Fabrication, characterization and methylene blue dye adsorption study of silk microparticles containing gold nanoparticles

In this work, gold nanoparticles (AuNPs) embedded silk fibroin microparticles (SFMPs) were successfully fabricated. The AuNPs were produced in situ in the SF solution and blended with hydroxypropyl methylcellulose (HPMC) polymer. The production of SFMPs is based on the phase separation between SF and HPMC. In a three-step process, SFMPs containing AuNPs (AuNPs-SFMPs) were obtained from the SF-AuNPs/HPMC blend. The air-dried blend film was prepared in the first step, then dissolved in water, and finally, HPMC was eliminated by centrifugation in the third step. The UV-visible spectrum of the SFMPs revealed the absorption band at λ = 534 nm, indicating the presence of AuNPs. X-ray diffraction and X-ray photoelectron spectroscopy confirmed the crystallne nature of AuNPs and the chemical environment of Au ⁰ atoms. The scanning electron microscopy revealed a honeycomb-like structure with different sizes in the SF-AuNPs/HPMC blends. The AuNPs-SFMPs were spherical or oval, with diameters ranging from about 0.3 to 6.4 µm and an average diameter of 2.19 µm. The energy dispersive spectrum showed multiple peaks of Au metal, validated the embedding of AuNPs to the surface of the microparticles. The in situ produced AuNPs were mostly spherical and polydisperse with an average diameter of 14.03 nm, exposed by transmission electron microscopy. The dye removal of the AuNPs-SFMPs was also investigated using a cationic dye, methylene blue (MB). Without any surfactants, the AuNPs-SFMPs had a maximum adsorption capacity of 202.84 mg g ^− 1 . The samples' adsorption performance effectively fit pseudo-second-order kinetics (R ²  = 0.989) and the Langmuir isotherm model (R ²  = 0.999).