Confinement-Controlled Aqueous Chemistry within Nanometric Slit Pores

Abstract

In this Focus Review, we put the spotlight on very recent insights into the fascinating world of wet chemistry in the realm offered by nanoconfinement of water in mechanically rather rigid and chemically inert planar slit pores wherein only monolayer and bilayer water lamellae can be hosted. We review the effect of confinement on different aspects such as hydrogen bonding, ion diffusion, and charge defect migration of H + (aq) and OH − (aq) in nanoconfined water depending on slit pore width. A particular focus is put on the strongly modulated local dielectric properties as quantified in terms of anisotropic polarization fluctuations across such extremely confined water films and their putative effects on chemical reactions therein. The stunning findings disclosed only recently extend wet chemistry in particular and solvation science in general toward extreme molecular confinement conditions.

Can electric fields drive chemistry for an aqueous microdroplet?

“…Presently we do not fully know what makes water droplets exceptional for accelerating reactions, and as such it is a current and highly active area of investigation. Factors that may contribute to the rate acceleration include concentration increases due to solvent evaporation 9 , partial solvation of reactants 2 , 10 , gas-phase channels 11 , 12 , changes in pH 13 , a localized dielectric constant that deviates from bulk 14 , and favorable entropy changes due to preferential orientations of the reactant molecules near the surface 15 . There is experimental evidence that the droplet enables or recruits a surface active species and/or the possibility that the droplet charge state is driving the accelerated reaction chemistry 16 – 18 .…”

Catalytic confinement effects in nanochannels: from biological synthesis to chemical engineering

“…33,87,88 The mass transport of ions or molecules, and the properties of aqueous solvent within the channels also play significant roles. 89 Comprehensive theories and in situ characterization techniques should thus be developed to probe the CCE and mechanism of catalysis. 90,91…”

Electrochemistry under confinement

“…The close-range effects appearing in such geometries are predominantly addressed by means of molecular dynamics and discussed in detail in recent reviews such as the ones by Khlobystov and co-workers 146 and Marx and Mun ˜oz-Santiburcio. 147 Closed shell soft nanoparticle systems are studied more frequently regarding electrochemistry. Examples ranging from single entity confined colloids over micelles, micro-and nanoemulsions to other liquid/liquid interface-based core shell particles.…”