Silk fibroin and silk fibroin-gold nanoparticles nanocomposite films: sustainable adsorbents for methylene blue dye

In this paper, the preparation of silk fibroin (SF) and silk fibroin-gold nanoparticles (SF-AuNPs) nanocomposites (NC) and their adsorbability of methylene blue (MB) dye is reported. SF is used in this work as a template to reduce gold salt (HAuCl4.H2O) into AuNPs. The optical absorption displays the AuNPs in SF by showing a band at lambda = 540 nm. The X-ray diffraction (XRD) and the transmission electron microscopy (TEM) study reveal the crystalline nature of the AuNPs. The TEM image indicates that the AuNPs are mostly spherical in shape with an average diameter of around 6.22 +/- 1.28 nm. The scanning electron microscopy (SEM) and micrograph shows the AuNPs as uniformly dispersed in the SF. The samples are evaluated as novel adsorbents, and influencing factors like solution pH, contact time, and kinetic models are investigated. The adsorption kinetics validates the practicality of the pseudo-second-order kinetics by best linear fit (R (2)=0.987 for SF film) and (R (2)=0.989 for SF-AuNPs NC film). The Langmuir and Freundlich isothermal models used in the study, maximum adsorption capacity for the dye is estimated to be 263.15 mg g(-1) (SF) and 313.47 mg g(-1) (SF-AuNPs). The decolorization percentage is about 95.62% (SF) and 98.66% (SF-AuNPs). The recycle tests demonstrate that the samples can be reused four times with removal efficiency of more than 80%. The results suggest that the SF and SF-AuNPs films can be used as efficient sorbents for MB dye removal from a solution.