Green synthesis of diatom-allophane bio-nanocomposites for highly efficient oxytetracycline adsorption.

ABSTRACT

The extensive use of the antibiotic oxytetracycline (OTC) has led to considerable environmental contamination and other negative impacts, prompting an urgent need for a green, effective, and innovative OTC adsorption material. In this study, diatom-allophane bio-nanocomposites were synthesized using a simple and eco-friendly method, yielding a homogeneous coating of allophane nanoparticles on diatom surfaces. The resultant bio-nanocomposites were found to have hierarchically porous structures and abundant active sites derived from successful allophane loading and dispersion on diatom surfaces. The OTC adsorption capacity of this novel adsorbent is remarkable (219.112 mg·g-1), surpassing the capacities of raw allophane and diatoms by >5 and 10 times, respectively. Mechanistically, OTC adsorption by the bio-nanocomposites was found to be driven primarily by chemisorption through a process involving complexation between the amide and amino groups on OTC and the aluminum hydroxyl and carboxyl groups on the adsorbent surface. Electrostatic interactions and hydrogen bonding also contribute significantly to OTC capture. Furthermore, the diatom-allophane bio-nanocomposites exhibit excellent performance over a wide pH range (4-7), in the presence of various cations (Na+, K+, Ca2+, Mg2+) and anions (Cl-, NO3-, SO42-), and in real water bodies. These findings demonstrate the potential of the diatom-allophane bio-nanocomposite as a green, efficient, and promising biological-mineral adsorbent for environmental remediation, leveraging the combined utilization of biological and mineral resources.