Dual benefits of resource recycling and pollution mitigation: Enhanced cadmium adsorption using modified biochar from traditional Chinese medicine straw

To address the dual challenges of traditional Chinese medicine (TCM) agricultural waste and heavy metal pollution, this study investigated the preparation of biochar from Asparagus cochinchinensis (Lour.) Merr. straw (BC) and its modification using H3PO4 (PBC), CO(NH2)2 (UBC), and CO(NH2)2 & sdot;H3PO4 (PUBC) for cadmium (Cd) removal. The addition of CO(NH2)2 and CO(NH2)2 & sdot;H3PO4 promoted pore formation, with UBC achieving the highest Cd adsorption capacity of 20.38 mg g- 1 at 25 degrees C, a 67.49 % improvement over unmodified BC. The Langmuir, Freundlich, and Temkin models suggested that both monolayer and multilayer chemisorption contributed to Cd adsorption. Electrostatic interaction, surface coordination and pores fillings were identified as the main adsorption mechanisms. Notably, PUBC exhibited stable Cd removal (77.98 %-83.40 %) under varying pH, highlighting the benefits of N-P co-doping for pH stability. In contrast, the performance improvement of PBC compared to BC was marginal, with only a 15.95 %-27.38 % increase in adsorption capacity. Recycling experiments over 10 cycles showed BC and PBC fell below 80 % recovery efficiency after the 9th cycle, while UBC and PUBC maintained around 82 % after 10 cycles, demonstrating superior regeneration potential and extended lifespans. This study underscores the dual advantages of recycling agricultural waste and enhancing environmental restoration through N, P, and N-P co-doping strategies. The findings provide a foundation for future applications of TCM-derived biochars and tailored modifications for Cd remediation, paving the way for sustainable resource utilization and pollution control.