Ethylenediamine modified ZnAlCu-LDO with high adsorption for phosphate

Abstract

Layered double hydroxides (LDHs) have emerged as an efficient and easily prepared class of anion adsorbents, showcasing remarkable potential in the adsorption and recovery of phosphate from wastewater, notably due to their unique “memory effect” post-calcination. This study focuses on the enhancement of phosphate adsorption capabilities of ZnAl layered double hydroxides (ZnAl-LDHs), which are particularly known for their high phosphate affinity, through the incorporation of copper and subsequent modification with ethylenediamine. The resultant ZnAlCu layered trimetallic oxide (ZnAlCu-1%-LDO), post-calcination, was modified with ethylenediamine to produce a novel inorganic metal/organic amine composite adsorbent, designated as ZACen-0.5. Characterization of ZACen-0.5 demonstrated an improvement in surface hydrophilicity, alongside a notable alteration in the adsorbent's skeletal structure, which manifested as degraded granular layers, an increased pore volume, and an enhanced specific surface area. The specific surface area of ZACen-0.5 was found to be 104.61 m² g⁻¹, marking a 51% increase compared to ZnAlCu-1%-LDO (69.27 m² g⁻¹). The adsorption capacity of ZACen-0.5 for phosphate was significantly elevated to 271.00 mg P g⁻¹, maintaining an efficiency of 88.2% over four regeneration cycles. The study elucidated the adsorption mechanism of ZACen-0.5, attributing it to monolayer and chemical adsorption processes, which involve electrostatic attraction, ligand exchange, and surface precipitation. In practical wastewater treatment, ZACen-0.5 achieved a phosphate removal efficiency of over 98% from wastewater with an initial phosphate concentration of 3.43 mg P L⁻¹, reducing the phosphate level to 0.0531 mg P L⁻¹, thereby surpassing the stringent first-level standard of GB 8978–1996 (0.5 mg P L⁻¹). The findings of this research underscore the effectiveness of ethylenediamine modification of ZnAlCu-1%-LDO in significantly enhancing the phosphate adsorption efficiency of LDH-based materials, presenting a promising avenue for the development of advanced wastewater treatment technologies.