Protein assisted hydrothermal synthesis of ultrafine magnetite nanoparticle built-porous oriented fibers and their structurally enhanced adsorption to toxic chemicals in solution

Abstract

A facile and green route is presented for mass production of oriented magnetite porous fibers (with >96% in yield), based on the protein assisted hydrothermal method in citric aqueous solution. The magnetite fibers are nearly cylindrical in shape, several ten micrometres in length and 120 nm in mean diameter. The whole single fibers are packed by the ultrafine Fe₃O₄ nanoparticles with similar crystal orientation (along [111] direction), and show porous structure with pore size below 5nm and high specific surface area (123 m² g⁻¹), exhibiting good magnetic property at room temperature. Further experiments have revealed that the formation of such porous submicro-fibers is mainly attributed to the protein directed/magnetic dipole-induced orientation assembling of Fe₃O₄ nanoparticles. The proper conditions, including the moderate protein and citric acid concentrations, pH value in the precursor solution and suitable reaction temperature, are crucial to formation of the magnetite porous fibers. More importantly, such magnetite porous fibers can be used as an effective adsorbent for removal of some toxic chemicals, not only heavy metal anions and cations with good recycling performance, but also some non-polar contaminant molecules in solution, and have exhibited significantly structurally enhanced adsorption performance and very high removal performance for Cr(VI) (anions), Hg(II) (cations) and the polychlorinated biphenyl (non-polar molecules). This material makes it possible to develop lower magnetic separation process to highly efficiently enrich and remove the toxic chemicals, which are usually difficult to remove, in one step. This is particularly important in environmental remediation.