Role of carbon nanotubes in boosting photocatalytic hydrogen production and pollutants degradation within S-Scheme g-C3N4/ZnO nanocomposite.

In this study, the carbon nanotubes (CNTs) modified g-C3N4/ZnO photocatalytic nanocomposite was synthesized through in-situ growth of ZnO nanoparticles on the CNT-loaded graphitic carbon nitride (g-C3N4) to evaluate its hydrogen production and dye degradation capabilities. The disc-like ZnO nanoparticles were spotted alongside the CNTs on the g-C3N4 surface with a specific surface area of 140.8 m2/g. The electrostatic interactions between conjugated bonds of g-C3N4 and π bonds of CNTs resulted in a well-bonded interface and high adsorption of CNTs. CNTs significantly increased the visible light absorption and reduced the band gap energy to 2.45 eV in CNT/g-C3N4/ZnO (CN/Zn/CNT) nanocomposite. Because of the S-scheme charge transfer mechanism between g-C3N4 (CN) and ZnO and the attendance of CNT as an electron transfer accelerator, CN/Zn/CNT demonstrated the best charge carrier separation and electron transfer to the surface among the samples according to photoluminescence (PL), photocurrent and electrochemical impedance spectroscopy (EIS) examinations. Mott-Schottky analysis and scavenger experiments confirmed the formation of the S-scheme mechanism with hydroxyl and superoxide radicals as the main reactive oxygen species. Due to the high conductivity and well-bonded interface, CNT significantly transferred and recombined ineffective charge carriers within the S-scheme mechanism by creating efficacious charge transfer channels. CN/Zn/CNT nanocomposite photodegraded 93 % of methylene blue (MB). Meanwhile, due to the similar surface charge potential of CN/Zn/CNT with methyl orange (MO) and phenol, only 25 and 52 % of these pollutants were degraded by the nanocomposite, respectively. The efficient charge transfer of the S-scheme mechanism in the water splitting process increased the thermodynamic tendency of the reaction, and the presence of carbon nanotubes as the electron transfer accelerators kinetically impressed the reaction. Hence, the hydrogen production rate in the CN/Zn/CNT nanocomposite reached 690 μmol/g.h, whereas it was 429 and 291 μmol/g.h for gCN/Zn and CN, respectively.