Charge transfer engineering in Phenyl-modified Carbon Nitride-based hybrid systems: from powder Photocatalysts to Thin films

The increasing demand for sustainable energy conversion and environmental remediation has intensified research on visible-light-active photocatalysts. Graphitic carbon nitride (g-C₃N₄) is a promising metal-free semiconductor due to its suitable bandgap, chemical stability, and low cost; however, its performance is limited by rapid charge carrier recombination, low mobility, and inefficient charge utilization. To overcome these intrinsic drawbacks, this thesis adopts charge transfer engineering as a central design strategy, focusing on controlling charge generation, separation, and transport rather than solely modifying band structures. Phenyl-modified carbon nitride (PhCN) is employed as a molecularly engineered platform to enhance the electronic structure of carbon nitride. Phenyl groups extends the π-conjugated network, promoting charge delocalization and strengthening interfacial electronic coupling. Unlike conventional doping approaches, phenyl groups act as active electronic bridges, enabling efficient and directional charge transfer in hybrid systems. Based on this concept, PhCN is combined with carbon nanotubes, titanium dioxide (TiO₂), and zinc oxide (ZnO) to construct hybrid photocatalysts and thin films. Powder-based systems provide insight into interfacial charge transfer mechanisms and photocatalytic performance under visible light. To address limitations associated with powders and enable device-relevant studies, the work further transitions to thin-film architectures, allowing precise control over morphology and interfaces. The investigation is extended from photocatalytic activity to photoconductivity measurements, enabling direct probing of charge transport, trapping, and recombination dynamics. This thesis establishes clear structure–property relationships linking molecular modification, hybrid composition, and morphology to charge transfer behavior, providing fundamental guidelines for the rational design of carbon nitride-based materials for environmental applications.