Photothermal responsive ultrathin Cu-TCPP nanosheets/sulfonated polystyrene nanocomposite photo-switch proton conducting membranes

Abstract

Applying different strategies, nanocomposite membranes formation from functionalized polymer(s) and compatible nanofillers is the most renowned way to make the membrane proton conductive without compromising their mechanical strength. Among different types of nanofillers, incorporating photothermal-responsive metal organic frameworks (MOFs) into the ion exchange polymer is the prominent strategy and has achieved advanced attention in smart protonic solids with versatile potential applications. In this work, ultrathin, highly ordered porous photothermal-responsive copper tetrakis(4-carboxyphenyl)porphyrin (Cu-TCPP) nanosheets are incorporated into sulfonated polystyrene (SPS) membranes as novel nanofillers. High loading and well dispersed Cu-TCPP nanosheets incorporated nanocomposite membranes are achieved and demonstrate photo-switchable protonic conductivity due to photothermal response of MOFs nanosheets to visible light. The nanocomposite membrane with highest MOFs content shows a high proton conductivity of 1.42 × 10−4 S cm−1 at 95 °C at 95% RH. The altered photo-switch proton conductivity of nanocomposite membranes is attributed to the formation and breakage of H-bonding networks with water molecules in the channels of proton transport pathways by the local photothermal heated Cu-TCPP nanosheets. Furthermore, after incorporation of the Cu-TCPP nanosheets into SPS, not only the thermal stability is increased but also almost zero swelling is achieved in water, which reflects the nice durability of nanocomposite membranes. This photo-switchable proton conductivity of polymer proton conducting nanocomposite membranes with nice thermal stability and negligible swelling serves as a new gate for photo-switching proton conductive membranes, photosensors, photoswitches etc.