Hierarchical nickel cobalt oxide spinel microspheres catalyze mineralization of humic substances during wet air oxidation at atmospheric pressure

• Published in: Applied catalysis. B, Environmental Environmental, 2019-11, Vol.256, p.117858, Article 117858
• Main Authors: Jing, Qi, Li, Huan
• Format: Article
• Language: English
• Subjects: Air temperature; Atmospheric pressure; Catalysis; Catalysts; Catalytic oxidation; Chemical synthesis; Cobalt; Cobalt oxides; Degradation; Dissolved oxygen; Free radicals; Humic substances; Hydroxyl radicals; Low temperature; Mars-van Krevelen Mechanism; Microspheres; Mineralization; Nickel; Nickel cobalt oxide; Organic carbon; Oxidation; Oxygen; Pollutants; Redox properties; Spinel; Surface area; Total organic carbon; Wastewater pollution; Wastewater treatment; Water pollution; Water supply; Water treatment; Wet oxidation process
• ISSN: 0926-3373; 1873-3883
• DOI: 10.1016/j.apcatb.2019.117858

[Display omitted] •NiCo2O4 microspheres were synthesized and used to CWAO of humic solution.•TOC decreased by 93.4% after 24 h treatment at atmospheric pressure and 90 °C.•Surface catalytic oxidation and hydroxyl free radicals contribute to mineralization.•High pH and high temperature can enhance catalytic performance of NiCo2O4. Humic substance (HS) is a key pollutant in water supply or wastewater treatment. In this work, hollow microspheres constituted of NiCo2O4 (NCO) spinel were synthesized and used as the catalyst of catalytic wet air oxidation, aiming to remove HS at atmospheric pressure and low temperature. The results show that NCO had excellent hierarchical architectures with large surface area (66.88 m2/g), solid-state redox couples, numerous surface oxygen species, and low reduction temperature. When NCO was used to treat HS solution at 90°C, total organic carbon concentration decreased by 93.4% after 24 h. NCO itself had the ability to mineralize the HS adsorbed on the surface, and dissolved oxygen can fill oxygen vacancies and recover NCO to its original state. Hydroxyl radicals also assisted the HS degradation. These findings provide some insight into the HS degradation process and promise an inexpensive and easy way to clean HS-rich water or wastewater.