Síntese, caracterização e avaliação da atividade catalitíca de sistemas a base de hidroxiapatitas modificadas com nióbio

Abstract

The hydroxyapatite Ca10(PO4)6(OH)2 is a compound belonging to the family of calcium phosphates, with structure allowing cationic substitutions. In the present study, pure hydroxyapatite, prepared by the co-precipitation method, was compared to two hydroxyapatite systems modified with niobium. In the first one, niobium doped oxalate (NH4[NbO(C2O4)3].3H2O or simply OANb) was synthesized in niobium doped hydroxyapatites, in the mass proportions of 1, 3, 5, 7, 10 ,20 and 30% with niobium pentachloride (NbCl5). The second system (HAP/NPNb) presented the hydroxyapatite impregnated with KNb3O8 nanoplates, from the exfoliation of this niobate with tetrabutylammonium hydroxide (TBAOH). The systems were characterized by DRX, IR, RAMAN, UV-Vis, BET, and EDS in order to evaluate the efficiency of the doping and impregnation processes. The HAP system modified with NbCl5 did not present secondary phases, but the system modified by the ammonium oxalate of niobium presented secondary phase, evidenced mainly by the X-ray diffraction and Raman analysis. The HAP/NPNb system was prepared with three different concentrations of impregnated nanoplates, from 5.4 to 16.1 μg g-1 HAP. The HAP-NbCl5 and HAP / NPNb systems were evaluated catalytically in the reaction of photo-discoloration of the synthetic dye Remazol Amarelo Ouro (RNL) under UV radiation. For comparative purposes, pure HAP was initially used in the photocatalytic reaction, exhibiting photo-discoloration activity around 10%. While the HAP-NbCl5 system showed 23% photo-discoloration, the HAP/NPNb system showed 50% photo-discoloration, even with the low concentrations of impregnated nanoplates, showing that this system has some synergism among its components.