The contamination of water by organic substances poses a significant global challenge. To address these pressing environmental and energy concerns, this study emphasizes the importance of developing effective photocatalysts powered by sunlight. In this research, we achieved the successful synthesis of a novel photocatalyst comprised of polymeric carbon nitride (CN) nanosheets embedded with Co3O4 material, denoted as CN-CO. The synthesis process involved subjecting the mixture to 500 °C for 10 h in a muffle furnace. Structural and morphological analyses confirmed the formation of CN-CO nanostructures, which exhibited remarkable enhancements in photocatalytic activity for the removal of methylene blue (MB) pollutants under replicated sunlight. After 90 min of exposure, the degradation rate reached an impressive 98.9%, surpassing the degradation rates of 62.3% for pure CN and 89.32% for pure Co3O4 during the same time period. This significant improvement can be attributed to the exceptional light captivation capabilities and efficient charge separation abilities of the CN-CO nanostructures. Furthermore, the CN-CO nanostructures demonstrated impressive photocurrent density-time (j-t) activity under sunlight, with a photocurrent density of 2.51 μA/cm2 at 0.5 V. The CN-CO nanostructure exhibited excellent methanol oxidation reaction (MOR) activity with the highest current density of 83.71 mA/cm2 at an optimal 2 M methanol concentration, benefiting from the synergy effects of CN and CO in the nanostructure. Overall, this study presents a straightforward and effective method for producing CN-based photocatalysts decorated with semiconductor nanosized materials. The outcomes of this research shed light on the design of nanostructures for energy-related applications, while also providing insights into the development of efficient photocatalytic materials for addressing environmental challenges.