Deciphering heterojunction layered double hydroxide-polyaniline-carbon nanotubes for phosphorus capture in capacitive deionization

Abstract

The capacitive deionization (CDI) has emerged as a robust technology due to its effective performance in removing and recovering phosphate in wastewater. However, there are still challenges in achieving fast charge transfer and high capacity phosphorus storage simultaneously. In this study, a layered double hydroxide-polyaniline-carbon nanotubes composite material (ZnFe-PANI/CNT) with heterojunction and pseudocapacitive characteristics was fabricated via a simple and effective precipitation strategy. The existence of heterojunction and pseudocapacitance of ZnFe-PANI/CNT was confirmed through material performance testing Moreover, with its fast charge transfer and high ion storage performance, it was achieved high phosphate adsorption efficiency (94 %) and sustainable electrode regeneration in low concentration phosphate wastewater. Ultraviolet photoelectron spectroscopy (UPS) and density functional theory revealed the ability to accelerate charge transfer, which was contributed by the heterojunction ZnFe-PANI/CNT. In addition, it was found that the synergies of electrostatic attraction, ligand exchange and surface complexation contributed to the high phosphate capture ability in the acidic environments. The binuclear bidentate or mononuclear bidentate structures dominated the surface configuration of phosphate adsorption at pH 4–9.