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

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 BixOy 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, [BixOy](N) > [BixOy-6% PVA](N) > [BixOy-C-6% PVA](N), and increased roughness for materials [BixOy](S), [BixOy-6% PVA](S), [BixOy-C-6% PVA](S), [BixOy](P), [BixOy-6% PVA](P) and [BixOy-C-6% PVA](P). The morphological analysis (electronic scanning microscopy) of the synthesized materials showed a wide variety of forms: overlapping nanoplates ([BixOy](N) or [BixOy](S)), clusters of angular forms ([BixOy-6% PVA](N)), pillars ([BixOy-6% PVA](S)-Au), needle particles ([BixOy-Au], [BixOy-6% PVA](S)-Au, [BixOy-C-6% PVA](S)-Au), spherical particles ([BixOy-C-6% PVA](P)-Pt), 2D plates ([BixOy](P)-Pt) and 3D nanometric plates ([Bi(x)Oy-C-6% PVA](S)-Au). For materials obtained in the first synthesis stage, antimicrobial activity increased in the series [BixOy](N) > [BixOy](S) > [BixOy](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 [BixOy-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 [BixOy-C-6% PVA](P). Materials synthesized and doped with metal ions (gold or platinum) showed significant antimicrobial activity for the tested microbial species.