Composite membranes based on self-crosslinking polyelectrolyte-wrapped ZIF-8/CNT nanoparticles for solar steam evaporation

Abstract

Zeolitic imidazolate frameworks (ZIFs) are widely studied for selective transport of small molecules with their designable channels and cage-like pores. Herein, we design solar-thermal hybrid membrane ZCP-20 (ZIF-8/CNTs@PCMVIMBr-20), where ZIF-8 is used as a water transmission channel. ZIF-8 was integrated with self-crosslinking PCMVIMBr (poly[1-cyanomethyl-3-vinylimidazolium bromide]), where its imidazole moiety coordinates with Zn ions to give a mechanically robust membrane. The hydrophobic channels of ZIF-8 enable the formation of discrete water clusters. Differential scanning calorimetry and dark water evaporation rate evaluation indicate that the water evaporation enthalpy in the ZCP-20 membrane is 1.00 kJ g⁻¹. Consequently, the ZCP-20 membrane exhibits a high evaporation rate of 2.48 kg m⁻² h⁻¹ under one sun irradiation and displays stable evaporation rates for 20 h. Remarkably, the ZCP-20 membrane can tolerate various water sources (e.g., dye-polluted water) or even strongly acidic (pH = 1) or basic (pH = 13) solutions.