We have prepared bio-inorganic nanohybrids consisting of magnetic inorganic nanolayers (iron-titanate) and protein molecules via exfoliation–restacking process in solution. It was found that the protein molecules were electrostatically and spontaneously incorporated into the interlayer space of the inorganic layered structure by adjusting the pH of the solution appropriately. The binding studies demonstrated the high affinity of the iron–titanate nanolayers for the proteins, and the immobilized protein preserved its activity after the hybridization. The catalytic activity measurement and magnetic separation experiment indicate the formation of magnetically applicable inorganic layer–biomolecule nanohybrids. The magnetic layer–biomolecule nanohybrid developed here would be a novel conspicuous material which shows different properties from those of conventional biomolecule-immobilized magnetic particles.

The presence of hexavalent chromium species (Cr^VI) in wastewater from manufacturing industries such as electroplating and leather production can pose serious health hazards. To address these concerns, this study developed a novel adsorbent based on activated carbon as the primary material to attract Cr^VI. Activated carbon has been modified with several other components to improve its comprehensive performance, including adsorption capacity, chemical stability, collectability, and reusability. Specifically, decoration with magnetite nanoparticles made it possible to collect the adsorbent magnetically and reuse it several times. On the one hand, the addition of chitosan not only increased the chemical stability of activated carbon, especially under acidic conditions, but also enhanced the Cr adsorption capacity at pH higher than 4, where adsorption of only activated carbon was significantly decreased, probably because the protonated amino groups attracted chromate anions. In addition, the co-existence of tannic acid did not increase the adsorption capacity significantly but appeared to promote the reductive adsorption of Cr^VI, where the reduction of Cr^VI means lowering the toxicity of Cr species. It was demonstrated that activated carbon modified with magnetite, chitosan, and tannic acid exhibited superior comprehensive performance that could be repeatedly used over a wide pH range as compared to the parent activated carbon.