| 1. |
- Barzegar, Hamid Reza, et al.
(författare)
-
Nitrogen Doping Mechanism in Small Diameter Single-Walled Carbon Nanotubes : Impact on Electronic Properties and Growth Selectivity
- 2013
-
Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 117:48, s. 25805-25816
-
Tidskriftsartikel (refereegranskat)abstract
- Nitrogen doping in carbon nanostructures has attracted interest for more than a decade, and recent implementation of such structures in energy conversion systems has boosted the interest even more. Despite numerous studies, the structural conformation and stability of nitrogen functionalities in small diameter single-walled carbon nanotubes (SWNTs), and the impact of these functionalities on the electronic and mechanical properties of the SWNTs, are incomplete. Here we report a detailed study on nitrogen doping in SWNTs with diameters in the range of 0.8?1.0 nm, with well-defined chirality. We show that the introduction of nitrogen in the carbon framework significantly alters the stability of certain tubes, opening for the possibility to selectively grow nitrogen-doped SWNTs with certain chirality and diameter. At low nitrogen concentration, pyridinic functionalities are readily incorporated and the tubular structure is well pertained. At higher concentrations, pyrrolic functionalities are formed, which leads to significant structural deformation of the nanotubes and hence a stop in growth of crystalline SWNTs. Raman spectroscopy is an important tool to understand guest atom doping and electronic charge transfer in SWNTs. By correlating the influence of defined nitrogen functionalities on the electronic properties of SWNTs with different chirality, we make precise interpretation of experimental Raman data. We show that the previous interpretation of the double-resonance G?-peak in many aspects is wrong and instead can be well-correlated to the type of nitrogen doping of SWNTs originating from the p- or n-doping nature of the nitrogen incorporation. Our results are supported by experimental and theoretical data.
|
|
| 2. |
- Barzegar, Hamid R., et al.
(författare)
-
Simple Dip-Coating Process for the Synthesis of Small Diameter Single-Walled Carbon Nanotubes-Effect of Catalyst Composition and Catalyst Particle Size on Chirality and Diameter
- 2012
-
Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 116:22, s. 12232-12239
-
Tidskriftsartikel (refereegranskat)abstract
- We report on a dip-coating method to prepare catalyst particles (mixture of iron and cobalt) with a controlled diameter distribution on silicon wafer substrates by changing the solution's concentration and withdrawal velocity. The size and distribution of the prepared catalyst particles were analyzed by atomic force microscopy. Carbon nanotubes were grown by chemical vapor deposition on the substrates with the prepared catalyst particles. By decreasing the catalyst particle size to below 10 nm, the growth of carbon nanotubes can be tuned from few-walled carbon nanotubes, with homogeneous diameter, to highly pure single-walled carbon nanotubes. Analysis of the Raman radial breathing modes, using three different Raman excitation wavelengths (488, 633, and 785 nm), showed a relatively broad diameter distribution (0.8-1.4 nm) of single-walled carbon nanotubes with different chiralities. However, by changing the composition of the catalyst particles while maintaining the growth parameters, the chiralities of single-walled carbon nanotubes were reduced to mainly four different types, (12, 1), (12, 0), (8, 5), and (7, 5), accounting for about 70% of all nanotubes.
|
|
| 3. |
- Hu, Guangzhi, et al.
(författare)
-
Palladium nanocrystals supported on helical carbon nanofibers for highly efficient electro-oxidation of formic acid, methanol and ethanol in alkaline electrolytes
- 2012
-
Ingår i: Journal of Power Sources. - : Elsevier BV. - 0378-7753 .- 1873-2755. ; 209, s. 236-242
-
Tidskriftsartikel (refereegranskat)abstract
- We present the synthesis of palladium nanocrystals self-assembled on helical carbon nanofibers functionalized with benzyl mercaptan (Pd-S-HCNFs) and their electrocatalytic activity toward the oxidation of formic acid, methanol and ethanol. Helical carbon nanofibers (HCNFs) were first functionalized with benzyl mercaptan based on the pi-pi interactions between phenyl rings and the graphitic surface of HCNFs. Palladium nano crystals (PdNC) were fixed on the surface of functionalized HCNF by Pd-S bonds in a simple self-assembly method. The as-prepared materials were characterized by high resolution transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), cyclic voltammetry (CV), and fuel cell tests. CV characterization of the as-prepared materials shows a very high electrocatalytic activity for oxidation of formic acid, ethanol and methanol in strong alkaline electrolyte. In comparison to commercial catalyst Vulcan XC-72 decorated with Pd nanoparticles, the proposed Pd-S-HCNFs nano composite material shows oxidation currents for formic acid, ethanol and methanol at the Pd-S-HCNF-modified electrode that are higher than that at the Pd/XC-72 modified electrode with a factor of 2.0, 1.5, and 2.3, respectively. In a formic acid fuel cell the Pd-S-HCNF modified electrode yields equal power density as commercial Pd/XC-72 catalyst. Our results show that Pd-decorated helical carbon nanofibers with diameters around 40-60 nm have very high potential as active material in fuel cells, electrocatalysts and sensors.
|
|
| 4. |
- Hu, Guangzhi, et al.
(författare)
-
Phase-transfer synthesis of amorphous palladium nanoparticle-functionalized 3D helical carbon nanofibers and its highly catalytic performance towards hydrazine oxidation
- 2012
-
Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 543, s. 96-100
-
Tidskriftsartikel (refereegranskat)abstract
- Amorphous palladium nanoparticles functionalized helical carbon nanofibers (ApPd-HCNFs) were synthesized using a phase-transfer method. Palladium nanoparticles (Pd-NP) were first prepared using n-dodecyl sulfide as reducing agent and stabilizing ligands in ethanol. The Pd-NPs were then modified with benzyl mercaptan and transferred into a toluene solution with HCNFs which were decorated with amorphous palladium. The materials were characterized with high-resolution transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, energy-dispersive X-ray spectroscopy and cyclic voltammetry showing that amorphous palladium nanoparticles were uniformly anchored at the HCNFs surface and that the ApPd-HCNFs exhibit high electrocatalytic activity towards hydrazine oxidation.
|
|
| 5. |
- Hu, Guangzhi, et al.
(författare)
-
Reduction free room temperature synthesis of a durable and efficient Pd/ordered mesoporous carbon composite electrocatalyst for alkaline direct alcohols fuel cell
- 2014
-
Ingår i: RSC Advances. - : RSC Publishing. - 2046-2069. ; 4:2, s. 676-682
-
Tidskriftsartikel (refereegranskat)abstract
- The development of easy and environmentally benign synthesis methods of efficient electrocatalysts for use in energy conversion applications motivates researchers all over the world. Here we report a novel and versatile method to synthesize well-dispersed palladium-functionalized ordered mesoporous carbons (Pd/OMCs) at room temperature without any reducing agent by one-pot mixing of tri(dibenzylideneacetone)palladium(0) (Pd2DBA3) and OMCs together in a common N,N-dimethylformamide (DMF) solution. The formation of Pd nanoparticles and their crystallization on the OMC is catalyzed by protons in the solution and can thus be controlled by the solution pH. The complete process and the as-prepared nanocomposite was characterized by UV-spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (HTEM), X-ray photoelectron spectrum (XPS), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). The electrocatalytic property of the as-decorated material was examined with cyclic voltammetry (CV). The Pd/OMC composite shows up to two times higher electrocatalytic ability with a significantly better durability towards ethanol and methanol oxidation in alkaline media compared to commercial high surface area conductive carbon black Vulcan XC-72 decorated with equivalent Pd nanoparticles. Our described method provides new insight for the development of highly efficient carbon based nanocatalysts by simple and environmentally sound methods.
|
|
| 6. |
- Hu, Guangzhi, et al.
(författare)
-
Self-assembled palladium nanocrystals on helical carbon nanofibers as enhanced electrocatalysts for electro-oxidation of small molecules
- 2012
-
Ingår i: Journal of Materials Chemistry. - : Royal Society of Chemistry (RSC). - 0959-9428 .- 1364-5501. ; 22:17, s. 8541-8548
-
Tidskriftsartikel (refereegranskat)abstract
- We present a novel approach to prepare helical carbon nanofibers homogeneously functionalized with single crystal palladium nanoparticles via a phase-transfer method. The materials were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray spectroscopy (EDX), thermogravimetric analysis (TGA) and electrochemical measurements. We find that homogeneous and small single-crystal Pd nanoparticles can be easily functionalized with phenyl mercaptan, transferred into the toluene phase from the dimethyl sulfoxide (DMSO) phase and then non-covalently self-assembled onto the surface of helical carbon nanofibers with a very good dispersion and homogeneous diameters of 4.5 +/- 0.6 nm. The palladium-helical carbon nanofiber composite exhibits significantly higher electrochemical active area and electrocatalytic activity towards the electrooxidation of formic acid, ethanol and methanol than the commercial electrocatalyst Pd/Vulcan XC-72. Our results show that the prepared material can be potentially used as an advanced nano-electrocatalyst in a direct alkaline fuel cell system.
|
|
| 7. |
- Hu, Guangzhi, et al.
(författare)
-
Small palladium islands embedded in palladium-tungsten bimetallic nanoparticles form catalytic hotspots for oxygen reduction
- 2014
-
Ingår i: Nature Communications. - : Macmillan Publishers Ltd.. - 2041-1723. ; 5, s. Article number: 5253-
-
Tidskriftsartikel (refereegranskat)abstract
- The sluggish kinetics of the oxygen reduction reaction at the cathode side of proton exchange membrane fuel cells is one major technical challenge for realizing sustainable solutions for the transportation sector. Finding efficient yet cheap electrocatalysts to speed up this reaction therefore motivates researchers all over the world. Here we demonstrate an efficient synthesis of palladium-tungsten bimetallic nanoparticles supported on ordered mesoporous carbon. Despite a very low percentage of noble metal (palladium: tungsten = 1:8), the hybrid catalyst material exhibits a performance equal to commercial 60% platinum/Vulcan for the oxygen reduction process. The high catalytic efficiency is explained by the formation of small palladium islands embedded at the surface of the palladium-tungsten bimetallic nanoparticles, generating catalytic hotspots. The palladium islands are similar to 1 nm in diameter, and contain 10-20 palladium atoms that are segregated at the surface. Our results may provide insight into the formation, stabilization and performance of bimetallic nanoparticles for catalytic reactions.
|
|
| 8. |
- Jia, Xueen, et al.
(författare)
-
Synthesis of Palladium/Helical Carbon Nanofiber Hybrid Nanostructures and Their Application for Hydrogen Peroxide and Glucose Detection
- 2013
-
Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 5:22, s. 12017-12022
-
Tidskriftsartikel (refereegranskat)abstract
- We report on a novel sensing platform for H2O2 and glucose based on immobilization of palladium-helical carbon nanofiber (Pd-HCNF) hybrid nanostnictures and glucose oxidase (GOx) with Nafion on a glassy carbon electrode (GCE). HCNFs were synthesized by a chemical vapor deposition process on a C-60-supported Pd catalyst. Pd-HCNF nanocomposites were prepared by a one-step reduction free method in dimethylformamide (DMF). The prepared materials were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), scanning electron microscopy (SEM), and Raman spectroscopy. The Nafion/Pd-HCNF/GCE sensor exhibits excellent electrocatalytic sensitivity toward H2O2 (315 mA M-1 cm(-2)) as probed by cyclic voltammetry (CV) and chronoamperometry. We show that Pd-HCNF-modified electrodes significantly reduce the overpotential and enhance the electron transfer rate. A linear range from 5.0 mu M to 2.1 mM with a detection limit of 3.0 mu M (based on the S/N = 3) and good reproducibility were obtained. Furthermore, a sensing platform for glucose was prepared by immobilizing the Pd-HCNFs and glucose oxidase (GOx) with Nafion on a glassy carbon electrode. The resulting biosensor exhibits a good response to glucose with a wide linear range (0.06-6.0 mM) with a detection limit of 0.03 mM and a sensitivity of 13 mA M-1 cm(-2). We show that small size and homogeneous distribution of the Pd nanoparticles in combination with good conductivity and large surface area of the HCNFs lead to a H2O2 and glucose sensing platform that performs in the top range of the herein reported sensor platforms.
|
|
| 9. |
- Sharifi, Hamid Reza
(författare)
-
Interplay between the Myc oncoprotein, cyclin-dependent kinases and E3 ubiquitin ligases
- 2013
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Mammalian cells grow, divide, and die in a precise and orderly fashion. For cells to grow and maintain their integrity they need to communicate at both intracellular and extracellular level. This communicative circuit is maintained by means of many different factors functioning at different level to for example receive, transmit and respond to the delivered message. Among these factors are transcription factors whose function is to regulate expression of genes downstream of transmitted signals. Myc is a transcription factor that is estimated to regulate 10%A15% of the genes in the genome and that plays an essential role in various cellular processes required for cell growth, cell division and survival. Often communication between the factors involved in signaling involves addition of small molecule moieties such as phosphate, acetyl, ubiquitin or methyl groups that is exerted through the function of enzymes like kinases, histone acetyltransferases, E3 ubiquitin ligases or histone methyltransferases. E3 ubiquitin ligases tag their substrates by mono or polyubiquitin chain molecules that will dictate the fate of the targeted protein. Ubiquitylated proteins are usually degraded by a cellular degradation machinery called the proteasome. However, depending how ubiquitin chain is formed it can serve other roles than for protein degradation, for instance in transcription. The work presented in this thesis provides insights into underlying the role of a kinase, Cdk2 as well as two E3 ubiquitin ligases, SCFFBXO28 and VHL in the regulating the function of Myc transcription factor/protoAoncoprotein. Deregulated function of Myc plays an important role in the development of many different cancer types. Despite extensive studies on the function of Myc the mechanism underlying its deregulation is still elusive. Another oncoprotein whose deregulation is involved in development of different cancers is Ras. Myc and Ras are known to cooperate in cellular transformation but the mechanism underlying their cooperation is unclear. In paper I we provided a mechanism by which these two oncogene work together in tumor development. We show that Cdk2 kinase phosphorylates Myc at SerA62 and that this phosphorylation is important for MycAmediated regulation of genes involved in cellular senescence. We show that Myc in this way suppresses RasAinduced senescence, which is one of the barriers for tumor development. This unique role of Cdk2 provides a potential therapeutical advantage to combat Myc and /or RasAdriven tumors. In paper II we identify a new E3 ubiquitin ligase, SCFFBXO28 that was found to target Myc for ubiquitylation and to play a critical role in regulation of Myc function in tumor progression. Our data further suggest that SCFFBXO28 plays an important role in transmitting Cdk activity to Myc function during the cell cycle, emphasizing the CdkAFBXO28AMyc axis as a potential molecular drug target in MycAdriven cancers. In paper III we show that Myc interacts with the tumor suppressor protein von Hippel Lindau (VHL) which is part of an E3 ubiquitin ligase complex. VHL was found to promote ubiquitylation of Myc in a nonAproteolytic fashion. We showed that VHL associates together with Myc at a subset of Myc target genes throughout the genome and activate or repress the expression of bound genes with functions in cancer development, gene expression, metabolism and other function. We also found that VHL and Myc bind to the MYC locus and regulate the MYC gene expression. Our data reveal novel functions and new modes of regulation of two of the most important oncoproteins and tumor suppressor proteins in human cancer, cAMyc and VHL, respectively. We anticipate that this work will have preclinical and potential clinical implications for cancer biology and treatment.
|
|
| 10. |
- Sharifi, Tiva, et al.
(författare)
-
Formation of nitrogen-doped graphene nanoscrolls by adsorption of magnetic gamma-Fe2O3 nanoparticles
- 2013
-
Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 4, s. 2319-
-
Tidskriftsartikel (refereegranskat)abstract
- Graphene nanoscrolls are Archimedean-type spirals formed by rolling single-layer graphene sheets. Their unique structure makes them conceptually interesting and understanding their formation gives important information on the manipulation and characteristics of various carbon nanostructures. Here we report a 100% efficient process to transform nitrogen-doped reduced graphene oxide sheets into homogeneous nanoscrolls by decoration with magnetic gamma-Fe2O3 nanoparticles. Through a large number of control experiments, magnetic characterization of the decorated nanoparticles, and ab initio calculations, we conclude that the rolling is initiated by the strong adsorption of maghemite nanoparticles at nitrogen defects in the graphene lattice and their mutual magnetic interaction. The nanoscroll formation is fully reversible and upon removal of the maghemite nanoparticles, the nanoscrolls return to open sheets. Besides supplying information on the rolling mechanism of graphene nanoscrolls, our results also provide important information on the stabilization of iron oxide nanoparticles.
|
|
