Porous hollow carbon microspheres for tetracycline removal from wastewater and subsequent reuse of the spent adsorbent as a soil amendment

Tetracycline (TET), one of the most widely used antibiotics, is frequently detected in water and soil environments due to its extensive usage and incomplete removal. Its persistence and accumulation in environmental media may pose potential ecological and agricultural risks, highlighting the need for efficient removal materials and sustainable post-treatment strategies. Hierarchical porous hollow carbon microspheres (HCM-750-3) were synthesized via a template-free approach using glucose as the carbon source, followed by KOH activation. The adsorbent was optimized by varying the activation temperature and KOH-to-precursor ratio, and was characterized by SEM, TEM, BET, FTIR, XPS, and Raman spectroscopy. The adsorption performance toward tetracycline was evaluated through kinetic, isotherm, and thermodynamic analyses, while a pot experiment with pakchoi was conducted to assess the soil amendment potential of the spent adsorbent. HCM-750-3 exhibited a high specific surface area (1869.7 m2/g) and a hierarchical micro/mesoporous structure, achieving a maximum adsorption capacity of 338.97 mg/g for TET. The adsorption process was spontaneous and endothermic, and was governed by pore filling, π-π interactions, hydrogen bonding, and electrostatic attraction. In addition, the spent adsorbent significantly improved soil properties and promoted pakchoi growth, demonstrating its dual functionality as an efficient adsorbent for tetracycline removal and a promising soil conditioner.