Polymer-Supported Bifunctional Amidoximes for the Sorption of Uranium from Seawater

Abstract

Bifunctional amidoxime fibers are synthesized from commercially available polyacrylonitrile as sorbents for the recovery of U­(VI) from seawater. The purpose of introducing a second ligand is to enhance the affinity of the amidoxime (AO) ligand via two possible mechanisms: by acting directly upon the AO to increase its ability to ion exchange or providing additional coordination sites to the uranyl ion. Amines are chosen as the second ligand since they have a high affinity for U­(VI) at ppm levels from synthetic seawater. Diethylenetriamine (DETA) is utilized as the amine because it is sufficiently flexible to interact with AO and able to bind metal ions. Along with AO and AO-DETA fibers, the primary NH2 moieties were modified with phosphonic acid ligands (AO-phon-DETA). All fibers have high affinities (>99% sorption) for the uranyl ion when initially present at 0.90 ppm in synthetic seawater. When contacted with actual seawater at the Pacific Northwest National Laboratory for 20.8 days, the loadings for the fibers are 124 μg/g (AO), 535 μg/g (AO-DETA), and 789 μg/g (AO-phon-DETA). For comparison, a polyethylene fiber on which was grafted polyacrylonitrile and then converted to AO at the Oak Ridge National Laboratory gave a uranyl loading of 2610 μg/g at the same contact time, perhaps due to its optimized support structure and/or the presence of diamidoxime groups. FTIR spectra indicate that the effect of DETA is through a hydrogen bonding interaction with the AO to facilitate dissociation of the acidic N–O–H. Continuing research on optimizing the loading onto the bifunctional fibers emphasizes the effect of phosphorus capacity, amine ligand, and synthesis conditions.

Bio-inspired nano-traps for uranium extraction from seawater and recovery from nuclear waste

“…In this context, it is anticipated that both the stability and selectivity of uranyl chelates will be enhanced when these concepts are included, in addition to coordinative binding with the metal center. Indeed, previous research demonstrates that the affinity of amidoxime functionalized adsorbents for uranyl can be enhanced by incorporation of auxiliary amine or carboxylic acid group, suggesting a potential synergism between these functionalities and the amidoxime group in achieving uranium binding 23 , 24 . However, the relative position of amidoxime to the auxiliary functionality is undefined in these adsorbents, compromising such a cooperation as well as rational improvement.…”

De novo synthesis of bifunctional conjugated microporous polymers for synergistic coordination mediated uranium entrapment

“…In this respect, a prerequisite for sorbent development is to effectively create synergistic functionalities located adjacent to amidoxime groups by taskspecific synthesis which allows the formation of synergistic binding to uranyl ions. This remains a considerable challenge for conventional synthetic strategies such as copolymerization, grafting, or post-modification [46][47][48], especially within the confined pore channels of CMP-based sorbents.…”

Cadmium and iron removal from phosphoric acid using commercial resins for purification purpose

“…Alexandratos' group documented the relative importance of polarizability (Alexandratos and Zhu 2015), hydrogen bonding (Alexandratos and Zhu 2017; Zhu and Alexandratos 2011), and bi-functionality (Alexandratos and Smith 2004) on the sorption performance of ligands (especially those bearing phosphonate and amidoxime groups) (Alexandratos et al 2016). The electronegativity of Cd (II) (i.e., χ aq 2.660) is close to that of Fe (II) (i.e., χ aq 2.636), while Fe(III) has a much higher χ aq value (i.e., 3.835) (Li et al 2012).…”

“…Activated carbon and clays are frequently used for the purification of phosphoric acid from organic impurities (Nasr et al 2005;Trabelsi and Tlili 2017) or metal ions (El-Bayaa et al 2011;Kussainova et al 2019;Kussainova et al 2016;Tjioe et al 1988), including metal-loaded clays (Hamza et al 2016). However, sorbents can be also operated for metal removal from crude phosphoric acid (Alexandratos and Zhu 2016;El-Bayaa et al 2011;Heres et al 2018;Kouzbour et al 2019;Zhu and Alexandratos 2015).…”