Smart Energy Storage: W18O49 NW/Ti3C2Tx Composite-Enabled All Solid State Flexible Electrochromic Supercapacitors.

Developing a highly efficient electrochromic energy storage device with sufficient color fluctuation and significant electrochemical performance is highly desirable for practical energy-saving applications. Here, to achieve a highly stable material with a large electrochemical storage capacity, a W18O49 NW/Ti3C2Tx composite has been fabricated and deposited on a pre-assembled Ag and W18O49 NW conductive network by Langmuir-Blodgett technique. The resulting hybrid electrode composed of 15 layers of W18O49 NW/Ti3C2Tx composite exhibits an areal capacitance of 125 mF cm-2, with a fast and reversible switching response. An optical modulation of 98.2% can be maintained at a current density of 5 mA cm-2. Using this electrode, a bifunctional symmetric electrochromic supercapacitor device having an energy density of 10.26 µWh cm-2 and a power density of 0.605 mW cm-2 is fabricated, with high capacity retention and full columbic efficiency over 4000 charge-discharge cycles. Meanwhile, the device displays remarkable electrochromic characteristics, including fast switching time (5 s for coloring and 7 s for bleaching), and a significant coloration efficiency of 116 cm2 C-1 with good optical modulation stability. In addition, the device exhibits significant mechanical flexibility and fast switching while being stable over 100 bending cycles, which is promising for real-world applications.

Tunable Molecular Sieving by Hierarchically Assembled Porous Organic Cage Membranes with Solvent-Responsive Switchable Pores.

Molecular separations involving solvents and organic impurities represent great challenges for environmental and water-intensive industries. Novel materials with intrinsic nanoscale pores offer a great choice for improvement in terms of energy efficiency and capital costs. Particularly, in applications where gradient and ordered separation of organic contaminants remain elusive, smart materials with switchable pores can offer efficient solutions. Here, we report a hierarchically networked porous organic cage membrane with dynamic control over pores, elucidating stable solvent permeance and tunable dye rejection over different molecular weights. The engineered cage membrane can spontaneously modulate its geometry and pore size from water to methanol and DMF in a reversible manner. The cage membrane exhibits ≥585.59 g mol-1 molecular weight cutoff preferentially in water and is impeded by methanol (799.8 g mol-1) and DMF (≈1017 g mol-1), reflecting 36 and 73% change in rejection due to self-regulation and the flexible network, respectively. Grazing incidence X-ray diffraction illustrates a clear peak downshift, suggesting an intrinsic structural change when the cage membranes were immersed in methanol or DMF. We have observed reversible structural changes that can also be tuned by preparing a methanol/DMF mixture and adjusting their ratio, thereby enabling gradient molecular filtration. We anticipate that such cage membranes with dynamic selectivity could be promising particularly for industrial separations and wastewater treatment.

Photochemical Creation of Covalent Organic 2D Monolayer Objects in Defined Shapes via a Lithographic 2D Polymerization.

In this work we prepare Langmuir-Blodgett monolayers with a trifunctional amphiphilic anthraphane monomer. Upon spreading at the air/water interface, the monomers self-assemble into 1 nm-thin monolayer islands, which are highly fluorescent and can be visualized by the naked eye upon excitation. In situ fluorescence spectroscopy indicates that in the monolayers, all the anthracene units of the monomers are stacked face-to-face forming excimer pairs, whereas at the edges of the monolayers, free anthracenes are present acting as edge groups. Irradiation of the monolayer triggers [4 + 4]-cycloadditions among the excimer pairs, effectively resulting in a two-dimensional (2D) polymerization. The polymerization reaction also completely quenches the fluorescence, allowing to draw patterns on the monomer monolayers. More interestingly, after transferring the monomer monolayer on a solid substrate, by employing masks or the laser of a confocal scanning microscope, it is possible to arbitrarily select the parts of the monolayer that one wants to polymerize. The unpolymerized regions can then be washed away from the substrate, leaving 2D macromolecular monolayer objects of the desired shape. This photolithographic process employs 2D polymerizations and affords 1 nm-thin coatings.

Colorimetric detection of ultrathin dielectrics on strong interference coatings.

Metal films covered with ultrathin lossy dielectrics can exhibit strong interference effects manifested as the broad absorption of the incident light resulting in distinct surface colors. Despite their simple bilayer structures, such surfaces have only recently been scrutinized and applied mainly to color printing. Here, we report the use of such surfaces for colorimetric detection of ultrathin dielectrics. Upon deposition of a nanometer-thick dielectric on the surface, the absorption peak red shifts, changing the surface color. The color contrast between the bare and dielectric-coated surfaces can be detected by the naked eye. The optical responses of the surfaces are characterized for nanometer-thick SiO2, Al2O3, and bovine serum albumin molecules. The results suggest that strong interference surfaces can be employed as biosensors.

Ultimate permeation across atomically thin porous graphene.

A two-dimensional (2D) porous layer can make an ideal membrane for separation of chemical mixtures because its infinitesimal thickness promises ultimate permeation. Graphene--with great mechanical strength, chemical stability, and inherent impermeability--offers a unique 2D system with which to realize this membrane and study the mass transport, if perforated precisely. We report highly efficient mass transfer across physically perforated double-layer graphene, having up to a few million pores with narrowly distributed diameters between less than 10 nanometers and 1 micrometer. The measured transport rates are in agreement with predictions of 2D transport theories. Attributed to its atomic thicknesses, these porous graphene membranes show permeances of gas, liquid, and water vapor far in excess of those shown by finite-thickness membranes, highlighting the ultimate permeation these 2D membranes can provide.

Evolutionary kinetics of graphene formation on copper.

It has been claimed that graphene growth on copper by chemical vapor deposition is dominated by crystallization from the surface initially supersaturated with carbon adatoms, which implies that the growth is independent of hydrocarbon addition after the nucleation phase. Here, we present an alternative growth model based on our observations that oppose this claim. Our Gompertzian sigmoidal growth kinetics and secondary nucleation behavior support the postulate that the growth can be controlled by adsorption-desorption dynamics and the dispersive kinetic processes of catalytic dissociation and dehydrogenation of carbon precursors on copper.

Near field detector for integrated surface plasmon resonance biosensor applications.

Integrated surface plasmon resonance biosensors promise to enable compact and portable biosensing at high sensitivities. To replace the far field detector traditionally used to detect surface plasmons we integrate a near field detector below a functionalized gold film. The evanescent field of a surface plasmon at the aqueous-gold interface is converted into photocurrent by a thin film organic heterojunction diode. We demonstrate that use of the near field detector is equivalent to the traditional far field measurement of reflectivity. The sensor is stable and reversible in an aqueous environment for periods of 6 hrs. For specific binding of neutravidin, the detection limit is 4 microg/cm(2). The sensitivity can be improved by reducing surface roughness of the gold layers and optimization of the device design. From simulations, we predict a maximum sensitivity that is two times lower than a comparable conventional SPR biosensor.