Hexagonal boron nitride (h-BN) is traditionally considered to be insoluble in water. However, here we demonstrate that water is effective to exfoliate the layered h-BN structures with the assistance of bath sonication, forming “clean” aqueous dispersions of h-BN nanosheets without the use of surfactants or organic functionalization. Besides few-layered h-BN nanosheets, there was also evidence on the presence of monolayered nanosheet and nanoribbon species. Most nanosheets were of reduced lateral sizes, which was attributed to the cutting of parent h-BN sheets induced by the sonication-assisted hydrolysis (evidenced by the ammonia test and spectroscopy results). The hydrolysis effect also assisted in the exfoliation of h-BN nanosheets in addition to the solvent polarity effect. The h-BN nanosheets in such “clean” aqueous dispersions were demonstrated to be conveniently processed via solution methods with retained physical properties. The dispersed h-BN nanosheets in water also exhibited strong affinity toward proteins such as ferritin, suggesting that the nanosheet surfaces were available for further bioconjugations. The above findings may pave the way for the applications of these novel 2-dimensional nanomaterials in various fields such as composites, electronics, and biology.

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In this paper, the interdisciplinary energy harvesting issues on piezoelectric energy harvesting were investigated using a '33' mode (mechanical stress and/or electric field are in parallel to the polarization direction) lead zirconate titanate multilayer piezoelectric stack (PZT-Stack). Key energy harvesting characteristics including the generated electrical energy/power in the PZT-Stack, the mechanical to electrical energy conversion efficiency, the power delivered from the PZT-Stack to a resistive load, the electrical charge/energy transferred from the PZT-Stack to a super-capacitor were systematically addressed. Theoretical models for power generation and delivery to a resistive load were proposed and experimentally affirmed. In a quasi-static regime, 70% generated electrical powers were delivered to matched resistive loads. A 35% mechanical to electrical energy conversion efficiency, which is more than 4 times higher than other reports, for the PZT-Stack had been obtained. The generated electrical power and power density were significantly higher than those from a similar weight and size cantilever-type piezoelectric harvester in both resonance and off-resonance modes. In addition, our study indicated that the capacitance and piezoelectric coefficient of the PZT-Stack were strongly dependent on the dynamic stress.

We have studied the adsorption of tetraphenylporphyrin (2HTPP) and its carboxylated counterpart mono-para-carboxyphenyltriphenylporphyrin (MCTPP) on an atomically defined Co3O4(111) film under ultrahigh vacuum (UHV) conditions. Using time-resolved infrared reflection absorption spectroscopy (TR-IRAS), we show that 2HTPP adsorbs molecularly in a flat-lying orientation, whereas MCTPP binds to the surface via formation of a chelating bidentate carboxylate upon deposition at 400 K. Combining TR-IRAS and density-functional theory (DFT), we determine the molecular tilting angle as a function of coverage. We show that the MCTPP adsorption geometry changes from a nearly flat-lying orientation (tilting angle <30°) at low coverage to a nearly perfectly upright-standing orientation (tilting angle of approximately 80°) in the full monolayer.