Microwave-assisted synthesis and prototype oxygen reduction electrocatalyst application of N-doped carbon-coated Fe3O4 nanorods.

Fe3O4 nanorods coated with nitrogen-doped mesoporous carbon (ND-Fe3O4@mC) shells of defined thicknesses have been prepared via a new microwave-assisted approach. Microstructural characterization of these ND-Fe3O4@mC structures was performed using x-ray diffraction, x-ray photoelectron spectroscopy, transmission electron microscopy, and scanning electron microscopy. Following identification, the electrochemical performance of the catalysts was evaluated using linear sweep voltammetry with a rotating disc electrode system. The present investigation reveals enhanced oxygen reduction reaction catalytic activity and the carbon layer thickness influences oxygen diffusion to the active Fe3O4 nanorod core.

Cellulose nanocrystal-derived hollow mesoporous carbon spheres and their application as a metal-free catalyst.

In this contribution, we demonstrate the fabrication of hollow mesoporous carbon spheres (HCSs) derived from cellulose nanocrystals (CNCs). The HCSs were prepared by templating CNCs onto sacrificial silica spheres followed by heat treatment. Mesoporous carbon spheres result from the removal of the silica spheres by etching. The walls of the HCSs are approximately 4 nm thick and are composed of amorphous and graphitic carbon. The catalytic activity of the HCSs was investigated for the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) by sodium borohydride (NaBH4). The present investigation reveals the outstanding catalytic activity of these particles. The reaction rate followed pseudo-first order kinetics with k value of 4.72 × 10-3 s-1 and activity parameter of 52.2 s-1 g-1, which showed superior performance compared to that of metal nanoparticle and metal nanoparticle-carbon hybrid based catalysts.

Alkoxy-Terminated Si Surfaces: A New Reactive Platform for the Functionalization and Derivatization of Silicon Quantum Dots.

Alkoxy-terminated silicon quantum dots (SiQDs) were synthesized via hydrosilylation of aliphatic ketones on hydride-terminated SiQD (H-SiQD) surfaces under microwave-irradiation. Aromatic ketones undergo hydrosilylation on H-SiQD surfaces at room temperature without requiring any catalyst. The alkoxy-terminated SiQDs are soluble in organic solvents, colloidally stable, and show bright and size dependent photoluminescence (PL). The alkoxy-functionalized silicon surfaces were used as reactive platform for further functionalization via unprecedented ligand exchange of the alkoxy-surface groups with alkyl or alkenyl-surface groups in the presence of BH3·THF. Proton nuclear magnetic resonance ((1)H NMR), Fourier transform infrared (FTIR), and X-ray photoelectron spectroscopy (XPS) spectroscopy confirmed alkoxy-terminated surfaces and their ligand exchange reactions in the presence of various alkenes and alkynes.

Ultrasound assisted wet media milling synthesis of nanofiber-cage LiFePO4/C.

To meet the objectives of the Intergovernmental Panel on Climate Change nations are adopting policies to encourage consumers to purchase electric vehicles. Electrification of the automobile industry reduces greenhouse gases but active metals for the cathode-LiCoO2 and LiNiO2-are toxic and represent an environmental challenge at the end of their lifetime. LiFePO4 (LFP) is an attractive alternative that is non-toxic, thermally stable, and durable but with a moderate theoretical capacity and a low electrical conductivity. Commercial technologies to synthesize LFP are energy-intensive, produce waste that incurs cost, and involve multiple process steps. Here we synthesize LFP precursor with lignin and cellulose in a sonicated grinding chamber of a wet media mill. This approach represents a paradigm shift that introduces mechanochemistry as a motive force to react iron oxalate and lithium hydrogen phosphate at ambient temperature. Ultrasound-assisted wet media milling increases carbon dispersion and reduces the particle size simultaneously. The ultrasound is generated by a 20 kHz,500 W automatic tuning ultrasound probe. The maximum discharge rate of the LFP synthesized this way was achieved with cellulose as a carbon source, after 9 h milling, at 70% ultrasound amplitude. After 2.5 h of milling, the particle size remained constant but the crystal size continued to drop and reached 29 nm. Glucose created plate-like particles, and cellulose and lignin produced spindle-shaped particles. Long mill times and high ultrasound amplitude generate smoother particle surfaces and the powder densifies after a spray drying step.

Spherical nitrogen-doped hollow mesoporous carbon as an efficient bifunctional electrocatalyst for Zn-air batteries.

Materials based upon porous carbon have gained considerable attention due to their high surface area, electric conductivity, thermal and chemical stability, low density, and availability. These superior properties make them ideal for diverse applications. Doping these carbon nanostructures holds promise of designing the properties of these structures and opening the door to practical applications. Herein, we report the preparation of hollow N-doped mesoporous carbon (HMC) spheres fabricated via polymerization and carbonization of dopamine on a sacrificial spherical SiO(2) template that is removed upon hydrofluoric acid etching. The morphology and structural features of these HMCs were evaluated using scanning electron microscopy and transmission electron microscopy and the N-doping (7.1 at%) was confirmed by X-ray photoelectron spectroscopy (XPS). The oxygen reduction/evolution reaction (ORR/OER) performance of N-doped HMC was evaluated using rotating disk electrode (RDE) voltammetry in an alkaline electrolyte. N-doped HMC demonstrated a high ORR onset potential of -0.055 V (vs. Hg/HgO) and excellent stability. The outstanding bifunctional activity was implemented in a practical Zn-air battery (ZAB), which exhibited a small charge-discharge voltage polarization of 0.89 V and high stability over repeated cycling.