Sol-Gel Mesoporous Silica Aerogels and Bio Hybrids for Functional Applications

The thesis covers a systematic investigation on the synthesis of silica aerogels and microspheres with tailored porosity, at ambient conditions by varying the experimental parameters as well as using organic templates. Organically modified silica-gelatin and silica-chitosan hybrids were developed for the first time using alkylalkoxysilanes such as MTMS and VTMS. Application of novel silica-biopolymer antiwetting coatings on different substrates such as glass, leather and textile is also demonstrated in the thesis.

‘‘catalysis by nano sulfated titania modified by transition metals"

in the present study, we have prepared and evaluated the physical and chemical properties and catalytic activities of transition metal loaded sulfated titania via the sol-gel route. Sol-gel method is widely used for preparing porous materials having controlled properties and leads to the formation of oxide particles in nano range, which are spherical or interconnected to each other. Characterization using various physico-chemical techniques and a detailed study of acidic properties are also carried out. Some reactions of industrial importance such as Friedel-Crafts reaction, fen-butylation of phenol,Beckmann rearrangement of cyclohexanone oxime, nitration of phenol and photochemical degradation of methylene blue have been selected for catalytic activity study in the present venture. The work is organized into eight chapters

Catalysis by Modified Pillared Clays and Porous Clay Heterostructures

In this venture three distinct class of catalysts such as, pillared clays and transition metal loaded pillared clays , porous clay heterostructures and their transition metal loaded analogues and DTP supported on porous clay heterostructures etc. were prepared and characterized by various physico chemical methods. The catalytic activities of prepared catalysts were comparatively evaluated for the industrially important alkylation, acetalization and oxidation reactions.The general conclusions drawn from the present investigation are  Zirconium, iron - aluminium pillared clays were synthesized by ion exchange method and zirconium-silicon porous heterostructures were Summary and conclusions 259 prepared by intergallery template method. Transition metals were loaded in PILCs and PCHs by wet impregnation method.  Textural and acidic properties of the clays were modified by pillaring and post pillaring modifications.  The shift in 2θ value to lower range and increase in d (001) spacing indicate the success of pillaring process.  Surface area, pore volume, average pore size etc. increased dramatically as a result of pillaring process.  Porous clay heterostructures have higher surface area, pore volume, average pore diameter and narrow pore size distribution than that of pillared clays.  The IR spectrum of PILCs and PCHs are in accordance with literature without much variation compared to parent montmorillonite which indicate that basic clay structure is retained even after modification.  The silicon NMR of PCHs materials have intense peaks corresponding to Q4 environment which indicate that mesoporous silica is incorporated between clay layers.  Thermo gravimetric analysis showed that thermal stability is improved after the pillaring process. PCH materials have higher thermal stability than PILCs.  In metal loaded pillared clays, up to 5% metal species were uniformly dispersed (with the exception of Ni) as evident from XRD and TPR analysis. Chapter 9 260  Impregnation of transition metals in PILCs and PCHs enhanced acidity of catalysts as evident from TPD of ammonia and cumene cracking reactions.  For porous clay heterostructures the acidic sites have major contribution from weak and medium acid sites which can be related to the Bronsted sites as evident from TPD of ammonia.  Pillared clays got more Lewis acidity than PCHs as inferred from α- methyl styrene selectivity in cumene cracking reaction.  SEM images show that layer structure is preserved even after modification. Worm hole like morphology is observed in TEM image of PCHs materials  In ZrSiPCHS, Zr exists as Zr 4+ and is incorporated to silica pillars in the intergallary of clay layers as evident from XPS analysis.  In copper loaded zirconium pillared clays, copper exists as isolated species with +2 oxidation state at lower loading. At higher loading, Cu exists as clusters as evident from reduction peak at higher temperatures in TPR.  In vanadium incorporated PILCs and PCHs, vanadium exist as isolated V5+ in tetrahedral coordination which is confirmed from TPR and UVVis DRS analysis.  In cobalt loaded PCHs, cobalt exists as CoO with 2+ oxidation state as confirmed from XPS.  Cerium incorporated iron aluminium pillared clay was found to be the best catalyst for the hydroxylation of phenol in aqueous media due to the additional surface area provided by ceria mesopores and its redox properties. Summary and conclusions 261  Cobalt loaded zirconium porous clay heterostructures were found to be promising catalyst for the tertiary butylation of phenol due to higher surface area and acidic properties.  Copper loaded pillared clays were found to be good catalyst for the direct hydroxylation of benzene to phenol.  Vanadium loaded PCHs catalysts were found to be efficient catalysts for oxidation of benzyl alcohol.  DTP was firmly fixed on the mesoporous channels of PCHs by Direct method and functionalization method.  DTP supported PCHs catalyst were found to be good catalyst for acetalization of cyclohexanone with more than 90% conversion.

Studies on Rubber Composition as Passive Acoustic Materials in Underwater Electro Acoustic Tranducer Technology and Their aging Characteristic

The research work has been in the area of compounding and characterization of rubbers for use in under water electro acoustic transducers. The study also covers specific material system such as encapsulation materials, baffle material, seal material, etc. Life prediction techniques of under water rubbers in general have been established with reference to more than one functional property. Ranges of passive materials, besides the active sensing material go into the construction of underwater electro acoustic transducers. Reliability of the transducer is critically dependent on these passive materials. Rubbers are a major class of passive materials. The present work concentrates on these materials. Conventional rubbers are inadequate to meet many of the stringent function specific requirements. There exists a large gap of information in the rubber technology of underwater rubbers, particularly relating to underwater electro acoustic transducers. This study is towards filling up the gaps of information in this crucial area. Water intake into rubber is considered as the single most important issue for the long-term performance of rubbers, especially Neoprene. In this study, the cause and effects of a range of parameters affecting the water absorption by diffusion and permeation have been investigated.

Radiopaque materials from natural polymers: Special emphasis on chitosan and natural rubber

The present work is to impart radiopacity in various natural polymers like chitosan, natural rubber and derivatives of chitosan and to characterize it. This thesis collated the radiopaque properties of these radiopaque polymers and various technological applications in the medical field. The applications of radiopaque polymers leads to an exploitation of radiopaque properties like X-ray visibility, optical density, effective atomic number, attenuation coefficient of biopolymers like chitosan, chitosan formate, chitosan acetate, carboxy methyl chitosan and natural rubber. The radiopaqe properties of these materials highly depend upon the size, shape, amount of radiopacifier and crystallinity of the radiopaque material. Radiopaque chitosan microspheres were prepared by cross linking with glutaraldehyde followed by the encapsulation of barium sulpahte. The effect of different emulsion systems on the morphology of chitosan microspheres were studied. The study concentrates radiopaque natural rubber for shielding applications. It reveals that to improve the particle size, morphology and crystalline phase of the zinc oxide particles, a novel method for the preparation of zinc oxide is adopted. A detailed radiopacity study was done in natural rubber containing 100phr precipitated zinc oxide prepared from different zinc salts. One of the significant findings of this investigation is that NR vulcanizates containing precipitated zinc oxide (from zinc acetate) shows higher attenuation coefficient. These interesting findings reveal the applications of these natural radiopaque systems in various fields like surgical tools, medical tubings, catheters, radiation shielding,etc.

Tailored Ion Imprinted Polymer Materials for the Preconcentrative Separation of Noble Metals

Tailored ion imprinted polymer materials for the preconcentrative separation of noble metals. This study deals with the synthesis, separation,characterization and analytical application of the noble metals especially palladium and platinum. Platinum group metals(PGM) are currently receiving world wide attention. This group include Palladium(Pt),rhodium(Rh), ruthenium(Ru), iridium(Ir) and osmium(Os).PGM are used as catalysts for a wide variety of hydrogenation, oxidation, isomerization,cyclization,dehydrogenation and dehalogenation reactions.The corrosion resistance of PGM enables them to use in jewellery,electrical and glass industries,extrusion of synthetic fibres,manufacture of laboratory utensils,dental and medical devices. This study clearly establishes selective recovery of platinum from other noble and transition elements.

Optical absorption studies in ion implanted and amorphous semiconductors - Investigations in some tetrahedrally co-ordinated and chalcogenide materials

The thesis provides an overall review and introduction to amorphous semiconductors, followed by a brief discussion on the important structural models proposed for chalcogenide glasses and their electrical, optional and thermal properties. It also gives a brief description of the Physics of thin films, ion implantation and Photothermal Deflection Spectroscopy. A brief description of the experimental setup of a photothermal deflection spectrometer and the details of the preparation and optical characterization of the thin film samples. It deals with the employment of the subgap optional absorption measurement by PDS to characterize the defects, amorphization and annealing behavior in silicon implanted with B+ ions and the profiles of ion range and vacancy distribution obtained by the TRIM simulation. It reports the results of all absorption measurements by PDS in nitrogen implanted thin film samples of Ge-Se and As-Se systems

A Simple Free-Space Method for Measuring the Complex Permittivity of Single and Compound Dielectric Materials

A simple and efficient method for determining the complex permittivity of dielectric materials from both reflected and transmitted signals is presented. It is also novel because the technique is implemented using two pyramidal horns without any focusing mechanisms. The dielectric constant of a noninteractive and distributive (NID) mixture of dielectrics is also determined

Synthesis, Characterization and Properties of Ca5A2TiO12 (A=Nb, Ta) Ceramic Dielectric Materials for Applications in Microwave Telecommunication Systems

Microwave ceramic dielectric materials Ca5Nb2TiO12 and Ca5Ta2TiO12 have been prepared by a conventional solid-state ceramic process. The structure was studied by X-ray diffraction and the dielectric properties were characterized at microwave frequencies. The ceramics posses a relatively high dielectric constant, very low dielectric loss (Q5 x f > 30000GHz) and small temperature variation of resonant frequency. These materials are potential candidates for dielectric resonator applications in microwave integrated circuits. [DOI: 10. 1 143/JJAP.41.3834]