Highly regenerative dual-functionalized mesoporous polymeric hollow spheres for efficient heavy metal removal

Abstract

Effectively removing and recovering heavy metal ions from wastewater and waterbodies, which are closely linked to the development of human society, has become increasingly important due to the rising demand for clean water environments and the recycling of valuable metal resources. In this study, dual-functionalized mesoporous polymeric hollow spheres containing carboxyl and sulfonate groups were specifically designed and synthesized as selective adsorbents for the efficient recovery of heavy metal ions. The strong coordination capability of carboxyl groups, combined with the enlarged interchain spacing brought by sulfonate groups, significantly facilitated mass transfer and synergistically improved the adsorption efficiency for Pb²⁺, Cd²⁺, and Cu²⁺ at both industrial wastewater levels and ultra-low concentration scenarios (initial concentration lower than 1 ppm). Surprisingly, the treated effluent could meet the WHO drinking water standards with optimized adsorption conditions. Equilibrium adsorption data for Pb²⁺ showed that the adsorption processes follow the pseudo-second-order (PSO) and the Langmuir model, indicating a single-layer adsorption nature dominated by chemical interactions. Interestingly, the adsorbents showed a crucial pH-dependent characteristic, and more than 92.8 % of the adsorption capability could be retained after 5 repeated cycles by adjusting the solution acidity. This incredible sensitivity towards pH highlights the ease and efficiency of regeneration and reusability of the adsorbents, and thus eventually a promising alternative for wastewater treatment with pH-tuning.