Non-Covalently Polymer-Modified Organc Framework Materials And Its Properties Of Pickering Emulsion

Metal organic frameworks?MOFs?and covalent organic frameworks?COFs?are porous framework materials formed by coordination and covalent bonding.Due to high specific surface area,high porosity,adjustable pore size,easy functional modification and thermochemical stability,they are widely used in the fields of adsorption,catalysis,electrochemistry,sensing,especially heterogeneous catalysis which become a research hotspot.Moreover,in order to develop more potential applications of MOFs and COFs,polymer modification plays a significant role in improving their performance and functional improvement.However,the methods of covalent bonding usually require higher reaction conditions that are not conducive to large-scale production fast and efficiently.In this paper,the non-covalent polymers modification of MOFs or COFs and the properties of their stable Pickering emulsions were studied with a view to their application value in heterogeneous catalysis.The main research contents and results are as follows.?1?First,the macromolecular chain transfer agent PNIPAM-CTA was synthesized by reversible addition-fracture chain transfer?RAFT?polymerization method using N-isopropylacrylamide?NIPAM?as monomer,S,S'-bis??,?'dimethylacetic acid?trisulfide?DMATC?as RAFT chain transfer agent?CTA?and azobisisobutyronitrile?AIBN?as initiators.Then the PNIPAM-CTA was reduced to obtain the carboxyl-terminated temperature-sensitive polymer HOOC-PNIPAM-SH using tributylphosphine?PBu₃?as reducing agent and ethanolamine as catalyst.Melamine-based COF was prepared by condensing reflux method performing Schiff-base reaction using cheap melamine and p-phthalaldehyde as raw materials.Then,the positively charged amino group of COF and the negatively charged terminal carboxyl group of HOOC-PNIPAM-SH were combined by electrostatic force to obtain a non-covalent polymer-modified COF-g-PNIPAM.Fourier transform infrared spectroscopy?FT-IR?,scanning electron microscope?SEM?,transmission electron microscope?TEM?,X-ray diffractometer technology?XRD?,and nitrogen adsorption-desorption curve?BET?were used to characterize the polymer modified composites.The results showed that COF-g-PNIPAM still retained the irregular morphology of COF and the size was larger than the original?from 52 nm to 78 nm?while the specific surface area was reduced from 505.8 m²/g to 33.6 m²/g.The performance of the COF-g-PNIPAM stabilized Pickering emulsion was studied.The results showed that the emulsion droplets were uniform and not easily aggregated when the water-oil ratio was 2:1 and the content was 0.8 wt%.After standing at room temperature for 20 days,the original performance was still maintained.?2?By solvothermal method,Uio-66-NH₂ was synthesized by 2-aminoterephthalic acid?H₂BDC-NH₂?and zirconium chloride?Zr Cl₄?under the condition of acetic acid catalysis through coordination bonds.Finally,the positive charge of Uio-66-NH₂ and the negative charge of HOOC-PNIPAM-SH self-assembled in water by electrostatic action to obtain a polymer-modified composite Uio-66-g-PNIPAM.In addition,the products were characterized by FT-IR,SEM,TEM,XRD,BET.The results showed that PNIPAM was successfully grafted to Uio-66-NH₂ through non-covalent interactions.And the modified Uio-66-NH₂ still maintained the original morphology with the grain size increasing from70 nm to 120 nm,the specific surface area reducing from 1160 m²/g to 438.3 m²/g.At the same time,Uio-66-g-PNIPAM stabilized Pickering emulsion was studied.The results showed that the optimal water-oil ratio?v:v=2:3?and solid mass fraction?1.2?1.6 wt%?to obtain a stable emulsion.In addition,the Uio-66-g-PNIPAM complex was successfully loaded with palladium nanoparticles?Pd NPs?to obtained Pd@Uio-66-g-PNIPAM.The content of Pd by ICP test was 8.4%.