Fig. 1. Anomalous Small Angle X-ray Scattering (ASAXS) data from cellulose nanocrystals (CNCs) and the parallelepiped structure of CNCs and ionic shells surrounding them
Nanocellulose, which is cellulose in nanostructure form that can be produced at an industrial scale of tons per day, is gaining a reputation as one of the most significant “green materials.” One prominent eco-positive potential application of this bio-based material is in water purification due to the material’s ability to remove metal ion contaminants. But to date, the actual structure of the absorbed metal ions on a cellulose surface has been a mystery. Researchers from The University of Chicago and Argonne National Laboratory employed anomalous small-angle x-ray scattering (ASAXS) at the Anomalous Small- and Wide-Angle X-ray Scattering facility at the NSF’s ChemMatCARS, Sector 15 x-ray beamline of the Advanced Photon Source at Argonne. Their objective was determining the three-dimensional quantitative distribution of metal ions of different valencies surrounding negatively charged carboxylate cellulose nanocrystals (CNCs), which has the potential to adversely affect the water and ionic permeabilities of these materials.
Their results reveal that increasing the density of carboxylate group functionalization on the surface of the CNCs from 740 mmol/kg to 1100 mmol/kg changes the distribution of metal ions surrounding the CNCs from a monolayer structure to a multilayer.
What’s more, their results show that CNCs can use a variety of mechanisms (such as electrostatic attraction or disrupting the hydrogen bonding network between water molecules and reducing the stability of the native state of proteins by weakening the hydrophobic ,i.e., the chaotropic effect) to adsorb ions of different valencies. Using this increased understanding of the metal ion spatial organization, the design of cellulose-based sorbents can be improved to increase their uptake capacity and selectivity in separation applications, thereby significantly advancing the applicability of CNCs as a tool in the ecological toolkit.
These researchers carried their experimentation further by developing a model for analyzing ASAXS data from parallelepiped-shaped nanoparticles such as CNCs.
The team projects that this work may enable future studies into the structure of other relevant water contaminants on cellulose nanocrystals, as well as supporting new methods for studying ways to improve the adsorptive capacity of these sorbents.
See: Harrison R. Paul1, Mrinal K. Bera1, Nicholas Macke1, Stuart J. Rowan1,2*, and Matthew V. Tirrell1,2**, “Quantitative Determination of Metal Ion Adsorption on Cellulose Nanocrystals Surfaces,” ACS Nano 2024 18 (3), 1921-1930.
Author affiliations: 1The University of Chicago, 2Argonne National Laboratory
Correspondence: *stuartrowan@uchicago.edu, **mtirrell@uchicago.edu
This work was supported in part by the National Science Foundation PIRE program under Grant No. NSF 1743475 and the NSF Center for Sustainable Polymers (CSP) (CHE-1901635) at the University of Minnesota. It made use of the shared facilities at the University of Chicago Materials Research Science and Engineering Center (MRSEC), supported by National Science Foundation (NSF) under Award No. DMR-2011854. Parts of this work were carried out at the Soft Matter Characterization Facility of the University of Chicago. NSF’s ChemMatCARS, Sector 15 at the Advanced Photon Source (APS), Argonne National Laboratory (ANL) is supported by the Divisions of Chemistry (CHE) and Materials Research (DMR), National Science Foundation, under Grant No. NSF/CHE-1834750. This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science user facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. This work was sup-ported as part of the Advanced Materials for Energy-Water Systems (AMEWS), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences.
For information about anomalous small-angle x-ray scattering at NSF’s ChemMatCARS:
Mrinal Bera
(630) 252-0472
mrinalkb@uchicago.edu