Estudo da fotodegradação de efluente de celulose e papel com fotocatalisadores sintetizados via precursores de TiO2

Abstract

Currently all effluents must be treated before disposal in the receiving bodies, however many effluents are resistant to conventional treatments, and it is necessary to study and develop alternative low cost treatments that are of easy industrial implantation. An industry that stands out for containing effluents of difficult treatment, is the one of pulp and paper. This is an important industry for Brazilian socioeconomic development, but it is also responsible for consuming large amounts of water and generating significant volumes of effluents. These industries employ physico-chemical and biological treatments, aiming to reduce the color, turbidity among other factors of their effluents, and some even use ultrafiltration as final polishing, but this method has low efficacy and a high cost. A promising alternative would be advanced oxidative processes (AOPs), especially heterogeneous photocatalysis, an excellent alternative to degrade these emerging pollutants. The process is based on the activation of a semiconductor by radiation with a suitable wavelength. The energy supplied in the form of photons to the catalyst must be equal to or greater than band gap energy, allowing an electronic transition between the valence band (VB) and the conduction band (CB) to occur. This mechanism originates the electron-gap pair, cationic and anionic sites (h + / e-) of high redox power that promote the oxidation of the organic ma during the catalytic reaction. Under specific conditions the pollutant may be mineralized into carbon dioxide (CO2), water and inorganic ions. Titanium dioxide (TiO2) is the most used semiconductor in photocatalytic reactions, due to its photostability, low cost and no toxicity. The aim of this work was to study different synthesis routes based on TiO 2 precursors (n-butoxide and TiO 2 tetraisopropoxide) by the sol gel method. These were tested for their photocatalytic efficiency in a lignin effluent (Lig) and actual effluent collected after the biological decanter (DPS) of a pulp and paper industry in the northern region of Paraná. The relationship between the methodology used in the synthesis and the final morphology of the oxide was also evaluated. Doping studies with silver nitrate (AgNO3) and hydrogen peroxide (H2O2) were also carried out to increase the efficiency of the photocatalyst. The obtained semiconductors were characterized by X-ray diffractometry (XRD) and the doped semiconductor was characterized by thermal analysis (TGA), X-ray diffractometry (XRD), scanning electron microscopy (SEM), infrared spectroscopy) And zero charge point (pHPCZ). The synthesis employing TiO2 n-butoxide precursor gave three oxides (oxy 1, 2 and 3), with crystalline phase (compared to the standards contained in the PDF2.DAT database) anatase and rutile for oxy 1 and 3, and Anatase phase for oxy 2 which was shown to be thermodynamically more stable at 500 ° C. The oxide synthesized via TiO 2 tetraisopropoxide precursor (O.S.) gave anatase and rutile phases at 450 ° C. For the doped oxide (doped O.S.) it was found that the silver content used did not influence the particle morphology, but increased the thermal stability of the anatase phase and the photocatalytic efficiency as expected. The photocatalytic efficiency was evaluated by reduction of chemical oxygen demand (COD), color and total phenolics. Among the synthesized semiconductors, oxy 2 reduced the color and total phenolics, the O.S. with and without doping significantly reduced COD, color and partially the phenolics of the studied effluents.