Multifunctional Roles of Ionic Microenvironments in the Preparation, Modification, and Application of g‐C3N4

Abstract As a visible light‐responsive metal‐free polymer semiconductor, graphitic carbon nitride (g‐C 3 N 4 ) has garnered increasing attention in photocatalysis but needs structural modification and functional enhancement. Recently, the rational design of ionic microenvironments (IMEs) by leveraging the tunability of various ions to endow catalysts with tailored functionalities has been elevated to a hot direction. To elucidate their respective effects on g‐C 3 N 4 , IMEs are categorized into three types, namely plasma IMEs, organic IMEs, and inorganic IMEs, according to the criteria of external field dependence, cation type, and application scenarios. These promotions include facilitated preparation, diversified modifications, and improved efficiencies. First, IMEs participate in constructing a functionalized microenvironment through dynamic interactions with the precursor during the preparation, facilitating structural customization, crystal nucleation and growth, surface performance enhancement, and process cleanliness. Second, IMEs create a tunable microenvironment for post‐modification of g‐C 3 N 4 , functioning as an electron reservoir, structural modifier, substrate adsorbent, and stabilizer. Lastly, through the synergistic effect between IME and g‐C 3 N 4 , they achieve targeted product regulation, enhanced chemical stability, efficient substrate adsorption, and improved application potential in fields like catalysis, energy storage, and gas adsorption. Also, the limitations, challenges, and prospects of IME strategies are discussed, offering systematic insights into IMEs‐based structure‐activity relationships of g‐C 3 N 4.