Ammonia (NH3) is one of the key agricultural fertilizers and to date, industries are using the conventional Haber-Bosh process for the synthesis of NH3 which requires high temperature and energy. To overcome such challenges and to find a sustainable alternative process, researchers are focusing on the photocatalytic nitrogen fixation process. Recently, the effective utilization of sunlight has been proposed via photocatalytic water splitting for producing green energy resource, hydrogen. Inspired by this phenomenon, the production of ammonia via nitrogen, water and sunlight has been attracted many efforts. Photocatalytic N2 fixation presents a green and sustainable ammonia synthesis pathway. Currently, the strategies for development of efficient photocatalyst for nitrogen fixation is primarily concentrated on creating active sites or loading transition metal to facilitate the charge separation and weaken the N–N triple bond. In this investigation, we review the literature knowledge about the photocatalysis phenomena and the most recent developments on the semiconductor nanocomposites for nitrogen fixation, following by a detailed discussion of each type of mechanism.

We tested an emerging hypothesis that carbon species may play an integral role in catalyzing dinitrogen adsorption and reduction to ammonia.

Graphitic carbon nitride nanosheets decorated by multiple functional groups (denoted as CN−KNa) were as a multipurpose material, both in photocatalytic applications and as a photo‐induced indicator. The presented g‐C3N4 is fabricated via a facile alkali‐salt‐assisted calcination method. The structural analysis reveals significant changes in the structure of the host CN−KNa nanosheets associated with the existence of multiple functional groups (for example, hydroxy, carbonyl, and cyano groups). Such modifications lead to enhanced light absorption and charge separation, resulting in an efficient photocatalyst not only for solar‐driven hydrogen production but also for primary amine detection in aqueous solution. Thus, the solar light driven photocatalytic hydrogen evolution yield using the synthesized CN−KNa sample is found to be 50.3 μmol h−1, which is approximately 14 times higher than that of bulk g‐C3N4. More importantly, this functional‐group‐decorated CN−KNa facilitated electron transportation between CN−KNa and amine compounds, causing a colour change in the solution mixture, which has been observed for the first time. This novel observation indicates that CN−KNa can be considered a new class of photo‐induced indicator agent to detect primary amine compounds in aqueous solution.