Comprehensive Characterization of Hafnium and Zirconium Microporous Oxides

XRD analysis was performed in a multi-functional high-intensity 2-Dimensional (2D) X-ray Diffraction system (RIGAKU RINT RAPID II with MicroMax 007HF Cu/Cr Dual-target Rotating-anode). Material Analysis Using Diffraction (MAUD^®)⁴² software was used to perform the Rietveld refinement of the XRD patterns and obtain the lattice constants. The atomic models were generated by CrystalMaker^® software. The morphology of MPOs was studied by scanning electron microscope (SEM, VERSA 3D, FEI). The DSC/TGA test was carried out with a Simultaneous Thermal Analyzer (STA) STA 449 F3 (NETSCZH GmbH). The sample was first kept in a muffle furnace at 300 °C under an air atmosphere for 4 h to drive out the moisture content and then sealed in a corundum pan for further DSC/TGA test. The sample was heated from 40 to 1500 °C under an air atmosphere at a ramp rate of 10 K/min. Raman-spectra were obtained using Renishaw inVia Qontor with a laser wavelength of 532 nm and laser beam spot of 1 µm. Two analytical transmission electron microscopes (JEOL ARM 200F) were used to characterize the microstructures of Hf-MPO and Zr-MPO. One of them, equipped with a cold field emission gun and an aberration corrector for the probe-forming lens system was used to obtain the atomic resolution STEM images. The other one, equipped with an aberration corrector for the objective lens system was used to obtain high-quality HRTEM images. Both TEMs were operated at 200 kV. High-angle annular dark-field scanning TEM (HAADF-STEM) images were recorded using an annular-type detector with a collection semi-angle of ∼100–269 mrad. STEM-EDX elemental maps were also acquired to reveal the chemical composition and phase distribution. For TEM sample preparation, the MPO powders were dispersed in ethanol under sonication for 3 min and then dropped on a copper grid with carbon membranes on it. Subsequently, the copper grid was dried under an oven lamp before loading onto a double-tilt TEM holder for structural characterization. The photoluminescence spectra were recorded using the FLS1000 Edinburgh Analytical Instrument. The photocatalytic performance was performed under a 500 Watt Xenon lamp.