Photoinduced directional proton transport through printed asymmetric graphene oxide superstructures: a new driving mechanism under full-area light illumination

2D-material-based membranes with densely packed sub-nanometer-height fluidic channels show exceptional transport properties, and have attracted broad research interest for energy-, environment-, and healthcare-related applications. Recently, light-controlled active transport of ionic species in abiotic materials have received renewed attention. However, its dependence on inhomogeneous or site-specific illumination is a challenge for scalable application. Here, directional proton transport through printed asymmetric graphene oxide superstructures (GOSs) is demonstrated under full-area illumination. The GOSs are composed of partially stacked graphene oxide multilayers formed by a two-step direct ink writing process. The direction of the photoinduced proton current is determined by the position of top graphene oxide multilayers, which functions as a photogate to modulate the horizontal ion transport through the beneath lamellar nanochannels. This transport phenomenon unveils a new driving mechanism that, in asymmetric nanofluidic structures, the decay of local light intensity in depth direction breaks the balance of electric potential distribution in horizontal direction, and thus generates a photoelectric driving force for ion transport. Following this mechanism, the GOSs are developed into photonic ion transistors with three different gating modes. The asymmetrically printed photonic-ionic devices provide fundamental elements for light-harvesting nanofluidic circuits, and may find applications for artificial photosynthesis and artificial electric organs.