Experimental Evidence for Self-Assembly of CeO₂ Particles in Solution: Formation of Single-Crystalline Porous CeO₂ Nanocrystals

Single-crystalline porous CeO 2 nanocrystals, with sizes of ∼20 nm and pore diameters of 1–2 nm, were synthesized successfully using a hydrothermal method. Using electron tomography, we imaged the three-dimensional structure of the pores in the nanocrystals and found that the oriented aggregation of small CeO 2 nanoparticles resulted in the growth of CeO 2 nanocrystals with an irregular truncated octahedral shape and pores extending along the ⟨110⟩ directions. Oxygen vacancies were found on the crystal surfaces and internal walls of the pores by scanning transmission electron microscopy and electron energy-loss spectroscopy. The oxygen vacancies might play an important role in oxygen diffusion in the crystals and the catalytic activities of single-crystalline porous CeO 2 structures.