Highly Luminescent Carbon‐Nanoparticle‐Based Materials: Factors Influencing Photoluminescence Quantum Yield

Unravelling the factors influencing photoluminescence (PL) quantum yield of the carbon nanoparticles (CNPs) is the prerequisite for preparing highly luminescent CNP‐based materials. In this work, an easy and effective method is reported for preparing highly luminescent CNP‐based materials. Water‐soluble luminescent CNPs (CNP‐Cs) with large size distribution (1–60 nm) with PL quantum yields of 22% are synthesized through a microwave pyrolysis approach. Energy transfer (ET) is confirmed to occur from small size CNPs (CNP‐Ss:1‐7 nm, blue emitters) to large size CNPs (CNP‐Ls:10–60 nm, green emitters). Further centrifugally separating CNP‐Cs resulted in an enhancement of the PL quantum yield up to 39% of CNP‐Ss aqueous solution. The PL quantum yield of CNP‐Ss could even be further improved in high‐viscosity solvents. PL quantum yield higher than 90% is achieved in films of commercial glue water embedded with the CNP‐Ss at embedding ratio lower than 3 wt%. By contrast, the yield is greatly decreased in the CNP‐C‐embedding films with embedding ratio higher than 1 wt%, which is due to self‐absorption, as well as enhanced ET between CNP‐Ss and CNP‐Ls. High‐viscosity solvents and polymer matrix are proposed to act as surface passivation reagents to enhance PL quantum yield of CNPs.     

Catalytic growth of nickel-encapsulated and hollow graphitic carbon nanoparticles during laser vaporization of cellulose char containing nickel

Nickel-encapsulated and hollow graphitic carbon nanoparticles (CNPs) with diameters of up to 200 nm were fabricated from cellulose char containing nickel, by continuous wave Nd:YAG laser vaporization. The relative yields of the Ni-encapsulated and hollow CNPs strongly depended on the laser power density and the quantity of Ni in the cellulose char. The hollow CNPs with yields of up to 90% were successfully formed with increasing laser power density. A net-like structure composed of small fragments of bending graphitic layers was also produced under an excess condition of the cellulose char. We discuss the formation mechanisms of the CNPs, in which the growth of graphitic layers around Ni particles and their separation repeatedly occur after the start of laser irradiation. PACS 81.05.Uw; 81.07.Wx; 81.16.Mk     

Impact of strong localization of the incident power density on the nano-amplifier characteristics of active coated nano-particles

Resonant, active coated nano-particles (CNPs) have been advocated as effective nano-amplifiers and nano-lasers. When it is properly designed to be in its super-resonant state, an electrically small active CNP captures significantly more of the incident field energy than its physical size suggests is possible. The corresponding enhancement of its extinction cross section is correlated with the concentration of the local field energy into its gain region. This energy localization can be visualized with the behavior of the flow lines of the Poynting vector field in the neighborhood of the CNP. Strong expulsion of the optical power generated from the interaction of the captured incident field energy with the gain medium creates an intense scattered field. As the interactions between the scattered field and the exciting plane wave increase, optical vortices form in the neighborhood of the active CNP. Gain depletion eventually occurs when the increase in the effective gain sufficiently detunes the resonance. A simple model for the gain enhancement effects observed in active CNPs is proposed that relates the enhanced effective size of the CNP caused by the field localization to the required gain necessary to achieve its super-resonant state. A comparison of the metal-covered, gain core, active CNP studied previously to the experimentally realized gain-impregnated silica-covered metal “SPASER” suggests that the active CNP design would require significantly less gain while offering a much larger enhancement of the incident field. Proposed modifications of both geometries that augment the field localization suggest further reductions in the gain values needed to achieve significant amplification of the output signal.     

链状Pt-Ni纳米颗粒的制备、表征及高效电催化性能

开发高效、稳定的电催化剂是燃料电池走向实用的关键.为了解决催化剂因尺寸效应引起的催化活性和稳定性之间的矛盾,采用简便的一步溶剂热法设计合成了具有一维链状结构的Pt-Ni合金纳米颗粒催化剂.链状Pt-Ni纳米颗粒由平均尺寸约为10 nm的纳米颗粒和直径约为3 nm,长度为几百纳米的纳米线组装而成,该结构具有零维纳米颗粒高的比表面积和一维纳米线高的结构稳定性优势,可显著提高甲醇氧化反应的催化活性和稳定性,其质量活性和比活性分别是商业Pt/C纳米催化剂的5.7倍和7.6倍.经1000圈循环伏安测试后,该纳米材料仍保留91.2%的比活性,远高于商业Pt/C的4.4%.制备的一维链状结构很好地解决了纳米颗粒催化剂在反应中的团聚问题,为获得同时具有较高催化活性和稳定性的Pt基纳米催化剂提供了新的途径,有望实现大范围工业化应用.     

Enhanced electrochemical performance of La- and Zn-co-doped LiMn2O4 spinel as the cathode material for lithium-ion batteries

We report on the nanoparticle uptake into MCF10A neoT and PC-3 cells using flow cytometry, confocal microscopy, SQUID magnetometry, and transmission electron microscopy. The aim was to evaluate the influence of the nanoparticles?? surface charge on the uptake efficiency. The surface of the superparamagnetic, silica-coated, maghemite nanoparticles was modified using amino functionalization for the positive surface charge (CNPs), and carboxyl functionalization for the negative surface charge (ANPs). The CNPs and ANPs exhibited no significant cytotoxicity in concentrations up to 500???g/cm³ in 24?h. The CNPs, bound to a plasma membrane, were intensely phagocytosed, while the ANPs entered cells through fluid-phase endocytosis in a lower internalization degree. The ANPs and CNPs were shown to be co-localized with a specific lysosomal marker, thus confirming their presence in lysosomes. We showed that tailoring the surface charge of the nanoparticles has a great impact on their internalization.     

纳米纤维素碱法制备及光谱性质

在纳米尺寸范围操控纤维素分子,由此创制出具有优异功能的新纳米材料是纤维素科学的前沿领域。纳米纤维素作为一种可再生生物材料已成为国内外研究热点,研究开发新型的简单、绿色、低能耗、快速、高效的纳米纤维素制备方法显得尤为重要。该研究采用简易可行的碱性水解法制备得到粒径较小且分散性较好的纳米纤维素。同时采用了电子显微镜、X射线粉末衍射仪和傅里叶红外光谱仪对所制备纳米纤维素进行了表征,研究了其结构与谱学性质。所制备样品为准球形纳米纤维素,颗粒尺寸约为20～40 nm,样品仍属于纤维素Ⅰ型,结晶度为79.71%,晶粒平均尺寸为3～6 nm。结果表明,碱水解法制备纳米纤维素方法具有简易可行、得率高的优点,研究可为纳米纤维素的高效制备提供一条新途径。     

Electrical parameters retrieval of carbon nanoparticle-based metal semiconductor metal structure by standard methods and beta-ray-induced charge

Semiconducting carbon nanoparticles (CNPs) represent various applications in sensing systems with exceptional electronic properties. The extraction of electronic parameters of a sensor is very important to interpret the sensing characteristics of the electronic devices. This work is concerned with the extraction of electronic parameters such as the ideality factor, the barrier height, the series resistance, and some other diode parameters of a CNP-based metal semiconductor metal structure. The parameters are determined from the experimental data and physical model using the standard current–voltage (I–V) analysis in the frame of the thermionic emission theory, impedance spectroscopy, and other methods. The mobility-lifetime products (μτ) for electrons and holes in CNP micro-wire were determined by beta-ray-induced charge with Schottky contacts.     

Solvothermal synthesis of green-fluorescent carbon nanoparticles and their application

A novel solvothermal approach to synthesize green-fluorescent carbon nanoparticles (CNPs) was developed using l-ascorbic acid as the carbon source, glycol and triple distilled water as the solvent. The CNPs emit strong green fluorescence under UV irradiation, and the fluorescence intensity showed a good linear relationship with pH value within a certain range. Direct yeast cell labeling was achieved through cell endocytosis of these CNPs.     

Improvement of field emission of graphite flakes using hydrogen thermal processing

In order to improve the field electron emission properties of the graphite, the carbon nanoparticles (CNPs) are synthesized on the micrographite flakes by hydrogen thermal processing. We spin the graphite solution on the silicon wafer and desiccate it, then produce the CNPs on the graphite flakes using hydrogen thermal processing in the furnace. The processing parameters such as the processing temperature, hydrogen flow rate and processing time, were varied to find the optimal conditions for the improvement of the field emission properties of the graphite flakes. The experimental results show that the field emission properties of the graphite flakes have glaring improvement after heat treatment owing to the increase of the defect density and the CNPs on above. The turn-on field was decreased from 7.7 of the untreated sample to 4.3 V/μm of the treated sample at the optimal processing conditions.     

Formation of multifunctional Fe_3O_4/Au composite nanoparticles for dual-mode MR/CT imaging applications

Recent advances with iron oxide/gold(Fe3O4/Au) composite nanoparticles(CNPs) in dual-modality magnetic resonance(MR) and computed tomography(CT) imaging applications are reviewed. The synthesis and assembly of "dumbbelllike" and "core/shell" Fe3O4/Au CNPs is introduced. Potential applications of some developed Fe3O4/Au CNPs as contrast agents for dual-mode MR/CT imaging applications are described in detail.     

A Novel Technique of Synthesis of Highly Fluorescent Carbon Nanoparticles from Broth Constituent and In-vivo Bioimaging of <Emphasis Type="Italic">C. elegans</Emphasis>

Here we have demonstrated a novel single step technique of synthesis of highly fluorescent carbon nanoparticles (CNPs) from broth constituent and in vivo bioimaging of Caenorhabditis elegans (C. elegans) with the synthesized CNPs has been presented. The synthesized CNPs has been characterized by the UV-visible (UV-Vis) absorption spectroscopy, transmission electron microscopy (TEM) and Raman studies. The sp ² cluster size of the synthesized samples has been determined from the measured Raman spectra by fitting it with the theoretical skew Lorentzian (Breit-Wigner- Fano (BWF)) line shape. The synthesised materials are showing excitation wavelength dependent tunable photoluminescence (PL) emission characteristics with a high quantum yield (QY) of 3 % at a very low concentration of CNPs. A remarkable increase in the intensity of PL emission from 16 % to 39 % in C. elegans has also been observed when the feeding concentration of CNPs to C. elegans is increased from 0.025 % to 0.1 % (w/v). The non-toxicity and water solubility of the synthesized material makes it ideal candidate for bioimaging.     

Effects of ultrasonic conditions on the interfacial property and emulsifying property of cellulose nanoparticles from ginkgo seed shells

Cellulose microparticles from ginkgo seed shells were treated by ultrasonic treatments within the selected output powders (150–600 W) and durations (10–60 min) to produce cellulose nanoparticles. The main aim of this study was to investigate effects of ultrasonic conditions on the interfacial property and emulsifying property of those cellulose nanoparticles. Compared to ultrasonic output powers, ultrasonic durations showed the greater influence on morphology and physical properties of cellulose nanoparticles. Atomic force microscopy revealed that noodle-like cellulose particles with 1100 nm in length gradually became the short rod-like nanoparticles with 300 nm in length with increasing of ultrasonic duration from 10 min to 60 min. Moreover, results of contact angles indicated that ultrasound could significantly improve hydrophobicity of cellulose nanoparticles. The interfacial shear rheology showed that although all cellulose nanoparticles exhibited the similar interface adsorption behavior which showed the initial lag-phase of adsorption, followed by the interface saturation, the time of this initial lag-phase was affected by ultrasonic conditions. The increase of ultrasonic duration and ultrasonic power could shorten the time of this initial lag-phase, suggesting the resulting cellulose nanoparticles easier adsorption at the O/W interface. It was probably attributed to its small size and high hydrophobicity induced by intense ultrasonic treatments. Meanwhile, the cellulose nanoparticles with small size and higher hydrophobicity exhibited the better emulsifying ability to stabilize oil-in-water emulsions due to the formation of the viscoelastic interfacial film. This study improved understanding about changes in interfacial and emulsifying properties of cellulose nanoparticles caused by ultrasonic treatments.     

Copper and copper oxide nanoparticles in a cellulose support studied using anomalous small-angle X-ray scattering

Microcrystalline cellulose is a porous natural material which can be used both as a support for nanoparticles and as a reducer of metal ions. Cellulose supported nanoparticles can act as catalysts in many reactions. Cu, CuO, and Cu₂O particles were prepared in microcrystalline cellulose by adding a solution of copper salt to the insoluble cellulose matrix and by reducing the copper ions with several reducers. The porous nanocomposites were studied using anomalous small angle X-ray scattering (ASAXS), X-ray absorption spectroscopy, and X-ray diffraction. Reduction of Cu²⁺ with cellulose in ammonium hydrate medium yielded crystalline CuO nanoparticles and the crystallite size was about 6–20 nm irrespective of the copper concentration. The size distribution of the CuO particles was determined with ASAXS measurements and coincided with the crystallite sizes. Using sodium borohydrate or hydrazine sulfate as a reducer both metallic Cu and Cu₂O nanoparticles were obtained and the crystallite size and the oxidation state depended on the amount of reducer.     

Effects of fullerene coalescence on the thermal conductivity of carbon nanopeapods

The heat conduction and its dependence on fullerene coalescence in carbon nanopeapods (CNPs) have been investigated by equilibrium molecular dynamics simulations. The effects of fullerene coalescence on the thermal conductivity of CNPs were discussed under different temperatures. It is shown that the thermal conductivity of the CNPs decreases with the coalescence of encapsulated fullerene molecules. The thermal transmission mechanism of the effect of fullerene coalescence was analysed by the mass transfer contribution, the relative contributions of phonon oscillation frequencies to total heat current and the phonon vibrational density of states (VDOS). The mass transfer in CNPs is mainly attributed to the motion of encapsulated fullerene molecule and it gets more restricted with the coalescence of the fullerene. It shows that the low-frequency phonon modes below 20 THz contribute mostly to thermal conductivity in CNPs. The analysis of VDOS demonstrates that the dominating contribution to heat transfer is from the inner fullerene chain. With the coalescence of fullerene, the interfacial heat transfer between the CNT and fullerene chain is strengthened; however, the heat conduction of the fullerene chain decreases more rapidly at the same time.     

Short electrospun composite nanofibers: Effects of nanoparticle concentration and surface charge on fiber length

Short composite nanofibers were fabricated by electrospinning polymer/TiO₂ nanoparticle solutions of 13 wt. % cellulose acetate as a polymer under a voltage of 5.5 kV and at a flow rate of 0.1 μL/min, and the nanoparticles could be added in concentrations as high as 50 wt. %. The length of the short composite nanofibers was significantly decreased from 112 to 70 μm by the addition of at least a 5 wt. % concentration of nanoparticles, and it gradually continued to decrease as the nanoparticle concentration was increased. The length of the short composite nanofibers with a low concentration of nanoparticles was affected by the surface charge of the nanoparticles, and negatively charged nanoparticles readily dispersed to the negatively charged polymers in solution, which resulted in an elongation of the fabricated short composite nanofibers.     

Sono-assisted TEMPO oxidation of oil palm lignocellulosic biomass for isolation of nanocrystalline cellulose

Highly stable and dispersible nanocrystalline cellulose (NCC) was successfully isolated from oil palm empty fruit bunch microcrystalline cellulose (OPEFB-MCC), with yields of 93% via a sono-assisted TEMPO-oxidation and a subsequent sonication process. The sono-assisted treatment has a remarkable effect, resulting in an increase of more than 100% in the carboxylate content and a significant increase of approximately 39% in yield compared with the non-assisted process. TEM images reveal the OPEFB-NCC to have rod-like crystalline morphology with an average length and width of 122 and 6 nm, respectively. FTIR and solid-state ¹³C-NMR analyses suggest that oxidation of cellulose chain hydroxyl groups occurs at C6. XRD analysis shows that OPEFB-NCC consists primarily of a crystalline cellulose I structure. Both XRD and ¹³C-NMR indicate that the OPEFB-NCC has a lower crystallinity than the OPEFB-MCC starting material. Thermogravimetric analysis illustrates that OPEFB-NCC is less thermally stable than OPEFB-MCC but has a char content of 46% compared with 7% for the latter, which signifies that the carboxylate functionality acts as a flame retardant.     

Effects of Replacement of Part of the Silica Reinforcement with Hybrid Modified Microcrystalline Cellulose on the Properties of their Rubber Composites

Hybrid modified microcrystalline cellulose (HMCC), with SiO₂ nanoparticles being in-situ loaded on the surface of microcrystalline cellulose (MCC), was obtained through a sol-gel process of tetraethoxysilane (TEOS) by using ammonia as catalyst. HMCC was characterized by thermogravimetric analysis and scanning electron microscopy. The results showed that the spherical nano-SiO₂ particles had been loaded successfully on the surface of the MCC with a loading ratio of approximately 10%. Then the HMCC was used in high vinyl solution-polymerized styrene butadiene rubber (SSBR)/silica compounds to replace part of the silica, and its effects on the physio-mechanical and dynamic mechanical properties of the vulcanizates were investigated. The results showed that the HMCC samples had improved physio-mechanical properties and lower heat build-up than that of MCC ones. Dynamic mechanical analysis (DMA) showed that the tanδ value of the compounds decreased at 60°C while increased obviously at 0°C, which meant that the tires would have improved wet-skid resistance while maintaining low rolling resistance when HMCC was used in tire tread compounds. As observed from scanning electron microscopy (SEM) photos, the sizes of the HMCC were in-situ decreased from 20–90 µm to 0.5–10 µm during the processing of the rubber compounds. Compared with MCC, the interfacial adhesion between HMCC and rubber was also improved greatly.     

Synthesis and characterization of polyester bionanocomposite membrane with ultrasonic irradiation process for gas permeation and antibacterial activity

Optically active bionanocomposite membranes composed of polyester (PE) and cellulose/silica bionanocomposite (BNCs) prepared with simple, green and inexpensive ultrasonic irradiation process. It is a novel method to enhance the gas separation performance. The novel optically active diol containing functional trifluoromethyl groups was prepared in four steps reaction and it was fully characterized by different techniques. Commercially available silica nanoparticles were modified with biodegradable nanocellulose through ultrasonic irradiation technique. Transmission electron microscopy (TEM) analyses showed that the cellulose/silica composites were well dispersed in the polymer matrix on a nanometer scale. The mechanical properties nanocomposite films were improved by the addition of cellulose/silica. Thermo gravimetric analysis (TGA) data indicated an increase thermal stability of the PE/BNCs in compared to the pure polymer. The results obtained from gas permeation experiments showed that adding cellulose/silica to the PE membrane structure increased the permeability of the membranes. The increase in the permeability of the gases was as follows: P_CH4 (38%) <P_N2 (58%) <P_CO2 (88%) <P_O2 (98%) Adding silica nanoparticles into the PE matrix, improved the separation performance of carbon dioxide/methane and carbon dioxide/nitrogen gases. Increasing the cellulose/silica mass fraction in the membrane increased the diffusion coefficients of gases considered in the current study. Further, antimicrobial test against pathogenic bacteria was carried out.     

Synthesis and characterization of conductive silver ink for electrode printing on cellulose film

Silver nanoparticles with size less than 50 nm were synthesized from silver nitrate, polyvinylpyrrolidone (PVP) and ethylene glycol, where these chemicals acted as metal precursor, stabilizer and reducing agent, respectively. Then a conductive silver ink was prepared with a suitable solvent by adding a viscosifier, hydroxyethyl-cellulose (HEC), and a surfactant, diethylene glycol (DEG). The combined effect of both viscosifier and surfactant on the physical property of the silver ink was analyzed by measuring the contact angle of the silver ink on a cellulose film. Moreover, the influences of PVP molecular weight and reaction temperature on the size of the silver nanoparticles were analyzed. Then the silver ink was coated on the cellulose film by spin coating and the effects of different solvents, sintering temperatures and solid contents on its electrical resistivity were examined. It was found that, with 50 % co-solvent of deionized water and DEG and solid content of around 50 %, the silver ink exhibited the lowest resistivity. This ink can be used for inkjet printing of conductive patterns on cellulose films.     

Preparation of Cellulose Acetate Supported Zero-Valent Iron Nanoparticles for the Dechlorination of Trichloroethylene in Water

Chlorinated hydrocarbons are an immense concern for human health and the environment because they␣are highly toxic and are present in many contaminated sites. Zero-valent iron has been shown to be very effective for the dechlorination of chlorinated olefins and paraffins. This behavior is enhanced when the particle size is in the nanometer range. The activity of these nanoparticles is very high, and thus supporting the particles is important to preserve their chemical nature by inhibiting oxidation until they can be contacted with the chlorinated stream. In this paper, we present the preparation of membrane (cellulose acetate) supported zero-valent iron nanoparticles. The highly active nanoparticles were synthesized in a water-oil micro-emulsion, mixed with cellulose acetate-acetone solution, and then formed into a porous membrane by phase inversion. The unsupported iron particles and membrane supported iron particles were characterized using transmission electron microscopy. Batch experiments were conducted to characterize the activity of the supported zero-valent iron nanoparticles to dechlorinate trichloroethylene in water, as well as to investigate synergistic effects of the polymer support matrix.