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Six new NiCr layered double hydroxides (LDHs) intercalated with different inter-layeranions, including diphenylamine-4-sulfonate (DPA), dodecyl sulfonate (DS), pentansulfonate (PS), terephthalate (TA), fumarate (FA) and 2-ethylhexyl hydrogenphosphate (EHP), were synthesized and used to removal of Cd 2+ , Pb 2+ , Cu 2+ , and Zn 2+ ions from water samples. The maximum adsorption capacities (q m ) for the mentioned LDHs based on their inter-layer anions were DPA>DS>PS>TA>FA>DEHP. This observation highlights the key role of the structure of the inter-layer anions in the adsorption behavior of LDHs. The sulfonate-based LDHs showed better adsorption efficiency than carboxylate-based LDHs, and phosphonatebased LDHs showed the lowest adsorption efficiency. Also, at both high and low concentrations of the metal ions, the length of R-groups and the type of functional groups of inter-layer anions play a key role in the adsorption process. Subsequently, DPA-LDH, due to having the highest q m value among intercalated-LDHs, was chosen as an efficient sorbent for the removal of the metal ions from aqueous samples and its selectivity for adsorption of metal ions was investigated. DPA-LDH displayed a selectivity order of Zn 2+

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