Caracterização e avaliação da atividade fotocatalítica de catalisadores baseados no TiO2, sintetizados mediante hidrólise em uma mistura de solventes

This study involved the synthesis of photocatalysts based on titanium dioxide (TiO2). The photocatalysts were synthesized by the sol-gel method using three different proportions of acetone (25%, 50% and 75% v/v) in water/acetone mixtures, in order to control the hydrolysis of the precursor of titanium (titanium tetraisopropoxide). Aiming to investigate the structural, morphological and electronic changes provoked by the use of the solvent mixtures, different methodologies were used to characterize the oxides, such as X-ray diffraction (XRD), RAMAN spectroscopy, UV-Vis diffuse reflectance spectroscopy, and measurements of specific surface area (BET). XRD combined to RAMAN analyses revealed that the products are two-phase highly crystalline oxides involving anatase as main phase and brookite. Besides, the refined XRD using the method of Rietveld demonstrated that the presence of acetone during the synthesis influenced in the composition of the crystalline phases, increasing the proportion of the brookite phase between 13 and 22%. The band gap energy of these oxides practically did not suffer changes as function of the synthesis conditions. As shown by the isotherm, these photocatalysts are mesoporous materials with mean diameter of pores of 7 nm and approximately 20% of porosity. The surface area of the oxides prepared by hydrolysis in presence of acetone was 12% higher compared to the bare oxide. After characterized, these oxides had their photocatalytic activities evaluated by photodegradation of the azo dyes Ponceau 4R (P4R), Tartrazine (TTZ) and Reactive Red 120 (RR120), and also by the ability to mediate the photocatalytic production of hydrogen. Using the most efficient photocatalyst, the mineralization achieved for the dyes P4R, RR120 and TTZ was of respectively 83%, 79% and 56% in 120 minutes of reaction, while the discoloration of P4R e RR120 reached 100% and 94% for TTZ. In addition, the same photocatalyst in the presence of 0.5% w/w of Platinum and suspended in a 5:1 v/v water/methanol mixture, produced 56 mmol of gaseous hydrogen in five hours of experiment, corresponding to a specific rate of hydrogen production of 139.5 mmol h-1 g-1.

Métodos de extração de fósforo e micronutrientes em latossolos com uso de energia ultrassônica

Assessing the soil nutrient availability to plants under lab conditions is one of the main challenges to Soil Fertility and Chemistry, due to the complex behavior and the interaction of the soil properties. Many extractant solutions associated with mechanical forms of agitation have been proposed, showing different correlations with plant growth and nutrients absorption. Using ultrasonic energy is a agitation procedure of the soil:extractant solution suspension (based on the cavitation phenomenon). It allows the establishment of relations between the amount of extracted nutrient and the ultrasonic energy level. Thus, this work aims: to evaluate the effect of cavitation intensity on the extraction of P, Zn, Cu, Mn and Fe in soil samples from five Latosols under different uses around Uberlândia and Uberaba, Minas Gerais State; to obtain extracting curves as function of ultrasonic energy levels; and to obtain an index from extracting curves to expresses the nutrient retention by the soil solid phase. A soil-solution suspension (ratio 1:10) was sonicated using a probe ultrasound equipment under different combinations of power and time: i) 30 W for 35, 70, 140 and 280 s; ii) 50 W for 21, 42, 84 and 168 s; and iii) 70 W for 15, 30, 60 and 120 s. The extractant solutions used were Mehlich-1 (for all elements), Olsen and distilled water for P. After each sonication, P concentration was quantified by molybdenum blue colorimetric method and Zn, Cu, Mn and Fe by flame atomic absorption spectrophotometry. The cavitation intensity did not affect the P extraction, only the total energy applied. The P extraction was influenced by extractant solution, decreasing as follows: Mehlich-1>Olsen>water. In cultivated Latosols, the P extraction increased linearly with ultrasonic energy, and the slope of the 1:1 linear regression reflects the P retention in the soil. The Zn and Fe extractions were influenced only by total energy applied. Mn and Cu extractions were influenced by both cavitation intensity and total ultrasonic energy. Soils containing similar amounts of P, Cu, Zn, Mn, and Fe may have a different extraction rate. Likewise, soils containing different amounts of those elements may have the same extraction rate.

Efeito da concentração de sólidos e de variáveis operacionais no desempenho de um hidrociclone concentrador

The hydrocycloning operation has a goal to separate solid-liquid suspensions and liquid-liquid emulsions through the centrifugal force action. Hydrocyclones are equipment with reduced size and used in both clarification and thickening. This device is used in many areas, like petrochemical and minerals process, and accumulate advantages like versatility and low cost of maintenance. However, the demand to improve the process and to reduce the costs has motivated several studies of equipment optimization. The filtering hydrocyclone is a non-conventional equipment developed at FEQUI/UFU with objective to improve the hydrocycloning separation efficiency. The purpose of this study is to evaluate the operating conditions of feed concentration and underflow diameter on the performance of a filtering geometry optimized to minimization of energy costs. The filtration effect was investigated through the comparison between the performance of the Optimized Filtering Hydrocyclone (HCOF) and the Optimized Concentrator Hydrocyclone (HCO). Because of the resemblance of hydrocyclones performance, the filtration did not represent significant effect on the performance of the HCOF. It was found that in this geometry the decrease of the variable underflow diameter was very favorable to thickening operation. The suspension concentration of quartzite at 1.0% of solids in volume was increased about 42 times when the 3 mm underflow diameter was used. The increase on the feed solid percentage was good for decreasing the energy spent, so that a minimum number of Euler of 730 was achieved at CVA = 10.0%v. However, a greater amount of solids in suspension leads to a lower efficiency of the equipment. Therefore, to minimize the underflow-to-throughput ratio and keep a high efficiency level, it is indicated to work with dilute suspension (CVA = 1.0%) and 3 mm underflow diameter (η = 67%). But if it is necessary to work with high feed concentration, the use of 5 mm underflow diameter provides a rise in the efficiency. The HCO hydrocyclone was compared to the traditional family of hydrocyclones Rietema and presented advantages like higher efficiency (34% higher in average) and lower energy costs (20% lower in average). Finally, the efficiency curves and project equation have been raised for the HCO hydrocyclone each with satisfactory adjust.