Synthesis Of Core-Shell Material With Rich Carboxyl Group And Its Applications In The Selective Adsorption

The ability to extract peptides and proteins from biological samples with excellent reusability,high adsorption capacity and selectivity become grand challenges for scientific research and medical applications.In this thesis,BTDA@SiO2,a covalent organic polymer composite with abundant carboxyl functional groups on the surface,was readily prepared by combining 1,3,5-benzenetricarboxaldehyde（BT）and 3,5Diaminobenzoic acid（DA）as monomers on the basis of silica cores and explored the application of this material in the field of separation and enrichment.This thesis mainly consists of four aspects:1.A review of the current types of porous adsorption materials and their applications in the field of separation and enrichment of natural antimicrobial peptides2.The aminosilica nanoparticles were produced through a solvothermal reaction.the amino group of spherical aminosilica was condensed with the aldehyde group on BT.On the silica center,the obtained BT@SiO2 was then reacted with DA to form the BTDA shell,a kind of Schiff’s base.The obtained BTDA@SiO2 materials were characterized by fourier transform infrared（FT-IR）,transmission electron microscope（TEM）,scanning electron microscope（SEM）,X-ray photoelectron spectroscopy（XPS）,Thermal gravimetric analysis（TGA）and other technologies.The resultant BTDA@SiO2 microspheres hold advantages over conventional adsorbent for its high surface area,thermal stability and abundant carboxyl functional groups,which makes them highly promising in application for capturing the positive molecules and repelling against interfering negative molecules to extract and separate small molecules.3.Most studies have shown that natural antimicrobial peptides are basic peptides.Therefore,this research first used basic standard peptides as template molecules（e.g.,KVFLGLK）.A standard peptide mixture from tryptic digestion of proteins（e.g.,lysozyme and BSA）was also used as the real sample to investigate the efficiency of the prepared core-shell BTDA@SiO2 material for peptide enrichment and might be employed as antimicrobial peptides.The adsorption conditions such as solvent,pH,adsorption thermodynamics,and adsorption kinetics were optimized.Adsorption equilibrium data achieved from a series of experiments were used with common isothermic equations,as an example Langmuir,Temkin and Freundlich.It was discovered the Langmuir equation shows to suit the equilibrium isotherm data better than that of the others.In addition,the adsorption kinetic data was fitted to usual kinetic models,such as pseudo-first order and second-order models have been evaluated to elucidate the adsorption mechanism.We also found that the kinetic data conformed to the pseudo-second order model,implying that chemisorptions and the obtained core-shell BTDA@SiO2 microspheres exhibited high adsorption capacity（833.33 mg g-1）and excellent reusability（97.55%）with fast adsorption kinetics（in 5 min）.Moreover,the adsorption capacity of BTDA@SiO2 for the basic peptide is significantly higher than that of acidic peptides;our work shows that BTDA@SiO2 has high selectivity for basic peptides.4.Further applications of core-shell material BTDA@SiO2 was also investigated in other fields:（1）Based on the coordination between carboxyl functional groups and metal ions,The BTDA@SiO2 core-shell materials have good adsorption behavior for heavy metal ions.The material has a good adsorption capacity for Ag（Ⅰ）,Cd（Ⅱ）,Co（Ⅱ）,Cr（Ⅲ）,Cu（Ⅱ）,Ni（Ⅱ）,and Mn（Ⅲ）and other metal ions that the maximum adsorption capacities of these heavy metal ions were 20.53,18.00,16.89,14.44,13.58,13.06 and 12.98mg/g,respectively,and the standard curve of the linear range is well fitted.The BTDA@SiO2 exhibited remarkable adsorption efficiency for heavy metal ions,which are promising to remove cationic heavy metal ions pollutants from wastewater.（2）The BTDA@SiO2 coreshell material is also applied as an adsorbent for the extraction of protein（e.g.,lysozyme）.The adsorption conditions such as the effect of pH,adsorption solvent and the adsorption isotherms were optimized.A mixture of lysozyme and b ovine serum albumin（BSA）were used as an adsorption target to show and investigate their selectivity and adsorption capacity for lysozyme.Based on the Langmuir equation,the maximum adsorption capacity of BTDA@SiO2 is as high as 714.28 mg/g for Lys calculated from Langmuir isotherm.The correlation coefficients were highest and better suited for the Langmuir isotherm model（R2=0.9941）than Temkin（R2=0.9633）and Freundlich（R2=0.9337）models.Furthermore,the dimensionless equilibrium parameter RL,also known as separation factor,can be used to express a key characteristic parameter of the Langmuir isotherm,using the form of the Langmuir equation for the data for the adsorption of lysozyme,since all results RL values lie between zero and one,which is an indication of the favorable adsorption of lysozyme on the BTDA@SiO2 adsorbent.Overall,the rich carboxyl groups in the BTDA@SiO2 material structure are electronegative,allowing the BTDA@SiO2 material to selectively extract Lys from the matrix.Overall,the designed core-shell material can be used as an adsorbent for basic peptides,basic protein and metal ions separation due to the material has selectivity for positively charged target components,simple preparation,stable performance,and large-scale preparation can be achieved.It is foreseeable that this research provides a new material and basis for the preliminary screening of natural antimicrobial peptides and other applications.