Synthesis and Catalytic Applications of Multi‐Walled Carbon Nanotube–Polyamidoamine Dendrimer Hybrids

Abstract

Polyamidoamine (PAMAM) dendrimers were covalently immobilized on multi-walled carbon nanotubes (MWNT) by two "grafting to" strategies. We demonstrate the existence of non-covalent interactions between the two components but outline the superiority of our two grafting approaches, namely xanthate and click chemistry. MWNT surfaces were functionalized with activated ester and propargylic moieties prior to their reaction with PAMAM or azido-PAMAM dendrimers, respectively. The grafting of PAMAM generations 0 to 3 was evaluated with X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), and transmission electron microscopy (TEM). The versatility of our hybrids was demonstrated by post-functionalization sequences involving copper alkyne-azide cycloaddition (CuAAC). We synthesized homogeneous supported iridium complexes at the extremities of the dendrimers. In addition, our materials were used as templates for the encapsulation of Pd nanoparticles (NPs), validating our nanocomposites for catalytic applications. The palladium-based catalyst was active for carbonylative coupling over five consecutive runs without loss of activity.

Modified Nanocarbons for Catalysis

“…Very recently, Riant and co‐workers reported the grafting of PAMAM‐dendrimers onto the modified surface of MWCNTs followed by immobilization of Pd nanoparticles . The resulting hybrid material has been employed as catalyst for carbonylative coupling during 5 consecutive cycles without loss of activity.…”

Carbon‐Nanotube‐Appended PAMAM Dendrimers Bearing Iron(II) α‐Keto Acid Complexes: Catalytic Non‐Heme Oxygenase Models

“…Following the same procedure, the amine‐terminated outer shell of the PAMAM dendrimers 1‐G 0 (20 wt % in methanol, generation G 0.0) were conveniently converted to azide moieties [ 2‐G 0 ] by using Cu II catalyst and imidazole‐1‐sulfonyl azide sulfuric acid salt (Scheme ) . Subsequent reaction with propargyl‐functionalized carbon nanotubes (prgCNT) in the same pot resulted in the anchoring of azido‐arm of [ 2‐G 0 ] onto CNTs through triazole formation to afford 3‐G 0 (Scheme ) . Sodium ascorbate was used at this point to reduce Cu II to Cu I in order to enable CuAAC click reaction.…”

“…Recently, efficient protocols towards covalent immobilization of PAMAM dendrimers on CNTs through “grafting to” strategies have been established by our group . Following the same procedure, the amine‐terminated outer shell of the PAMAM dendrimers 1‐G 0 (20 wt % in methanol, generation G 0.0) were conveniently converted to azide moieties [ 2‐G 0 ] by using Cu II catalyst and imidazole‐1‐sulfonyl azide sulfuric acid salt (Scheme ) .…”

“…The PAMAM dendrimers can non‐covalently wrap around CNTs through charge‐transfer interactions . It is also established that the covalent immobilization approach affords higher number of grafted dendrimers . Indeed, a lower amount of loaded dendrimers (3.8 % mass loss) was recorded for the non‐covalent conjugate 1‐G 0 (nc)CNT formed after incubation of 1‐G 0 with p ‐CNTs for 48 h (Figure b).…”

“…Recently,e fficient protocols towards covalent immobilization of PAMAM dendrimers on CNTst hrough "graftingt o" strategies have been established by our group. [15] Following the same procedure, the amine-terminated outer shell of the PAMAM dendrimers 1-G 0 (20 wt %i nm ethanol, generation G0.0) were conveniently converted to azide moieties [2-G 0 ]b yu sing Cu II catalysta nd imidazole-1-sulfonyla zide sulfuric acid salt (Scheme 1). [16] Subsequent reaction with propargyl-functionalized carbon nanotubes (prgCNT) in the same pot resulted in the anchoring of azido-arm of [2-G 0 ]o nto CNTst hrough triazole formation to afford 3-G 0 (Scheme 1).…”