Nano Technology - Theses

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Phenomenological and physical modelling of high homologous temperature deformation

(University of Hyderabad, 2016-04-01) Sriharsha, Sripathi ; Dibakar Das

The main focus of this study is to critically assess the relevance or otherwise of a mesoscopic grain boundary sliding controlled flow model, which has been proposed as the common basis for explaining superplastic deformation in different classes of materials. The rationale behind this approach is that, as superplasticity is observed to be a near-ubiquitous phenomenon, there could be an underlying physical phenomenon responsible for this. If this were the case, the phenomenology of the superplastic flow process should also be similar for different classes of materials, i.e. there should be a universal curve for superplastic flow in all systems if the experimental variables like stress, strain-rate, strain-rate sensitivity and temperature of deformation are correctly normalized. Starting from these premises, it has been shown that under isothermal conditions the    log logσ ε plots of superplastic materials of different classes and the variation of the strain-rate sensitivity with  log ε for materials of different classes have near-identical features. The viscosity and the free energy of activation of all the alloy systems at (nearly) the same homologous temperature also vary quite similarly. Thus, the universality in the mechanical response of superplastic alloys is demonstrated. Further, the mesoscopic-grain boundary sliding controlled flow model for superplastic deformation, initially proposed for micron-grained metallic materials, but later extended to include dispersion strengthened alloys, intermetallics, metals with a quasi-crystalline phase, ceramics and ceramic-composites was taken up for consideration. An algorithm was developed to analyze the experimental data in terms of this model, so that many systems could be analyzed successfully. It has been shown that the mesoscopic-grain boundary sliding model satisfactorily describes superplastic deformation in metals and alloys, dispersion strengthened alloysceramics, composites, intermetallics, nanostructured materials and a material containing a quasi-crystalline precipitates and of grain sizes ranging from a few micrometers to a few nanometers. Also, the same approach has been used to satisfactorily explain superplasticity in geological materials and ice. In the present state of its development, in the mesoscopic-grain boundary sliding controlled model, even though theoretical expressions exist, the values of the free energy of activation and the threshold stress needed for the onset of mesoscopic- grain boundary sliding are treated as fitting constants. By way of applying the ideas to an allied, relevant situation, the mesoscopic-grain boundary sliding controlled model was also used to satisfactorily account for the inverse/ reverse Hall- Petch effect observed in materials when the grain size is in the lower ranges of the nanometer scale. Future efforts could be towards a theoretical framework at a mesoscopic level, by estimating the threshold stress necessary for the onset of mesoscopic-grain boundary sliding a priori
Study of the influence of the different synthesis parameter on the structure, morphology, bonding and properties of the graphene oxide (GO), reduced graphene oxide and graphene/alumina nanocomposites

(University of Hyderabad, 2017-03-01) Demudubabu, Dommisa ; Dash, Raj Kishora

Graphene is an emerging material due to its unique properties such as electrical, mechanical, optical, chemical and thermal properties and hence it has a lot of potentials to use in several applications. The graphene oxide is generally defined as a single layer of graphene with oxygen functional groups present in basal planes and edges of the graphene structures. These functional groups are mostly hydroxyl, epoxide, ketone and carboxyl on the surface of graphene layer at basal plane and edges. Therefore, GO is easily dispersible in water and other organic solvents and hence, mostly applicable in different forms such as thin films, composites and hybrid materials. Composites are novel type materials and have unique properties than host matrix. Graphene can be used in the composite material as filler to develop novel composites which have novel and unique properties. Comparative other nanomaterial graphene is more suitable for making the nanocomposite because of easy synthesis process of graphene with large-scale production for industrial application. To prepare the graphene-based composite mostly used graphene derivatives, it has tunable electrical and optical properties, based on the composite properties the applicationsFrom the recent literature, we have concluded that graphene oxide can be synthesized by a chemical process which is a simple, cost- effective and more economical. Further, the obtained GO can be reduced by using suitable reducing agents to obtain reduced graphene oxide(RGO), which has a lot of potentials to be used in several applications. However, most of current studied mainly focus on the synthesis of the graphene oxide and the corresponding reduced graphene oxide by using one size graphite precursor material (~45μm). Therefore, the impacts of the different size graphite precursors ( very smaller to a larger size) as starting material for synthesis of GO and RGO and the details study of the oxidation process, structure, Morphology, bonding characteristics etc are not addressed to our best knowledge. Therefore, there is a lack of clear understanding of the influence of different sizes graphite precursor on the synthesis of GO and RGO by a chemical process. Thus, these issues and challenges need to be addressed. Further, the oxidation reaction temperature is a key factor for controlling the properties of the GO, and further, the quality of RGO obtain from the as-synthesized GO. Hence, the influence of the reaction temperature of the oxidation process need to be addressed and a more details investigation of its effects on the structure, morphology, bonding to be required. Moreover, the reduction of GO to RGO is generally carried out in a few solutions, so more work is still required to understanding the solution effects on the reduction of GO to RGO. In the second part of literature review part, we have thoroughly searched all the recent literature on the synthesis and characterization of the graphene/alumina nanocomposite for its potential to be utilized as potential materials for several applications such as energy, storage devices, capacitors, memory devices and so.on. Though, there are several existing syntheses processes has been reported by several groups and also mentioned that electrical and mechanical properties can be improved by 7 fabrication of the graphene alumina nanocomposite. It is observed that most of the reported work has chosen the α – phase alumina nanoparticles to synthesize the nanocomposites due to the stable phase of the alumina. Also, few reported work are existing, where they have prepared alumina by choosing the alumina precursor to synthesize the alumina by chemical processes such as sol-gel method, finally fabricating the graphene/alumina nanocomposites. Moreover, the most of the reported work mainly focuses on the fabrication of the bulk materials by SPS process and then to investigate the different properties of the nanocomposites. Therefore, to the best of our knowledge, still, there is a lacking of clearly understanding the graphene /alumina nanocomposite structure, morphology, and bonding characteristics, when γ – phase alumina is employed as matrix material insisted of α – phase alumina. Further, the as the obtained powder form of the graphene /alumina nanocomposite need to be studied in details, as these powder form can be used as starting material for thin films formation, for another hybrid material synthesis and also for utilizing as filler material for more complex hybrid material fabrication. Thus there are still more challenges are there to clearly understand the GO and RGO synthesis process by a chemical method and also for fabrication of graphene /alumina nanocomposites for effectively using these materials for mass production and also for several practical applications. In this thesis research work, the influence of the synthesis parameters such as oxidation reaction temperature (low and high) on the structure, morphology, bonding and properties of the graphene oxide(GO) and the corresponding chemically and thermally reduced graphene oxide(RGO) was studied by using the standard Modified Hummers synthesis method. In the second part of the thesis work, the influence of the different sizes source graphite on the synthesis of graphene oxide (GO) and corresponding reduced graphene oxide (RGO) was investigated by choosing the optimum synthesis parameters as obtained from the first part of the research work. The impacts of host graphite powder sizes on the structure, morphology, disorder, bonding and properties were also investigated by using the different analytical instruments. In the final part of the thesis work, a set of six GO/RGO-Al2O3 nanocomposite was synthesized by choosing -phase Al2O3 using the colloidal mixing process and the effects of the different additives such as HCl, Hydrazine hydrate and without any additives were investigated. The corresponding nanocomposites structure, morphology, bonding, interface and thermal stability were investigated by using different analytical instruments such as XRD, FESEM, TEM, FT IR, Raman spectroscopy and TGA/DTA for understanding the nanocomposite formation. Graphene oxide was synthesized by varying the reaction temperature (low and high) by using the equal ratios of graphite, H2SO4, NaNO3 and KMnO4. All the samples were analyzed by using the XRD, FT IR, Raman, TEM, FESEM, UV and TGA/DTA for structural, molecular & bonding characteristics, morphological and thermal analysis. Experimental results indicated that oxidation reaction temperature has an effective role in the synthesis of GO. It was observed that low- temperature reaction showed the good quality of graphene oxide(GO) with better structural, less disorder and 2-3 layers of GO as compared to the higher reaction temperature. Further, the 8 corresponding reduced graphene oxide (RGO) was obtained by using hydrazine hydrate and thermal reduction process, and experimental results confirmed that the RGO which was obtained by using the lower reaction temperature GO showed less disorder, more graphical structure, flat type and 2-3 layers as compared to the GO obtained at higher temperature. Three different sizes graphite precursor (2-15 μm, <45 μm, and 170-840μm,) were oxidized by MHM method and then corresponding RGO were synthesized by the hydrazine hydrate reduction process. The experimental results indicated that the smaller size precursor graphite was fully oxidized in comparison to the large size graphite as source material. Hence, oxidation of graphite to graphene oxide is size depended on the source graphite and also showed better quality of reduced graphene oxide than other sizes. Further, from the TGA and DTA analysis, it is observed that different weight loss and different exothermic peak position in the graphite oxide which suggest that weight loss also depends on the size graphite due to the oxidation rate. UV spectroscopy analysis shows different abortion peaks which indicated that all the sizes graphite oxidized differently. Hence, the precursor graphite size has a key role in the synthesis of GO and corresponding RGO. A set of six GO/RGO-Alumina nanocomposites were prepared by colloidal mixing process by varying the reaction temperature (at RT and 800c) and different additives such as HCL and hydrazine hydrate. From all the analytical analysis results such as XRD, FESEM, FTIR, Raman, TEM is TGA and DTA, it was concluded that only when hydrazine hydrate was used as an additive GO was reduced during the synthesis process and RGO – Al2O3 nanocomposite was formed. All other cases GO – Al2O3 nanocomposites formed. Hence, RGO-Alumina nanocomposite can be synthesized by using hydrazine hydrate as an additive during fabrication process by using a smaller size -phase alumina nanoparticles. Different GO/RGO- Al2O3 nanocomposites were synthesized by using the optimum process parameters as obtained by varying the wt% GO (0.5, 1, 3, 5, 10 and 20 wt %) and all the samples were analyzed by using XRD, FT IR, Raman and TEM. Experimental results indicated that as the GO content increases more disorder and less agglomeration of the alumina nanoparticles are observed. Further, it was seen that as the GO content increases the oxygen-related function groups are removed because of more interaction between the GO and alumina nanoparticles. In this thesis work, GO/RGO- alumina nanocomposites were synthesized and formation of the graphene-alumina nanocomposite was confirmed based on the structural, bonding, morphological and TGA/DTA analysis, however still to use such nanocomposites in practical application such as energy storage, memory devices and other applications, properties such as mechanical, catalytic and electrical are needed to be addressed. Therefore, the future scope of this thesis works to investigate the electrical, mechanical properties and the percolation threshold in order to utilize this nanocomposite for practical memory devices and energy applications.
Synthesis and characterization of advanced multifunctional magnetic nanoparticles for biomedical applications

(University of Hyderabad, 2017-03-01) Qasim, Mohd. ; Dibakar Das

Magnetic nanoparticles (MNPs) have potential applications in the various biomedical fields including anticancer drug delivery, magnetic resonance imaging (MRI), destruction of the tumor via hyperthermia, bio-separation, catalysis, etc. Development of multifunctional magnetic nanoparticles (MFMNPs) could significantly expand the properties of existing magnetic nanoparticles as it combines many different functionalities in a single platform which make them suitable candidates to achieve simultaneous diagnosis and therapy for cancer treatment. Particularly, the design and synthesis of MFMNPs is an extremely focused and dynamic area of present biomedical research because of their potentials applications in targeted drug delivery, multimodal imaging, hyperthermia, photothermal therapy etc. Different combinations of functional materials with different size and shape have been explored to develop MFMNPs based nanocarriers aiming to enhance the effectiveness and safety of anticancer drugs. In this thesis, preparation, characterization and biomedical applications of various advanced multifunctional magnetic nanoparticles have been discussed. First, different types of MNPs have been synthesized and characterized. Then, different multifunctional nanocomposites nanoparticles such as NZF@Alb, Fe3O4@Alb, CF@Alb, mSiO2- CaFe2O4@P(Nipam-Aa), mesoCaCO3@CaFe2O4, NZF@mSiO2, NZF@mSiO2-CuS- PEG, NZF/Zn0.95Ni0.05O, NZF/Zn0.95Ni0.05O-mSiO2, mesoCaFe2O4 NPs, mSiO2@AgNPs and mSiO2@Ag-Fe3O4@P(Nipam) have been prepared. The structural, morphological, thermal, optical, magnetic properties and drug loading/release behaviour as well as biocompatibility/cytotoxicity of prepared multifunctional magnetic nanoparticles have been investigated. Anticancer activities of prepared anticancer drug-loaded multifunctional nano-formulations have been studied against Hela cells. Obtained results show that the present study could be extremely useful for the advancement of multifunctional magnetic nanocarrier’s design and development for biomedical applications.
Synthesis and dielectric behavior of various novel metal oxide decorated reduced-graphene oxide composites

(University of Hyderabad, 2017-04-01) Rama Krishna, Jammula ; Srikanth, V.V.S.S

Developing novel dielectric materials has always been an interesting area in material’s research owing to their importance especially in capacitive energy storage. In this context, at the time of problem formulation for this thesis work (i.e., during the year 2012), the dielectric behavior of graphene filled polymers has attracted good attention. However, at that time there were no reported works on “dielectric behavior” of metal oxides (time tested dielectric materials) and graphene containing nanocomposites. Therefore in this thesis work elucidation of various aspects of dielectric behavior of reduced-graphene oxide (r-GO) and metal oxide containing nanocomposites has been taken up. Owing to the presence of residual oxygen functional groups and defects in r-GO, it is hypothesized that it will have a unique influence on the dielectric behavior of metal oxides and r-GO containing nanocomposites. As anticipated, a unique and strong interfacial polarization (Maxwell-Wagner polarization) was observed in metal oxide decorated r-GO nanocomposites synthesized by molecular level mixing technique which resulted in homogenous distribution of metal oxide particles on the surfaces of r-GO sheets. In this thesis work, CuO/r-GO, ZnO/r-GO, MgO/r-GO and NiO/r- GO nanocomposites were synthesized and their dielectric behavior in correlation with their morphology, crystallinity/phase and composition has been elucidated. This thesis also provides a comprehensive treatment to understand the dielectric behavior, especially the dielectric relaxation in metal oxide and r-GO containing nanocomposites. The treatment involves fitting experimental results with suitable theoretical models (for example, Havriliak- Negami relaxation model) that enable the intricate examination of physical mechanisms that controlled the dielectric behavior of the nanocomposites under consideration. Percolation effect on the dielectric permittivity was elucidated in the case of NiO/r-GO nanocomposite which exhibited a giant dielectric permittivity of 3688. This work will pave a way to understand and control the possible physical mechanisms that might take place at a very small length scales and in turn will be useful to control the dielectric behavior of graphene based nanocomposites in particular and nanocomposites, in general
Few layered graphene and its composites as anode materials in Li-ion batteries and EMI shielding materials

(University of Hyderabad, 2017-06-01) Sandeep Kumar, Marka ; Srikanth, V.V.S.S

In this thesis, few layered graphene (FLG) and its composites are synthesized using easy and novel synthesis routes. The synthesized composites are tested as anode materials in Li ion batteries and as materials for electromagnetic interference (EMI) shielding. Two novel graphene based composites namely Co2Mo3O8/reduced graphene oxide (Co2Mo3O8/rGO) and Germanium/reduced graphene oxide (Ge/rGO) composites are synthesized and tested as anode materials in Li ion batteries while two other novel composites namely few layered graphene (FLG)/poly vinyl alcohol (PVA) and graphene wrapped magnesium oxide (G@MgO)/PVA composites are synthesized and tested as EMI shielding materials. Co2Mo3O8/rGO composite is constituted with hierarchical and submicron sized Co2Mo3O8 hexagonal nanoplatelets (50 nm thick) entrenched in between thin graphene layers. When cycled in the voltage range of 0.005-3.0 V at a current density of 60 mA/g, Co2Mo3O8/rGO composite delivered an excellent reversible specific capacity of ~954 mA h/g that corresponds to 82% capacity retention at the end of the 60th cycle which is higher than the theoretical capacity of both Co2Mo3O8 and graphene. Co2Mo3O8/rGO composite also showed excellent rate capability. Electrochemical conversion and electrochemical adsorption and desorption are found to be the primary reasons for Li storage in Co2Mo3O8/rGO composite. Excellent synergy between Co2Mo3O8 and rGO in the composite is attributed for the observed high specific capacity, long cycle life and good rate capability. When Ge/rGO composite was cycled in the voltage range of 0.005-3.0 V at a current density of 160 mA/g, it showed an excellent reversible capacity of ~539 mA h/g that corresponds to 98% capacity retention at the end of the 100th cycle. Ge/rGO composite also showed high reversible capacity retention, good rate capability, and excellent cycle life. Alloying, de-alloying and electrochemical adsorption and desorption type reaction mechanism are the primary reasons for lithium storage in germanium and graphene, respectively. In the case of EMI shielding materials, 1 mm thick FLG/PVA composite sheets containing 0.2 and 0.6 wt.% of FLG as filler are prepared using a simple casting process. A maximum electromagnetic interference (EMI) shielding effectiveness (SE) of ~19.5 dB (in the X-band, 8.2–12.4 GHz) was obtained in case of the FLG/PVA composite with 0.6 wt.% of FLG. Absorption is found to be the dominant mechanism for EMI shielding. The high EMI SE is attributed to the network-like features formed by FLG in PVA matrix. In another work, temperature (30-120 °C) dependent complex permittivity of 1 mm thick G@MgO/PVA_Coag (0.4, 0.6, 0.8, 1.0, 3.0, 10.0, and 15.0wt.%) and G@MgO/PVA_ac (0.4, and 3.0wt.% as-casted) composite samples in low frequency (20 Hz - 2 MHz), and high frequency (i.e., 8.2-12.4 GHz)ranges are measured. In both the frequency ranges, G@MgO/PVA_Coag composites performed superior dielectric properties than PVA, and G@MgO/PVA_ac composites. A strong interfacial polarization (from M” vs. log (f) plots) is observed in coagulated, and as-casted G@MgO/PVA composites. It is noticed from the calculated activation energies that conduction is the dominating mechanism for energy transfer in both the composites, however, it is predominant in G@MgO/PVA_Coag composites than in G@MgO/PVA_ac composites. In the X-band, EMI SE of the G@MgO/PVA_Coag composites is greater than that of the G@MgO/PVA_ac composites at a particular weight fraction of G@MgO. At 30 and 120 °C, the average EMI SE values of ~14.2 and ~18.9 dB, respectively, are measured for 10.0 G@MgO/PVA_Coag while 15.0G@MgO/PVA_Coag composite showed EMI SE of ~20.6 and ~27.5 dB, respectively. In the case of G@MgO/PVA_Coag and G@MgO/PVA_ac composites too absorption is found to be the dominating mechanism for EMI SE.
Study on uniquely modified diamond, diamond / B-SiC nanocomposite and graphene nitride (g-C3 N4) surfaces

(University of Hyderabad, 2017-08) Vara Lakshmi, Bommidi

Diamond and diamond/β-SiC composite films are being widely studied for their wear resistant, structural and electronic properties. Of the various methods researchers use to modify the structure of these films, using irrradiation techniques in particular are of interest due to their versatility. This thesis work was carried out to: (i) understand the indentation damage and electrical properties of diamond/β-SiC nanocomposite thin films, (ii) modify (i.e., phase, structural and/or morphological) the diamond films by using ion beam implantation/irradiation technique, (iii) modify the surface morphology of g-C3N4 by using ion implantation/irradiation, (iv)Fabricate the metal-insulator-semiconductor active structures in diamond films. The forms of diamond and diamond/β-SiC nanocomposite films resulting from such modifications are investigated using Raman spectroscopy in conjunction with scanning electron microscopy and x-ray diffraction were carried out to understand the microstructure and phase information. Also as-grown diamond/β-SiC nanocomposite films are investigated with mechanical and electrical testing. The impact of these characterizations will provide the valuable perspective to researchers in materials science. Understanding the changes to the structure and properties of this class of thin films which can be induced through various mechanisms will allow future researchers to refine these films towards technological applications in areas of hard coatings, electronics and biosensing. Raman scattering experiments in conjunction with scanning electron microscopy and x-ray diffraction were carried out to extract microstructure and phase information of the gamma and nitrogen ion irradiated diamond thin film surfaces. The γ-irradiation of diamond films showed no phase, surface and structural changes. The nitrogen ion implantation with 100 keV results increase in sp2-C network in diamond films which leads to improve the surface conductivity of these films. This nitrogen ion implantation of diamond films fabricate the metal-insulator-semiconductor (MIS) active surfaces which are used in electronic device applications. The graphene nitride (g-C3N4) materials are used in energy applications. The silicon implanted/irradiated g-C3N4 showed sheet like morphology with stable phase and structure of graphene nitride which are used in lithium ion batteries applications.
Development of metal-assisted chemical etching (MACE) based silicon (Si) nano/microstructures and their applications in surface enhanced Raman spectroscopy (SERS) for chemical sensing

(University of Hyderabad, 2018-04-01) Borgohain, Debabrot ; Dash, Raj Kishora

Surface-enhanced Raman Scattering (SERS) has emerged as a key research area for its excellent detection capability and fingerprint identification of the various chemicals such as methylene blue (MB), malachite green (MG), melamine etc. Recently, it has drawn tremendous attention for potential application in the food sector, medical sector, security sector etc. Though some progresses have already been achieved in the molecular level detection of chemical species with SERS technique, still more challenges are there such as repeatability, scalability, reproducibility, shelf life. One of the key factors is the development of the SERS substrates for improvements in the SERS signal and detection limit as well. In this regard, significant progress has already been achieved in the fabrication of the SERS-active substrates by using both the top-down and bottom-up approaches. Bottom-up approaches, such chemical synthesis, self-assembly, electrodeposition, dip-coating processes are successfully employed to fabricate SERS-active substrates. On the other hand, the top-down approaches, such as lithography, oblique angle metal film deposition and metal-assisted chemical etching (MACE) and which are mainly used to fabricate various nanostructures, has shown very effective and reproducible SERS-active substrates preparation. However, still preparation of the SERS substrates with enhanced Raman signal and also with higher detection limit have been considered as the main challenges and need to be addressed. Though, several existing approaches such as conventional or unconventional nanofabrication methods are used for the preparation of Si-based SERS substrates by top-down approach, MACE process is emerging as a very simple and cost-effective process for fabrication of the nanostructures and hence, it has gained sufficient attention globally. Thus, the main objective of this present work is to fabricate Si nano/microstructure by using MACE process and then utilizing these Si substrates for detection of the methylene blue (MB).Different nano/microstructures were fabricated on Si by using noble metals catalyst such as gold (Au) and silver (Ag). The effect of different etching parameters such as thermal annealing of the metal catalyst, effect of the concentration of the oxidising agent, those are directly associated with the MACE process were investigated. The experimental results revealed that the thermal annealing process eliminated the pin-holes present in the metal catalyst when 50 nm thick Au acted as metal catalyst and successfully fabricated deeper micro-trenches on Si substrates than the un-annealed counterpart of it. Moreover, it also indicated that higher thickness of the metal catalyst micro-stripes help to fabricate flat bottom type deeper trench than the thinner counterpart. Furthermore, the mechanism for the obtained results are discussed in the thesis. The morphological effect of the metal micro-stripes was also examined and the results indicated that various nano/microstructures could be fabricated by controlling the morphology of the used metal catalyst. As it is very well known fact that the SERS detection limit or enhancement of Raman signal primarily depend on the fabricated nano/microstructures present on the surface of the Si substrate and incorporated with the noble metal (Ag) nanoparticles. The performance of the Si-based SERS substrates was tested for the chemical detection of MB with very low concentrations starting from nM to pM, and the result indicated that nanostructured Si substrate showed better SERS detection than its microstructured counterpart. The probable reasons for such behaviours are also discussed. More studies were also carried out to enhance the detection limit of the MB, since higher the detection limit is better for the usability of these substrates for molecular level detection of different chemical species. Thus, combination of discontinuous Au film and Ag nanoparticles (NPs) were deposited on the nanoporous Si substrates, those were obtained by MACE process and the result suggested that the detection limit of MB can be further improved by depositing discontinuous Au thin film with various thicknesses. It is also noticedfrom the experimental results that up to certain thickness of the Au discontinuous thin films, it helps to improve the limit. On the other hand, higher thickness of the Au discontinuous thin films, degrades the detection limit. Thus, there is a direct correlation between the detection limit and the thickness of the Au discontinuous film on the nanoporous Si substrate. Our experimental findings suggested that the best detection could be achieved when a combination of 30 nm Au discontinuous thin film and Ag NPs were used for preparation of the SERS-active substrates which can detect 10 pM MB. Furthermore, highest enhancement factor of the order of 108 is also achieved with this same combination of Au discontinuous thin film and Ag NPs. Thus, we believe that the prepared SERS-active substrate in this work can have the capability to detect MB at molecular level. We believe that the easy, simple and reusable SERS-active substrates will be more helpful to develop chemical sensors to detect molecular level chemical species other than MB with higher enhancement factor and can be utilized for the food safety, environmental monitoring, security and medical diagnosis in the near future.
Design of novel mesoporous nanocapsules and their therapeutic efficiencies as a drug delivery carrier and to enhance the immunological responses

(University of Hyderabad, 2018-11-01) Pradip Paik

With passing time medical field has been improving rapidly, because of incessant new inventions by researches in this particular field. Presently, nanotechnology has strengthened its root in all trajectory of the biomedical field with a focused persistence for human healthcare and together it can be termed as nanobiotechnology. Consequently, it has shown potential in drug formation, preventing and curing any disease, cancer therapy, drug delivery system, tissue engineering, MRI contrast agent and many more. Biocompatible and biodegradable nanomaterials play a noteworthy part in this trait. Currently, porous nanomaterials have enlightened the tremendous possibilities in the applied field of biotechnology by offering void space to encapsulate or entrapped particles in it like a nanocargo followed by delivery those encapsulated particles in the site of interest by a sustained controlled release and after unloading that nanocargo in physiological condition without leaving any side effects. Encapsulated particles can be drugs, biomolecules, gene, protein and a range of therapeutics. From a healthcare point of view, these nanomaterials with characteristic porous structures can decrease the doses of drugs thereby reducing toxicity occurred due to the therapeutics and also increase the possibility of bioavailability of therapeutics. Then the challenge occurred with the size of the nanocarrier along with the size of the pores. Therefore, synthesis of nanomaterials with all required characteristics as a carrier has become vital. However, polymer nanostructures are getting additional highlights because of their biocompatible and biodegradable nature but few metal NPs like silica, zinc oxide, quantum dots, titanium dioxide, iron oxide, etc. have also proved their efficiency as nanodrugcarrier with small size, rigid arrangements, long shelf life as well as interact with cellular biomolecules thereby facilitates admittance into the cell. This dissertation comprises a detail synthesis approach of three types of polymeric and inorganic nanomaterials with varying sizes, followed by a complete systematic characterization for the biomedical application. Conventional sole gel techniques, chemical synthesis by using nanotemplates and surfactant free sonochemical technique have been followed for the synthesis of nanomaterials with different characteristics such as core-shell, hollow porous and mesoporous. Three different therapeutic fields have been included in this work for theapplication purpose of synthesized porous structured nanomaterials and the fields are Malaria, Immunology and Cancer Therapy. Malaria is becoming a big threat in human by becoming resistant to almost all available malaria medications and thereby causing about 216 million cases in 91 countries annually with 445000 deaths according to WHO. There instant proper up gradation in the Malaria treatment is becoming a very urgent issue. The first part of this dissertation includes the development of a coreshell nanostructure where different sizes of SiO2 NPs synthesized by sole gel technique have been used as core and PCL polymer formed the outer shell layer. Later the templates SiO2 NPs have been etching out to create a new PCL NC with hollow porous morphological characteristics. This novel amorphous hollow porous PCL NCs are biocompatible biodegradable and have a great encapsulation efficiency while loaded with antimalarial drugs Dihydroartemisinin and Chloroquine and Sulfadoxine. Their antimalarial activities have been studied with Malaria causing P. falciparum parasitic cell culture where these NCs have efficiently inhibit the growth of the parasite-infected RBCs compared to free drugs. These NCs are unique because they can be tuned as a “time temperature clock” module i.e., they can be tuned with predetermined drug dosses obligatory for the Malaria treatment with an increase of body temperature due to the infection. This nanodrugcarrier has the potential to control the release of confined drugs from it as soon as the temperature arises gradually reduces the release of drug with a gradual decrease in the temperature to normal. Therefore, this unique polymer based NCs can be used as nanodrug carrier for eradicating P. falciparum growth efficiently. In the field of nanobiotechnology, nanostructures based on metal have received importance recently for the formation of vaccines. Moreover, nanostructured with porous morphology is an excellent candidate in that regard. The second part of this dissertation included designing of nanostructured ZnO with mesoporous morphology by surfactantfree sonochemical method. This unique stable mesoporous ZnO NCs showed outstanding loading efficiency by encapsulating protein Ova. These protein loaded metal oxide NCs have immunized in mice model to investigate the enrichment of immunological responses. Ova has worked as an antigen in this regard for improvement in CD8+ and CD4+ T-cell effector responses. Antigen-specific IgG levels and IgG2a or IgG2b levels in serum has also increased when lymph node and serum of Ova loaded mZnO immunized mice have studied. The role of mesoporous ZnO NCs in enriching the immune response makes it as a good promoter to design nanovaccines in the field of medicine to prohibit various ailments. Later these mesoporous nanocarriers have been used to encapsulate antimalarial drugs Dihydroartemisinin,Chloroquine and Sulfadoxine and anticancer drugs DOX and paclitaxel and a systematic sustained controlled drug release pattern can be observed in each drug conjugate nanoformulations. The cellular level interaction of drugs loaded mZnO NCs with cancer cell line K562 have been studied where these NCs entirely deformed the malignant cell structures and thereby proved their efficiency as a drug carrier. With the development of biomedical field, the therapeutic field Cancer has also developed. A part of credit can be claimed by the involvement of nanotechnology in this particular medical field with new innovative researches to avoid complications related to the treatment. The third part of this dissertation includes engineering of a core-shell nanostructure with mesoporous ZnO NCs as a template and polymer PCL as coating layer where 2-3 templates were coated by a polymeric shell. Later these temples were etched out by leaving pores in the polymer nanostructures. This amorphous NC is biocompatible and biodegradable in nature with a great drug encapsulation efficiency. Biocompatibility of this NCs with the templates as well as without templates were investigated with two different breast cancer cell lines MCF 7 and MDA-MB-231 respectively. The drug Paclitaxel has been used to load inside the NCs pores and cell inhibition assay have been conducted by using MCF 7 and MDA-MB-231 where drug loaded with NCs performed more malignant cell inhibition property compared to free Paclitaxel drug. Moreover, this nanocarrier showed lower IC50 compared to free drug. Thus these polymer-based nanodrug carriers can decrease the toxic drug doses thereby reducing side effects and also can increase the bioavailability of therapeutics.
Integration of solution processed novel graphenaceous materials as functional layers in dye sensitized and polymer solar cells

(University of Hyderabad, 2019-04-01) Charanadhar, Nagavolu ; Srikanth, V.V.S.S

Harnessing renewable solar energy through different technologies is greatly dependent on the advancement of solar grade materials’ science and engineering. Worldwide, scientists and engineers are focusing on developing novel solar cell designs which can be easily manufactured at low cost. In this context, 3rd generation (3G) solar energy technologies namely Gratzel cells or Dye Sensitized Solar Cells (DSSCs) and Bulk heterojunction organic photovoltaics (BHJ OPV) are expected to challenge the performance of Si based solar cells and compete for a significant market share in the field of next generation solar cells. These technologies gained prominence due to their low cost, light weight construction and printable nature over large area flexible substrates. This thesis work demonstrates an integration of inexpensive novel Graphenaceous Materials solution, for the above mentioned solar technologies energy harvesting, explore selection of suitable material for their energy efficient utilization and fabrication method. Initially, Graphene oxide (GO) was synthesized using a modified Hummers method and was reduced by using focused sunlight to obtain solar reduced graphene oxide (SRGO). GO and SRGO are then used as Pt free counter electrode materials in dye sensitized solar cells (DSSCs). GO and SRGO counter electrodes were prepared by a simple spray coating method to produce homogeneous electrode layers. The DSSCs with GO and SRGO counter electrodes exhibited an overall power conversion efficiencies of ~3.4 and ~4%, respectively. Cyclic voltammetry and electrochemical impedance spectroscopy reveal that the DSSC with SRGO counter electrode exhibits higher electro-catalytic activity and lower charge transfer resistance at the electrode/electrolyte interface (in comparison to the DSSC with GO) resulting in higher conversion efficiency. Moreover, the microstructural features of SRGO are found to be suitable for its improved interaction with the liquid electrolyte and the enhanced electro-catalytic activity at its surface.

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