Dithiocarbamate-decorated adsorbent based on hyper-crosslinked PolyHIPE for Pb²⁺ removal from aqueous solution

The adsorption of hazardous metals by chelating resins provides many advantages such as cost effectiveness, high efficiency and selectivity. The ideal adsorbent has characteristics of high specific surface area to bond functional groups and large pores to facilitate the utilization of functional groups. However, these two aspects are contradictory in principle, saying concretely, larger pores inevitably lead to low surface area. To address this problem, a dithiocarbamate (DTC) adsorbent is reported herein, using polymerized high internal phase emulsion (PolyHIPE) as matrix, followed by hyper-crosslinking technology, polyamine grafting and CS₂ modification. The interconnected macroporous structure endows the PolyHIPE with enhanced mass transport and the SSA of the PolyHIPE skeleton increases significantly by the hyper-crosslinking. The adsorption capacity for Pb²⁺ increases by 5.0 times after the hyper-crosslinking. The Freundlich isothermal model also indicates that the adsorption force for metal ions is enhanced significantly by the hyper-crosslinking. The adsorption mechanism is proposed based on XPS analysis, which shows that Pb²⁺ binds to the DTC functional groups in two ways, forming chelates with the sulfur atoms and complexes with the -NH- groups.