Starch-based carbon microspheres for highly selective adsorption of carbon dioxide and acetylene

To develop environmentally friendly and energy efficient starch-based carbon microspheres (CMSs) as an alternative to metal-organic frameworks and conventional porous carbon and for efficient adsorption and separation of a wide range of gases, the CMSs were prepared by hydrothermal and pyrolysis methods using soluble starch as the carbon source. The CMSs were characterized by Fourier Transform Infrared Spectroscopy (FTIR), Specific Surface Area and Pore Size Analyser (BET), X-ray Diffractometer (XRD), Field Emission Scanning Electron Microscopy (SEM), and X-ray Photoelectron Spectroscopy (XPS). The results indicated that the prepared CMSs were spherical with relatively uniform particle size, possessing an amorphous structure and partial graphitic carbon, and were rich in oxygen-containing functional groups on the surface. The CMSs had microporous and mesoporous structures, with an average pore size of 3.388 nm and a specific surface area of 532.598 m²·g⁻¹. The adsorption properties of CMSs for gases such as CO₂, C₂H₂, CH₄, N₂, and CO were investigated. It was found that the adsorption amounts of CMSs for C₂H₂ and CO₂ at 273 K and 298 K were 3.58 mmol·g⁻¹ and 3.47 mmol·g⁻¹, 2.76 mmol·g⁻¹ and 2.61 mmol·g⁻¹, respectively, while the adsorption amounts for CH₄, N₂, and CO were much lower. The adsorption isotherms of C₂H₂, CO₂, CH₄, N₂, and CO on CMSs can be fitted well by the DSL (dual site Langmuir) model. The adsorption selectivity of CMSs for binary gas mixtures such as C₂H₂/CH₄, CO₂/CH₄, CO₂/N₂, C₂H₂/CO₂ and CO₂/CO was calculated using the IAST theoretical model, and all the adsorption selectivities were greater than 2, indicating that CMSs could effectively separate the above five binary gas mixtures.