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From Material Design to Engineering Application: Graphitic Carbon Nitride Based Photocatalysis for Sustainable Water Treatment and Value-added Chemical Production Open Access

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Graphitic carbon nitride (g-C3N4) has emerged as a promising photocatalyst because of its capability to utilize visible light and more solar energy, low cost in fabrication, great stability, and biocompatibility. However, the poor photocatalytic performance due to various factors and undesired design of photocatalytic reactors have limited the practical application of g-C3N4. This dissertation focuses on the development of an effective g-C3N4 and the fabrication of a desired reactor to promote its application for organic micropollutants removal and value-added chemical production in practice. In the first part of this dissertation, a carbon-doped g-C3N4 was rationally designed by density functional theory (DFT) simulations and synthesized by an innovative synthesis method. It showed a reaction rate enhancement of 2.3-10.5-fold for the degradation of water contaminants compared to that of conventional, melamine-based g-C3N4 under the irradiation of simulated visible sunlight. In the second part, the mechanism of photocatalytic oxidation of pollutants on g-C3N4 was illustrated via integrated computational simulations and experimental quantification of the production of reactive species. Surprisingly, the holes instead of other reactive oxidative species contribute substantially for the degradation of contaminants, which was largely overlooked in previous studies. In the third part, 3D printed compound parabolic collector (CPC) reactor was designed and fabricated to promote engineering applications of photocatalysis for water purification. The immobilization of g-C3N4 powder in chitosan hydrogel beads showed promise in removing micropollutants under sunlight irradiation with the less operational complexity and cost for the separation and recovery of photocatalyst.In the last part, a chlorine (Cl)-doped g-C3N4 was discovered for producing a notable amount of value-added chemical (i.e., hydrogen peroxide (H2O2)) in photocatalysis. The dopant Cl in g-C3N4 was proved to play an important role in promoting H2O2 production on g-C3N4 based on experimental results, and computational simulations are needed for the further understanding of the mechanism. Through molecular simulations, material synthesis, performance evaluation, and reactor design, this dissertation has demonstrated a promising technology that can utilize renewable energy and less chemicals for small-scale water purification and value-added chemical production, which has broader impacts on the sustainable development of water treatment and chemical production systems for the future, especially in rural areas, small communities, single households, and developing countries.

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