Enhanced mechanism and experimental research of laser cavitation degradation of methylene blue by AuNPs

As a novel degradation method, laser cavitation degradation suffers from low degradation efficiency in the absence of medium gain. An enhancement method of laser cavitation using Au nanoparticles (AuNPs) is proposed for degrading organic dye wastewater. Methylene blue (MB) aqueous solution was employed as the simulated organic dye wastewater. The strong absorption characteristics of AuNPs and the mechanism underlying AuNPsenhanced laser cavitation degradation were analyzed. The local field enhancement effect and shock wave signal were obtained. The relationships among the AuNPs, laser energy, the number of irradiations number and the degradation effect were investigated. The results show that the local field enhancement coefficient of AuNPs in Methylene blue (MB) aqueous solution reached 1.9, and the degradation degree increased by three times compared with that of pure solution because that thermal decomposition and oxidation of hydroxyl (center dot OH) radicals were enhanced by AuNPs. With the laser energy levels increasing (70-110 mJ), the intensity of shock wave increased by 2-4 times and the degree of degradation increased by three times. The degradation rate reached 37.7 % within 3 min and the irradiation number reached 1600. Compared with other methods, the AuNPs-enhanced laser cavitation approach has exhibited remarkable controllability together with a higher degradation efficiency.

Automated summary

Laser cavitation degradation has low efficiency without medium gain, but can be enhanced using Au nanoparticles (AuNPs) for degrading organic dye wastewater. The strong absorption characteristics of AuNPs and the mechanism underlying the enhancement were analyzed. The local field enhancement effect and shock wave signal were obtained, and the relationships among AuNPs, laser energy, irradiations number and degradation effect were investigated. Compared with other methods, AuNPs-enhanced laser cavitation approach exhibits remarkable controllability and higher degradation efficiency.