Cai-Feng Wang

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

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.

Versatile Bifunctional Magnetic‐Fluorescent Responsive Janus Supraballs Towards the Flexible Bead Display

electrophoretic displays, [ 4 , 5 ] self-assembly of multidimensional ordered structures, [ 6 ] and sensors. [ 7 ] A variety of Janus particles with complex shapes, anisotropic nature, and diverse functionalities have been developed by using elegant methods including electrifi ed co-jetting, [ 8 ] the spinning disks technique, [ 9 ] surface modifi cation, [ 10 ] microcontact printing, [ 11 ] the microfl uidic technique, [ 12 ] and others. [ 13 ] Particularly, Janus particles with magnetic, electric, or optical characteristics have aroused special interest because of their ability to undergo switching in response to a stimulus (e.g., magnetic or electric fi elds or light). In this respect, Yang et al. developed a light-curing technology to generate magnetoresponsive Janus microparticles for remotecontrolled locomotion. [ 2 ] Doyle and co-workers reported the preparation of Janus hydrogel particles with anisotropic superparamagnetism and demonstrated that these particles could be aligned and assembled by an external magnetic fi eld. [ 14 ]

Plant leaf-derived fluorescent carbon dots for sensing, patterning and coding

We report a simple, low-cost and green route for fabrication of fluorescent carbon dots (CDs), and demonstrate their applications in sensing, patterning, and coding. Pyrolysis of various plant leaves yielded bright blue-emitting CDs, providing a one-step way for large-scale production of CDs without surface passivation treatment or the use of toxic/expensive solvents and starting materials. Also, further improvement in the fluorescence intensity of CDs was achieved after treatment using plasma and microwave-assisted techniques. The obtained CDs were applied as a fluorescent sensing platform for sensitive and selective detection of Fe3+ ions, and as fluorescent inks for printing luminescent patterns useful in anti-counterfeit and optoelectronic applications. Moreover, uniform fluorescent microbeads of polymer-encapsulated CDs, CD/QD nanocomposites, and CD/organic fluorescent dye nanocomposites were prepared via a microfluidic process, which may expand the potential applications of CDs in coding, bioimaging, and drug delivery.

Interface-Directed Assembly of One-Dimensional Ordered Architecture from Quantum Dots Guest and Polymer Host

Assembly of inorganic semiconductor nanocrystals into polymer host is of great scientific and technological interest for bottom-up fabrication of functional devices. Herein, an interface-directed synthetic pathway to polymer-encapsulated CdTe quantum dots (QDs) has been developed. The resulting nanohybrids have a highly uniform fibrous architecture with tunable diameters (ranging from several tens of nanometers to microscale) and enhanced optical performance. This interfacial assembly strategy offers a versatile route to incorporate QDs into a polymer host, forming uniform one-dimensional nanomaterials potentially useful in optoelectronic applications.

Versatile superhydrophobic and photocatalytic films generated from TiO2–SiO2@PDMS and their applications on fabrics

We report a simple and practical approach to for the facile production of TiO2–SiO2@PDMS versatile hybrid films via a sol–gel process, which possess superhydrophobic and photocatalytic properties. The as-prepared films presented herein have high thermal stability even up to 400 °C, and then switch to superhydrophilicity upon calcination at 470 °C. Also, we successfully employed the TiO2–SiO2@PDMS hybrid solution to coat onto flexible polyester–cotton fabrics on a large scale, allowing them to be made superhydrophobic. The superhydrophobic fabrics are wash-resistant and resistant to strong acid attack, and can be applied as a filter cloth for both oil–water separation and colorful pattern printing. We further applied the TiO2–SiO2@PDMS hybrid solution to treat dye waste water, which became colorless under UV irradiation. More interestingly, small balls coated with the TiO2–SiO2@PDMS hybrid solution can move faster than the control sample owing to their smooth superhydrophobic surface. These findings suggest that this multifunctional TiO2–SiO2@PDMS hybrid material can be applied to fabric treatment and water-repellent ship coatings.

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

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

Fluorescent nanomaterial-derived white light-emitting diodes: what's going on

White light-emitting diodes (white LEDs) have recently attracted substantial interest owing to their remarkable energy conservation. The evolution of fluorescent nanomaterials with tunable optical properties has provided an opportunity for light source design of white LEDs. However, the stability and performance of fluorescent nanomaterial-derived white LEDs still fail to meet the requirements of practical applications. It is therefore imperative to boost their overall device performance, which depends on not only the exploitation of advanced fluorescent nanomaterials but also the design of a superior light source. In this review, the achievements regarding fluorescent nanomaterials as color converters towards white LEDs are highlighted, including semiconductor nanocrystals or colloidal quantum dots (QDs), carbon-based nanoparticles, silicon QDs, and organic–inorganic fluorescent nanocomposites. The challenges and future perspectives in this research area are also discussed.

Hair-derived carbon dots toward versatile multidimensional fluorescent materials

We report a simple and green route to the fabrication of fluorescent carbon dots (CDs), and demonstrate their versatile applications. Hair, a kind of natural and nontoxic raw material, was chosen as the precursor to prepare CDs via a one-step pyrolysis process. The structure and fluorescence properties of the CDs were thoroughly investigated. The obtained CDs can emit bright blue light under UV light with the quantum yield of ca. 17%, and exhibit excitation-, pH- and solvent-dependent fluorescence. The functional groups on the surface of CDs confer these nanomaterials with excellent dispersibility in water and most polar organic solvents, as well as good compatibility with polymer matrices such as poly(methyl methacrylate) and polyvinylpyrrolidone. Then multidimensional CD–polymer hybrid materials, including one-dimensional (1D) microfibers, 2D patterned films and 3D microbeads were constructed with excellent overall performance, which are useful in fluorescent patterns, flat panel displays and anti-counterfeiting labeling fields.

Fast synthesis of versatile nanocrystal-embedded hydrogels toward the sensing of heavy metal ions and organoamines

We report a facile and rapid approach for the fabrication of CdTe-embedded hydrogels and the selective sensing of these hydrogels toward different analytes. We first synthesized N-acetyl-L-cysteine (NAC)-capped CdTe nanocrystals (NCs) via a microwave-assistance method. Then, taking advantage of frontal polymerization (FP) for fast and easy handling, we facilely prepared CdTe/poly(N-methylolacrylamide) (CdTe/PNMA) and CdTe/poly(N-methylolacrylamide-co-dimethyl diallyl ammonium chloride) (CdTe/poly(NMA-co-DMDAAC)) fluorescent hydrogels. A variety of features for the preparation of CdTe-embedded hydrogels, such as the initiator, solvent concentrations and the ratio of different monomers were thoroughly investigated. The spectroscopic studies reveal that the CdTe-embedded hydrogels prepared via FP exhibit high quantum yield and excellent photoluminescence (PL) stability. By measuring the change in PL properties of the samples, we found that the CdTe/PNMA hydrogels are responsive to different kinds of heavy metal ions, and the CdTe/poly(NMA-co-DMDAAC) fluorescent slices exhibit fluorescent sensing toward organoamines.

Ferroelectric heterobimetallic clusters with ferromagnetic interactions.

Two homochiral trinuclear clusters, {(MeTp)2Fe2(CN)6Ni[(1R,2R)-chxn]2} (1) and {(MeTp)2Fe2(CN)6Ni[(1S,2S)-chxn]2} (2) [chxn = 1,2-diaminocyclohexane; MeTp = methyltris(pyrazolyl)borate], have been synthesized and structurally characterized. Ferroelectric and magnetic measurements reveal that they are rare examples of metal-organic compounds bearing ferroelectricity and intramolecular ferromagnetic interactions.