Neutron Imaging of Paramagnetic Ions: Electrosorption by Carbon Aerogels and Macroscopic Magnetic Forces.

Tim A Butcher,Pierre Boillat,J M D Coey,Pavel Trtik,Aran Rafferty,Lucy Prendeville

doi:10.1021/acs.jpcc.1c06031

Abstract

The electrosorption of Gd3+ ions from an aqueous 70 mM Gd(NO3)3 solution in monolithic carbon aerogel electrodes was recorded by dynamic neutron imaging. The aerogels have a bimodal pore size distribution consisting of macropores and mesopores centered at 115 and 15 nm, respectively. After the uptake of Gd3+ ions by the negatively charged surface of the porous structure, an inhomogeneous magnetic field was applied to the system of discharging electrodes. This led to a convective flow and confinement of Gd(NO3)3 solution in the magnetic field gradient. Thus, a way to desalt and capture paramagnetic ions from an initially homogeneous solution is established.

Highlights

Desalination is the process of removing dissolved ions from water
We report a neutron imaging study of the capacitive deionization of a paramagnetic Gd(NO3)[3] solution with a magnetic field gradient imposed during the discharge process
A quantitative determination of the pore size distribution was accomplished with mercury (Hg) porosimetry and Brunauer−Emmett− Teller (BET) surface area analysis

Summary

Introduction

Desalination is the process of removing dissolved ions from water. The minimum energy required to separate 1 M of solvated ions from bulk aqueous solution is related to the1ch0ankgJ emionl−1th(eR:chgeams iccoanl stpaontte,nTti:alroΔoEmmitnem=pe−raRtTure,lna(nxdi)= xi: mole fraction of the ions). ∇B is applied to such solutions, it exerts the magnetic field gradient force[1] χ F∇B = (B·∇)B μ0 (1) This is a force density with the magnetic susceptibility of the solution χ and the permeability of free space μ0 [see Figure 1a for an example with Gd3+ ions in the stray field of a permanent neodymium−iron−boron (Nd−Fe−B) magnet]. It allows magnetic levitation of submerged objects[3,4] or the inhibition of density-difference-driven convection.[5,6] The latter is of particular interest since it follows that paramagnetic liquids can be manipulated in non-magnetic miscible liquids. This is readily understandable when comparing the aforementioned chemical potential, whose derivative governs diffusion, and the magnetic energy sguivsecnepbtyibEilmitayg5=

Methods

Results

Conclusion