Yeast-activated carbon/montmorillonite nanosheets with porous spherical shells for efficient tetracycline degradation

Abstract

A bio-derived carbon composite catalyst was successfully prepared by loading yeast onto the assembled montmorillonite nanosheets (MMTNS-L), followed by calcination, which effectively prevented catalyst aggregation. MMTNS assembled in a two-dimensional direction to form large sheets, providing a robust support structure. After carbonization, yeast cells, as natural biological entities rich in nitrogen, exhibited a distinctive hollow thin-layer spherical shell with a large specific surface area and abundant pores. The evaporation of internal water vapor further contributed to the formation of this porous structure. The spherical shells uniformly distribute on the assembled MMTNs, resisting aggregation and exposing more active sites, which enhances the catalyst's efficiency. The pyridine N and pyrrole N formed after carbonization provide additional active sites to facilitate electron transfer, while the stable graphite N and NO enhance the catalyst's stability and promote the non-radicals generation. During the degradation process, potassium peroxymonosulfate (PMS) was introduced and activated by the catalyst, generating both free and non-free radicals to effectively degrade tetracycline (TC). Under optimal conditions, the assembly of MMTNS with a lamellar structure, followed by high-temperature yeast carbonization, achieved an 84 % TC degradation rate within 15 min. In this process, $•{\mathrm{SO}}_4^{–}$, $•O_2^{–}$, and ¹O₂ all participated in TC degradation, with ¹O₂ being the dominant reactive species. As a highly reactive non-radical, ¹O₂ interacts with organic matter to facilitate its degradation. This structure significantly enhances photocatalytic performance and shows great potential for antibiotic removal. This technique aims to enhance the exposure of active sites on carbonized yeast and improve the catalyst's stability, thereby supporting the efficient treatment of antibiotic wastewater and the application of biocarbon catalytic materials.