| Summary: | The nanocomposite preparation procedure plays an important role in achieving a well-established heterostructured junction, and hence, an optimized photocatalytic activity. In this study, a series of g-C<sub>3</sub>N<sub>4</sub>/ZnO nanocomposites were prepared through two distinct procedures of a low-cost, environmentally-friendly, in-situ fabrication process, with urea and zinc acetate being the only precursor materials. The physicochemical properties of synthesized g-C<sub>3</sub>N<sub>4</sub>/ZnO composites were mainly characterized by XRD, UV⁻VIS diffuse reflectance spectroscopy (DRS), N<sub>2</sub> adsorption-desorption, FTIR, TEM, and SEM. These nanocomposites’ photocatalytic properties were evaluated in methylene blue (MB) dye photodecomposition under UV and sunlight irradiation. Interestingly, compared with ZnO nanorods, g-C<sub>3</sub>N<sub>4</sub>/ZnO nanocomposites (<i>x</i>:1, obtained from urea and ZnO nanorods) exhibited weak photocatalytic activity likely due to a “shading effect„, while nanocomposites (<i>x</i>:1 CN, made from g-C<sub>3</sub>N<sub>4</sub> and zinc acetate) showed enhanced photocatalytic activity that can be ascribed to the effective establishment of heterojunctions. A kinetics study showed that a maximum reaction rate constant of 0.1862 min<sup>-1</sup> can be achieved under solar light illumination, which is two times higher than that of bare ZnO nanorods. The photocatalytic mechanism was revealed by determining reactive species through adding a series of scavengers. It suggested that reactive ●O<sub>2</sub><sup>−</sup> and h<sup>+</sup> radicals played a major role in promoting dye photodegradation.
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