Selective phosphate adsorption from wastewater using dual Lewis acid catalyst: A metal-free approach

Abstract

Excess phosphate in aquatic environments is a major contributor to eutrophication, disrupting the ecological balance and posing serious threats to aquatic life. This study investigates the application of a metal-free, boron-based dual Lewis acid (DLA) catalyst for the selective removal of phosphate anions from contaminated water sources. The DLA catalyst combines robust stability, dual binding sites, charge delocalization, high selectivity and recyclability, making it a suitable adsorbent. Density functional theory calculations were employed to evaluate adsorption energies, replacement energies, and charge transfer interactions between various anions and the boron-based DLA catalyst. Phosphate anions exhibited more negative adsorption and replacement energies than competing ions (\({\text {NO}_{2}^{-}}\), \({\text {SO}_{4}^{2-}}\), \({\text {NO}_{3}^{-}}\), \({\text {HCO}_{3}^{-}}\) and \({\text {Cl}^{-}}\)), hence possesses a stronger and more selective binding affinity. Natural bond orbital analysis validate significant charge transfer from phosphate to the DLA catalyst, stabilizing boron centers by occupying vacant p-orbitals. Speciation graphs identified optimal pH for targeted removal or reaction. Hence, this boron-based DLA catalysts can act as a metal-free, recyclable materials for selective removal of phosphate ions from contaminated water sources.

Graphical abstract

A metal-free, boron-based dual lewis acid catalyst selectively adsorbs phosphate anions from wastewater sources. Density functional theory calculations revealed that dual lewis acid catalyst exhibits strong binding affinity, high selectivity over competing anions (e.g. NO₂⁻, HCO₃⁻ etc.), establishing it as an effective adsorbent for phosphate removal and water purification.

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