Black phosphorus (BP) has attracted significant interest as a monolayer or few-layer material with extraordinary electrical and optoelectronic properties. However, degradation in air and other environments is an unresolved issue that may limit future applications. In particular the role of different ambient species has remained controversial. Here, we report systematic experiments combined with ab-initio calculations that address the effects of oxygen and water in the degradation of BP. Our results show that BP rapidly degrades whenever oxygen is present, but is unaffected by deaerated (i.e., O 2 depleted) water. This behavior is rationalized by oxidation involving a facile dissociative chemisorption of O 2 , whereas H 2 O molecules are weakly physisorbed and do not dissociate on the BP surface. Oxidation (by O 2 ) turns the hydrophobic pristine BP surface progressively hydrophilic. Our results have implications on the development of encapsulation strategies for BP, and open new avenues for exploration of phenomena in aqueous solutions including solution-gating, electrochemistry, and solutionphase approaches for exfoliation, dispersion, and delivery of BP.

Graphite is exfoliated into graphene by shearing vortex fluidic films of N-methyl-pyrrolidone (NMP), as a controlled process for preparing oxide free graphene, and for exfoliating the corresponding boron nitride sheets.

A vortex fluidic device (VFD) involving a rapidly rotating tube open at one end forms dynamic thin films at high rotational speed for finite sub-millilitre volumes of liquid, with shear within the films depending on the speed and orientation of the tube. Continuous flow operation of the VFD where jet feeds of solutions are directed to the closed end of the tube provide additional tuneable shear from the viscous drag as the liquid whirls along the tube. The versatility of this simple, low cost microfluidic device, which can operate under confined mode or continuous flow is demonstrated in accelerating organic reactions, for model Diels-Alder dimerization of cyclopentadienes, and sequential aldol and Michael addition reactions, in accessing unusual 2,4,6-triarylpyridines. Residence times are controllable for continuous flow processing with the viscous drag dominating the shear for flow rates >0.1 mL/min in a 10 mm diameter tube rotating at >2000 rpm.

Through understanding that the fluid in the vortex fluidic device (VFD) housing an inclined rapidly rotating tube exhibits resonance behaviours from the confining boundaries of the glass surface and the...

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