Lignin-Based Nanocapsules with Tunable Size for Cu(II) Ion Absorption

Functional nanocapsules from low-cost and renewable materials are an urgent need for environmental applications. Herein, lignin-based nanocapsules with tunable size are synthesized using an interfacial miniemulsion polymerization method under mild conditions. To form the nanoabsorbent with a hollow structure, the epoxy–amine addition reaction between amphiphilic lignin-based epoxy and polyethyleneimine is designed to occur at the cyclohexane/water interface. Then, cyclohexane as the sacrificed nanocore template is removed to form a hollow structure. Both FTIR and 1H NMR spectra indicate the success of grafting amine groups and epoxy groups on lignosulfonate. The synthesized lignin-based nanocapsules have particle sizes ranging from 100 to 400 nm and tunable interior pores. They also own a much higher BET surface area (36.445 m2/g) than pure lignosulfonate and epoxy-modified lignosulfonate for improved copper ion absorption. The absorption kinetics and isotherm studies combined with the XPS spectra indicate that the nanocapsules adsorb copper ions by monolayer chemisorption mechanism. The lignin-based nanocapsules shed light on the design of biowaste-based nanocapsules with controllable size for metal absorption, e.g., heavy metal remediation and a metal-based catalyst.