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 Bi 2 O 3 , as a precursor of HNO 3 dissolution, and intermediate oxides, such as Bi x O y when using H 2 SO 4 and H 3 PO 4 . 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 Bi 2 O 3 bands when using HNO 3 and of crystalline phases of "bismuth oxide sulphate" when using H 2 SO 4 and "bismuth phosphate" when using H 3 PO 4 . The TG curves showed major mass losses and specific thermal effects, delimited in four temperature zones for materials synthesized with HNO 3 (with loss of mass between 24% and 50%) and H 2 SO 4 (with loss of mass between 45% and 76%), and in three temperature zones for materials synthesized with H 3 PO 4 (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 x O y ] N > [Bi x O y -6% PVA] N > [Bi x O y -C-6% PVA] N , and increased roughness for materials [Bi x O y ] S , [Bi x O y -6% PVA] S , [Bi x O y -C-6% PVA] S , [Bi x O y ] P , [Bi x O y -6% PVA] P and [Bi x O y -C-6% PVA] P . The morphological analysis (electronic scanning microscopy) of the synthesized materials showed a wide variety of forms: overlapping nanoplates ([Bi x O y ] N or [Bi x O y ] S ), clusters of angular forms ([Bi x O y -6% PVA] N ), pillars ([Bi x O y -6% PVA] S -Au), needle particles ([Bi x O y -Au], [Bi x O y -6% PVA] S -Au, [Bi x O y -C-6% PVA] S -Au), spherical particles ([Bi x O y -C-6% PVA] P -Pt), 2D plates ([Bi x O y ] 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 [Bi x O y ] N > [Bi x O y ] S > [Bi x O 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 x O 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 x O y -C-6% PVA] P . Materials synthesized and doped with metal ions (gold or platinum) showed significant antimicrobial activity for the tested microbial species.