The Microemulsion Synthesis of Hydrophobic and Hydrophilic Silicon Nanocrystals

Silicon nanocrystals, also called quantum dots, have unique optical properties when in the quantum‐confinement regime. These optical properties make silicon nanocrystals promising materials for a wide variety of applications ranging from optoelectronic devices to fluorophores in biological imaging. A liquid‐phase synthetic approach is reported using surfactant molecules to control particle growth, producing highly monodisperse silicon particles. The surface of the nanocrystals are capped by functional organic molecules that passivate and protect the silicon particles from oxidation, enabling the particles to be used in hydrophobic and hydrophilic applications. The use of hydrophilic silicon quantum dots as optical probes is illustrated by the imaging of Vero cells.     

Rhodium nanoparticles from cluster seeds: control of size and shape by precursor addition rate

The size-tunable synthesis of poly(vinylpyrrolidone)-stabilized cuboctahedral rhodium nanoparticles with mean diameters ranging between 3-7 nm and multipod structures was accomplished using seeded growth methods. Isotropic PVP-capped 2.9 nm seeds were prepared by ligand exchange on rhodium-triphenylphosphine metal-organic clusters. Quantitative investigation of reaction parameters in ethylene glycol revealed that size and shape could be controlled at a single reaction temperature of 120 degrees C. The rate of rhodium monomer addition was found to be critical for monodispersity and shape control, regardless of thermodynamic factors. Solvent viscosity, varied by changing the polyol solvents, indicated that autocatalytic addition kinetics are responsible for isotropic versus anisotropic growth.     

Low-cost struvite production using source-separated urine in Nepal

This research investigated the possibility of transferring phosphorus from human urine into a concentrated form that can be used as fertilizer in agriculture. The community of Siddhipur in Nepal was chosen as a research site, because there is a strong presence and acceptance of the urine-diverting dry toilets needed to collect urine separately at the source. Furthermore, because the mainly agricultural country is landlocked and depends on expensive, imported fertilizers, the need for nutrient security is high. We found that struvite (MgNH₄PO₄·6H₂O) precipitation from urine is an efficient and simple approach to produce a granulated phosphorus fertilizer. Bittern, a waste stream from salt production, is a practical magnesium source for struvite production, but it has to be imported from India. Calculations show that magnesium oxide produced from locally available magnesite would be a cheaper magnesium source. A reactor with an external filtration system was capable of removing over 90% of phosphorus with a low magnesium dosage (1.1 mol Mg mol P), with coarse nylon filters (pore width up to 160 ± 50 μm) and with only one hour total treatment time. A second reactor setup based on sedimentation only achieved 50% phosphate removal, even when flocculants were added. Given the current fertilizer prices, high volumes of urine must be processed, if struvite recovery should be financially sustainable. Therefore, it is important to optimize the process. Our calculations showed that collecting the struvite and calcium phosphate precipitated spontaneously due to urea hydrolysis could increase the overall phosphate recovery by at least 40%. The magnesium dosage can be optimized by estimating the phosphate concentration by measuring electrical conductivity. An important source of additional revenue could be the effluent of the struvite reactor. Further research should be aimed at finding methods and technologies to recover the nutrients from the effluent.     

Electrocatalytic Water Oxidation at Neutral pH by a Nanostructured Co(PO3)2 Anode

Cobalt metaphosphate Co(PO₃)₂ nanoparticles are prepared via the thermolytic molecular precursor (TMP) method. A Ni form electrode decorated with Co(PO₃)₂ nanoparticles is evaluated as an anode for water oxidation electrocatalysis in pH 6.4 phosphate‐buffered water. Catalytic onset occurs at an overpotential of ca. 310 mV, which is 100 mV lower than that observed for Co₃O₄ nanoparticles, with a comparable surface area under identical conditions. A per‐metal turnover frequency (TOF) of 0.10–0.21 s^?1 is observed at an overpotential, η, of 440 mV, which is comparable to the highest rate reported for a first‐row metal heterogeneous catalyst. Post‐catalytic characterization of the catalyst resting state by X‐ray photoelectron spectroscopy (XPS) and Raman spectroscopy reveals that surface rearrangement occurs, resulting in an oxide‐like surface overlayer.