279 research outputs found
Struktureller Elektronentransfer und spektroskopische Studien von Übergangsmetall-Komplexen mit redoxaktiven "Non- Innocent"-Liganden
No full textIn this doctoral thesis structural and electronic properties of transition metal complexes of redox-active non-innocent ligands such as nitrosyl, 4,6-di-tert-butyl-N-phenyl-o-iminobenzoquinone and 3,5-di-tert-butyl-o-quinone are described. Additionally, the thesis covers the synthesis, mode of binding and electron transfer behaviors of metal complexes of an air-stable chiral diphosphine derived chelating ligand, R,R-QuinoxP.
In the first part of my thesis the synthetic aspects, the structural, spectroscopic and electronic properties of new transition metal (Ru and Re) nitrosyl complexes are described. The actual form of coordinated NOm (m = +/0/−) is established based on the experimental results supported by calculations.
In Chapter 2, different oxidation states of [Ru(OEP)(NO)(X)]n+ (n = +2, +1, 0, −1, OEP = octaethylporphyrin dianion) with varying axial sixth ligands X (H2O, pyridine, 4-cyanopyridine, 4-dimethylaminopyridine) are studied spectroscopically and the electronic structures of the complexes have been rationalized through DFT calculations.
Chapter 3 describes the complex (PPh4)4[(CN)4(NO)Re(μ-O)Re(NO)(CN)4] , an oxo-bridged rhenium dinitrosyl complex with cyanide as a co-ligand. The complex has been structurally and spectroscopically characterized. Crystal structure analysis confirms the linear coordination of the nitrosyl groups and of the linear mode of Re-O-Re unit. The complex exhibits two sharp ν(NO) bands at 1710 and 1670 cm−1 and two sharp ν(CN) bands at 2118 and 2129 cm−1 in CH3CN.
In the second part of this thesis several complexes with 1,2-dioxolene type non-innocent ligands (Q or QO) or sometimes combining two non-innocent ligands Q and NO in one system are described.
Chapter 4 describes four ruthenium o-iminoquinone complexes with the objective of establishing the metal-ligand valence state distribution. The complexes are isolated in the monocationic form and have also been characterized crystallographically. The C1-O1, C2-N1 bond lengths and the C-C intra-ring distances suggest that Q binds to the metal center in the iminosemiquinonato (Q·−) oxidation state, resulting in an [RuIII(Q·–)] electronic formulation in all four cases.
Chapter 5 deals with two paramagnetic complexes [Ru(NO)(Q)(terpy)](PF6)2 and [Ru(NO)(Q)(tppz)](PF6)2 combining three redox sensitive components such as RuII/RuIII, NOm and (Q)n. The co-ligands terpy and tppz are redox invariant in the present cases. The most stable positional isomer of [Ru(NO)(Q)(terpy)](PF6)2 with NO trans to the O donor atom of Q was isolated and characterized by single crystal X-ray analysis. In conjunction with the experimental Ru-N-O angle and the metrical parameters in the quinonoid ligand especially the C1-O1 distance and with ν(NO), the EPR studies at 9.5 and 285 GHz reveal a narrow radical-type signal, suggesting [RuII(NO+)(Q·−)(terpy)]2+ as the most valid oxidation state formulation.
Chapter 6 describes the structural, electrochemical and spectroscopic properties of [Cl(Q)Ru(μ-tppz)Ru(Q)Cl]n. The complex [Cl(Q)Ru(μ-tppz)Ru(Q)Cl](PF6)2, containing five component redox system [(Q)n-Rum-(μ-tppzx)-Rum'-(Q)n'], has been structurally characterized as anti isomer, the only configuration obtained. The combined structural and spectroscopic results allow the oxidation state assignment as [(Q·−)-RuIII-(μ-tppzo)-RuIII-(Q·−)]. One-electron oxidation of [Cl(Q·−)RuIII(μ-tppz0)RuIII(Q•−)Cl]2+ results in the appearance of a rhombic EPR signal as is typical for distorted ruthenium (III). The emergence (on first oxidation) and subsequent disappearance (on second oxidation) of an intense near-infrared band at 1853 nm strongly suggests a mixed-valent configuration with a low-energy IVCT transition and a sizeable comproportionation constant 106.1
Chapter 7 describes a detail spectroelectrochemical (UV-Vis-NIR and EPR) and theoretical studies of the redox series [Ru(QO)3]n, [Os(QO)3]n and [Ru(Q)3]n (n = +2 to −2). The [Ru(QO)3]0 and [Os(QO)3]0 complexes were reported earlier by Pierpont et. al. and the redox states of (QO) in the complexes have been formulated as semiquinonato (QO·−) and catecolate (QO2−), respectively. Based on this assignment the newly synthesized complex [Ru(Q)3]0 can also be attributed to antiferromagnetically coupled tris-iminosemiquinonato [RuIII(QO·−)3] system. Consequently the compound [RuIII(Q·−)3]0 is EPR-silent and shows unshifted 1H-NMR lines.In dieser Arbeit werden die strukturellen sowie elektronischen Eigenschaften von Übergangsmetallkomplexen mit redoxaktiven Liganden wie Nitrosyl, 4,6-Di-tert-butyl-N-phenyl-o-iminobenzochinon und 3,5-Di-tert-butyl-o-benzochinon vorgestellt. Zusätzlich werden in dieser Arbeit die Synthese, die Bindungsverhältnisse und das Elektronentransferverhalten von Übergangsmetallkomplexen mit dem luftstabilen chiralen chelatisierenden Diphosphinliganden R,R-QuinoxP beschrieben.
Im ersten Teil dieser Arbeit werden die synthetischen Aspekte, die Strukturen, spektroskopische- und elektronische Eigenschaften neuer Nitrosylkomplexe mit den Übergangsmetallen Ru und Re beschrieben. Die tatsächliche Form des koordinierten NOm (m = +/0/-) wurde durch experimentelle Ergebnisse und von quantenchemischen Rechnungen unterstützt.
Im zweiten Kapitel werden die verschiedenen Oxidationsstufen des [Ru(OEP)(NO)(X)]n+ (n = +2, +1, 0, −1, OEP = Octethylporphyrindianion) mit verschiedenen axialen Liganden X (H2O, Pyridin, 4-Cyanopyridin, 4-Dimethylaminopyridin) spektroskopisch untersucht. Die elektronische Struktur der Komplexe wurde zufriedenstellend durch DFT Rechnungen geklärt.
In Kapitel 3 wird der Komplex (PPh4)4[(CN)4(NO)Re(μ-O)Re(NO)(CN)4], eine sauerstoffverbrückte Rheniumdinitrosylverbindung mit Cyanid als Co-Ligand, beschrieben. Der Komplex ist strukturell und spektroskopisch charakterisiert. Molekülstrukturanalyse bestätigen die lineare Anordnung der Nitrosylgruppen sowie der Re-O-Re Einheit. Die Verbindung weist zwei scharfe ν(NO) Banden bei 1710 cm−1 und 1670 cm−1 und zwei deutliche ν(CN) Banden bei 2118 und 2129 cm-1 in Acetonitril auf.
Im zweiten Teil dieser Arbeit werden verschiedene Komplexe mit 1,2-Dioxolen-artigen "non-innocent" Liganden (Q bzw. Q0) oder die Kombination zweier nicht unschuldiger Liganden Q und NO in einem System, beschrieben.
In Kapitel 4 werden vier Ruthenium o-Iminochinonkomplexe und die tatsächliche Verteilung der Ladung zwischen Metall und Ligand, diskutiert. Die Verbindungen wurden in der monokationischen Form isoliert und ebenfalls kristallographisch analysiert. Die C1−O1, C2−N1 Bindungslängen sowie die C−C Abstände im Ring legen die Vermutung nahe, dass Q an das Metallzentrum in der Iminosemichinonform (Q·−) gebunden ist. Somit ergibt sich für alle Verbindungen die Formulierung [RuIII(Q·−)].
Kapitel 5 beinhaltet die zwei paramagnetischen Komplexe [Ru(NO)(Q)(terpy)](PF6)2 und [Ru(NO)(Q)(tppz)](PF6)2 bei denen drei redoxaktive Komponenten, RuII/RuIII, NOm und (Q)n verknüpft sind. Die Co-Liganden terpy und tppz sind in diesem Falle nicht redoxaktiv. Das stabilste Isomer des [Ru(NO)(Q)(terpy)](PF6)2 mit NO trans zum Sauerstoffdonor von Q wurde isoliert und strukturell charakterisiert. In Verbindung mit dem experimentellen Ru−N−O Winkel, den Bindungsabständen im Chinonliganden vor allem der C1−O1 Abstand, mit ν(NO) und den ESR-Messungen bei 9.5 und 285 GHz die ein schmales radikalisches Signal zeigen, kann [RuII(NO+)(Q·−)(terpy)]2+ als gültige Formulierung angenommen werden.
In Kapitel sechs werden die Struktur, Elektrochemie und die spektroskopischen Eigenschaften des [Cl(Q)Ru(μ-tppz)Ru(Q)Cl]n beschrieben. Die Verbindung [Cl(Q)Ru(μ-tppz)Ru(Q)−Cl](PF6)2 beinhaltet fünf Redoxsysteme [(Q)n-Rum-(μ-tppzx)-Rum'-(Q)n'] und kann über die Einkristallanalyse als anti Isomer identifiziert werden.
Durch die spektroskopischen und strukturellen Ergebnisse kann die Verbindung als [(Q·−)-RuIII-(μ-tppzo)-RuIII-(Q·−)] formuliert werden. Ein-Elektronenoxidation des [Cl(Q·−)RuIII(μ-tppz0)RuIII(Q·−)Cl]2+ führt zu einem rhombischen ESR-Signal, welches typisch für verzerrtes Ruthenium(III) ist. Das Erscheinen (während der ersten Oxidation) und anschließendes Verschwinden (nach der zweiten Oxidation) einer starken NIR-Bande bei 1850 nm deutet auf einen gemischtvalenten Zustand mit einem energetisch tief liegenden IVCT Übergang hin. Die Komproportionierungskonstante von 106.1 ist beträchtlich.
Kapitel 7 beschreibt im Detail die Spektroelektrochemie (UV-Vis-NIR und ESR) und theoretische Rechnungen der Redoxprodukte der Reihe [Ru(QO)3]n, [Os(QO)3]n und [Ru(Q)3]n (n = +2 bis −2). Über die Verbindungen [Ru(QO)3]0 und [Os(QO)3]0 wurde schön früher von Pierpont et al. berichtet. Die Oxidationstufe des Liganden (QO) wurde als Semichinon (QO·−) beziehungsweise als Catechol (QO2-) formuliert. Darauf basierend kann der neu dargestellte Komplex [Ru(Q)3]0 als antiferromagnetisch gekoppelte Trisiminosemichinonato [RuIII(Q·−)3] Verbindung aufgefasst werden. Der Komplex zeigt kein ESR-Signal und weist 1H-NMR-Signale an den erwarteten Positionen
Open access and institutional repositories – a developing country perspective: a case study of India
No full textIn the recent years much discussions and initiatives are taken in the area of open access. Open access, a philosophy facilitates availability and distribution of scholarly communication freely, as a means to solve the problem of inaccessibility primarily due to financial constraint particularly in the context of developing countries. Many scholarly literature are freely accessible now without any hindrance. Open access endeavours to reduce barriers to scholarly communication. The open access literature available in various forms like open access archives, institutional repositories, open access journals and off late open courseware. The availability of open source software has accelerated this development. In India, various open access initiatives have been undertaken and are operational. Some more are in developmental stage. This paper discusses various such initiatives in India. Some initiatives have also been taken in the area of metadata harvesting services. Gradually, there has been a realization of the usefulness of the open access by various institutions particularly, the public funded ones. The future of open access in India is dependent upon a proper policy and a framework. In the implementation of open access LIS professionals should play a pro-active role in the growth of collection in the institutional repositories. The paper provides information about the present state of open access Literature by various institutions of the country
Bio-based composites from bagasse using carbohydrate enriched cross-bonding mechanism: A formaldehyde-free approach
No full textIn this study, cross-bonded self-binding and bone glue-bonded particleboards were manufactured from sugarcane (Saccharum officinarum L.) bagasse with different pre-treatments of particles. Six types of panels were manufactured from bagasse particles with and without bone glue. The physical, mechanical, and thermal properties of the panels were examined according to the standards. Fourier Transform Infrared (FTIR) spectroscopy and thermogravimetric analysis (TG) were performed to investigate the changes in the chemical bonds and thermal stability of the fabricated composites, respectively. It was found that cross-bonded bagasse self-binding (TC) and bone glue-bonded (T3) panels fabricated from non-boiled bagasse particles showed higher physical and mechanical properties compared to the other types of panels. Non-boiled bagasse particles with bone glue panels showed the highest mechanical properties, i.e., modulus of rupture (MOR = 26.22 MPa), modulus of elasticity (MOE = 4302 MPa), tensile strength = 8.35 MPa, and hardness = 1.72 MPa. TC and T3 panels also showed higher thermal stability compared to the other types of panels. A new peak at 3331-3334 cm-1 for the N-H stretching vibration in the FTIR analysis represents the presence of bone glue in the cross-bonded particleboards. Thus, this research advances the production of formaldehyde-free bagasse particleboard, introducing the cross-bonding technique and sustainable bone glue
Production and characterisation of pine wood powders from a multi-blade shaft mill
No full textWood is an important raw material for the manufacture of consumer products and in achieving societal goals for greater sustainability. Wood powders are feedstock for many biorefining and conversion techniques, including chemical, enzymatic and thermochemical processes and for composite manufacture, 3D printing and wood pellet production. Size reduction, therefore, is a key operation in wood utilisation and powder characteristics, such as shape, particle size distribution and micromorphology play a role in powder quality and end-use application. While in a green state, the native chemical composition and structure of wood are preserved. Powders are commonly produced from wood chips using impact mills, which require pre-sized, pre-screened and pre-dried chips. These steps necessitate repeated handling, intermediate storage and contribute to dry matter losses, operation-based emissions and the degradation of the wood chemistry.This thesis investigated a new size reduction technology, known as the multi-blade shaft mill (MBSM). The MBSM performance was studied through the milling of Scots pine (Pinus sylvestris L.) wood using a designed series of experiments and through modelling with multi-linear regression (MLR) analyses. Light microscopy combined with histochemical techniques were used to investigate particle micromorphology and distribution of native extractives in powders. The aim was to evaluate the technical performance of the MBSM with relation to operational parameters, to characterise the produced powders and to evaluate the technology through comparison with impact milling.The results showed that the MBSM could effectively mill both green and dry wood. Produced powders showed distinct differences compared to those obtained using a hammer mill (HM). The specific milling energy of the MBSM was lowest for green wood and within the range of other established size reduction technologies. However, much narrower particle size distributions were observed in MBSM powders and they had significantly greater amounts of finer particles. Particles with high aspect ratio and sphericity were a characteristic of MBSM powders and this Production and characterisation of pine wood powders from a multi-blade shaft mill was true for wood milled above and below its fibre saturation point. MBSM powders from green wood showed evidence of higher specific surface area, larger pore volume and greater micropore diameter than those from HM powder. Preliminary microscopic examination suggested that cell walls in MBSM powders showed evidence of retaining their original native wood structure. Consequently, their extractive content appeared intact. This was in contrast to HM powder and it may reflect the differences between the two size reduction mechanisms. According to the produced MLR models, the results suggest that MBSM milling is more akin to a sawing process and opposite to that of impact-based mills
Production and characterisation of pine wood powders from a multi-blade shaft mill
No full textWood is an important raw material for the manufacture of consumer products and in achieving societal goals for greater sustainability. Wood powders are feedstock for many biorefining and conversion techniques, including chemical, enzymatic and thermochemical processes and for composite manufacture, 3D printing and wood pellet production. Size reduction, therefore, is a key operation in wood utilisation and powder characteristics, such as shape, particle size distribution and micromorphology play a role in powder quality and end-use application. While in a green state, the native chemical composition and structure of wood are preserved. Powders are commonly produced from wood chips using impact mills, which require pre-sized, pre-screened and pre-dried chips. These steps necessitate repeated handling, intermediate storage and contribute to dry matter losses, operation-based emissions and the degradation of the wood chemistry.This thesis investigated a new size reduction technology, known as the multi-blade shaft mill (MBSM). The MBSM performance was studied through the milling of Scots pine (Pinus sylvestris L.) wood using a designed series of experiments and through modelling with multi-linear regression (MLR) analyses. Light microscopy combined with histochemical techniques were used to investigate particle micromorphology and distribution of native extractives in powders. The aim was to evaluate the technical performance of the MBSM with relation to operational parameters, to characterise the produced powders and to evaluate the technology through comparison with impact milling.The results showed that the MBSM could effectively mill both green and dry wood. Produced powders showed distinct differences compared to those obtained using a hammer mill (HM). The specific milling energy of the MBSM was lowest for green wood and within the range of other established size reduction technologies. However, much narrower particle size distributions were observed in MBSM powders and they had significantly greater amounts of finer particles. Particles with high aspect ratio and sphericity were a characteristic of MBSM powders and this Production and characterisation of pine wood powders from a multi-blade shaft mill was true for wood milled above and below its fibre saturation point. MBSM powders from green wood showed evidence of higher specific surface area, larger pore volume and greater micropore diameter than those from HM powder. Preliminary microscopic examination suggested that cell walls in MBSM powders showed evidence of retaining their original native wood structure. Consequently, their extractive content appeared intact. This was in contrast to HM powder and it may reflect the differences between the two size reduction mechanisms. According to the produced MLR models, the results suggest that MBSM milling is more akin to a sawing process and opposite to that of impact-based mills.</p
Bioderived Chemical Extraction from Spruce Needles : Adding Value to Forest Logging Residues
No full textNanocomposites in energy storage applications
No full textThe development of energy storage devices for the growing energy demand is a prerequisite for modern society. Specific characteristics, i.e., thermal, electrochemical, and mechanical properties, of nanocomposites are essential for their application in energy storage appliances. Biobased nanocomposites are being considered environmentally friendly. Nanocellulose, lignin, and chitosan are obtained from an abundant source of natural renewable materials. Using them in developing batteries and supercapacitors has great potential for a sustainable supply of energy. Nanocellulose and the lignin-based electrode have shown excellent electrochemical properties for application in a battery. Nanocellulose, lignin, and chitosan-based electrode have also exhibited excellent electrochemical properties for their utilization in supercapacitors. In addition, their low-cost, high conductivity, and environment-friendly nature are being considered for the preparation of energy storage devices. In this chapter, the development strategy and performance of batteries and supercapacitors obtained from biobased nanocomposites have been discussed.</p
An overview of different types and potential of bio-based adhesives used for wood products
No full textBio-based adhesives have shown promise in the engineered wood products industry, and there is a substantial growth of research on bio-based bonding agents. Wood is a renewable resource, and most of the engineered wood products are synthetic adhesive-bonded composites and laminates. Environmental concerns exist for the use of adhesives made from fossil fuels lowering the bio-content of the bonded wood products. Bio-based adhesives are getting more attention since they are environmentally friendly green products without any adverse effects on the environment. However, there is a remaining challenge for the industry to make them more effective than synthetic ones in terms of their mechanical properties and long-term durability. These adhesives, with different components such as cellulose, proteins, lignins, and tannins are adhesives which exhibit great potential for the bonding of specially engineered wood products. The modification of bio-based adhesives with different dispersing agents and cross-linkers can improve their strength and water resistance properties to compete with synthetic adhesives. The blending of proteins and carbohydrates can yield good bio-adhesives with acceptable adhesive properties. All these improvements of bio-based adhesives help us move towards ‘sustainable’ products where clean synthesis, biomass and water-based processing are highly desirable. Based on studies conducted in recent decades, the objective of this article is to review the production processes of adhesives from different bio-resources, their necessary modification for improving properties and their utilization in the wood-based industries. Finding the research gaps would also help to hasten the research activities for applying these bio-based adhesives at the industrial scale.</p
Constraints on light Dark Matter fermions from relic density consideration and Tsallis statistics
No full textAbstract The cold dark matter fermions with mass MeV scale, pair produced inside the supernova SN1987A core, can freely stream away from the supernovae and hence contributes to its energy loss rate. Similar type of DM fermions (having similar kind of coupling to the standard model photon), produced from some other sources earlier, could have contributed to the relic density of the Universe. Working in a theory with an effective dark matter-photon coupling (inversely proportional to the scale Λ) in the formalism of Tsallis statistics, we find the dark matter contribution to the relic density and obtain a upper bound on Λ using the experimental bound on the relic density for cold non-baryonic matter i.e. Ωh 2 = 0.1186 ± 0.0020. The upper bound obtained from the relic density is shown with the lower bound obtained from the Raffelt’s criterion on the emissibity rate of the supernovae SN1987A energy loss ε⋅e+e−→χχ¯≤1019 erg g−1s−1 and the optical depth criteria on the free streaming of the dark matter fermion (produced inside the supernovae core). As the deformation parameter q changes from 1.0 (undeformed scenario) to 1.1 (deformed scenario), the relic density bound on Λ is found to vary from ∼ 4.9 × 107 TeV to 1.6 × 108 TeV for a fermion dark matter (χ) of mass m χ = 30 MeV, which is almost 10 times more than the lower bound obtained from the SN1987A energy loss rate and the optical depth criteria
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