One-Step Synthesis of Bamboo Biochar for Efficiency Adsorption of Tetracycline: Characterization, Kinetics and Cost–Benefit Analysis

Tetracycline has been widely used as an efficient broad-spectrum antibiotic, while its long-term environmental pollution characteristics have gradually gained recognition and attention, highlighting the urgent need to identify a low-cost and effective method for removing tetracycline pollutants. This study aims to develop a one-step bamboo-based biochar preparation method based on a KCl-ZnCl2 molten salt system; the potential application of obtained bamboo-based biochar as a tetracycline adsorbent was characterized and analyzed. Results show that the biochar prepared at 900 °C possesses abundant microporous and mesoporous structures, with abundant surface functional groups. Also, it exhibits a composite type I/IV isotherm, with a specific surface area of 1305.91 m2·g−1, a total pore volume of 0.944 cm3·g−1, demonstrating excellent tetracycline adsorption capacity of 298.93 mg·g−1. XRD analysis confirmed that increasing the activation temperature significantly enhanced the graphitization degree of the biochar, which is a key factor influencing its tetracycline adsorption performance. Kinetic studies indicated that the adsorption kinetic process was better described by the Elovich model and Freundlich isotherm. Furthermore, cost-effectiveness analysis revealed that the cyclic preparation cost of biochar via this technique could be reduced to 18.25 USD per kilogram owing to the low consumption characteristics of the KCl-ZnCl2 molten salt, which represents a 93.4% reduction compared with conventional preparation methods, underscoring the economic applicability of this technology in the field of tetracycline removal. The findings of this study are expected to lay a foundation for the industrial preparation of low-cost, high-performance bamboo-based biochar for tetracycline removal.