Avaliação da propriedade fotocatalítica de nanopartículas de hidroxiapatita dopadas com Fe3O4@W6+/γ-Fe2O3@W6+ aplicadas na degradação de corantes

Abstract

In this work, the synthesis of hydroxyapatite (HA) nanoparticles (NPs) doped with Fe3O4/γ-Fe2O3 and/or W6+ ions was carried out, in order to potentiate the kinetics of the unmodified HA NPs for the degradation of 100 mg L-1 methylene blue (MB) and fast green FCF (FG) dye at pH 2.5, 7.0 and 9.0. All NPs were characterized by XRD, SEM/EDS, FTIR, Raman Spectroscopy, Thermogravimetry analysis, Fluorescence spectrometry and Point of Zero Charge (pHPZC). When the unmodified HAP NPs were used in the process with 1.33 mL of hydrogen peroxide (H2O2) 30% (v/v) and UVC radiation of 125 W, the discoloration value of 88.44, 44.81 and 58.14% was observed in the acid, neutral and alkaline media, respectively. By modifying HAP NPs with Fe3O4/γ-Fe2O3 using the proportion of 25, 50 and 25% of Fe2+, Fe3+ and Ca2+ (Ca2.5FeII 2.5FeIII 5(PO4)6(OH)2), respectively in the photo-Fenton based process, showed 100% of discoloration for acid and neutral pH and 95.2% for alkaline pH after 120 min. For the change in proportion of 21% (Fe2+ ), 4% (W6+), 50% (Fe3+ ) and 25% of (Ca2+ ) (Ca4FeII 1.92W0.08FeIII 4(PO4)6(OH)2), was obtained the best results, with ~100% of discoloration at pH 2.5 and 9.0 in 90 min. For the study of FG dye degradation, the results of discoloration of 36.4; 69.8 and 95.5% when used unmodified HAP NPs and 100; 45.9 and 89.4% when used NPs Ca4FeII 1.92W0.08FeIII 4(PO4)6(OH)2 was obtained at pH 2.5; 7.0 and 9.0, respectively. This increase in discoloration for unmodified against modified HA NPs, is due to the insertion of the photo-Fenton process and the co-catalytic effect of tungsten ions, i.e., occurs an increase in the production of hydroxyl radicals ( ●OH) and, consequently, an attack on the chromophore group. In order to confirm the effectiveness of Ca2.5FeII 2.5FeIII 5(PO4)6(OH)2 and Ca4FeII 1.92W0.08FeIII 4(PO4)6(OH)2 NPs in the degradation process, total organic carbon (TOC), toxicity effect using Lactuca Sativa L. and reproducibility test at pH 2.5 were performed. Study of TOC obtained ~ 90% of removal, and in the toxicity experiments there was a total reduction in the toxicity of the MB dye after 120 min. of reaction for the both NPs. In the reproducibility test of the catalyst using Ca2.5FeII 2.5FeIII 5(PO4)6(OH)2, NP, it was possible to reuse the NPs for 11 consecutive degradation experiments, being physically stable in the face of the tests carried out.