Synthesis of Fibrous Metal Adsorbent with a Piperazinyl-Dithiocarbamate Group by Radiation-Induced Grafting and Its Performance

Abstract

A fibrous grafted metal adsorbent with a piperazinyl-dithiocarbamate (PZ-DTC) group was synthesized by radiation-induced emulsion grafting of glycidyl methacrylate onto a polyethylene-coated polypropylene nonwoven fabric (PE/PP-NF) and subsequent three-step chemical modifications consisting of amination with N-(tert-butoxycarbonyl)piperazine (N-Boc-piperazine, NBPZ), deprotection of the Boc group with HCl, and dithiocarbamation with carbon disulfide (CS₂). By using the NBPZ reagent in the amination step, the self-cross-linking of piperazine (PZ) could be completely suppressed, unlike using the PZ reagent. Consequently, the PZ-DTC group density of the fibrous grafted metal adsorbent synthesized through NBPZ attained 2.122 mmol-PZ-DTC/g-adsorbent, which was approximately 6 times higher than that of the metal adsorbent synthesized through PZ. The fibrous grafted metal adsorbent with the PZ-DTC group selectively adsorbed heavy metal ions over light metal ions. Furthermore, it exhibited high adsorption capacity, particularly for Cu²⁺. The Cu²⁺ adsorption capacity was determined to be 1.903 mmol-Cu²⁺/g-adsorbent by a batchwise adsorption test using a single-metal-ion aqueous solution at pH 6. The order of metal ion selectivity of the fibrous grafted metal adsorbent with the PZ-DTC group was Na⁺ < Mg²⁺, Ca²⁺, Co²⁺, Cd²⁺ < Pb²⁺ ≪ Cu²⁺, and Co²⁺ ≈ Ni²⁺ < Zn²⁺ ≪ Cu²⁺. In addition, the fibrous grafted metal adsorbent with the PZ-DTC group did not lose its metal adsorption function even under highly alkaline conditions (pH 15). It could recover Cu²⁺ efficiently and selectively from a high-concentration Na⁺ aqueous solution at this pH. The Cu²⁺ adsorption capacity of the fibrous grafted metal adsorbent with the PZ-DTC group was 0.754 mmol-Cu²⁺/g-adsorbent under a highly alkaline condition, a 10 M NaOH aqueous solution at pH 15. This value was approximately 2.4 times higher than that of the other grafted adsorbent with an amine-type functional group.