CO2 Pickering emulsion in water templated hollow porous sorbents for fast and highly selective uranium extraction

Conventional methods for preparing amidoxime-based hollow porous sorbents (HPS) for uranium (U(VI)) extraction usually use solution or emulsion process with surfactant and expensive pore template, so they cannot meet requirements of economic and environmentally friendly evaluation. Here, hollow porous microspheres functionalized with abundant amidoxime (AO-HP-MF) are prepared via CO2 Pickering emulsion (or bubble) templated interfacial polymerization and assembly of site chains for highly efficient U(VI) extraction. For this strategy, in situ generated CO2 bubbles are utilized as core template, SiO2 nanoparticles serve dual roles of an emulsion stabilizer and pore template for polymer shell. Meanwhile, assembled polyvinyl polyamine (PEA) chains provide lots of sites for post-modification with amidoxime. Taking the advantages of well-defined hollow porous morphology, uniform size, and high-density of amidoxime, AO-HP-MF is expected to possess excellent adsorption capacity, fast equilibrium rate, and high selectivity. The equilibrium time and maximum adsorption capacity are 1.0 h and 553.3 mg g(-1) at 298 K, respectively, and the monolayer chemisorption based on chelation between U(VI) and amidoxime is main mechanism of selective uranium extraction. Their uniform size may be associated with the pressure-dependent formation condition of in situ generated CO2 bubbles, which is different from traditional emulsion templated microspheres with fairly irregular size. Most importantly, AO-HP-MF has remarkable selectivity for U(VI), even if massive amounts of Ca2+, Mg2+, Na+, Zn2+, and other ions exist in the simulated solution. Therefore, this work not only presents a new clue to fabricate high performance sorbents via simple bubble templates, but also provides a novel platform for U(VI) extraction.