35 / 2021-06-29 00:27:15

Biochar-loaded cerium-based MOFs for their highly efficient phosphate removal

biochar,phosphate,adsorption,cerium,MOFs

A series of cerium-based metal-organic frameworks (MOFs) with structural design and valence state modulation were fabricated for effective phosphate uptake, which were named as Ce-MOF-1, Ce-MOF-2, Ce-MOF-3 and Ce-MOF-4. The XRD pattern revealed that Ce-MOF-3 was highly coordinatively unsaturated MOF. The BET confirmed that Ce-MOF-1 possessed the largest specific surface area of 1285.57 m²/g, two-fold higher than the area of Ce-MOF-3, Ce-MOF-4 and thousand times larger than that of Ce-MOF-2. The result of XPS demonstrated that the dominant valence state of cerium in Ce-MOF-2 was Ce (Ⅲ), while Ce-MOF-1 and Ce-MOF-3, Ce-MOF-4 were totally Ce (Ⅳ)-based materials. Impressively, although the physicochemical characteristics were quite divergent, the four samples showed relatively close phosphate removal capacities (the maximum adsorption capacities of them were 242.0, 211.7, 254.3 and 218.9 mg/g, respectively). Then biochar-loaded Ce-based MOFs (B-Ce-MOF) were prepared by a solvothermal synthesis and applied as adsorbents to adsorb phosphate from water. Among them, B-Ce-MOF-2 and B-Ce-MOF-4 exhibited a fast adsorption kinetics for phosphate and the maximum phosphate adsorption capacity were up to 155.6 and 225.0 mg/ g. The variety of structure modification or valence state selection would in return affect their adsorption performances, leading to show their own advantage in different removal characteristics like fast adsorption speed, superb uptake capacity in solution with low or high concentration. This study provided three different strategies for preparing high-effective cerium-based adsorbents and revealed the relationship among physicochemical characteristics, adsorption mechanisms and adsorption performances, which might contribute to the design of new metal-based adsorbents.