Surfactant-Aided Hydrothermal Synthesis and Carbon Dioxide Adsorption Behavior of Three-Dimensionally Mesoporous Calcium Oxide Single-Crystallites with Tri-, Tetra-, and Hexagonal Morphologies

摘要

Three-dimensionally (3D) mesoporous single-crystalline CaO nano- and microparticles with tri-, tetra-, and hexagonal morphologies have been successfully fabricated using a surfactant (P123, CTAB, or PEG) assisted hydrothermal dissolution—recrystallization strategy with irregular nonporous CaO powders as the starting material. The as-synthesized calcium oxide samples are characterized by means of techniques such as X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy/selected area electron diffraction, Fourier-transfer infrared spectroscopy, thermogravimetric analysis/differential scanning calorimetry, and N2 adsorption—desorption. It is shown that the introduction of a surfactant has an important effect on the morphology and pore structure of the synthesized CaO samples. With P123 or PEG as template, a higher hydrothermal temperature and longer hydrothermal time favor the generation of more regular morphological CaO entities with a higher surface area. Among the surfactants adopted in the present work, PEG is the most effective in the fabrication of high-surface-area 3D mesoporous CaO. Under the conditions of hydrothermal temperature of 240 °C and hydrothermal time of 72 h in the presence of PEG and after calcination at 600 °C for 3 h in an oxygen flow, one can obtain a single-crystalline 3D mesoporous CaO material with a surface area of 257 m~2/g. The possible formation mechanism of single-crystalline 3D wormhole-like mesoporous CaO is also discussed. These high-surface-area mesoporous CaO samples exhibit excellent CO2 adsorption behavior. The highest amount of CO2 desorbed from the CaO hydrothermally fabricated with PEG at 240 °C for 72 h and calcination at 600 °C for 3 h achieves 770 μmol CO2/g. It is suggested that the rise in surface area and the formation of 3D wormhole-like mesopores contribute to the enhanced CO2 adsorption capacity of CaO.