Beyond surface area: Unraveling the synergistic role of size-matching confinement and defect-induced electron transfer in tetracycline sequestration

Although a high specific surface area is a prerequisite for efficient adsorption, it fails to fully explain the superior sequestration of bulky antibiotics such as tetracycline (TCH). This study transcends the traditional surface area-governed paradigm by synthesizing a hierarchically porous biochar (PRBC) from rice straw via KOH activation. It achieves a benchmark adsorption capacity of 831.950 mg·g −1 . We discovered a critical “size-matching” confinement mechanism that goes beyond simple pore filling: the engineered average pore diameter (2.01 nm) serves as a tailored vessel for TCH molecules (∼1.4 nm), effectively minimizing steric hindrance while maximizing contact potential. Density functional theory (DFT) calculations revealed the pivotal role of defect-induced electron transfer. We demonstrate that lattice defects and oxygenated edges serve as high-energy active sites, facilitating significant charge transfer (up to 0.139 |e| at mesoporous defect sites) and strengthening interfacial binding via donor-acceptor interactions. Consequently, the exceptional performance of PRBC is attributed to the synergistic coupling of physical confinement and electronic modulation. This work provides a mechanistic blueprint for the rational design of defect-rich carbon materials for the targeted removal of emerging organic contaminants.