Insight into the Mechanisms of Low Coverage Adsorption of N-Alcohols on Single Walled Carbon Nanohorn.

We report for the first time the chromatographic study of n-alcohols (from methanol to butanol) adsorption on single walled carbon nanohorn (SWCNH). Using measured temperature dependence of adsorption isotherms (373-433 K) the isosteric adsorption enthalpy is calculated and compared with the data reported for a graphite surface. It is concluded that a graphite surface is more homogeneous, and the enthalpy of adsorption on SWCNHs at zero coverage correlates well with molecular diameter and polarizability, suggesting leading role of dispersive interactions, i.e., no heteroatoms presence in the walls of SWCNH structures. Next using modern DFT approach we calculate the energy of n-alcohols interactions with a graphene sheet and with a single nanocone finally proposing a more realistic-double nanocone model. Obtained results suggest alcohols entrapping between SWCNH with OH groups located toward nanocones ends, leading to the conclusions about very promising future applications of SWCNHs in catalytic reactions with participation of n-alcohols.

Ullmann Reactions of Carbon Nanotubes-Advantageous and Unexplored Functionalization toward Tunable Surface Chemistry.

We demonstrate Ullmann-type reactions as novel and advantageous functionalization of carbon nanotubes (CNTs) toward tunable surface chemistry. The functionalization routes comprise O-, N-, and C-arylation of chlorinated CNTs. We confirm the versatility and efficiency of the reaction allowing functionalization degrees up to 3.5 mmol g-1 by applying both various nanotube substrates, i.e., single-wall (SWCNTs) and multi-wall CNTs (MWCNTs) of various chirality, geometry, and morphology as well as diverse Ullmann-type reagents: phenol, aniline, and iodobenzene. The reactivity of nanotubes was correlatable with the nanotube diameter and morphology revealing SWCNTs as the most reactive representatives. We have determined the optimized conditions of this two-step synthetic protocol as: (1) chlorination using iodine trichloride (ICl3), and (2) Ullmann-type reaction in the presence of: copper(I) iodide (CuI), 1,10-phenanthroline as chelating agent and caesium carbonate (Cs2CO3) as base. We have analyzed functionalized CNTs using a variety of techniques, i.e., scanning and transmission electron microscopy, energy dispersive spectroscopy, thermogravimetry, comprehensive Raman spectroscopy, and X-ray photoelectron spectroscopy. The analyses confirmed the purely covalent nature of those modifications at all stages. Eventually, we have proved the elaborated protocol as exceptionally tunable since it enabled us: (a) to synthesize superhydrophilic films from-the intrinsically hydrophobic-vertically aligned MWCNT arrays and (b) to produce printable highly electroconductive pastes of enhanced characteristics-as compared for non-modified and otherwise modified MWCNTs-for textronics.

Selective carboxylation versus layer-by-layer unsheathing of multi-walled carbon nanotubes: new insights from the reaction with boiling nitrating mixture.

We have studied the oxidation of multi-wall carbon nanotubes (MWCNTs) by boiling them in a nitrating mixture composed of conc. HNO3/H2SO4 (v/v = 1/3). By analysis of the morphology and surface physicochemistry of the oxidation products as a function of MWCNT treatment time, we have revealed two interrelated phenomena. Firstly, the most outer walls were becoming more functionalized with carboxylic groups to the point of quasi-saturation where, secondly, oxidized MWCNTs could be desheathed uncovering the yet non-functionalized wall. These phenomena were manifested by the periodic-like nature of functionalization and de-functionalization. In the products of MWCNT oxidation - the number of graphitized MWCNT walls was determined by HR-TEM while quantification of oxygen functionalities was performed via Boehm titration. The above techniques coupled with the analysis of zeta potential and Raman spectroscopy allowed us to propose a pseudo-1st order kinetic model for MWCNT oxidation translatable to other sp2-C allotropes. The findings mean that prolonged oxidation does not necessarily yield nanotubes of higher levels of functionalization. The final outcome is of great relevance in all fields of MWCNT applications from medicine to sensors to nanomaterials engineering.