Sustainable earth-abundant bismuth catalytic nanointerfaces using biopolymeric silk fibroin for efficient pollutant reduction

Abstract

We unveiled a new route to synthesize catalytic core–shell Bi/SF nanointerfaces using a highly abundant, bioinspired, eco-friendly, low-cost, and multifunctional silk fibroin (SF) scaffold and metallic Bi. SF was first extracted from traditional Rajshahi silk and then dissolved in ethylene glycol using Bi³⁺ ions. Then, Bi/SF nanointerfaces were produced via the in situ auto-reduction of Bi³⁺ ions and concomitant surface functionalization of metallic Bi with dispersed-SF. Fourier transform infrared, UV-vis, X-ray photoelectron spectroscopy and X-ray diffraction analyses confirmed the successful synthesis of Bi/SF. The multifunctionality and sheeted structure of SF predominantly improved the dispersity, colloidal stability, mesoporosity, spherical shape, and interfacial activity and maintained the rhombohedral structure of the core Bi. Bi/SF nanointerfaces serve as versatile and recyclable catalysts for the sustained reduction of organic pollutants. The catalytic reduction performance was evaluated using four model molecules, namely, Congo red (CR), methyl orange (MO), Eriochrome black-T (EBT) and p-nitroaniline (p-NA), in the presence of NaBH₄. The designed nanointerface competently interacted with electron deficient functionality and exhibited the most efficient reductions against the azo (97.8%, 97.1%, and 83%) and nitro (96.2%) moieties of CR, MO, EBT, and p-NA, respectively. These reduction reactions were performed in an aqueous medium at room temperature without any co-catalysts, photoactivation or H₂(g) supply, and were completed within 2–5 min. Time-dependent UV-vis spectra and kinetic studies revealed pseudo-first-order reduction behavior for all substrates, and the rate constants followed the order of EBT > CR > MO > p-NA. The recyclability study revealed the sustained activity of the Bi/SF nanointerfaces over five cycles for CR and EBT, maintaining an efficiency above 95%, while MO and p-NA showed minor declines. The findings emphasize the synergetic role of the active nanointerfaces in Bi/SF for accelerating redox transformations under mild and sustainable conditions.