A dithiocarbamate-grafted porous organic polymer for efficient and selective capture of silver ions: synthesis, performance and mechanism

The strategic precious metal, silver (Ag(I)), has two important concerns regarding resource depletion and ecological toxicity due to increasing demand from multiple industries. The efficient recovery of silver is of great significance for a sustainable environment. The study emphasizes a porous polymer precursor, synthesized by solvothermal Friedel–Crafts alkylation from pyrrole and phenothiazine in DMF using FeCl 3 as catalyst. The precursor was then functionalized through 1-aminopyrrole and subsequent dithiocarbamate grafting to obtain PPF-3. Its highest adsorption capacity for Ag(I) is 518 mg/g at 318 K and pH = 5, which is higher than the same class of other adsorbents. Based on isothermal, kinetic, and thermodynamic analysis, it was found that the spontaneous adsorption process was a heterogeneous chemical adsorption, endothermic in nature, and entropy-driven. The N and S active sites of the pristine framework dominated the adsorption process, following the soft-hard acid-base theory. PPF-3 unveiled remarkable selectivity for Ag(I) and retained its adsorption efficiency even after 5 adsorption-desorption cycles in simulated and actual leachate of waste catalysts. The applicability of PPF-3 in continuous flow processing systems was confirmed by the fixed-bed column adsorption experiment. The various characterizations and DFT calculations proved that the adsorption was achieved by coordination, electrostatic interaction, and partial reduction of Ag(I). The facile fabrication of PPF-3 proved to be stable and high-capacity with good selectivity and demonstrated application prospects in resource recovery of industrial silver-containing wastewater and also gave new ideas for separation and recovery of other precious metals.