Silk-based 2D nanocomposites for superior oily wastewater remediation

Oil spills hazard has increased along with the increase of industrial production, transportation and refining of oil. Therefore, it is becoming urgent to develop natural and efficient adsorbents for oily wastewater remediation. Herein, we report the development of superhydrophobic silk-based nanocomposites via plasma treatment followed by controlled surface decoration. The oxygen-plasma process was optimized to improve the surface properties and enhancing the adhesion of 2D nanomaterials on the natural silk fibers (SF). The SF was decorated with reduced graphene oxide (rGO) or molybdenum disulfide (MoS2) nanosheets to obtain robust silk-based nanocomposites (rGO@PSF and MoS2@PSF) with high oil selectivity. Detailed characterizations confirmed the presence of the composite structure with ultrathin coating of rGO or MoS2 nanosheets over the entire surface of SF. The water uptake of the silk-based nanocomposites was substantially suppressed after the decoration with nanosheets. The silk-based nanocomposites showed outstanding chemical stability and durability after the exposure to several corrosive solutions and organic solvents. On the contrary, the pristine SF was chemically unstable hindering their applicability under harsh conditions. The rGO@PSF and MoS2@PSF nanocomposites showed excellent oil adsorption capacity up to-120 g/g and-90 g/g for oil/water mixtures, respectively. In case of high concentration (up to 30 g/l) and highly stable oil-in-water emulsions, the composites demonstrated high adsorption capacity for crude, pump, and shell oil-in-water emulsions. rGO@PSF was more efficient than MoS2@PSF in crude oil-in-water emulsion separation with an adsorption capacity up to 8203 and 8018 mg/g for rGO@PSF and MoS2@PSF, respectively. Whereas MoS2@PSF demonstrated a higher performance for pump oil in-water emulsions separation with an adsorption capacity up to 3079 and 3529 mg/g for rGO@PSF and MoS2@PSF, respectively. These differences in oil-in-water emulsions adsorption for both nanocomposites could be attributed to the materials flake size in relation to oil droplet size. Both silk-based nanocomposites exhibited excellent recyclability after ten adsorption cycles. Detailed separation mechanisms were introduced for the developed nanocomposites.

Automated summary

In this study, superhydrophobic silk-based nanocomposites were developed through plasma treatment and controlled surface decoration, showing high adsorption capacity and recyclability for oil-in-water emulsions.