Layer-by-layer grafting synthesis of silicon-based zirconium organophosphate for the enhanced and selective adsorption of lanthanides

For the adsorption of radioactive lanthanides in radioactive wastewater, a new hybrid adsorbent (MCM-Zr-TBP) was designed based on the mesoporous silica MCM-41, which surface modified by the hydrolysis of zirconium n-propoxide, and then functionalized with tributyl phosphate. The scatter-distributed zirconium organophosphate groups provided enhanced acid resistance and improved the lanthanide adsorption capacity significantly. Various characterization techniques containing SEM, EDS, TG, and FT-IR were utilized for the microscopic characterization of the adsorbent, and the results revealed that zirconium organophosphate groups were grafted on the silica surface successfully. Based on the chemical similarity with other lanthanides, Eu(III) was used as the surrogate in this study. XPS was exploited to explore the adsorption mechanism of MCM-Zr-TBP to Eu(III), revealed that Eu(III) was mainly complexed with the P=O bonds in the grafted functional groups. The adsorbent achieved an excellent Eu(III) adsorption amount at pH>3. Multi-factors affecting the Eu(III) adsorption was investigated, containing initial ionic concentration, contact time and temperature, and the adsorption process was confirmed to be chemical, endothermic, and spontaneous. The MCM-Zr-TBP possessed a desirable selectivity to lanthanides due to the grafting of organophosphate groups. Thus, this new adsorbent was concluded to be a promising candidate for the adsorption of radioactive lanthanides in radioactive solutions. • A Zr(IV) organophosphate-functionalized MCM-41 was prepared via layer-by-layer grafting. • Zr-O-P bond as a versatile acid-resistant platform greatly promoted material stability. • The scattered distribution of organophosphate improved the adsorption efficiency. • The synthesized adsorbent showed excellent adsorption properties to lanthanides.