ZnAl2O4 as a novel high-surface-area ozonation catalyst: One-step green synthesis, catalytic performance and mechanism

• A novel design strategy for efficient ozonation catalyst with high surface area was proposed.
• ZnAl2O4 was developed as a robust and stable ozonation catalyst for the first time.
• Porous ZnAl2O4 catalyst was prepared by a one-step green hydrothermal method.
• Surface hydroxyl groups and chemisorbed water acted as catalytic active sites.
• The transformation from ozone to hydroxyl radicals was responsible for catalysis.

Due to the great importance of high-surface-area metal oxide catalysts in catalytic ozonation, green and facile synthesis of a novel robust ozonation catalyst with high surface area is greatly attractive. In this paper, using inexpensive inorganic salts as starting materials, a high-surface-area (196 m2/g) porous nanocrystalline ZnAl2O4 was prepared by a one-step green hydrothermal method without organic template, high temperature treatment and supported substance. ZnAl2O4 was developed as a novel ozonation catalyst with enhanced catalytic activity in removal of phenol with a high concentration (300 mg/L) and the removal rate of phenol reached 73.4% within 60 min. The slight decrease by 5.7% on phenol removal rate after being used 4 times of catalyst illustrated the good reusability of ZnAl2O4 in catalytic ozonation. The positive linear correlation between catalytic activity and the density of surface hydroxyl groups of catalyst was established. Surface hydroxyl groups and chemisorbed water of catalyst acted as catalytic active sites for the generation of hydroxyl radicals. In the presence of catalyst, ozone transformed into high active hydroxyl radicals, leading to the enhanced removal of phenol in bulk solution. Moreover, ZnAl2O4 can be applied in a wide pH range from 3.3 to 9.3 and is a promising ozonation catalyst.

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