We reported the preparation of carbon nanotubes adhering BaTiO 3 nanoparticles (BT@CNTs) via chemical vapor deposition (CVD). Scanning electron microscopy, transmission electron microscope and Raman spectroscopy were carried out in order to confirm the successful adhesion. Dielectric properties of the PVDF-HFP composites filled by BT@CNTs were also studied. With the content of BT@CNTs increasing, the dielectric constant of composites remarkably increased, but the loss tangent gradually decreased. At 10 vol%, the dielectric constant of the PVDF-HFP/BT@CNTs composite was significantly increased to 27.7 at 50 Hz, which was 3 times and 65% higher than that of the pure PVDF-HFP and PVDF-HFP/BT composite, respectively. The loss tangent of the PVDF-HFP/BT@CNTs composite was lower even than that of pure PVDF-HFP. These attractive features of the PVDF-HFP/BT@CNTs composites suggested that the method proposed herein was a new approach to develop high performance composites, especially those with high dielectric constant and low dielectric loss.
Phosphate (P) fixed on Fe‐ and Al‐(hydr)oxides can be released into solution by coexisting anions or molecules that have strong reactivity with the mineral surfaces. Bacteria have been shown to adhere strongly on to the (hydr)oxides through physical or chemical forces, or both. It is still unknown, however, whether bacteria can desorb P from oxides. We examined the desorption of P from haematite (α‐Fe2O3) by Bacillus subtilis and Pseudomonas fluorescens through the combined use of in‐situ attenuated total reflectance Fourier‐transform infrared (ATR‐FTIR) spectroscopy and macroscopic batch experiments. The ATR‐FTIR data of ternary bacteria–P–haematite systems indicated a release of P that was concurrent with the attachment of bacteria on to the haematite surface, giving direct and in‐situ evidence for the displacement of P by bacteria. The P‐desorbing ability of bacteria was quantified by batch desorption experiments, and was further supported by the inhibitory role of bacteria in P adsorption on to haematite under varying concentrations of P and amounts of bacteria. In‐situ ATR‐FTIR investigations and Derjaguin–Landau–Verwey–Overbeek (DLVO) prediction suggested that bacteria might compete for sorption sites with P through their electrostatic and chemical interactions (coordination of bacterial phosphate and carboxyl groups on the haematite surface) with the haematite surface. In addition, the bacteria reduced greatly the positive charge of haematite, and the reduction correlated non‐linearly with the decline in P adsorption. Therefore, the P‐mobilizing ability of bacteria is probably attributed to the competition between P and bacterial surface groups and reduction in the positive charge on haematite by bacteria. These findings elucidate a potential role for bacteria in mobilizing P that is chemically adsorbed on Fe‐oxides, which enhances the availability of P to plants and its mobility in natural environments. Highlights Whether bacteria can desorb phosphate from oxides remained unknown. Bacteria enhanced desorption of phosphate from haematite and inhibited its adsorption by haematite. Electrostatic and chemical interactions might help bacteria compete with phosphate. Reduction in positive charges might also contribute to phosphate‐mobilizing ability of bacteria.
All-optical locking of the frequency difference between two laser diodes onto a Raman transition is demonstrated. The properties of Raman-type polarization spectroscopy are discussed and exemplified in the cases of the 3.036 GHz Raman resonance of the 85Rb D2 line. The generation of a polarization-selective Raman resonant optical feedback ensures the Raman optical locking of the slave diode laser onto the master oscillator.
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