A high-intensity low-frequency acoustic generator based on the Helmholtz resonator and airflow modulator.

The high-intensity low-frequency acoustic sources have essential applications in acoustic biological effects research, airport bird repelling, and boiler ash removal. However, generating high-intensity low-frequency acoustic waves in open space is difficult. In this paper, a low-frequency acoustic generator with a resonant cavity used to enhance the acoustic intensity in open space was developed, which is an aerodynamic acoustic generator to radiates a high-intensity acoustic wave of 52Hz. Some experiments were carried out to measure this generator's internal flow field and radiated acoustic field characteristics, including the propagation characteristics at 100m. The experimental results show that the resonant enhancement effect is presented near the predetermined resonance frequency, and the enhanced value is about 4dB. The acoustic intensity for 52Hz at 1m position is 124dB. By combining the Helmholtz resonator with the airflow modulator, the airflow resonance in the resonator enhances the air pressure pulsation inside the chamber and increases the disturbance of acoustic radiation to the air. So as to improve the sound intensity and radiation efficiency in the low-frequency range.

Cubic AgBiS2 Powder Prepared Using a Facile Reflux Method for Photocatalytic Degradation of Dyes.

The ternary chalcogenide AgBiS2 has attracted widespread attention in the field of photovoltaic and photoelectric devices due to its excellent properties. In this study, AgBiS2 powders with an average diameter of 200 nm were prepared via a simple and convenient reflux method from silver acetate, bismuth nitrate pentahydrate, and n-dodecyl mercaptan. The adjustment of the ratios of Ag:Bi:S raw materials and of the reaction temperatures were carried out to investigate the significance of the synthesis conditions toward the composition of the as-synthesized AgBiS2. The results of XRD indicated that the powders synthesized at a ratio of 1.05:1:2.1 and a synthesis temperature of 225 °C have the lowest bismuth content and the highest purity. The synthesized AgBiS2 crystallizes in a rock salt type structure with the cubic Fm3¯m space group. Scanning and transmission electron microscopy, thermogravimetric analysis, ultraviolet-visible-near-infrared spectra, and photocatalytic degradation performance were employed to characterize the as-synthesized samples. The results demonstrated that AgBiS2 powders display thermal stability; strong absorption in the ultraviolet, visible, and partial infrared regions; and an optical bandgap of 0.98 eV. The obtained AgBiS2 powders also have a good degradation effect on the methylene blue solution with a degradation efficiency of 58.61% and a rate constant of 0.0034 min-1, indicating that it is an efficient strategy for sewage degradation to reduce water pollution.

Solvent engineering to regulate the phase of copper zinc tin sulfide nanocrystals.

Copper zinc tin sulfide (Cu2ZnSnS4, CZTS) is attracting interest in photovoltaic applications due to its proper band gap, low cost and low toxicity. It has been found that two phases can be fabricated, i.e. kesterite and wurtzite CZTS structures. Though kesterite CZTS is proven to be thermodynamically stable, the free energy difference between kesterite and wurtzite CZTS is rather small. So, wurtzite CZTS can also stably exist under ambient conditions. Controlling the phase formation can expand the dimensions to optimize the performance of applications based on CZTS. In this study, we found that phase control can be achieved by simply using a mixed solvent of ethylene glycol and triethylenetetramine (TETA) in a two-stage heating process. It is found that the incorporation of the reductive solvent of TETA during the 1st heating process converts the phase of the precipitates from CuS (TETA poor) to Cu7S4 (TETA rich). In the subsequent 2nd heating stage, the phase of the final products is determined to be kesterite CZTS originating from CuS and wurtzite CZTS from Cu7S4, respectively. Thus, the key to control the phases of the final products is to control the chemical environment of Cu under Cu1+-rich or Cu2+-rich conditions in the fabrication process, which corresponds to the phase of the final products of wurtzite CZTS or kesterite CZTS, respectively. This summarized principle can not only be used to explain the previous versatile experimental results but also to guide the controlled synthesis of various phases of CZTS and CZTS-like materials in applications.