Highly selective adsorption of phosphate by pyromellitic acid intercalated ZnAl-LDHs: Assembling hydrogen bond acceptor sites

• ZnAl LDHs intercalated with pyromellitic acid was prepared for adsorbing phosphate.
• The LDHs had ∼100% selectivity towards phosphate at pH 3–9 in a hybrid solution.
• Hydrogen bond helped the highly selective adsorption of phosphate was verified.
• Phosphate adsorption behaviors were studied in artificial wastewater and real one.

Selective adsorption of phosphate from a complex solution is the key step for phosphate recovery from industrial wastewater. Despite recent research progress, phosphate removal with high selectivity has been found challenging, largely due to the complicated dynamic adsorption behavior of other competing anions in the aqueous waste solution. In the present study, pyromellitic acid (PMA) intercalated layered double hydroxides ([Zn0.68Al0.32(OH)2](PMA)0.08·0.3H2O, denoted as Zn2Al-PMA-LDHs) were synthesized and shown to possess a high selectivity (97.41% at pH 7.0) towards phosphate in a hybrid solution containing H2PO4−, SO42−, CO32−, NO3− and Cl−. In addition, benzoic acid (BA), terephthalic acid (TA) and trimesic acid (TMA) intercalated LDHs also showed similar adsorption performance. The hydrogen bond between hydroxyl group of phosphate as the donor and oxygen of dissociated aromatic carboxyl group as the acceptor was found to play a key role in phosphate adsorption, as suggested by FT-IR and XPS analysis. This work not only presented a well performed material but also a useful method for better design of efficient LDHs for selective phosphate adsorption.

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