Stephen Mezyk

First-ever Arrhenius parameter determinations for radical cation reactions with lanthanide-TODGA complexes in n-dodecane.

Given their proposed use as trivalent actinide–lanthanide separation ligands, the role of molecular architecture on the radiation robustness of diglycolamide (DGA) molecules has been investigated.

Correction for ‘Impact of lanthanide ion complexation and temperature on the chemical reactivity of N,N,N′,N′-tetraoctyl diglycolamide (TODGA) with the dodecane radical cation’ by Gregory P. Horne et al., Phys. Chem. Chem. Phys., 2023, 25, 16404–16413, https://doi.org/10.1039/D3CP01119D.

Complexation off-elements by 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (HEH[EHP]) promoted significantly enhanced radiation-induced chemical reactivity resulting in accelerated HEH[EHP] degradation.

Steady-state and time-resolved irradiations of diaminoguanidine have shown that the longevity of this potential TcO₄⁻ redox control reagent will be limited by its reaction with nitrous acid and oxidizing radicals from nitric acid radiolysis.

First-ever rate constant data for NO₃˙ radical reactions with organophosphorus and amidic extraction ligands in liquid n-dodecane. Reaction mechanisms were identified as H-atom (amidic) and electron (phosphorus) abstraction based on DFT calculations.

The reactivity of chromium(III) species with the major oxidizing and reducing radiolysis products of water was investigated in aqueous solutions at temperatures up to 150 °C. The reaction between the hydrated electron (e_aq⁻) and Cr(III) species showed a positive temperature dependence over this temperature range. The reaction was also studied in pH 2.5 and 3.5 solutions for the first time. This work also studied the reaction between acidic Cr(III) species and the hydroxyl radical (⋅OH). It was found that Cr³⁺ did not react significantly with the ⋅OH radical, but the first hydrolysis species, Cr(OH)²⁺, did with a rate coefficient of k= (7.2±0.3)×10⁸ M⁻¹ s⁻¹ at 25 °C. The oxidation of Cr(OH)²⁺ by the ⋅OH radical formed an absorbing product species that ultimately oxidized to give Cr(VI). These newly measured reaction rates allow for the development of improved models of aqueous chromium speciation for the effective remediation of liquid high‐level nuclear waste via vitrification processes.

Acetohydroxamic acid (AHA) has been proposed for inclusion in advanced, single‐cycle, used nuclear fuel reprocessing solvent systems for the reduction and complexation of plutonium and neptunium ions. For this application, a detailed description of the fundamental degradation of AHA in dilute aqueous nitric acid is required. To this end, we present a comprehensive, multiscale computer model for the coupled radiolytic and hydrolytic degradation of AHA in aqueous sodium nitrate and nitric acid solutions. Rate coefficients for the reactions of AHA and hydroxylamine (HA) with the oxidizing nitrate radical were measured for the first time using electron pulse radiolysis and used as inputs for the kinetic model. The computer model results are validated by comparison to experimental data from steady‐state gamma ray irradiations, for which the agreement is excellent. The presented model accurately predicts the yields of the major degradation products of AHA: acetic acid, HA, nitrous oxide, and molecular hydrogen.

Ln(iii) complexation by TODGA led to enhanced chemical reactivity with RH˙⁺ from electron pulse irradiation. Average local ionization energy calculations indicate that this enhancement is likely due to preferential reaction at nitrate counter ions.

A comprehensive multiscale model determines the fundamental reaction mechanisms of the radical-induced degradation of acetohydroxamic acid in acidic aqueous solutions.

Pulsed electron reaction kinetic data for Cm(iii) suggest that radiation-induced Cm(ii) and Cm(iv) transients could exist in aqueous solutions and be available to undergo subsequent redox chemistry.

Used nuclear fuel uranium complexants (TBP, DEHBA, and DEHiBA) exhibit significantly different radiation-induced reactivities upon uranyl complexation as dictated by a combination of electron density distribution and reaction pathway energetics.

The radiation stability of the candidate An(III)/Ln(III) separation ligand hexa-n-octylnitrilo-triacetamide (HONTA) under envisioned process conditions was investigated using a combination of solvent test loop gamma and pulsed electron irradiation.

The incorporation of 1-octanol as a phase modifier in TODGA solvent system formulations promotes TODGA radiolysis under organic-only conditions, and radioprotection under biphasic nitric acid conditions.

Complexation of nitric acid by ligands containing conjugated aromatic phosphine oxide functionalities affords activated radioprotection through quenching n-dodecane excited states originating from gamma radiolysis.

Gamma-radiolysis of the ligand DEHBA is accelerated under biphasic acidic conditions and yields one or more plutonium complexing degradation products.

Advanced analytical techniques and predictive multi-scale modeling calculations show that gamma radiolysis of hydrophilic diglycolamides in concentrated, aqueous nitrate solutions is significantly slower and less structurally sensitive than under pure water conditions.

A predictive computer model was developed and successfully employed to evaluate fundamental mechanisms underpinning the radiation robustness of two sulfonated bis-triazinyl-(bi)pyridine ligands, designed as hydrophilic complexants.

Dye probe molecules were used to investigate lanthanide complexation and verify the viability of the ligand displacement methodology for measuring DTPA complexation rate constants. Results showed that dye probes underestimate the rate constants.

This study evaluates the contribution of indirect photolysis to the environmental fate of the lampricides TFM and niclosamide.