Nano-nebula superstructure decorated wood-derived biochar for efficient and rapid antibiotic degradation

Fe-based biochar catalysts are widely recognized as promising materials for activating peroxymonosulfate (PMS) to degrade antibiotics in wastewater, owing to their high catalytic activity, notable environmental compatibility, and cost-effectiveness. In this study, wood-derived biochar was first obtained via the pyrolysis of natural wood, and subsequently utilized as a substrate for the strategic assembly of an Fe-based biochar catalyst (referred to as BCNNSP), which possesses a nano-nebula superstructure (NNSP) derived from consecutive hydrothermal and co-precipitation processes. This unique NNSP architecture is characterized as a hierarchical assembly in which the MoS₂ nanoflowers, self-assembled from monolayer nanosheets, and the highly dispersed Fe₃O₄ NPs surface-anchored onto them are referred to as the clouds and stars, respectively. The resulting BCNNSP served as a high-performance catalytic platform to trigger PMS activation, thereby achieving rapid degradation of tetracycline (TC). Experimental results indicated that under optimal conditions, the BCNNSP/PMS system achieved a superior TC removal efficiency of 94% (initial [TC] = 20 mg L^-1) within 60 min. Additionally, BCNNSP demonstrated remarkable catalytic persistence and interference resistance, sustaining excellent removal efficiency across a wide pH range and in diverse real-water backgrounds. Moreover, BCNNSP demonstrated excellent reusability, maintaining a TC removal efficiency over 91.2% after six consecutive cycles. Quenching experiments and electron paramagnetic resonance (EPR) analyses identified singlet oxygen (¹O₂) as the predominant reactive oxygen species (ROS) driving the TC degradation process in the BCNNSP/PMS system. Moreover, X-ray photoelectron spectroscopy (XPS) analysis further elucidated that MoS₂ promoted the Fe²⁺/Fe³⁺ redox cycle and interfacial electron transport, which consequently improved PMS activation performance. Additionally, the wood-derived biochar exhibits intrinsic electrical conductivity, which facilitates interfacial charge transport during the catalytic process. This work provides an innovative strategy for the rational design of high-performance Fe-based biochar catalysts for practical antibiotic wastewater treatment.