Dumbbell-Shaped Nanoporous CaCO₃ for Phosphate Removal

With the accelerated development of industrial and agricultural activities, phosphorus pollution has emerged as a global environmental issue. The adsorption method has been widely applied to treat phosphorus contamination. The development of a cost-effective adsorbent for phosphate removal is crucial for the adsorption process. In this study, dumbbell-shaped nanoporous CaCO3 (DNPCC) featuring a mesoporous nanorod-assembled structure was synthesized via a simple precipitation-calcination method as the adsorbent for phosphorus-containing wastewater. Hierarchical calcium oxalate monohydrate (COM) was first prepared using ethylene glycol (EG) and sodium alginate (SA) as morphology-directing agents, then DNPCC was obtained through calcination of COM. The influence of EG and SA on DNPCC was systematically investigated. DNPCC exhibited remarkable phosphate removal performance in simulated phosphorus wastewater and landfill leachate, respectively, which was attributed to the synergistic effects of high Brunauer–Emmett–Teller (BET) surface area, mesoporous architecture, and positive surface charge. Kinetic studies revealed that the adsorption process was predominantly governed by chemical adsorption. It had a theoretical maximum adsorption capacity of 94.3 mg/g, surpassing that of most reported adsorbents. Thermodynamic analysis further demonstrated that the adsorption process was spontaneous, endothermic, and characterized by increased randomness. Additionally, DNPCC effectively overcomes the interference of various competing ions and maintains a high phosphate removal rate of 83.15%, even after five adsorption cycles. The electrostatic attraction and ligand exchange were the dominant adsorption mechanisms of phosphorus using DNPCC. This study highlighted DNPCC as a highly efficient and selective adsorbent for phosphate removal, offering promising potential for addressing water pollution challenges.