Sonochemical functionalization of mesoporous carbon for uranium extraction from seawater

Extracting uranium from seawater is challenging due to its low concentration (3.3 ppb) and the myriad of competing ions. Mesoporous carbon materials provide a high surface area alternative to the traditional polymeric fiber braids developed for seawater extractions, specifically uranium extraction. In this work, sonochemical grafting of acrylonitrile onto the pores of soft-templated mesoporous carbons followed by its conversion to amidoxime functionalities was used to prepare an effective sorbent material with a high density of binding sites. Pore blockage, often observed for free radical polymerization, leads to poor adsorbent performance but can be easily overcome by the use of ultrasound during polymerization. Parameters such as surface area and surface pre-treatment, sonication intensity, solvent system, and monomer/initiator ratios were varied to optimize the polymerization and uranium adsorption capacity while not blocking the porosity, a significant hurdle in the utilization of functionalized porous materials. The results show that neither the surface oxidation with nitric acid nor CO₂ activation alone is sufficient to cause significant improvement in grafting and uranium uptake. However, when coupled together, a greatly enhanced performance of the adsorbent materials was observed.