Metal Nanoparticles Attached on Carbon Nanotubes Modified with NH₂-terminated Poly(amidoamine) Dendrimer

Abstract

Carbon nanotubes (CNTs) were covalently modified with 3rd –generation NH₂- terminated poly(amidoamine) (PAMAM) dendrimer, named CNTs-3. The reduction of sodium tetrachloropalladate(II) (or chloroauric acid, silver nitrate, potassium tetrachloroplatinate (II)) in the presence of CNTs-3 having amine groups results in the formation of stable Pd (or Au, Ag, Pt) nanoparticles, called CNTs-3-Pd (or Au, Ag, Pt). The growing dendrimer on CNTs were confirmed by Fourier transform infrared spectroscopy (FT-IR) and elemental analysis. Raman spectra showed growing PAMAM dendrimer anchored on the CNTs sidewalls. High resolution-transmission electron microscopy (HR-TEM) images showed the metal nanoparticles were well decorated on CNTs-3. Inductively coupled plasma optical emission spectrometer (ICP-OES) analysis indicated 22.51 wt% of palladium was deposited onto MWNTs-3-Pd. X-ray photoelectron spectroscopy (XPS) of MWNTs-3-Pd indicated that the palladium was a mixture of Pd0 and PdII in ca. 2.77 : 1 ratio. In case of SWNTs-3-Pd, 12.09 wt% of palladium was decorated on SWNTs-3. Also, Pd0 and PdII were mixed in the ratio of 1.33 to 1. Catalytic activity of CNTs-3-Pd was tested by Suzuki-Miyaura cross coupling reactions. The SWNTs-3-Pd does not show good catalytic activity. However, in the case of MWNTs-3-Pd, various aryl iodides were readily converted to the corresponding coupled products in excellent yields within 1-3 days at low temperature. We tested recycle reaction of MWNTs-3-Pd for 6 times. Even though reactions time was increased, products were synthesized with fine yields.;탄소나노튜브에 3rd–generation NH2- terminated poly(amidoamine) (PAMAM) 덴드리머를 붙인 후 그 물질을 CNTs-3로 명명하였다. sodium tetrachloropalladate(II) (또는 chloroauric acid, silver nitrate, potassium tetrachloroplatinate (II)) 용액에 CNTs-3를 넣고 환원시켜 안정한 Pd (또는 Au, Ag, Pt) 나노파티클을 탄소나노튜브 표면에 도입하였으며, 그 물질을CNTs-3-Pd (또는 Au, Ag, Pt)로 명명하였다. 덴드리머가 탄소나노튜브의 표면에서 잘 자라고 있다는 것을 FT-IR, 원소분석, Raman spectra를 통해 확인하였으며, HR-TEM을 통해 금속 나노파티클들이 CNTs-3 표면에 잘 붙어있음을 보였다. ICP-OES 결과 22.51 wt%의 Pd가 MWNTs-3에, 12.09 wt%의 Pd가 SWNTs-3에 붙어있음을 확인하였고, XPS결과 Pd가 Pd0와 PdII의 혼합으로 이루어졌으며, SWNTs의 경우 Pd0가 PdII의 1.3배, MWNTs의 경우 2.8배 더 많은 것으로 확인되었다. SWNTs-3-Pd는 Suzuki-Miyaura cross coupling 반응에서 낮은 촉매활성을 보인 반면 MWNTs-3-Pd는 높은 촉매활성을 보였다. 또한 recycle 반응을 통해 cycle이 진행될수록 반응시간은 증가하지만 계속 좋은 수득률로 product이 합성되었음을 확인하였다.