Three-Dimensional, Vertical Platelets of ZnO Carriers for Selective Extraction of Cobalt Ions from Waste Printed Circuit Boards

Controlled design of low-cost, ecofriendly, and efficient metal recycling process of waste printed circuit boards (PCBs) is essential for sustainable industries. In this study, a metal extractor (ME) design was fabricated by anchoring organic chromophore chelate [(E)-4-((3-amino-4-hydroxyphenyl)diazenyl)naphthalen-1-ol (AHPDN)] into three-dimensional (3D) and vertical platelets of ZnO platforms to continuously extract and sensitively and selectively detect ultratrace Co2+ concentration (similar to 95.7%) in real e-waste leach liquor. Results reveal that the microscopic ZnO platelet hierarchy is successfully fabricated with nonstacked 3D platelet morphology through hydrothermal-assisted methodology. The 3D nonstacked ZnO platelets are oriented in horizontal and vertical domains, thereby enabling fabrication of potential ME for multidirectional diffusion and efficient adsorptivity of Co2+ ions. Multidiffusible, intermingled platelets and numerous active sites that decorated the ME hierarchy promote the ultratrace separation and recovery of Co2+ ions from PCBs. This scalable immobilization and accommodation of AHPDN along ZnO platelet surfaces effectively controls the Co2+ ion-recovery/extraction process. The selective adsorption of Co2+ ions in the presence of other competitive ions strongly depends on pH control assay. The consumed MEs can be repeatedly recycled, their platelet hierarchy and surface features are retained, and their selective adsorption functionalities are negligibly altered. Hierarchical MEs are suitable for the extraction of Co2+ from the waste PCBs.