Co 3 O 4 nanocrystals/3D nitrogen-doped graphene aerogel: A synergistic hybrid for peroxymonosulfate activation toward the degradation of organic pollutants Ruixia Yuan a, b , Lin Hu a , Peng Yu c , Zhaohui Wang d, * , Huaiyuan Wang a, ** , Jingyun Fang b a Provincial Key Laboratory of Oil & Gas Chemical Technology, College of Chemistry and Chemical Engineering, Northeast Petroleum University, Daqing, 163318, China b Guangdong Provincial Key Laboratory of Environmental Pollution Control and RemediationTechnology, Sun Yat-sen University, Guangzhou 510275, China c Oil Refinery of Daqing Petrochemical Company, Daqing 163711, China d International Centre for Balanced Land Use (ICBLU), The University of Newcastle, Callaghan, NSW 2308, Australia highlights graphical abstract  Co 3 O 4 nanocrystals were supported on 3D monolith N-doped graphene aerogel (NGA).  Co 3 O 4 /NGA possesses excellent long- term stability and recycling performance.  Kinetic modeling was developed to simulate transformation of main active radicals.  Macroscopic Co 3 O 4 /NGA can be easily separated and reused with low cobalt leaching. article info Article history: Received 2 May 2018 Received in revised form 24 June 2018 Accepted 13 July 2018 Available online 17 July 2018 Handling Editor: Jun Huang Keywords: Nitrogen doping Graphene aerogel Cobalt oxide Peroxymonosulfate Sulfate radical abstract 3D porous Co 3 O 4 /nitrogen-doped graphene aerogel (NGA) hybrid for heterogeneous activation of per- oxymonosulfate (PMS) was prepared by feasible hydrothermal and freeze-drying methods. The morphology, crystal structure and chemical composition of the catalyst were investigated by scanning electron microscopy, X-ray diffractometer, X-ray photoelectron spectroscopy, Raman spectra and Fourier transform infrared spectroscopy. Co 3 O 4 /NGA at a high N doping level of 7.6% (in atomic percentage) exhibited excellent catalytic performance for acid orange 7 (AO7) degradation, with almost complete removal within 30 min. Moderate PMS content, higher temperature and lower solution pH conditions would facilitate the decomposition of AO7. The catalyst possesses excellent long-term stability and recycling performance with simple separation and post-treatment approaches. Kinetic model was developed to simulate the transformation of main active radical species and the AO7 oxidation profiles, considering effects of coexisting ions (Cl  and HCO 3  ). Based on results of electron spin resonance, typical quenching tests and kinetic calculation, sulfate radicals play dominate role in AO7 degradation. Co 3 O 4 nanocrystals and the new active sites created by nitrogen doping into graphene honeycomb network should synergistically contribute to the high degradation efficiency. This work has expanded the pos- sibility of recyclable catalysts design for heterogeneous activation of PMS, with a dual catalytically active center and desirable stability. © 2018 Elsevier Ltd. All rights reserved. * Corresponding author. ** Corresponding author. E-mail addresses: zhaohui.wang@newcastle.edu.au (Z. Wang), wanghyjiji@163.com (H. Wang). Contents lists available at ScienceDirect Chemosphere journal homepage: www.elsevier.com/locate/chemosphere https://doi.org/10.1016/j.chemosphere.2018.07.065 0045-6535/© 2018 Elsevier Ltd. All rights reserved. Chemosphere 210 (2018) 877e888