Lignin-based few-layered graphene-encapsulated iron nanoparticles for water remediation

The potential of iron nanoparticles as adsorbents for water remediation has not been fully exploited because of their intrinsically low stability. Herein, few-layered graphene-encapsulated iron nanoparticles (FLG@Fe-0) supported on and within lignin-derived carbon were synthesized via an in-situ thermal conversion of ferric nitrate-loaded kraft lignin, i.e., ferric nitrate as a Fe source and lignin as a carbon source. The structure and morphology analyses indicated that these lignin-based FLG@Fe-0 particles sized 5-15 nm in diameter were composed of nanoscale zero-valent iron (nZVI) cores shelled with 1-3 graphene layers. The 'few-layered' graphene shell protects nZVI cores from fast passivation. The lignin-derived carbon support prevents the FLG@Fe-0 sites from agglomeration. These two features can enhance the stability and applicability of FLG@Fe-0 for water remediation. Consequently, these lignin-based FLG@Fe-0 particles exhibited superior uptake capacities of 127.5, 107.2, 214.7, and 356.8 mg/g for Pb(II), As(III), phosphate, and nitrate, respectively. The removal mechanism analyses indicated that precipitation, redox reaction, and catalytic degradation were involved. This versatile lignin-derived carbon-supported FLG@Fe-0 particles (LC-FLG@Fe-0) could be a promising renewable adsorbent for offering green and economic alternatives to conventional nZVI adsorbents synthesized using hazardous and expensive NaBH4 process.

Automated summary

This study synthesized lignin-derived FLG@Fe-0 particles with excellent stability and adsorption performance for water remediation, showing high uptake capacities for Pb(II), As(III), phosphate, and nitrate. The innovative adsorbent could offer a green and economic alternative to traditional nZVI adsorbents.