# Water vapour sorption properties of a family of square lattice topology porous coordination networks

## TL;DR

Researchers studied a family of porous materials that efficiently absorb water vapor at low humidity, making them suitable for water harvesting in arid regions.

## Contribution

The study reveals the water vapour sorption properties and stability of sql-M-aqua coordination networks for potential use in water harvesting.

## Key findings

- sql-M-aqua materials show S-shaped water sorption isotherms at low relative humidity.
- They maintain stability and performance over 100 sorption cycles.
- These materials also demonstrate CO2/N2 selectivity.

## Abstract

Porous coordination networks (PCNs) such as metal–organic frameworks are of topical interest thanks to their potential utility as sorbents for gas and vapour separations and/or storage. Interpenetrated PCNs, some of which offer promise for gas separations, remain relatively understudied in the context of water vapour sorption. Herein, we report an in-depth study of the water vapour sorption properties of a family of square lattice topology (sql) PCNs of general formula sql-[bipy,squa]-M-aqua (sql-M-aqua, M = Mn, Co, Ni, Zn, bipy = 4,4-bipyridine, squa = squarate). This family, several of which have been previously reported (Co, Ni, Mn), exist as rectangular grids that exhibit 2-fold inclined interpenetration, thereby forming ultramicroporous 3D supramolecular networks. Water vapour sorption studies of sql-M-aqua (M = Mn, Co, Ni, Zn) revealed S-shaped water vapour sorption isotherms with steps consistently below 10% relative humidity (RH) and little hysteresis. Such properties are pertinent to atmospheric water harvesting in arid regions (<30% RH). Water vapour humidity swing experiments (0–30% RH, 300 K) indicated hydrolytic stability for sql-M-aqua (M = Mn, Co, Ni, Zn) and retention of working capacity over 100 sorption/desorption cycles. sql-M-aqua (M = Mn, Co, Ni, Zn) also exhibit CO2/N2 selectivity.

The family of coordination networks sql-M-aqua (M = Mn, Ni, Co, Zn) each exhibit an S-shaped water sorption isotherm, fast uptake kinetics, and hydrolytic stability over 100 cycles, ideal for atmospheric water harvesting at 0–30% relative humidity.