Research advances on adsorption materials for the purification of radioactive wastewater

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Table 4

Summary of functional groups, adsorption mechanisms, and representative materials for various radioactive nuclides.

Target Ion	Functional groups/ligands	Adsorption mechanism	Representative materials
Sr²⁺	Crown Ethers	The cavity size of crown ethers matches that of Sr²⁺ ions, enabling the formation of host–guest complexes.	Crown ether-functionalized silica gels and crown ether-grafted polymers.
	Carboxylic Groups (–COOH)	Electrostatic attraction between negatively charged carboxylate groups and Sr²⁺ facilitates coordination bonding.	Carboxymethyl cellulose (CMC), poly acrylic acid (PAA).
	Phosphate Groups (–PO₃H₂/ ${- PO}_{3}^{2 -}$ ${-\mathrm{PO}}_3^{2-}$ )	Strong ion exchange interactions between phosphate groups and Sr²⁺ lead to the formation of Sr–PO₄ complexes.	Phosphate-functionalized mesoporous materials, zirconium phosphate composites.
Cs⁺	Calixarene Derivatives	The cavity size of calixarenes matches that of Cs⁺, enabling selective adsorption via hydrophobic interactions and electrostatic attraction.	Sulfonated calixarenes, calixarene-modified resins [4].
	Crown Ethers	Crown ethers exhibit strong coordination with Cs⁺, with enhanced selectivity at high pH.	Crown ether-grafted polymers, inorganic/organic hybrid crown ether materials.
	Phosphate Groups (–PO₃H₂)	Cs⁺ is preferentially adsorbed via ion exchange due to the high affinity of phosphate groups for monovalent cations.	Titanium phosphate, zirconium phosphate-based ion exchange materials.
	Prussian Blue Analogs	Specific structures and functional groups exhibit spatial and electronic compatibility with Sr²⁺ ions.	Potassium cobalt/nickel/titanium/copper/cadmium ferrocyanides.
I⁻/ ${IO}_{3}^{-}$ ${\mathrm{IO}}_3^{-}$	Quaternary Ammonium Groups (–NR₃⁺)	Anion exchange occurs as the positively charged quaternary ammonium groups attract I⁻, forming ion pairs.	Strong-base anion exchange resins.
	Amino Groups (–NH₂)	Protonated amino groups (– ${NH}_{3}^{+}$ ${\mathrm{NH}}_3^{+}$ ) adsorb I⁻ via electrostatic interactions or form hydrogen bonds with ${IO}_{3}^{-}$ ${\mathrm{IO}}_3^{-}$ .	Chitosan, amino-functionalized mesoporous silica.
	Porous Materials Loaded with Ag⁺	Ag⁺ reacts with I⁻ to form insoluble AgI precipitates.	Silver-loaded zeolites, Ag@MOF composites.
Co²⁺/Co³⁺	Amino Groups (–NH₂)	Amino groups form coordination bonds with Co²⁺/Co³⁺, with polyamine structures enhancing chelation.	Polyethyleneimine (PEI), ethylenediamine-modified materials.
	Thiol Groups (–SH)	Strong coordination between thiol groups and Co²⁺/Co³⁺ results in stable complex formation.	Thiol-functionalized silica, thiol-modified magnetic nanoparticles.
	Carboxylic Groups (–COOH)	Carboxylate groups chelate Co²⁺/Co³⁺ to form multidentate coordination structures.	Poly acrylic acid (PAA), carboxylic acid-functionalized MOFs.
	Dendritic Polyamines	Highly branched amine networks offer multiple coordination sites for selective Co²⁺/Co³⁺ adsorption.	PAMAM dendrimer-grafted nanomaterials

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