Influence of hydrophilic groups and metal-ion adsorption on polymer-chain conformation of amidoxime-based uranium adsorbents

Alexander I. Wiechert, Wei Po Liao, Eunice Hong, Candice E. Halbert, Sotira Yiacoumi, Tomonori Saito, Costas Tsouris

Research output: Contribution to journalArticlepeer-review

35 Scopus citations

Abstract

This study focuses on the influence of hydrophilic groups and metal-ion loading on adsorbent polymer conformation, which controls access to adsorption sites and may limit adsorption capacity. Gaining a better understanding of the factors that influence conformation may yield higher-capacity adsorbents. Polyamidoxime (PAO), deuterated-PAO polyacrylic acid diblock copolymers (d-PAO-b-PAA), and randomly configured copolymers (PAO-co-PAA) were synthesized and characterized by neutron reflectometry in air and D2O. For d-PAO-b-PAA, characterization was also performed after alkali conditioning and in simulated seawater. PAO and PAO-co-PAA, with similar molecular weight and grafting density, extended from 95-Å thickness in air to 180 and 280-Å in D2O, respectively. This result suggests that polymer swelling may cause the additional adsorption capacity observed when polymer hydrophilicity increases. Two d-PAO-b-PAA samples, A and B, with a d-PAO thickness of 55-Å swelled to 110-Å and 140-Å respectively, with an overall thickness increase of ∼160% in D2O. After alkali conditioning, molecular interactions increased the density of PAA near the PAO-PAA interface, while the d-PAO thickness only decreased by ∼10 Å. The d-PAO thickness of both samples declined to ∼90-Å after adsorption in simulated seawater due to polymer-chain crosslinking. These results are expected to aid in improving adsorbent synthesis to increase uranium capacity.

Original languageEnglish
Pages (from-to)399-408
Number of pages10
JournalJournal of Colloid and Interface Science
Volume524
DOIs
StatePublished - Aug 15 2018

Funding

This research is supported by the U.S. Department of Energy, Office of Nuclear Energy , under Contract No. DEAC05-00OR22725 with Oak Ridge National Laboratory (ORNL), managed by UT-Battelle, LLC and at Georgia Tech by the Nuclear Energy University Program under Project 14-6789 . The authors are thankful to Dr. David Uhrig for his help in GPC measurements, which were conducted at the Center for Nanophase Materials Sciences a DOE Office of Science User Facility at ORNL. The authors are also thankful to Dr. J. Casey Johnson for his help on ATRP initiator synthesis and to Dr. Austin Ladshaw for reviewing the manuscript prior to submission.

Keywords

  • Amidoxime
  • Neutron reflectometry
  • Polymer conformation
  • Seawater
  • Uranium

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