Synthesis and Evaluation of the Photocatalytic Activity of Nanostructured Composites Based on SiO2 Recovered by TiO2

Almost spherical SiO2 nanoparticles were recovered by thin films of TiO2 (highly crystalline anatase) produced in situ sol-gel syntheses. Silica coating was proven by scanning electron microscopy and infrared measurements. The outstanding photocatalytic efficiency of this material was proven by the degradation of the dye Ponceau 4R (P4R) in aqueous solution, by monitoring its discoloration as well as by the photocatalytic production of gaseous hydrogen. In the first case, the color of the solutions submitted to the photocatalytic process was reduced to zero in 140 minutes of reaction. Regarding the hydrogen production, 5.5 mmol of H2 were obtained in 5 hours of reaction, corresponding to a specific rate of production of 13.6 mmol g-1h-1, a value much higher than that obtained using TiO2 P25 (2.66 mmol g-1h-1) under similar conditions, or even with other photocatalysts reported in the literature. This outstanding photocatalytic activity is coherent with the specific surface area and porosity (respectively 70 m2/g and 15%), estimated for this material. On the other hand, this material presents noticeably superior band gap energy (Eg), 3.3 eV, when compared to the typical values found for TiO2. This small discrepancy, of 3%, may be the result of the mixture of electronic states of both materials. DOI: http://dx.doi.org/10.17807/orbital.v11i2.1347 &nbsp

Synthesis and Evaluation of the Photocatalytic Activity of Nanostructured Composites Based on SiO2 Recovered by TiO2

Almost spherical SiO2 nanoparticles were recovered by thin films of TiO2 (highly crystalline anatase) produced in situ sol-gel syntheses. Silica coating was proven by scanning electron microscopy and infrared measurements. The outstanding photocatalytic efficiency of this material was proven by the degradation of the dye Ponceau 4R (P4R) in aqueous solution, by monitoring its discoloration as well as by the photocatalytic production of gaseous hydrogen. In the first case, the color of the solutions submitted to the photocatalytic process was reduced to zero in 140 minutes of reaction. Regarding the hydrogen production, 5.5 mmol of H2 were obtained in 5 hours of reaction, corresponding to a specific rate of production of 13.6 mmol g-1h-1, a value much higher than that obtained using TiO2 P25 (2.66 mmol g-1h-1) under similar conditions, or even with other photocatalysts reported in the literature. This outstanding photocatalytic activity is coherent with the specific surface area and porosity (respectively 70 m2/g and 15%), estimated for this material. On the other hand, this material presents noticeably superior band gap energy (Eg), 3.3 eV, when compared to the typical values found for TiO2. This small discrepancy, of 3%, may be the result of the mixture of electronic states of both materials. DOI: http://dx.doi.org/10.17807/orbital.v11i2.1347

Determination of the Critical Micelle Concentration of Triton X-100 Using the Compound 3-(benzoxazol-2-yl)-7-(N,N-diethylamino)chromen-2-one as Fluorescent Probe

In the present study we estimated the Critical Micelle Concentration (CMC) of Triton X-100 in an aqueous buffered medium (PBS buffer, pH 7.4), using 3-(benzoxazol-2-yl)-7-(N,N-diethylamino)chromen-2-one (BDC), a push-pull compound, as extrinsic fluorescence probe. The CMC value found, 0.33 mmol L-1, shows good agreement with data from literature obtained using the fluorescence probe technique. Additionally, the polarity, in terms of the ET(30) scale, and the viscosity of the micelle microenvironment in which the probe is preferentially allocated, was estimated as being 46.9 kcal mol-1 and 70.3 cP, respectively, confirming that this microdomain is polar and highly viscous, with characteristics of polyethylene glycol groups consisting in the palisade layer at the micelle-water interface. DOI: http://dx.doi.org/10.17807/orbital.v0i0.92

Treatment of Effluent from a Factory of Paints Using Solar Photo-Fenton Process

We evaluated the use of Fenton reactions induced by solar radiation in the treatment of effluent from a factory of paints for buildings, after prior removal of the suspended solids. The increase of H2O2 concentration from 100 to 2500 mg L−1 for a [Fe2+] = 105 mg L−1 contributed to the reduction of DOC, COD, and toxicity. Our best results were achieved using 1600 mg L−1 H2O2, with 90% of DOC and COD removal and a complete removal of the toxicity with respect to Artemia salina. Additionally, through increasing Fe2+ concentration from 15 to 45 mg L−1, the DOC removal rate increased 11 times, remaining almost constant in the range above 45 until 105 mg L−1. Under our best experimental conditions, 80% of DOC removal was achieved after an accumulated dose of 130 kJ m−2 of UVA radiation (82±17 min of solar irradiation under an average UVA irradiance of 34.1±7.3 W m−2), while 40% of DOC removal was reached after 150 min under only thermal Fenton reactions. The results suggest the effectiveness of implementation of solar photo-Fenton process in the decontamination and detoxification of effluents from factories of paints for buildings