Layer-by-layer synthesis of copper hexacyanoferrate on 3D-printed scaffolds for efficient ammonium recovery

• Layer-by-layer synthesis enhanced CuHCF immobilization on PLA scaffolds. • Modified filters exhibited rapid ammonium adsorption kinetics within 2 h. • High ammonium adsorption capacity of 1 mg/g achieved using the LBL method. • Filters maintained effective performance over 10 days in a continuous column test. • Regeneration cycles showed >90 % efficiency, confirming filter stability and reusability. Ammonium contamination in wastewater, which originates from various sources such as agriculture and livestock activities, poses significant environmental challenges while also serving as a valuable resource for recovery. Effective ammonium removal is essential for mitigating its impact on aquatic ecosystems, where it disrupts ecological balance and promotes toxic algal blooms. This study explores the potential of copper hexacyanoferrate (CuHCF), a widely recognized adsorbent among Prussian blue analogs (PBAs), for efficient ammonium adsorption due to its remarkable capacity and selectivity. CuHCF was immobilized on a three-dimensional (3D) printed scaffold using a layer-by-layer synthesis method, which significantly enhanced immobilization efficiency and adsorption performance compared to conventional single-layer methods. Analytical techniques, including Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), X-ray diffraction (XRD), inductively coupled plasma mass spectrometry (ICP-MS), and thermogravimetric analysis (TGA), confirmed the introduction of carboxyl groups on the polylactic acid (PLA) scaffold through surface modification, enabling higher CuHCF loading. Adsorption tests revealed fast kinetics within 2 h, sustained adsorption performance for up to 10 days in continuous column experiments, and significant regeneration potential over five continuous cycles. These findings demonstrate the potential of the layer-by-layer synthesized CuHCF-immobilized filter for ammonium recovery from wastewater.