Strategic design and fabrication of lightweight sesame ball-like hollow double-layer hybrid magnetic molecularly imprinted nanomaterials for the highly specific separation and recovery of tetracycline from milk

Magnetic surface molecularly imprinted polymers (SMIPs) allow for tailored adsorption, separation, and recovery of antibiotic residues and are recognized as important systems for control of these pollutants. However, traditional SMIPs contain heavy inner carriers that do not contribute to the adsorption capacity per unit mass of the adsorbent. In addition, most SMIPs are prepared using organic reagents, tedious operation processes, or non-mild conditions, promoting environmental pollution. To solve these problems with existing SMIPs, lightweight hollow double-layer hybrid magnetic molecularly imprinted polymers (HD-MMIPs) are developed in this work using green and sustainable chemistry. The distinct sesame ball-like structures create more opportunities for tetracycline (TC) to reach the imprinted sites through both the inner and outer layers, which improves the adsorption capacity (Q = 70.23 mg g⁻¹) and the rebinding rate of TC (t = 15 min) improving their performance over traditional SMIPs. The Fe₃O₄ nanoparticles, embedded like sesame seeds, significantly facilitate the separation process. Additionally, our HD-MMIPs are synthesized in water, an environmentally benign solvent, creating a more sustainable molecular imprinting technology. Moreover, with HPLC analysis, the HD-MMIPs were shown to specifically recognize and adsorb trace TC from milk samples and the proposed method shows a lower LOD (0.83 ng mL⁻¹) and a high TC recovery (94.8 to 98.5%), demonstrating great potential in monitoring and controlling of TC contamination in real samples. This work establishes a framework for developing green methods for synthesizing adsorbents for specific small molecule pollutants.