Highly Uniform Nanodiamond-Graphene Composites Microspheres for Electrocatalytic Hydrogen Evolution.

To progress the clean hydrogen-gas-based energy economy, there is a demand for cost-effective, highly efficient catalysts to facilitate the hydrogen evolution reaction process (HER). Due to the amazing catalytic capabilities of two-dimensional materials, extensive research has been done on these structures. However, most of the described syntheses take a lot of time, are challenging, and are ineffective. The present work demonstrates the performance of the recently reported nanodiamond/graphene composite microsphere ND-GCSs as a catalyst for HER. These spheres were produced via the microwave-irradiation approach. A modified process was adopted to improve the particle size uniformity and yield. The prepared composite spheres showed very interesting catalytic activity for the HER when assembled on a screen-printed carbon electrode. The prepared ND-GCSs@SPCE showed a significant shift of the onset potential to ca. -450 mV and a small Tafel slope value of ca. 85 mV/decade. The electron transfer was drastically enhanced with a tremendous decrease in charge transfer resistance to ca. 265 Ω. The electrocatalyst showed excellent long-term stability for the HER application. Additionally, this novel composite structure might be beneficial for diverse applications including batteries, supercapacitors, catalyst supports, and more.

Thermoelectric and power generation of 2D structured pieces of graphene-nanodiamonds nanocomposite.

Recently, the ultrafine 2D structured nanocomposite of graphene (Gr)-nanodiamonds (NDs) produced by a microwave-assisted chemical route was found to have attractive structural properties. This new 2D structured nanocomposite may be employed for a wide spectrum of applications including thermoelectricity (TE) applications. It is well established that TE materials should be highly effective to be used for designing operative devices for powering or cooling small devices. To fulfill such an objective, the functional TE material should possess a high-power factor and low thermal conductivity. In this study, NDs were successfully integrated into Gr with a magnificent structural alteration to the Gr layers/sheets. This structural modification was found to impact the TE final outcome above and below room temperature (RT). The obtained results showed that at 215 K the power factor value was increased from 4 µW m-1 K-2 for the pure Gr to ∼20 µW m-1 K-2 for the Gr-NDs nanocomposite. At higher T, e.g. 365 K, these values slightly decreased, but with clear superiority for the Gr-NDs nanocomposite. The thermal conductivity of the Gr-NDs nanocomposite was significantly reduced to ∼12% of that of the pure Gr, which could reflect a significant enhancement in the value of the figure of merit by >45 times. Furthermore, the output power generated by a single small leg module made of the Gr-NDs nanocomposite was measured and found to be measurable. The obtained values are still relatively low for practical application, but this newly produced material has great potential to be further developed for TE applications.

Sub-micron moulding topological mass transport regimes in angled vortex fluidic flow.

Shear stress in dynamic thin films, as in vortex fluidics, can be harnessed for generating non-equilibrium conditions, but the nature of the fluid flow is not understood. A rapidly rotating inclined tube in the vortex fluidic device (VFD) imparts shear stress (mechanical energy) into a thin film of liquid, depending on the physical characteristics of the liquid and rotational speed, ω, tilt angle, θ, and diameter of the tube. Through understanding that the fluid exhibits resonance behaviours from the confining boundaries of the glass surface and the meniscus that determines the liquid film thickness, we have established specific topological mass transport regimes. These topologies have been established through materials processing, as spinning top flow normal to the surface of the tube, double-helical flow across the thin film, and spicular flow, a transitional region where both effects contribute. The manifestation of mass transport patterns within the film have been observed by monitoring the mixing time, temperature profile, and film thickness against increasing rotational speed, ω. In addition, these flow patterns have unique signatures that enable the morphology of nanomaterials processed in the VFD to be predicted, for example in reversible scrolling and crumbling graphene oxide sheets. Shear-stress induced recrystallisation, crystallisation and polymerisation, at different rotational speeds, provide moulds of high-shear topologies, as 'positive' and 'negative' spicular flow behaviour. 'Molecular drilling' of holes in a thin film of polysulfone demonstrate spatial arrangement of double-helices. The grand sum of the different behavioural regimes is a general fluid flow model that accounts for all processing in the VFD at an optimal tilt angle of 45°, and provides a new concept in the fabrication of novel nanomaterials and controlling the organisation of matter.

Vertically aligned laser sliced MWCNTs.

Applications of multi-walled carbon nanotubes (MWCNTs) benefit from the availability of specific lengths of the material while keeping the outer walls pristine, for example, for applications requiring vertically aligned tubes. To this end, a simple and effective continuous flow 'top down' process to control the length of sliced MWCNTs has been developed using a vortex fluidic device (VFD) coupled with a 1064 nm pulse laser, with the process in the absence of chemicals and any auxiliary substances. Three different length distributions of the sliced MWCNTs, centered at 75 ± 2.1 nm, 300 ± 1.8 nm and 550 ± 1.4 nm, have been generated with the length depending on the VFD operating parameters and laser energy, with the processing resulting in a decrease in side wall defects of the material. We also show the ability to vertically self assemble short MWCNTs on a silicon substrate with control of the surface density coverage using a simple dipping and rinsing method.

Controlling the growth of fullerene C60 cones under continuous flow.

Micromixing of an o-xylene solution of C60 with N-N-dimethylformamide (DMF) at room temperature under continuous flow in a vortex fluidic device (VFD) results in the formation of symmetrical right cones in high yield with diameters 0.5 to 2.5 µm, pitch angle 25° to 55° and wall thickness 120 to 310 nm. Their formation is in the absence of surfactants and any other reagents, and is scalable. The cones are formed at specific operating parameters of the VFD, including rotational speed, flow rate and concentration, and varying these results in other structures such as grooved fractals. Other aromatic solvents in place of o-xylene results in the formation of rods, spicules and prisms, respectively for m-xylene, p-xylene and mesitylene.