Immobilization Of MOFs To Polysaccharides And Protein For Sulfanilamide Adsorption And Mechanistic Study

Sulfanilamide is one of the most stable and widely used synthetic antibiotics.Sulfanilamide is difficult to degrade in the environment and quickly accumulates after being ingested by organisms,which seriously threatens food safety and public health.Metal-Organic Frameworks(MOFs)have been the most promising pharmaceutical pollutant disposal material in recent years.They have a very high specific surface area,uniform pore structure,and satisfying mechanical strength.However,most of the MOFs are of micro-nano-scale,which are difficult to be utilized in water treatment.From the practical perspective of the sustainable and green application of MOF materials,immobilizing them on environmentally friendly biopolymer carriers has become an essential approach to improve the application efficiency of MOF,prolong the storage lifespan of materials,and simplify the recycling process.Here,biopolymers with structural adaptability to MOFs were selected as the immobilization substrates,resulting in biomass polymer-MOF composite materials with high adsorption capacity,which not only simplified the application and recycling of MOF particles but also showed high-efficiency adsorption of sulfanilamide.These materials show promising application prospects in the removal of water pollutants.In this study,porous starch was employed as the immobilization matrix,and Ui O-66-COOH nanoparticles were grafted to the internal and external surfaces of porous starch by chitosan.The resulted composite material shows a multi-layered pore structure that can effectively remove the sulfanilamide.Porous starch provides a stable macroporous structure to accommodate Ui O-66-COOH particles,and chitosan serves as an adhesive for the two components through hydrogen bonding and electrostatic interactions.The mass fraction of Ui O-66-COOH within the composite is about 10.8%,and its integrity of crystal structure and chemical accessibility are effectively preserved.The adsorption study of sulfanilamide showed that the adsorption behavior of the composite conformed to the pseudo-second-order kinetic model and the Langmuir isotherm adsorption model,indicating that the adsorption process was uniform monolayer chemisorption.The adsorption of sulfanilamide by the composite is mainly attributed to the high affinity of the Zr-O binding site in Ui O-66-COOH for the sulfur atom within the sulfanilamide molecule,and the MOF can also generate hydrogen bonds and π-πconjugation with sulfanilamide which largely promote the adsorption.The genipin cross-linked chitosan microreactor was constructed by the emulsion template method,and then the macroporous chitosan microgel material was prepared.ZIF-8 type MOF materials were synthesized in situ on the surface of this microgel.The microgel shows an open macroporous channel,and its surface can generate affinity with 2-methylimidazole.The mass fraction of ZIF-8 in the genipin-crosslinked chitosan-ZIF-8 composite was 19.0%,and its Langmuir maximum fitted adsorption capacity was 153.28 mg/g.The results from Zeta potential and molecular docking indicated that the adsorption mechanism of sulfanilamide was the electrostatic interaction between the adsorbent and guest molecules and the π-π conjugation between the unsaturated bonds of organic ligands on the surface of ZIF-8 and the sulfabenzene ring from sulfanilamide.The composite material can be applied to inhibit the growth of Staphylococcus aureus,Escherichia coli,and Salmonella enteritidis after adsorbing sulfanilamide pollutants,which not only realizes the reuse of the adsorption material but also avoids secondary pollution.The chitosan-Ui O-66-COOH and chitosan-nanocellulose-ZIF-8 composite aerogels were constructed by ex situ and in situ synthesis of MOFs in carbohydrate systems,respectively.The effects of synthesis strategies on composite aerogels’ structure and functional properties were explored.The chitosan-Ui O-66-COOH composite aerogel contains about 29.53% MOF components,and the X-ray computational tomography results show that the MOF material agglomerates within the aerogel system.The mass fraction of ZIF-8 in the chitosannanocellulose-ZIF-8 composite aerogel is 23.91%.The MOF distribution in the aerogel is uniform,and the aerogel shows a highly anisotropic structure.Due to the introduction of MOF materials,the two aerogel materials all developed satisfying hydrophobicity.The calculated Langmuir adsorption capacities of chitosan-Ui O-66-COOH and chitosan-nanocellulose-ZIF-8composite aerogels for sulfanilamide were 72.10 mg/g and 93.26 mg/g,respectively,indicating that the latter MOF aerogel has higher adsorption efficiency towards sulfanilamide.These results reflect that the in situ synthesis method ensures the chemical accessibility of MOFs in aerogel composite materials.Protein amyloid fibrils were fabricated by β-lactoglobulin under an acid-induced fibrillization strategy.Amyloid fibril-ZIF-8 hybrid aerogel was then prepared by using the protein fibril as a biodegradable carrier matrix for immobilizing ZIF-8.The composite aerogel shows ultralight property.Due to the mutual protection mechanism between the ZIF-8mineralized layer and the protein fibrils,the hybrid aerogel produces satisfying acid tolerance.The hybrid aerogel has a hierarchical porous structure that can effectively remove nine different heavy metal ions from solutions.EDTA can effectively regenerate the composite aerogel from hazardous metal ions so that it can efficiently and repeatedly adsorb mercury ions and lead ions more than five times.The introduction of ZIF-8 material endows the composite aerogels hydrophobic properties,which can be utilized for oil-water separation.In addition,the composite aerogel has a strong adsorption capacity for sulfanilamide,and its Langmuir fitting adsorption capacity reaches 102.78 mg/g.Considering the facile preparation process,efficient decontamination ability,low cost,and regeneration property of amyloid fibril-ZIF-8 composite aerogel,it has a good application prospect in sewage treatment.