Perfect graphene is believed to be the strongest material. However, the useful strength of large-area graphene with engineering relevance is usually determined by its fracture toughness, rather than the intrinsic strength that governs a uniform breaking of atomic bonds in perfect graphene. To date, the fracture toughness of graphene has not been measured. Here we report an in situ tensile testing of suspended graphene using a nanomechanical device in a scanning electron microscope. During tensile loading, the pre-cracked graphene sample fractures in a brittle manner with sharp edges, at a breaking stress substantially lower than the intrinsic strength of graphene. Our combined experiment and modelling verify the applicability of the classic Griffith theory of brittle fracture to graphene. The fracture toughness of graphene is measured as the critical stress intensity factor of 4:0 AE 0:6 MPa ffiffiffiffi m p and the equivalent critical strain energy release rate of 15.9 J m À 2 . Our work quantifies the essential fracture properties of graphene and provides mechanistic insights into the mechanical failure of graphene.

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Extremely asymmetric wettability, high wetting selectivity, instantaneous superwetting behaviors (low transmembrane resistance), and superior resistance to chemicals and solvents are needed for Janus membranes for switchable oil/water separation. However, it is still challenging to obtain Janus membranes with such properties. In this study, a surface with metastable hydrophobicity is constructed on one side of the chemically stable superhydrophilic TiO 2 @PPS membrane by adjusting the hydrophobization depth and the morphology of the hydrophobic layer via a water−oil interfacial grafting. The prepared Janus membrane exhibits a high water contact angle difference of ∼150°between its two surfaces with maintaining the superior penetrability of the original membrane, which makes it capable to separate both oil-in-water and waterin-oil emulsions with high fluxes and accuracy. The separation efficiency is higher than 98% for the separation of the two kinds of emulsions. The fluxes of the surfactant-free toluene-in-water and water-in-toluene emulsions are up to 6.4 × 10 2 and 9.5 × 10 2 L m −2 h −1 , respectively. Furthermore, the Janus membrane exhibits desirable antifouling performance and reusability during usage.

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Electronic waste (E-waste) contain large environmental contaminants such as toxic heavy metals and hazardous chemicals. These contaminants would migrate into drinking water or food chains and pose a serious threat to environment and human health. Biodegradable green electronics has great potential to address the issue of E-waste. Here, we report on a novel biodegradable and flexible transparent electrode, integrating three-dimensionally (3D) interconnected conductive nanocomposites into edible starch-chitosan-based substrates. Starch and chitosan are extracted from abundant and inexpensive potato and crab shells, respectively. Nacre-inspired interface designs are introduced to construct a 3D interconnected single wall carbon nanotube (SCNT)-pristine graphene (PG)-conductive polymer network architecture. The inorganic one-dimensional SCNT and two-dimensional PG sheets are tightly cross-linked together at the junction interface by long organic conductive poly(3,4-ethylenedioxythiophene) (PEDOT) chains. The formation of a 3D continuous SCNT-PG-PEDOT conductive network leads to not only a low sheet resistance but also a superior flexibility. The flexible transparent electrode possesses an excellent optoelectronic performance: typically, a sheet resistance of 46 Ω/sq with a transmittance of 83.5% at a typical wavelength of 550 nm. The sheet resistance of the electrode slightly increased less than 3% even after hundreds of bending cycles. The lightweight flexible and biocompatible transparent electrode could conform to skin topography or any other arbitrary surface naturally. The edible starch-chitosan substrate-based transparent electrodes could be biodegraded in lysozyme solution rapidly at room temperature without producing any toxic residues. SCNT-PG-PEDOT can be recycled via a membrane process for further fabrication of conductive and reinforcement composites. This high-performance biodegradable transparent electrode is a promising material for next-generation wearable green optoelectronics, transient electronics, and edible electronics.

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