Research Progress of Graphitic Carbon Nitride Composites in Photocatalytic Nitrogen Fixation

As a carbon-free energy carrier with high energy density, ammonia has been extensively utilized across various industrial sectors. However, the conventional Haber–Bosch process for industrial ammonia synthesis faces critical limitations, including harsh operational conditions (high temperature/pressure), excessive energy consumption, and substantial CO2 emissions, which fundamentally restrict its sustainable development. Photocatalytic nitrogen reduction emerges as a promising alternative strategy, offering advantages of ambient reaction conditions and environmental benignity. Among various photocatalysts, graphitic carbon nitride (g-C3N4) has gained significant attention in photocatalytic nitrogen fixation due to its tunable band structure and facile modification characteristics. Nevertheless, pristine g-C3N4 suffers from intrinsic limitations, prompting researchers to focus on g-C3N4-based composite photocatalysts. This review systematically addresses the current challenges in photocatalytic nitrogen fixation and g-C3N4 photocatalysts, followed by a critical analysis of strategies for constructing composite architectures to overcome these limitations. In particular, the merits and drawbacks of different modification approaches were evaluated, while proposing future research directions for g-C3N4-based composites in nitrogen photofixation. This comprehensive analysis provides valuable insights and foundational references for advancing photocatalytic nitrogen fixation technologies.