Recyclable aqueous metal adsorbent: Synthesis and Cu(II) sorption characteristics of ternary nanocomposites of Fe3O4 nanoparticles@graphene-poly-N-phenylglycine nanofibers.

Metal pollutant adsorbents are an essential material platform for sustainable environmental remediation, but the adsorbents are typically disposable after sorption, which secondarily contaminates the environment. We report on recyclable Cu(II) adsorbent of deprotonated poly-N-phenylglycine nanofibers (d-PPG NFs)-grafted reduced graphene oxide (rGO) sheets intercalated with Fe3O4 nanoparticles (NPs), which are synthesized via wet chemical process. The adsorption performances of ternary Fe3O4 NPs@rGO-d-PPG NFs and binary Fe3O4 NPs@rGO composites are compared, and the ternary ones exhibit much higher Cu2+-adsorption capacity than binary ones under diverse pH conditions due to both high specific surface area and high cationic affinity of d-PPG NFs that follow the Freundlich adsorption model. Density-functional theory calculation results explain why/how the ternary composites show greater Cu2+ adsorption capability in higher pH environment. The ternary composites present stable, high Cu2+ adsorption capability, irrespective of Co2+ concentration in bimetallic Cu and Co aqueous solution. The Fe3O4 NPs in the ternary composites allow magnet-assisted collection after adsorption batches, whose collection yield is ∼95 % without adsorption capacity degradation in repeated adsorbent reuses over 10 times. This study provides a general, promising pathway to synthesize reusable sorptive materials for water purification/remediation.