X‑ray Absorption Spectroscopy Investigation of Iodine Capture by Silver-Exchanged Mordenite

Capture of radioactive iodine is a significant consideration during reprocessing of spent nuclear fuel and disposal of legacy wastes. While silver-exchanged mordenite (AgZ) is widely regarded as a benchmark material for assessing iodine adsorption performance, previous research efforts have largely focused on bulk material properties rather than the underpinning molecular interactions that achieve effective iodine capture. As a result, the fundamental understanding necessary to identify and mitigate deactivation pathways for the recycle of AgZ is not available. We applied X-ray Absorption Fine Structure (XAFS) spectroscopy to investigate AgZ following activation, adsorption of iodine, regeneration, and recycle, observing no appreciable degradation in performance due to the highly controlled conditions under which the AgZ was maintained. Fits of the extended XAFS (EXAFS) data reveal complete formation of Ag⁰ nanoparticles upon treatment with H₂, and confirm the formation of α-AgI within the mordenite channels in addition to surface γ/β-AgI nanoparticles following iodine exposure. Analysis of the nanoparticle size and fractional composition of α-AgI to γ/β-AgI supports ripening of surface nanoparticles as a function of recycle. This work provides a foundation for future investigation of AgZ deactivation under conditions relevant to spent nuclear fuel reprocessing

Graphene-Immobilized Monomeric Bipyridine‑M^<i>x</i>+ (M^<i>x</i>+ = Fe³⁺, Co²⁺, Ni²⁺, or Cu²⁺) Complexes for Electrocatalytic Water Oxidation

Covalent anchoring of 2,2′-bipyridine (<b>L</b>) to a graphene (Gr) modified electrode followed by treatment with an M^<i>x</i>+(NO₃)_<i>x</i> solution (M = Fe³⁺, Co²⁺, Ni²⁺, or Cu²⁺) results in surface-bound catalysts with high redox activity in neutral water at ambient temperature. Raman and IR spectroscopies indicate the successful <b>L</b> grafting and Gr deposition onto the electrodes, whereas metal concentration was determined by inductively coupled plasma mass spectrometry (ICP-MS). Cyclic voltammetry measurements were used to investigate catalytic performances, whereas a rotating ring-disk electrode was used to measure the faraday efficiencies of oxygen evolution reaction and determine experimental turnover frequencies (TOFs). Of the four metal-<b>L</b> complexes investigated, Co-<b>L</b> on a Gr-modified indium tin oxide (ITO) electrode exhibits the best catalytic activity. Washing with a solution containing catalytically inert Zn²⁺ removes Co weakly bound by surface carboxylate functionalities, and ensures the presence of only covalently attached active catalytic species. This process results in an experimental TOF of 14 s^–1 at an overpotential of 834 mV. Functionalization of Gr-modified electrodes with appropriate metal-binding moieties thus provides a feasible strategy for loading first row transition metals onto conductive surfaces for the generation of highly active water oxidation catalysts

Functionalized Porous Aromatic Framework for Efficient Uranium Adsorption from Aqueous Solutions

We demonstrate the successful functionalization of a porous aromatic framework for uranium extraction from water as exemplified by grafting PAF-1 with the uranyl chelating amidoxime group. The resultant amidoxime-functionalized PAF-1 (PAF-1-CH₂AO) exhibits a high uranium uptake capacity of over 300 mg g^–1 and effectively reduces the uranyl concentration from 4.1 ppm to less than 1.0 ppb in aqueous solutions within 90 min, well below the acceptable limit of 30 ppb set by the US Environmental Protection Agency. The local coordination environment of uranium in PAF-1-CH₂AO is revealed by X-ray absorption fine structure spectroscopic studies, which suggest the cooperative binding between UO₂²⁺ and adjacent amidoxime species

Successful Coupling of a Bis-Amidoxime Uranophile with a Hydrophilic Backbone for Selective Uranium Sequestration

The amidoxime group (−RNH₂NOH) has long been used to extract uranium from seawater on account of its high affinity toward uranium. The development of tunable sorbent materials for uranium sequestration remains a research priority as well as a significant challenge. Herein, we report the design, synthesis, and uranium sorption properties of bis-amidoxime-functionalized polymeric materials (BAP <b>1</b>–<b>3</b>). Bifunctional amidoxime monomers were copolymerized with an acrylamide cross-linker to obtain bis-amidoxime incorporation as high as 2 mmol g^–1 after five synthetic steps. The resulting sorbents were able to uptake nearly 600 mg of uranium per gram of polymer after 37 days of contact with a seawater simulant containing 8 ppm uranium. Moreover, the polymeric materials exhibited low vanadium uptake with a maximum capacity of 128 mg of vanadium per gram of polymer. This computationally predicted and experimentally realized selectivity of uranium over vanadium, nearly 5 to 1 w/w, is one of the highest reported to date and represents an advancement in the rational design of sorbent materials with high uptake capacity and selectivity

Toward the Design of a Hierarchical Perovskite Support: Ultra-Sintering-Resistant Gold Nanocatalysts for CO Oxidation

An ultrastable Au nanocatalyst based on a heterostructured perovskite support with high surface area and uniform LaFeO₃ nanocoatings was successfully synthesized and tested for CO oxidation. Strikingly, small Au nanoparticles (4–6 nm) are obtained after calcination in air at 700 °C and under reaction conditions. The designed Au catalyst not only possessed extreme sintering resistance but also showed high catalytic activity and stability because of the strong interfacial interaction between Au and the heterostructured perovskite support

A Poly(acrylonitrile)-Functionalized Porous Aromatic Framework Synthesized by Atom-Transfer Radical Polymerization for the Extraction of Uranium from Seawater

In order to ensure a sustainable reserve of fuel for nuclear power generation, tremendous research efforts have been devoted to developing advanced sorbent materials for extracting uranium from seawater. In this work, a porous aromatic framework (PAF) was surface-functionalized with poly­(acrylonitrile) through atom-transfer radical polymerization (ATRP). Batches of this adsorbent were conditioned with potassium hydroxide (KOH) at room temperature or 80 °C prior to contact with a uranium-spiked seawater simulant, with minimal differences in uptake observed as a function of conditioning temperature. A maximum capacity of 4.81 g-U/kg-ads was obtained following 42 days contact with uranium-spiked filtered environmental seawater, which demonstrates a comparable adsorption rate. A kinetic investigation revealed extremely rapid uranyl uptake, with more than 80% saturation reached within 14 days. Relying on the semiordered structure of the PAF adsorbent, density functional theory (DFT) calculations reveal cooperative interactions between multiple adsorbent groups yield a strong driving force for uranium binding