Co-reporter:Lasse Jürgensen, Michael Frank, Myeongwhun Pyeon, Lisa Czympiel, and Sanjay Mathur
Organometallics June 26, 2017 Volume 36(Issue 12) pp:2331-2331
Publication Date(Web):June 2, 2017
DOI:10.1021/acs.organomet.7b00275
A new heteroleptic Ir(I) compound exhibiting high volatility and defined thermal decomposition under CVD conditions is reported. The new iridium precursor [(COD)Ir(ThTFP)] (COD = cyclooctadiene, ThTFP = (Z)-3,3,3-trifluoro-1-(thiazol-2-yl)prop-1-en-2-olate) unifies both reactivity and sufficient stability through its heteroleptic constitution to provide a precise control over compositional purity in CVD deposits. The solution integrity of the monomeric Ir(I) complex was investigated by 1D and 2D NMR spectroscopy and EI mass spectrometry, whereas the molecular structure was confirmed by single-crystal diffraction. CVD experiments demonstrated the suitability of the iridium compound for an atom-efficient (high molecule-to-precursor yield) gas-phase deposition of nanocrystalline iridium films that could be converted into crystalline iridium dioxide upon heat treatment to demonstrate their electrocatalytic potential in the oxygen evolution reaction.
Co-reporter:David Graf, Johannes Schläfer, Simon Garbe, Axel Klein, and Sanjay Mathur
Chemistry of Materials July 25, 2017 Volume 29(Issue 14) pp:5877-5877
Publication Date(Web):July 3, 2017
DOI:10.1021/acs.chemmater.7b01018
Phase selective chemical vapor deposition of nanostructured vanadium dioxide (VO2) and sesquioxide (V2O3) was achieved by deploying [V(OR)4]n (R = tBu, n = 1 (1), R = Et, n = 3 (2), R = Me, n = 4 (3)). Use of [V(OtBu)4] (1) produced thin films of monoclinic VO2 (M1) at 700 and 800 °C consisting of anisotropic nanostructures with high crystallinity and small hysteresis in the metal-to-semiconductor transition (MST). Film morphologies manifested strong dependence on growth temperatures and exhibited pronounced texturing effects at high temperatures (>700 °C). The microstructure of the films was found to significantly affect the MST behavior of VO2 films. DTA measurements of VO2 films showed MST at 63 °C (700 °C) and 65 °C (800 °C), much lower than the transition temperature observed in single crystal material (68 °C). Precursors were characterized in the solid state (XRD) and solution state (temperature dependent EPR, NMR) to reveal an association–dissociation equilibrium in solution (complexes 2 and 3), involving monomeric, dimeric, and oligomeric species. Use of 2 and 3 as single precursors produced thin films of crystalline V2O3 consisting of nanosheets (5 nm) with a flower-like morphology.
Co-reporter:Tim HeidemannSanjay Mathur
Inorganic Chemistry 2017 Volume 56(Issue 1) pp:234-240
Publication Date(Web):December 13, 2016
DOI:10.1021/acs.inorgchem.6b02069
New structural motifs in ternary metal alkoxides are demonstrated through synthetic strategies that enable overcoming statistical barriers and solution equilibrium. Tetradentate dimetalate unit, {M2(OiPr)9}− (M = Hf (1), Zr (2)), used to sequester the coordination sphere of the central metal atom (Ba), allowed step-by-step construction of termetallic molecules [{M′(OiPr)4}(HOiPr)Ba{M2(OiPr)9}] (M′ = Al (3), Ga (4), M = Hf; M′ = Al, M = Zr (5)). In contrast to a common “coordinative-fit” approach mainly used for bimetallic compounds, this stepwise rational construction using fast successive salt metathesis reactions circumvents general challenges in the syntheses of termetallic alkoxides by avoiding the thermodynamically preferred formation of bimetallic alkoxide molecules. The presented compounds exhibit for the first time gas phase stable termetallic alkoxide frameworks.
Co-reporter:Lisa Czympiel, Jean-Marius Lekeu, Corinna Hegemann, Sanjay Mathur
Inorganica Chimica Acta 2017 Volume 455(Part 1) pp:197-203
Publication Date(Web):30 January 2017
DOI:10.1016/j.ica.2016.10.023
•Four dihalo tin(IV) heteroarylalkenolate compounds are presented.•Synthetic approaches through oxidative halogenation and ligand exchange have been exploited.•The chloro-, bromo- and iodo-derivative feature an unusual trans-configuration.•The structures have been elucidated by spectroscopic and X-ray techniques.A series of novel tin(IV)-heteroaryl alkenolates of the general formula [Sn(DMOTFP)2X2] (3–6, X = F, Cl, Br, I) were prepared by direct oxidative halogenation of the corresponding tin(II) derivative [SnII(DMOTFP)2] (2) and by cleavage of the carbon-tin bonds in diphenyltin dichloride [Ph2SnCl2] by (4,5-dimethyloxazolyl)-1,1,1-trifluoropropen-2-ol, (H-DMOTFP, 1) with a subsequent halide exchange reaction. The molecular structures elucidated in solution (multi-nuclear NMR spectroscopy) and by single crystal X-ray diffraction confirmed the sixfold coordination of the tin(IV) center with a distorted octahedral arrangement of ligands. An unusual centrosymmetric octahedral trans-dihalo configuration was found for the compounds [SnIV(DMOTFP)2X2] (X = Cl, Br, I), while the compound [Sn(DMOTFP)2F2] adopted a cis-dihalide configuration.Four new dihalo tin(IV) heteroarylalkenolate complexes were readily accessible by oxidative halogenation and ligand exchange reactions. This very atom economic approach led to the formation of the unusual trans-dihalo configuration of the complexes [Sn(DMOTFP)2X2] where X = Cl, Br, I.
Co-reporter:Rishabh Garg;Corinna Hegemann
European Journal of Inorganic Chemistry 2017 Volume 2017(Issue 28) pp:3383-3389
Publication Date(Web):2017/08/02
DOI:10.1002/ejic.201700331
Attempts to synthesize Cd–M (M = Nb, Ta) heterobimetallic complexes by salt metathesis reaction resulted in the unexpected structural motif [I2CdII2MV(OiPr)7]2 [M = Nb (2), Ta (3)]. Multinuclear NMR analysis revealed the coexistence of multiple products in solution. Donor solvents influenced the formation of different intermediate species in solution, as was proven by 113Cd NMR spectroscopic data. The isolation of trimetallic [I2Cd{Ta(OiPr)6}K(HOiPr)2]4 (4) and the adduct [I2CdTa(OiPr)5(thf)] (5) provided insight into the reaction mechanism. By exploiting the Lewis acidic nature of cadmium alkoxides, different compounds could be synthesized and thoroughly characterized by spectroscopic methods and single-crystal X-ray diffraction studies. Heterobimetallic compounds with the formula [CdIIMV(OiPr)7]2 [M = Nb (6), Ta (7)] produced pyrochlore phases from an amorphous ceramic homogenate, which indicates their potential as single-source precursors, as was confirmed by thermogravimetric/differential thermal analysis, which showed that complexes 6 and 7 undergo facile two-step thermal decomposition at 600 °C to produce Cd2Nb2O7 and Cd2Ta2O7, respectively. Variable-temperature X-ray diffraction analysis of 6 additionally proved the formation of crystalline Cd2Nb2O7 phase.
Co-reporter:Jing Su, Dongfang Wang, Lena Nörbel, Jianlei Shen, Zhihan Zhao, Yanzhi Dou, Tianhuan Peng, Jiye Shi, Sanjay MathurChunhai Fan, Shiping Song
Analytical Chemistry 2017 Volume 89(Issue 4) pp:
Publication Date(Web):January 25, 2017
DOI:10.1021/acs.analchem.6b04729
Uniform silver-containing metal nanostructures with strong and stable surface-enhanced Raman scattering (SERS) signals hold great promise for developing ultrasensitive probes for biodetection. Nevertheless, the direct synthesis of such ready-to-use nanoprobes remains extremely challenging. Herein we report a DNA-mediated gold–silver nanomushroom with interior nanogaps directly synthesized and used for multiplex and simultaneous SERS detection of various DNA and RNA targets. The DNA involved in the nanostructures can act as not only gap DNA (mediated DNA) but also probe DNA (hybridized DNA), and DNA’s involvement enables the nanostructures to have the inherent ability to recognize DNA and RNA targets. Importantly, we were the first to establish a new method for the generation of multicolor SERS probes using two different strategies. First Raman-labeled alkanethiol probe DNA was assembled on gold nanoparticles, and second, thiol-containing Raman reporters were coassembled with the probe DNA. The ready-to-use probes also give great potential to develop ultrasensitive detection methods for various biological molecules.
Co-reporter:Mehtap Büyükyazi;Thomas Fischer;Penmgei Yu;Mariona Coll
Dalton Transactions 2017 vol. 46(Issue 38) pp:12996-13001
Publication Date(Web):2017/10/03
DOI:10.1039/C7DT02757E
We present a new and efficient cobalt precursor, CoII(DMOCHCOCF3)2, to prepare Co3O4 thin films and conformal coatings. In the synthesis of this Co complex, heteroaryl moieties and CF3-groups were combined leading to the precursor with high thermal stability and volatility. The suitability of this precursor for ALD deposition was tested on flat silicon substrates and TiO2/C nanofibers upon process optimization. Deposition at 200 °C results in homogeneous and smooth Co3O4 thin films with a growth rate of 0.02 nm per cycle. Conformal coatings have been successfully obtained on TiO2/C nanofibers, making them an attractive platform for surface chemistry studies on high aspect ratio structures for future photocatalysts, sensors, supercapacitors and batteries.
Co-reporter:Raquel Fiz, Linus Appel, Antonio Gutiérrez-Pardo, Joaquín Ramírez-Rico, and Sanjay Mathur
ACS Applied Materials & Interfaces 2016 Volume 8(Issue 33) pp:21423
Publication Date(Web):July 15, 2016
DOI:10.1021/acsami.6b03945
We report here on the controlled synthesis, characterization, and electrochemical properties of different polymorphs of niobium pentoxide grown by CVD of new single-source precursors. Nb2O5 films deposited at different temperatures showed systematic phase evolution from low-temperature tetragonal (TT-Nb2O5, T-Nb2O5) to high temperature monoclinic modifications (H–Nb2O5). Optimization of the precursor flux and substrate temperature enabled phase-selective growth of Nb2O5 nanorods and films on conductive mesoporous biomorphic carbon matrices (BioC). Nb2O5 thin films deposited on monolithic BioC scaffolds produced composite materials integrating the high surface area and conductivity of the carbonaceous matrix with the intrinsically high capacitance of nanostructured niobium oxide. Heterojunctions in Nb2O5/BioC composites were found to be beneficial in electrochemical capacitance. Electrochemical characterization of Nb2O5/BioC composites showed that small amounts of Nb2O5 (as low as 5%) in conjunction with BioCarbon resulted in a 7-fold increase in the electrode capacitance, from 15 to 104 F g–1, while imparting good cycling stability, making these materials ideally suited for electrochemical energy storage applications.Keywords: biomorphic carbon; chemical vapor deposition; electrochemical energy storage; niobium oxides; precursors
Co-reporter:J. Schläfer, D. Graf, G. Fornalczyk, A. Mettenbörger, and S. Mathur
Inorganic Chemistry 2016 Volume 55(Issue 11) pp:5422-5429
Publication Date(Web):May 9, 2016
DOI:10.1021/acs.inorgchem.6b00348
High-yield synthesis of four new fluorinated enaminones LH2 (RfC(O)C2H2NH)2C2H4 (Rf = CF3 (2a), C2F5 (2b), C3F7 (2c)) and (F3CC(O)C2H2NH)2C3H6 (2a′) as dianionic ligands is described. The ligands were characterized in solution (via nuclear magnetic resoannce (NMR)) as well as in the solid state (via X-ray diffraction (XRD)). The ligating ability of the enaminones was verified by reacting them with [Ce2(OiPr)8(HOiPr)2], which resulted in monomeric cerium(IV) complexes [CeL2] (3a–c, 3a′) based on tetradentate chelation of the ligands. Cerium enaminolates were comprehensively analyzed by NMR spectroscopy, mass spectrometry, and single-crystal XRD studies to verify their monomeric nature. High stability under ambient conditions and high volatility makes them a potential precursor for the gas-phase synthesis of CeO2. Complexes 3a and 3b were applied as precursors in thermal and plasma-enhanced chemical vapor deposition to obtain crystalline ceria films with different surface morphologies. The purity and surface states of the films were analyzed by X-ray photoelectron spectroscopy, which revealed a high amount of Ce3+ on the subsurface of CeO2 films.
Co-reporter:Aida Jamil, Johannes Schläfer, Yakup Gönüllü, Ashish Lepcha, and Sanjay Mathur
Crystal Growth & Design 2016 Volume 16(Issue 9) pp:5260-5267
Publication Date(Web):August 10, 2016
DOI:10.1021/acs.cgd.6b00815
Single phase rare earth pyrochlores, Ln2M2O7, were produced as nanofibers and thin films by electrospinning and spin-coating of chemical sols obtained from bimetallic metal–organic precursors, LnIIIMII(OtBu)5Py (LnIII = La, Pr, Nd, Sm, Er, Yb; MII = Ge, Sn, Pb; Py = pyridine). Compatibility of the metal ratio in the single-source compounds was confirmed by single crystal X-ray diffraction analyses and the ratio was preserved during the processing as the crystalline pyrochlore materials originated from an amorphous preceramic aggregate as confirmed by powder XRD and TEM studies. The photocatalytic activity of the Nd2Sn2O7 nanofibers was found to be significantly higher than that of TiO2. Nd2Sn2O7 thin films deposited on F:SnO2 as bilayered Nd2Sn2O7//Fe2O3 photoanodes showed superior photoelectrochemical (PEC) efficiency for water splitting reaction with an over 3-fold higher photocurrent density than bare Fe2O3 photoanodes.
Co-reporter:Ali Kaouk, Tero-Petri Ruoko, Myeongwhun Pyeon, Yakup GönüllüKimmo Kaunisto, Helge Lemmetyinen, Sanjay Mathur
The Journal of Physical Chemistry C 2016 Volume 120(Issue 49) pp:28345-28353
Publication Date(Web):November 18, 2016
DOI:10.1021/acs.jpcc.6b10432
The effects of intermittent thin ITO layers on the water-splitting efficiency of α-Fe2O3 films grown by PECVD on FTO substrates are reported. The α-Fe2O3 was codoped with indium and tin by temperature-driven ionic transport and diffusion from the ultrathin ITO layer sputtered between the α-Fe2O3 layer and FTO substrate. The α-Fe2O3/ITO/FTO photoanodes showed a remarkable interdependence between the thickness of the ITO layer and PEC efficiency. Hematite photoanodes with a 32 nm thick ITO underlayer showed the highest photocurrent density of 2.5 mA cm–2, corresponding to an approximate 3-fold enhancement over pristine α-Fe2O3 at 1.23 V vs RHE, whereas the thinner (8 nm) ITO underlayer yielded the lowest onset potential at 0.6 V vs RHE. Although the electrode with a thicker 72 nm ITO underlayer showed a higher onset potential of 0.9 V vs RHE, it still showed an enhancement in the photocurrent density at higher bias voltages. α-Fe2O3 was also deposited on metallic titanium substrates with intermittent sputtered tin and ITO layers. The codoping with indium and tin from ITO was observed to yield greatly enhanced performance when compared with both α-Fe2O3 alone and tin-doped α-Fe2O3. Transient absorption decays in the sub-nanosecond time scale were not affected by the doping, indicating that the doping had little effect on the primary charge carrier generation and recombination. On the other hand, fewer trapped electrons on the microsecond to millisecond time scale and a greatly increased amount of long-lived surface photoholes were observed for the ITO-doped samples. The transient absorption results imply that the large increases in photoelectrochemical efficiency were obtained due to higher electron mobility, which reduces recombination and leads to more efficient electron extraction from the electrodes.
Co-reporter:O. Arslan, L. Belkoura and S. Mathur
Journal of Materials Chemistry A 2015 vol. 3(Issue 45) pp:11965-11973
Publication Date(Web):04 Nov 2015
DOI:10.1039/C5TC03377B
Stable oleate capped, visible light emitting ZnO quantum dots (QDs) have been synthesized by a modified sol–gel method and examined for large-scale synthesis. Surface chelation with oleate ligands and their implications on particle growth were investigated by comprehensive NMR experiments and photoluminescence measurements. High-resolution electron microscopy and X-ray diffraction confirmed the high crystallinity and well-dispersed character of the ZnO QDs. The here investigated ZnO nanocrystals were found to be suitable for phase transfer synthesis (non-polar to polar dispersion medium) even after prolonged storage time that was verified by unchanged visible light emission. The absorption wavelength could be tuned by adjusting the nucleation kinetics and upon anchoring bulky ligands that provide control over the surface defects responsible for the optical (visible) properties. The demonstrated phase transfer studies make visible light emitting ZnO QDs accessible for a wide range of applications like ink-jet printing for nano-electronics, cell labelling or theranostic studies.
Co-reporter:Lisong Xiao, Marianne Mertens, Laura Wortmann, Silke Kremer, Martin Valldor, Twan Lammers, Fabian Kiessling, and Sanjay Mathur
ACS Applied Materials & Interfaces 2015 Volume 7(Issue 12) pp:6530
Publication Date(Web):March 2, 2015
DOI:10.1021/am508404t
Fully green and facile redox chemistry involving reduction of colloidal iron hydroxide (Fe(OH)3) through green tea (GT) polyphenols produced water-soluble Fe3O4 nanocrystals coated with GT extracts namely epigallocatechin gallate (EGCG) and epicatechin (EC). Electron donating polyphenols stoichiometrically reduced Fe3+ ions into Fe2+ ions resulting in the formation of magnetite (Fe3O4) nanoparticles and corresponding oxidized products (semiquinones and quinones) that simultaneously served as efficient surface chelators for the Fe3O4 nanoparticles making them dispersible and stable in water, PBS, and cell culture medium for extended time periods. As-formed iron oxide nanoparticles (2.5–6 nm) displayed high crystallinity and saturation magnetization as well as high relaxivity ratios manifested in strong contrast enhancement observed in T2-weighted images. Potential of green tea-coated superparamagnetic iron oxide nanocrystals (SPIONs) as superior negative contrast agents was confirmed by in vitro and in vivo experiments. Primary human macrophages (J774A.1) and colon cancer cells (CT26) were chosen to assess cytotoxicity and cellular uptake of GT-, EGCGq-, and ECq-coated Fe3O4 nanoparticles, which showed high uptake efficiencies by J774A.1 and CT26 cells without any additional transfection agent. Furthermore, the in vivo accumulation characteristics of GT-coated Fe3O4 nanoparticles were similar to those observed in clinical studies of SPIONs with comparable accumulation in epidermoid cancer-xenograft bearing mice. Given their promising transport and uptake characteristics and new surface chemistry, GT-SPIONs conjugates can be applied for multimodal imaging and therapeutic applications by anchoring further functionalities.Keywords: biocompatible probes; green tea catechins; iron oxide nanoparticles; magnetic resonance imaging (MRI); superparamagnetic carriers
Co-reporter:David Zopes, Corinna Hegemann, Johannes Schläfer, Wieland Tyrra, and Sanjay Mathur
Inorganic Chemistry 2015 Volume 54(Issue 8) pp:3781-3787
Publication Date(Web):April 9, 2015
DOI:10.1021/ic502924s
Multiple silver(I)-aurates(I) have been prepared by salt metathesis reactions that act as efficient single-source precursors to colloidal gold silver alloys with the highest possible atom economy in the chemical synthesis of nanostructures. The CF3 group present on the Au cation acts as an in situ reducing agent and can be converted into CO ligands by simple hydrolysis. This ligand-mediated activation and subsequent decomposition of metal–organic precursors impose a molecular control over the nucleation process, producing homogeneously alloyed (Ag–Au) nanoparticles with an atomic Au:Ag ratio of 1:1. The concept also works for the Au–Cu system and acts as a pointer to replace Au (Ag) with less expensive (Cu) metals.
Co-reporter:Lisa Czympiel; Johannes Pfrommer; Wieland Tyrra; Mathias Schäfer
Inorganic Chemistry 2015 Volume 54(Issue 1) pp:25-37
Publication Date(Web):December 19, 2014
DOI:10.1021/ic502549m
Synthesis and characterization (gas phase, solution, and solid-state) of a series of four-, five- and six-fold coordinated heteroaryl-alkenolato aluminum complexes were performed to demonstrate the delicate interplay of structural and chemical influences of ligands in the design of new precursors for chemical vapor deposition. We are investigating the properties of heteroaryl alkenols as O^N chelating ligands [where O^N is 3,3,3-trifluoro(pyridin-2-yl)propen-2-ol (H-PyTFP), 3,3,3-trifluoro(1,3-benzimidazol-2-yl)propen-2-ol (H-BITFP), 3,3,3-trifluoro(dimethyl-1,3-oxazol-2-yl)propen-2-ol (H-DMOTFP), 3,3,3-trifluoro(1,3-benzoxazol-2-yl)propen-2-ol (H-BOTFP), 3,3,3-trifluoro(1,3-benzthiazol-2-yl)propen-2-ol (H-BTTFP), and 3,3,3-trifluoro(dimethyl-1,3-thiazol-2-yl)propen-2-ol (H-DMTTFP)] to prepare volatile and air-stable compounds. All three methyl groups in highly reactive AlMe3 could be replaced by H-PyTFP, H-BITFP, H-DMOTFP, and H-BOTFP yielding octahedral complexes of the type Al(O^N)3; under similar conditions H-BTTFP and H-DMTTFP produced heteroleptic MeAl(O^N)2 compounds with five-fold coordinated aluminum centers. Various attempts to obtain tris-alkenolato derivatives by choosing higher temperatures and prolonged reaction times were not successful. The reaction of H-PyTFP with [Al(OtBu)3]2 produced the dimeric heteroleptic [Al(PyTFP)(OtBu)2]2 complex with Al atoms present in both octahedral (Oh) and tetrahedral (Td) coordination in a single molecular unit. The introduction of the chelating ligand H-PyTFP in the dimeric framework of [Al(OtBu)3]2 enhanced the stability against hydrolyses significantly. The tendency of Al(III) centers to preferably coordinate in Td or Oh environment was elucidated by hydrolysis studies of monomeric Al(PyTFP)3, Al(BOTFP)3, and MeAl(BTTFP)2 that produced hydroxo-bridged dimers to retain the octahedral environment for Al atoms. Surprisingly, hydrolysis of monomeric MeAl(DMTTFP)2 yielded an oxo-bridged dimer with two five-fold coordinated aluminum centers. The structural features of all new complexes were investigated in solution, vapor, and solid state by multinuclear NMR spectroscopy, EI-MS spectrometry, and single-crystal X-ray diffraction analyses, respectively.
Co-reporter:Eva Hemmer, Christian Cavelius, Volker Huch, and Sanjay Mathur
Inorganic Chemistry 2015 Volume 54(Issue 13) pp:6267-6280
Publication Date(Web):June 12, 2015
DOI:10.1021/acs.inorgchem.5b00529
Four new praseodymium alkoxo and amido compounds ([Pr3(μ3-OtBu)2(μ2-OtBu)3(OtBu)4(HOtBu)2] (1), [Pr{OC(tBu)3}3(THF)] (2), [PrCl{N(SiMe3)2}2(THF)]2 (3), and [PrCl{OC(tBu)3}2(THF)]2 (4)) were synthesized and structurally characterized by single-crystal X-ray diffraction analysis. Application of these compounds in solvothermal synthesis of praseodymium oxide/hydroxide nanostructures showed their templating influence on the morphology and phase composition of the resulting solid-state materials. Differential reactivity of the chosen alkoxide ligands toward water and the different arrangements of metal–oxygen units in the studied precursor compounds strongly influenced the kinetics of hydrolysis and cross-condensation reactions as manifested in the morphological changes and phase composition of the final products. Thermal decomposition studies of 1–4 confirmed their conversion into the corresponding oxide phases. Activation of compounds 1, 2, and 4 by either a base or a stoichiometric amount of water showed the distinct influence of their chemical configuration on the obtained nanopowders: whereas 1 solely produced nanorods of Pr(OH)3, 2 predominantly formed a mixture of rod-shaped and spherical particles. The solvothermal decomposition of 4 resulted in Pr(OH)2Cl or PrOCl due to the presence of Cl ligands in the molecular precursor. The resultant materials were thoroughly characterized to demonstrate the relationship between precursor chemistry and the processing parameters that are clearly manifested in the morphology and phase of the final ceramics.
Co-reporter:Linus Appel, Raquel Fiz, Wieland Tyrra, Ingo Pantenburg, and Sanjay Mathur
Crystal Growth & Design 2015 Volume 15(Issue 3) pp:1141-1149
Publication Date(Web):February 3, 2015
DOI:10.1021/cg501438k
Synthesis and structural characterization of six monomeric, heteroleptic tantalum(V) complexes of the general formula Ta(OiPr)4(ArTFP), where Ar = pyridine (1), 4,5- dimethyloxazole (2), 4,5-dimethylthiazole (3), benzimidazole (4), benzoxazole (5), benzthiazole (6), and TFP = trifluoropropenol, are described. Introduction of a donor-functionalized β-heteroarylalkenolate in the coordination sphere of Ta in the dimeric Ta2(OiPr)10 increases significantly the stability and volatility of these precursors, simplifying the depositions of Ta2O5. The molecular structures of 1–6 exhibited a distorted octahedral coordination around the tantalum center by four isopropoxide groups and one β-heteroarylalkenolate. Thermal decomposition studies (TG/DTA) and analysis of byproducts by NMR spectroscopy confirmed the decomposition mechanism and gas-phase stability of the heteroleptic compounds necessary for Ta2O5 depositions. Chemical vapor deposition studies with 1 and 2 demonstrated their suitability as efficient precursors for the growth of Ta2O5 thin films, whose properties were compared with Ta2O5 thin films obtained from homoleptic alkoxides.
Co-reporter:Jennifer Leduc, Rajitha Ravithas, Lisa Rathgeber and Sanjay Mathur
New Journal of Chemistry 2015 vol. 39(Issue 10) pp:7571-7574
Publication Date(Web):23 Jul 2015
DOI:10.1039/C5NJ00647C
Herein we report the synthesis and characterization of new air-stable uranium(IV) complexes based on three different heteroarylalkenolate ligands namely DMOPFB (1) (1-(4,5-dimethyl-oxazol-2-yl)-3,3,4,4,4-pentafluoro-but-1-en-2-ol) with an elongated fluorinated alkyl chain compared to DMOTFP (2) (3,3,3-trifluoro-1-(4,5-dimethyloxazol-2-yl) propen-2-ol) and the tetradentate enaminone TFB-en (3) (N,N′-bis-(4,4,4-trifluorobut-1-en-3-on)-ethylenediamine). These new complexes exhibit sufficiently high volatilities, with respect to previously reported uranium compounds, and are thus promising precursors for chemical vapor deposition (CVD) of uranium oxide materials.
Co-reporter:Trilok Singh, Ralf Müller, Jai Singh, Sanjay Mathur
Applied Surface Science 2015 Volume 347() pp:448-453
Publication Date(Web):30 August 2015
DOI:10.1016/j.apsusc.2015.04.126
Highlights
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WO3 thin films have been synthesized by reactive sputtering under oxygen atmosphere.
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Surface treatment of WO3 influences the optical and photoelectrochemical properties.
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Tailoring the surface properties by (i) hydrogen plasma treatment and (ii) anchoring plasmonic nanoparticles (Au and Ag) altered the light harvesting and charge separation/transport processes of WO3 photoanodes.
Co-reporter:A. Kaouk, T.-P. Ruoko, Y. Gönüllü, K. Kaunisto, A. Mettenbörger, E. Gurevich, H. Lemmetyinen, A. Ostendorf and S. Mathur
RSC Advances 2015 vol. 5(Issue 123) pp:101401-101407
Publication Date(Web):13 Nov 2015
DOI:10.1039/C5RA18330H
Interfacial modification of α-Fe2O3/TiO2 multilayer photoanodes by intercalating few-layer graphene (FLG) was found to improve water splitting efficiency due to superior transport properties, when compared to individual iron and titanium oxides and heterojunctions thereof. Both metal oxides and graphene sheets were grown by plasma-enhanced chemical vapor deposition. Compared to the onset potential achieved for α-Fe2O3 films (1 V vs. RHE), the α-Fe2O3/TiO2 bilayer structure yielded a better onset potential (0.3 V vs. RHE). Heterojunctioned bilayers exhibited a higher photocurrent density (0.32 mA cm−2 at 1.23 V vs. RHE) than the single α-Fe2O3 layer (0.22 mA cm−2 at 1.23 V vs. RHE), indicating more efficient light harvesting and higher concentration of photogenerated charge carriers. For more efficient charge transport at the interface, a few layer graphene sheet was intercalated into the α-Fe2O3/TiO2 interface, which substantially increased the photocurrent density to 0.85 mA cm−2 (1.23 V vs. RHE) and shifted the onset potential (0.25 V vs. RHE). Ultrafast transient absorption spectroscopy studies indicated that the incorporation of FLG between the α-Fe2O3 and TiO2 layers resulted in reduced recombination in the α-Fe2O3 layer. The results showed that graphene intercalation improved the charge separation and the photocurrent density of the FTO/α-Fe2O3/FLG/TiO2 system.
Co-reporter:A. Lepcha
The Journal of Physical Chemistry C 2015 Volume 119(Issue 33) pp:18835-18842
Publication Date(Web):July 20, 2015
DOI:10.1021/acs.jpcc.5b02767
This work encompasses a facile method for tailoring surface defects in electrospun TiO2 nanofibers by employing hydrogen plasma treatments. This amiable processing method was proven with SQUID, EPR, and XPS to be highly effective in generating oxygen vacancies, accompanied by the reduction of Ti4+ centers to Ti3+, resulting in the formation of black titania. The treatment temperature was found to affect the Ti3+/Ti4+ ratios and surface valence, while preserving the original 1D morphology of the titania fibers. Ab initio DFT calculations showed that a high concentration of oxygen vacancies is highly efficient in producing midgap states that enhance the system absorption over the whole visible range, as observed with UV/vis/NIR diffuse reflectance spectroscopy. Pristine TiO2 nanofibers produced a photocurrent density of ∼0.02 mA/cm2 at 1.23 V vs RHE, whereas the hydrogen plasma treatment resulted in up to a 10-fold increase in the photoelectrochemical performance.
Co-reporter:Mehtap Büyükyazi, Sanjay Mathur
Nano Energy 2015 Volume 13() pp:28-35
Publication Date(Web):April 2015
DOI:10.1016/j.nanoen.2015.02.005
•Fabrication of 3D electrode architecture for Li-ion batteries based on electrospun α-LiFeO2 and α-LiFeO2/C composites.•The experimental findings underscore that the synergic mechanisms in nanomaterials and nanocomposite often depend on the preparation methods and judicious choice of phase-forming elements.•High discharge capacities of 756 mAh/g for α-LiFeO2 and 821 mAh/g for α-LiFeO2/C were achieved.Hydrodynamic structuring of alkoxide-based sols in an electrical field is a promising technique to fabricate one-dimensional materials as free-standing fiber mats with high surface area and precisely controlled microstructure. Hollow α-LiFeO2 and composite α-LiFeO2/C nanofibers were prepared as self-supported 3D architectures of ceramic fibers by single-step electrospinning of metal alkoxide sols. The spinel fibers exhibited a crystalline spinel phase with uniform fiber diameter and morphology that was modified by a thin sheath of amorphous carbon in the composite fibers that enhances the electrical conductivity and also has a structure-holding influence. The atomic scale mixing and pre-existing LiOFe units in the spinning solution were the delivers of observed phase purity and control over the surface properties verified by high resolution TEM data. Galvanostatic and potentiostatic studies confirmed the superior electrochemical behaviors of α-LiFeO2 and α-LiFeO2/C nanofibers as high-energy density anode materials in half-cell configuration. α-LiFeO2/C composite nanofibers showed after 50 cycles a discharge capacity of 821 mAh/g at 0.1 C with a capacity retention of 75% from the 2nd to 50th cycle, whereas the discharge capacity of α-LiFeO2-hollow nanofibers was found to be 756 mAh/g with a capacity retention of 68%. Flexible composite nanofiber networks are promising solution enabling improved electronic and ionic conductivity and mechanical stability for the development of lithium-ion batteries with high power and energy densities. Investigations on the stability and rate capability of α-LiFeO2/C-composite electrode studied at different rates of 0.1 C, 0.25 C and 0.5 C for 75 cycles also showed high capacity values that indicated their potential as anode materials.Self-supporting 3D Nanoarchitectures of α-LiFeO2 and α-LiFeO2/C Nanofibers for High Power Lithium-Ion Batteries.Self-supported 3D architectures of hollow α-LiFeO2 and composite α-LiFeO2/C nanofibers fabricated by coaxial electrospinning of metal alkoxide sols are high-energy density anode materials with superior electrochemical performance.
Co-reporter:Laura Wortmann, Shaista Ilyas, Daniel Niznansky, Martin Valldor, Karim Arroub, Nadja Berger, Kamil Rahme, Justin Holmes, and Sanjay Mathur
ACS Applied Materials & Interfaces 2014 Volume 6(Issue 19) pp:16631
Publication Date(Web):September 3, 2014
DOI:10.1021/am503068r
A facile bottom-up approach for the synthesis of inorganic/organic bioconjugated nanoprobes based on iron oxide nanocubes as the core with a nanometric silica shell is demonstrated. Surface coating and functionalization protocols developed in this work offered good control over the shell thickness (8–40 nm) and enabled biovectorization of SiO2@Fe3O4 core–shell structures by covalent attachment of folic acid (FA) as a targeting unit for cellular uptake. The successful immobilization of folic acid was investigated both quantitatively (TGA, EA, XPS) and qualitatively (AT-IR, UV–vis, ζ-potential). Additionally, the magnetic behavior of the nanocomposites was monitored after each functionalization step. Cell viability studies confirmed low cytotoxicity of FA@SiO2@Fe3O4 conjugates, which makes them promising nanoprobes for targeted internalization by cells and their imaging.Keywords: bioconjugated nanoprobes; cytotoxicity; folic acid; iron oxide-silica core−shell particles; magnetic properties
Co-reporter:Vanchiappan Aravindan, Jayaraman Sundaramurthy, Elumalai Naveen Kumar, Palaniswamy Suresh Kumar, Wong Chui Ling, Robin von Hagen, Sanjay Mathur, Seeram Ramakrishna, Srinivasan Madhavi
Electrochimica Acta 2014 Volume 121() pp:109-115
Publication Date(Web):1 March 2014
DOI:10.1016/j.electacta.2013.12.141
In this paper, we report the influence of carbon coating on the electrochemical performance of hollow structured SnO2 electrospun nanofibers. The electrospun nanofibers are subjected to plasma enhanced chemical vapour deposition for a conformal carbon coating of ∼6 nm thickness without destroying the one dimensional morphological features of the fiber mats. Li-storage properties are evaluated in half-cell configuration between two different potential windows i.e. 0.005-0.8 V and 0.005-2.5 V vs. Li. The potential regions tested corresponds to the alloying/de-alloying and alloying/de-alloying & conversion reactions for former and latter cases, respectively. Very high reversibility over 3.6 moles of Li is feasible for both bare and carbon coated SnO2, without an obvious difference between the electrochemical profiles noted during cycling. In contrary, huge differences in the electrochemical performances are observed for bare and carbon coated SnO2 when the test cell is cycled for conversion reaction. This result clearly shows the importance of carbon coating for conversion reaction compared to alloying/de-alloying reaction.
Co-reporter:Mehtap Büyükyazi, Corinna Hegemann, Thomas Lehnen, Wieland Tyrra, and Sanjay Mathur
Inorganic Chemistry 2014 Volume 53(Issue 20) pp:10928-10936
Publication Date(Web):October 2, 2014
DOI:10.1021/ic501157e
Two new cobalt precursors, CoII(PyCHCOCF3)2(DMAP)2 (1) and CoIII(PyCHCOCF3)3 (2), based on Co(II) and Co(III) centers were synthesized using a redox active ligand system. The different chemical configurations of 1 and 2 and differential valence states of cobalt were confirmed by crystal structure determination and comprehensive analytical studies. Whereas 1 could not be studied by NMR due to the paramagnetic nature of the central atom, 2 was unambiguously characterized by multinuclear 1D and 2D NMR experiments in solution. Both compounds are efficient precursors for catalyst-free growth of Co3O4 nanowires on Si and Al2O3 substrates by a chemical vapor deposition process. The different valence states of cobalt species influenced their chemical decomposition pathways in the gas phase; for instance, 1 was partially oxidized (Co2+ → Co3+), and 2 underwent reduction (Co3+ → Co2+) to form pure cobaltite in both cases that verified the metal–ligand redox interplay. Co3O4 nanowires with nanometric diameters (50–100 nm) were obtained irrespective of the chosen cobalt precursor. Investigations on the humidity sensing behavior of CVD deposits demonstrated their potential as promising sensor materials.
Co-reporter:Johannes Schläfer, Wieland Tyrra, and Sanjay Mathur
Inorganic Chemistry 2014 Volume 53(Issue 6) pp:2751-2753
Publication Date(Web):March 3, 2014
DOI:10.1021/ic4025876
An advanced synthesis for the homometallic derivative [Ce2(OtBu)8] (1) starting from [Ce(OtBu)2{N(SiMe3)2}2] was developed. Structural characterization of a cerium(IV) complex and its decomposition products confirmed the coexistence of both ether elimination and Ce–O bond cleavage processes, which lead to the formation of [Ce3O(OtBu)10] and [Ce3(OtBu)11] (2) derivatives, respectively. Variable-temperature NMR spectroscopy under strict exclusion of moisture enabled insight into the decomposition processes in noncoordinating solvents and at elevated temperature. In addition, structural analysis of the heterovalent 2 and of two new complexes of the general formula [Ce2(OtBu)8(L)] [L = HOtBu (3), OCPh2 (4)] is described.
Co-reporter:Gregor Fornalczyk, Martin Valldor, and Sanjay Mathur
Crystal Growth & Design 2014 Volume 14(Issue 4) pp:1811-1818
Publication Date(Web):February 27, 2014
DOI:10.1021/cg401930n
Aryl substituted β-alkenol 1-(dimethyl-1,3-thiazol-2-yl)-3,3,3-trifluoropropenol (DMTTFP) was employed as an efficient metal chelator to obtain volatile monomeric precursors containing FeII and FeIII centers. [Fe(DMTTFP)2] (1) and [Fe(DMTTFP)2(OBut)] (2) were synthesized by reacting suitable starting materials with DMTTFP. The molecular structures were elucidated by single-crystal X-ray diffraction analyses, which revealed a distorted tetrahedral and a trigonal-bipyramidal arrangement of ligands around iron atoms in 1 and 2, respectively. Magnetic investigations confirmed [Fe(DMTTFP)2] to exhibit a thermally populated spin-state transition that becomes apparent below 10 K. The high-spin state was gradually transferred to a low-spin state on cooling, suggesting a nonmagnetic ground state. [Fe(DMTTFP)2(OBut)] exhibited enhanced stability, sufficient volatility, and decomposition behavior serving as an efficient FeIII precursor for the growth of iron oxide layers on an Al2O3 substrate via chemical vapor deposition.
Co-reporter:Andreas Mettenbörger, Trilok Singh, Aadesh P. Singh, Tommi T. Järvi, Michael Moseler, Martin Valldor, Sanjay Mathur
International Journal of Hydrogen Energy 2014 Volume 39(Issue 10) pp:4828-4835
Publication Date(Web):26 March 2014
DOI:10.1016/j.ijhydene.2014.01.080
•Hematite films were deposited using PE-CVD at room temperature.•Films were modified by hydrogen plasma treatment at various temperatures.•Modified sample showed enhanced photocurrent density (3.5 mA/cm2).•Photocurrent onset potential reduced up to 0.4 V.We demonstrate the effect of hydrogen plasma treatment on hematite films as a simple and effective strategy for modifying the existing substrate to improve significantly the band edge positions and photoelectrochemical (PEC) performance. Plasma treated hematite films were consist of mixed phases (Fe3O4:α-Fe2O3) which was confirmed by XPS and Raman analysis, treated films also showed higher absorption cross-section and were found to be a promising photoelectrode material. The treated samples showed enhance photocurrent densities with maximum of 3.5 mA/cm2 at 1.8 V/RHE and the photocurrent onset potentials were shifted from 1.68 VRHE (untreated) to 1.28 VRHE (treated). Hydrogen plasma treatment under non-equilibrium conditions induced a valence dynamics among Fe centers in the sub-surface region that was sustained by the incorporation of hydrogen in the hematite lattice as supported by the density functional theory calculations.
Co-reporter:Trilok Singh, Thomas Lehnen, Tessa Leuning, Diptiranjan Sahu, Sanjay Mathur
Applied Surface Science 2014 Volume 289() pp:27-32
Publication Date(Web):15 January 2014
DOI:10.1016/j.apsusc.2013.10.071
Highlights
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ZnO thin films with high conductivity were grown by atomic layer deposition.
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Preferred orientation and surface microstructure changed during film growth.
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Thickness dependent changes of optical and electrical properties are reported.
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Increase in film thickness caused a decrease in bandgap by relaxation of stress.
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Contribution of excitonic and phonon replica in PL-spectra are discussed.
Co-reporter:Tim Heidemann
European Journal of Inorganic Chemistry 2014 Volume 2014( Issue 3) pp:506-510
Publication Date(Web):
DOI:10.1002/ejic.201301054
Abstract
Homoleptic germanium(II), tin(II), and lead(II) complexes of the general formula M(2-PyCHCOCF3)2 (M = Ge, Sn, Pb; Py = pyridine) were synthesized by treating the corresponding silyl amides [M{N(SiMe3)2}2] with two equivalents of a 3,3,3-trifluoro-1-(2-pyridyl)prop-1-en-2-ol (2-PyCHCOHCF3) ligand. Single-crystal X-ray diffraction revealed the bidentate chelation of 2-PyCHCOHCF3, which imposes a distorted trigonal bipyramidal geometry for all three molecular structures; this distortion is highest for the lead compound, probably as a result of the high s character of the lone pair of electrons present on the metal centers. The monomeric nature of the compounds in solution was confirmed by multinuclear NMR spectroscopy, whereas a polymeric structure is observed for the lead complex in the solid state.
Co-reporter:Trilok Singh;Shuangzhou Wang;Nabeel Aslam;Hehe Zhang;Susanne Hoffmann-Eifert
Chemical Vapor Deposition 2014 Volume 20( Issue 7-8-9) pp:291-297
Publication Date(Web):
DOI:10.1002/cvde.201407122
Abstract
Atomic layer deposition (ALD) offers nearly pinhole-free, conformal, and with good thickness control, metal oxide nanometric thin films required for next-generation memory devices. Here we report on the ALD of VOx thin films grown at about 100°C from a vanadium tri-isopropoxide (VTIP) precursor, with water as the co-reactant, followed by their post-growth treatments, for potential applications in resistive switching (RS) devices. As-grown VOx films are amorphous, and transform into polycrystalline layers upon annealing. Capacitor structures fabricated from amorphous VOx films show current-voltage (I-V) characteristics, interesting for RS applications. Depending on the electroforming conditions, bipolar-type memory switching with a resistance ratio ROFF/RON > 103 is obtained, as well as a combination of memory and threshold switching. The latter is attractive for its highly non-linear I-V characteristics, which is attributed to the temperature-induced insulator-to-metal transition (IMT) in vanadium dioxide.
Co-reporter:Annette Krais, Laura Wortmann, Laura Hermanns, Neus Feliu, Marie Vahter, Stefan Stucky, Sanjay Mathur, Bengt Fadeel
Nanomedicine: Nanotechnology, Biology and Medicine 2014 Volume 10(Issue 7) pp:1421-1431
Publication Date(Web):October 2014
DOI:10.1016/j.nano.2014.01.006
Targeted delivery of nanoparticles to cells or tissues of interest is arguably the “holy grail” of nanomedicine. Using primary human macrophages and ovarian cancer cells, we evaluated the biocompatibility and specific targeting of folic acid (FA)-conjugated iron oxide nanoparticles with organic [poly(ethylene glycol), PEG] or inorganic (SiO2) intermediate surface coatings. Reduction of folate receptor-α expression using specific siRNA resulted in a significant decrease in cellular uptake of the SiO2-coated nanoparticles, but did not affect uptake of PEG-coated nanoparticles. Notably, specific (i.e. FA-dependent) uptake was observed only in the presence of serum proteins. The strategy presented here for receptor-mediated uptake of nanoparticles with pre-defined surface chemistry may enable targeting of nanoparticles for therapeutic and imaging applications.From the Clinical EditorIn this study the receptor specific uptake of folic acid-functionalized iron oxide nanoparticles was determined in ovarian cancer cells. It was found that the presence of serum proteins is an absolute requirement for the uptake of these nanoparticles. The described strategy for receptor-mediated uptake of nanoparticles with pre-defined surface chemistry may enable a better targeting of nanoparticles for additional therapeutic and imaging applications.Targeted, i.e. receptor-mediated cellular uptake of folic acid (FA)-conjugated iron oxide nanoparticles is shown for particles with SiO2 coating, but not for particles with poly(ethylene glycol), PEG coating. Both particles displayed excellent biocompatibility.
Co-reporter:Irina Giebelhaus, Elena Varechkina, Thomas Fischer, Marina Rumyantseva, Vladimir Ivanov, Alexander Gaskov, Joan Ramon Morante, Jordi Arbiol, Wieland Tyrra and Sanjay Mathur
Journal of Materials Chemistry A 2013 vol. 1(Issue 37) pp:11261-11268
Publication Date(Web):10 Jul 2013
DOI:10.1039/C3TA11867C
Highly crystalline SnO2 nanowires were synthesized and functionalized with copper particles in a CVD using Sn(OBut)4 and [CuII((C5H4N)(CHCOCF3))2]2 (1) as precursors respectively. Controlled oxidation of Cu to CuO led to the formation of CuO@SnO2 p–n heterojunctions, which were found to be highly sensitive and selective towards the detection of H2S gas. The change in the conductance upon exposure to H2S gas was attributed to the formation of CuS resulting in the shrinkage of the space charge region along the SnO2 nanowire and a concomitant increase of the conductivity channel in an individual nanowire.
Co-reporter:Johannes Schläfer, Stefan Stucky, Wieland Tyrra, and Sanjay Mathur
Inorganic Chemistry 2013 Volume 52(Issue 7) pp:4002-4010
Publication Date(Web):March 12, 2013
DOI:10.1021/ic400030j
The reaction of Cerium Ammonium Nitrate (CAN) with varying amounts of KOtBu produced homometallic Ce(OtBu)4(NC5H5)2 (1) and the heterometallic derivative KCe2(OtBu)10 (3) characterized by X-ray diffraction and NMR spectroscopy. The oxo-alkoxide cluster Ce3O(OtBu)9 (2) was obtained from a solution of cerium(IV) tetrakis(tert-butoxide) in n-heptane under stringent precautions to avoid any adventitious hydrolysis. Lewis acid-base reactions of in situ generated Ce(OtBu)4(THF)2 (THF = tetrahydrofuran) with bi- and trivalent metal alkoxides [M(OtBu)x]n (M = Ge, Sn; x = 2; n = 2; M = Pb, x = 2; n = 3; M = Al, Fe; x = 3; n = 2) resulted in volatile products of the general formula MCe(OtBu)4+x (M = Al (4), Fe (5); x = 3; M = Ge (8), Sn (9), Pb (10); x = 2) in high yields. By dissolving 4 and 5 in pyridine the solvent adducts MCe(OtBu)7(NC5H5) (M = Al (6), Fe (7)) were formed, whereas 8 and 9 reacted with Mo(CO)6 in boiling toluene to yield the termetallic complexes (CO)5MoM(μ2-OtBu)3Ce(OtBu)3 (M = Ge (11), Sn (12)). The new compounds were characterized by comprehensive spectral studies, mass spectroscopy, and single crystal X-ray diffraction analysis.
Co-reporter:Jessica Altmayer, Sven Barth and Sanjay Mathur
RSC Advances 2013 vol. 3(Issue 28) pp:11234-11239
Publication Date(Web):11 Feb 2013
DOI:10.1039/C3RA00050H
Nanocrystalline titanium oxide (TiO2) coatings with different phases and surface topographies were deposited using chemical vapor deposition (CVD) of different homo- and heteroleptic titanium precursors of general formula [XTi(OiPr)3] (X = Cl (1), –NEt2 (2), –N(SiMe3)2 (3), –C5H5 (4), –OiPr (5) and –OtBu (6)) to elucidate the influence of molecular configuration on resulting material properties. The interdependence of precursor chemistry and materials features of the CVD deposits was verified by performing film growth under similar conditions using different precursor molecules (1–6). Studies on composition (XPS), structure (SEM, XRD) and bio-functional properties (cell tests) revealed that the decomposition process is markedly influenced by the auxiliary ligands, which led to incorporation of heteroelements (Si, Cl, N) in the films. Cell tests performed to evaluate the biocompatibility of the coatings towards the growth of bone cells showed a pronounced correlation between cell adhesion and surface morphology as well as the chemical composition. Growth of osteoblast cells was strongly enhanced on films obtained using [Ti(OiPr)4] and [CpTi(OiPr)3], whereas TiO2 coatings produced by [ClTi(OiPr)3] significantly inhibited the cell growth and their proliferation due to Cl contamination. Also, the nanomorphological features of the films were found to stimulate the cell adhesion and growth.
Co-reporter:Davide Barreca, Giorgio Carraro, Alberto Gasparotto, Chiara Maccato, Cinzia Sada, Aadesh P. Singh, Sanjay Mathur, Andreas Mettenbörger, Elza Bontempi, Laura E. Depero
International Journal of Hydrogen Energy 2013 Volume 38(Issue 33) pp:14189-14199
Publication Date(Web):4 November 2013
DOI:10.1016/j.ijhydene.2013.08.119
•Novel PE-CVD approach to β-Fe2O3 nanomaterials on ITO substrates.•Fabrication of columnar arrays with an homogeneous in-depth fluorine doping.•First example of β-Fe2O3 application in photoelectrochemical water splitting.•Modulation of optical and photoelectrochemical properties as a function of fluorine content.A single-step plasma enhanced-chemical vapor deposition (PE-CVD) route for the synthesis of F-doped iron(III) oxide nanomaterials is presented. Growth experiments, performed from a fluorinated Fe(II) β-diketonate precursor on Indium Tin Oxide (ITO) between 200 and 400 °C, yielded columnar β-Fe2O3 arrays with a preferential (100) growth direction. The fluorine content in the deposits could be adjusted by the sole variation of the deposition temperature controlling, in turn, the optical absorption and energy bandgap. Photocurrent measurements and Mott–Schottky analyses, carried out in Na2SO4 solution under one sun illumination, evidenced a conductivity switch from n- to p-type upon increasing fluorine amount in the obtained nanomaterials. The sample photocurrent density, donor content and flatband potential support the hypothesis that a progressive substitution of oxygen by fluorine in the iron(III) oxide lattice can alter electronic structure and extend charge carrier lifetimes, making anion-doped β-Fe2O3 an efficient water oxidation catalyst.
Co-reporter:Martin W.G. Hoffmann, Alaa Eldin Gad, J. Daniel Prades, Francisco Hernandez-Ramirez, Raquel Fiz, Hao Shen, Sanjay Mathur
Nano Energy 2013 Volume 2(Issue 4) pp:514-522
Publication Date(Web):July 2013
DOI:10.1016/j.nanoen.2012.12.003
Herein we report a solar diode sensor (SDS) based on new designed CdS@n-ZnO/p-Si nanoelements which unify gas sensing (CdS@n-ZnO) and solar energy harvesting (n-ZnO/p-Si diode) functionalities in a singular material unit and device. A novel The SDS sensing mechanism (change of open circuit voltage, ΔVoc), in comparison to the well-known conductometric sensors (change of resistance, ΔR), is systematically studied and explained in terms of gas–material surface interactions and the subsequent changes in the doping level (ND) of n-ZnO, which is manifested in the variation of Voc in CdS@n-ZnO/p-Si. The fabricated SDS was capable of quantitatively detecting oxidising and reducing gases with reproducible response at room temperature and without the need of any other energy sources except solar illumination to deliver a self-sustained gas sensor.Graphical abstractAn autonomous gas sensor with a concentration-dependent self generated signal, solely driven by solar light illumination, was realized by the inclusion of a diode (n-ZnO/p-Si) and gas sensing unit (CdS@n-ZnO) in a singular heterostructure. The sensing mechanism of this solar diode sensor is systematically studied by ON/OFF gas sensing and gas-dependent C–V measurements.Highlights► Autonomous gas sensor with self-generated signal solely driven by solar light. ► Based on a diode (n-ZnO/p-Si) and gas sensing unit (CdS@n-ZnO) in a singular heterostructure. ► Capable of quantitatively detecting oxidizing and reducing gases. ► Novel sensing mechanism verified by ON/OFF gas sensing and gas-dependent C-V measurements.
Co-reporter:Robin von Hagen, Ashish Lepcha, Xuefeng Song, Wieland Tyrra, Sanjay Mathur
Nano Energy 2013 Volume 2(Issue 2) pp:304-313
Publication Date(Web):March 2013
DOI:10.1016/j.nanoen.2012.10.002
A new alkoxide-based sol containing lithium isopropoxide, vanadylisopropoxide, di-n-butyl-phosphate, acetic-acid and polyvinylpyrrolidone, was used for the synthesis of monoclinic α-Li3V2(PO4)3/C composites by sol-gel and electrospinning techniques. The precursor mixture was highly soluble in organic solvents and thereby suitable for different synthesis techniques like sol-gel electrospinning or conventional sol-gel synthesis, to generate α-Li3V2(PO4)3/C nanocomposites with zero- and one-dimensionality. Electrospinning resulted in well-defined nanofibers and conventional sol-gel synthesis in polydisperse, isotropic nanoparticles. Phase composition and morphology in the composite nanostructures was examined by XRD, TGA, FT-IR, Raman, SEM and HR-TEM analysis. Comparative constant-current and cyclovoltammetric measurements of α-Li3V2(PO4)3/C composite applied as conventional film electrodes (nanoparticles and nanofibers) and self-supporting nanofiber electrodes revealed the influence of electrode texturing on the electrochemical performances. The nanofibrous self-supported electrodes showed superior cycling stability giving an initial discharge capacity of 124 mA h g−1 at 0.2 °C with retention of 95% after 50 cycles with rate variation in a voltage range of 3–4.3 V.Graphical abstractAn alkoxide based precursor sol could be used for Li3V2(PO4)3/C nanocomposite preparation by electrospinning or classical sol-gel method and the electrochemical performance as cathode material in lithium ion batteries was studied according to the obtained materials morphology and electrode type (self-supported vs. film electrode). Highlights► Synthesis of morphologically defined Li3V2(PO4)3/C-nanocomposites as cathode material in lithium ion batteries. ► Li3V2(PO4)3/C- (i) fibers by electrospinning and (ii) powder by sol-gel method. ► Dependency of the electrochemical performance on composite morphology (nanofiber vs. nanoparticle) and electrode architecture (self-supported vs. film electrode).
Co-reporter:David Zopes, Benjamin Stein, Sanjay Mathur, and Christina Graf
Langmuir 2013 Volume 29(Issue 36) pp:11217-11226
Publication Date(Web):August 2, 2013
DOI:10.1021/la4012058
Unprotected (“naked”) gold nanoparticles with high monodispersity (⟨d⟩, 5.5± 0.5 nm) were obtained in a facile and single-step microwave-assisted hydrolytic decomposition of the molecular precursor [NMe4][Au(CF3)2]. Given their chloride-free surface chemistry, the as-obtained gold nanoparticles were in situ functionalized with mono-, di-, and trivalent thiolated PEG ligands in order to study the influence of multivalent character of the ligands on the stability of the colloidal solutions. For this purpose, a novel tridentate ligand was synthesized and the previously reported syntheses of mono- and divalent thiol ligands were improved. Owing to the pristine character of the Au nanoparticles no ligand exchange was required, and the colloidal and chemical stability of the mono- and multivalent functionalized particles purely depended on the ligating ability of the thiolated groups. In situ-functionalized Au nanoparticles showed a strikingly (2 orders of magnitude higher) improved stability against small nucleophiles such as sodium cyanide compared to gold nanoparticles coated with citrate ligands and functionalized via a ligand-exchange reaction. The monovalent thiol PEG ligand produced most stable colloids against cyanide, which is explained by a strongly increased numerical ligand-density on the surface. Gold colloids stabilized by di- and trivalent ligands exhibited high stability in aqueous solutions with high NaCl concentrations (2 M) in contrast to those functionalized with the monovalent PEG ligand, which were only temporally stable in dilute NaCl solutions. The beneficial effect of the multivalence of the ligands was further demonstrated by the incorporation of an additional chelating ligand (dithiothreitol) to the colloidal dispersions.
Co-reporter:Shaista Ilyas, Muhammad Ilyas, Renier A. L. van der Hoorn, and Sanjay Mathur
ACS Nano 2013 Volume 7(Issue 11) pp:9655
Publication Date(Web):October 21, 2013
DOI:10.1021/nn402382g
Superparamagnetic iron oxide nanoparticles (SPIONs) coated with azide groups were functionalized at the surface with biotin (biotin@SPIONs) and cysteine protease inhibitor E-64 (E-64@SPIONs) with the purpose of developing nanoparticle-based assays for identifying cysteine proteases in proteomes. Magnetite particles (ca. 6 nm) were synthesized by microwave-assisted thermal decomposition of iron acetylacetonate and subsequently functionalized following a click chemistry protocol to obtain biotin and E-64 labeled particulate systems. Successful surface modification and covalent attachment of functional groups and molecules were confirmed by FT-IR spectroscopy and thermal gravimetric analysis. The ability of the surface-grafted biotin terminal groups to specifically interact with streptavidin (either horseradish peroxidase [(HRP)-luminol-H2O2] or rhodamine) was confirmed by chemiluminescent assay. A quantitative assessment showed a capture limit of 0.55–1.65 μg protein/100 μg particles. Furthermore, E-64@SPIONs were successfully used to specifically label papain-like cysteine proteases from crude plant extracts. Owing to the simplicity and versatility of the technique, together with the superparamagnetic behavior of FeOx-nanoparticles, the results demonstrate that click chemistry on surface anchored azide group is a viable approach toward bioconjugations that can be extended to other nanoparticles surfaces with different functional groups to target specific therapeutic and diagnostic applications.Keywords: biotin; click chemistry; cysteine protease inhibitor E-64; iron oxide magnetite nanoparticles; microwave-assisted synthesis; streptavidin−HRP and rhodamine
Co-reporter:Raquel Fiz ; Francisco Hernandez-Ramirez ; Thomas Fischer ; Lluis Lopez-Conesa ; Sonia Estrade ; Francesca Peiro
The Journal of Physical Chemistry C 2013 Volume 117(Issue 19) pp:10086-10094
Publication Date(Web):April 15, 2013
DOI:10.1021/jp3121066
Nanostructured metal oxide semiconductors are ideally suited for their integration in different devices due to their high thermal and mechanical stability, unique electronic characteristics, and low-cost fabrication. The modification of their surface allows the design of heterostructures with novel properties. In this work, we have synthesized single-crystalline niobium pentoxide (Nb2O5) nanorods and niobium-pentoxide-coated tin oxide (Nb2O5/SnO2) heterostructures by chemical vapor deposition. HR-TEM analysis and computer simulation studies showed the low density of defects and high crystallinity of the Nb2O5 nanorods, which exhibited high sensitivity toward humidity at low temperatures (60 °C). The fabrication of SnO2/Nb2O5 core–shell heterostructures combines the high sensitivity of Nb2O5 shell toward moisture with the good electrical conductivity of SnO2. The growth of the nanoscopic Nb2O5 overlayer on SnO2 nanowires introduces defects in the structure, which influence the electronic properties of the material and enable the design of more efficient humidity sensors.
Co-reporter:Robin von Hagen;Henning Lorrmann;Kai-Christian Möller
Advanced Energy Materials 2012 Volume 2( Issue 5) pp:553-559
Publication Date(Web):
DOI:10.1002/aenm.201100534
Abstract
LiFe1−yMnyPO4/C nanofiber composites are applied as cathode materials in Li-ion batteries and their electrochemical properties are explored. Nanofiber meshes are synthesized via electrospinning of commercially available precursors (LiOH·H2O, FeSO4·7H2O, MnSO4·H2O, H3PO4, and polyvinylpyrrolidone). Nanofibers calcined at 850 °C under Ar/H2 (95/5 vol%) atmosphere are directly used as self-supporting electrodes in Swagelok half cells without the need for any conductive additive or polymer binder. The morphology, phase, and chemical composition of as-prepared and heat-treated samples are analyzed by means of X-ray powder diffraction, thermogravimetric analysis, and electron and scanning microscopy techniques. Brunauer–Emmett–Teller gas adsorption–desorption measurements show a high specific surface area (111m2 g−1) for LiFe0.5Mn0.5PO4. The influence of different Fe/Mn ratios on the morphology, electrical, and electrochemical performances are analyzed.
Co-reporter:Ralf Müller, Francisco Hernandez-Ramirez, Hao Shen, Hongchu Du, Werner Mader, and Sanjay Mathur
Chemistry of Materials 2012 Volume 24(Issue 21) pp:4028
Publication Date(Web):October 14, 2012
DOI:10.1021/cm300913h
Tin oxide (SnO2) nanowires (NWs) were synthesized via the gold-catalyzed chemical vapor deposition of tin(IV) and tin(II) precursors, namely, [Sn(OtBu)4] (1) and [Sn(OtBu)2]2 (2). Nanowires were deposited on gold-coated Si(001) substrates, following the vapor–liquid–solid mechanism. Energy-dispersive X-ray (EDX) analysis and high-resolution transmission electron microscopy (HR-TEM) measurements on individual nanostructures showed that the change in tin valence from +IV to +II has significant influence on the morphology and composition of the resulting NWs. Whereas 1 led directly to the growth of SnO2 nanowires, 2 underwent a disproportionation reaction whereby the elemental phase (Sn0) reacted with Au nanoparticles to form a Au–Sn intermetallic catalyst. Comparative analysis of gas-sensing behaviors of nanowires grown from 1 and 2 illustrated that crystallographic imperfections, such as oxygen deficiency and a change in the oxidation states of the cations, are subject to the precursor configurations (Sn:O ratio in 1 and 2) and can significantly alter the surface properties, such as transduction behavior and electronic transport, that are responsible for their sensitivity toward analyte gases.Keywords: chemical vapor deposition; gas sensing; molecular precursor; Sn2+ disproportionation; tin alkoxide; VLS growth mechanism;
Co-reporter:Thomas Lehnen, David Zopes and Sanjay Mathur
Journal of Materials Chemistry A 2012 vol. 22(Issue 34) pp:17732-17736
Publication Date(Web):04 Jul 2012
DOI:10.1039/C2JM32924G
An efficient synthesis of highly crystalline and single phase Zn2SnO4 quantum dots (ZTO QDs) with a narrow size distribution was achieved by microwave-assisted hydrothermal synthesis. Printed structures fabricated from aqueous suspensions of ZTO QDs showed typical semiconducting I–V behaviors and were used for reproducible detection of humidity.
Co-reporter:Jiangtian Li, Martin W. G. Hoffmann, Hao Shen, Cristian Fabrega, Joan Daniel Prades, Teresa Andreu, Francisco Hernandez-Ramirez and Sanjay Mathur
Journal of Materials Chemistry A 2012 vol. 22(Issue 38) pp:20472-20476
Publication Date(Web):13 Aug 2012
DOI:10.1039/C2JM33404F
TiO2 nanorod arrays grown on conductive substrates were converted using chemical strategies into CdS@TiO2 and CdS@anatase@rutile TiO2 heterostructures to fabricate visible-light harvesting assemblies. Compared to pure TiO2 nanorods, CdS@TiO2 heterostructures evidently extended the absorption edge and exhibited enhanced photoelectrochemical (PEC) response in the visible region. Further enhancement of PEC performance was achieved by introducing an intermediate anatase TiO2 layer in the CdS@rutile TiO2 heterostructures. An excitonic cascade of band alignment (CdS, anatase-TiO2 and rutile-TiO2) was constituted by arranging different semiconductors in order to align the edges of their conducting band, which improved charge separation and suppressed the recombination processes by facilitating the transfer of forward electrons and limiting the reverse processes due to spatial separation of the electron and hole in different material regions.
Co-reporter:Jakob Wilfert, Robin von Hagen, Raquel Fiz, Martin Jansen and Sanjay Mathur
Journal of Materials Chemistry A 2012 vol. 22(Issue 5) pp:2099-2104
Publication Date(Web):13 Dec 2011
DOI:10.1039/C1JM14497A
Preceramic polymers obtained from the aminolysis of dichloroboryl-methyl-trichlorosilyl-amine (DMTA) were processed to ceramic felts of SiBNC by electrospinning, followed by curing in ammonia and subsequent pyrolysis. An amorphous ceramic with the composition SiBN2.4C1.4 was obtained in 60% yield, which was stable against crystallization and mass loss above 1565 °C. The pyrolysed felts showed a fiber thickness ranging between 2 and 3 μm and revealed seamless connectivity among the fibers. The rheological properties of the precursor could be tuned by adjusting the polymer/solvent ratio. Solutions with 40 wt% polymer were reproducibly spun into preceramic felts, whereas lower concentrations (10 wt%) mainly led to agglomerated powders containing few fibers. Given their intertwined morphology and high-temperature stability, the SiBNC felts were used as substrates to grow tin oxide nanowires by chemical vapour deposition for potential application as electrode materials in gas sensing, demonstrated by preliminary experiments.
Co-reporter:David Zopes, Corinna Hegemann, Wieland Tyrra and Sanjay Mathur
Chemical Communications 2012 vol. 48(Issue 70) pp:8805-8807
Publication Date(Web):06 Jul 2012
DOI:10.1039/C2CC33735E
A new gold(II) species [(CF3)4Au2(C5H5N)2] with a very short unsupported Au–Au bond (250.62(9) pm) was generated by photo irradiation of a silver aurate, [Ag(Py)2][Au(CF3)2], unambiguously characterized by 19F and 109Ag NMR studies.
Co-reporter:Lisa Brückmann, Wieland Tyrra, Stefan Stucky, and Sanjay Mathur
Inorganic Chemistry 2012 Volume 51(Issue 1) pp:536-542
Publication Date(Web):December 15, 2011
DOI:10.1021/ic201996r
Six novel homoleptic palladium(II) and platinum(II) complexes of donor-substituted alkenol ligands [PyCHC(R)OH; Py = pyridine, R = CH3, CF3, C2F5, C3F7] of the general formula M[PyCHC(R)O]2 (M = Pd, Pt) were synthesized by reacting the deprotonated ligands with PdCl2 and K2PtCl4, respectively. Molecular structures, revealed by single-crystal X-ray diffraction analyses, showed a square-planar arrangement of ligands around palladium and platinum centers, with the pyridine-ring nitrogen atoms situated in a mutually trans position. The monomeric nature of the compounds in the solution state was confirmed by multinuclear (1H, 13C, and 19F) NMR spectroscopy. Thermal decomposition profiles recorded under a nitrogen atmosphere suggested their potential as volatile precursors to palladium and platinum materials. The volatility was increased upon elongation of the perfluoroalkyl chain, which suppressed the intermolecular interactions, as is evident in crystal packings. The volatility of these compounds was attributed to bidentate chelation of the alkenol units and cooperativity among the electron-back-donating nitrogen atom and interplay of electron-withdrawing CxFy groups, resulting in an effective steric shielding of the metal atoms.
Co-reporter:Christian Cavelius, Karsten Moh, and Sanjay Mathur
Crystal Growth & Design 2012 Volume 12(Issue 12) pp:5948-5955
Publication Date(Web):October 15, 2012
DOI:10.1021/cg300936t
We describe here a chemically controlled pathway for the designed synthesis of iron oxide nanoparticles by thermal decomposition of iron(II) and iron(III) oxalates in high-boiling solvents in the presence of oleylamine and oleic acid acting as capping ligands. The phase composition of the nanocrystals (Fe, FeO, Fe3O4, or α-Fe2O3) could be precisely controlled by adjusting the synthesis conditions or by addition of appropriate oxidants, such as trimethylamine-N-oxide (TMAO), which produced highly monodisperse iron(III) oxide particles in the range of 6–25 nm in good yields. The decomposition behavior of different precursor/TMAO mixtures was elucidated by differential scanning calorimetry and thermogravimetry, and resulting particles were characterized by comprehensive HR-TEM and XRD analyses.
Co-reporter:Linus Appel, Raquel Fiz, Wieland Tyrra and Sanjay Mathur
Dalton Transactions 2012 vol. 41(Issue 7) pp:1981-1990
Publication Date(Web):16 Dec 2011
DOI:10.1039/C1DT11668A
The synthesis and characterization of nine new heteroleptic alkoxides of niobium is described. Metathesis reactions of Nb2Cl10 with tBuCH2OH and pyridine (py) or 4-dimethylaminopyridine (DMAP) affords monomeric octahedral complexes Nb(OCH2tBu)5py (1) and Nb(OCH2tBu)5DMAP (2), respectively, in high yields (>60%). The same reaction with tBuOH resulted in a chloro functionalized alkoxide Nb(OtBu)4pyCl (3) and could not be pushed to complete removal of remaining Cl− ligand. The introduction of a chelating bidental ligand 3,3,3-trifluoro-1-(pyridine-2-yl)propen-2-ol (2-PyCHCOHCF3) (4′′) in the dimeric framework of Nb2(OiPr)10 (4′) produced a heteroleptic, monomeric niobium complex Nb(OiPr)4(2-PyCHCOCF3) (4) with significantly enhanced stability and volatility. As a comparison to (4), five different heteroaryl systems (5–9) with the same side chain have been synthesized and examined in order to understand the influence upon physio-chemical properties. All the new compounds (1–9) have been characterized by microanalysis, variable temperature multinuclear NMR spectroscopy, mass spectrometry, thermal analysis and single crystal X-ray diffraction studies ((3), (4) and (9)). The molecular structure of (3) revealed mononuclear species with Nb atoms present in the distorted octahedral environment of four tBuO, one chloride and one pyridine ligand. Compounds (4) and (9) consisting of four iPrO and a trifluoroheteroarylenolate exhibited a stronger distortion in the molecular geometry due to the rigidity of chelating β-alkenolate moiety.
Co-reporter:Aadesh P. Singh, Andreas Mettenbörger, Peter Golus, Sanjay Mathur
International Journal of Hydrogen Energy 2012 Volume 37(Issue 19) pp:13983-13988
Publication Date(Web):October 2012
DOI:10.1016/j.ijhydene.2012.06.097
Nanostructured α-Fe2O3 thin films were grown by plasma-enhanced chemical vapor deposition (PE-CVD) using iron pentacarbonyl (Fe(CO)5) as precursor. Influence of the plasma parameters on photoelectrochemical (PEC) properties of the resulting hematite thin films toward solar oxidation of water was investigated under one sun illumination in a basic (1 M NaOH) electrolyte. PEC data analyzed in conjunction with the data obtained by scanning electron microscopy, X-ray diffraction and Mott–Schottky analysis showed 100 W plasma power to be an optimal RF-power value for achieving a high photocurrent density of ∼1098 μA/cm2 at 0.9 V/SCE external applied potential. The donor density, flat band potential, grain size and porosity of the films were observed to be highly affected by RF-power, which in turn resulted in enhanced photoresponse.
Co-reporter:Frank Heinrich;Michael T. Keßler;Stephan Dohmen;Mrityunjay Singh;Martin H. G. Prechtl
European Journal of Inorganic Chemistry 2012 Volume 2012( Issue 36) pp:6027-6033
Publication Date(Web):
DOI:10.1002/ejic.201200380
Abstract
Two new palladium complexes [Pd(MEA)2Cl2] (1) and [Pd(MEA)2Br2] (2) [MEA = (2-methoxyethyl)amine] were synthesized by the reaction of 2 equiv. of MEA with PdCl2 or [(cod)PdBr2] (cod = cycloocta-1,5-diene), respectively. Single-crystal X-ray diffraction analysis of 1 and 2 revealed the formation of square-planar trans complexes with palladium coordinated by chloride/bromide ions and N-atoms of MEA bonded in a monodentate fashion. Given their molecular form and solubility, 1 and 2 act as intractable precursors to Pd nanoparticles by microwave-assisted synthesis. The influence of the reaction temperature, irradiation time and surfactant (PVP) concentration on the size (5–40 nm) of the resulting particles was studied by DLS (hydrodynamic diameter) and TEM analyses (particle size). The growth mechanism of the nanoparticles depended on the type of halide ligand. Powder X-ray diffractometry confirmed the formation of elemental Pd particles that were embedded in carbonized wood to examine their potential as a catalyst. The catalytic activity of these nanoscale particles was evaluated in carbon–carbon cross-coupling reactions by using Heck, Suzuki and Sonogashira reactions as benchmark models. The investigations included recycling experiments that resulted in total turnover numbers of 4321 (Heck), 6173 (Sonogashira) and 8223 (Suzuki).
Co-reporter:A.E. Gad, M.W.G. Hoffmann, F. Hernandez-Ramirez, J.D. Prades, H. Shen, S. Mathur
Materials Chemistry and Physics 2012 Volume 135(2–3) pp:618-622
Publication Date(Web):15 August 2012
DOI:10.1016/j.matchemphys.2012.05.034
Radial p–n nanowire heterojunction devices represent a favorable geometry to maximize the interfacial area and charge carrier separation due to the built-in field established across the junction. This report presents the functional characterization of a heterojunction device based on a single coaxial p-Si/n-ZnO nanowire that was integrated in a circuit by FIB nanolithography to study the electrical properties. Specifically, their photovoltaic and gas sensing performances were preliminary assessed. The gas sensing response of the p–n heterojunction could be usefully modulated by controlling the bias currents through the device, showing a complementary functionality of these nanoarchitectured devices.Highlights► Coaxial p-Si/n-ZnO core/shell nanowires (NWs) were produced. ► Heterojunction devices based on one single NW were produced by FIB nanolithography. ► These devices displayed photovoltaic and gas sensing properties. ► Non-linear I–V characteristic allowed us to tune their sensibility to gases by modulating the bias.
Co-reporter:Ales Styskalik;David Skoda;Jiri Pinkas
Journal of Sol-Gel Science and Technology 2012 Volume 63( Issue 3) pp:463-472
Publication Date(Web):2012 September
DOI:10.1007/s10971-012-2808-5
Novel non-hydrolytic syntheses of titanosilicate xerogels by polycondensation of silicon acetate, Si(OAc)4, with titanium (IV) dimethylamide or diethylamide, Ti(NR2)4 (R = Me, Et), are presented. The reactions are based on acetamide elimination and yield gels with a high content of Si–O−Ti bonds in comparison with the ester elimination route. Although a ligand exchange was observed, it was interestingly not followed by homo-condensation and during the synthesis the phase separation to SiO2 and TiO2 was avoided. The degree of condensation reached up to 68 %. The xerogels prepared for a comparison by ester elimination from Si(OAc)4 and titanium (IV) isopropoxide featured a significantly lower content of the Si–O–Ti bonds. The initial tests in the epoxidation of cyclohexene by cumyl hydroperoxide (CHP) indicated a high selectivity and moderate activity of the xerogels. The catalytic properties were significantly improved by combining non-hydrolytic and hydrolytic methods yielding mesoporous and homogeneous Si/Ti mixed oxides. The catalysts prepared by these methods provided a complete epoxidation of cyclohexene in 2 h at 65 °C.
Co-reporter:Nadia E. A. El-Gamel, Laura Wortmann, Karim Arroub and Sanjay Mathur
Chemical Communications 2011 vol. 47(Issue 36) pp:10076-10078
Publication Date(Web):10 Aug 2011
DOI:10.1039/C1CC13708E
Silica-coated Fe2O3 nanoparticles were synthesized as carriers for the covalent immobilization and release of antimicrobial drug sparfloxacin (SPFX). SPFX-loaded nanoparticles exhibited time-dependent drug release, with no measurable in vitro cytotoxicity, making the drug@nanoparticle conjugates potentially relevant for nanomedicine applications.
Co-reporter:David Zopes;Silke Kremer;Harald Scherer;Lhoussaine Belkoura;Ingo Pantenburg;Wiel Tyrra
European Journal of Inorganic Chemistry 2011 Volume 2011( Issue 2) pp:273-280
Publication Date(Web):
DOI:10.1002/ejic.201000863
Abstract
Monodisperse gold nanoparticles (AuNPs) were obtained by hydrolytic decomposition of a new molecular precursor, tetramethylammonium bis(trifluoromethyl)aurate(I), [NMe4][Au(CF3)2], which has been characterised by spectroscopic and single-crystal X-ray diffraction analyses. On account of the simple and high-yield synthesis, the title compound represents a versatile synthon and an alternative to the commonly used chloroauric acid (HAuCl4).
Co-reporter:Eva Hemmer;Volker Huch;Matthias Adlung;Claudia Wickleder
European Journal of Inorganic Chemistry 2011 Volume 2011( Issue 13) pp:2148-2157
Publication Date(Web):
DOI:10.1002/ejic.201000963
Abstract
Terbium alkoxides in homometallic ― [Tb3(μ3-OtBu)2(μ2-OtBu)3(OtBu)4 (HOtBu)2] (1), [Tb{OC(tBu)3}3(THF)] (2) ― and heterometallic configurations ― [TbAl(μ2-OiPr)3(OiPr)3(iPrOH)]2 (3), [TbAl3(μ2-OiPr)6(OiPr)6] (4) ― were synthesized and characterized by single-crystal X-ray diffraction. Decomposition of 1 and 2 under solvothermal conditions produced Tb(OH)3 nanorods, whereby the material formation and crystallization were influenced by the steric profile of the organic ligand, which controlled the hydrolysis and condensation reactions of the precursor molecules. Monophasic terbium aluminate in the perovskite phase (TbAlO3) was obtained by the sol–gel processing of 3. Heterometallic frameworks present in 3 and 4 were, however, unstable under solvothermal conditions and resulted in hydroxide–oxide composites [Tb(OH)3/Al2O3/Al(OH)3]. Compound 4 exhibited sufficient vapour pressure to be used in the chemical vapour deposition (CVD) process to grow Tb–O–Al thin films. Crystalline compositions obtained on MgAl2O4 and SiO2 (quartz) substrates were garnet and perovskite phases, and were ascribed to the crystallographic relationship between the substrate and CVD deposits. The optical properties of the powders obtained were studied by photoluminescence spectroscopy.
Co-reporter:Irina Giebelhaus, Ralf Müller, Wieland Tyrra, Ingo Pantenburg, Thomas Fischer, Sanjay Mathur
Inorganica Chimica Acta 2011 Volume 372(Issue 1) pp:340-346
Publication Date(Web):15 June 2011
DOI:10.1016/j.ica.2011.02.052
A novel tin(II)-compound, bis(η2-N,O-2-[4,5-dimethyloxazolyl]-1,1,1-trifluoro-propen-2-olato)tin, SnII[(Me2C3NO)(CHCOCF3)]2 (1), was obtained by reacting Sn[N(SiMe3)2]2 with 2 M equivalents of the β-heteroarylalkenol, (Me2C3NO)(CHCOHCF3) (2). The molecular structures of ligand and the tin derivative were elucidated by single crystal X-ray diffraction and multi-nuclear NMR spectroscopic studies, which confirmed the monomeric nature and fourfold coordination of the tin(II) center with a pseudo-pyramidal geometry. The bidentate chelating mode of 2 imparted intriguingly high air stability to 1, which together with its high volatility make it an interesting precursor for the chemical vapor deposition (CVD) process. CVD of 1 on gold-coated Al2O3 substrates produced single crystalline SnO2 nanowires by vapor–liquid–solid growth mechanism. Transmission electron microscopy studies and X-ray diffraction data confirmed the high crystallinity of SnO2 nanowires possessing an average diameter of 90 nm.Graphical abstractThe article features the synthesis and structural characterization of new fluorinated β-alkenolate ligand (Me2C3NO)(CHCOHCF3) and its tin(II) derivate. The introduction of fluorinated unit in the ligand framework endows remarkable air stability to the title compound. In the view of the above and high volatility of the tin(II) compound, the CVD experiments have also been carried out, which resulted in the formation of nanostructured tin oxide deposits.Highlights► Synthesis and characterization of a new fluorinated β-alkenolate ligand and its tin(II) derivative. ► Application of the tin(II) compound as first air stable CVD precursor to produce tin oxide nanowires. ► CVD process revealed no disproportionation reaction as known in tin(II) alkoxides.
Co-reporter:Xuefeng Song ; Lian Gao
The Journal of Physical Chemistry C 2011 Volume 115(Issue 44) pp:21730-21735
Publication Date(Web):October 5, 2011
DOI:10.1021/jp208093s
A novel approach was employed to synthesize porous NiO nanotubes with controllable interior voids based on an effective interplay of Kirkendall effect and volume change upon phase transformation. For this purpose, nickel nanowires were chemically converted into Ni3S2/Ni core–shell structures, followed by a controlled oxidation, whereby the associated volume change (Ni → NiO conversion) resulted in 1D porous structure with voids. The voids between the Ni core and Ni3S2 shell could be controlled by adjusting the oxidation conditions that enabled fabrication of hollow and double-walled morphologies. Phase composition, morphological evolution, and porosity of double-walled NiO nanotubes were analyzed by X-ray diffraction, scanning and transmission electron microscopy, and N2 adsorption–desorption studies. Gaseous sulfur oxides formed during the oxidation of Ni3S2/Ni structures resulted in a perforated structure with multiple voids with pores ranging between 1 and 14 nm. The unique complex structure with the interpenetrating voids and the surface porosity resulted in a high specific surface area of 161.6 m2·g–1. The gas sensing property of such double-walled structure was found to vary as a function of the concentric void between the core and the shell. Gas-sensing measurements in hollow porous core–shell NiO nanotubes exhibited excellent sensitivity toward ethanol, originating from efficient adsorption of target molecules in the interior voids and their rapid diffusion and transport through the porous structures.
Co-reporter:Lisong Xiao, Jiangtian Li, Dermot F. Brougham, Eoin K. Fox, Neus Feliu, Alexey Bushmelev, Annette Schmidt, Natascha Mertens, Fabian Kiessling, Martin Valldor, Bengt Fadeel, and Sanjay Mathur
ACS Nano 2011 Volume 5(Issue 8) pp:6315
Publication Date(Web):July 26, 2011
DOI:10.1021/nn201348s
Ultrasmall superparamagnetic Fe3O4 nanoparticles (USIRONs) were synthesized by a novel, easily scalable chemical reduction of colloidal iron hydroxide under hydrothermal conditions. The average crystallite size (5.1 ± 0.5 nm) and good crystallinity of the samples were supported by HR-TEM analysis and the saturation magnetization value (47 emu g–1). Vitamin C, used as a chemical reducing agent, also served as a capping agent in the oxidized form (dehydroascorbic acid, DHAA) to impart nanoparticles with exceptional solubility and stability in water, PBS buffer, and cell culture medium. Detailed physicochemical analysis of the USIRON suspensions provided insight into the magnetic ordering phenomena within the colloid, arising from the formation of uniform clusters displaying a hydrodynamic size of 41 nm. Phantom experiments on the contrast agent (clinical 3 T MRI scanner) revealed an enhanced r2/r1 ratio of 36.4 (r1= 5 s–1 mM–1 and r2= 182 s–1 mM–1) when compared to the clinically approved agents. The potential of the DHAA-Fe3O4 nanoparticles as negative contrast agents for MRI with optimal hydrodynamic size for extended blood circulation times was confirmed by strong contrast observed in T2- and T2*-weighted images. The cell tests performed with primary human immune-competent cells confirmed the excellent biocompatibility of USIRONs.Keywords: biocompatibility; contrast agents; magnetic nanoparticles; magnetic resonance imaging; superparamagnetic iron oxide
Co-reporter:Jun Pan ; Hao Shen ; Ulf Werner ; Joan Daniel Prades ; Francisco Hernandez-Ramirez ; Flavio Soldera ; Frank Mücklich
The Journal of Physical Chemistry C 2011 Volume 115(Issue 31) pp:15191-15197
Publication Date(Web):June 13, 2011
DOI:10.1021/jp202685a
Oriented SnO2 nanowire (NW) arrays were grown on TiO2(001) substrates by molecule-based chemical vapor deposition of Sn(OtBu)4. Preferred growth directions ([101], [−101], [011], and [0–11]) of SnO2 NWs were correlated to surface energy consideration and crystallographic relationship between the substrate and NW material by comprehensive electron microscopy and bulk tomographic studies. The proposed growth incubation model (tilting of catalyst/NW interface due to driving force of surface energy) explains the formation mechanism of oriented SnO2 NWs on TiO2 substrates. These results allowed us to also study the I–V characteristics and gas-sensing properties of individual SnO2 NWs grown with a perfectly defined crystal orientation ([101]).
Co-reporter:Jun Pan ; Sven-Martin Hühne ; Hao Shen ; Lisong Xiao ; Philip Born ; Werner Mader
The Journal of Physical Chemistry C 2011 Volume 115(Issue 35) pp:17265-17269
Publication Date(Web):July 19, 2011
DOI:10.1021/jp201901b
Two-step chemical vapor deposition (CVD) in combination with metal-catalyzed vapor–liquid–solid (VLS) growth mechanism was used as a new approach to synthesize and modify the morphology of SnO2–TiO2 core–shell nanowires. SnO2 nanowires were grown by decomposition of Sn(OtBu)4 precursor on Au-coated Al2O3 substrates followed by the growth of a TiO2 overlayer by the CVD of Ti(OiPr)4. Structural characterization of SnO2–TiO2 heterostructures by X-ray diffraction and high-resolution TEM revealed the formation of mixed SnxTi1–xO2 compositions (x = 0.857–1.0) at the SnO2–TiO2 phase boundaries, where x depended on the annealing temperatures. The observed oriented attachment of TiO2 nanoclusters on single crystal SnO2 core was possibly due to low lattice mismatch. The photocatalytic studies suggested an enhanced activity in SnO2–TiO2 heterostructures due to higher surface area and change in the electronic structures caused by Sn4+ doping in TiO2.
Co-reporter:David Zopes, Robin von Hagen, Ralf Müller, Raquel Fiz and Sanjay Mathur
Nanoscale 2010 vol. 2(Issue 10) pp:2091-2095
Publication Date(Web):04 Aug 2010
DOI:10.1039/C0NR00131G
Nanosized (20–30 nm) colloidal gold, silver and their alloys were obtained by reductive transformation of corresponding metal salts. Dispersions of metal nanoparticles (σ < 4%) in aqueous solutions were obtained by appropriate surface functionalization which led to inorganic inks with solid fraction ranging from 0.01–4%. Judicious choice of a polymer additive (polyethylene glycol or carboxymethyl cellulose) was found to be crucial to avoid the agglomeration of nanocrystals in the ink-jetted structures upon solvent evaporation. The versatility of the nanoparticle-based printing technology was demonstrated by fabrication of dot-matrices and circuitry patterns on different substrates. Characterization of printed structures showed a homogeneous topography (AFM) and uniform distribution of metallic nanoparticles (SEM/TEM) within the ink-jetted microdrops. The site-specific patterning on silicon (001) substrates with nanoparticle (mono)layers could also be achieved by printing the linker molecule, aminopropyltriethoxysilane, followed by selective attachment of gold nanoparticles. Positionally ordered and chemically bonded gold catalyst patterns were used for the chemical vapour deposition (CVD) of nanowires, which led to site-specific growth of nanowires via the vapour-liquid-solid (VLS) mechanism and unlike in the case of spin-coated metal colloids no significant lateral diffusion of metal nanoparticles was observed, in chemically anchored Au nanoparticles. Nanoparticle containing inks allow a user-defined dilution to vary the density of CVD grown nanowires, which was utilized to show the differences in catalytic activities of silver and gold catalysts in the VLS growth.
Co-reporter:Lisong Xiao, Hao Shen, Robin von Hagen, Jun Pan, Lhoussaine Belkoura and Sanjay Mathur
Chemical Communications 2010 vol. 46(Issue 35) pp:6509-6511
Publication Date(Web):09 Aug 2010
DOI:10.1039/C0CC01156H
An efficient synthesis of highly crystalline SnO2 QDs with a narrow size distribution (4.27 ± 0.67 nm) was achieved by microwave-assisted decomposition of Sn(OtBu)4 in ionic liquid. Printed structures fabricated from SnO2 QDs showed typical semiconducting I–V behaviors, and gas sensing properties.
Co-reporter:Jun Pan, Rajesh Ganesan, Hao Shen and Sanjay Mathur
The Journal of Physical Chemistry C 2010 Volume 114(Issue 18) pp:8245-8250
Publication Date(Web):April 12, 2010
DOI:10.1021/jp101072f
Tin oxide (SnO2) nanowires grown by chemical vapor deposition were modified by Ar/O2 plasma treatment through preferential etching of the lattice oxygen atoms, which produced nonstoichiometric surface compositions that imparted a manyfold higher sensitivity toward gas absorption on such surfaces. Microstructures of as-grown and plasma-treated SnO2 nanowires confirmed the gradual change in the chemical composition and morphologies. Surficial disorder caused by the bombardment of argon and oxygen ions present in the plasma was visible as a disordered overlayer in high-resolution TEM micrographs, when compared to single crystalline as-grown SnO2 nanowires. Gas-sensing experiments on modified SnO2 nanostructures showed higher sensitivity for ethanol gas at lower operating temperatures and exhibited an improved transduction response toward changing gas atmospheres, attributed to the increased concentration of oxygen vacancies on the surface of SnO2 nanowires. Modulation of surface chemistry was also supported by photoluminescence and X-ray photoemission spectroscopy studies.
Co-reporter:Eva Hemmer, Yvonne Kohl, Victoria Colquhoun, Hagen Thielecke, Kohei Soga and Sanjay Mathur
The Journal of Physical Chemistry B 2010 Volume 114(Issue 12) pp:4358-4365
Publication Date(Web):March 10, 2010
DOI:10.1021/jp911607h
Gadolinium hydroxide, Gd(OH)3, nanostructures were examined for their possible use in imaging and tracking of cells and tissues by investigating their cellular interactions and cytotoxic behaviors. For this purpose, Gd(OH)3 nanorods (length, several hundred nanometers; diameter, ∼40 nm) and spherical nanoparticles (average diameter, <10 nm) were synthesized by solvothermal decomposition of gadolinium containing molecular precursors. After comprehensive characterization of material properties, human colon adenocarcinoma (Caco2) and human lung epithelial (A549) cells were incubated with Gd(OH)3 nanostructures in concentrations up to 900 μg/mL to perform cytotoxicity assays (BrdU (5-bromo-2′-deoxyuridine), WST-1 (4-[3-(4-iodophenyl)-2-(4-nitrophenyl)-2H-5-tetrazolio]-1,3-benzol-disulfonate)) and living/dead staining. As observed in all in vitro assays, the investigated Gd(OH)3 nanostructures do not induce any significant cytotoxic effect, making them promising candidates for a new class of contrast agents, which may overcome the limitations of organic stains such as photobleaching and single usage.
Co-reporter:Sven Barth, Sonia Estrade, Francisco Hernandez-Ramirez, Francesca Peiro, Jordi Arbiol, Albert Romano-Rodriguez, Joan Ramon Morante and Sanjay Mathur
Crystal Growth & Design 2009 Volume 9(Issue 2) pp:1077
Publication Date(Web):December 4, 2008
DOI:10.1021/cg8009095
Investigations on shape and chemical composition of one-dimensional magnetite nanostructures grown by a catalyst-assisted vapor phase procedure are reported. Intrinsic crystal chemistry (preferred growth of most stable surfaces) could be modulated by seeding the magnetite growth through Au nanoclusters, which led to elongated nanostructures (VLS mode); however, the structures have similar facets as observed in uncatalyzed growth. Geometric and energetic contributions to the evolution of the predominately observed {111} surface facets are discussed on the basis of high-angle annular dark field (HAADF) images and electron energy loss spectroscopy (EELS). The Fe:O stoichiometry in magnetite nanowire was determined by EELS, which manifested the reproducibility of nanowire growth by molecule-based CVD and the slightly nonstoichiometric nature of magnetite (Fe3O4−0.15). In combination with HAADF-TEM techniques, Au nanoclusters were identified on the surface of single-crystalline nanowires, which ably result from the surface diffusion of the catalyst (Au) material. In addition, core−shell SnO2/Fe3O4 1 D nanostructures were fabricated by sequential deposition of Sn and Fe precursors. Cross-sections of the coaxial nanostructures revealed polycrystalline magnetite shells on single-crystalline SnO2 wires constituted by well-defined single-crystalline facetted grains of slightly nonstoichiometric magnetite.
Co-reporter:Sanjay Mathur, Arzum Erdem, Christian Cavelius, Sven Barth, Jessica Altmayer
Sensors and Actuators B: Chemical 2009 Volume 136(Issue 2) pp:432-437
Publication Date(Web):2 March 2009
DOI:10.1016/j.snb.2008.11.049
Metal oxide nanostructures offer interesting possibilities to design functional surfaces for bio-sensing applications, for instance, through higher surface area leading to enhanced immobilization of biomolecules, which increases the detection limit. Herein, an amplified electrochemical sensing method has been presented for the detection of DNA based on the readout resulting from chemical oxidation of guanine on nanoscaled metal oxides (TiO2, SnO2 and Fe3O4) obtained by chemical vapor deposition (CVD) onto pencil graphite electrode (PGE) as electrochemical transducer. The proposed strategy is suitable to produce cost-effective disposable sensor elements enabling quantitative detection of nanomolar concentrations of DNA. When preparing these metal oxide surfaces by CVD onto PGEs, the various experimental conditions; such as, the effect of different concentrations of 20 mer-bases DNA oligonucleotide (ODN20), and the surface pretreatment steps were studied to obtain better surface properties for DNA immobilization. The detection limit estimated for signal-to-noise ratios >3 corresponds to 21.3, 53.9 and 45.8 nmole/ml ODN20 concentrations for PGEs modified with TiO2, SnO2 and Fe3O4 films, respectively. The electrochemical detection of DNA onto metal oxide@PGEs is discussed together with the application potential.
Co-reporter:Irina Giebelhaus, Elena Varechkina, Thomas Fischer, Marina Rumyantseva, Vladimir Ivanov, Alexander Gaskov, Joan Ramon Morante, Jordi Arbiol, Wieland Tyrra and Sanjay Mathur
Journal of Materials Chemistry A 2013 - vol. 1(Issue 37) pp:NaN11268-11268
Publication Date(Web):2013/07/10
DOI:10.1039/C3TA11867C
Highly crystalline SnO2 nanowires were synthesized and functionalized with copper particles in a CVD using Sn(OBut)4 and [CuII((C5H4N)(CHCOCF3))2]2 (1) as precursors respectively. Controlled oxidation of Cu to CuO led to the formation of CuO@SnO2 p–n heterojunctions, which were found to be highly sensitive and selective towards the detection of H2S gas. The change in the conductance upon exposure to H2S gas was attributed to the formation of CuS resulting in the shrinkage of the space charge region along the SnO2 nanowire and a concomitant increase of the conductivity channel in an individual nanowire.
Co-reporter:Jiangtian Li, Martin W. G. Hoffmann, Hao Shen, Cristian Fabrega, Joan Daniel Prades, Teresa Andreu, Francisco Hernandez-Ramirez and Sanjay Mathur
Journal of Materials Chemistry A 2012 - vol. 22(Issue 38) pp:NaN20476-20476
Publication Date(Web):2012/08/13
DOI:10.1039/C2JM33404F
TiO2 nanorod arrays grown on conductive substrates were converted using chemical strategies into CdS@TiO2 and CdS@anatase@rutile TiO2 heterostructures to fabricate visible-light harvesting assemblies. Compared to pure TiO2 nanorods, CdS@TiO2 heterostructures evidently extended the absorption edge and exhibited enhanced photoelectrochemical (PEC) response in the visible region. Further enhancement of PEC performance was achieved by introducing an intermediate anatase TiO2 layer in the CdS@rutile TiO2 heterostructures. An excitonic cascade of band alignment (CdS, anatase-TiO2 and rutile-TiO2) was constituted by arranging different semiconductors in order to align the edges of their conducting band, which improved charge separation and suppressed the recombination processes by facilitating the transfer of forward electrons and limiting the reverse processes due to spatial separation of the electron and hole in different material regions.
Co-reporter:Jakob Wilfert, Robin von Hagen, Raquel Fiz, Martin Jansen and Sanjay Mathur
Journal of Materials Chemistry A 2012 - vol. 22(Issue 5) pp:NaN2104-2104
Publication Date(Web):2011/12/13
DOI:10.1039/C1JM14497A
Preceramic polymers obtained from the aminolysis of dichloroboryl-methyl-trichlorosilyl-amine (DMTA) were processed to ceramic felts of SiBNC by electrospinning, followed by curing in ammonia and subsequent pyrolysis. An amorphous ceramic with the composition SiBN2.4C1.4 was obtained in 60% yield, which was stable against crystallization and mass loss above 1565 °C. The pyrolysed felts showed a fiber thickness ranging between 2 and 3 μm and revealed seamless connectivity among the fibers. The rheological properties of the precursor could be tuned by adjusting the polymer/solvent ratio. Solutions with 40 wt% polymer were reproducibly spun into preceramic felts, whereas lower concentrations (10 wt%) mainly led to agglomerated powders containing few fibers. Given their intertwined morphology and high-temperature stability, the SiBNC felts were used as substrates to grow tin oxide nanowires by chemical vapour deposition for potential application as electrode materials in gas sensing, demonstrated by preliminary experiments.
Co-reporter:Nadia E. A. El-Gamel, Laura Wortmann, Karim Arroub and Sanjay Mathur
Chemical Communications 2011 - vol. 47(Issue 36) pp:NaN10078-10078
Publication Date(Web):2011/08/10
DOI:10.1039/C1CC13708E
Silica-coated Fe2O3 nanoparticles were synthesized as carriers for the covalent immobilization and release of antimicrobial drug sparfloxacin (SPFX). SPFX-loaded nanoparticles exhibited time-dependent drug release, with no measurable in vitro cytotoxicity, making the drug@nanoparticle conjugates potentially relevant for nanomedicine applications.
Co-reporter:Thomas Lehnen, David Zopes and Sanjay Mathur
Journal of Materials Chemistry A 2012 - vol. 22(Issue 34) pp:NaN17736-17736
Publication Date(Web):2012/07/04
DOI:10.1039/C2JM32924G
An efficient synthesis of highly crystalline and single phase Zn2SnO4 quantum dots (ZTO QDs) with a narrow size distribution was achieved by microwave-assisted hydrothermal synthesis. Printed structures fabricated from aqueous suspensions of ZTO QDs showed typical semiconducting I–V behaviors and were used for reproducible detection of humidity.
Co-reporter:O. Arslan, L. Belkoura and S. Mathur
Journal of Materials Chemistry A 2015 - vol. 3(Issue 45) pp:NaN11973-11973
Publication Date(Web):2015/11/04
DOI:10.1039/C5TC03377B
Stable oleate capped, visible light emitting ZnO quantum dots (QDs) have been synthesized by a modified sol–gel method and examined for large-scale synthesis. Surface chelation with oleate ligands and their implications on particle growth were investigated by comprehensive NMR experiments and photoluminescence measurements. High-resolution electron microscopy and X-ray diffraction confirmed the high crystallinity and well-dispersed character of the ZnO QDs. The here investigated ZnO nanocrystals were found to be suitable for phase transfer synthesis (non-polar to polar dispersion medium) even after prolonged storage time that was verified by unchanged visible light emission. The absorption wavelength could be tuned by adjusting the nucleation kinetics and upon anchoring bulky ligands that provide control over the surface defects responsible for the optical (visible) properties. The demonstrated phase transfer studies make visible light emitting ZnO QDs accessible for a wide range of applications like ink-jet printing for nano-electronics, cell labelling or theranostic studies.
Co-reporter:Linus Appel, Raquel Fiz, Wieland Tyrra and Sanjay Mathur
Dalton Transactions 2012 - vol. 41(Issue 7) pp:NaN1990-1990
Publication Date(Web):2011/12/16
DOI:10.1039/C1DT11668A
The synthesis and characterization of nine new heteroleptic alkoxides of niobium is described. Metathesis reactions of Nb2Cl10 with tBuCH2OH and pyridine (py) or 4-dimethylaminopyridine (DMAP) affords monomeric octahedral complexes Nb(OCH2tBu)5py (1) and Nb(OCH2tBu)5DMAP (2), respectively, in high yields (>60%). The same reaction with tBuOH resulted in a chloro functionalized alkoxide Nb(OtBu)4pyCl (3) and could not be pushed to complete removal of remaining Cl− ligand. The introduction of a chelating bidental ligand 3,3,3-trifluoro-1-(pyridine-2-yl)propen-2-ol (2-PyCHCOHCF3) (4′′) in the dimeric framework of Nb2(OiPr)10 (4′) produced a heteroleptic, monomeric niobium complex Nb(OiPr)4(2-PyCHCOCF3) (4) with significantly enhanced stability and volatility. As a comparison to (4), five different heteroaryl systems (5–9) with the same side chain have been synthesized and examined in order to understand the influence upon physio-chemical properties. All the new compounds (1–9) have been characterized by microanalysis, variable temperature multinuclear NMR spectroscopy, mass spectrometry, thermal analysis and single crystal X-ray diffraction studies ((3), (4) and (9)). The molecular structure of (3) revealed mononuclear species with Nb atoms present in the distorted octahedral environment of four tBuO, one chloride and one pyridine ligand. Compounds (4) and (9) consisting of four iPrO and a trifluoroheteroarylenolate exhibited a stronger distortion in the molecular geometry due to the rigidity of chelating β-alkenolate moiety.
Co-reporter:Lisong Xiao, Hao Shen, Robin von Hagen, Jun Pan, Lhoussaine Belkoura and Sanjay Mathur
Chemical Communications 2010 - vol. 46(Issue 35) pp:NaN6511-6511
Publication Date(Web):2010/08/09
DOI:10.1039/C0CC01156H
An efficient synthesis of highly crystalline SnO2 QDs with a narrow size distribution (4.27 ± 0.67 nm) was achieved by microwave-assisted decomposition of Sn(OtBu)4 in ionic liquid. Printed structures fabricated from SnO2 QDs showed typical semiconducting I–V behaviors, and gas sensing properties.
Co-reporter:David Zopes, Corinna Hegemann, Wieland Tyrra and Sanjay Mathur
Chemical Communications 2012 - vol. 48(Issue 70) pp:NaN8807-8807
Publication Date(Web):2012/07/06
DOI:10.1039/C2CC33735E
A new gold(II) species [(CF3)4Au2(C5H5N)2] with a very short unsupported Au–Au bond (250.62(9) pm) was generated by photo irradiation of a silver aurate, [Ag(Py)2][Au(CF3)2], unambiguously characterized by 19F and 109Ag NMR studies.
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![N-[4-[[(2-amino-3,4-dihydro-4-oxo-6-pteridinyl)methyl]amino]benzoyl]-L-Glutamic acid 5-(2,5-dioxo-1-pyrrolidinyl) ester](http://img.cochemist.com/ccimg/153500/153445-05-7_b.png)
![Erbium Tris[bis(trimethylsilyl)amide]](http://img.cochemist.com/ccimg/103500/103457-72-3.png)
![Erbium Tris[bis(trimethylsilyl)amide]](http://img.cochemist.com/ccimg/103500/103457-72-3_b.png)
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![Lanthanum Tris[bis(trimethylsilyl)amide]](http://img.cochemist.com/ccimg/35800/35788-99-9_b.png)
![[[[BIS(TRIMETHYLSILYL)AMINO]PLUMBYL-TRIMETHYLSILYLAMINO]-DIMETHYLSILYL]METHANE](http://img.cochemist.com/ccimg/55200/55147-59-6.png)
![[[[BIS(TRIMETHYLSILYL)AMINO]PLUMBYL-TRIMETHYLSILYLAMINO]-DIMETHYLSILYL]METHANE](http://img.cochemist.com/ccimg/55200/55147-59-6_b.png)
