The Design And Performance Of A New Type Of Magnetically-Recoverable "Triazole-Transition Metal" Catalyst

In this paper, Both 4-Azidobenzoicacid and alkyne-modified methoxy polyethylene glycol(m PEG-alkyne) as raw materials and then it designs and preparation a kind of triazole stabilizer(Trz) by ?click chemistry? reaction. In brief, The triazole stabilizer with carboxylic acid in one termini and poly ethylene oxide in the other termini. On the one hand, The oil-soluble Fe3O4 nanoparticles(NPs) could be modified with Trz via the ligand exchange reaction because of the coordination between the carboxylic acid and the Fe 3O4 surface. So the Fe3O4-Trz NPs have good water solubility as well as m PEG. On the other hand, due to the good coordination between the triazole and the transition metal Au NPs or Pd NPs. Therefore, a novel magnetic recyclable Fe3O4-Trz-Au/Pd catalyst with composite structure of microspheres can be obtained by reduction of corresponding transition metal precursor on the Fe 3O4-Trz NPs surface with sodium borohydride. The structure and composition, size dist ribution and morphology of Trz or Fe3O4-Trz-Au/Pd were characterized by proton nuclear magnetic resonance(1HNMR), transmission electron microscopy(TEM), Energy Dispersive X-Ray Spectroscopy(EDX), ultraviolet spectrophotometer(UV). The analysis results indicated that those catalysts have good water soluble, uniform particle size and regular spherical morphology. The average particle diameter of catalysts is 5nm and well dispersed. The metal NPs are uniformly distributed on the Fe3O4-Trz NPs surface and no agglomeration which would changed with molecular weight varies.Furthermore, The magnetic composite catalysts were studied on the catalytic performance for the reduction of 4-nitrophenol(4-NP) and Suzuki-Miyaura reaction. The experimental show that Fe3O4-Trz-Au/Pd have excellent catalytic activity for the reduction of 4-NP. Wherein, the catalytic activity of Pd NPs was superior to the catalytic activity of Au NPs. The catalytic activity was decreased with the amount of catalysts decreases. What's more, The loading of the metal nanoparticles on the surface of Fe3O4-Trz NPs and the molecular weight of m PEG also have a significant effect on the catalytic activity. It can be drawn from the experimental data when the loading of Au NPs and Pd NPs is 0.7wt% and 1.4wt%, respectively, molecular weight of m PEG is 500, the catalysts show the best catalytic performance. Fe3O4-Trz-Pd also exhibited good catalytic activity for the Suzuki-Miyaura reaction with trace amounts. It still could catalyzed the above reaction when the amount of catalyst as low as 0.0001mmol%(1ppm). Additionally, Owing to the structural characteristics of the catalyst, it could be recycled easily and rapidly with an external magnetic field. high reusability was demonstrated without visible decrease in the catalytic performance after use for more than 6 times. At last, it would be the minimum impact on the catalytic activity during the recycling process when the molecular weight of m PEG equal to 500.