Photocatalytic degradation of methylene blue by tetragonal tungsten bronze modified by a heterojunction with graphitic-C3N4 in the presence of sunlight

The protection of aquatic ecosystems from harmful pollutants is now an essential priority that is receiving a good deal of attention. Especially methylene blue (MB), a poison capable of damaging marine life at extremely low concentrations. In this work, we report the preparation of a new heterojunction g-C₃N₄/Sr₅CaTi₂Nb₈O₃₀ for the decomposition of methylene blue contaminants, by employing a self-assembly ultrasonic-assisted technique. The composite prepared was characterised by various techniques. The formation of g-C₃N₄/Sr₅CaTi₂Nb₈O₃₀, together with the production of a highly reactive material interface, was demonstrated by X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). Compared with pure g-C₃N₄ and Sr₅CaTi₂Nb₈O₃₀, the prepared g-C₃N₄/Sr₅CaTi₂Nb₈O₃₀ composite displays significant enhancement of the activity photocatalytic for methylene blue degradation under sunlight irradiation. The g-C₃N₄/Sr₅CaTi₂Nb₈O₃₀ also exhibited excellent reusability, with a degradation rate of 87.61 % even after the 5th cycle. The kinetics of photocatalytic degradation are of pseudo-first order. The scavenging of active species revealed that superoxide radical ${(O}_2^{•-})$, hydroxyl radical $\left({\mathrm{OH}}^{•}\right)$ and holes $\left(h^{+}\right)$ are the principal active species participating in the photocatalytic reaction. The adsorption of g-C₃N₄ molecules on Sr₅CaTi₂Nb₈O₃₀ and methylene blue (MB) molecules on g-C₃N₄/Sr₅CaTi₂Nb₈O₃₀ surface was applied by using Monte Carlo (MC) simulation. The negative values of adsorption energy were signified the stability of g-C₃N₄/Sr₅CaTi₂Nb₈O₃₀ and the adsorption of methylene blue (MB) on g-C₃N₄/Sr₅CaTi₂Nb₈O₃₀ surface.