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Synthesis, Characterization, and Enhanced Optical/Electronic Properties of g-C3N4 Nanosheets for Water Remediation

Yousefi, Mahdieh | 2020

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 54016 (48)
  4. University: Sharif University of Technology
  5. Department: Institute for Nanoscience and Nanotechnology
  6. Advisor(s): Moshfegh, Alireza; Asgari, Reza; Naseri, Naimeh
  7. Abstract:
  8. A global concern has arisen owing to rapid industrial development and population growth, resulting in energy scarcity and earth pollution. In this regard, developing green and sustainable methods for producing clean energy and solving environmental pollution problems have absorbed enormous attention. Among various auspicious strategies, semiconductor photocatalysis has been widely studied in recent years owing to its capabilities to obtain hydrogen as an energy carrier, to remove organic pollutants, and to reduce CO2 emission by converting solar energy into chemical energy. Recently, a metal-free semiconductor photocatalyst based on graphitic carbon nitride, g-C3N4, has received much attention from a photocatalytic perspective because of its high thermal stability, chemical stability, and visible-light absorption. However, pure g-C3N4 displays a poor photocatalytic efficiency owing to the low surface area, high recombination rate of photogenerated electron-hole pairs, and poor optical absorption above 420 nm. In this regards, different efforts have been made so as to enhance the photocatalytic efficiency including metal and non-metal doping, coupling with metals, inorganic semiconductors, and layered materials such as graphene, oxidizing or introducing oxygenenous groups, etc. We have studied and compared the electronic and optical properties of s-triazinebased graphitic carbon nitride (GCN) monolayers mono-doped with B and P as well co-doped with B/P using density functional theory calculations. The single-layer GCN 2D system is found to have an increased band gap of 3.10 eV in comparison to that of 2.7 eV of the bulk GCN due to the quantum confinement effect. B-doped GCN monolayers exhibited a metallic character, while P-doped systems showed a metallic behavior. Therefore, both systems were not suitable for using in photocatalytic applications. Interestingly enough, the co-doped system displayed an appropriate band gap of 1.95 eV, making this configuration a promising candidate for the water splitting reaction. Moreover, since more activating π∗ electronic transitions in the distorted configurations are observed, the optical absorption coefficient of the P-doped and B/P-codoped systems increased in the visible region which are beneficial in photocatalytic applications. The synthesis of oxidized GCN was elaborated by conducting an improved Hummer’s method using H2 SO4 as a protonation agent and KMnO4 as an oxidant. The amount of oxygeneous groups was manipulated by the amount of adding KMnO4 and controlling the synthesis temperature. Then, the effect of oxidation on surface chemical states, the elemental composition, and surface morphologies of the starting material and resulting products was investigated by different Characterization methods including scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), etc. Finally, the adsorption of different dyes and a drug including methylene blue (MB), methylene orange (MO), Methylene green (MG), basic fuchsin (BF), rhodamine B (RhB), rose Bengal (RB), and tetracycline (TC) by bulk GCN and oxidized products was studied. Among all organic pollutants/drug, TC indicated the highest amount of adsorption capacity of 895 mg/g
  9. Keywords:
  10. Adsorbent ; Density Functional Theory (DFT) ; Graphitic Carbon Nitride ; Chemical Oxidation ; Hummer's Method ; Tetracyclines

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