Controlled Nanostructured Synthesis Of Graphitic Carbon Nitride: Energy Storage And Photocatalytic Properties

Graphitic carbon nitride(GCN) is one of the most fascinating materials with excellent mechanical strength, thermal conductivity, water resistivity and reliable chemical inertness; with major applications as catalyst for organic synthesis, photoelectric converter, gas and fluorescent sensors, field emitters, electrode for fuel cells and hydrogen storage material. This thesis presents the research work on GCN specially preparation, characterization, growth mechanism and their properties.Advanced techniques such as FESEM, XRD, XPS, EDX, TEM, HRTEM and SAED have been employed for the characterization of novel morphologies obtained for GCN. Potential properties of this material are photocatalyst, supercapacitors, oxygen reduction reaction, oxygen evolution reaction and hydrogen evolution reaction. New growth scheme has been employed to prepare these materials by using chemical method.Initially, an easy, scalable and environmentally benign chemical method has been developed to synthesize micro strings of graphitic carbon nitride(ms-GCN) through pretreatment of melamine with HNO3 at low temperature. This methodology results in unique string type morphology of ms-GCN with higher surface area. These ms-GCN were used as a photocatalyst under visible light for photodegradation of Rhodamine B, Methyl Blue and Methyl Orange. The ms-GCN show enhanced photodegradation efficiency due to high surface area and favorable bandgap. The first order rate constant for ms-GCN was measured that confirms the higher performance of ms-GCN in comparison to other reported materials such as GCN, Fe2O3/GCN and Ti O2 nanotubes. Thus, the method developed here is favorable for the synthesis of materials with higher surface area and unique morphology, which are favorable for high photodegradation activity.Later on, we established a facile and scale up approach to fabricate tubular graphitic carbon nitride(TGCN) using melamine. The construction of unique tubular morphology is based on pre-treatment of melamine with HNO3. Here, first time we have explored the electrochemical properties of TGCN as electrode for supercapacitors. The tubular TGCN has significant advantages due to its distinctive morphology, high surface area(182.61m2/g) and existence of carbon with nitrogen. Therefore, TGCN exhibited High specific capacitance of 233 F/g at current density 0.2A/g in 6M KOH electrolyte. Furthermore, the tubular TGCN maintained excellent capacitance retention capability(90%) after 1000 cycles. The photocatalytic activity of TGCN was evaluated by organic dyes like Methylene Blue(MB) and Methylene Orange(MO) under visible light. The TGCN showed good photocatalytic activity and enhanced stability in comparison to bulk GCN. The enhancement in performance is because of high surface area which contains more active sites for reaction. Encouraging performance of TGCN as a supercapacitors and photocatalyst pointed it to be a prospective material for energy storage and clean environment.Afterward we have developed a facile, scale up and efficient method for the preparation of GCN nanofibers(GCNNF) as electrode for supercapacitors and photocatalyst. The assynthesized GCNNF have 1D structnure with higher concentration of nitrogen that is favorable for higher conductivity and electrochemical performance. Secondly, high surface area of GCNNF provides large electrode-electrolyte contact area, sufficient light-harvesting and mass-transfer as well as increased redox potential.Thus, GCNNF supercapacitor electrode shows high capacitance of 263.75 F/g and excellent cyclic durability in 0.1 M Na2SO4 aqueous electrolyte with the capacitance retention of 93.6% after 2000 cycles at 1 A/g current density. GCNNF exhibits high capacitance of 208F/g even at 10 A/g, with the appreciable capacitance retention of 89.5%, which proves its better rate capability. Moreover, the GCNNF shows enhanced photocatalytic activity in the photodegradation of Rh B in comparison to the bulk GCN. The degradation rate constant of GCNNF photocatalyst is almost 4 times higher than GCN. The enhanced photocatalytic activity of GCNNF is mainly due to higher surface area, appropriate bandgap and fewer defects in GCNNF as compared to GCN. As an economical precursor(melamine) and harmless, facile and template-free synthesis method with excellent performance both in supercapacitors and photodegradation make GCNNF a strong candidate for energy storage and environment protection applications.After this we have used TGCN and GCNNF like structures in order to o explore the effect of morphology on catalytic properties of graphitic carbon nitride(GCN), we have studied Oxygen reduction reaction(ORR) performance of these two morphologies of GCN in alkaline media. Among both, tubular GCN react with dissolved oxygen in the ORR with an onset potential close to commercial Pt/C. Furthermore, the higher stability and excellent methanol tolerance of tubular GCN compared to Pt/C emphasizes its suitability for fuel cells.In the last we have developed a facile, large scale and novel Co3O4 decorated tubular nanostructures of GCN, fabricated through simple chemical method at low temperature. Strong synergistic effect among GCN and Co3O4 results excellent performance as a bifunctional catalyst for oxygen(OER) and hydrogen evolution reactions(HER). High surface area, unique structure and composition of composite bring all redox sites easily available for catalysis. Co3O4@GCN composite exhibits superior over-potential(0.12 V) and current density(147 m A/cm2) for OER than benchmark Ir O2 and Ru O2 with better durability in alkaline media. Furthermore, the Co3O4@GCN composite demonstrate excellent performance for HER with much lower onset over-potential and a stable current density. It is anticipated that Co3O4@GCN composite developed here is an attractive catalyst than Noble metals for large-scale water splitting and fuel cells.