Metal-Organic Frameworks with Novel Catenane-like Interlocking: Metal-Determined Photoresponse and Uranyl Sensing.

The assembly of two tripyridinium-tricarboxylate ligands and different metal ions leads to seven isostructural MOFs, which show novel 2D→2D supramolecular entanglement featuring catenane-like interlocking of tricyclic cages. The MOFs show tripyridinium-afforded and metal-modulated photoresponsive properties. The MOFs with d10 metal centers (1-Cd, 1-Zn, 2-Cd, 2-Zn) show fast and reversible photochromism and concomitant fluorescence quenching, 1-Ni displays slower photochromism but does not fluoresce, and 1-Co and 2-Co are neither photochromic nor fluorescent. It is shown here that the network entanglement dictates donor-acceptor close contacts, which enable fluorescence originated from interligand charge transfer. The contacts also allow photoinduced electron transfer, which underlies photochromism and concomitant fluorescence response. The metal dependence in fluorescence and photochromism can be related to energy transfer through metal-centered d-d transitions. In addition, 1-Cd is demonstrated to be a potential fluorescence sensor for sensitive and selective detection of UO2 2+ in water.

Distinct and Selective Amine- and Anion-Responsive Behaviors of an Electron-Deficient and Anion-Exchangeable Metal-Organic Framework.

Smart materials that respond to chemical stimuli with color or luminescence changes are highly desirable for daily-life and high-tech applications. Here, we report a novel porous metal-organic framework (MOF) that shows multiple, selective, and discriminative responsive properties owing to the combination of different functional ingredients [tripyridinium chromogen, Eu(III) luminophore, cationic framework, and special porous structure]. The MOF contains two interpenetrated three-dimensional cationic coordination networks built of a tetrahedral [Eu4(µ3-OH)4] cluster and a tripyridinium-tricarboxylate zwitterionic linker. It shows reversible and discriminative chromic response to aliphatic amines and aniline through different host-guest interactions between electron-deficient pyridinium and electron-rich amines. The size- and shape-selective response to aliphatic amines is ascribed to the radical formation through host-guest electron transfer, whereas the response to aniline is ascribed to the formation of sandwich-type acceptor-donor-acceptor complexes. The MOF is capable of reversible anion exchange with various anions and shows selective and discriminative ionochromic response to iodide, bromide, and thiocyanate, which is attributed to charge-transfer complexation. The above chromic behaviors are accompanied by efficient quenching of Eu(III) photoluminescence. The MOF represents a multi-stimuli dual-output responsive system. It can be used for discrimination and identification of anions and amines. The potential use in invisible printing, reusable sensory films, and optical switches was demonstrated by the ink and the membrane made of the MOF and organic polymers.

Transparent Conductive Silver Nanowire Embedded Polyimide/Reduced Graphene Oxide Hybrid Film.

A highly flexible, transparent, and conductive polyimide (PI) hybrid film with good thermal stability was fabricated by embedding reduced graphene oxide (rGO) coated silver nanowire (AgNW) into 4,4'-(hexa fluoroisopropylidene)diphthalic anhydride(6FDA)/2,2'-bis(trifluoromethyl)benzidine (TFDB) poly(amic acid) using a spray coating method, followed by thermal imidization. The PI/AgNW/rGO conductive film exhibited good thermal stability up to 553 °C, low sheet resistance (37 Ω/sq), high optical transparency (81%), and high hydrophobic surface (water contact angle, 89°). The rGO protected the surface of AgNW, which is weak to oxidation in air condition, and thus effectively reduced the surface resistance of the PI hybrid film. The hybrid film may offer a good potential for application as flexible transparent conducting electrodes.

Transparent conductive film based on silver nanowires and single-wall carbon nanotubes for transparent heating films.

In this paper, hybrid transparent conductive films (TCFs) are designed by combining silver nanowires with the single-wall carbon nanotubes (SWCNTs) and the transparent heating films (THFs) based on the TCFs are evaluated for possible vehicle applications. By comparing the properties, including the transmittance, sheet resistance, microstructure and heating curves, we found that the SWCNTs/AgNWs are considerably suitable for making THFs. The after-treatment methods, such as physical method (hot roll pressing) and chemical method (nitric acid and Poly (diallydimethylammonium chloride) solution, (PDAC)) were researched in detail to optimize the sheet resistance and transparency to fit the THF requirements. A careful study of the different after-treatment methods revealed that hot roll pressing can quickly and efficiently improve the properties, while the nitric acid is more helpful than PDAC for the long-term stability. The results showed that a small amount of SWCNTs addition can promote the endurable maximum electric current by spreading the heat fast and efficiently, and the maximum current flow can be as high as 4 A. The thermal stability of the THFs and the de-frog performance were tested, indicating that the hybrid film had an advantage in resisting current shock and good thermal efficiency was obtained. The fabricated TCFs of stable thermal properties are qualified as a windshield-glass heater.

Photoelectrocatalytic degradation of methylene blue using F doped TiO2 photoelectrode under visible light irradiation.

Photoelectrocatalysis (PEC) has attracted great interest due to cost effectiveness and high efficiency in water treatment. In this study, F doped TiO2 (F-TiO2) photoelectrodes with honeycomb like morphology were prepared, and the PEC performance was investigated. F-TiO2 particles that showed enhanced absorption of visible light were synthesized via a sol-gel method. F-TiO2 particles were anchored onto the surface of F-doped SnO2 glass by a screen-printing method to prepare the F-TiO2 photoelectrodes. The PEC performance of the F-TiO2 photoelectrodes was investigated via the degradation of methylene blue (MB) under visible light irradiation. The results show that the F-TiO2 photoelectrodes exhibited an excellent PEC performance that was affected by the F doping content, applied bias and solution pH. A maximum decolorization percentage of 97.8% was achieved by the FT-15 photoelectrode, with a 1.4 V bias at pH 9.94 after 4.0 h of visible light irradiation. The high PEC performance of the F-TiO2 photoelectrodes is mainly ascribed to the efficient separation of electron-hole (e--h+) pairs and the creation of active radicals such as hydroxyl radicals (OH). The PEC decolorization kinetic data were analyzed using the first-order kinetic model and the Langmuir-Hinshelwood (L-H) model. The data indicates that the PEC degradation of MB molecules mainly occurred on the surface of the F-TiO2 photoelectrodes, and the MB molecules were discolored mainly by h+ (41.5%) and OH (46.5%). In addition, 8.2% of the MB molecules were discolored by other oxidative species, and 3.8% of the MB molecules were discolored by self-sensitized oxidation.

Zn-doped CaTiO3:Eu(3+) red phosphors for enhanced photoluminescence in white LEDs by solid-state reaction.

Zn-doped CaTiO3:Eu(3+) red phosphors for enhanced photoluminescence in white light-emitting diodes (LEDs) were synthesized by a solid-state method. The structure and morphology of the obtained phosphor samples were observed by X-ray diffraction (XRD) and scanning electron microscopy (SEM), and the impact of Ca, Zn and Eu content on their photoluminescence properties was studied. The results indicated that Zn not only participates in the formation of defects in suitable lattice matrices but also has a role in flux in the transformation from ZnO to Zn2TiO4, which is beneficial for the enhancement of photoluminescence properties. Photoluminescence test data showed that the Zn-doped phosphor is excited efficiently by near-ultraviolet (NUV) light at wavelengths around 398 nm and emits an intense red light with a broad peak around 616 nm corresponding to the (5) D0 →(7) F2 transition of Eu(3+). The intensity of this phosphor emission is three times stronger than that without Zn-doping. Furthermore, this phosphor has very good thermal stability, high color purity and a low sintered temperature, all of which suggest its potential as a promising red phosphor for white LEDs.

Long afterglow Sr4Al14O25:Eu,Dy phosphors as both scattering and down converting layer for CdS quantum dot-sensitized solar cells.

Long afterglow Sr4Al14O25:Eu,Dy phosphors were introduced into the TiO2 photoanode of CdS quantum dot-sensitized solar cells (QDSSCs) as both a scattering and down converting layer, and the photovoltaic performances of the cells were investigated. The results show that the cell with Sr4Al14O25:Eu,Dy achieves a power conversion efficiency of 1.40%, which is an increase of 38% compared to the cell without Sr4Al14O25:Eu,Dy (1.02%). The performance improvement is attributed to enhanced light harvesting via improved light absorption and scattering processes. After a single sun illumination for 1 min and subsequent removal of the light source, the cell with Sr4Al14O25:Eu,Dy could be driven even in the dark by the long persistent light from Sr4Al14O25:Eu,Dy.

Enhanced performance of cadmium selenide quantum dot-sensitized solar cells by incorporating long afterglow europium, dysprosium co-doped strontium aluminate phosphors.

CdSe quantum dot-sensitized solar cells based on an efficient bifunctional structured layer composed of long afterglow SrAl2O4:Eu,Dy phosphors on top of a transparent layer of nanocrystalline TiO2 were fabricated and their photovoltaic performances were investigated. The results show that a high power conversion efficiency of 1.22% is achieved for the cell with SrAl2O4:Eu,Dy at one sun illumination (AM 1.5 G, 100 mW cm(-2)), which is an increase of 48% compared to the cell without SrAl2O4:Eu,Dy (0.82%). After one sun illumination for 1 min and subsequent turn off of the light source, the cell with SrAl2O4:Eu,Dy still shows an efficiency of 0.04% under dark condition due to the irradiation by the long persistent light from SrAl2O4:Eu,Dy. The present strategy should provide a possibility to fulfill the operation of solar cells even in the dark.