A Reusable Catalyst for Antibiotic Removal
Sulfamethoxazole, a widely used antimicrobial, can persist in aquatic environments and pose risks to ecosystems and human health. Researchers led by Xuejiao Tang at Nankai University developed millimeter-scale magnetic carbon beads, designated CoNC@cPAN/rGO-800, to address the limited recoverability and metal-leaching concerns associated with powdered cobalt catalysts. The material combines a polyacrylonitrile carbon framework , reduced graphene oxide, and cobalt-containing active sites.
Porous Structure, Rapid Degradation
The beads were prepared from a cobalt-containing zeolitic imidazolate framework, polyacrylonitrile, and graphene oxide, followed by calcination under nitrogen at different temperatures. Microscopy, spectroscopy, diffraction, surface-area analysis, electrochemical measurements, and density functional theory calculations were used to characterize the material and assess its catalytic behavior. Under optimized conditions, 0.1 g L⁻¹ of catalyst and 0.1 g L⁻¹ of peroxymonosulfate removed 100% of 10 mg L⁻¹ sulfamethoxazole within 20 min at pH 7.
The graphene-derived component produced a hierarchical honeycomb-like pore structure and reduced electronic impedance, supporting the distribution of cobalt sites and facilitating electron transfer. The catalyst retained complete sulfamethoxazole degradation across pH 2–11 within 30 min, although acidic and strongly alkaline conditions required longer reaction times than neutral or mildly alkaline conditions. Humic acid and several inorganic anions caused only modest inhibition, whereas bicarbonate exerted a stronger suppressive effect.
Superoxide Links Oxygen to Peroxymonosulfate Activation
Quenching experiments and electron paramagnetic resonance measurements identified hydroxyl radicals, sulfate radicals, superoxide radicals, and singlet oxygen as contributors to pollutant removal. Probe-based estimates assigned contribution ratios of 36.3% for hydroxyl radicals, 27.3% for sulfate radicals, 19.5% for superoxide radicals, and 16.9% for singlet oxygen. The results indicate that oxygen vacancies convert dissolved oxygen into superoxide radicals , which can subsequently activate peroxymonosulfate to form additional reactive species or combine to generate singlet oxygen.
The proposed mechanism involves spatially differentiated reactivity within the beads. Cobalt nanoparticles near the shell directly activate peroxymonosulfate during the early reaction stage, whereas oxygen-vacancy-rich cobalt oxide in the bead core contributes increasingly during the later stage. Reduced graphene oxide supports electron transport and promotes oxygen-vacancy formation, helping explain the accelerated second-stage kinetics observed for CoNC@cPAN/rGO-800.
Stability and Engineering Potential
The catalyst maintained 82.4% sulfamethoxazole degradation after eight batch cycles. Its saturation magnetization reached 34.45 emu g⁻¹, allowing magnetic recovery from aqueous suspensions. Cobalt leaching reached a maximum of 0.28 mg L⁻¹ during degradation, substantially below the leaching observed for a powder cobalt control prepared from the same precursor. In a fixed-bed column configuration, complete sulfamethoxazole degradation was maintained over five cycles at a flow rate of 1 mL min⁻¹.
The authors also detected degradation intermediates and used ECOSAR predictions to assess their aquatic toxicity. Most intermediates showed lower predicted acute and chronic toxicity than sulfamethoxazole, although these predictions do not replace direct toxicity testing. The work was conducted primarily under controlled laboratory conditions, with additional tests in campus lake water, river water, and a laboratory-scale flow reactor. Long-term performance, regeneration requirements, cobalt fate, and treatment behavior in diverse full-scale wastewater matrices remain to be established.
Further work can examine extended continuous-flow operation, catalyst regeneration, treatment of mixed antibiotic contaminants, and direct biological assessment of transformation products. Optimizing bead dimensions, pore architecture, peroxymonosulfate consumption, and cobalt immobilization could help determine whether the material can provide a practical balance between rapid oxidation , low secondary pollution, and scalable operation.
Corresponding Author: Xuejiao Tang
Original Source: https://doi.org/10.1007/s44246-026-00288-y
Contributions: Jingang Wang contributed to writing the original draft, conceptualization, validation, and funding acquisition; Zhenlei Hu contributed to writing the original draft, formal analysis, methodology, and data curation; Zhipeng Zheng contributed to data curation and methodology; Cuiping Wang contributed to writing, review and editing, methodology, and data curation; Hongwen Sun contributed to supervision and funding acquisition; Yawei Du contributed to software; and Xuejiao Tang contributed to writing, review and editing, supervision, conceptualization, and funding acquisition.
Carbon Research
Experimental study
Not applicable
New magnetic carbon beads doped with graphene and cobalt to efficiently degrade sulfamethoxazole: superoxide radical acceleration strategy
27-Aug-2026
Hongwen Sun is an editorial board member for Carbon Research but was not involved in the editorial review, and the decision to publish, this article. All authors declare that there are no competing interests.