Marla Azário Lansarin

A study of process variables for the photocatalytic degradation of rhodamine B

The photoactivated degradation reaction of rhodamine B (RB) was studied using P-25 TiO2 (Degussa) as catalyst. Three process variables - temperature, initial pH, and catalyst concentration - were evaluated. Temperature had a slight effect on reaction rate; however, the combined effect of pH and catalyst concentration was greater. pH affected the catalyst particles adsorption of RB, altering the reaction rate. The concentration of the catalyst was significant only up to 0,65 g L-1. The effect of temperature was studied at optimum pH and 50oC was found to be the optimum operational temperature. The effect of the presence of a surfactant (sodium dodecylsulfate, SDS) and ionic contaminants (Cl- and SO4-) in the reaction system was also studied. The surfactant improved the catalysts adsorption of RB by more than 80%, increasing the degradation reaction rate as well. The ionic contaminants reduced the reaction rate.

Synthesis of molecularly imprinted photocatalysts containing low TiO2 loading: Evaluation for the degradation of pharmaceuticals.

A molecularly imprinted (MI) photocatalyst containing a low TiO2 loading (7.00-16.60mgL(-1) of TiO2) was prepared via an acid-catalyzed sol-gel route using different classes of pharmaceutical compounds (i.e., Atorvastatin, Diclofenac, Ibuprofen, Tioconazole, Valsartan, Ketoconazole and Gentamicine) as the template. Herein, our main goal was to test the hypothesis that photocatalysts based on molecular imprinting may improve the degradation performance of pharmaceutical compounds compared to that of a commercial sample (Degussa P25) due to presence of specific cavities in the silica domain. To elucidate certain trends between the performance of photocatalysts and their structural and textural properties, as well the effect of the structure of the drugs on molecular imprinting, the data were analyzed in terms of pore diameter, pore volume, surface area, zeta potential and six-membered ring percentage of silica. In comparison to the commercial sample (P25), we have shown that adsorption and degradation were enhanced from 48 to 752% and from 5 to 427%, respectively. A comparison with the control system (non-imprinted) indicates that the increased performance of the MI systems was due to the presence of specific cavities on the silica domain, and the textural and structural aspects also support this conclusion. The MI photocatalyst was reusable for seven cycles of reuse in which approximately 60% of its photocatalytic efficiency was preserved for the system containing Diclofenac as the template.

Reduction of hexavalent chromium: photocatalysis and photochemistry and their application in wastewater remediation

Hexavalent chromium present in wastewater discharge of galvanic industries is toxic to most microorganisms and potentially harmful to human health. This work examines the photochemical reduction of Cr(VI) with ethanol under ultraviolet (UV) and visible radiation, and photocatalytic reduction of Cr(VI) with TiO2 in the presence of ethanol under UV radiation. By means of different experimental designs, this study investigates the influence of the initial pH, ethanol amount, catalyst concentration and initial Cr(VI) concentration on total Cr(VI) reduction. The results obtained showed that photochemistry with ethanol under UV radiation (96.10%) was more efficient than photochemistry with ethanol under visible light (48.07%). Furthermore, photocatalysis with TiO2 in the presence of ethanol under UV radiation showed high values of total Cr(VI) reduction: 94.15%, under the optimal conditions established by the experimental design. Finally, experiments were carried out with wastewater discharge from an electroplating plant in its original concentration, and higher values of total Cr(VI) reduction were observed.

Modeling, simulation, and optimization of a front-end system for acetylene hydrogenation reactors

The modeling, simulation, and dynamic optimization of an industrial reaction system for acetylene hydrogenation are discussed in the present work. The process consists of three adiabatic fixed-bed reactors, in series, with interstage cooling. These reactors are located after the compression and the caustic scrubbing sections of an ethylene plant, characterizing a front-end system; in contrast to the tail-end system where the reactors are placed after the de-ethanizer unit. The acetylene conversion and selectivity profiles for the reactors are optimized, taking into account catalyst deactivation and process constraints. A dynamic optimal temperature profile that maximizes ethylene production and meets product specifications is obtained by controlling the feed and intercoolers temperatures. An industrial acetylene hydrogenation system is used to provide the necessary data to adjust kinetics and transport parameters and to validate the approach.

Photocatalytic degradation of nicotine in an aqueous solution using unconventional supported catalysts and commercial ZnO/TiO2 under ultraviolet radiation

Nicotine, a highly toxic alkaloid, has been detected in effluents, surface and groundwater and even bottled mineral water. The present work studied the photocatalytic degradation of nicotine in aqueous solution, under ultraviolet irradiation. The experiments were carried out using commercial (ZnO, TiO2) and non-conventional catalysts, which were prepared from industrial and laboratory waste. Two experimental designs (CCD) were performed for both commercial catalysts, and initial nicotine concentration, catalyst concentration and initial solution pH effects were studied. Then, the synthesized catalysts were tested under the optimal conditions which were found through CCDs. Using commercial catalysts, about 98% of the alkaloid was degraded by ZnO, and 88% by TiO2, in 1h. Among the non-conventional catalysts, the highest photocatalytic degradation (44%) was achieved using the catalyst prepared from a petrochemical industry residue.

Styrene photocatalytic degradation reaction kinetics

The aqueous styrene photocatalytic degradation reaction was evaluated using TiO2 P-25 (Degussa) as a catalyst. These experiments were accomplished in a batch slurry reactor with temperature control and a UV lamp. The effects of the initial styrene concentration, the catalyst concentration, the hydrogen peroxide addition and the initial pH of the solution on the reaction were evaluated. The experimental results showed that in 90 min, 95% of the initial styrene was degraded by photocatalysis. It was verified that the styrene degradation rate fits a pseudo-first-order kinetics for initial styrene concentrations between 15.27 and 57.25 ppm, at 30oC. The chromatographic analysis of the samples collected during the photocatalytic degradation revealed benzaldehyde as one of the intermediates. The addition of H2O2 accelerated the degradation reaction until the system reached a certain optimum peroxide concentration in the reactor. Further H2O2 additions resulted in a reaction rate reduction.

Photocatalytic degradation of rosuvastatin: Analytical studies and toxicity evaluations

Photocatalytic degradation of rosuvastatin, which is a drug that has been used to reduce blood cholesterol levels, was studied in this work employing ZnO as catalyst. The experiments were carried out in a temperature-controlled batch reactor that was irradiated with UV light. Preliminary the effects of the photocatalyst loading, the initial pH and the initial rosuvastatin concentration were evaluated. The experimental results showed that rosuvastatin degradation is primarily a photocatalytic process, with pseudo-first order kinetics. The byproducts that were generated during the oxidative process were identified using nano-ultra performance liquid chromatography tandem mass spectrometry (nano-UPLC-MS/MS) and acute toxicity tests using Daphnia magna were done to evaluate the toxicity of the untreated rosuvastatin solution and the reactor effluent.

Degradação fotocatalítica do fungicida tebuconazole em solução aquosa

The tebuconazole photocatalytic degradation kinetics was studied in a batch reactor using TiO2 (P25-Degussa) as catalyst and a high pressure mercury lamp. The photolysis, adsorption and irradiation effects in the reaction rate were evaluated. Afterward, the suspension catalyst concentration and initial pH to the maximum reaction rate was determined. It was observed that the reaction rate can be approached by a pseudo-first order, with a maximum kinetics constant at 260 mg L-1catalyst concentration and pH 7.7.

Industrial and agroindustrial wastes: an echotechnological approach to the production of supported photocatalysts

Agroindustrial wastes (rice husk, exhausted bark acacia, and tobacco dust) and foundry sands from the iron foundry industry were employed as a support source for photocatalysts. TiCl4 was used as the titanium precursor in the preparation of the supported photocatalysts. The solids were characterized by scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX), diffuse reflectance spectroscopy over the ultraviolet range (DRS-UV), X-ray diffraction (XRD), small-angle X-ray scattering (SAXS), nitrogen adsorption-desorption at -196 °C and zeta potential (ZP) measurements. The systems were evaluated for the photodegradation of rhodamine B (RhB). Among the tested systems, the highest percentage of dye degradation was reached by the catalyst prepared with foundry sand supports, with values of 65% under ultraviolet and 39% under visible radiation, whereas under the same conditions, the catalyst prepared with rice husk showed the best photocatalytic performance among the samples prepared with agroindustrial wastes with values of 43% under ultraviolet and 38% under visible radiation. Strong Spearmans correlations among the photocatalytic activity, the zeta potential (ζp>0.900) and the band gap energy (ζp>0.895) were observed. Exploratory tests with tap water samples revealed that the system may be sensitive to other analytes present in these environmental samples.

OBTAINING ZnO IMMOBILIZED OVER DIFFERENT SUBSTRATES BY HYDROTHERMAL TREATMENT FOR PHOTOCATALYSIS APPLICATION

The aim of this work is to systematically explore the effect of the synthesis conditions of ZnO structures, immobilized on different substrates by hydrothermal treatment, in its photocatalytic activity. A circumscribed central composite design of experiments was used to analyze the effects of reagents stoichiometry, reaction time and temperature, covering a wide range of these variables. The substrates used were etched glass, copper and zinc foils. The photocatalytic activity of the as-obtained ZnO samples was evaluated through photocatalytic degradation of rhodamine B (RhB) in aqueous solution under UV irradiation. Zinc foils presented the best immobilized film quality and the maximum dye removal was 80% in one hour of UV exposure.