Facile synthesis of NiO-loaded g-C3N4 heterojunction photocatalyst for efficient photocatalytic degradation of 4-nitrophenol under visible light irradiation

Finding acceptable noble-metal-free cocatalyst-modified photocatalysts has gotten a lot of interest in the field of photocatalysis. In this study, an environmentally friendly ultrasonic-assisted approach was used to make NiO-loaded g-C3N4. The crystal, morphological structure, surface analysis, and optical properties of the pure g-C3N4 and NiO-loaded g-C3N4 were characterized by PXRD, TEM, BET, XPS, and UV–vis (DRS), respectively. UV–vis (DRS) results investigated that NiO-loaded g-C3N4 photocatalysts exhibit a reduction in the optical band gap energy related to the bare g-C3N4 that is particularly good for visible light absorption. TEM images prove the existence of the NiO in the NiO-loaded g-C3N4 which is very beneficial for the enhancement of the charge separation and transfer that is revealed using the electrochemical methods. Furthermore, Mott-Schottky plots showed that both bare g-C3N4 and NiO-loaded g-C3N4 photocatalysts have negative flat band potential. Importantly, the photocatalytic activity of NiO-loaded g-C3N4 photocatalysts was evaluated for the photodegradation of 4-nitrophenol (4-NP) in an aqueous solution under visible light irradiation. The optimized ratio of NiO-loaded g-C3N4 (11 wt% loaded g-C3N4) displays the highest activity performance and is almost 4 times higher than that of bulk g-C3N4. The remarkable photocatalytic improvement of NiO-loaded g-C3N4 is mainly attributed to the decreased band gap energy and synergistically enhanced charge separation and transfer. Additionally, the proposed photodegradation mechanism of NiO-loaded g-C3N4 was also deliberated in more detail. Hence, the NiO-loaded g-C3N4 photocatalyst is an attractive photocatalyst for photocatalytic water treatment.