From phosphate removal to slow-release fertilizer: A closed-loop strategy enabled by Fe-BTC@sponge continuous-flow...

Confronted with the dual challenges of global water eutrophication and phosphorus resource scarcity, developing efficient and sustainable phosphorus recovery technologies is of paramount importance. In this study, a three-dimensional porous Fe-BTC composite supported on cellulose sponge (Fe-BTC@sponge) was synthesized via a facile impregnation-crosslinking-in situ self-loading strategy. The composite was integrated into a custom-designed continuous-flow filtration system, enabling rapid mass transfer and sustained high-rate phosphate removal under dynamic flow conditions. Results demonstrate that Fe-BTC@sponge possesses a hierarchical porous structure with abundant active sites, exhibiting high adsorption efficiency and excellent selectivity for phosphate across a broad pH range (3-11) and in the presence of high concentrations of coexisting ions. In the continuous-flow reactor, it maintained a phosphate removal rate exceeding 95% at a flow rate of 50 mL min^-1 and operated stably for 24 h. Mechanistic studies reveal that the high removal performance is synergistically achieved through electrostatic attraction, hydrogen bonding, and ligand exchange. Furthermore, the spent adsorbent (Fe-BTC@sponge-P) can be repurposed as a slow-release phosphorus fertilizer to promote plant growth, thereby realizing closed-loop recycling of phosphorus resources. This work provides a high-performance phosphate adsorbent and an innovative technical strategy for sustainable wastewater purification and resource recovery.