By DUV exposure GO is photocatalytically reduced to rGO. In addition, the photocatalytic activity of titania triggers the formation of radicals which initiate polymerization and cross-linking reactions in organic materials. After 80 min DUV exposure the AFM bulge tests were repeated revealing a significantly increased stiffness for both membranes (cf. Figure and Figure , Supporting Information). As seen by the values presented in Table , the Young's modulus of both membranes increased to ∼35 GPa. In addition, the membranes' prestress increased from ∼15 MPa to ∼32 MPa. We attribute the enhanced mechanical properties to photocatalytically induced cross-linking between the different components of the membranes. For comparison, Hu et al. reported an increase in the mechanical strength of GO/SF biopapers upon electrochemical microstamping caused by the reduction of GO and the crosslinking of the SF. Further, upon DUV exposure the thickness of the membranes decreased from ∼28 nm to ∼19 nm (cf. Table and Figure , Supporting Information). This observation suggests a significant compaction of the membrane material due to cross-linking. The loss of material is possible due to the formation of volatile reaction products during DUV irradiation.