Reticular poly(pyrrole methylene)s synthesized by synchronous-cross-linking process for the capture of Hg(ll) from water: Adsorption performance and mechanism

Abstract

The development of novel high-capacity porous materials is critical to advancing the treatment of mercury-containing wastewater. In this study, two reticular poly(pyrrole methylene) adsorbent materials (PPB2E and PPD2E) were synthesized by a synchronous cross-linking method and successfully employed for Hg(II) adsorption in water. Their adsorption performance on Hg(II) in water was investigated. The results showed that PPB2E and PPD2E have large specific surface areas (535.43 m2/g and 523.23 m2/g, respectively) and are abundant microporous, with the molecular chains partially cross-linked and partially oxidized to form a conjugated structure. The adsorption of Hg(II) by the two adsorbents could reach equilibrium within 120 min, and the adsorption behavior followed the pseudo-second-order model. The adsorption isotherms were more in line with the Langmuir model, and the maximum adsorption capacities of PPB2E and PPD2E for Hg(II) were up to 1537.46 mg/g and 1511.94 mg/g (298 K, pH = 4), respectively. The two adsorbents exhibited excellent adsorption selectivity for Hg(II) in mixed metal salt solutions with good cycling stability. The primary adsorption mechanism of the synthesized materials for Hg(II) was jointly verified by characterization and DFT calculations: Hg(OH)2 molecules were adsorbed by forming hydrogen bonds with pyrrole N and carboxyl O in the adsorbents. Compared with other metal ions, the materials have more active sites for Hg(II) adsorption, higher utilization, and easier formation of stable adsorption configurations, thus exhibiting highly selective adsorption.