An uranyl sorption study inside functionalised nanopores

U Pinaeva,E Balanzat,O Cavani,T L Wade,M.-C Clochard,M Al-Sheikhly,N Ollier

doi:10.1038/s41598-020-62792-4

Abstract

Sorption mechanism of uranyl by poly(bis[2-(methacryloyloxy)ethyl] phosphate) (PB2MP) functionalised polyvinylidene fluoride (PVDF) track-etched membranes, PB2MP-g-PVDF, was investigated. It was found that uranyl sorption obeyed Langmuir isotherm model giving a maximum U(VI) membrane uptake of 6.73 μmol g−1 and an affinity constant of 9.85 ⋅ 106 L mol−1. XPS and TRPL measurements were performed to identify sorbed uranyl oxidation state and its environment. Uranyl was found to be mainly in its hexavalent state, i.e. U(VI), showing that the trapping inside the PB2MP-g-PVDF nanoporous membranes did not change the ion speciation. Two sorbed uranyl life-times (τ1 = 8.8 μs and τ2 = 102.8 μs) were measured by TRPL which pointed out different complexations taking place inside the nanopores. Uranyl sorption by PB2MP-g-PVDF membranes was also found to be pH dependent demonstrating the highest performance at circumneutral pH. In addition, TRPL was demonstrated to be not only a remarkable technique for U(VI) characterization, but also an alternative to voltammetry detection for trace on-site uranyl monitoring using PB2MP-g-PVDF nanoporous membranes.

Highlights

Sorption mechanism of uranyl by poly(bis[2-(methacryloyloxy)ethyl] phosphate) (PB2MP) functionalised polyvinylidene fluoride (PVDF) track-etched membranes, PB2MP-g-poly(vinylidene fluoride) (PVDF), was investigated
We investigated uranyl sorption behaviour of recently developed PB2MP-g-PVDF functionalised nanoporous membranes using Langmuir, Freundlich, and Temkin sorption isotherm models
Uranyl sorption obeyed Langmuir isotherm model pointing out that uranyl sorption is limited to a monolayer

Summary

Introduction

Sorption mechanism of uranyl by poly(bis[2-(methacryloyloxy)ethyl] phosphate) (PB2MP) functionalised polyvinylidene fluoride (PVDF) track-etched membranes, PB2MP-g-PVDF, was investigated. To address fast and simple on-site analysis, we have recently proposed a portable electrochemical sensor for trace uranium detection in water[4] These sensors are made of track-etched poly(vinylidene fluoride) (PVDF). Polyacrylic acid (PAA) and poly(4-vinyl pyridine) (P4VP) were grafted into similar track-etched PVDF membranes to efficiently trap Pb(II) and Hg(II) ions respectively. These two systems exhibit two very different well-known complexation states from a weaker affinity constant due to electrostatic interaction between Pb(II) ions and the weak acids of PAA up to a high affinity constant resulting in a strong metal/ligand interaction between Hg(II) ions and pyridine functional groups of P4VP. TRPL measurements were carried out and compared to XPS data to verify uranyl oxidation state and sorbed species environment

Methods

Results

Conclusion