Selective fabrication of iron oxide particles in halloysite lumen

• Fe3O4@HNT was prepared.
• Fe3O4@HNT was characterized.
• Fe3O4 particles were selectively synthesized in the lumen of HNT.

As the adsorbents or the supports of photocatalysts, halloysite nanotubes (HNT) were expected to have intact external surface for adsorption or catalyst immobilization, when Fe3O4 particles was introduced to prepare magnetic HNTs for easy separation. The negatively charged urease was loaded inside positively charged HNT lumen, and urease catalyzed the hydrolysis of urea and resulted in the alkaline environment in HNT lumen. When Fe3+ and Fe2+ diffused in, Fe3O4 particles were selectively synthesized in the lumen of HNT. The obtained Fe3O4@HNT is characterized by transmission electron microscopy and Fourier transform infrared spectroscopy, X-ray diffraction and hysteresis loops. The obtained magnetic Fe3O4@HNT can be magnetically collected with intact external surface, which can support photocatalysts or remove the pollutants.