Transformation of Bismuth and β-Bi2O3 Nanoparticles into (BiO)2CO3 and (BiO)4(OH)2CO3 by Capturing CO2: The Role of Halloysite Nanotubes and “Sunlight” on the Crystal Shape and Size

The present work describes and discusses some novel aqueous colloidal generation of Bi, (BiO)2CO3, and (BiO)4(OH)2CO3 nanoparticles (NPs) and their structural characterization. These Bi NPs are transformed into (BiO)2CO3 NPs by capturing atmospheric CO2 at room temperature. This transformation is highly dependent on pH, temperature, and the presence of halloysite nanotubes (HNTs) in the solution. When halloysite was present, small (7 nm) nanospheres were obtained. A substantial change in the relative intensity of the peaks in the X-ray patterns for (BiO)2CO3 was observed. In some cases, that change was due to water molecules within the (BiO)2CO3 powder. The crystallite sizes associated with the crystallographic planes parallel to the (040) plane were smaller than for the remaining planes. This difference was more appreciable for (BiO)2CO3 nanoplates and nanorods that have the ability to float on water. β-Bi2O3 NPs, suspended in water and exposed to the light from a xenon arc lamp for 16 h, produced a mixture of (BiO)4(OH)2CO3 and (BiO)2CO3. These β-Bi2O3 NPs are an interesting material to capture atmospheric CO2 dissolved in water, in comparison with the capture of CO2 dissolved in air, increasing the carbon dioxide amount trapped. Transmission electron microscopy (TEM) images revealed that the shape of the bismuth subcarbonate are mainly large nanoplates with rectangular shape (edge lengths vary from 280 to 400 nm).