Investigation Of Drug Adsorption And Release Performance Of Functionalized Metal-Organic Frameworks

Metal-organic frameworks（MOFs）,due to its high specific surface area,designable structures and good biocompatibility,show promising applications in adsorption and release of drug pollutant.However,drug molecules usually have ionizable functional groups（such as carboxylic acid,amino or hydroxyl groups）and exhibit in multiple ionization states in water,while most MOFs have electrically neutral surfaces,limiting their adsorption performance towards pharmaceutical pollutants.Therefore,it is significant to develop novel functionalized MOFs to achieve efficient adsorption of drugs in water.To improve the utilization of pharmaceutical contaminants and enhance the practical value of MOFs,further research on the release（desorption）behaviour of pharmaceuticals from MOFs is necessary to implement the environmentally friendly concept of"pharmaceutical contaminant reduction,pharmaceutical resource recovery and pharmaceutical reuse".In this work,a full-chain study was conducted on the design and synthesis of functionalised MOFs,the efficient adsorption of drugs and the controlled release of drugs.A series of functionalised MOFs with excellent performance in the adsorption of trace drug pollutants in water were constructed by introducing active sites（functional groups of positive and negative charges and defective sites）as well as magnetic substances.The release performance of the drugs on the adsorbents was investigated by adjusting the external excitation conditions（e.g.p H and H₂S concentration）to achieve targeted release and recycling of the drugs,thereby improving drug utilisation and reducing environmental pollution.The main studies are as follows:（1）By introducing specific functional groups,the adsorption sites of MOFs can be increased and their surface chemical properties can be changed,enhancing the interaction with target molecules and significantly improving their adsorption capacity and selectivity.A new adsorbent（MIL-125-NH-RSO₃H-X,R=CH₂CH₂CH₂,X represents the amounts of 1,3-propanesultone（1,3-PS））was constructed via the post-synthesis covalent reaction between MIL-125-NH₂ and 1,3-propanesultone.As a result,the adsorption capacity of MIL-125-NH-RSO₃H can reach 164 mg·g^-1,superior to the unmodified sample and other reported porous materials.The adsorption behavior follows the Langmuir model and pseudo-second-order model.Experimental verification and DFT theoretical calculations proved that H-bond interaction,electrostatic attraction interaction and enhanced hydrophobicity play important roles in the adsorption process.Furthermore,MIL-125-NH-RSO₃H-2adsorbents demonstrated good resistance to interference and regeneration.（2）Defect engineering may effectively change the framework structure of MOFs,which not only increases the average pore size but also exposes more metal active sites,promoting the rapid diffusion and mass transfer of the guest molecules in MOFs.DUT-67（PZDC）-AA（PZDC=3,5-pyrazoledicarboxylic acid,AA=acetic acid）was synthesized by a green synthesis method.A series of defective DUT-67（PZDC）-SH-X with varying pore sizes and morphologies was synthesized by employing mercaptoacetic acid（MAA）as a modifier instead of AA.Compared with the pristine DUT-67（PZDC）-AA,DUT-67（PZDC）-SH-2 exhibited fast adsorption equilibrium and high removal efficiency,which could reach 99.3%removal efficiency in 60 min.The saturated adsorption capacity was 356.4 mg·g^-1,which was attributed to the introduction of additional adsorption sites and the increase in specific surface area and pore size.DUT-67（PZDC）-SH-2 exhibited good selectivity for p-ASA in the coexisting ion solution,and the adsorption amount decreased by only 5%after five adsorption-desorption cycles.（3）To reduce the impact of antibiotics on the environment and improve their utilization,the deep removal and in vitro release performance of trace tinidazole（TNZ）in water were studied.Considering the negative properties of the TNZ molecule and its abundance of functional groups（-NO₂ and-S=O）,CAU-1 was selected as the drug carrier,which is positively charged,modified by abundant-OH and-NH₂ groups,and water-stable.CAU-1 exhibits excellent TNZ saturation adsorption capacity(～450 mg·g^-1),outperforming previously reported porous adsorbents and other common MOFs,which can be attributed to the H-bond interactions and electrostatic interactions.At the same time,the release amount of TNZ molecules from the TNZ@CAU-1carrier can be controlled by the p H value of the solution,indicating that CAU-1 has the potential to release TNZ in response to p H.（4）The properties of magnetic MOFs prompt their efficient separation and recovery under an external magnetic field,simplifying the process of MOF recovery and increasing material reusability.By doping Fe²⁺into ZIF-8,Fe-Zn bimetallic magnetic MOFs（Fe-Zn/ZIF）was synthesized.In contrast to other magnetic composites,the synthesis of Fe-Zn/ZIF is straightforward and does not necessitate the incorporation of magnetic nanostructures.The Fe-Zn/ZIF for the efficient loading of phenolic compounds and p H-responsive release properties was investigated.Due to the synergistic effect of strong electrostatic attraction,hydrogen bonding,andπ-πinteractions,the adsorption process of SA on Fe-Zn/ZIF can reach equilibrium in about 360 min,with a high adsorption capacity of 450.6 mg·g^-1,which is superior to the reported adsorbents Moreover,the cumulative release of SA from SA-Fe-Zn/ZIF in neutral（p H=7.4）and weakly acidic（p H=5.8）phosphate buffer saline（PBS）was 31.7%and 45.2%,respectively,within 180 minutes.To prevent the burst release of ZIF material in an acidic environment,calcium alginate（CA）was selected as the optimal encapsulation material.The CA-encapsulated SA-Fe-Zn/ZIF（CA@SA-Fe-Zn/ZIF）released only 30.6%of SA within 180 min at p H=5.8,which was 14.8%less than the unencapsulated SA-Fe-Zn/ZIF.In addition,to expand the application range of Fe-Zn/ZIF,its p H-and H₂S-responsive release performance against the anticancer drug 5-fluorouracil（5-FU）was investigated.Fe-Zn/ZIF can rapidly release 5-FU in PBS solution with p H of 5.8 and Na HS solution with a concentration of 500μM,with cumulative release rates of 68%and 36%,respectively（within 200 minutes）.The release behavior can be described by second-order polynomial model and first-order model,respectively.