Study On Green Preparation And Gas Adsorption Separation Of MIL-100(Cr)Based Material

In recent years,metal-organic frameworks（MOFs）with rich pore structures and diverse functional characteristics have been considered by many research fields to have considerable application potential,such as gas storage,separation,catalysis,drug transport,and sensing.These application potentials were based on MOFs materials with large specific surface were adjustable pore structure,open channels and huge pore volume.Among the broad branches of MOFs materials,MIL（Materials of Institute Lavoisier）series materials with ultra-high specific surface and unique frame structure were favored.Among them,MIL-100（Cr）was a very representative material in the MIL series,because of its large specific surface area(1770～1980 m²·g^-1)and porosity（59.1%）,and had good physical and chemical stability.More importantly,it has abundant Cr（Ⅲ）-based coordination unsaturated sites,which makes MIL-100（Cr）have excellent adsorption and catalytic properties.According to literature research,the current conventional method for preparing MIL-100（Cr）was hydrothermal synthesis,which took long time to react（96 h）and uses hydrofluoric acid（HF）,which was extremely harmful to the environment and human body And,after the reaction,cumbersome multiple washing and drying steps were required for treatment to obtain a sample with a certain purity.The basis of the application of MOFs materials needs to consider the economics of atoms,so the preparation process should avoid the use of highly corrosive or toxic solvents,and simplify the synthesis process as much as possible,so it was urgent to optimize the synthesis conditions.For this research status,MIL-100（Cr）-LSAC and monolithic material MIL-100（Cr）mono were prepared in this work using Loaded Steam-assisted Conversion（LSAC）and Sol-gel methods,respectively.MIL-100（Cr）mono（mono,monolith）.Subsequent characterization proved that both methods can achieve one-step synthesis of MIL-100（Cr）,and its adsorption and separation performance was evaluated.The main findings were as follows:（1）For the synthesis of MIL-100（Cr）by the steam-assisted conversion method,the synthesis conditions were first explored.Without the mineralizer HF,MIL-100（Cr）-LSAC can be synthesized within 9 h,its BET specific surface area was 2077 m²·g^-1 characterized by nitrogen adsorption,and it had a high yield（96%）.The gas adsorption performance of MIL-100（Cr）-LSAC after activation under high vacuum at 523 K was investigated.The results showed that MIL-100（Cr）-LSAC has the same N₂ absorbed preference as MIL-100（Cr）synthesized by hydrothermal method,the adsorption amount of N₂ reached 0.65 mmol·g^-1,while the adsorption amount of CH₄ was slightly lower of 0.6 mmol·g^-1.These results indicated that the MIL-100（Cr）-based material synthesized by the LSAC method MIL-100（Cr）-LSAC has a Cr（Ⅲ）coordination unsaturated site in the raw material.（2）For the synthesis of MIL-100（Cr）by the Sol-gel method,MIL-100（Cr）mono can be directly prepared within 9 h without the mineralizer HF,and the product was a whole with high mechanical strength type MIL-100（Cr）-based material,with a strength of more than 50 N·mm^-2,and its BET specific surface area reached 2257 m²·g^-1,MIL-100（Cr）mono was investigated at 523 K and showed the high gas adsorption performance after vacuum activation,also showed that MIL-100（Cr）mono had the same N₂ selective adsorption behavior as hydrothermal synthesis of MIL-100（Cr）;the breakthrough curve showed that the air component N₂/O₂ separation can be carried out.The separation indicated that O₂ can be enriched to a higher concentration,which means that this work provides an alternative MIL-100（Cr）synthesis pathway for the air separation oxygen enrichment project.At the same time,due to the increasing true density,the volume storage capacity of CH₄ under high pressure（20 bar）has increased to 85v/v,which exceeds the reserves of powder samples and compression molded samples.