High-throughput continuous hydrothermal flow synthesis of Zn–Ce oxides: unprecedented solubility of Zn in the nanoparticle fluorite lattice

Abstract

High-throughput continuous hydrothermal flow synthesis has been used as a rapid and efficient synthetic route to produce a range of crystalline nanopowders in the Ce–Zn oxide binary system. High-resolution powder X-ray diffraction data were obtained for both as-prepared and heat-treated (850°C for 10 h in air) samples using the new robotic beamline I11, located at Diamond Light Source. The influence of the sample composition on the crystal structure and on the optical and physical properties was studied. All the nanomaterials were characterized using Raman spectroscopy, UV–visible spectrophotometry, Brunauer–Emmett–Teller surface area and elemental analysis (via energy-dispersive X-ray spectroscopy). Initially, for ‘as-prepared’ Ce 1− x Zn x O y , a phase-pure cerium oxide (fluorite) structure was obtained for nominal values of x =0.1 and 0.2. Biphasic mixtures were obtained for nominal values of x in the range of 0.3–0.9 (inclusive). High-resolution transmission electron microscopy images revealed that the phase-pure nano-CeO 2 ( x =0) consisted of ca 3.7 nm well-defined nanoparticles. The nanomaterials produced herein generally had high surface areas (greater than 150 m 2  g −1 ) and possessed combinations of particle properties (e.g. bandgap, crystallinity, size, etc.) that were unobtainable or difficult to achieve by other more conventional synthetic methods.