Solvothermal synthesis is the most preferable preparation technique of metal-organic frameworks (MOFs) that consists of reactants mixing, ultrasonication, solvothermal reaction, product washing, and solvent evacuation. Owing to fast reaction kinetics in solvothermal reaction, this technique allows for production of uniform MOF particles with high crystallinity, high phase purity, and small particle sizes. However, it exhibits some difficulties of washing processes that may involve the blockage of pores due to incomplete removal of reactive medium from MOF products. The present study proposes an improvement of washing processes by introducing centrifugal separations with optimized parameters at two different stages: after reaction and after product washing. Nickel-based MOF-74 was synthesized as the experimental material for this purpose. The quality of the produced sample was evaluated by gas adsorption performance using CO2 at 1 bar and 25 Celcius. The final sample of the optimized synthesis routes was able to adsorb 5.80 mmol/g of CO2 uptake, which was competitive with literature data and significantly higher than the sample of the basic synthesis. Fourier-transform infrared spectroscopy (FTIR) and powder X-ray diffraction (PXRD) analysis revealed that the sample displayed much higher crystallinity structure and was clean from impurities after centrifugations. The outcome indicated the success of separation between MOF products and reactive medium during washing processes, leading to the effective pore activation of MOFs.

---

For the first-batch systhesis, the washing processes were repeated to improve the separation of MOF product from the reactive medium, marked green in Figure. For the second-batch systhesis, the centrifugal separations were introduced in the synthesis routes (without any washing repitition) at two different points, between reaction and product washing, and between product washing and solvent evacuation. Methanol was used as the washing solvent in centrifugation. A solution of 360 mg of MOF powder and fresh methanol was poured into six centrifuge tubes for 50 ml each. An optimization study of centrifugal time and rotation speed was carried out to obtain the best separation quality. It consisted of varying the parameters one by one and observing the separation between MOF products and methanol after each centrifugation. The incomplete separation was indicated by the dispersion of MOF particles in methanol shown by murky methanol color, indicating that both centrifugal parameters were insufficient. A good separation was observed by total sedimentation of MOFs, but without any detachment of MOF "flakes" from the sendimentation, failing which either centrifugal time or rotation speed was overestimated.As a result, the optimized centrifugal time and rotation speed for 50 ml solution of 60 mg MOFs were determinedas 7 min and 8000 rpm, respectively.As a result, the optimized centrifugal time and rotation speed for 50 mL solution of 60 mg MOFs in methanol were determined as 7 min and 8000 rpm, respectively.The produced MOFs were denoted as the sample of the second-batch synthesis

RIPinduction =induction timeinhibitor-induction timewater/induction timewater (n) where n is the number of QAHs tested in this work.

---

Enhanced CO2 Adsorption Performance:The introduction of centrifugal separations and optimization of the washing processes led to a significantly higher CO2 adsorption uptake.

Complete Activation of MOF Pores:The outcome of the optimization indicated the effectiveness of the separation steps in the washing processes. Complete activation of MOF pores was achieved, showcasing the success of the optimization in improving the material's gas adsorption properties.

---

The optimized synthesis routes resulted in a Ni-MOF-74 sample with enhanced CO2 adsorption capabilities. This improvement could have significant implications for applications related to gas storage and separation, particularly in industries focused on carbon capture or storage technologies. The competitive CO2 adsorption performance of the final sample makes it a promising candidate for use in environmental and industrial processes where efficient gas adsorption materials are crucial. Industries involved in gas separation technologies, environmental sustainability, and clean energy may find potential applications for this optimized Ni-MOF-74 material.

---