Transparent luminescent nanopaper based on g-C3N4 nanosheet grafted oxidized cellulose nanofibrils with excellent thermal and mechanical properties

Functional nanopaper based on cellulose nanofibrils (CNF) has attracted growing interest due to its renewability, biodegradability and enhanced printability. In this study, we developed novel transparent and luminescent nanopaper with excellent mechanical flexibility by grafting graphitic carbon nitride (g-C3N4) nanosheets with TEMPO-mediated oxidation CNF (TCNF) using a pressured extrusion paper-making technique. The carboxyl groups on the TCNF surface acting as active sites are covalently cross-linked with -NH2 or -NH groups of g-C3N4 nanosheets via EDC/NHS coupling chemistry, and then the g-C3N4@TCNF nanopaper with heterogeneous network structures is finally assembled. The hybrid nanopaper combines the advantages of TCNF and g-C3N4, exhibiting outstanding transparency and luminescent properties. Moreover, the transparent luminescent nanopaper possesses excellent thermal stability and mechanical flexibility. The intelligent design of high-performance nanopaper based on TCNF grafted with g-C3N4 nanosheets provides a potential strategy for applications in the easily identifiable and difficult-to-copy anti-counterfeiting fields.