In Situ Spectroscopic Studies on the Mechanism of CO₂ Adsorption and Photocurrent Applications over g‐C₃N₅

Carbon nitride (g‐C₃N₅) is becoming a hot spot in energy‐conversion and CO₂ photoreduction (CPR) applications owing to its tunable optoelectronic properties and high stability. In the CPR, CO₂ adsorption step is extremely important and energy consuming due to its inert nature. Therefore, it is critical to understand the interactions between weakly acidic CO₂ and Lewis‐base sites of C₃N₅ for investigating the CPR process. In this study, in‐situ Fourier transform infrared spectroscopy (FTIR) and X‐ray photoelectron spectroscopy (XPS) techniques are used for the first time to investigate the nature of interaction between CO₂ and g‐C₃N₅, which is prepared at different temperatures (300–500 °C) using aminotriazole. In‐situ FTIR results prove that CO₂ adsorption on the samples occurs only through the physisorption route, not by chemisorption. The solid‐state ¹³C and ¹⁵N‐nuclear magnetic resonance, XPS, and FTIR data reveal that this physisorption pathway is essentially due to the limited overlap between the orbitals of CO₂ and saturated N in the g‐C₃N₅, as confirmed by the formation of secondary and tertiary types of N functionalities. The increase in photocurrent with synthesis temperature can be attributed to larger charge carrier densities and lifetimes, as observed in electron paramagnetic resonance and photoluminescence studies. This study paves the way for designing catalyst surfaces for CO₂ adsorption and photoreduction systems.