Surface chemistry of graphitic carbon nitride: doping and plasmonic effect, and photocatalytic applications

Abstract

To achieve the United Nations' Sustainable Development Goal (SDG7) of limiting global temperature rise to less than 1.5 °C, it is crucial to reduce non-renewable energy sources and curb the production of greenhouse gases like CO2. In this context, graphitic carbon nitride (g-C3N4) has emerged as a promising metal-free semiconductor photocatalyst for converting solar energy into clean fuels and valuable chemicals. However, there are challenges associated with g-C3N4, such as high electron–hole recombination, low photocurrent generation, limited specific surface area, and an absorption edge below 450 nm, which can be attributed to the arrangement of monomeric units. This review focuses on recent developments in designing single g-C3N4 as a metal-free catalyst through atomic-level doping and tuning surface chemical properties. Various doping techniques, including nonmetal and bi-nonmetal doping, as well as vacancy creation within the polymer framework and the effect of surface plasmonic nanoparticles, are explored as effective ways to fine-tune the polymer's conduction band (CB) edge potential, bandgap, and structural properties. The impact of doping and vacancy creation on the distribution of molecular orbitals, density of states (DOS), and adsorption energy on the polymer surface is investigated using computational calculations based on first principles and density functional theory (DFT). The review also examines the influence of doping on the photocatalytic reactions occurring in the polymer's CB, such as water splitting and carbon dioxide (CO2) reduction, and their selectivity in producing desired products. Last, the review summarizes the current challenges. It provides future perspectives on developing metal-free photocatalysts, emphasizing the need to address unresolved structural, electronic, chemical, and optical properties to advance sustainable solutions. Overall, it is hoped that this review will inspire further research to unlock the full potential of metal-free photocatalysts and contribute to a more sustainable future.Graphical