Calix[n]arene/Pillar[n]arene-Functionalized Graphene Nanocomposites and Their Applications

Calix[n]arenes and pillar[n]arenes, which contain repeating units of phenol and methane, are class of synthetic cyclic supramolecules. Their rigid structure, tunable cavity size, flexible functionalization, and rich host-guest properties make them ideal surface modifiers to construct functional hybrid materials. Introduction of the calix[n]arene/pillar[n]arene species to the graphene may bring new interesting or enhanced physicochemical/biological properties by combining their individual characteristics. Reported methods for the surface modification of graphene with calix[n]arene/pillar[n]arene utilize either covalent or non-covalent approaches. This mini-review presents the recent advancements in the functionalization of graphene nanomaterials with calix[n]arene/pillar[n]arene and their applications. At the end, the future outlook and challenges for the continued research of calix[n]arene/pillar[n]arene-functionalized graphene nanohybrids in the development of applied nanoscience are thoroughly discussed.

Self-assembled calixarene aligned patterning of noble metal nanoparticles on graphene

Patterns of noble metal nanoparticles (NMNPs) of ruthenium and platinum are formed on p-phosphonic acid calix[8]arene stabilised graphene in water. This involves hydrogen gas induced reduction of metal ions absorbed on the stabilised graphene, with TEM revealing the patterns being comprised of domains of parallel arrays of NMNPs ∼7 nm apart. The domains are orientated in three directions on each graphene sheet at an angle of ∼60° or ∼120° with respect to each other. AFM of self-assembled p-phosphonic acid calix[8]arene on the surface of a highly ordered pyrolytic graphite (HOPG) revealed a similar pattern, implying that the orientation of the assembly of p-phosphonic acid calix[8]arene is governed by the hexagonal motif of graphite/graphene.

Multifunctional p-phosphonated calixarenes

p-Phosphonic acid calix[n]arenes and their O-alkylated lower rim analogues are remarkably versatile macrocycles, with applications in selective diameter uptake of single walled carbon nano-tubes, as surfactants in stabilising and protecting nano-particles and graphene sheets, as crystal growth modifiers for inorganic systems, in encapsulating molecules of anti-cancer carboplatin, self assembly into nano-arrays, including nano-fibres and molecular capsules, and for binding metal ions including biologically relevant Ca(2+). They are readily accessible via five or six high yielding steps from the parent p-Bu(t) substituted compounds.