Multi-shelled hollow metal-organic frameworks for optimizing the adsorption performance of antibiotics

Abstract

Antibiotics have been widely used in the prevention and treatment of diseases such as humans, poultry and aquaculture due to their remarkable antibacterial effects. Nowadays, the infections caused by antibiotic-resistant bacteria are increasing, and resistance to antibiotics is probably the major public health problem. Therefore, the effective removal of trace antibiotic technology and materials in water has gradually attracted the attention of all parties in recent years. However, due to the difficulty in pore size, porosity, physical and chemical properties modification, the application of traditional porous materials, such as activated carbon, zeolites and silicates, are limited to some extent. As a new type of porous materials, metal-organic frameworks (MOFs) are considered as a promising platform for the adsorption applications. Inspired by the favorable structure and morphology of inorganic materials, hollow structures are promising materials for enhancing the adsorption performance. Herein, we fabricated multi-shelled hollow MOFs through step-by-step crystal growth and subsequent etched by acetic acid. The solid MOFs particles size about 200 nm, and the hollow cavity of single shell hollow MOFs (SSHM) about 100 nm. The diameters of double shell hollow MOFs (DSHM) inner cavity and outer shell were 50 and 50 nm, respectively. Triple shell hollow MOFs (TSHM) inner cavity and outer shell diameters were 20 and 70 nm, respectively. Powder X-ray diffraction (XRD) and N2 sorption confirmed the crystallographic structure and porosity of the resulting hollow MOFs. The hollow MOFs showed similar diffraction peaks position and intensity with pristine MOFs, which indicated that the high phase purity of the product MOFs. The BET surface of solid, single, double and triple shell MOFs were 2389.1, 2454.2, 2052.7 and 2396.2 m2/g, respectively. The hollow structured MOFs exhibited higher adsorption capacity than the solid MOFs, and the adsorption capacity increased with the number of layers. Particularly, the triple-shelled hollow MOFs (TSHM) for oxytetracycline and tetracyclines adsorption capacity is about 76 and 95 mg/g, respectively, which is three times higher than the solid MIL-101. The high adsorption capacity and removal efficiency may be attributed to the enhanced active site in each layer of multi hollow structure that can sorption more molecules. The recycling experiment showed that the adsorption efficiency of antibiotics in water by TSHM was relatively stable, and it still showed good crystallinity and morphological stability after reuses of up to 4 cycles. The enhanced adsorption capacity and excellent reusability obtained in this study demonstrated the potential of multi-shelled hollow MOFs structures as a novel adsorbent for the removal of organic molecules.