Pure and erbium (Er)-doped ZnO samples were synthesized through a sonochemical method and characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV-Vis spectroscopy, and X-ray photoelectron spectroscopy (XPS) analysis. The synthesized samples were used as a catalyst for the sonocatalytic decolorization of Reactive Orange 29 (RO29) as a model organic pollutant. The decolorization efficiency was 63%, 68%, 88%, and 75% for undoped, 2%, 4%, and 6% Er-doped ZnO, respectively. The effect of different experimental parameters including catalyst content, dye concentration and ultrasound power was investigated on the sonocatalytic decolorization of RO29. Among several radical scavengers (i.e. chloride, carbonate and sulfate anions and t-butanol), the chloride anion showed the most inhibitive effect on the sonocatalysis performance. Improvement of the sonocatalytic process by K2S2O8 and H2O2 enhancers was also studied. The reusability of the synthesized sonocatalyst was evaluated in several consecutive runs, and a decline of only 4% was observed in the process performance after five runs. The intermediates produced during the degradation of RO29 were identified by GC-MS analysis.

Pure and Sm-doped ZnO nanoparticles were synthesized applying a simple sonochemical method. The nanocatalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) techniques which confirmed the successful synthesis of the doped sonocatalyst. The sonocatalytic degradation of Acid Blue 92 (AB92), a model azo dye, was more than that with sonolysis alone. The 6% Sm-doped ZnO nanoparticles had a band gap of 2.8 eV and demonstrated the highest activity. The degradation efficiency (DE%) of sonolysis and sonocatalysis with undoped ZnO and 6% Sm-doped ZnO was 45.73%, 63.9%, and 90.10%, after 150 min of treatment, respectively. Sonocatalytic degradation of AB92 is enhanced with increasing the dopant amount and catalyst dosage and with decreasing the initial AB29 concentration. DE% declines with the addition of radical scavengers such as chloride, carbonate, sulfate, and tert-butanol. However, the addition of enhancers including potassium periodates, peroxydisulfate, and hydrogen peroxide improves DE% by producing more free radicals. The results show adequate reusability of the doped sonocatalyst. Degradation intermediates were recognized by gas chromatography-mass spectrometry (GC-MS). Using nonlinear regression analysis, an empirical kinetic model was developed to estimate the pseudo-first-order constants (kapp) as a function of the main operational parameters, including the initial dye concentration, sonocatalyst dosage, and ultrasonic power.

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The degradation of Acid Blue 92 (AB92) solution was investigated using a sonocatalytic process with pure and neodymium (Nd)-doped ZnO nanoparticles. The nanoparticles were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The 1% Nd-doped ZnO nanoparticles demonstrated the highest sonocatalytic activity for the treatment of AB92 (10 mg/L) with a degradation efficiency (DE%) of 86.20% compared to pure ZnO (62.92%) and sonication (45.73%) after 150 min. The results reveal that the sonocatalytic degradation followed pseudo-first order kinetics. An empirical kinetic model was developed using nonlinear regression analysis to estimate the pseudo-first-order rate constant (kapp) as a function of the operational parameters, including the initial dye concentration (5-25 mg/L), doped-catalyst dosage (0.25-1 g/L), ultrasonic power (150-400 W), and dopant content (1-6% mol). The results from the kinetic model were consistent with the experimental results (R(2)=0.990). Moreover, DE% increases with addition of potassium periodate, peroxydisulfate, and hydrogen peroxide as radical enhancers by generating more free radicals. However, the addition of chloride, carbonate, sulfate, and t-butanol as radical scavengers declines DE%. Suitable reusability of the doped sonocatalyst was proven for several consecutive runs. Some of the produced intermediates were also detected by GC-MS analysis. The phytotoxicity test using Lemna minor (L. minor) plant confirmed the considerable toxicity removal of the AB92 solution after treatment process.

The sonocatalytic degradation of reactive orange 29 (RO29) was examined from the reaction kinetics point of view. Sonochemically synthesized lanthanides (Ho and Er)-doped ZnO nanoparticles were utilized as catalyst during the sonocatalytic process. The prepared nanoparticles were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The aqueous RO29 solution was irradiated with a 36kHz ultrasonic bath (150W) for investigation of the degradation kinetics by varying of the initial dye concentration (10-30mg/L) and catalyst dosage (0.25-1g/L). A novel kinetic model was developed and validated for prediction of the RO29 sonocatalytic degradation efficiency using generally accepted intrinsic elementary reactions. The proposed kinetic model clearly demonstrates the dependence of the apparent first-order rate constant on the mentioned operational parameters. The predicted values of degradation efficiency and experimental results were in good agreement with appropriate correlation coefficient (R>0.945).