A new metal free carbon catalyst made from seaweed could offer a greener way to clean antibiotic polluted water, according to a new study in Biochar X. The team reports that its porous carbon material, derived from a common marine polysaccharide and doped with nitrogen and sulfur, rapidly breaks down the antibiotic norfloxacin in water while avoiding the use of toxic metals or sulfur chemicals.
Turning seaweed into clean water materials
In the study, researchers transformed kappa carrageenan, a sulfated polysaccharide extracted from red algae and widely used as a food thickener, into a highly porous carbon catalyst. By combining the biomass with melamine as a nitrogen source and potassium carbonate as an activator, then heating the mixture in an inert atmosphere, they produced an N and S co doped porous carbon they call NSPC 700.
"The idea was to use a natural material that already contains sulfur, so we do not need additional toxic sulfur reagents during synthesis," says corresponding author Bin Hui of Qingdao University. He explains that the sulfate groups in kappa carrageenan are converted in situ into sulfur species that become catalytically active sites in the final carbon framework, simplifying production and improving sustainability.
High performance removal of norfloxacin
The new material shows a very high specific surface area of about 1,219 square meters per gram, with a network of micro and mesopores that expose abundant active sites for catalysis. When combined with peroxymonosulfate, a common oxidant, NSPC 700 removed 97.16 percent of norfloxacin from water within 90 minutes and reached 49.30 percent mineralization, indicating substantial breakdown of the antibiotic into small inorganic molecules.
Control experiments revealed that unactivated biochar or peroxymonosulfate alone removed little norfloxacin, while the co doped porous carbon greatly accelerated degradation, giving the highest apparent reaction rate among the tested samples. The authors attribute this performance to the synergy between graphitic nitrogen and thiophenic sulfur species in the carbon lattice, which tune electron distribution and strengthen oxidant activation.
Non radical pathways improve robustness
Mechanistic tests suggest that the catalyst does not rely mainly on highly reactive free radicals, which can be easily quenched by other substances in real water. Quenching experiments and electron paramagnetic resonance measurements showed that singlet oxygen and a direct electron transfer pathway together contributed about 84 percent of the overall degradation, while classic radical species such as hydroxyl and sulfate radicals played only a minor role.
"Dominant non radical pathways make the system more resistant to interference from common ions and natural organic matter," notes co corresponding author Dongjiang Yang. The team found that even in the presence of chloride, sulfate, bicarbonate, phosphate, or humic acid, the catalyst maintained more than 66 percent removal of norfloxacin, underscoring its potential in complex water matrices.
Stable operation in continuous flow
Beyond batch tests, the researchers evaluated NSPC 700 in a simple continuous flow device, packing the powder into a small column through which a norfloxacin solution containing peroxymonosulfate was circulated. Under these conditions, the catalyst sustained about 94 percent removal for the first 2.5 hours and still achieved 89 percent removal after 5 hours of operation.
In repeated batch cycles, the material retained over 90 percent of its initial activity after five runs, with only minor changes in the key nitrogen and sulfur active sites observed by X ray photoelectron spectroscopy. This stability, together with the high activity, suggests that the seaweed derived carbon could be adapted for practical wastewater treatment configurations.
Green route to metal free catalysts
Unlike many advanced oxidation systems that rely on transition metals such as cobalt, iron, or copper, the NSPC 700 catalyst is totally metal free, helping to avoid the risk of secondary metal contamination. By using kappa carrageenan as both carbon and intrinsic sulfur source, the method also eliminates the need for hazardous sulfur compounds commonly used in heteroatom doping.
The authors argue that this strategy offers a scalable route to convert marine biomass waste into value added functional materials for environmental remediation, particularly for antibiotics that are difficult to remove by conventional treatment. "This work shows that natural sulfur containing biomass can be directly upgraded into efficient, stable catalysts, providing a greener option for protecting water resources from emerging pollutants," says Hui.
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Journal reference: Wang X, Shi L, Chen H, Sun Y, Yang D, et al. 2025. κ-carrageenan-derived N-, S-codoped porous carbon promotes peroxymonosulfate activation for norfloxacin degradation. Biochar X 1: e012
https://www.maxapress.com/article/doi/10.48130/bchax-0025-0012
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About the Journal:
Biochar X is an open access, online-only journal aims to transcend traditional disciplinary boundaries by providing a multidisciplinary platform for the exchange of cutting-edge research in both fundamental and applied aspects of biochar. The journal is dedicated to supporting the global biochar research community by offering an innovative, efficient, and professional outlet for sharing new findings and perspectives. Its core focus lies in the discovery of novel insights and the development of emerging applications in the rapidly growing field of biochar science.
