A novel flexible zinc oxide/poly­(vinylidene fluoride) (ZnO/PVDF) nanocomposite was prepared by electrospinning for fabricating a piezoelectric nanogenerator (PNG). The ZnO nanoparticles (NPs) and nanorods (NRs) were used as nanofillers of piezoelectric PVDF to prepare fibrous nanocomposite membranes. It has been found that the addition of piezoelectric ZnO NPs and NRs can improve the overall performance of the PNGs fabricated with the electrospun membranes. A large electrical throughput (open circuit voltage ∼85 V and short circuit current ∼2.2 μA) from the ZnO NR/PVDF fiber membrane-based PNG (ZR-PNG) indicates that ZnO NRs are effective functional fillers for PVDF. The high aspect ratio and flexibility characteristics of ZnO NRs were found to be highly beneficial for improving the piezoelectric properties of the nanocomposites. ZnO NRs act as nucleating agents of β-phase PVDF, and ZnO NRs can also produce piezoelectric charges when they deform with the composite fibrous membrane. It has been concluded that the obvious synergistic effects between the piezoelectric nanofillers and electroactive β-crystals of PVDF in the ZnO NRs/PVDF composites are useful for the construction of the high-performance flexible PNG. In addition, the fabricated ZR-PNG can light up commercial light emitting diodes (40 white, 36 blue) and charge the capacitors in a very short time (3 V is accomplished in 25 s), which indicates the potential of the ZR-PNG for portable, wearable, flexible, or self-powered electronic devices.

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For the first time we observed well-resolved Ca(I) and Ca(II) signal changes in fluorohydroxyapatites with different fluorine contents by solid state NMR. The experiment results show that fluorine ions perturb the chemical environment of Ca(II) ions and OH À ions more than phosphorus tetrahedra and Ca(I) ions.Hydroxyapatite (HA) is the main mineral in teeth and bones within the human body. Tooth enamel, the hardest and most highly mineralized substance in the human body, contains roughly 96 percent of hydroxyapatite. Fluorine-substituted hydroxyapatite (FHA) is chemically more stable than hydroxyapatite in acid environments. 1 A higher concentration of FHA in tooth enamel decreases tooth dissolution and therefore decreases the incidence of tooth decay. It has also been reported that uorine-substituted hydroxyapatites support cellular proliferation and colonization and promote bone growth. 2 Over recent years, uorohydroxyapatite has been used as bioactive ceramic coatings due to its enhanced biocompatibility as compared to other ceramic coatings. 3,4 Fluoride-containing bioactive glasses are of particular interest in many elds of dentistry and orthopedics because they are osteoconductive and can combine the benets of uorapatite (FA) with the boneregenerative properties of bioactive glasses. 5-10 In the FHA composition, part of the OH À ions are substituted by F À ions in order to improve the material stability. However, most studies so far have focused on the preparation methods of FHA and its thermal and chemical stability. 11 The effects of different uo-rine contents on the structure have seldom been studied systematically. The resistance of uorohydroxyapatite to acids depends largely on its chemical structure; it is of great interest to determine its structure that prevents the process of erosion.The hydroxyapatite structure and substitution of hydroxyapatite by different anions and cations including Pb 2+ , Mg 2+ , Ti 4+ , CO 3 2À , Cl À and F À ions 12-18 have been extensively studied and characterized by X-ray diffraction (XRD), 5-10,14-16,23 solid state NMR 12-14,17-23 and Raman spectroscopy. 18 Molecular dynamics simulations have also been used to investigate the transport of uorine in uorapatite and this study found that a sequence of F À ions move along the c-axis in a concerted mechanism, via lattice and interstitial sites. 24 In this study, a series of FHAs with varying uorine levels (Ca 10 (PO 4 ) 6 (OH) 2Àx F x from x ¼ 0 to 2) were synthesized by the wet precipitation method using Ca(NO 3 ) 2 $4H 2 O and (NH 4 ) 2 HPO 4 as starting materials and NH 4 F as a source for uorine incorporation (see ESI † for material synthesis and experimental details). The structures of the synthesized FHAs were characterized by 1 H, 43 Ca, 31 P and 19 F NMR MAS solid-state NMR, XRD and Raman spectroscopy to examine the effect of uorine substitution on the hydroxyapatite structure. XRD patterns of uorohydroxyapatites containing different uorine levels are shown in Fig. 1. The typical peaks of apatites are ...