(143g) Development of Double-Functionalized Halloysite Nanotubes with Improved Adsorption Capacity for Carbon Capture

Amine-functionalized porous supports as adsorbents for CO₂ capture has been widely studied however, improving the adsorption capacity of these amine functionalized adsorbents is the current focus. Recently, double amine-functionalization of porous adsorbent to increase the amine density using different amine sources has been studied. The pores of the support are covalently functionalized with amines from alkoxy silanes and polymeric amines to form a class 1/class 2 hybrid adsorbent. However, the polymeric amine and silanes both compete for space the same space. In this study, we show a simple concept of dual amine functionalization of halloysite nanotubes (HNT) to form a hybrid adsorbent with no competition for anchoring site between the two amine sources. Halloysite nanotubes are natural aluminosilicate hollow tubular clay materials with inner diameter (lumen) of 15 − 30 nm and length of 0.5 − 3 μm. First, the silanol external surface of HNT is functionalized with 3-Aminopropyl triethoxysilane to covalently bind the amine group via silylation. Afterwards, 30wt% polyethyleneimine is loaded into the available lumen of the already functionalized HNT (A_HNT) by vacuum suction. The final morphology (A_HNT30PEI) is such that the HNT lumen is infiltrated with PEI while the external surface is tethered with covalently bonded amine group. Characterization result show that the structure of the HNTs remained unaltered after silane modification. Adsorption of CO₂ was performed using thermogravimetric analysis (TGA) at 45 °C and atmospheric pressure. The results show that the adsorption capacity of A_HNT30PEI is equivalent to that of A_HNT and HNT30PEI (30 wt% PEI in HNT) combined. This shows that we can leverage on the dual surface modification of HNT to create a class 1/class 2 hybrid adsorbent with enhanced CO₂ capture capability.