Development Of Novel Graphitic Carbon Nitride Based Catalysts For Enhanced Photocatalytic Activity

Photocatalysis is currently considered one of the cleanest technological processes in environmental remediation and sustainable energy in the research world.Heterogeneous photocatalysis refers to the process of absorption of light by a catalyst to facilitate a reaction with both the reactants and photocatalyst in different phases.These semiconductor catalysts are activated by photon energy to initiate an electron-transfer process.Photocatalytic dye degradation and hydrogen production are widely used applications of photocatalysis.Graphitic carbon nitride（g-C₃N₄）is a commonly used photocatalyst for photocatalytic dye degradation and hydrogen evolution.Howbeit,due to the drawbacks of single semiconductors,such as fast recombination rate and low light absorption,composite photocatalyst have been studied and developed.Hence,this thesis aimed to study,fabricate and develop g-C₃N₄ based photocatalysts from earth abundant materials by various facile fabrication strategies with high photocatalytic efficiency and slow recombination rate.This work includes:The construction of 0D/2D WO3/g-C3N4 Z-scheme hybrid for enhanced photocatalytic degradation.g-C₃N₄ has gained research interests over the decades as a promising metal-free catalyst to combat dye pollutants by photocatalytic degradation.Herein,we reported the construction of a zero-dimensional/two-dimensional（0D/2D）tungsten trioxide/graphitic carbon nitride（WO₃/g-C₃N₄）Z-scheme hybrid by a simple calcination process.The photocatalytic property of the WO₃/g-C₃N₄hybrids was assessed through their efficiency in the degradation of toxic industrial dye pollutant,Rhodamine B（Rh B）and phenol under visible light irradiation.From the results and analysis,the 1%WO₃/g-C₃N₄ composite with a larger Brunauer-Emmett-Teller（BET）surface area of 41.14 m²g^-1compared to the pristine g-C₃N₄(25.25 m²g^-1)presented the uppermost improvement in the photocatalytic performance contrasted to both WO₃ and g-C₃N₄.The WO₃/g-C₃N₄ achieved the degradation of Rh B and phenol with an efficiency of 96%in 15 min and 98.5%in 30 min,respectively.X-ray photoelectron spectroscopy（XPS）results confirmed the existence of the internal electric field.The enhanced activity was attributed to the homogeneous distribution of the WO₃nanoparticles on the g-C₃N₄ nanosheets with intimate interface and matched band gap structure which favored the construction of the Z-scheme hybrid,therefore boosting the electron-hole separation efficiency and maintaining the strong redox capability for photocatalytic degradation.In the third chapter of this thesis,we report of nickel phosphide（Ni2P）nanoparticles integrated onto 2D g-C3N4 nanosheets for enhanced hydrogen evolution.The noble metal free co-catalyst,Ni₂P,was integrated onto metal-free g-C₃N₄ nanosheets via a facile phosphating process,resulting in the Ni₂P/g-C₃N₄hybrid photocatalysts which provided an efficient transfer route for the acceleration of charge separation and slow recombination of charges.The optimized Ni₂P-3/g-C₃N₄nanohybrid displayed enhanced photocatalytic hydrogen evolution(30.9 mmol g^-1),approximately 25 times higher than pure g-C₃N_4.The favorable optoelectronic properties of the Ni₂P nanoparticles as cocatalyst allowed the photo-induced electrons of g-C₃N₄ to effectively move to the surface of the Ni₂P,hugely repressing the quick recombination of electron hole pairs.The above studies furnished a heightened understanding of the photocatalytic mechanisms of dye degradation and hydrogen production using earth abundant and noble metal free photocatalysts and co-catalyst.It revamped and introduced promising factors for the enhancement of photocatalytic environmental remediation and clean energy.