Mechanical interlocking of SWNTs with N-rich macrocycles for efficient ORR electrocatalysis

UV-Vis quantification of the iron content in iteratively steam and HCl purified single-walled carbon nanotubes

As-produced carbon nanotubes contain impurities which can dominate the properties of the material and are thus undesired. Herein we present a multi-step purification treatment that combines the use of steam and hydrochloric acid in an iterative manner. This allows the reduction of the iron content down to 0.2 wt. % in samples of single-walled carbon nanotubes (SWCNTs). Remarkably, Raman spectroscopy analysis reveals that this purification strategy does not introduce structural defects into the SWCNTs' backbone. To complete the study, we also report on a simplified approach for the quantitative assessment of iron using UV-Vis spectroscopy. The amount of metal in SWCNTs is assessed by dissolving in HCl the residue obtained after the complete combustion of the sample. This leads to the creation of hexaaquairon(III) chloride which allows the determination of the amount of iron, from the catalyst, by UV-Vis spectroscopy. The main advantage of the proposed strategy is that it does not require the use of additional complexing agents.

Mechanical Interlocking to Unlock the Reinforcing Potential of Carbon Nanotubes

Single-walled carbon nanotubes (SWNTs) present extraordinary mechanical properties, with Youngs' modulus>1 TPa and tensile strength>50 GPa; this makes them ideal candidates as fillers for the reinforcement of polymers. However, the performance of SWNTs in this field has fallen behind expectations. This is due to a combination of imperfect individualization of the SWNTs and poor load transfer from the polymer to the SWNTs. Here, we study the reinforcement of polymers of different chemical nature using mechanically interlocked derivatives of single-walled carbon nanotubes (MINTs). We compare the mechanical properties of fibers made of poly (methyl methacrylate) (PMMA) and polysulfone (PSU) and their composites made with pristine SWNTs, MINTs, and the corresponding supramolecular models. With very low loading of MINTs (0.01 % w/w), improvements of more than 100 % on Youngs Modulus and the tensile strength are observed for both the nonpolar aliphatic PMMA and the very polar aromatic PSU polymers, while pristine carbon nanotubes and the supramolecular nanofillers showed smaller reinforcement. These data, together with our previous report on the reinforcement of polystyrene (nonpolar and aromatic), indicate that derivatization of SWNTs as MINTs is a valid general strategy to optimize the interaction between SWNT fillers and the polymer matrix.

Interlocking Matrix and Filler for Enhanced Individualization and Reinforcement in Polymer-Single-Walled Carbon Nanotube Composites

Poor individualization and interfacial adhesion prevent single-walled carbon nanotube (SWNT)-polymer composites from reaching outstanding mechanical properties. With much larger diameters, but common structural features (high aspect ratio and absence of functional groups for covalent or supramolecular attachment with the polymer), carbon fibers face similar problems, which are addressed by covering the fibers with a thin layer of polymer. This sizing strategy has allowed carbon fibers to become the filler of choice for the highest performing materials. Inspired by this, here we investigate the use of the mechanical bond to wrap SWNTs with a layer of polymeric material to produce SWNTs mechanically interlocked with a layer of polymer. We first validate the formation of mechanically interlocked nanotubes (MINTs) using mixtures of SWNTs of relatively large average diameter (1.6 ± 0.4 nm), which are commercially available at reasonable prices and therefore could be technologically relevant as polymer fillers. We then design and synthesize by ring-opening metathesis polymerization (ROMP) a polymer decorated with multiple U-shaped molecules, which are later ring-closed around the SWNTs using metathesis. The obtained hybrids contain a high degree of individualized SWNTs and exhibit significantly increased mechanical properties when compared to the matrix polymer. We envision that this strategy could be employed to produce SWNTs interlocked with polymer layers with various designs for polymer reinforcement.

Mechanical Interlocking Enhances the Electrocatalytic Oxygen Reduction Activity and Selectivity of Molecular Copper Complexes

Efficient O₂ reduction reaction (ORR) for selective H₂O generation enables advanced fuel cell technology. Nonprecious metal catalysts are viable and attractive alternatives to state-of-the-art Pt-based materials that are expensive. Cu complexes inspired by Cu-containing O₂ reduction enzymes in nature are yet to reach their desired ORR catalytic performance. Here, the concept of mechanical interlocking is introduced to the ligand architecture to enforce dynamic spatial restriction on the Cu coordination site. Interlocked catenane ligands could govern O₂ binding mode, promote electron transfer, and facilitate product elimination. Our results show that ligand interlocking as a catenane steers the ORR selectivity to H₂O as the major product via the 4e^- pathway, rivaling the selectivity of Pt, and boosts the onset potential by 130 mV, the mass activity by 1.8 times, and the turnover frequency by 1.5 fold as compared to the noninterlocked counterpart. Our Cu catenane complex represents one of the first examples to take advantage of mechanical interlocking to afford electrocatalysts with enhanced activity and selectivity. The mechanistic insights gained through this integrated experimental and theoretical study are envisioned to be valuable not just to the area of ORR energy catalysis but also with broad implications on interlocked metal complexes that are of critical importance to the general fields in redox reactions involving proton-coupled electron transfer steps.

Mechanically interlocked derivatives of carbon nanotubes: synthesis and potential applications

An introduction to mechanically interlocked derivatives of single-walled carbon nanotubes: their main structural features, their potential advantages compared to covalent and supramolecular derivatives, how to synthesize them, and their most promising fields for application.