Síntese e caracterização de fotocatalisador G-C3N4/PTCDA, com avaliação para degradação fotocatalítica de fármacos em efluentes hospitalares

Abstract

In recent decades, concern about water contamination by pharmaceuticals and the need for environmentally friendly alternatives for their degradation have driven research in innovative technologies for wastewater treatment. Thus, the present study aims to evaluate the photocatalytic efficiency of photocatalysts synthesized from graphitic carbon nitride (g-C₃N₄) and 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) in the degradation of pharmaceuticals found in hospital wastewater from a specialized tuberculosis treatment facility. The synthesized photocatalysts showed increased absorption in the visible spectrum, presenting bandgap energies equal to or lower than 2.72 eV (g-C₃N₄). From the physicochemical analyses, it was possible to observe the accumulation of PTCDA on the surface of g-C₃N₄, as well as the identification of characteristic crystallographic peaks of g-C₃N₄ at the (002) and (100) planes due to the graphitic structure and aromatic frameworks, respectively. The photocatalysts that exhibited higher amounts of PTCDA deposited on the g-C₃N₄ surface showed shifts around 27.4° and 24.6°, which are characteristic peaks of PTCDA. FTIR analyses allowed the identification of characteristic regions of g-C₃N₄, such as stretching vibrations of terminal NH₂ groups, the formation of tri-s-triazine units, and bending vibrations of the heptazine rings. Peaks corresponding to stretching vibrations of imide carbonyl groups (O=C‒N) were also identified, indicating that the imidization reaction occurred and, therefore, confirming the formation of the covalent bond O=C‒N‒C=O. To evaluate the efficiency of the photocatalysts, preliminary tests were carried out through the photodegradation of a Rhodamine B solution. Among the 12 synthesized photocatalysts, M2_05P showed the highest efficiency, with photodegradation rates of 17.48% and 80.76% in experiments using 0.1 and 0.5 g/L of photocatalyst, respectively, after 120 minutes of reaction. After the preliminary tests, the photocatalyst that showed the best efficiency in the degradation of Rhodamine B was selected for the photodegradation of pharmaceuticals present in hospital wastewater after biological treatment. Through the photodegradation experiments of the hospital effluent, it was possible to identify a considerable decrease in the concentration of volatile acids of up to 62%, while for pharmaceuticals the highest photodegradation was observed for pyrazinamide, reaching 21%. Despite the potential of photocatalysis for the removal of micropollutants, the complexity of hospital wastewater significantly influenced the efficiency of the photocatalytic process. For future research, complementary analyses (XPS, DSC, and TGA) are recommended in order to further deepen the chemical and structural characterization of the photocatalysts. It is also suggested to perform photocatalytic assays with pharmaceuticals in water using M2_05P and pure g-C₃N₄ for evaluation and comparison purposes, as well as to repeat experiments with the M2_05P and g-C₃N₄ materials to assess the efficiency in a real matrix and the reproducibility of the process.