Naturally Occurring Exopolysaccharide Nanoparticles for Dye Adsorption

The properties of nanomaterials can be tuned by engineering the size, surface chemistry, and morphology, enabling the design of nanomaterials with desired structures. Following up our previous work on producing spherical exopolysaccharide nanoparticles (EPS-605 NPs), herein we realized the morphology transformation of EPS-605 NPs by the treatments with different solvents. The EPS-605 NPs can be transformed into the filamentous structures in NaOH (0.01 M) and ethanol (50%, v/v). In contrast, sodium dodecyl sulfate (SDS, 0.01 M) or dimethyl sulfoxide solution treatment only reduced the size of EPS-605 NPs without changing their spherical shape. After dialysis against distilled water, the spherical structure of EPS-605 NPs and the as-formed filamentous structure in NaOH were still well maintained. However, we observed the formation of network structures in EPS-605 NPs treated with ethanol, and some nanoparticles were distributed along the network. Furthermore, the formation of spherical EPS-605 NPs is proved to be driven by hydrophobic interactions, hydrogen bonding, and electrostatic association. The results from Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy demonstrate that EPS-605 NPs interact with NaOH and SDS to form the coassembled structures, while SDS reacts with EPS-605 NPs via a chemical process. As a green-based bioadsorbent, the SDS-treated EPS-605 NPs exhibited a significantly increased adsorption capacity toward methylene blue compared with EPS-605 NPs treated with others. The present study is beneficial to the designing of EPS-605 NPs with tailored morphology, thus expanding their applications in a variety of fields, such as biomedicine, biosorption, and biofabrication.