mater.scichina.com link.springer.com Published online 1 March 2021 | https://doi.org/10.1007/s40843-020-1602-5 Sci China Mater 2021, 64(8): 1997–2007 Photogated proton conductivity of ZIF-8 membranes co-modified with graphene quantum dots and polystyrene sulfonate Shuaikang Fan, Shilin Wang, Xiaobin Wang, Zhuoyi Li, Xu Ma, Xinyi Wan, Shabab Hussain and Xinsheng Peng * ABSTRACT Smart proton conductive metal-organic frame- work (MOF) membranes with dynamic remote control over proton conduction show high potential for use in advanced applications, such as sensors and bioprocesses. Here, we report a photoswitchable proton conductive ZIF-8 membrane by coencapsulating polystyrene sulfonate and graphene quantum dots into a ZIF-8 matrix (GQDs-PSS@ZIF-8) via a solid- confined conversion process. The proton conductivity of the GQDs-PSS@ZIF-8 membrane is 6.3 times higher than that of pristine ZIF-8 and can be reversibly switched by light due to photoluminescence quenching and the photothermal conver- sion effect, which converts light into heat. The local increase in temperature allows water molecules to escape from the porous channels, which cuts off the proton transport pathways and results in a decrease in proton conductivity. The proton con- ductivity is restored when the light is off owing to regaining water molecules, which act as proton carriers, from the sur- roundings. The GQDs-PSS@ZIF-8 membrane responds effi- ciently to light and exhibits an ON/OFF ratio of 12.8. This photogated proton conduction in MOFs has potential for the development and application of MOF-based protonic solids in advanced photoelectric devices. Keywords: ZIF-8, graphene quantum dots, photoswitchable proton conductivity, photoluminescence quenching, photo- thermal conversion INTRODUCTION Recently, solid-state proton conduction membranes have been increasingly studied due to their wide applications in devices, such as fuel cells, chemical or biological sen- sors, supercapacitors and information processing devices [1,2]. Based on their compositions, proton conducting solid membranes are chemically composed of inorganic oxides, ionic crystals, solid acid membranes, metal- organic frameworks (MOFs), porous coordination poly- mers (PCPs) and polymeric membranes [3,4]. MOFs are a subclass of highly porous and crystalline solid coordina- tion compounds that are an assembly of metal clusters and organic linkers. MOFs possess versatile properties, such as well-defined porous structures, large surface areas and high structural diversity, which make MOFs suitable for use in gas storage, separation, catalysis and photo- luminescence. The MOF structure can also be designed by pre- and post-synthetic methods to tailor the chemical stability and/or reactivity of the framework, enabling various functionalities for the utility mentioned above [5– 8]. These appealing merits make MOFs exhibit promising potentials not only as host materials but also as excellent candidates for conducting ions, in particular protons, in the pores. Proton conduction in MOFs has been widely studied in the past few years, with conductivities increasing from approximately 10 −3 to 1 S cm −1 [4,9,10]. Currently, many studies focus on achieving high proton conductivity via structural design, encapsulation of proton carriers, pore surface functionalization and so on in two distinct re- gimes—under hydrated conditions below 100°C and un- der anhydrous conditions above 100°C [5,11]. However, the efficient and feasible control of proton conduction in response to external stimuli may be critical for a wide range of applications. To realize a dynamic switch of proton conduction in advanced devices, some external stimuli have been attempted, such as changing the heat, light, pressure, electric field and pH [12]. For example, pyranine was doped into a melt coordination polymer to State Key Laboratory of Silicon Materials, School of Materials Science and Engineering, ERC of Membrane and Water Treatment, Ministry of Education, Zhejiang University, Hangzhou 310027, China * Corresponding author (email: pengxinsheng@zju.edu.cn) SCIENCE CHINA Materials ................................ ARTICLES August 2021 | Vol. 64 No.8 1997 © Science China Press and Springer-Verlag GmbH Germany, part of Springer Nature 2021