High-Efficiency Photocatalysts: Synergizing Graphitic Carbon Nitride With Phthalocyanine Sensitizers

Graphitic carbon nitride (g-C₃N₄ or g-CN) is an extensively studied photocatalyst; however, its efficiency is hampered by a high rate of recombination reaction and limited solar energy harvesting capability. To maximize its photocatalytic activity, researchers have engineered diverse strategies. Among different methods, dye sensitization improves the absorption region and also facilitates the separation of photogenerated charge carriers between dyes and g-C₃N₄ (sensitization) or vice versa (dyes as cocatalyst) depending on band potentials and their alignment at the interface. This article reviews the effect of sensitization of g-C₃N₄ with phthalocyanine dye for various photocatalytic applications. The photophysical properties of phthalocyanine can be tailored via central metal incorporation (e.g., Fe, Ni, and Zn), periphery or ring functionalization, molecular engineering, anchoring bulky groups, embedding it on a polymeric support, etc., to enhance the photocatalytic properties of phthalocyanine/g-C₃N₄ composites. When combined with g-C₃N₄, its high molar extinction coefficient strengthens the absorption sensitivity across the solar spectrum for enhanced visible light activity. This review article provides guidance for the structural design and construction of highly efficient dye-sensitized g-C₃N₄ catalysts employed for photocatalytic applications in hydrogen generation, carbon dioxide reduction, and degradation of toxic pollutants. In the end, perspectives and challenges of dyes on g-C₃N₄ as a photocatalyst have been analyzed and discussed.