New Class Of Multifunctional Materials Research Articles

Intertwining of Localized (d) and Delocalized (π) Spins in Magnetically Frustrated Two-Dimensional Metal-Organic Frameworks.

Two-dimensional metal-organic frameworks (2D MOFs) are emerging as a new class of multifunctional materials for diversified applications, although magnetic properties have not been widely explored. The metal ions and organic ligands in some of the 2D MOFs are arranged in the well-known Kagome lattice, leading to geometric spin frustration. Hence, such systems could be the potential candidates to exhibit an exotic quantum spin liquid (QSL) state, as was observed in Cu3(HHTP)2 (HHTP = hexahydroxytriphenylene), with no magnetic transition down to 38 mK. Hereto, we have investigated the spin intertwining in a bimetallic 2D MOF system, M3(HHTP)2 (M = Cu/Zn), arising from the localized (d-electron) and delocalized (π-electron) S = 1/2 spins from the Cu(II) ions and the HHTP radicals, respectively. The origin of the spin frustration (down to 5K) was critically examined by varying the metal composition in bimetallic systems, CuxZn3-x(HHTP)2 (x = 1, 1.5, 2), containing both S = 1/2 and S = 0 spins. Additionally, to gain a deeper understanding, we studied the spin interaction in the pristine Zn3(HHTP)2 system containing only S = 0 Zn(II) ions. In view of the quantitative estimate of the localized and delocalized spins, the d-π spin correlation appears essential in understanding the unusual magnetic and/or other physical properties of such hybrid organic-inorganic 2D crystalline solids.

Multi-component liquid-infused systems: a new approach to functional coatings.

Antifouling liquid-infused surfaces have generated interest in multiple fields due to their diverse applications in industry and medicine. In nearly all reports to date, the liquid component consists of only one chemical species. However, unlike traditional solid surfaces, the unique nature of liquid surfaces holds the potential for synergistic and even adaptive functionality simply by including additional elements in the liquid coating. In this work, we explore the concept of multi-component liquid-infused systems, in which the coating liquid consists of a primary liquid and a secondary component or components that provide additional functionality. For ease of understanding, we categorize recently reported multi-component liquid-infused surfaces according to the size of the secondary components: molecular scale, in which the secondary components are molecules; nanoscale, in which they are nanoparticles or their equivalent; and microscale, in which the additional components are micrometer size or above. We present examples at each scale, showing how introducing a secondary element into the liquid can result in synergistic effects, such as maintaining a pristine surface while actively modifying the surrounding environment, which are difficult to achieve in other surface treatments. The review highlights the diversity of fabrication methods and provides perspectives on future research directions. Introducing secondary components into the liquid matrix of liquid-infused surfaces is a promising strategy with significant potential to create a new class of multifunctional materials. Keywords: Active surfaces; Antimicrobial; Antifouling; Interfaces; Sensing surfaces.

Multichannel Control of PersL/Upconversion/Down-Shifting Luminescence in a Single Core-Shell Nanoparticle for Information Encryption.

Persistent luminescence (PersL) has been attracting substantial attention in diverse frontier applications such as optical information security and in vivo bioimaging. However, most of the reported PersL emissions are based on the dopants instead of the host matrix, which also plays an important role. In addition, there are few works on the PersL-based multifunctional nanoplatform in nanosized materials. Here, we report a class of novel nanostructure designs with PersL, upconversion, and down-shifting luminescence to realize the fine-tuning of emission colors under different excitation modes including steady-state irradiation, time-gating, and PersL generation. Blue, orange, and green emissions were easily achieved in such a single nanoparticle under suitable excitation modes. Moreover, the physical origin of the PersL of the CaF2 matrix was discussed by simulating the energy band structure with CaxFy defects. Our results provide new opportunities for the design of a new class of multifunctional materials, showing great promise in the field of information encryption security and multilevel anticounterfeiting.

Multifunctional Mechanical Metamaterials with Embedded Triboelectric Nanogenerators

AbstractThe flexibility of planar triboelectric nanogenerators (TENGs) enables them to be embedded into structures with complex geometries and to conform with any deformation of these structures. In return, the embedded TENGs function as either strain‐sensitive active sensors or energy harvesters while negligibly affecting the structure's original mechanical properties. This advantage inspires a new class of multifunctional materials where compliant TENGs are distributed into local operational units of mechanical metamaterial, dubbed TENG‐embedded mechanical metamaterials. This new class of metamaterial inherits the advantages of a traditional mechanical metamaterial, in that the deformation of the internal topology of material enables unusual mechanical properties. The concept is illustrated with experimental investigations and finite element simulations of prototypes based on two exemplar metamaterial geometries where functions of self‐powered sensing, energy harvesting, as well as the designated mechanical behavior are investigated. This work provides a new framework in producing multifunctional triboelectric devices.

Retraction of "Cyclodextrin Metal-Organic Frameworks: From the Research Laboratory to the Marketplace".

ConspectusCyclodextrin-based metal-organic frameworks (CD-MOFs), derived from γ-cyclodextrin (γ-CD) and potassium ions, constitute a new class of porous, renewable, and edible MOFs that can be synthesized wholly from naturally occurring starting materials on a large scale. γ-CD is a C8 symmetrical cyclic oligosaccharide, composed of eight asymmetric α-1,4-linked d-glucopyranosyl residues, which possesses a bucket-shaped cavity with an inner diameter of ∼1 nm and a depth of ∼0.8 nm. Upon combining 1 equiv of γ-CD with 8 equiv of potassium hydroxide in aqueous solution, followed by vapor-diffusion of MeOH (or EtOH) into the solution during several days, CD-MOF-1 is obtained as cubic crystals. It was discovered serendipitously in 2010 as the first CD-MOF with a cubic cell of space group I432 and unit cell dimensions of approximately 31 × 31 × 31 Å3. Other CD-MOFs, namely, CD-MOF-2 and CD-MOF-3, can be obtained, respectively, wherein potassium is replaced with rubidium and cesium ions. CD-MOFs comprise infinite body-centered frameworks of (γ-CD)6 cubic units linked by alkali metal cations with spherical pores which reside at the center of the cubes interconnected by both cylindrical and triangular channels.During the past decade, CD-MOFs have emerged as a new class of multifunctional materials based on a porous framework with an extended structure displaying robust crystallinity, permanent porosity, and biocompatibility. The family of CD-MOFs has been enlarged by a growing collection of metal nodes involving alkali metal cations (Li+, Na+, K+, Rb+, Cs+) and γ-CD as well as its derivatives. As a result of the ability of their porous extended frameworks to absorb guest molecules, including gases, drug molecules, metal-based nanoclusters, and nanoparticles, CD-MOFs have potential applications in areas as disparate as adsorption and separation, sensing, template syntheses of metal-based nanoparticles and gels, electrical memory, drug delivery, and catalyst stabilization.In this Account, we tell the story of CD-MOFs, a scientific discovery that was made in our research laboratory at the Northwestern University, and the subsequent commercialization of CD-MOF technology on the part of a spinoff company, which developed a line of successful skin care products. This Account includes representative synthetic methods for the preparation of CD-MOFs, along with a brief overview of their structural features and a general summary of their state-of-the-art applications. The examples, however, are only illustrative, and a significant body of additional findings is emanating from our own laboratory and others, especially in the development of new synthetic strategies, tuning the framework stabilities, and exploring the guest-inclusion properties of CD-MOFs. We refer readers to communications, papers, and reviews on CD-MOFs and to references therein. We also put on record how CD-MOFs have been rebranded as organic molecular vessels (OMVs), a smart, functional, environmentally friendly delivery platform for commercial skin care applications. We hope that, in the telling and retelling of the story of CD-MOFs, this Account may encourage the commercialization of discoveries that have been made in other research laboratories.

The Influence of Anions on Electron-Transfer Photochromism of Bipyridinium-Derived Metal–Organic Materials

As a new class of multifunctional materials, photochromic materials have received much attention due to their potential applications in many fields. In order to investigate the effect of anions on ...

Switchable luminescent properties in two photochromic naphthalene diimide coordination networks

Photochromic materials as a new class of multifunctional materials have received much attention owing to their potential applications in many fields. In order to investigate the electron-transfer photochromic behaviour of coordination polymers, two new coordination polymers based on the electron-deficient naphthalene diimide (NDI) and dicarboxylate ligand, namely [Zn2(DPNDI)(TPDC)2] (1) [Cd6(DPNDI)(TPDC)6(DMF)6] (2) (DPNDI = N,N′-di(3-pyridyl)-1,4,5,8-naphthalene tetracarboxydiimide, H2TPDC = thiophene-2,5-dicarboxylic acid, DMF = N,N′-dimethylformamide), were synthesized under solvothermal condition and were characterized by elemental analysis, IR spectroscopy, thermogravimetric analyses, and single-crystal X-ray diffraction. Complex 1 is a three-dimensional coordination with rhombus channels, whereas complex 2 shows a sandwiched layer structure. Because of the presence of electron-deficient NDI moieties, complexes 1 and 2 can easily undergo photoinduced electron transfer and eye-detectable photochromic behaviour. Moreover, their luminescence can be switched by UV–Vis light irradiation and standing in the air.

Identification and preparation of stable water dispersions of protein - Carbon nanotube hybrids and efficient design of new functional materials

Carbon nanotubes, CNTs, and proteins could not be more chemically and physically distant. CNTs are hardly soluble and strongly hydrophobic. They are smooth wires, mechanically strong, with electronic properties that make them unique. Many proteins are water soluble and hydrophilic. They are highly corrugated and elastic. They can recognize a target molecule with high selectivity and sensitivity and can have catalytic activity. Integration of the remarkably different features of CNTs and proteins would create a new class of multifunctional materials. The conundrum to solve lies in how to best match proteins and CNTs. High-throughput virtual screening is used to predict the ability of 1207 proteins to recognize carbon tubes with a well-defined 1.3 nm diameter. The propensity for formation of protein-CNT hybrids is ranked. Experiments carried out in this work validated the computational results and show that the identified proteins are able to bind and disperse in water the selected CNTs. The highest scoring proteins are further examined in detail to identify general rules for binding and discussed for a variety of practical applications.

Enhanced Field Emission Performance of MoO3 Nanorods and MoO3‐rGO Nanocomposite

AbstractThe graphene and semiconducting hybrid based nanostructures have emerged as a new class of multifunctional materials with improved performance in comparison to the pristine semiconductors. Here, as‐synthesized MoO3‐reduced graphene oxide (rGO) nanocomposite emitter exhibits enhanced field emission (FE) behavior as compared to the pristine 1D MoO3 nanorods. The hydrothermally synthesized 1D MoO3 nanorods (1D) are grafted on the rGO sheet (2D) using a simple room temperature sonochemical method. The morphological and structural analysis confirms the attachment of MoO3 nanorods with rGO and the improved conductivity of the sample indicates a strong electronic interaction between them. Furthermore, the FE studies of as‐synthesized MoO3 nanorods and MoO3‐rGO nanocomposite emitters, carried out at a base pressure ∼1×10−8 mbar, reveals the values of turn on field (required to draw an emission current density of 1 μA/cm2) as 1.6 and 1.4 V/μm, respectively. Interestingly, the maximum emission current density of 2810 μA/cm2 is achieved at a lower applied field of 2.7 V/μm from the MoO3‐rGO nanocomposite emitter. The enhancement in FE performance of MoO3‐rGO nanocomposite is attributed to the improved electrical conductivity, mechanical properties and higher concentration of protruding edges (emission sites). This observation can be extended to other graphene‐based 1D inorganic hybrid semiconductor nanocomposites, which can provide a valuable opportunity to explore novel hybrid materials for vacuum nano‐electronic devices.

Multifunctional Porous Organic Polymers: Tuning of Porosity, CO2, and H2 Storage and Visible-Light-Driven Photocatalysis.

A series of porous organic polymers (POPs) were fabricated based on a boron dipyrromethene (BODIPY) core. The variation of the substituents in the BODIPY core and the fine-tuning of the Sonogashira polycondenzation reaction with 1,3,5-triethynylbenzene led to the formation of POPs with a wide range of surface area and porosity. A 10-fold increase in surface area from 73 m2 g-1 in BDT1a polymer to 1010 m2 g-1 in BDT3 was obtained. Simultaneously, the porosity was changed from mesoporous to ultramicroporous. The surface area of BDT3 turned out to be the highest reported so far for BODIPY-based POPs. Molecular dynamics simulation coupled with Grand Canonical Monte Carlo simulations revealed the effect of substituents alkyl groups and rigidity of the core structures on the surface properties of the POPs. Detailed gas adsorption studies of the polymers revealed a high uptake of CO2 and H2. The highest uptake capacity of 16.5 wt % for CO2 at 273 K and 2.2 wt % for H2 at 77 K was observed for BDT3 at 1 bar pressure. The isosteric heat of adsorption (Qst) of BDT3 for CO2 was found to be as high as 30.6 kJ mol-1. Electron paramagnetic resonance studies revealed the generation of singlet oxygen upon photoexcitation of these polymers. The BODIPY-based POPs turned out to be excellent catalysts for visible-light-driven photo-oxidation of thioanisole. The present study establishes BODIPY-based POPs as a new class of multifunctional materials.

Evidence for spin to charge conversion in GeTe(111)

GeTe has been predicted to be the father compound of a new class of multifunctional materials, ferroelectric Rashba semiconductors, displaying a coupling between spin-dependent k-splitting and ferroelectricity. In this paper, we report on epitaxial Fe/GeTe(111) heterostructures grown by molecular beam epitaxy. Spin-pumping experiments have been performed in a radio-frequency cavity by pumping a spin current from the Fe layer into GeTe at the Fe ferromagnetic resonance and detecting the transverse charge current originated in the slab due to spin-to-charge conversion. Preliminary experiments indicate that a clear spin to charge conversion exists, thus unveiling the potential of GeTe for spin-orbitronics.

Effect Of Nickel Ferrite On Bismuth Ferrite To Generate Nanocomposite In Relation To Structure, Characterization, Magnetic Properties And Band Gap Evaluation

Multiferroic materials are new class of multi-functional materials which possess both ferro-electric and magnetic properties. This type of material has wide range of applications like semi-conducting to sensors applications. Nanocomposite of equimolar perovskite-spinel is synthesized by chemical route by blending of Nickel ferrite as second phase on Bismuth ferrite after heat treatment at 500 °C for 2, 3 and 4 hours soaking period. From the diffractogram data of XRD, the phase, and planes of orientation are analyzed of the synthesized materials. The crystallite size is calculated by Scherrer's formula. FESEM studies reveal the morphological features having interconnected agglomerates with spherical, irregular polygonal or some elongated shape of the synthesized nanocomposite. FTIR result shows the molecular signature of the nanocrystalline material to verify the M-O coordination. Interplanar spacings and SAED pattern are revealed from HRTEM images which are very close to the experimental findings from XRD phase analysis. UV-VIS analysis is performed in the transmission mode of spectra within the scan range of 200-1100 nm. From the spectra, using Tauc relation band gap is calculated. Band gap are found of the order of 2.847 eV, 2.78 eV, 2.69 eV respectively for 2, 3 and 4 hours soaking period close to semiconducting material. With the increase of soaking time band gap is found to decrease following Arrhenius activation of electronic mobility overwhelming the energy barrier at respective lattice sites. M-H analysis of Nanocomposite at 500 °C for 2 hrs is closer towards ferromagnetic with incomplete loop but for sample at 500 °C for 4hrs it is closer towards superparamagnetic one. The property of this material reflects it has many interesting characteristics suitable for opto-electronic, photo-magnetic devices and other electronic applications. Copyright © 2015 VBRI Press.

Dielectric properties and magnetoelectric effects in FeCo-MgF insulating nanogranular films

Multifunctional properties of matter, including dielectric and magnetic properties, are of great interest in physics and applications. Here, we investigate the dielectric properties and magnetoelectric effects in FeCo-MgF insulating nanogranular films. These films have a nanogranular structure in which Fe-Co alloy-based magnetic granules are dispersed in an Mg-F insulator-based matrix. Both a large dielectric constant of about 420 at 100 kHz and a large magnetoelectric effect of about 6.2% are obtained at room temperature. Insulating nanogranular films are a new class of multifunctional materials. The dielectric properties and the magnetoelectric effects originate in the nano-structure which consists of a magnetic metal and an insulator, and are explained by the spin-dependent tunneling charge oscillation between a pair of magnetic granules.

Giant dielectric and magnetoelectric responses in insulating nanogranular films at room temperature.

The electric and magnetic properties of matter are of great interest for materials science and their use in electronic applications. Large dielectric and magnetoelectric responses of materials at room temperature are a great advantage for electromagnetic device applications. Here we present a study of FeCo-MgF nanogranular films exhibiting giant dielectric and magnetoelectric responses at room temperature; with dielectric constant ε′=490 and magnetoelectric response Δε′/ε′0=3%. In these films, Fe-Co alloy-based nanometer-sized magnetic granules are dispersed in a Mg-fluoride-based insulator matrix. Insulating nanogranular films are a new class of multifunctional materials. The giant responses are caused by spin-dependent charge oscillation between magnetic granules via quantum-mechanical tunnelling. A possible application of such insulating nanogranular materials with giant response is in the construction of a tunable device, in which impedance components such as capacitance and inductance are tunable at room temperature.

Heusler nanoparticles for spintronics and ferromagnetic shape memory alloys

Heusler nanoparticles emerge as a new class of multifunctional materials. In this critical review, the latest progress in studies on Heusler nanoparticles is summarized. The authors discuss their structural and physical properties interesting for research fields such as spintronics and ferromagnetic shape memory alloys. As a young research field, the majority of studies on Heusler nanoparticles focus on their synthesis, structure, and magnetic characterizations. Important issues such as size dependent structure, phase transition, magnetic, and spin-related properties are still open. Further investigations are needed to verify the technical significance of Heusler nanoparticles for practical applications such as data storage, magnetic sensors, and microactuators.

Electronic Structure of Spinel-Type Nitride CompoundsSi3N4,Ge3N4, andSn3N4with Tunable Band Gaps: Application to Light Emitting Diodes

In this Letter using experimental and theoretical methods, we show that the solid solutions of group 14 nitrides having spinel structure (γ-M3N4 where M=Si, Ge, Sn) exhibit mainly direct electronic band gaps with values that span the entire visible wavelength region, making these hard and thermally stable materials suitable for optoelectronic devices and, in particular, lighting applications. Using the simulated band structure, we also calculate the exciton binding energy. The combination of large exciton binding energies and the tunable electronic band gaps in the visible range makes these binary spinel nitrides and their solid solutions a new class of multifunctional materials with optoelectronic properties that can be engineered to suit the desired application.

Dimeric Gold Nanoparticle Assemblies as Tags for SERS‐Based Cancer Detection

Herein, a new class of multifunctional materials combining a clustered nanoparticle-based probe is presented for surface enhanced Raman scattering (SERS)-based microscopy and surface functionalization for tissue targeting. Controlled assembly of spherical gold nanoparticles into dimers (DNP-REP) is engineered using a small, rigid Raman-active dithiolated linking reporter (REP) to yield narrow internanoparticle gaps and to strategically generate the "hot spot" while concurrently placing the reporter within the region of highest SERS enhancement. Peptide functionalized DNP-REP materials are highly stable even upon incubation with living cells and show controlled levels of binding and intracellular endocytosis. To demonstrate the functionality of such probes for disease detection, differentially targeted DNP-REPs are incubated over various time points with cultured human glioblastoma cells. Using human glioblastoma cells, the SERS maps of targeted tumor cells show the markedly enhanced signals of the DNP-REP, compared to conventional confocal fluorescence based approaches, especially at low incubation times. Even with as few as 40 internalized DNP-REP, a relatively intense SERS signal is measured, demonstrating the high signal to noise ratio and inherent biocompatibility of the materials. Thus, these Raman reporter-based nanoparticle cluster probes present a promising and versatile optical imaging tool for fast, reliable, selective, and ultrasensitive tissue targeting and disease detection and screening.

HIERARCHICAL CARBON NANOTUBE-INORGANIC HYBRID STRUCTURES INVOLVING CNT ARRAYS AND CNT FIBERS

Carbon nanotube-inorganic hybrid materials have stimulated a new boost in CNT research as a new class of multifunctional materials with properties distinct from the well-known CNT composites. Synergistic effects based on interfacial charge and heat transfer processes commend these hybrids for use in photocatalysis, gas sensors and in electrochemical devices. A major challenge is the synthesis of hybrids with hierarchical architectures and controlled interfaces. Common wet-chemical techniques have the major drawback that the CNT array typically collapses upon drying due to stresses imposed by the surface tension of the solvent. In this work, we synthesized hierarchical hybrids with coherent 3D architectures using unique CNT fibers, based on the "Cambridge process" as well as vertical arrays of CNTs ("carpets"). We demonstrate that separating the liquid reactants from the CNT array is key to preserving the hybrid's architecture. In addition, we show that the presence of benzyl alcohol as a linking agent is beneficial to maximizing the interfacial area in TiO 2-coated CNT fibers.

Carbon Nanotube-Silver Composite for Mercury Capture and Analysis

The carbon nanotube-silver composite (Ag-CNT) is a new class of multifunctional materials with potential applications such as sensors, catalysts, biodisinfection, and sorbents. A simple method combining wet-chemistry and thermal reduction was adopted to synthesize silver on the surface of the CNT. The synthesized Ag-CNT was tested as a sorbent for the removal of elemental mercury from flue gases of coal-fired power plants and as a mercury trap for elemental mercury analysis. A complete capture of mercury by the Ag-CNT was achieved up to a capture temperature of 150 °C, similar to the temperature of flue gases in coal-fired power plants. The captured mercury could be quickly and completely released by simple heating at 330 °C, to restore its mercury adsorption capacity. Silver on the Ag-CNT was shown to be the main active component for the mercury capture via an amalgamation mechanism in contrast to simple physical adsorption on the undoped CNT . Compared to silver-coated quartz beads (Ag-beads) and gold-coated quartz beads (Au-beads), which is conventionally used as a mercury trap for mercury measurements, the Ag-CNT showed a much higher mercury capture capacity and a minimal memory effect. With the Ag-CNT as a mercury preconcentration trap, calibration results showed a satisfactory linear coefficient of ≥0.9998 between known amounts of standard mercury and their corresponding fluorescence signals of cold vapor atomic fluorescence spectrophotometry (CVAFS). The presence of SO2, NOx, CO2, or O2 showed a negligible impact on the mercury capture performance of the Ag-CNT.

Catalytic effect of metal oxides on the oxidation resistance in carbon nanotube–inorganic hybrids

Hybridising carbon nanotubes (CNTs) with metal oxide nanostructures creates a new class of multifunctional materials with greatly enhanced performances as photocatalysts, chemical sensors, and in fuel cells and batteries. The low resistance of CNT towards oxidation often limits their applicability. On the other hand, exactly this ability to degrade CNTs at low temperatures is beneficial when using them as sacrificial templates for the synthesis of inorganic nanotubes. In this work, we investigate the oxidation resistance of 20 new hybrids and reveal that the presence of metal oxides can both inhibit and catalyse the oxidation of CNTs. As a result, the oxidation temperatures range from nearly 800 °C with Al2O3 to values as low as 330 °C with PbO and Bi2O3. We further demonstrate that the catalytic activity of the metal oxides correlates directly with their reducibility, i.e. the ability to create oxygen vacancies, and propose a mechanistic model based on Mars and van Krevelen, which allows prediction of the chemical stability of a wide range of CNT–metal oxide hybrids.