1
|
Ye R, Xiang C, Lin J, Peng Z, Huang K, Yan Z, Cook NP, Samuel ELG, Hwang CC, Ruan G, Ceriotti G, Raji ARO, Martí AA, Tour JM. Coal as an abundant source of graphene quantum dots. Nat Commun 2014; 4:2943. [PMID: 24309588 DOI: 10.1038/ncomms3943] [Citation(s) in RCA: 346] [Impact Index Per Article: 31.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2013] [Accepted: 11/14/2013] [Indexed: 12/24/2022] Open
Abstract
Coal is the most abundant and readily combustible energy resource being used worldwide. However, its structural characteristic creates a perception that coal is only useful for producing energy via burning. Here we report a facile approach to synthesize tunable graphene quantum dots from various types of coal, and establish that the unique coal structure has an advantage over pure sp2-carbon allotropes for producing quantum dots. The crystalline carbon within the coal structure is easier to oxidatively displace than when pure sp2-carbon structures are used, resulting in nanometre-sized graphene quantum dots with amorphous carbon addends on the edges. The synthesized graphene quantum dots, produced in up to 20% isolated yield from coal, are soluble and fluorescent in aqueous solution, providing promise for applications in areas such as bioimaging, biomedicine, photovoltaics and optoelectronics, in addition to being inexpensive additives for structural composites.
Collapse
|
Research Support, U.S. Gov't, Non-P.H.S. |
11 |
346 |
2
|
Xiang C, Han P, Lutziger I, Wang K, Oliver DJ. A mini binary vector series for plant transformation. PLANT MOLECULAR BIOLOGY 1999; 40:711-7. [PMID: 10480394 DOI: 10.1023/a:1006201910593] [Citation(s) in RCA: 317] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Abstract
A streamlined mini binary vector was constructed that is less than 1/2 the size of the pBIN19 backbone (3.5 kb). This was accomplished by eliminating over 5 kb of non-T-DNA sequences from the pBIN19 vector. The vector still retains all the essential elements required for a binary vector. These include a RK2 replication origin, the nptIII gene conferring kanamycin resistance in bacteria, both the right and left T-DNA borders, and a multiple cloning site (MCS) in between the T-DNA borders to facilitate cloning. Due to the reduced size, more unique restriction sites are available in the MCS, thus allowing more versatile cloning. Since the traF region was not included, it is not possible to mobilize this binary vector into Agrobacterium by triparental mating. This problem can be easily resolved by direct transformation. The mini binary vector has been demonstrated to successfully transform Arabidopsis plants. Based on this mini binary vector, a series of binary vectors were constructed for plant transformation.
Collapse
|
|
26 |
317 |
3
|
Yan Z, Lin J, Peng Z, Sun Z, Zhu Y, Li L, Xiang C, Samuel EL, Kittrell C, Tour JM. Toward the synthesis of wafer-scale single-crystal graphene on copper foils. ACS NANO 2012; 6:9110-7. [PMID: 22966902 DOI: 10.1021/nn303352k] [Citation(s) in RCA: 242] [Impact Index Per Article: 18.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
In this research, we constructed a controlled chamber pressure CVD (CP-CVD) system to manipulate graphene's domain sizes and shapes. Using this system, we synthesized large (~4.5 mm(2)) single-crystal hexagonal monolayer graphene domains on commercial polycrystalline Cu foils (99.8% purity), indicating its potential feasibility on a large scale at low cost. The as-synthesized graphene had a mobility of positive charge carriers of ~11,000 cm(2) V(-1) s(-1) on a SiO(2)/Si substrate at room temperature, suggesting its comparable quality to that of exfoliated graphene. The growth mechanism of Cu-based graphene was explored by studying the influence of varied growth parameters on graphene domain sizes. Cu pretreatments, electrochemical polishing, and high-pressure annealing are shown to be critical for suppressing graphene nucleation site density. A pressure of 108 Torr was the optimal chamber pressure for the synthesis of large single-crystal monolayer graphene. The synthesis of one graphene seed was achieved on centimeter-sized Cu foils by optimizing the flow rate ratio of H(2)/CH(4). This work should provide clear guidelines for the large-scale synthesis of wafer-scale single-crystal graphene, which is essential for the optimized graphene device fabrication.
Collapse
|
|
13 |
242 |
4
|
Yang Y, Fei H, Ruan G, Xiang C, Tour JM. Edge-oriented MoS2 nanoporous films as flexible electrodes for hydrogen evolution reactions and supercapacitor devices. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2014; 26:8163-8. [PMID: 25355037 DOI: 10.1002/adma.201402847] [Citation(s) in RCA: 236] [Impact Index Per Article: 21.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/26/2014] [Revised: 09/11/2014] [Indexed: 05/18/2023]
Abstract
A simple method to fabricate edge-oriented MoS2 films with sponge-like morphologies is demonstrated. They are directly fabricated through the reaction of sulfur vapor with anodically formed Mo oxide sponge-like films on flexible Mo substrates. The edge-oriented MoS2 film delivers excellent hydrogen evolution reaction (HER) activity with enhanced kinetics and long-term cycling stability. The material also has superior energy-storage performance when working as a flexible, all-solid-state supercapacitor device.
Collapse
|
|
11 |
236 |
5
|
Xiang C, Oliver DJ. Glutathione metabolic genes coordinately respond to heavy metals and jasmonic acid in Arabidopsis. THE PLANT CELL 1998; 10:1539-50. [PMID: 9724699 PMCID: PMC144077 DOI: 10.1105/tpc.10.9.1539] [Citation(s) in RCA: 230] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Abstract
Glutathione plays a pivotal role in protecting plants from environmental stresses, oxidative stress, xenobiotics, and some heavy metals. Arabidopsis plants treated with cadmium or copper responded by increasing transcription of the genes for glutathione synthesis, gamma-glutamylcysteine synthetase and glutathione synthetase, as well as glutathione reductase. The response was specific for those metals whose toxicity is thought to be mitigated through phytochelatins, and other toxic and nontoxic metals did not alter mRNA levels. Feeding experiments suggested that neither oxidative stress, as results from exposure to H2O2, nor oxidized or reduced glutathione levels were responsible for activating transcription of these genes. Jasmonic acid also activated the same suite of genes, which suggests that it might be involved in the signal transduction pathway for copper and cadmium. Jasmonic acid treatment increased mRNA levels and the capacity for glutathione synthesis but did not alter the glutathione content in unstressed plants, which supports the idea that the glutathione concentration is controlled at multiple levels.
Collapse
|
research-article |
27 |
230 |
6
|
Paulose-Murphy M, Ha NK, Xiang C, Chen Y, Gillim L, Yarchoan R, Meltzer P, Bittner M, Trent J, Zeichner S. Transcription program of human herpesvirus 8 (kaposi's sarcoma-associated herpesvirus). J Virol 2001; 75:4843-53. [PMID: 11312356 PMCID: PMC114239 DOI: 10.1128/jvi.75.10.4843-4853.2001] [Citation(s) in RCA: 181] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Human herpesvirus 8 (HHV-8), a gammaherpesvirus implicated in Kaposi's sarcoma, primary effusion lymphoma, and Castleman's disease, encodes several pathogenically important cellular homologs. To define the HHV-8 transcription program, RNA obtained from latently infected body cavity-based lymphoma 1 cells induced to undergo lytic replication was used to query a custom HHV-8 DNA microarray containing nearly every known viral open reading frame. The patterns of viral gene expression offer insights into the replication and pathogenic strategies of HHV-8.
Collapse
|
research-article |
24 |
181 |
7
|
Xiang C, Werner BL, Christensen EM, Oliver DJ. The biological functions of glutathione revisited in arabidopsis transgenic plants with altered glutathione levels. PLANT PHYSIOLOGY 2001; 126:564-74. [PMID: 11402187 PMCID: PMC111149 DOI: 10.1104/pp.126.2.564] [Citation(s) in RCA: 180] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/13/2001] [Accepted: 02/22/2001] [Indexed: 05/18/2023]
Abstract
A functional analysis of the role of glutathione in protecting plants from environmental stress was undertaken by studying Arabidopsis that had been genetically modified to have altered glutathione levels. The steady-state glutathione concentration in Arabidopsis plants was modified by expressing the cDNA for gamma-glutamyl-cysteine synthetase (GSH1) in both the sense and antisense orientation. The resulting plants had glutathione levels that ranged between 3% and 200% of the level in wild-type plants. Arabidopsis plants with low glutathione levels were hypersensitive to Cd due to the limited capacity of these plants to make phytochelatins. Plants with the lowest levels of reduced glutathione (10% of wild type) were sensitive to as little as 5 microM Cd, whereas those with 50% wild-type levels required higher Cd concentrations to inhibit growth. Elevating glutathione levels did not increase metal resistance. It is interesting that the plants with low glutathione levels were also less able to accumulate anthocyanins supporting a role for glutathione S-transferases for anthocyanin formation or for the vacuolar localization and therefore accumulation of these compounds. Plants with less than 5% of wild-type glutathione levels were smaller and more sensitive to environmental stress but otherwise grew normally.
Collapse
|
research-article |
24 |
180 |
8
|
Menke EJ, Thompson MA, Xiang C, Yang LC, Penner RM. Lithographically patterned nanowire electrodeposition. NATURE MATERIALS 2006; 5:914-9. [PMID: 17057701 DOI: 10.1038/nmat1759] [Citation(s) in RCA: 170] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/14/2006] [Accepted: 09/06/2006] [Indexed: 05/12/2023]
Abstract
Nanowire fabrication methods can be classified either as 'top down', involving photo- or electron-beam lithography, or 'bottom up', involving the synthesis of nanowires from molecular precursors. Lithographically patterned nanowire electrodeposition (LPNE) combines attributes of photolithography with the versatility of bottom-up electrochemical synthesis. Photolithography defines the position of a sacrificial nickel nanoband electrode, which is recessed into a horizontal trench. This trench acts as a 'nanoform' to define the thickness of an incipient nanowire during its electrodeposition. The electrodeposition duration determines the width of the nanowire. Removal of the photoresist and nickel exposes a polycrystalline nanowire--composed of gold, platinum or palladium--characterized by thickness and width that can be independently controlled down to 18 and 40 nm, respectively. Metal nanowires prepared by LPNE may have applications in chemical sensing and optical signal processing, and as interconnects in nanoelectronic devices.
Collapse
|
|
19 |
170 |
9
|
Lin J, Peng Z, Xiang C, Ruan G, Yan Z, Natelson D, Tour JM. Graphene nanoribbon and nanostructured SnO2 composite anodes for lithium ion batteries. ACS NANO 2013; 7:6001-6006. [PMID: 23758123 DOI: 10.1021/nn4016899] [Citation(s) in RCA: 167] [Impact Index Per Article: 13.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
A composite made from graphene nanoribbons (GNRs) and tin oxide (SnO2) nanoparticles (NPs) is synthesized and used as the anode material for lithium ion batteries (LIBs). The conductive GNRs, prepared using sodium/potassium unzipping of multiwall carbon nanotubes, can boost the lithium storage performance of SnO2 NPs. The composite, as an anode material for LIBs, exhibits reversible capacities of over 1520 and 1130 mAh/g for the first discharge and charge, respectively, which is more than the theoretical capacity of SnO2. The reversible capacity retains ~825 mAh/g at a current density of 100 mA/g with a Coulombic efficiency of 98% after 50 cycles. Further, the composite shows good power performance with a reversible capacity of ~580 mAh/g at the current density of 2 A/g. The high capacity, good power performance and retention can be attributed to uniformly distributed SnO2 NPs along the high-aspect-ratio GNRs. The GNRs act as conductive additives that buffer the volume changes of SnO2 during cycling. This work provides a starting point for exploring the composites made from GNRs and other transition metal oxides for lithium storage applications.
Collapse
|
|
12 |
167 |
10
|
|
|
25 |
164 |
11
|
Chu J, Xiang C, Sue HJ, Hollis RD. Scratch resistance of mineral-filled polypropylene materials. POLYM ENG SCI 2004. [DOI: 10.1002/pen.11222] [Citation(s) in RCA: 114] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
|
|
21 |
114 |
12
|
Yang Y, Fei H, Ruan G, Xiang C, Tour JM. Efficient electrocatalytic oxygen evolution on amorphous nickel-cobalt binary oxide nanoporous layers. ACS NANO 2014; 8:9518-23. [PMID: 25134007 DOI: 10.1021/nn503760c] [Citation(s) in RCA: 103] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/07/2023]
Abstract
Nanoporous Ni-Co binary oxide layers were electrochemically fabricated by deposition followed by anodization, which produced an amorphous layered structure that could act as an efficient electrocatalyst for water oxidation. The highly porous morphologies produced higher electrochemically active surface areas, while the amorphous structure supplied abundant defect sites for oxygen evolution. These Ni-rich (10-40 atom % Co) binary oxides have an increased active surface area (roughness factor up to 17), reduced charge transfer resistance, lowered overpotential (∼325 mV) that produced a 10 mA cm(-2) current density, and a decreased Tafel slope (∼39 mV decade(-1)). The present technique has a wide range of applications for the preparation of other binary or multiple-metals or metal oxides nanoporous films. Fabrication of nanoporous materials using this method could provide products useful for renewable energy production and storage applications.
Collapse
|
|
11 |
103 |
13
|
Yang Y, Ruan G, Xiang C, Wang G, Tour JM. Flexible Three-Dimensional Nanoporous Metal-Based Energy Devices. J Am Chem Soc 2014; 136:6187-90. [DOI: 10.1021/ja501247f] [Citation(s) in RCA: 102] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
|
|
11 |
102 |
14
|
Teoh EJ, Tan KC, Xiang C. Estimating the Number of Hidden Neurons in a Feedforward Network Using the Singular Value Decomposition. ACTA ACUST UNITED AC 2006; 17:1623-9. [PMID: 17131674 DOI: 10.1109/tnn.2006.880582] [Citation(s) in RCA: 99] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
In this letter, we attempt to quantify the significance of increasing the number of neurons in the hidden layer of a feedforward neural network architecture using the singular value decomposition (SVD). Through this, we extend some well-known properties of the SVD in evaluating the generalizability of single hidden layer feedforward networks (SLFNs) with respect to the number of hidden layer neurons. The generalization capability of the SLFN is measured by the degree of linear independency of the patterns in hidden layer space, which can be indirectly quantified from the singular values obtained from the SVD, in a postlearning step. A pruning/growing technique based on these singular values is then used to estimate the necessary number of neurons in the hidden layer. More importantly, we describe in detail properties of the SVD in determining the structure of a neural network particularly with respect to the robustness of the selected model.
Collapse
|
|
19 |
99 |
15
|
Ye R, Peng Z, Metzger A, Lin J, Mann JA, Huang K, Xiang C, Fan X, Samuel ELG, Alemany LB, Martí AA, Tour JM. Bandgap engineering of coal-derived graphene quantum dots. ACS APPLIED MATERIALS & INTERFACES 2015; 7:7041-7048. [PMID: 25757413 DOI: 10.1021/acsami.5b01419] [Citation(s) in RCA: 85] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
Bandgaps of photoluminescent graphene quantum dots (GQDs) synthesized from anthracite have been engineered by controlling the size of GQDs in two ways: either chemical oxidative treatment and separation by cross-flow ultrafiltration, or by a facile one-step chemical synthesis using successively higher temperatures to render smaller GQDs. Using these methods, GQDs were synthesized with tailored sizes and bandgaps. The GQDs emit light from blue-green (2.9 eV) to orange-red (2.05 eV), depending on size, functionalities and defects. These findings provide a deeper insight into the nature of coal-derived GQDs and demonstrate a scalable method for production of GQDs with the desired bandgaps.
Collapse
|
|
10 |
85 |
16
|
Xiang C, Young CC, Wang X, Yan Z, Hwang CC, Cerioti G, Lin J, Kono J, Pasquali M, Tour JM. Large flake graphene oxide fibers with unconventional 100% knot efficiency and highly aligned small flake graphene oxide fibers. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2013; 25:4592-4597. [PMID: 23828201 DOI: 10.1002/adma.201301065] [Citation(s) in RCA: 72] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/08/2013] [Revised: 05/08/2013] [Indexed: 05/28/2023]
Abstract
Two types of graphene oxide fibers are spun from high concentration aqueous dopes. Fibers extruded from large flake graphene oxide dope without drawing show unconventional 100% knot efficiency. Fibers spun from small sized graphene oxide dope with stable and continuous drawing yield in good intrinsic alignment with a record high tensile modulus of 47 GPa.
Collapse
|
|
12 |
72 |
17
|
Sun Z, Raji ARO, Zhu Y, Xiang C, Yan Z, Kittrell C, Samuel ELG, Tour JM. Large-area Bernal-stacked bi-, tri-, and tetralayer graphene. ACS NANO 2012; 6:9790-9796. [PMID: 23110694 DOI: 10.1021/nn303328e] [Citation(s) in RCA: 69] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Few-layer graphene, with Bernal stacking order, is of particular interest to the graphene community because of its unique tunable electronic structure. A synthetic method to produce such large area graphene films with precise thickness from 2 to 4 layers would be ideal for chemists and physicists to explore the promising electronic applications of these materials. Here, large-area uniform Bernal-stacked bi-, tri-, and tetralayer graphene films were successfully synthesized on a Cu surface in selective growth windows, with a finely tuned total pressure and CH(4)/H(2) gas ratio. On the basis of the analyses obtained, the growth mechanism is not an independent homoexpitaxial layer-by-layer growth, but most likely a simultaneous-seeding and self-limiting process.
Collapse
|
|
13 |
69 |
18
|
Xiang C, Miao Z, Lam E. DNA-binding properties, genomic organization and expression pattern of TGA6, a new member of the TGA family of bZIP transcription factors in Arabidopsis thaliana. PLANT MOLECULAR BIOLOGY 1997; 34:403-415. [PMID: 9225852 DOI: 10.1023/a:1005873500238] [Citation(s) in RCA: 64] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
The TGA genes encode a family of basic domain-leucine zipper (bZIP) transcription factors that are conserved in higher plants. We have continued to unravel the complexity of this gene family by using a polymerase chain reaction (PCR)-based approach. Taking advantage of the conserved amino acid sequence in the bZIP domain found in all members of this gene family, two degenerate oligonucleotides were synthesized based on the sequence of this region in order to amplify by PCR the analogous genomic fragments from the various TGA loci in Arabidopsis. This approach has led us to the finding of a new member of the TGA gene family, and subsequently the isolation of a gene designated as TGA6. Further characterization of the TGA6 locus confirmed our prediction that the gene structure of this family is remarkably conserved. Genomic Southern blot analysis revealed that TGA6 is a single-copy gene in Arabidopsis. Based on the genomic sequence information, gene-specific primers were synthesized for isolating the cDNA that corresponds to the coding region. Subsequently, the cDNA for TGA6 was cloned and sequenced. Gel mobility shift assays with in vitro translated TGA6 protein showed that TGA6 is more like TGA5 in terms of its in vitro DNA-binding properties. The expression of TGA6 in different tissues was estimated by using reverse transcriptase (RT)-PCR and further analyzed in transgenic Arabidopsis lines expressing a TGA6 promoter-GUS fusion. TGA6 promoter activity is found primarily in roots of young seedlings. As seedlings develop, TGA6 is expressed in aging cotyledons, mesophyll cells of hydathodes on leaf margins, vascular tissue and trichomes of senescing rosette leaves, but is very low in primary roots of mature plants. High levels of expression persist in young lateral roots and in regions of the primary root where lateral roots are emerging. In flowers, the activity is localized predominantly to mature pollen grains. The expression pattern of TGA6 reported here is strikingly similar to that of an Arabidopsis acidic chitinase gene. Possible biological significance of TGA6 in cellular defense against pathogens and abiotic stress is discussed.
Collapse
|
|
28 |
64 |
19
|
Xiang C, Miao ZH, Lam E. Coordinated activation of as-1-type elements and a tobacco glutathione S-transferase gene by auxins, salicylic acid, methyl-jasmonate and hydrogen peroxide. PLANT MOLECULAR BIOLOGY 1996; 32:415-26. [PMID: 8980490 DOI: 10.1007/bf00019093] [Citation(s) in RCA: 61] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
The molecular mechanism of signal transduction pathways which mediate the action of phytohormones are poorly understood. Recently, we and others have shown that the as -1 type cis-acting elements can respond to auxin and salicylic acid, two well-characterized signaling molecules in plants. In the present work, we have examined a comprehensive set of physiological and abiotic agents and found that auxin, salicylic acid and methyl-jasmonate are three effective inducers of the as-1-type elements in transgenic tobacco. Using a cell suspension culture containing a synthetic promoter-GUS fusion, we demonstrated rapid and sensitive induction of the as-1-type element by these phytohormones. Furthermore, a tobacco glutathione S-transferase gene, GNT35, that contains an as-1-type binding site in its promoter is also inducible by auxin, salicylic acid and methyl-jasmonate with similar kinetics. As Ulmasov et al. have recently reported, we found that the as-1-type elements can also respond to weak/inactive analogues of auxin and salicylic acid. In addition, we show that hydrogen peroxide can also effectively activate the expression of GNT35 as well as the as-1-type element in a cell suspension culture, but not with whole seedlings. These results are discussed with respect to the possible mechanism(s) through which a single cis element may respond to a diverse array of molecules.
Collapse
|
|
29 |
61 |
20
|
Xiang C, Baubet V, Pal S, Holderbaum L, Tatard V, Jiang P, Davuluri RV, Dahmane N. RP58/ZNF238 directly modulates proneurogenic gene levels and is required for neuronal differentiation and brain expansion. Cell Death Differ 2012; 19:692-702. [PMID: 22095278 PMCID: PMC3307985 DOI: 10.1038/cdd.2011.144] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2011] [Revised: 09/13/2011] [Accepted: 09/16/2011] [Indexed: 01/02/2023] Open
Abstract
Although neurogenic pathways have been described in the developing neocortex, less is known about mechanisms ensuring correct neuronal differentiation thus also preventing tumor growth. We have shown that RP58 (aka zfp238 or znf238) is highly expressed in differentiating neurons, that its expression is lost or diminished in brain tumors, and that its reintroduction blocks their proliferation. Mice with loss of RP58 die at birth with neocortical defects. Using a novel conditional RP58 allele here we show that its CNS-specific loss yields a novel postnatal phenotype: microencephaly, agenesis of the corpus callosum and cerebellar hypoplasia that resembles the chr1qter deletion microcephaly syndrome in human. RP58 mutant brains maintain precursor pools but have reduced neuronal and increased glial differentiation. Well-timed downregulation of pax6, ngn2 and neuroD1 depends on RP58 mediated transcriptional repression, ngn2 and neuroD1 being direct targets. Thus, RP58 may act to favor neuronal differentiation and brain growth by coherently repressing multiple proneurogenic genes in a timely manner.
Collapse
|
Research Support, N.I.H., Extramural |
13 |
58 |
21
|
Yan Z, Peng Z, Casillas G, Lin J, Xiang C, Zhou H, Yang Y, Ruan G, Raji ARO, Samuel ELG, Hauge RH, Yacaman MJ, Tour JM. Rebar graphene. ACS NANO 2014; 8:5061-8. [PMID: 24694285 PMCID: PMC4046778 DOI: 10.1021/nn501132n] [Citation(s) in RCA: 57] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/25/2014] [Accepted: 04/02/2014] [Indexed: 05/24/2023]
Abstract
As the cylindrical sp(2)-bonded carbon allotrope, carbon nanotubes (CNTs) have been widely used to reinforce bulk materials such as polymers, ceramics, and metals. However, both the concept demonstration and the fundamental understanding on how 1D CNTs reinforce atomically thin 2D layered materials, such as graphene, are still absent. Here, we demonstrate the successful synthesis of CNT-toughened graphene by simply annealing functionalized CNTs on Cu foils without needing to introduce extraneous carbon sources. The CNTs act as reinforcing bar (rebar), toughening the graphene through both π-π stacking domains and covalent bonding where the CNTs partially unzip and form a seamless 2D conjoined hybrid as revealed by aberration-corrected scanning transmission electron microscopy analysis. This is termed rebar graphene. Rebar graphene can be free-standing on water and transferred onto target substrates without needing a polymer-coating due to the rebar effects of the CNTs. The utility of rebar graphene sheets as flexible all-carbon transparent electrodes is demonstrated. The in-plane marriage of 1D nanotubes and 2D layered materials might herald an electrical and mechanical union that extends beyond carbon chemistry.
Collapse
|
Research Support, N.I.H., Extramural |
11 |
57 |
22
|
Yang Y, Li L, Ruan G, Fei H, Xiang C, Fan X, Tour JM. Hydrothermally formed three-dimensional nanoporous Ni(OH)2 thin-film supercapacitors. ACS NANO 2014; 8:9622-9628. [PMID: 25198148 DOI: 10.1021/nn5040197] [Citation(s) in RCA: 57] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
A three-dimensional nanoporous Ni(OH)2 thin-film was hydrothermally converted from an anodically formed porous layer of nickel fluoride/oxide. The nanoporous Ni(OH)2 thin-films can be used as additive-free electrodes for energy storage. The nanoporous layer delivers a high capacitance of 1765 F g(-1) under three electrode testing. After assembly with porous activated carbon in asymmetric supercapacitor configurations, the devices deliver superior supercapacitive performances with capacitance of 192 F g(-1), energy density of 68 Wh kg(-1), and power density of 44 kW kg(-1). The wide working potential window (up to 1.6 V in 6 M aq KOH) and stable cyclability (∼90% capacitance retention over 10,000 cycles) make the thin-film ideal for practical supercapacitor devices.
Collapse
|
|
11 |
57 |
23
|
Xiang C, Behabtu N, Liu Y, Chae HG, Young CC, Genorio B, Tsentalovich DE, Zhang C, Kosynkin DV, Lomeda JR, Hwang CC, Kumar S, Pasquali M, Tour JM. Graphene nanoribbons as an advanced precursor for making carbon fiber. ACS NANO 2013; 7:1628-1637. [PMID: 23339339 DOI: 10.1021/nn305506s] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Graphene oxide nanoribbons (GONRs) and chemically reduced graphene nanoribbons (crGNRs) were dispersed at high concentrations in chlorosulfonic acid to form anisotropic liquid crystal phases. The liquid crystal solutions were spun directly into hundreds of meters of continuous macroscopic fibers. The relationship of fiber morphology to coagulation bath conditions was studied. The effects of colloid concentration, annealing temperature, spinning air gap, and pretension during annealing on the fibers' performance were also investigated. Heat treatment of the as-spun GONR fibers at 1500 °C produced thermally reduced graphene nanoribbon (trGNR) fibers with a tensile strength of 378 MPa, Young's modulus of 36.2 GPa, and electrical conductivity of 285 S/cm, which is considerably higher than that in other reported graphene-derived fibers. This better trGNR fiber performance was due to the air gap spinning and annealing with pretension that produced higher molecular alignment within the fibers, as determined by X-ray diffraction and scanning electron microscopy. The specific modulus of trGNR fibers is higher than that of the commercial general purpose carbon fibers and commonly used metals such as Al, Cu, and steel. The properties of trGNR fibers can be further improved by optimizing the spinning conditions with higher draw ratio, annealing conditions with higher pretensions, and using longer flake GONRs. This technique is a new high-carbon-yield approach to make the next generation carbon fibers based on solution-based liquid crystal phase spinning.
Collapse
|
|
12 |
54 |
24
|
Kovalchuk A, Huang K, Xiang C, Martí AA, Tour JM. Luminescent Polymer Composite Films Containing Coal-Derived Graphene Quantum Dots. ACS APPLIED MATERIALS & INTERFACES 2015; 7:26063-8. [PMID: 26551046 DOI: 10.1021/acsami.5b06057] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
Luminescent polymer composite materials, based on poly(vinyl alcohol) (PVA), as a matrix polymer and graphene quantum dots (GQDs) derived from coal, were prepared by casting from aqueous solutions. The coal-derived GQDs impart fluorescent properties to the polymer matrix, and the fabricated composite films exhibit solid state fluorescence. Optical, thermal, and fluorescent properties of the PVA/GQD nanocomposites have been studied. High optical transparency of the composite films (78 to 91%) and excellent dispersion of the nanoparticles are observed at GQD concentrations from 1 to 5 wt %. The maximum intensity of materials photoluminescence has been achieved at 10 wt % GQD content. These materials could be used in light emitting diodes (LEDs), flexible electronic displays, and other optoelectronic applications.
Collapse
|
|
10 |
49 |
25
|
Yan Z, Liu Y, Ju L, Peng Z, Lin J, Wang G, Zhou H, Xiang C, Samuel ELG, Kittrell C, Artyukhov VI, Wang F, Yakobson BI, Tour JM. Large hexagonal bi- and trilayer graphene single crystals with varied interlayer rotations. Angew Chem Int Ed Engl 2014; 53:1565-9. [PMID: 24453109 DOI: 10.1002/anie.201306317] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2013] [Indexed: 11/07/2022]
Abstract
Bi- and trilayer graphene have attracted intensive interest due to their rich electronic and optical properties, which are dependent on interlayer rotations. However, the synthesis of high-quality large-size bi- and trilayer graphene single crystals still remains a challenge. Here, the synthesis of 100 μm pyramid-like hexagonal bi- and trilayer graphene single-crystal domains on Cu foils using chemical vapor deposition is reported. The as-produced graphene domains show almost exclusively either 0° or 30° interlayer rotations. Raman spectroscopy, transmission electron microscopy, and Fourier-transformed infrared spectroscopy were used to demonstrate that bilayer graphene domains with 0° interlayer stacking angles were Bernal stacked. Based on first-principle calculations, it is proposed that rotations originate from the graphene nucleation at the Cu step, which explains the origin of the interlayer rotations and agrees well with the experimental observations.
Collapse
|
Journal Article |
11 |
49 |