Amidoxime-modified mesoporous silica for uranium adsorption under seawater conditions

Amidoxime-modified ordered mesoporous silica (AO-OMS) materials were prepared by a two-step process involving: (1) co-condensation synthesis of cyanopropyl-containing ordered mesoporous silica (CP-OMS), and (2) conversion of cyanopropyl into amidoxime groups. The aforementioned co-condensation synthesis is simple and less time consuming as compared to the post-synthesis grafting and assures high loading of organic groups. The intermediate CP-OMS exhibited ordered mesoporosity, high specific surface area, and narrow pore size distribution. Interestingly, conversion of CP-OMS to AO-OMS further improved its properties by enhancing the specific surface area and porosity and achieving high loading of amidoxime groups. High affinity of these groups towards uranium species makes the AO-OMS material an attractive sorbent for uranium recovery as evidenced by very high uranium uptake reaching 57 mg of uranium per gram of AO-OMS under seawater conditions.