Degradação de paracetamol empregando tecnologia oxidativa avançada baseada em fotocatálise heterogênea usando irradiação artificial e solar

In this work, the oxidation and mineralization of paracetamol, based in an advanced oxidative process promoted by heterogeneous photocatalysis, was evaluated. The action of two photocatalysts (titanium dioxide, and a composite based on the association between titanium dioxide and zinc phthalocyanine dye) was studied. First of all, experiments in laboratory scale were performed using as radiation font a 400 W high pressure mercury lamp. The mineralization of paracetamol, promoted by both photocatalysts, was evaluated working with 4L of solution containing 10 mg L-1 of paracetamol and 100 mg L-1 of photocatalyst. To find the best experimental conditions, the influence of hydrogen peroxide concentration and pH was evaluated for the reactions. The best results for the reactions in laboratory scale was obtained using 33,00 mg L-1 of hydrogen peroxide in natural pH (6,80). Under these conditions, 100% oxidation was reached in just 40 minutes of reaction using TiO2 P25, while the mineralization was 78%. Using the composite, the mineralization was 63% in 2 hours of reaction and a oxidation of almost 100% was reached after 60 minutes. A CPC reactor (compound parabolic concentrator) was employed in the expanded work scale, using the sun as irradiation source. In this case the experiments were performed using 50 L of aqueous solution containing 10 mg L-1 of paracetamol and 100 mg L-1 of photocatalyst. The assays were done at pH 3,00 and natural pH (6,80). The used concentration of hydrogen peroxide was 33,00 mg L-1, adopted after laboratory scale studies. The reaction at pH 3,00 shows to be more advantageous, since under natural pH (6,80), the use of deionized water was necessary to prepare the solutions, probably because the deleterious action of carbonate ions, known hydroxyl radical scavengers. Using solar irradiation, the reaction mediated by the composite was more efficient when compared with the assays under laboratory scale since the composite presents the advantage of promoting a better use of visible radiation. Under these conditions, the mineralization increased from 40% to 56% under pH 3,00. At natural pH the oxidation occurred more slowly and the mineralization decreased from 56% to 50%. Thus, the use of pH 3,00 will be more interesting in real scale applications, even if it is necessary the pH correction before the discard of the treated effluent to the environment.

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.

Influência da utilização do fluido de corte com adição de grafeno na temperatura de usinagem e formação de rebarba no processo de micro fresamento

As time passed, humanity needed the development of new materials used in various activities. High strength materials such as titanium and Inconel for example, had been studied because they are widely used for implants in biomedicine, as well as their use in aerospace and automotive industries. Because of its thermal and mechanical properties, these materials are considered difficult to machine, promoting a rapid wear of cutting tools, primarily caused by the high temperatures in machining. With the development of new materials has emerged the need of developing new manufacturing processes. One of today’s innovative processes is the micro-manufacturing. Being a process with a defined cutting tool geometry, burr formation is a constant and undesirable phenomenon formed during the machininig process. Being detrimental to the manufacturing process, overspending deburring operations are constantly employed leading to increase the aggregate cost to the manufactured material. Assembly components are also impaired if there is no control of the burr, with consequences including the disposal of components due to the occurence of this phenomenon. This paper presents the study of micro-milling Inconel 718, investigating influential parameters in the formation of burrs in order to minimize the occurrence of this phenome non. Different feed rates per tooth and cutting speed are evaluated, and different cutting fluids with different methods of applying the fluid. Adding graphene to cutting fluids was considered as a variable to be investigated, which is considered an excellent solid lubricant, in addition to increasing the thermal conductivity of the cooling solution (AZIMI; MOZAF FARI, 2015). The micro-milling temperature was evaluated in the present work. It was observed a new phenomenon that causes the machined surface temperature decreases below room temperature when using the solution water + oil. This phenomenon is explained in further chapters. In order to unravel this phenomenon, a new test was proposed and, from this test, it can be concluded, comparatively, which cutting fluid has a better cooling property.Using cutting fluid with different thermal properties has shown influence when analy zing burr formation and reducing machining temperature.