Materiais baseados em carvão de PET e lama vermelha ativados com CO2 para remoção de paracetamol em água

Abstract

In this work were studied catalysts based on PET (poly (ethylene terephthalate)) powder, generated through the recycling of bottles, and red mud (RM), an important residue of aluminum production by the Bayer process. These residues were mechanically mixed at the same weight proportion followed by a controlled thermal treatment in tubular furnace at 300°C for 1 h under N2 and then activated using CO2 physical activation at different times (2 and 5 h) and temperatures (800 and 900°C). The materials were characterized using different physicochemical techniques and evaluated for paracetamol removal from water by Fenton heterogeneous-type process using hydrogen peroxide as the oxidant. The Thermogravimetric Analysis (TGA) indicated highest loss of weight, about 40% for the material non-activated (PET-LV), 6% for the activate at 800°C (PET-LV 800/2h and PET-LV 800/5h) and 1% for activated at 900°C (PET-LV 900/5h). In the case of PET-LV, the highest loss weight is related to decomposition of carbonaceous materials from PET, and the weight loss of 6% is possibly to the decomposition of iron carbonates, formed during CO2 physical activation. The X-ray Diffraction (XRD) analysis revealed that the catalyst are formed by a complex mixture of crystalline phases, such as gibbsite (Al(OH)3), hematite (-Fe2O3), magnetite (Fe3O4) and/or maghemite (γ-Fe2O3) and Siderite (FeCO3). The CO2 activation at different times (2 and 5 h) and temperatures (800 and 900°C) of the PET/LV composites affected the surface areas and reactivity of the materials. The catalyst exhibit surface areas of 84, 114, 78 and 8 m2g-1 for PET-LV, PET-LV 800/2h, PET-LV 900/5h and PET-LV 900/5h, respectively. The Scanning Electron Microscopy (SEM) indicated that the materials morphology changed after the thermal treatment in different conditions CO2 activation. The Catalyst PET-LV presented irregular shape and rough surface with cavities whereas the PET-LV 800/2h and PET-LV 800/5h exhibit appearance of spongy-like along with cavities and the PET-LV 900/5h showed agglomerates of different shapes and sizes. The analysis of the magnetic properties indicates that all the catalysts present magnetic iron phases, possibly magnetite and/or maghemite. The Mössbauer Spectroscopy revealed the presence of Fe3+ in PET-LV catalyst. Fe3+ and Fe2+ in the PET-LV 800/2h and PET-LV 800/5h catalyst. The Mössbauer spectrum for PET-LV 900/5h catalyst suggests the increase in the size of the iron oxide crystallites. The pH analysis confirmed that synthesis process of catalyst was able to decrease the basicity of the red mud (possibly NaOH) and the stability test revealed that activity of PET-LV 800/5h catalyst gradually decreased until fourth cycle, leading to negligible catalytic activity. Catalytic tests for paracetamol removal showed PET-LV and PET-LV 900/5h catalyst presented similar drug removal (about 18%, after 30 min of reaction). The catalyst activated at 800°C (PET-LV 800/2h and PET-LV 800/5h) removed a higher amount of paracetamol (26 and 40%, respectively), possibly due to the presence of Fe2+. The adsorption test with PET-LV 800/2h presented 16% of paracetamol remove, thus confirming the contribution of the combined adsorption and oxidation process through Fenton-like heterogeneous process. It can be concluded that use of PET powder and red mud residues for catalyst production can be considered an environmental and promising alternative, since it uses solid residues generate in large amount in the industry as precursors for the catalyst production that can be applied for wastewater treatment.