spraying solution, with the photocatalytic efficiency of the ZnO films. We found that the maximum photodegradation of methyl orange in the solution occurs using ZnO films obtained with Γ = 0.12.

Solar Water Disinfection Studies With Supported TiO2 and Polymer-Supported Ru(II) Sensitizer in a Compound Parabolic Collector

Solar water disinfection was performed using TiO 2 and a Ru(II) complex as fixed catalysts located in a compound parabolic collector photoreactor. Studies were performed in the laboratory as well as at a greenfield site. Under laboratory conditions, natural water contaminated with cultured bacteria was photocatalytically treated and the influence of the photolysis as well as of both catalysts was studied. Experiments were performed with contaminated water flowing at 12 l/min; under these conditions, photocatalytic experiments performed with a supported heterogeneous photocatalyst (Ahlstrom paper impregnated with TiO 2 ) showed it to be effective in degrading bacteria in water. The Ru complex catalyst, however, showed no clear evidence for disinfecting water, and its efficiency was comparable to the simple photolysis. Under on-site experiments, bacteria contaminated water from the Yaurisque river at Cusco, Peru was treated. As a general trend, after photocatalytic treatment a reduction in the E-coli population present in water was observed. Whenever disinfection was achieved in the experiments, no regrowth of bacteria was observed after 24 h. However, a reduction in the prototype efficiency was observed both in laboratory and on-site experiments. This was ascribed to aging of the photocatalyst as well as due to the deposition of particles onto its surface. In cases in which incomplete disinfection resulted, a low rate of E-coli growth was observed 24 h after ending the experiment. However, pseudomones seem to be resistant to the treatment.

In vivo Prompt Gamma Neutron Activation Analysis Facility for Total Body Nitrogen and Cd

A Prompt Gamma Neutron Activation Analysis (PGNAA) system has been designed and constructed to measure the total body nitrogen and Cd for in vivo studies. An aqueous solution of KNO3 was used as phantom for system calibration. The facility has been used to monitor total body nitrogen (TBN) of mice and found that is related to their diet. Some mice swallowed diluted water with Cl2Cd, and the presence of Cd was detected in the animals. The minimum Cd concentration that the system can detect was 20 ppm.