Facile and Green Approach to Synthesize Biomass‐Derived Zero‐/Two‐Dimensional Carbon Dots/g‐C ₃ N ₄ Heterojunction for Efficient Photocatalytic and Photoelectrocatalytic Applications

Developing efficient photoactive materials from bio‐derived resources is vital yet challenging for achieving effective water splitting performance. In this work, nano carbon dots (CDs) of zero‐dimensional (0D) were synthesized from papaya peel through a simple and eco‐friendly process and subsequently anchored onto the two‐dimensional (2D) layered structure of graphitic carbon nitride (g‐C 3 N 4 , GCN) at various composite ratios to obtain a 0D/2D nanohybrid. The optical and physicochemical properties of the resulting nanohybrids were comprehensively characterized using various analytical techniques. The catalysts were evaluated for both Rhodamine B (RhB) dye photodegradation and photoelectrochemical (PEC) water splitting applications. Among all the samples, GCN‐CD‐3 exhibited superior photocatalytic activity under visible‐light irradiation due to its enhanced light absorption, efficient electron transfer, and effective separation of photogenerated charge carriers, achieving a rate constant of 0.0316 min −1 , approximately 3.8 times higher than that of pristine GCN. Moreover, GCN‐CD‐3, as a photoelectrode for PEC water splitting, demonstrated an impressive photocurrent density of 3.62 mA/cm 2 at a low onset potential of 0.63 V versus Ag/AgCl, surpassing the performance of other catalysts. These results demonstrate that the bio‐derived nanohybrid functions as an efficient catalyst for sustainable water‐splitting applications, without raising toxicity concerns.