These films are fairly robust and can be transfer-printed onto substrates with cavities or through holes to form membranes with freestanding sections of up to ∼60 000 µm 2 . An interesting feature of these membranes is the tunability of their mechanical and electrical properties which is based on the photocatalytic activity of the TNRs. As shown by AFM and AFM-bulge tests, DUV exposure results in a compaction of the composite material along with an increase of Young's modulus from ∼22 GPa to ∼35 GPa. This enhancement of the mechanical properties is most likely due to photo-induced cross-linking of the membranes' organic components (GO, SF). The toughness of the irradiated membranes is in the range of 1.25 MJm -3 while the ultimate biaxial tensile stress and strain are in the range of ∼377 MPa and ∼0.68 %, respectively. Furthermore, DUV irradiation lends the initially insulating material electrical conductivity due to the photocatalytic reduction of GO to rGO. Hence, these membranes can be employed as electrostatically driven actuators, which are interesting candidates for applications as sensors and optical devices. 4 Experimental Materials. Methanol (≥99.8 %), 2-propanol (99.7 %), toluene (99.5 %), acetone (≥99.8 %), chloroform (99 %), and hydrochloric acid (37 %) were purchased from VWR Chemicals. Hydrogen peroxide (30 %), 1-octadecene (ODE, 90 %), oleic acid (OLAC, 90 %), oleyl amine (OLAM, 98 %), and titanium(IV) chloride (99 %) were purchased from Merck. Graphite (-325 mesh, 99.8 %) and potassium permanganate (99 %) were purchased from Alfa Aesar. Silk Fibroin solution (SF, 50 mg/mL ∼100 kDa), methoxyperflourobutane (MPFB, ≥99 %), and poly methyl methacrylate (PMMA, 120 kDa) were purchased from Sigma-Aldrich. Sulfuric acid (95 %) was purchased from Chemsolute. Chlorobenzene (≥99 %) was purchased from Burdick Johnson. Polydimethylsiloxane (PDMS, Sylgard 184) was purchased from Dow Corning Inc. Polyvinyl alcohol (PVA, 15 kDa) was purchased from Fluka. All chemicals were used as received without further purification. DI water (18.2 MΩcm) was provided using an ELGA LabWater purification system.