Controllable fabrication of hierarchically porous adsorbent via natural particles stabilized Pickering medium internal phase emulsion for high-efficiency removal of Rb+ and Cs+

Hierarchical porous adsorbent with well-defined macro-pores and interconnected meso- and micro-pores provides better accessibility and active sites for adsorbate. However, most synthesis techniques usually require multiple steps, or based on surfactants and block-copolymers as soft templates, which are time consuming, costly and non-renewable. Herein, we demonstrated a novel strategy to fabricate a highly interconnected hierarchical 3D porous composite adsorbent chitosan-g-poly(acrylamide)/attapulgite (CTS-g-PAM/APT) with tunable pore size via one-step Pickering emulsion polymerization without any surfactant. Stable, low-cost and environment-friendly canola oil-in-water (O/W) Pickering medium internal phase emulsions (MIPEs) was solely stabilized by a pH-responsive APT/CTS composite particle derived from the electrostatic assembly of non-toxic natural APT nanorods and biopolymer CTS. Then, the acrylamide (AM) monomers in Pickering MIPEs were in-situ polymerized to produce CTS-g-PAM/APT composite with hierarchical and interconnected pores. The size of pore can be regulated by varying the pH values due to the pH-dependent of droplet size of emulsion. The composite has large amounts of chelating groups (e.g., –NH2 and –COO−) and high porosity, so it was capable of capturing Rb+ and Cs+ with high adsorption capacities of 178.88 mg/g and 221.56 mg/g, and rapid adsorption rate of 600 and 900 s for Rb+ and Cs+, respectively. Moreover, the composite can be regenerated and reused for multiple cycles. This new approach provided a potential and economical pathway to develop hierarchically porous materials for wastewater treatment.