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Showing papers by "Zhen Li published in 2013"


Proceedings ArticleDOI
23 Jun 2013
TL;DR: The decision function for verification is proposed to be viewed as a joint model of a distance metric and a locally adaptive thresholding rule, and the inference on the decision function is formulated as a second-order large-margin regularization problem, and an efficient algorithm is provided in its dual from.
Abstract: This paper considers the person verification problem in modern surveillance and video retrieval systems. The problem is to identify whether a pair of face or human body images is about the same person, even if the person is not seen before. Traditional methods usually look for a distance (or similarity) measure between images (e.g., by metric learning algorithms), and make decisions based on a fixed threshold. We show that this is nevertheless insufficient and sub-optimal for the verification problem. This paper proposes to learn a decision function for verification that can be viewed as a joint model of a distance metric and a locally adaptive thresholding rule. We further formulate the inference on our decision function as a second-order large-margin regularization problem, and provide an efficient algorithm in its dual from. We evaluate our algorithm on both human body verification and face verification problems. Our method outperforms not only the classical metric learning algorithm including LMNN and ITML, but also the state-of-the-art in the computer vision community.

533 citations


Journal ArticleDOI
TL;DR: The antireflection treatment was realized by a simple spin-coating process, which significantly increased the short-circuit current density and the incident photon-to-electron conversion efficiency to about 90% across the visible range.
Abstract: Carbon nanotube-Si and graphene-Si solar cells have attracted much interest recently owing to their potential in simplifying manufacturing process and lowering cost compared to Si cells. Until now, the power conversion efficiency of graphene-Si cells remains under 10% and well below that of the nanotube-Si counterpart. Here, we involved a colloidal antireflection coating onto a monolayer graphene-Si solar cell and enhanced the cell efficiency to 14.5% under standard illumination (air mass 1.5, 100 mW/cm2) with a stable antireflection effect over long time. The antireflection treatment was realized by a simple spin-coating process, which significantly increased the short-circuit current density and the incident photon-to-electron conversion efficiency to about 90% across the visible range. Our results demonstrate a great promise in developing high-efficiency graphene-Si solar cells in parallel to the more extensively studied carbon nanotube-Si structures.

314 citations


Journal ArticleDOI
TL;DR: In this article, four 4,4-bis(1,2,2-triphenylvinyl)biphenyl (BTPE) derivatives were successfully synthesized and their thermal, optical, and electronic properties fully investigated.
Abstract: Four 4,4-bis(1,2,2-triphenylvinyl)biphenyl (BTPE) derivatives, 4,4-bis(1,2,2-triphenylvinyl)biphenyl, 2,3-bis(1,2,2-triphenylvinyl)biphenyl, 2,4-bis(1,2,2-triphenylvinyl)biphenyl, 3,3-bis(1,2,2-triphenylvinyl)biphenyl and 3,4-bis(1,2,2-triphenylvinyl)biphenyl (oTPE-mTPE, oTPE-pTPE, mTPE-mTPE, and mTPE-pTPE, respectively), are successfully synthesized and their thermal, optical, and electronic properties fully investigated. By merging two simple tetraphenylethene (TPE) units together through different linking positions, the -conjugation length is effectively controlled to ensure the deep-blue emission. Because of the minor but intelligent structural modification, all the four fluorophores exhibit deep-blue emissions from 435 to 459 nm with Commission Internationale de l'Eclairage (CIE) chromaticity coordinates of, respectively, (0.16, 0.14), (0.15, 0.11), (0.16, 0.14), and (0.16, 0.16), when fabricated as emitters in organic light-emitting diodes (OLEDs). This is completely different from BTPE with sky-blue emission (0.20, 0.36). Thus, these results may provide a novel and versatile approach for the design of deep-blue aggregation-induced emission (AIE) luminogens.

268 citations


Journal ArticleDOI
TL;DR: The study of the adsorption of CO2, CH4, and H2 on boron nitride (BN) nanosheets and nanotubes (NTs) with different charge states demonstrates that BN nanomaterials are excellent absorbents for controllable, highly selective, and reversible capture and release ofCO2.
Abstract: Increasing concerns about the atmospheric CO2 concentration and its impact on the environment are motivating researchers to discover new materials and technologies for efficient CO2 capture and conversion. Here, we report a study of the adsorption of CO2, CH4, and H2 on boron nitride (BN) nanosheets and nanotubes (NTs) with different charge states. The results show that the process of CO2 capture/release can be simply controlled by switching on/off the charges carried by BN nanomaterials. CO2 molecules form weak interactions with uncharged BN nanomaterials and are weakly adsorbed. When extra electrons are introduced to these nanomaterials (i.e., when they are negatively charged), CO2 molecules become tightly bound and strongly adsorbed. Once the electrons are removed, CO2 molecules spontaneously desorb from BN absorbents. In addition, these negatively charged BN nanosorbents show high selectivity for separating CO2 from its mixtures with CH4 and/or H2. Our study demonstrates that BN nanomaterials are exce...

224 citations


Journal Article
TL;DR: In this paper, the adsorption of CO2, CH4, and H2 on boron nitride (BN) nanosheets and nanotubes (NTs) with different charge states was investigated.
Abstract: Increasing concerns about the atmospheric CO2 concentration and its impact on the environment are motivating researchers to discover new materials and technologies for efficient CO2 capture and conversion. Here, we report a study of the adsorption of CO2, CH4, and H2 on boron nitride (BN) nanosheets and nanotubes (NTs) with different charge states. The results show that the process of CO2 capture/release can be simply controlled by switching on/off the charges carried by BN nanomaterials. CO2 molecules form weak interactions with uncharged BN nanomaterials and are weakly adsorbed. When extra electrons are introduced to these nanomaterials (i.e., when they are negatively charged), CO2 molecules become tightly bound and strongly adsorbed. Once the electrons are removed, CO2 molecules spontaneously desorb from BN absorbents. In addition, these negatively charged BN nanosorbents show high selectivity for separating CO2 from its mixtures with CH4 and/or H2. Our study demonstrates that BN nanomaterials are excellent absorbents for controllable, highly selective, and reversible capture and release of CO2. In addition, the charge density applied in this study is of the order of 1013 cm–2 of BN nanomaterials and can be easily realized experimentally.

192 citations


Journal ArticleDOI
TL;DR: It is reported that the unidirectional suppression of hydrogen oxidation in photocatalytic water splitting can be fulfilled by controlling the valence state of platinum; this platinum-based cocatalyst in a higher oxidation state can act as an efficient hydrogen evolution site while suppressing the undesirable hydrogen back-oxidation.
Abstract: Solar-driven water splitting to produce hydrogen may be an ideal solution for global energy and environment issues. Among the various photocatalytic systems, platinum has been widely used to co-catalyse the reduction of protons in water for hydrogen evolution. However, the undesirable hydrogen oxidation reaction can also be readily catalysed by metallic platinum, which limits the solar energy conversion efficiency in artificial photosynthesis. Here we report that the unidirectional suppression of hydrogen oxidation in photocatalytic water splitting can be fulfilled by controlling the valence state of platinum; this platinum-based cocatalyst in a higher oxidation state can act as an efficient hydrogen evolution site while suppressing the undesirable hydrogen back-oxidation. The findings in this work may pave the way for developing other high-efficientcy platinum-based catalysts for photocatalysis, photoelectrochemistry, fuel cells and water-gas shift reactions.

187 citations


Journal ArticleDOI
TL;DR: In this article, the direct synthesis of multi-layer graphene and porous carbon woven composite films by chemical vapor deposition on Ni gauze templates is reported, and the composite films integrate the dual advantages of porous carbon, having not only the excellent electrical properties and flexibility of graphene but also the porous characteristics of amorphous carbon.
Abstract: New porous materials are of great importance in many technological applications. Here, the direct synthesis of multi-layer graphene and porous carbon woven composite films by chemical vapor deposition on Ni gauze templates is reported. The composite films integrate the dual advantages of graphene and porous carbon, having not only the excellent electrical properties and flexibility of graphene but also the porous characteristics of amorphous carbon. The multi-layer graphene/porous carbon woven fabric film creates a new platform for a variety of applications, such as fiber supercapacitors. The designed composite film has a capacitance of 20 μF/cm2, which is close to the theoretical value and a device areal capacitance of 44 mF/cm2.

150 citations


Journal ArticleDOI
Dengyu Pan1, Chen Xi1, Zhen Li1, Liang Wang1, Zhiwen Chen1, Bo Lu1, Minghong Wu1 
TL;DR: The controllable electrophoretic fabrication of highly robust, efficient, and benign photoelectrocatalysts based on graphene-quantum-dot sensitized TiO2 nanotube arrays was reported in this article.
Abstract: We report the controllable electrophoretic fabrication of highly robust, efficient, and benign photoelectrocatalysts based on graphene-quantum-dot sensitized TiO2 nanotube arrays. Their catalytic activities under visible-light irradiation remain steady for continuous cycles (400 min) with a negligible decrease, whereas CdS and CdSe sensitized TiO2 nanotube arrays show a high cycling instability due to serious photooxidization.

126 citations


Journal ArticleDOI
02 Aug 2013-Polymer
TL;DR: The development of organic/polymeric materials with second-order nonlinear optical (NLO) performance became more and more important, due to the increasing potential for the applications in photonic devices and many advantages over conventional inorganic crystalline materials in the last few decades, especially after 1980s.

102 citations


Journal ArticleDOI
Xiaohong Cheng1, Hui-Zhen Jia1, Jun Feng1, Jingui Qin1, Zhen Li1 
TL;DR: In this article, a new ratiometric optical probe for hydrogen sulfite detection, P-1, was proposed and applied to the detection of HeLa cells with fluorescent methods.
Abstract: 4-(1H-Phenanthro[9,10-d]imidazol-2-yl)benzaldehyde (P-1) was prepared as a new ratiometric optical probe for hydrogen sulfite. Upon the addition of HSO3−, it displayed large emission wavelength shift (Δλ = 120 nm) and the detection limit was determined to be as low as 2 μM. In addition to its high selectivity for hydrogen sulfite rather than other common anions, P-1 was successfully applied to the detection of hydrogen sulfite in HeLa cells with ratiometric fluorescent methods.

97 citations


Journal ArticleDOI
22 Aug 2013-ACS Nano
TL;DR: It is shown that a helical nanotube yarn can be overtwisted into highly entangled, macroscopically random but locally organized structures, consisting of mostly double-helix segments intertwined together, which represent a complex self-assembled system with applications as large-range strain sensors and robust rotational actuators.
Abstract: Introducing twists into carbon nanotube yarns could produce hierarchical architectures and extend their application areas. Here, we utilized such twists to produce elastic strain sensors over large strain (up to 500%) and rotation actuators with high energy density. We show that a helical nanotube yarn can be overtwisted into highly entangled, macroscopically random but locally organized structures, consisting of mostly double-helix segments intertwined together. Pulling the yarn ends completely resolved the entanglement in an elastic and reversible way, yielding large tensile strains with linear change in electrical resistance. Resolving an entangled yarn and releasing its twists could simultaneously rotate a heavy object (30 000 times the yarn weight) for more than 1000 cycles at high speed. The rotational actuation generated from a single entangled yarn produced energy densities up to 8.3 kJ/kg, and maintained similar capacity during repeated use. Our entangled CNT yarns represent a complex self-assemb...

Journal ArticleDOI
TL;DR: MIONs were conjugated with the anti-cancer drug doxorubicin and its efficacy, as a model drug delivery system, was determined using HepG2 cells and the efficiency of the drug-NP conjugates was found to be significantly higher than that of the free drug (DOX).
Abstract: We report a simple one step protocol for the preparation of fairly monodisperse and highly water-soluble magnetic iron oxide nanoparticles (MIONs) through a co-precipitation method using a novel multifunctional, biocompatible and water-soluble polymer ligand dodecanethiol–polymethacrylic acid (DDT–PMAA). DDT–PMAA owing to its several intrinsic properties, not only efficiently controls the size of the MIONs but also gives them excellent water solubility, long time stability against aggregation and oxidation, biocompatibility and multifunctional surface rich in thioether and carboxylic acid groups. The molecular weight and concentration of the polymer ligand were optimized to produce ultrasmall (4.6 ± 0.7 nm) MIONs with high magnetization (50 emu g−1). The MIONs obtained with 1.5 mM DDT–PMAA (5330 g mol−1) are highly stable in solution as well as in dry powder form for an extended period of time. These MIONs show a high degree of monodispersity and are superparamagnetic at room temperature. The polymer ligand and MIONs@Polymer were characterized by GPC, 1H NMR, DLS, TEM, FTIR-Raman, XRD, TGA and VSM. In order to demonstrate the bio-applications of these magnetic nanoparticles (NPs), their toxicity was determined by MTT assay and they were found to be non-toxic and biocompatible. Finally, MIONs were conjugated with the anti-cancer drug doxorubicin (DOX) and its efficacy, as a model drug delivery system, was determined using HepG2 cells. The efficiency of the drug–NP conjugates i.e., covalently bound DOX–MIONs and electrostatically loaded DOX/MIONs, was found to be significantly higher than that of the free drug (DOX).

Journal ArticleDOI
04 Jan 2013-ACS Nano
TL;DR: It is shown that CNTs can be made into a highly twisted yarn-derived double-helix structure by a conventional twist-spinning process and indicated that it is possible to create higher-level, more complex architectures from CNT yarns and fabricate multifunctional nanomaterials with potential applications in many areas.
Abstract: The strength and flexibility of carbon nanotubes (CNTs) allow them to be constructed into a variety of innovated architectures with fascinating properties. Here, we show that CNTs can be made into a highly twisted yarn-derived double-helix structure by a conventional twist-spinning process. The double-helix is a stable and hierarchical configuration consisting of two single-helical yarn segments, with controlled pitch and unique mechanical properties. While one of the yarn components breaks early under tension due to the highly twisted state, the second yarn produces much larger tensile strain and significantly prolongs the process until ultimate fracture. In addition, these elastic and conductive double-helix yarns show simultaneous and reversible resistance change in response to a wide range of input sources (mechanical, photo, and thermal) such as applied strains or stresses, light illumination, and environmental temperature. Our results indicate that it is possible to create higher-level, more complex...

Journal ArticleDOI
TL;DR: Reducing ferromagnetic particle size is an important strategy to improve their positive effect on imaging through the suppression of their negative effect, demonstrated by ultrasmall manganese ferrite nanoparticles prepared from an environmentally-friendly aqueous route.
Abstract: Reducing ferromagnetic particle size is an important strategy to improve their positive effect on imaging through the suppression of their negative effect, demonstrated by ultrasmall manganese ferrite nanoparticles prepared from an environmentally-friendly aqueous route. These ultrasmall particles exhibit pronounced paramagnetic characteristics and nontoxicity, making them efficient T1-positive contrast agent and manganese contrast agents for manganese enhanced MRI.

Journal ArticleDOI
TL;DR: In this paper, carbon nanotube (CNT) sponges were used to cleanup oil slicks on sea waters, which was compared with two traditional representative sorbents, including polypropylene fiber fabric and woolen felt.
Abstract: Oil spills in the sea have caused many serious environmental problems worldwide. In this study, carbon nanotube (CNT) sponges were used to cleanup oil slicks on sea waters. This method was compared with two traditional representative sorbents, including polypropylene fiber fabric and woolen felt. The CNT sponges had a larger oil sorption capacity than the other two sorbents. The maximum oil sorption capacity (Q m) of the CNT sponge was 92.30 g/g, which was 12 to 13.5 times larger than the Q m of the other two sorbents (the Q m of the polypropylene fiber fabric and woolen felt were 7.45 and 6.74 g/g, respectively). In addition, unlike the other two sorbents, the CNT sponge was superhydrophobic and did not adsorb any water during oil spill cleanup. CNT sponges are potentially very useful for cleaning up oil spills from sea water.

Journal ArticleDOI
Xiaohong Cheng1, Hui-Zhen Jia1, Jun Feng1, Jingui Qin1, Zhen Li1 
TL;DR: Taking advantage of the special nucleophilic addition reaction with aldehyde, a "switching-on" fluorescent probe (C1) for hydrogen sulfite was synthesized using intramolecular charge transfer (ICT) as a signal mechanism and was successfully applied to the detection of hydrogen sulfites in HeLa cells with turn-on fluorescent methods.
Abstract: Taking advantage of the special nucleophilic addition reaction with aldehyde, a “switching-on” fluorescent probe (C1) for hydrogen sulfite was synthesized using intramolecular charge transfer (ICT) as a signal mechanism Upon the addition of HSO3− ions, the probe displayed apparent fluorescence changes from non-emission to strong green fluorescence C1 gave response to hydrogen sulfite with high sensitivity and the detection limit was determined to be as low as 30 μM In addition to its high selectivity for hydrogen sulfite rather than other common anions, C1 was successfully applied to the detection of hydrogen sulfite in HeLa cells with turn-on fluorescent methods

Journal ArticleDOI
Qi Xue1, He Huang1, Liang Wang1, Zhiwen Chen1, Minghong Wu1, Zhen Li1, Dengyu Pan1 
TL;DR: A novel procedure involving polyethylenimine-assisted hydrothermal cutting and subsequent ultrafiltration for fabricating nearly monodisperse graphene quantum dots with a uniform lateral size and confined layer number is reported.
Abstract: We report a novel procedure involving polyethylenimine-assisted hydrothermal cutting and subsequent ultrafiltration for fabricating nearly monodisperse graphene quantum dots with a uniform lateral size and confined layer number. The isolated monolayer quantum dots exhibit a sharp band-edge absorption feature and strong photoluminescence (quantum yield of 21%) independent of excitation wavelength and pH. Their preliminary application in bioimaging has been demonstrated.

Journal ArticleDOI
TL;DR: The current state-of-the-art of the synthesis, modification, bioconjugation, and applications of QDs for in vivo targeted imaging, and QD-based multifunctional nanoprobes are summarized.
Abstract: Fluorescent semiconductor quantum dots (QDs) have attracted tremendous attention over the last decade. The superior optical properties of QDs over conventional organic dyes make them attractive labels for a wide variety of biomedical applications, whereas their potential toxicity and instability in biological environment have puzzled scientific researchers. Much research effort has been devoted to surface modification and functionalization of QDs to make them versatile probes for biomedical applications, and significant progress has been made over the last several years. This review article aims to describe the current state-of-the-art of the synthesis, modification, bioconjugation, and applications of QDs for in vivo targeted imaging. In addition, QD-based multifunctional nanoprobes are also summarized.

Journal ArticleDOI
Shuqin Xu1, Yi Lin1, Jing Huang1, Zhen Li1, Xiaojuan Xu1, Lina Zhang1 
TL;DR: In this article, hollow fibers with high strength were constructed from a polysaccharide aqueous solution at a concentration of 0.02 g mL−1 using a hierarchical self-assembly process, and they exhibited excellent tensile strength, biocompatibility, organic solvent resistance and birefringence.
Abstract: The development of biological high-performance materials fabricated from natural polysaccharides has attracted great attention for a sustainable world. In this work, hollow fibers with high strength were spun from a polysaccharide aqueous solution at a concentration of 0.02 g mL−1. The polysaccharide was a comb-like β-glucan with short branches isolated from Auricularia auricula-judae, coded as AF1. Atomic force microscopy (AFM) and transmission electron microscopy (TEM) confirmed directly that AF1 existed as a stiff chain conformation in water, and displayed parallel self-orientation behavior. AF1 could self-assemble into well defined hollow nanofibers with diameters less than 100 nm and lengths of tens of micrometers in dilute solution, supported by scanning electron microscopy (SEM). Moreover, AF1 in the disulfonated tetraphenylethene (TPE-SO3Na) aqueous solution exhibited strong luminescence, indicating that the TPE-SO3Na molecules without luminescence in water were trapped in the cavities of the hollow nanofibers through hydrophobic interactions, leading to the aggregation-induced emission (AIE). The nanofibers were composed of relatively hydrophobic inner-walls and hydrophilic shells in water. Interestingly, SEM and polarized light microscopy verified that the nanofibers fused to form an ordered architecture of lamella and then tended to curl into hollow fibers in relatively concentrated solution. The hollow fibers exhibited excellent tensile strength, biocompatibility, organic solvent resistance and birefringence. A schematic model was proposed to describe the construction of the hollow fibers via the hierarchical self-assembly process. The new materials would have potential applications such as drug release as a new class of fibrous carrier, indicators with fluorescence to detect cell growth in cell transplantation, and biomolecular recognition (e.g., DNA).

27 Oct 2013
TL;DR: In this article, S2−4 and S8/S2-4 composites with highly ordered microporous carbon as a confining matrix are fabricated and the electrode mechanism of the S2 −4 cathode is investigated.
Abstract: In lithium-sulfur batteries, small S2–4 molecules show very different electrochemical responses from the traditional S8 material. Their exact lithiation/delitiation mechanism is not clear and how to select proper electrolytes for the S2–4 cathodes is also ambiguous. Here, S2–4 and S8/S2–4 composites with highly ordered microporous carbon as a confining matrix are fabricated and the electrode mechanism of the S2–4 cathode is investigated by comparing the electrochemical performances of the S2–4 and S2–4/S8 electrodes in various electrolytes combined with theoretical calculation. Experimental results show that the electrolyte and microstructure of carbon matrix play important roles in the electrochemical performance. If the micropores of carbon are small enough to prevent the penetration of the solvent molecules, the lithiation/delithiation for S2–4 occurs as a solid-solid process. The irreversible chemically reactions between the polysulfudes and carbonates, and the dissolution of the polysulfides into the ethers can be effectively avoided due to the steric hindrance. The confined S2–4 show high adaptability to the electrolytes. The sulfur cathode based on this strategy exhibits excellent rate capability and cycling stability.

Journal ArticleDOI
TL;DR: It is proposed that the H3.3 nucleosomes at enhancers may be split by an active mechanism to regulate cell-type specific transcription.
Abstract: Previously, we reported that little canonical (H3.1–H4)2 tetramers split to form “hybrid” tetramers consisted of old and new H3.1–H4 dimers, but approximately 10% of (H3.3–H4)2 tetramers split during each cell cycle. In this report, we mapped the H3.3 nucleosome occupancy, the H3.3 nucleosome turnover rate and H3.3 nucleosome splitting events at the genome-wide level. Interestingly, H3.3 nucleosome turnover rate at the transcription starting sites (TSS) of genes with different expression levels display a bimodal distribution rather than a linear correlation towards the transcriptional activity, suggesting genes are either active with high H3.3 nucleosome turnover or inactive with low H3.3 nucleosome turnover. H3.3 nucleosome splitting events are enriched at active genes, which are in fact better markers for active transcription than H3.3 nucleosome occupancy itself. Although both H3.3 nucleosome turnover and splitting events are enriched at active genes, these events only display a moderate positive correlation, suggesting H3.3 nucleosome splitting events are not the mere consequence of H3.3 nucleosome turnover. Surprisingly, H3.3 nucleosomes with high splitting index are remarkably enriched at enhancers in a cell-type specific manner. We propose that the H3.3 nucleosomes at enhancers may be split by an active mechanism to regulate cell-type specific transcription.

Journal ArticleDOI
Jun Wang1, Zhongwei Yan1, Zhen Li1, Weidong Liu, Yingchun Wang 
TL;DR: In this article, a homogenized dataset of daily mean, maximum and minimum temperature (Tm, Tmax and Tmin) observations at 20 stations in Greater Beijing (GBJ) from 1978 to 2008 is analyzed.
Abstract: To quantify the impact of urbanization on changes in observed surface air temperature and extremes, a homogenized dataset of daily mean, maximum and minimum temperature (Tm, Tmax and Tmin) observations at 20 stations in Greater Beijing (GBJ) from 1978 to 2008 is analyzed. In contrast with previous studies, a cluster analysis is done to objectively classify observing stations into four categories (urbanized, suburban, rural and mountain), which is checked with remote-sensing night-light images since the 1990s. At urbanized sites, there is an added warming trend in annual mean Tm representing an average of 10.9% (up to 18.4% or 0.12°C/decade at the most strongly influenced site) of overall warming. Corresponding contributions for Tmin are 12.7% (up to 20.8% or 0.19°C/decade) and 24% for diurnal temperature range DTR (up to 37.4% or 0.149°C/decade) over the last three decades. Although it has not had a significant impact on daytime records (Tmax), urbanization has enhanced the increasing (decreasing) trend of extremely warm (cold) nights by an average of 12.7% or 2.07 d/decade (29.0% or 5.06 d/decade) at the urbanized sites since the 1970s.

Journal ArticleDOI
11 Mar 2013-Langmuir
TL;DR: It is demonstrated that the loading of SnO2 quantum dots was an effective way to prevent graphene nanosheets from being restacked during the reduction of graphene composites by a facile ultrasonic method.
Abstract: Nanocomposites have significant potential in the development of advanced materials for numerous applications. Tin dioxide (SnO2) is a functional material with wide-ranging prospects because of its high electronic mobility and wide band gap. Graphene as the basic plane of graphite is a single atomic layer two-dimensional sp(2) hybridized carbon material. Both have excellent physical and chemical properties. Here, SnO2 quantum dots/graphene composites have been successfully fabricated by a facile ultrasonic method. The experimental investigations indicated that the graphene was exfoliated and decorated with SnO2 quantum dots, which was dispersed uniformly on both sides of the graphene. The size distribution of SnO2 quantum dots was estimated to be ranging from 4 to 6 nm and their average size was calculated to be about 4.8 ± 0.2 nm. This facile ultrasonic route demonstrated that the loading of SnO2 quantum dots was an effective way to prevent graphene nanosheets from being restacked during the reduction. During the calcination process, the graphene nanosheets distributed between SnO2 nanoparticles have also prevented the agglomeration of SnO2 nanoparticles, which were beneficial to the formation of SnO2 quantum dots.

Journal ArticleDOI
01 Apr 2013
TL;DR: Novel visible light-driven phtotocatalysts composed by silver halides and graphitic carbon nitride showed significant enhancement in photocatalytic degradation of methyl orange under the irradiation of visible light.
Abstract: Novel visible light-driven phtotocatalysts composed by silver halides and graphitic carbon nitride (i.e. AgX@g-C3N4, X = Cl, Br, I) were synthesized by in situ precipitation of AgX nanoparticles on the surface of sheet-like g-C3N4. The resultant AgX@g-C3N4 nanocomposites were characterized with state-of-the-art instruments, showing significant enhancement in photocatalytic degradation of methyl orange under the irradiation of visible light. Their excellent photocatalytic performance is attributed to the efficient separation of photogenerated electron–hole pairs and their higher photostability in comparison with pure AgX.

Journal ArticleDOI
TL;DR: The effective protection from CdS shell and MSA enables CdTe QDs to be chemically stable in a pH range of 6-9 and less toxic, which makes them very promising for bio-imaging applications.

Journal ArticleDOI
TL;DR: Porous titania nanohybrids as photoanodes play a trifunctional role (light harvesting, dye adsorption, and electron transfer) in improving the efficiency of the dye-sensitized solar cells.
Abstract: Porous titania nanohybrids (NHs) were successfully prepared by hybridizing the exfoliated titania nanosheets with anatase TiO2 nanoparticles. Various characterizations revealed that the titania NHs as photoanodes play a trifunctional role (light harvesting, dye adsorption, and electron transfer) in improving the efficiency (η) of the dye-sensitized solar cells. The optimized photoanode consisting layered NHs demonstrated a high overall conversion efficiency of 10.1%, remarkably enhanced by 29.5% compared to that (7.8%) obtained from the benchmark P25 nanoparticles under the same testing conditions.

Journal ArticleDOI
TL;DR: Adsorption of CO2, CH4, and H2 on BN nanosheets and nanotubes with different charge states was investigated by DFT calculations.
Abstract: Adsorption of CO2, CH4, and H2 on BN nanosheets and nanotubes with different charge states are investigated by DFT calculations.

Journal ArticleDOI
TL;DR: The improvement in photodegradation activity and electron-hole separation of Cu-Cu2O-TiO2 (3 h) can be ascribed to the rational coupling of components and dimensional control.
Abstract: Multicomponent Cu-CuO-TiO nanojunction systems were successfully synthesized by a mild chemical process, and their structure and composition were thoroughly analyzed by X-ray diffraction, transmission electron microscopy, field-emission scanning electron microscopy, and X-ray photoelectron spectroscopy. The as-prepared Cu-CuO-TiO (3 and 9 h) nanojunctions demonstrated higher photocatalytic activities under UV/Vis light irradiation in the process of the degradation of organic compounds than those of the Cu-CuO, Cu-TiO, and Cu O-TiO starting materials. Moreover, time-resolved photoluminescence spectra demonstrated that the quenching times of electrons and holes in Cu-CuO-TiO (3 h) is higher than that of Cu-CuO-TiO (9 h); this leads to a better photocatalytic performance of Cu-CuO-TiO (3 h). The improvement in photodegradation activity and electron-hole separation of Cu-Cu O-TiO (3 h) can be ascribed to the rational coupling of components and dimensional control. Meanwhile, an unusual electron-hole transmission pathway for photocatalytic reactions over Cu-CuO- TiO nanojunctions was also identified.

Journal ArticleDOI
TL;DR: The results demonstrated that both the size (bulk and shape) and the linkage mode between the D-π-A chromophores and the isolation groups, could affect the performance of sensitizers in DSCs in a large degree, providing a new approach to optimize the chemical structure of dyes to achieve high conversion efficiencies.
Abstract: Four new pyrrole-based organic sensitizers with different isolation groups were conveniently synthesized and applied to dye sensitized solar cells (DSCs). The introduction of isolation group in the side chain could both suppress the formation of dye aggregates and electron recombination. Especially, when two pieces of D-π-A chromophore moieties shared one isolation group to construct the “H” type dye, the performance was further improved. Consequently, in the corresponding solar cell of LI-57, a short-circuit photocurrent density (Jsc) was tested to be 13.85 mA cm–2, while 0.72 V for the open-circuit photovoltage (Voc), 0.64 for the fill factor (FF), and 6.43% for the overall conversion efficiency (η), exceeding its analogue LI-55 (5.94%) with the same isolation group. The results demonstrated that both the size (bulk and shape) and the linkage mode between the D-π-A chromophores and the isolation groups, could affect the performance of sensitizers in DSCs in a large degree, providing a new approach to op...

Journal ArticleDOI
TL;DR: In this paper, two series of dendrimers, which contain normal phenyl or pentafluorophenyl as the end-capped group, were conveniently prepared with high purity and satisfactory yields, through the combination of divergent and convergent approaches, coupled with the utilization of the powerful Sharpless reaction.
Abstract: In this paper, two series of dendrimers, which contain normal phenyl or pentafluorophenyl as the end-capped group, were conveniently prepared with high purity and satisfactory yields, through the combination of divergent and convergent approaches, coupled with the utilization of the powerful Sharpless “click” reaction. Due to the Ar–ArF self-assembly effect, as well as their perfect 3D structure and the isolation effects of the interior triazole rings, G4-PFPh-TB exhibited a very large d33 value of 252 pm V−1, which should be one of the highest values for simple azo chromophore moieties.