Showing papers by "Nanjing Tech University published in 2012"

Amphiphilic Egg-Derived Carbon Dots: Rapid Plasma Fabrication, Pyrolysis Process, and Multicolor Printing Patterns

Abstract: Carbon-based photoluminescent nanoparticles have recently received increased interest, owing to their favorable optical properties along with their biocompatibility and low toxicity. Such nascent nanomaterials, the so-called carbon dots (CDs or C-dots), are a promising alternative to more toxic metal-based semiconductor quantum dots (QDs) for applications such as bioimaging. Recent advances in the synthesis of CDs allow them to be formed from fine carbon structures (like graphene and multi-wall carbon nanotubes) by topdown methods, or from chemical precursors (like ammonium citrate and ethylenediaminetetraacetic acid) by bottom-up approaches. Typically, these CDs require surface oxidation and/or further passivation to emit fluorescence, which also makes them hydrophilic. Alternatively, some one-step strategies to fabricate surface-passivated CDs have also been shown. We reported a one-step synthesis of multicolor CDs from pyrolysis of epoxy-enriched polystyrene photonic crystals and their potential for use in light-emitting diodes. Herein, we present a simple and rapid strategy to fabricate CDs from cheap and natural carbon sources and further extend their application as printing “inks”. The fluorescent CDs developed herein have the following notable characteristics: 1) one-step generation in minutes from low-cost, natural, edible chicken eggs by plasma-induced pyrolysis; 2) good amphiphilicity with high solubility in a broad range of aqueous and organic solvents; 3) resistance to acids and bases; 4) versatile applications as fluorescent carbon inks for luminescent patterns. Figure 1 shows the fabrication of egg-derived fluorescent CDs and their application as “inks” for luminescent patterns using inkjet or silk-screen printing. We chose chicken eggs as the starting material to maintain low toxicity and affordability of the final product. Low-temperature plasma with highenergy, inherently charged particles (electrons or cations) and excited neutral species was used to create an active chemical environment for the synthesis of the nanostructures. As shown in Figure 1, the egg was separated into egg white and egg yolk, using an egg-separator, prior to use. A glass dish filled with egg white or yolk was placed between two quartz slides (height= 1.5 cm) of the plasma generator. Subsequently, intense and uniform plasma beams generated from the upper electrode (voltage= 50 V, current= 2.4 A) irradiated the egg samples for 3 min to yield dark black products, referred to as CDpew and CDpey for the plasma-treated egg white and yolk, respectively. The yield of CDs from the egg sample was calculated to be approximately 5.96%. Elemental analysis showed an increase in the carbon content of the products (62.42% for CDpey and 56.75% for CDpew) in comparison to that of the starting material (57.55% for egg yolk and 43.50% for egg white), implying carbonization occurs during the plasma treatment (Supporting Information, Table S1). Significantly, solutions of CDpew and CDpey display bright blue fluorescence under UV light (lex= 302 nm). Figure 2 shows high-resolution transmission electron microscope (HRTEM) images of the CDs. CDpey had uniform dispersion without apparent aggregation and a mean particle diameter (Dp) of 2.15 nm (Figure 2a and Figure S2). Detectable rings in the selected-area electron-diffraction (SAED) pattern revealed the crystalline structure of CDpey (Figure 2a inset). Well-resolved lattice fringes with an interplanar spacing of 0.208 nm were observed (Figure 2b), which is close to the (100) facet of graphite. On the other hand, CDpew was well distributed (Dp= 3.39 nm) and appeared Figure 1. Digital photographs of plasma-induced fabrication of eggderived CDs and their application as fluorescent carbon inks. Egg white or yolk, after a few minutes of plasma treatment under ambient conditions, were transformed into well-defined CDs with bright blue emission under UV light. The CD solutions can also be used as inks for making luminescent patterns by inkjet or silk-screen printing.

Energy decomposition analysis

Abstract: The energy decomposition analysis (EDA) is a powerful method for a quantitative interpretation of chemical bonds in terms of three major components. The instantaneous interaction energy ΔEint between two fragments A and B in a molecule A–B is partitioned in three terms, namely (1) the quasiclassical electrostatic interaction ΔEelstat between the fragments; (2) the repulsive exchange (Pauli) interaction ΔEPauli between electrons of the two fragments having the same spin, and (3) the orbital (covalent) interaction ΔEorb which comes from the orbital relaxation and the orbital mixing between the fragments. The latter term can be decomposed into contributions of orbitals with different symmetry which makes it possible to distinguish between σ, π, and δ bonding. After a short introduction into the theoretical background of the EDA we present illustrative examples of main group and transition metal chemistry. The results show that the EDA terms can be interpreted in chemically meaningful way thus providing a bridge between quantum chemical calculations and heuristic bonding models of traditional chemistry. The extension to the EDA–Natural Orbitals for Chemical Valence (NOCV) method makes it possible to breakdown the orbital term ΔEorb into pairwise orbital contributions of the interacting fragments. The method provides a bridge between MO correlations diagrams and pairwise orbital interactions, which have been shown in the past to correlate with the structures and reactivities of molecules. There is a link between frontier orbital theory and orbital symmetry rules and the quantitative charge- and energy partitioning scheme that is provided by the EDA–NOCV terms. The strength of the pairwise orbital interactions can quantitatively be estimated and the associated change in the electronic structure can be visualized by plotting the deformation densities. For further resources related to this article, please visit the WIREs website.

Biosensors and chemosensors based on the optical responses of polydiacetylenes

Abstract: Polydiacetylenes (PDAs), a family of conjugated polymers, have very unique electrical and optical properties. Upon environmental stimulation, such as by viruses, proteins, DNAs, metal ions, organic molecules etc., the blue PDAs can undergo a colorimetric transition from blue to red, which is accompanied by a fluorescence enhancement. Since the first report on polymerized diacetylene molecules as sensors of influenza virus, the development of efficient sensory systems based on PDAs continues to be of great interest. This tutorial review highlights the recent advances in bio- and chemo-sensors derived from polydiacetylenes.

La-doped BaFeO3−δ perovskite as a cobalt-free oxygen reduction electrode for solid oxide fuel cells with oxygen-ion conducting electrolyte

Abstract: Cobalt-free small La3+-doped BaFeO3−δ is synthesized and systematically characterized towards application as an oxygen reduction electrode material for intermediate temperature solid oxide fuel cells (IT-SOFCs) with oxygen-ion conducting electrolyte. The formation of an oxygen vacancy-disordered perovskite oxide with cubic lattice symmetry is demonstrated by XRD, after the doping of only 5 mol% La3+ into BaFeO3−δ parent oxide with the formation of Ba0.95La0.05FeO3−δ (BLF). The structural, thermal, electrical and electrochemical properties of BLF have been evaluated. High structural stability, high thermal expansion coefficient, high oxygen vacancy concentration, and relatively low electrical conductivity, are demonstrated. BLF shows a superior electrocatalytic activity, which is comparable to those state-of-the-art cobalt-based mixed conducting cathodes, in addition, it demonstrates a favorable long-term operational stability. It thus promises as a new cathode candidate for IT-SOFCs with oxygen-ion conducting electrolyte.

Triphase Microfluidic-Directed Self-Assembly: Anisotropic Colloidal Photonic Crystal Supraparticles and Multicolor Patterns Made Easy

Abstract: However, it is stilla great challenge to mount or shape CPCs into a desiredmorphology (e.g., spheres, Janus, ellipsoids, and dumbbell-like supaparticles); efficient pathways are needed to selec-tively endow CPCs with versatile functions whilst preservingtheir original optical properties.Herein, we developed a triphase microfluidic-directedself-assembly to construct CPC supraparticles with control-lable and predictable shape, and selectively introducedadvanced functions to them. The triphase microfluidictechnique is a co-flowing system that produces continuousmicrodroplets comprising two immiscible phases. By adjust-ing the interfacial tension of each phase in the microfluidicsystem, CPC supraparticles with tunable shape, varying fromcrescent, meniscus, and ellipsoid to spherical were preparedbytheself-assemblyofthemonodispersecolloidalparticlesinthese microdroplet templates. Importantly, studying theinterfacechemistryindicatedthatthestructureofthebiphasicmicrodroplets and the resulting CPCs might be predicted inour strategy. The further introduction of photoinducedconsolidation into the triphase microfluidic system yieldedcore–shell or Janus CPC superstructures. The encapsulationof magnetic nanoparticles created Janus CPC supraparticleswith superparamagnetism and a photonic bandgap in twodistincthemispheres.ThesemultifunctionalJanusCPCsupra-particles exhibit “Dark” and “Light” switchable behaviorsunder an external magnetic field, and thus can be processedinto rewritable and color-tunable photonic patterns. To ourknowledge, this is the first example of the utilization of thetriphase microfluidic technique for the design of anisotropicCPCs. This facile strategy can be extended to build up aseriesofnovelmultidimensionalcolloidalstructures,withtheaimofcollecting colloidal particles and orgnizing them into func-tional materials for pratical application.Figure 1a illustrates the fabrication of shape-controllableCPC supraparticles in a triphase microfluidic flow-focusingdevice composed of a cylindrical polydimethylsiloxane(PDMS) capillary and a pair of inner cylindrical 25G steelneedles. We chose three immiscible fluids, an aqueoussolution of monodisperse polystyrene (PS) microspheres in

Hydrogenation of TiO2 nanosheets with exposed {001} facets for enhanced photocatalytc activity

Abstract: Hydrogenated {001}-facets-dominated anatase TiO2 nanosheets have O–H bonds and O− on their surface. The high reactive {001} facets were maintained by the formation of Ti–H bonds. A large number of Ti3+ ions and oxygen vacancies were produced by hydrogenation, resulting in improved light absorption and enhanced photocatalytic activity.

Research and application of evaporative cooling in China: A review (I) – Research

Abstract: Evaporative cooling is an energy efficient and environmentally friendly air conditioning technology. Research and application of evaporative cooling in China have been very fruitful; however, they were little known to the world because most of works were published in Chinese. Therefore, this paper intends to present a comprehensive summary on them. The working principles and thermodynamic characteristics of different types of evaporative cooling, including direct, indirect and semi-indirect evaporative cooling, are first introduced. Experimental and theoretical research works on feasibility studies, performance test and optimization as well as heat and mass transfer analysis are then reviewed in detail. The feasibilities of evaporative cooling under different climates, efficiencies of various evaporative cooling equipment, and critical parameters and techniques for improving the efficiencies as well as numerical modeling of evaporative cooling processes are recalled. The typical systems and equipments of evaporative cooling adopted in China are reviewed in Part II.

Synthesis of zeolitic imidazolate framework-78 molecular-sieve membrane: defect formation and elimination

Abstract: Metal–organic frameworks (MOFs) are ideal micro- and mesoporous materials for molecular separation. A defect-free MOF membrane supported on a porous substrate is required for high separation performance, however it is rather difficult to eliminate the micro-defects or intercrystalline gaps in the membranes. In this work, a ZIF-78 membrane was synthesized on a porous ZnO support. The defect formation mechanism in the membrane was illustrated by in situ thermal expansion analysis. A novel strategy was proposed to eliminate not only the macroscopic defects but also the intercrystalline gaps in the membrane by controlling the diffusion of solvent molecules through the channels of the ZIF-78 crystal. The ZIF-78 membrane exhibited high performance in separating H2. The ideal selectivity and mixture separation factor of H2–CO2 are 11.0 and 9.5, respectively. The approach reported in this paper offers an efficient and universal strategy for the facile synthesis of high-quality MOF membranes on porous supports.

Mechanical property and structure of alkali-activated fly ash and slag blends

Abstract: Mechanical property and structure of alkali-activated fly ash (FA)/ground granulated blast furnace slag (GGBFS) blends were investigated via compressive strength testing, X-ray diffractometry (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy/energy dispersive spectroscopy. It is shown that the incorporation of slag into solid precursors can improve compressive strength of the geopolymer binders and the optimal slag content ratio which will result in the highest strength is 0.8. GGBFS is relatively more reactive than FA in alkaline activation. The binder is predominantly a class of Al-substituted sodium calcium silicate hydrate (N-C-A-S-H) gel phase, which distributes around the solid particles homogeneously. Combining the results obtained from the glass diffraction maximum of XRD and the wavenumber of T-O-Si bands displayed in FTIR, it suggests that the degree of polymerization of geopolymer binders decreases and increases. This means that the microstructure of the bi...

Effects of MgO-based expansive additive on compensating the shrinkage of cement paste under non-wet curing conditions

Abstract: Expansive additives are widely used to compensate the drying shrinkage of cement-based materials to avoid cracking. However, the expansion of conventional ettringite-bearing expansive additive depends strongly on wet curing and is mainly generated at early age, and hence it may not work well in concretes without sufficient water supply or exhibit long-term shrinkage. MgO-based expansive additive, for which less water is needed for the formation of Mg(OH) 2 in comparison to ettringite, was prepared and its compensating effect on the autogenous shrinkage and late age thermal shrinkage of Portland and fly ash cement pastes at low water-to-cement ratio was investigated. The tests were conducted under sealed condition, so that the moisture exchange with the environment was prevented. Results show that, even under the non-wet curing condition, the shrinkages of cement pastes can be compensated effectively. Microstructure analysis by scanning electron microscope indicates that the macro-expansion of cement pastes is probably caused by the locally restrained expansion of MEA due to the hydration of MgO.

Nitrogen- and TiN-modified Li4Ti5O12: one-step synthesis and electrochemical performance optimization

Abstract: It is believed that a TiN coating can increase the electrical conductivity, and consequently the performance, of an electrode. In this work, a simple one-step synthesis of nitrogen- and TiN-modified Li4Ti5O12, i.e. solid-state reaction of Li2CO3 and TiO2 anatase in an ammonia-containing atmosphere, is introduced. The reducing ammonia atmosphere could cause the partial reduction of Ti4+ to Ti3+ and the doping of nitrogen into the Li4Ti5O12 lattice, in addition to the formation of the TiN phase. By controlling the ammonia concentration of the atmosphere and using a slight Ti excess in the reactants, Li4Ti5O12, nitrogen-doped Li4Ti5O12, or TiN-coated nitrogen-doped Li4Ti5O12 were obtained. Both the electrical conductivity and the TiN thickness were closely related to the ammonia concentration in the atmosphere. Synthesis under reducing atmosphere also resulted in powders with a different plate shape particulate morphology from that synthesized in air, and such plate-shape powders had an ultrahigh tap density of ∼1.9 g cm−3. Interestingly, the formation of TiN was not beneficial for capacity improvement due to its insulation towards lithium ions, unlike the nitrogen doping. The sample prepared under 3% NH3–N2, which was free of TiN coating, showed the best electrode performance with a capacity of 103 mA h g−1 even at 20 C with only 3% capacity decay after cycling 100 times.

Construction of hollow and mesoporous ZnO microsphere: a facile synthesis and sensing property.

Abstract: Mesoporous and hollow structure have been attracting increasing attention for their special properties and potential applications. Here we show a facile fabrication of hollow and mesoporous ZnO microsphere via a one-step wet chemical process using polyethylene glycol (PEG, MW 200) as the solvent and soft template. The morphology and structure of the products were characterized by using scanning electron microscopy and X-ray powder diffraction techniques. Thermal analysis and Fourier transform infrared spectroscopy techniques were also performed to show the properties of the precursor and annealed product. A possible growth mechanism of hollow and mesoporous ZnO microsphere was also proposed. The Brunauer–Emmett–Teller surface area of ZnO microsphere is 28.5 m2g–1 and the size of mesopores is about 10 nm. The Photoluminescence spectra of the as-synthesized ZnO hollow microspheres were also presented. The mesoporous and hollow structure enhance the gas sensitivity of ZnO microsphere, and the obtained ZnO mi...