DESIGN AND OPTIMIZATION OF GRAPHITIC CARBON NITRIDE HYBRID NANOSTRUCTURES FOR ENHANCED PHOTOCATALYTIC ACTIVITY

Abstract

Carbon nanomaterials (CNMs), ever since their discovery have gained widespread attention due to their remarkable properties like high tensile strength, Young’s modulus, surface area to volume ratio, thermal and electrical conductivities, carrier mobility and many more. Due to their phenomenal features, CNMs have catered to several fields of research ranging from aerospace to drug delivery applications. The present study was an effort to develop and understand the photocatalytic behaviour of CNMs-based graphitic carbon nitride (g-C3N4) hybrid photocatalyst materials for effective degradation of rhodamine B (RhB) dye. Hence, the overall objective of this thesis work was to develop g-C3N4 photocatalyst material by optimizing the synthesis parameters and study its photocatalytic dye degradation property. Further, to enhance the photocatalytic performance of g-C3N4 by synergistically coupling with the CNMs and finally to compare & study the photocatalytic property and eventually propose a degradation mechanism based on morphology of the developed photocatalyst materials. In this thesis work, 2D g-C3N4 was synthesized using a conventional thermal decomposition process using melamine as the precursor material. The synthesis parameters like reaction temperature and atmosphere were optimized to obtain the near-ideal g-C3N4 material. This optimized photocatalyst was further improved by incorporating ammonium chloride (NH4Cl) during the synthesis process. The role of NH4Cl was to act as a bubbling agent and provide porous and thin sheets of g-C3N4. The structure, morphology, and optical properties of the developed photocatalyst materials were investigated using XRD, SEM, TEM, UV-DRS, FTIR, PL, BET and XPS techniques. The photocatalytic behaviour was evaluated with the help of an in-house fabricated reactor taking RhB as the target dye. It was observed that the improved g-C3N4 removed 94% of the RhB dye (Conc. = 10 mg/L) in 30 minutes whereas the initially prepared g-C3N4 showed only 35% efficiency. Further, various CNMs like carbon nanotubes (CNTs) and carbon soot nanoparticles (CS) were prepared using the arc discharge technique. It is a conventional physical method of preparing CNMs where two graphite rods are brought near and a high current is applied in an inert atmosphere. The sublimation of one of the graphite electrodes and deposition on the cooler surfaces results in the formation of the CNTs and CS. Besides, graphene nanoplatelets (GNP) were synthesized through microwave exfoliation of graphite intercalated compound followed by sheer mixing in a solvent mixture (DMSO & DI water). The obtained CNMs were coupled v with g-C3N4 to attain higher degradation efficiencies. It was observed that CS coupled g C3N4hybrid photocatalyst showed 97% degradation of RhB (conc. = 20 mg/L) in 90 minutes however, pristine g-C3N4 showed 88% in similar conditions. Moreover, the CNT-coupled g C3N4 hybrid photocatalyst also showed 97% degradation in 90 minutes under visible light irradiation. Further, the 2D/2D hybrid photocatalysts showed the highest performance. Here, GNP-coupled g-C3N4hybrid photocatalyst showed 96% degradation in 60 minutes whereas pristine g-C3N4 showed 55% efficiency. The enhanced performance of CNMs coupled hybrid photocatalyst was essentially due to the effective charge separation of photogenerated charge carriers resulting in reduced recombination rates. It was discovered that the 2D/2D coupling showed faster degradation rates than 1D/2D and other coupling systems. This was further proved by developing another 2D/2D system using commercial hexagonal boron nitride (hBN) coupled g-C3N4. It was observed that 91% of RhB was removed in 60 minutes under the visible light source. Therefore, the morphology played a significant role in deciding the overall performance of the materials.