Ultrasonic-Assisted Hydrothermal Synthesis of Nap Zeolite and Doping with Cu or Fe for Effective Removal of Organic Dyes in Fenton-Like Oxidation Systems

NaP zeolite was synthesized via ultrasonic-assisted hydrothermal synthesis. The methods for Cu or Fe doping were screened while exploring element distributions in liquid and solid phases. Oxidation process of methylene blue (MB) and methyl violet-6B (MV-6B) by doped NaP zeolites was surveyed. NaPultra zeolite exhibited higher crystallinity (94.99%), while crystallization temperature and time decreased from 120oC to 90oC and from 8 h to 4 h than hydrothermal synthesis. At an ultrasonic power intensity of 30% and density of 60 mL/W, conversion of Si and Al increased from 66.46% to 84.68% and from 73.75% to 95.25%. Complexation method demonstrated superior results in crystallinity (Fe-NaPultra: 92.37% and Cu-NaPultra: 94.14%) at an n(Fe(NO3)3):n(Al2O3) ratio of 4 and an n(Cu(NO3)2):n(Al2O3) ratio of 6. Ultrasound resulted in smaller crystal sizes for Fe-NaPultra (1.90 μm) and Cu-NaPultra (1.80 μm). Cu-NaPultra Fenton-like catalyst displayed better performance in the oxidation of MB (93.22%) and MV-6B (98.71%) within 30 min. Through combined action of adsorption and Fenton-like oxidation, rapid enrichment of organic dyes on the surface of zeolite was realized, and dyes were removed efficiently. Cu-NaPultra maintained good removal performance over four cycles, suggesting that it is a promising catalyst for Fenton-like reactions in the removal of organic dyes