Synthesis, Characterization and Antimicrobial Activity of Multiple Morphologies of Gold/Platinum Doped Bismuth Oxide Nanostructures

Abstract

Bismuth oxides were synthesized from bismuth carbonate using the sol-gel method. Studies have described the formation of Bi₂O₃, as a precursor of HNO₃ dissolution, and intermediate oxides, such as Bi_xO_y when using H₂SO₄ and H₃PO₄. The average size of the crystallite calculated from Scherrer's formula ranged from 9 to 19 nm, according to X-ray diffraction. The FTIR analysis showed the presence of specific Bi₂O₃ bands when using HNO₃ and of crystalline phases of "bismuth oxide sulphate" when using H₂SO₄ and "bismuth phosphate" when using H₃PO₄. The TG curves showed major mass losses and specific thermal effects, delimited in four temperature zones for materials synthesized with HNO₃ (with loss of mass between 24% and 50%) and H₂SO₄ (with loss of mass between 45% and 76%), and in three temperature zones for materials synthesized with H₃PO₄ (with loss of mass between 13% and 43%). Further, the thermal stability indicates that materials have been improved by the addition of a polymer or polymer and carbon. Confocal laser scanning microscopy showed decreased roughness in the series, [Bi_xO_y]^N > [Bi_xO_y-6% PVA]^N > [Bi_xO_y-C-6% PVA]^N, and increased roughness for materials [Bi_xO_y]^S, [Bi_xO_y-6% PVA]^S, [Bi_xO_y-C-6% PVA]^S, [Bi_xO_y]^P, [Bi_xO_y-6% PVA]^P and [Bi_xO_y-C-6% PVA]^P. The morphological analysis (electronic scanning microscopy) of the synthesized materials showed a wide variety of forms: overlapping nanoplates ([Bi_xO_y]^N or [Bi_xO_y]^S), clusters of angular forms ([Bi_xO_y-6% PVA]^N), pillars ([Bi_xO_y-6% PVA]^S-Au), needle particles ([Bi_xO_y-Au], [Bi_xO_y-6% PVA]^S-Au, [Bi_xO_y-C-6% PVA]^S-Au), spherical particles ([Bi_xO_y-C-6% PVA]^P-Pt), 2D plates ([Bi_xO_y]^P-Pt) and 3D nanometric plates ([Bi_xOy-C-6% PVA]^S-Au). For materials obtained in the first synthesis stage, antimicrobial activity increased in the series [Bi_xO_y]^N > [Bi_xO_y]^S > [Bi_xO_y]^P. For materials synthesized in the second synthesis stage, when polymer (polyvinyl alcohol, PVA) was added, maximum antimicrobial activity, regardless of the microbial species tested, was present in the material [Bi_xO_y-6% PVA]^S. For the materials synthesized in the third stage, to which graphite and 6% PVA were added, the best antimicrobial activity was in the material [Bi_xO_y-C-6% PVA]^P. Materials synthesized and doped with metal ions (gold or platinum) showed significant antimicrobial activity for the tested microbial species.

Keywords: antimicrobial activity; bismuth oxide; gold; platinum; sol-gel; structural morphology.