Protonation and deprotonation of edges in graphene oxide and MXenes as a driving force for actuation in responsive 2D membranes

Abstract

Controlling bending in two-dimensional (2D) materials is essential for the development pf responsive systems and miniaturized actuators. Traditional approaches, particularly for graphene oxide (GO), rely on mismatched thermal expansion between GO and its reduced form. Here, we report a scalable method for assembling anisotropic membranes with chemically distinct top and bottom surfaces, achieved through pH-programmed control of flake protonation. Actuation is driven by edge-to-edge interactions among GO and MXene (Ti3C2Tx) flakes, where differential protonation induces localized strain and in-plane flake sliding during thermal dehydration. This gradient in charged and neutral functional groups enables directional bending upon mild heating. Extending this approach to MXenes yields robust, low-dimensional actuators with tunable chemical and mechanical properties. Demonstrated applications include soft robotics and climate-adaptive architecture. Systematic analysis of thermal response, water retention, and fabrication scalability underscores the broad potential of this platform for 2D material-based devices. A scalable strategy to assemble anisotropic GO and MXene membranes with pH-tuned edge functionalization enables programmable bending via thermo-responsive water release, with applications in soft robotics and adaptive bionic architecture