Radical-initiated support: Xanthates were used as chemical reagents for the sidewall covalent functionalization of carbon nanotubes (see figure). The best grafting yields were obtained with stoichiometric ratios of xanthate and the radical initiator lauroyl peroxide. One grafted function was used as a tether for bimetallic cluster compounds, which were converted into very small (1-2 nm) supported nanoparticles upon heating.

Graphene has attracted much attention for sensing applications in recent years. Its largest surface-to-volume ratio makes graphene sensors able to potentially detect a single molecule and its extremely high carrier mobility ensures low electrical noise and energy consumption. However, pristine graphene is chemically inert and weakly adsorbs gas molecules, while defective and/or doped graphene has stronger adsorption ability (high sensitivity). The high sensitivity is related to the increased number of defects or traps in graphene where the gas molecules can be readily grafted, changing the sensor resistance. Nonetheless, similar resistance changes could be induced under exposure to different gases, resulting in a lack of selectivity. Functional groups differ drastically from defects or traps since the former selectively anchor specific molecules. Here, we comparatively investigate three functionalization routes and optimize a defect-free one (2,3,5,6,-Tetrafluorohydroquinone, TFQ molecules) for the fabrication of graphene gas sensors. We use TFQ organic molecules as chemical recognition links between graphene and formaldehyde, the most common indoor pollutant gas. The sensor demonstrates a high response and a good selectivity for formaldehyde compared with interfering organic vapours. Particularly, the sensor has a strong immunity to humidity. Our results highlight that defect-free functionalization based on organic molecules not only increases the sensor's response but also its selectivity, paving the way to the design of efficient graphene-based sensors.

The covalent grafting of xanthates onto carbon nanotubes (CNTs) by using peroxides as radical initiators was studied. Carbon nanotubes were functionalized with seven different xanthates by employing dilauroyl peroxide as a radical initiator. This allowed for the concomitant double functionalization by both xanthate and peroxide moieties. This one‐step double functionalization was demonstrated by the use of a heteroatom‐containing peroxide, and optimization reactions were performed to determine the maximum grafting yields of each component. The maximum grafting yield of the xanthate occurred when the xanthate and peroxide were introduced in stoichiometric amounts, whereas the grafting yield of the peroxide was simply a function of the quantity of peroxide introduced to the reaction. On the basis of these results, a mechanism for this double functionalization is proposed. Finally, some postfunctionalization reactions of the grafted moieties were performed as proof that their chemical integrity was retained after being anchored to the CNT surface.

Catalysis plays a crucial role in chemical research and industry, yet its dynamics at the nanoscale has been little explored. Here, we use carbon nanotube transistors to measure in real time the catalytic activity of metallic nanoparticles. First, we present a method based on covalent nanotube functionalization to selectively attach a small number of nanoparticles on an individual carbon nanotube device. We demonstrate the covalent attachment of bimetallic Ru-Pt clusters and their aggregation into less than 10 nanoparticles (RuPtNP) on each nanotube device, using a combination of techniques including electrical spectroscopy and atomic force microscopy. Second, we monitor the catalytic transformation of dimethylphenylsilane in dimethylphenylsilanol with water in real-time, through changes in the nanotube electrical conductance. Upon exposure to silane, RuPtNP-decorated carbon nanotube devices show a rapid change in electrical conductance that decays slowly back to its initial state. We present the effect of silane concentration and electrostatic doping of the nanotube, and discuss possible mechanisms for the interaction between the catalytic reaction and the electrical signature. Carbon nanotube electronic sensors form a powerful tool to investigate various catalysis reactions, providing real-time monitoring over a broad range of time scales.