Nanostructured carbon materials decorated with organophosphorus moieties: synthesis and application

Abstract

A new synthetic approach for the production of carbon nanomaterials (CNM) decorated with organophosphorus moieties is presented. Three different triphenylphosphine oxide (TPPO) derivatives were used to decorate oxidized multiwalled carbon nanotubes (ox-MWCNTs) and graphene platelets (GPs). The TPPOs chosen bear functional groups able to react with the CNMs by Tour reaction (an amino group), nitrene cycloaddition (an azido group) or CuAAC reaction (one terminal C-C triple bond). All the adducts were characterized by FTIR, Raman spectroscopy, TEM, XPS, elemental analysis and ICP-AES. The cycloaddition of nitrene provided the higher loading on ox-MWCNTs and GPs as well, while the Tour approach gave best results with nanotubes (CNTs). Finally, we investigated the possibility to reduce the TPPO functionalized CNMs to the corresponding phosphine derivatives and applied one of the materials produced as heterogeneous organocatalyst in a Staudinger ligation reaction.

Keywords: azides; click chemistry; heterogeneous catalysis; organocatalysis; phosphorus.

Figure 1

Structure of phosphine oxide derivatives 1–3, of ox-MWCNTs 4 and of GPs 5.

Scheme 1

The Tour reaction applied on CNMs 4 and 5.

Scheme 2

The [1 + 2] nitrene cycloaddition on CNMs 4 and 5.

Scheme 3

The Tour reaction with 4-azido aniline (10) on CNMs 4 and 5 and the subsequent CuAAC reaction.

Figure 2

Fitting of the XPS spectrum characteristic of P collected on GPs-Nit-PO 9 showing the two components (2p_1/2 and 2p_3/2) relative to the phosphine oxide group (for XPS spectra of the other compounds see Supporting Information File 1).

Figure 3

Raman spectra: GPs 5 vs GPs-Nit-PO 9 (top), ox-MWCNTs 4 vs ox-MWCNTs-Nit-PO 8 (bottom).

Figure 4

TEM images of ox-MWCNTs 4 (1), ox-MWCNTs-PO 6 (2), ox-MWCNTs-Nit-PO 8 (3), GPs 5 (4) GPs-PO 7 (5), GPs-Nit-PO 9 (6).

Scheme 4

Reduction of phosphine oxide 6 to the corresponding phosphine 6-red.

Figure 5

XPS analysis of samples form the reduction reaction of compound 6: starting material (top), after 24 h (middle), after 48 h (bottom).

Scheme 5

The Staudinger ligation reaction performed with benzoic acid (15) or cinnamic acid (18), and benzyl azide (16) or 4-azidoanisole (20) and compound 8-red as catalyst.