Green synthesis of MOF-808 with modulation of particle sizes and defects for efficient phosphate sequestration

In this work, a facile and green method is applied to synthesize hydrophilic MOF-808(Zr) and modulate its defect content and particle size using different amounts of iron nitrate (denoted as F) to obtain serial XF-MOF-808 (“X” implied the dosage of used F). The development of additional adsorption sites and the fine-tune of pore and particle size based on MOF-808 significantly improved phosphate adsorption performance. In particular, the 0.5F-MOF-808 shows excellent adsorption capacity (305.5 mg/g) and rapid diffusion rate (37.51 mg/g·min0.5) for phosphate at 298 K and initial pH = 6.5, outperforming pristine MOF-808 and most previously reported adsorbents. 0.5F-MOF-808 possesses a wide pH tolerance, outstanding reusability and excellent selectivity for phosphate adsorption from simulated wastewater, verified in environmental implication and regeneration experiments. Phosphate loaded on the adsorbent can be converted to struvite for agricultural fertilizer via a simple crystallization process. Compared to MOF-808, the exceptional sorption performance of 0.5F-MOF-808 is supported by decreased internal diffusion limitation, enlarged pore size and the development of new adsorption sites, which can be proved by advanced characterizations and batch adsorption experiments. This work presents a promising modification strategy of MOF materials for phosphate adsorption and recovery.