Interlocking dendritic fibrous nanosilica into microgranules by polyethylenimine assisted assembly: in situ neutron diffraction and CO2 capture studies

Abstract

Solid amine-based nano-adsorbents have shown tremendous potential for mitigating CO₂ emissions. The conventional approaches for achieving these nano-adsorbents utilize the loading of the amines in well-defined mesopores, which face several challenges, including pore blocking and slow adsorption kinetics. In this work, we report an evaporation induced assembly approach to achieve dendritic fibrous nano-silica (DFNS)–polyethylenimine (PEI) microgranules using a mixed colloidal dispersion of nanometer-sized DFNS particles and PEI. The PEI incorporated DFNS microgranules were studied using small-angle X-ray scattering, electron microscopy, and N₂ gas adsorption techniques in a detailed fashion. Two-dimensional fast Fourier transform (2D FFT) of the high-resolution micrographs shows an intriguing order to disorder transition in the jamming of DFNS in the presence of PEI. This disordered jamming of DFNS led to the formation of voids, causing increased accessibility of DFNS internal pores. Furthermore, the interstices between the jammed DFNS in microgranules provided additional space to immobilize more PEI molecules, which was not possible in bare DFNS particles. The CO₂ adsorption characteristics have been found to be excellent with good regeneration capability up to 50 cycles due to the unique morphology of the DFNS microgranules and strong PEI confinement. The CO₂ specific interaction of amine sites in PEI allows high selectivity of CO₂ adsorption against N₂ and H₂O except at low temperatures. The fast kinetics of DFNS–PEI was attributed to the connectivity between mesopores and macropores as evident from in situ neutron diffraction studies, which provided crucial experimental evidence of the connectivity of mesopores and macropores for the first time, refining the enigmatic DFNS structure.