Padilla Rivera, Gabriela I.

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    TNT and MO photodegradation in deionized and salt waters with visible light assisted by photoactivation of modified TiO2
    (2020-05-22) Padilla Rivera, Gabriela I.; Hernández Rivera, Samuel P.; College of Arts and Sciences - Sciences; Cropek, Donald; Vega Olivencia, Carmen A.; Román Velázquez, Félix R.; Department of Chemistry; Cancelos, Silvina
    The release of munitions during military combat events or training exercises represents an alarming situation to the marine environment. Since nitroaromatic compounds (NACs) that are released from these weapons remain in the environment for years, it is essential to develop appropriate methodologies for their degradation. This work proposes the use of photocatalysis as a remediation method for water treatment using the visible region of solar light. To enhance the light absorption of TiO2 and apply photocatalysis to environmental conditions, salicylic acid (SA) and methyl 4-hydroxybenzoate (methyl paraben; MP) were used as surface modifiers for TiO2 nanoparticles. The photocatalyst characterization was conducted by Raman spectroscopy, FTIR-ATR, and UV-Vis spectrophotometry. In the synthesis of TiO2 nanoparticles for the study, the anatase phase of TiO2 was confirmed by RS. Surface modification of TiO2 with SA and MP were studied by FTIR-ATR. The results indicate TiO2-SA and TiO2-MP complexes were formed through bidentate and monodentate coordination, respectively. Also, UV-Vis results were used to calculate the optical bandgap for each photocatalyst. The TiO2 band gap of 3.0 eV decreased when the modifiers were adsorbed to the TiO2 surface by a ligand to metal charge transfer complex. TiO2-SA and TiO2-MP show a bandgap of 2.82 eV and 2.50 eV, respectively, increasing the absorption of the photocatalyst into the visible spectrum. Based on these results, TiO2 and modified-TiO2 were used to photodegrade methyl orange (MO) and 2,4,6-trinitrotoluene (TNT) under visible light. MO and TNT photodegradation were evaluated for each photocatalyst by analyzing samples following white light irradiation of 0, 30, 60, 90, and 120 min. After 2 h of visible light irradiation, higher degradation of MO and TNT was obtained with TiO2-SA (79.6%) and TiO2-MP (83.8%), respectively. Since MO and TNT can also be found in a maritime environment, the photodegradation of each pollutant was evaluated in saltwater. This study reveals that the free ions in saltwater decrease the photocatalysis efficiency. Finally, SA and MP photoactivated TiO2 with visible light irradiation. The affinity between the pollutants and the TiO2 surface was demonstrated to play an essential role during photocatalysis. However, further studies should be performed to better understand how ions interfere with the photocatalytic process.