The increasing presence of emerging contaminants (ECs) has attracted considerable attention due to their potential harm to human health and ecosystems. Graphitic carbon nitride (g-C₃N₄), a semiconductor devoid of metals, stands out due to its distinctive optical properties and strong resistance to chemical degradation, which holds significant promise in the photocatalytic degradation of ECs. However, the inherent limitations of g-C₃N₄, such as its reduced specific surface area and the swift recombination of photogenerated electron-hole pairs, have prompted extensive research on modification strategies to enhance its photocatalytic performance. Current research on g-C₃N₄-based materials is often constrained in scope, with most reviews focusing solely on modification strategies or its application in degrading a single category of emerging contaminants (ECs). In this review, a systematic overview of synthesis methods and advanced modification strategies for g-C₃N₄-based materials is discussed, highlighting their recent advances in the photocatalytic degradation of various ECs using g-C₃N₄-based materials, which underscores their potential for environmental remediation. Moreover, this article critically examines the current challenges and outlines future research directions, with particular emphasis on integrating artificial intelligence and machine learning to accelerate the development of g-C₃N₄-based photocatalysts and optimize degradation processes, thereby promoting their efficient application in the photocatalytic degradation of ECs.

As a metal-free, visible-light-responsive two-dimensional (2D) layered semiconductor, graphitic carbon nitride (g-C₃N₄) has been extensively studied for photocatalytic water purification owing to its high chemical stability, facile synthesis, and low cost. However, single-phase g-C₃N₄ still suffers from bottlenecks including rapid photogenerated electron–hole pair recombination, low visible-light utilization efficiency, insufficient specific surface area, and a limited number of exposed surface active sites, which severely restrict its practical photocatalytic performance. Rational construction of heterojunctions with matched band alignment and intimate interfacial contact serves as an effective strategy to boost the photocatalytic activity of g-C₃N₄. This review introduces the structural characteristics and photocatalytic mechanisms of g-C₃N₄, summarizes the primary types of g-C₃N₄-based heterojunctions along with their charge transfer pathways, and highlights recent research progress in emerging contaminant degradation, pathogenic microbial disinfection, and reduction of high-valence and highly toxic heavy-metal ions for water decontamination. The review closes with critical perspectives on the rational design and practical engineering prospects of g-C₃N₄-based heterojunctions. By bridging heterojunction mechanisms with water-purification applications and engineering considerations, this review is expected to guide the rational design of high-performance g-C₃N₄-based heterojunctions and accelerate their translation toward practical water purification.