In the present thesis, cellulose sponges prepared using 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) oxidized and ultra-sonicated cellulose nanofibers (TOUS-CNFs) as three-dimensional scaffolds, and branched polyethyleneimine (bPEI) as crosslinking agent, underwent to a systematic Small Angle Neutron Scattering (SANS) and Fourier-Transform Infrared Spectroscopy (FTIR) investigation, by varying the amount of cross-linker, water content and temperature. The aim was to provide an experimental evidence of nano-porosity in the TOUS-CNFs network of these nanosponges (CNS) by investigating the water nano-confinement geometries in the adsorbent material. Moreover, we also verified how the breaking/reformation of specific intermolecular hydrogen bond interactions between water and the chemical groups present in the architecture of the CNS can contribute to regulate the water adsorption process observed at macroscopic level. Concerning SANS measurements, the analysis of the experimental data, performed in terms of a Correlation Length Model (CLM), allowed us to extract the short-range correlation length ξ, interpreted as a very first indirect estimation of the effective nano-dimension of the cavities produced by the cross-linking of the reticulated cellulose nanofibers. From the model, a power-law (n) and Lorentzian (m) exponents have been also obtained, respectively associated to the density of TOUS-CNFs at high (larger than hundreds of Å) and low (∼ 10 - 100 Å) spatial scale. These parameters turned out to be all sensitive to the structural variations induced by the progressive uptake of water on the bPEI/TOUS-CNFs sponges with different ratios. Finally, the effect of the addition of citric acid in the CNS formulation was investigated, confirming its role in increasing cross-linking density and sponge rigidity. In addition, a preliminary investigation of the molecular connectivity and the extent of hydrogen-bond patterns of water molecules confined in the bPEI/TOUS CNFs sponges was also performed by FTIR spectroscopy. The proposed spectroscopic method exploits the combined analysis of the vibrational spectra of polymers hydrated with water and deuterated water, which allows us to separate and selectively investigate the temperature-evolution of the HOH bending mode of engaged water molecules. As main results, we find a strong experimental evidence of a liquid-like behaviour of water molecules confined in the sponge nano-cavities and we observe a characteristic destructuring effect on the hydrogen-bonds network of confined water induced by thermal motion. The obtained results appear crucial in order to rationalize the design of these sponges and to track the changes in the ability of the final products as efficient nano-confinement systems for water decontamination.
|Titolo:||Branched polyethyleneimine/TEMPO-oxidized cellulose nanofibers xerogels for water remediation: a structural and dynamical study by small angle neutron scattering (SANS) and Fourier-transform infrared spectroscopy (FTIR)|
|Data di pubblicazione:||28-nov-2019|
|Appare nelle tipologie:||Tesi di dottorato|