Department of Chemistry

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Browsing Department of Chemistry by Author "Halder, Arnab"

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    Photoluminescence study of the synthesized nanomaterials in presence of macromolecules and heavy metal ions
    Halder, Arnab
    This work illustrates synthesis, structure, band modulation and optical tuning of many kinds of carbon-based nanomaterials. Among the different types of natural and synthesised carbonbased materials, graphene and graphene oxide based nanomaterials, which include graphene oxide, functionalized graphene oxide, graphene oxide quantum dots, graphene quantum dots have wide range of multidimensional applicability in various field of science and technologies. Non emitting behaviour of graphene and very low photoluminescence quantum yield of graphene oxide restrict their utilities in optoelectronics and optical tracking in biology. As a new approach, incorporation of lanthanide metal ion, cerium, in to graphene oxide based nanoparticles becomes successful to increase a 100-fold amplification of photoluminescence intensity is obtained. The origin of this enhancement of GO-Ce nanoparticles is investigated by examining the interactions between cerium ions and GO nanoparticles as well as the structural modification of the GO nanoparticles in presence of cerium. A mechanism that includes energy pumping of cerium by photoexcited GO nanoparticles and photoinduced reduction of non-emissive Ce (IV) to luminous Ce (III) is supported by experimental data. To understand the interactions based on the local environment of the cerium ions, we have explored the effect of aromatic nitro compounds and fluoride ions on the photoluminescence of cerium incorporated GO nanoparticles. Experimental observation on the basis of fluorescence quenching reveals the role of accessibility and local polarity of the excited cerium (III) ions. By incorporating surface functional groups, photoluminescence from graphene oxide (GO), and hydroxyl enriched graphene oxide quantum dots (OH-GO QDs) in the UV-visible range, we have examined the interaction between the graphene oxide layers. The contribution of the visible PL band is noticeably increased along with the decrease in the PL band in the UV region as the concentration of OH-GO QDs in the aqueous medium increases. Hydrogen bonding interaction between the hydroxyl functional groups on the surface of OH-GO QDs favours to form the aggregates exhibiting the PL band in the visible spectrum. In order to investigate the modification of photoluminescence bands caused by the interaction between GO and PANI in GO-PANI nanocomposites at three different pH levels the effect of temperature on the PL of GO-PANI has been examined. Experimental findings indicate the role of temperature on the charge transfer interaction between GO and PANI is prominent at pH 6. We have synthesised graphitic carbon nitride (g-C3N4) and studied its photoluminescence properties at three distinct pH. The intensity of the defect-induced luminescence band is found to be significantly influenced by protonation-deprotonation on the nitrogen atoms in graphitic carbon nitride through experimental observation. Finally, we have studied the effect of a co-polymer, Pluronic F-127 (PF-127) on the PL bands of GO. Anchorbuoy type adsorption of PF-127 on the GO sheets significantly modulates the intensity and peak positions of the photoluminescence bands of graphene oxide (GO), in both acidic and alkaline media.
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    Tunable Luminescence of Graphene Based Nanomaterials: Role of Surfactants and Macromolecules
    Halder, Arnab
    The present thesis entitled “Tunable Luminescence of Graphene Based Nanomaterials: Role of Surfactants and Macromolecules” addresses the synthesis of graphene based nano materials like graphene oxide (GO), chemically modified graphene oxide (CM-GO), graphene oxide polyaniline (GO-PANI) nanocomposite with tunable photoluminescence nature (PL). The role surfactants like sodium dodecyl sulphate (SDS), cetyl trimethyl ammonium bromide (CTAB) has been also described to modulate the PL of GO. This thesis comprises of eight chapters. Chapter 1 deals with the general introduction and brief description of the summary of the research work. The motivation, objectives and plan of the present investigation are also stated in this chapter. Chapter 2 deals with the properties and structure of graphene, the different method of synthesis of graphene existing in literature and the literature review on the photoluminescence properties of GO and GO based nanomaterials till 2020. Chapter 3 describes the method of synthesis with the characterization of GO, CM-GO and GO-PANI nano-composite. Chapter 4 discusses the effect of pH on the PL properties of GO-PANI nano-composite. The interaction between polyanilne and GO changes with the change in pH, which strongly affects the PL properties of the GO-PANI nanocomposite. Chapter 5 includes the study of PL of GO in the aqueous medium in the presence of different concentration of surfactants (SDS and CTAB).The mode interaction between GO and surfactant strongly depends on the pH of the medium which modulates the band gap of GO are described in this chapter. Chapter 6 includes the study of PL of GO-PANI in the aqueous medium in the presence of an anionic surfactant (SDS) at both acidic and alkaline medium. The interaction between GO-PANI and SDS is different in different pH, which modulates the PL of the GO-PANI nano-composite material. Chapter 7 describes the PL properties of both GO and CM-GO in aqueous medium with proper explanation of the origin of the luminescence. The modulation of luminescence both GO and CM-GO by changing concentration also described in this chapter. The conclusion of the research work along with the future prospects obtained from this thesis are presented in Chapter 8.