Designed synthesis of multifunctional lignin-based adsorbent for efficient heavy metal ions removal and electromagnetic wave absorption.

Multifunctional lignin-based adsorbents, which have shown great application prospect, have attracted widespread attention. Herein, a series of multifunctional lignin-based magnetic recyclable adsorbents were prepared from carboxymethylated lignin (CL), which was rich in carboxyl group (-COOH). After optimizing the mass ratio of CL to Fe ₃ O ₄ , the prepared CL/Fe ₃ O ₄ (3:1) adsorbent showed efficient adsorption capacities for heavy metal ions. The kinetic and isotherm nonlinear fitting studies revealed that the adsorption process followed the second-order kinetic and Langmuir models, and the maximum adsorption capacities (Q _max ) of CL/Fe ₃ O ₄ (3:1) magnetic recyclable adsorbent for Pb ²⁺ , Cu ²⁺ and Ni ²⁺ ions reached 189.85, 124.43 and 106.97 mg/g, respectively. Meanwhile, after 6 cycles, the adsorption capacities of CL/Fe ₃ O ₄ (3:1) for Pb ²⁺ , Cu ²⁺ and Ni ²⁺ ions could keep at 87.4 %, 83.4 % and 82.3 %, respectively. In addition, CL/Fe ₃ O ₄ (3:1) also exhibited excellent electromagnetic wave absorption (EMWA) performance with a reflection loss (RL) of -28.65 dB at 6.96 GHz under the thickness of 4.5 mm, and its effective absorption bandwidth (EAB) achieved 2.24 GHz (6.08-8.32 GHz). In short, the prepared multifunctional CL/Fe ₃ O ₄ (3:1) magnetic recyclable adsorbent with outstanding adsorption capacity for heavy metal ions and superior EMWA capability opens a new avenue for the diversified utilization of lignin and lignin-based adsorbent.
Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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