Highly Stable and Recyclable Sequestration of CO₂ Using Supported Melamine on Layered-Chain Clay Mineral

A type of highly stable and recyclable clay-based composite was developed for sequestration of CO₂, which was synthesized by loading melamine (MEL) onto attapulgite (ATT) via a wet impregnation method. The synthesized materials were characterized by N₂ adsorption-desorption, Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TG), and transmission electron microscopy (TEM). By means of thermal and acidic treatments more active sites of ATT were exposed, and large surface areas were obtained. The MEL molecules were well combined with those exposed sites, which enhanced stability and cyclability for CO₂ sequestration. On the basis of CO₂ adsorption-desorption measurements, the composite of ATT-MEL was found to have a higher CO₂ adsorption capacity (4.91 cm³/g) which was much higher than that of CO₂ absorption on bare MEL (1.30 cm³/g) at 30 °C. After ten cycles of reusing, the composite exhibited even higher capacity for CO₂ adsorption by an increased percentage of 5.91% (30 °C) and 5.77% (70 °C) compared to the capacity in the first cycle. The reason lies in the strong interaction between melamine and attapulgite matrix which was further confirmed by DFT calculations. The MEL was validated to have advantages over aliphatic amines (TEPA) in modifying ATT to get high stability of CO₂-adsorbents.