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Although carbon dots (CDs) have been widely investigated as the fluorescence material, research on room temperature phosphorescence (RTP) CDs is still limited. In this work, diethylenetriaminepentaacetic acid (DTPA) was employed as the raw material to synthesize carbon quantum dots (denoted as CQDs-1) by a hydrothermal method. The resulting CQDs-1 inherited CO groups and N atoms from DTPA, which promoted the formation of triplet excitons under light excitation. On this basis, the CQDs-1 were dispersed in a poly-(vinyl alcohol) (PVA) matrix to prepare CQDs-1-PVA composites that exhibited an optimal emission peak at ∼466 nm and emitted the visible afterglow lasting for 8 s. Moreover, tartaric acid (TA) was combined with DTPA as the raw material to synthesize CQDs-2, which induced the formation of π–π conjugated areas in CQDs. As a result, the emission wavelength was slightly red-shifted, and the duration time of afterglow of the CQDs-2-PVA composite was increased to 9 s. Due to the ultralong-lifetime RTP properties of the CQDs-based composites, their applications in the fields of information encryption and anticounterfeiting have also been investigated. Overall, our work offered a convenient avenue for the synthesis of high-quality RTP CQDs. [ABSTRACT FROM AUTHOR]

Graphene quantum dots (GQDs) are promising for bioimaging applications due to their unique optical properties and good biocompatibility. However, the facile synthesis of GQDs with long-wavelength emission and high quantum yield (QY) under long-wavelength excitation is still a challenge. Herein, dual-emissive GQDs were synthesized via a facile one-pot solvothermal method using 2,7-dihydroxynaphthalene (2,7-DHN) and piperazine anhydrous (PA) as the raw materials. The obtained GQDs exhibited a green-emission band (core state emission) and a red-emission band (surface state emission), which originated from the inner π-conjugated structure and various surface functional groups, respectively. The π-conjugated structure mainly comes from the aromatic rings in 2,7-DHN, and the N–H of PA acts as the main nitrogen source, which is beneficial for the QY. The obtained GQDs showed obvious concentration-dependent optical properties. Importantly, they are able to generate red emission with a high absolute QY of 54.9% in ethanol and 24.9% in water, among the best values of reported GQDs. In addition, the prepared GQDs have good water-solubility, low cytotoxicity, and superior stability against photobleaching. Based on the above advantages, the as-prepared GQDs were successfully applied for labeling HeLa cells in vitro. Therefore, our prepared GQDs demonstrated that they can be an efficient biomarker for fluorescent bioimaging. [ABSTRACT FROM AUTHOR]

We report the synthesis of a novel type of carbon-based nanostructure, which is composed of a string of carbon nanopearl chains (CNPCs) with a connection structure of carbon nanofibers using a chemical vapor deposition method. Regularly spaced, nanometer-sized balls of graphitic carbon are found on the amorphous nanofibers. The nanopearls have nanometer-sized spheres, bodies in diameter varying from tens of nanometers to hundreds of nanometers, with solid interiors. The chain connections have a length ranging from several nanometers up to micrometers between two nanopearls. The nanopearls connect each other by the nanofibers, thus forming a chain. The CNPCs have potential for use as reinforcing matrix to produce strong and tough carbon-based nanocomposites. [ABSTRACT FROM AUTHOR]

Efficient synthesis of large-scale vertically aligned nitrogen-doped carbon nanotube arrays (VA-NCNTs) has always been a challenge. In this study, we proposed a facile way to obtain mass VA-NCNTs between vermiculite layers by horizonal chemical vapor deposition (CVD). Vermiculite with layered compound as the catalyst substrate, Fe and Mo as the active metal phase is evenly distributed between the vermiculite layers, melamine is pyrolyzed as a single source for both carbon and nitrogen to synthesize nitrogen-doped carbon nanotube (CNT) array materials with relatively uniform length and diameter at an optimum temperature of 800 °C. We explored the effect of temperature on synthesis of VA-NCNTs, the results indicated that the VA-NCNTs are sensitive to temperature changes during the CVD synthesis process, the arrangement, diameter, nitrogen content, and the type of nitrogen function of CNTs could be modified. This work contributes to the study of how the growth temperature affecting the morphology of the as-prepared CNTs, and provides a potential method for the controllable mass production of oriented NCNTs. [ABSTRACT FROM AUTHOR]

The composites consisting of nitrogen-doped carbon nanotubes (N-CNTs) and nitrogen-doped carbon nanofibers (N-CNFs) were fabricated using a mixture of nickel foam (template) and imidazole (solid precursor) in a facile one-step chemical vapor deposition (CVD) process. The morphology and microstructure of the N-doped carbon nanotubes/N-doped carbon nanofibers hierarchical composites (N-CNTs/N-CNFs) were determined by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Raman spectra, and X-ray photoelectron spectroscopy. The results indicated that the sample manifests regular hierarchical composites, great graphitization, and nitrogen doping. Furthermore, a probable growth mechanism is presented to analyze the composites. [ABSTRACT FROM AUTHOR]

N-doped well-aligned thin multiwall carbon nanotubes (CNTs) have been prepared by a facile water-assisted chemical vapor deposition (CVD) process using melamine as both the carbon precursor and N-dopant and ferrocene as both the catalyst and carbon precursor. It is shown that the synthetic temperature has strong effects on the growth of carbonaceous structure. Carbon films started to grow at reaction temperature of 700 °C, and the optimal temperature for the synthesis of aligned CNTs, based on the experiment results, was found to be 900 °C. The lengths of the CNTs can be tuned by changing the annealing time of the pyrolysis process, it could reach as long as 40.2 μm. The atomic percentage of nitrogen doping in aligned CNTs could be achieved to 1.71%. It was found that there were many joints and defects in the as-prepared CNTs which may offer more nucleation sites on the chemically inert CNT surface for various specialized applications such as supercapacitor. [ABSTRACT FROM AUTHOR]

We report here the one-step water-assisted CVD growth of metal oxide nanosheets/carbon nanotubes (CNTs) composites. The cross-linked composites were characterized by scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy. The results showed that helical CNTs were obtained when the CVD growth process was prolonged to 1 h, and the typical fish-bone-type CNTs can be observed by HRTEM. Moreover, a related growth mechanism is proposed to explain the growth of such novel nanocomposites. [ABSTRACT FROM AUTHOR]

The effects of carbon black specific surface area and morphology were investigated by characterizing four different carbon black additives and then evaluating the effect of adding them to the negative electrode of valve-regulated lead–acid batteries for electric bikes. Low-temperature performance, larger current discharge performance, charge acceptance, cycle life and water loss of the batteries with carbon black were studied. The results show that the addition of high-performance carbon black to the negative plate of lead–acid batteries has an important effect on the cycle performance at 100% depth-of-discharge conditions and the cycle life is 86.9% longer than that of the control batteries. The excellent performance of the batteries can be attributed to the high surface area carbon black effectively inhibiting the sulfation of the negative plate surface and improving the charge acceptance of the batteries. [ABSTRACT FROM AUTHOR]

U-shaped graphene domains have been prepared on a copper substrate by chemical vapor deposition (CVD), which can be precisely tuned for the shape of graphene domains by optimizing the growth parameters. The U-shaped graphene is characterized by using scanning electron microscopy (SEM), atomic force microscopy (AFM), transmission electron microscopy (TEM), and Raman. These show that the U-shaped graphene has a smooth edge, which is beneficial to the seamless stitching of adjacent graphene domains. We also studied the morphology evolution of graphene by varying the flow rate of hydrogen. These findings are more conducive to the study of morphology evolution, nucleation, and growth of graphene domains on the copper substrate. [ABSTRACT FROM AUTHOR]

We report here the synthesis of metal oxide nanosheets (MONs) directly grown on stainless steel substrates by thermal oxidation in the presence of trace amounts of water. The morphology and microstructure of MONs were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), and atomic force microscopy (AFM). The composition of MONs was determined by the energy dispersive system and X-ray diffraction patterns. The results showed that the as-synthesized MONs were ultrathin, vertically aligned, and mostly transparent. They were polycrystalline and were composed primarily of Cr2O3 and (Fe, Mn)3O4. The optimal condition to synthesize the MONs with an optimal ultra-high surface atom ratio were determined by varying the temperature and time required for the growth of the MONs. It was found that the lateral size of MONs gradually increases as the temperature rises from 1000 to 1100 °C. An optimal temperature of 1100 °C is obtained in terms of the growth density, size and transparency degree growth morphology, and quality. The structure of MONs changes from two-dimensional to three-dimensional networks when the synthesis time is prolonged to more than 1 h. [ABSTRACT FROM AUTHOR]