Cobalt single-atom catalyst in a fixed-bed reactor degrades over 90% of tetracycline in a 15-day lab run
Teams in Wuhan and Shenzhen placed cobalt single-atom sites on a foam–graphene support and passed antibiotic-contaminated water through it continuously in a laboratory-scale test.
A team led by Jiangbo Xi at Wuhan Institute of Technology, together with the group of Zhongxin Chen at The Chinese University of Hong Kong (Shenzhen), built a structured single-atom cobalt catalyst and used it in a fixed-bed reactor for continuous-flow degradation of antibiotics and organic dyes. The work was published in Science China Chemistry and is available via dx.doi.org. dx.doi.org
dx.doi.orgdx.doi.orgOpen source ↗ The catalyst, Co1/PUF-NG, carries cobalt single-atom sites with asymmetric Co-N3O1 coordination on a matrix of polyurethane foam and nitrogen-doped graphene.
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dx.doi.orgdx.doi.orgOpen source ↗ The reactor works through peroxymonosulfate (PMS) activation in a Fenton-like reaction, and the authors report over 90% tetracycline degradation after 15 days of continuous operation.
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dx.doi.orgdx.doi.orgOpen source ↗
Synthesis and structure of the catalyst
The material was made in a one-step hydrothermal process at 120 °C from graphene oxide, cobalt nitrate and polyurethane foam, which served as both the three-dimensional framework and the nitrogen source. According to the release, the product keeps an interconnected porous structure that lowers flow resistance and improves mass transfer. Aberration-corrected transmission electron microscopy showed cobalt dispersed as single atoms. X-ray absorption spectroscopy indicated coordination with about three nitrogen atoms and one oxygen atom. A control sample prepared at 180 °C mainly formed a symmetric Co-N4 structure.
Flow performance and mechanism
The fixed-bed reactor reached a maximum flow rate of 206 mL min-1, about twice that of the powder system, the authors report. Under continuous flow, 92% of tetracycline was removed within 2 min, with a turnover frequency of 1.23 min-1, higher than for the Co-N4 sample. In a stirred batch system the same catalyst removed 58% in 14 min, while the flow system ultimately reached 98%. After operation, the framework and the single-atom dispersion remained essentially stable.
Radical quenching, competitive kinetics, electron paramagnetic resonance and density functional theory calculations were used to study the mechanism. The relative contributions of •OH, SO4•- and 1O2 were about 20%, 33% and 47%. The calculated PMS adsorption energy was -2.43 eV on Co-N3O1 sites versus -2.28 eV on Co-N4 sites. The barrier for 1O2 generation was lower by about 0.25 eV, and Co-N3O1 transferred about 0.78 e⁻ to PMS.
