Amino group exhibits alkaline properties. Amino functionalized imidazole-modified silicas would benefit the adsorption of phenolic compounds. Coupling agent between the silica and the imidazolium ring has an effect on adsorption performance. In this paper, two adsorbents were synthesized for the surface bonding of N-(3-aminopropyl)-imidazole onto silicas modified by 3-chloropropyltriethoxysilane and 3-mercaptopropyltrimethoxysilane, respectively. Infrared spectra, elemental analysis, thermogravimetric analysis and N 2 adsorptiondesorption isotherms were used to characterize the two adsorbents, and their adsorption capacities of 2,4-dinitrophenol from aqueous solutions were investigated in detail. The experimental results indicated that amino group plays an important role in the enhancement of adsorption capacities of 2,4-dinitrophenol. The adsorbent with 3-mercaptopropyltrimethoxysilane as coupling agent exhibited lower adsorption capacity due to a weak electron-electron repulsion between the non-bonding electrons of sulfur atom and p electrons of benzene ring of 2,4-dinitrophenol. The adsorption kinetics fitted well with pseudo-second-order model. The two adsorbents could be regenerated and reused eight times at least by washing with HCl. The adsorption mechanism was also discussed.
Very low-frequency (VLF) and ultralow-frequency (ULF) electromagnetic waves have the advantage of high penetration and low propagation loss in wireless communication systems and are mainly used for underwater and underground communications, as well as for earthquake and lightning forecasting. At present, VLF and ULF antennas are mostly bulky and require hundreds of antennas and more to be set up, which is costly and inefficient. In this paper, we propose to generate VLF and ULF signals by rotating a multilayer multipair electret thin-film electret driven by an excitation device, which improves the problem of low radiation efficiency of VLF and ULF signals and the large size of conventional low-frequency transmitting antennas. Based on a multilayer, multipair electret film mechanical antenna, a magnetic field propagation model is developed, and the relationship between the magnetic flux density mode and the number of layers of electret films, as well as the relationship between the antenna emission frequency and the motor rotation frequency and the number of pairs of electret films, is analyzed. The selection of a suitable model for practical situations based on conditions such as antenna size and propagation distance is illustrated. The research work is of great importance for guiding the design of mechanical antennas and optimizing antenna structures.
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