Cooperative Synthesis of Raspberry-Like Covalent Organic Framework-Polymer Particles with a Radial Single-Crystal Grain Orientation.

Despite many efforts devoted toward the design of covalent organic frameworks (COFs) at the framework level by selecting the building blocks, their organization in the nano to meso regimes is often neglected. Moreover, the importance of processability for their applications has recently emerged and the synthesis of COF nanostructures without agglomeration is still a challenge. Herein, the first example of hybrid COF-polymer particles for which polymers are used to manipulate the 2D COF growth along a specific direction is reported. The study examines how the nature, chain-end functionality, and molar mass of the polymer influence the shaping of hybrid 2D boronate ester-linked COF-polymer particles. Catechol-poly(N-butyl acrylate) leads to the self-assembly of crystallites into quasi-spherical structures while catechol-poly(N-isopropylacrylamide) mediates the synthesis of raspberry-like COF-polymer particles with radial grain orientation. Scanning and transmission electron microscopies (SEM and TEM) and 4D-STEM-ACOM (automated crystal orientation mapping) highlight the single-crystal character of these domains with one plane family throughout the particles. Interestingly, the presence of PNIPAm on the particle surface allows their drying without co-crystallization and enables their resuspension. Kinetic investigations show that catechol-PnBuA acts as a modulator and catechol-PNIPAm induces a template effect, introducing supramolecular self-assembly properties into particles to create new morphologies with higher structural complexity, beyond the framework level.

Explosive percolation yields highly-conductive polymer nanocomposites.

Explosive percolation is an experimentally-elusive phenomenon where network connectivity coincides with onset of an additional modification of the system; materials with correlated localisation of percolating particles and emergent conductive paths can realise sharp transitions and high conductivities characteristic of the explosively-grown network. Nanocomposites present a structurally- and chemically-varied playground to realise explosive percolation in practically-applicable systems but this is yet to be exploited by design. Herein, we demonstrate composites of graphene oxide and synthetic polymer latex which form segregated networks, leading to low percolation threshold and localisation of conductive pathways. In situ reduction of the graphene oxide at temperatures of <150 °C drives chemical modification of the polymer matrix to produce species with phenolic groups, which are known crosslinking agents. This leads to conductivities exceeding those of dense-packed networks of reduced graphene oxide, illustrating the potential of explosive percolation by design to realise low-loading composites with dramatically-enhanced electrical transport properties.

Optoelectronic Properties of Atomically Thin MoxW(1-x)S2 Nanoflakes Probed by Spatially-Resolved Monochromated EELS.

Band gap engineering of atomically thin two-dimensional (2D) materials has attracted a huge amount of interest as a key aspect to the application of these materials in nanooptoelectronics and nanophotonics. Low-loss electron energy loss spectroscopy has been employed to perform a direct measurement of the band gap in atomically thin MoxW(1-x)S2 nanoflakes. The results show a bowing effect with the alloying degree, which fits previous studies focused on excitonic transitions. Additional properties regarding the Van Hove singularities in the density of states of these materials, as well as high energy excitonic transition, have been analysed as well.

Laser-Deposited Carbon Aerogel Derived from Graphene Oxide Enables NO2-Selective Parts-per-Billion Sensing.

Laser-deposited carbon aerogel is a low-density porous network of carbon clusters synthesized using a laser process. A one-step synthesis, involving deposition and annealing, results in the formation of a thin porous conductive film which can be applied as a chemiresistor. This material is sensitive to NO2 compared to ammonia and other volatile organic compounds and is able to detect ultra-low concentrations down to at least 10 parts-per-billion. The sensing mechanism, based on the solubility of NO2 in the water layer adsorbed on the aerogel, increases the usability of the sensor in practically relevant ambient environments. A heating step, achieved in tandem with a microheater, allows the recovery to the baseline, making it operable in real world environments. This, in combination with its low cost and scalable production, makes it promising for Internet-of-Things air quality monitoring.

Sulfur-doped graphene/transition metal dichalcogenide heterostructured hybrids with electrocatalytic activity toward the hydrogen evolution reaction.

A facile route for the preparation of molybdenum disulfide (MoS2) and tungsten disulfide (WS2), uniformly deposited onto sulfur-doped graphene (SG), is reported. The realization of the SG/MoS2 and SG/WS2 heterostructured hybrids was accomplished by employing microwave irradiation for the thermal decomposition of ammonium tetrathiomolybdate and tetrathiotungstate, respectively, in the presence of SG. Two different weight ratios between SG and the inorganic species were used, namely 3 : 1 and 1 : 1, yielding SG/MoS2 (3 : 1), SG/MoS2 (1 : 1), SG/WS2 (3 : 1) and SG/WS2 (1 : 1). SG and all newly developed hybrid materials were characterized by ATR-IR and Raman spectroscopy, TGA, HR-TEM and EELS. The electrocatalytic activity of the SG/MoS2 and SG/WS2 heterostructured hybrids was examined against the hydrogen evolution reaction (HER) and it was found that the presence of SG not only significantly improved the catalytic activity of MoS2 and WS2 but also made it comparable to that of commercial Pt/C. Specifically, hybrids containing higher amounts of SG, namely SG/MoS2 (3 : 1) and SG/WS2 (3 : 1), exhibited extremely low onset overpotentials of 26 and 140 mV vs. RHE, respectively. The latter results highlighted the beneficial role of SG as a substrate for immobilizing MoS2 and WS2 and stressed its significance for achieving optimum electrocatalytic performance toward the HER. Finally, examination of the Tafel slopes as extracted from the electrocatalytic polarization curves, manifested the adsorption of hydrogen as the rate-limiting step for SG/MoS2 (3 : 1), while for SG/WS2 (3 : 1) the electrochemical desorption of adsorbed hydrogen atoms to generate hydrogen was revealed to be the rate-limiting step.