Ben Wu,Xue Jiang,Shuning Yu,Peng Bai,Xianghai Guo,Jiafei Lyu
A growing demand of boric acid has been forecasted with the rapid development of industries while the world is suffering the consequence from boron-containing wastewater. Metal–organic frameworks (MOFs) with exceptional stability and remarkable surface area have been preliminarily identified as effective boron adsorbents, adsorption mechanism has yet been elucidated though. Herein Zr 6 /Hf 6 -based NU-1008 and NU-903 were studied for boron removal from water for the first time where around 4.82, 6.27, 3.49 and 6.34 boron were captured per Zr 6 /Hf 6 cluster for Zr-NU-1008, Hf-NU-1008, Zr-NU-903 and Hf-NU-903 through a spontaneous endothermic process with fast kinetics by means of chemisorption. Larger capacity of Hf 6 -based MOFs than Zr 6 -based MOFs can be explained by the weaker electronegativity of hafnium than zirconium. The increased binding energy of Zr 3d, Hf 4f and O 1s as well as reduced binding energy of B 1s suggested the interaction between electron-deficient boron and the hexanuclear clusters (M 6 ). Owing to the crystalline nature of NU-1008, the boron binding sites were precisely elucidated by single crystal X-ray diffraction where boric acid was attached to the available coordinative sites on the M 6 clusters through the M 6 -O-B(OH) 2 connection.
Shuning Yu,Chengyu Huangfu,Yulin Li,Anni Yang,Qinglei Xing,Yue Wu,Xianghai Guo,Jiafei Lyu
With the growing demand for sustainable energy, developing new technologies based on biomass has caused deep interest. Glucose conversion into fructose is a crucial step in the sustainable biorefinery industry. Metal–organic frameworks with abundant active metal centers have shown potential, but their specific contribution is not yet fully understood. In this study, mesoporous Zr-NU-1008 with hexanuclear clusters (M 6 ) exhibited a higher glucose conversion of 54.7 % with a fructose selectivity of 85.3 % under optimized conditions compared with its hafnium counterpart, highlighting the significance of strong Lewis acidity of metal species. By adjusting the amount of the capped formate on the hexanuclear zirconium (IV) cluster (Zr 6 ) of Zr-NU-1008, a positive correlation with the catalytic activity was realized, suggesting the lability of the capping modulator during catalysis, which enables tuning the activity by manipulating the capping modulator. Further saturating the Zr 6 cluster with the electron-withdrawing trifluoroacetate modulator achieved an excellent glucose conversion of 63.3 % with a superior fructose selectivity of 86.0 %. Besides, the recovered catalyst can be easily regenerated by reinstalling the modulator on the M 6 cluster, restoring its catalytic activity.
The past two decades have witnessed the potentials of metal–organic frameworks (MOFs) for the adsorptive separation of difficult mixtures due to their designable porosity and significant surface area. In this work, two Zr 6 -based metal–organic framework materials with different pore sizes, NU-906 and NU-1008, were synthesized and evaluated as adsorbents for fructose/glucose separation, which is very important for sustainable biomass utilization. The two materials were characterized and studied, including the kinetics, isotherms, and thermodynamics by batch adsorption experiments, which can be well described by pseudo-second-order kinetics and Langmuir model (NU-906), Freundlich model (NU-1008), and the adsorption mechanism is described in terms of pore exclusion. The experimental results showed that NU-906 exhibited record-breaking adsorption selectivity towards fructose, whose static selectivity factor was up to 13.7. The NU-906 material with expanded particle size was further studied as filling of the chromatographic column for dynamic adsorption, and the dynamic selectivity factor was about 4.0, which was much higher than the column selectivity factor (∼2.5) used in the industry at present. In addition, three adsorption/regeneration experiments demonstrated its reusability.
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