Novel application of Ag/PbBiO2I nanocomposite in piezocatalytic degradation of rhodamine B via harvesting ultrasonic vibration energy

Ag/PbBiO₂I nanocomposite was synthesized and firstly applied in piezocatalytic degradation of rhodamine B (RhB) under ultrasonic vibration. The two-dimensional structure endows PbBiO₂I nanosheets piezoelectric property, so that it can drive the piezocatalytic reaction under ultrasonic vibration. The loading of Ag nanoparticles forms Schottky barriers between the Ag-PbBiO₂I contact region, which improves the separation of charge carriers and subsequently increases the piezocatalytic efficiency. The RhB degradation rate of the optimal Ag/PbBiO₂I sample is 0.0165 min⁻¹, which reaches 6.8 times that of pure PbBiO₂I. This work indicates that the PbBiO₂I nanosheet shows promising potential in utilizing ultrasonic vibration energy.     

A novel NiO/BaTiO3 heterojunction for piezocatalytic water purification under ultrasonic vibration

This work designed and prepared a novel heterojunction composite NiO/BaTiO₃ through a method of photodeposition and used it in piezocatalytic dye removal for the first time. Results of the piezocatalytic test indicated that the NiO/BaTiO₃ composite presented superior efficiency and stability in the RhB degradation under the vibration of ultrasonic waves. The best NiO/BaTiO₃ sample synthesized under light irradiation for 2 h displayed an RhB degradation rate of 2.41 h⁻¹, which was 6.3 times faster than that of pure BaTiO₃. By optimizing the piezocatalytic reaction conditions, the degradation rate constant of NiO/BaTiO₃ can further reach 4.14 h⁻¹ A variety of systematic characterizations were executed to determine the reason for the excellent piezocatalytic performance of NiO/BaTiO₃. The band potentials of NiO and BaTiO₃ are found to coincide, and at their contact interface, they may create a type-II p-n heterojunction structure. Driven by the potential difference and the built-in electric field, piezoelectrically enriched charge carriers can migrate between NiO and BaTiO₃, resulting in improved efficiency in charge separation and an increase in the piezoelectric catalytic performance. This study may provide a potential composite catalyst and a promising idea for the design of highly efficient catalysts in the field of piezoelectric catalysis.     

Sonocatalytic degradation of acid red B and rhodamine B catalyzed by nano-sized ZnO powder under ultrasonic irradiation

Nano-sized ZnO powder was introduced to act as the sonocatalyst after the treatment of high-temperature activation, and the ultrasound of low power was used as an irradiation source to induce nano-sized ZnO powder performing sonocatalytic degradation of acid red B and rhodamine B. At the same time, the effects of operational parameters such as solution pH value, initial concentration of dyestuff and addition amount of nano-sized ZnO powder have been examined in this paper. We found that the degradation ratios of acid red B and rhodamine B in the presence of nano-sized ZnO powder were much higher than that with only ultrasonic irradiation. However, the degradation ratio of acid red B was about two times higher than that of rhodamine B for the initial concentration of 10.0 mg/L, addition amount of 1.0 g/L nano-sized ZnO powder, solution acidity of pH 7.0 and 60 min irradiation experimental condition. The difference of the degradation ratios can be illustrated by the difference of chemical forms of acid red B and rhodamine B in aqueous solution and the surface properties of nano-sized ZnO particles. In addition, the researches on the kinetics of sonocatalytic reactions of acid red B and rhodamine B have also been performed and found to the follow pseudo first-order kinetics. All the experiments indicated that the sonocatalytic method in the presence of nano-sized ZnO powder was an advisable choice for the treatments of non- or low-transparent organic wastewaters in future.     

Effect of multi-walled carbon nanotubes loaded with Ag nanoparticles on the photocatalytic degradation of rhodamine B under visible light irradiation

Multi-walled carbon nanotubes loaded with Ag nanoparticles (Ag/MWNTs) were prepared by two methods (direct photoreduction and thermal decomposition). The photocatalytic activity of Ag/MWNTs for the degradation of rhodamine B (RhB) under visible light irradiation was investigated in detail. The adsorption and photocatalytic activity tests indicated that the MWNTs served as both an adsorbent and a visible light photocatalyst. The photocatalytic activity of MWNTs was remarkably enhanced when the Ag nanoparticles were loaded on the surface of MWNTs. Moreover, the visible light photocatalytic activity of Ag/MWNTs depended on the synthetic route. On the basis of the experimental results, a possible visible light photocatalytic degradation mechanism was discussed.     

Sono-enhanced degradation of dye pollutants with the use of H2O2 activated by Fe3O4 magnetic nanoparticles as peroxidase mimetic

Sono-enhanced degradation of a dye pollutant Rhodamine B (RhB) was investigated by using H₂O₂ as a green oxidant and Fe₃O₄ magnetic nanoparticles (MNPs) as a peroxidase mimetic. It was found that Fe₃O₄ MNPs could catalyze the break of H₂O₂ to remove RhB in a wide pH range from 3.0 to 9.0 and its peroxidase-like activity was significantly enhanced by the ultrasound irradiation. At pH 5.0 and temperature 55 °C, the ultrasound-assisted H₂O₂–Fe₃O₄ catalysis removed about 95% of RhB (0.02 mmol L⁻¹) in 15 min with a apparent rate constant of 0.15 min⁻¹ for the degradation of RhB, being 6.5 and 37.6 folds of that in the simple catalytic H₂O₂–Fe₃O₄ system, and the simple ultrasonic US-H₂O₂ systems, respectively. The beneficial synergistic behavior between Fe₃O₄ catalysis and ultrasonic was demonstrated to be dependent on Fe₃O₄ dosage, H₂O₂ concentration, pH value and temperature. As a tentative explanation, the observed significant synergistic effects was attributed to the positive interaction between cavitation effect accelerating the catalytic breakdown of H₂O₂ over Fe₃O₄ nanoparticles, and the function of Fe₃O₄ MNPs providing more nucleation sites for the cavitation inception.