In-situ preparation of double Z-scheme Ag6Si2O7/C3N4/NH2-MIL-125(Ti) composite for visible-light photocatalytic degradation of organic pollutants in water

To develop photocatalysts with strong reactivity under visible light irradiation, economic feasibility, and superior effectiveness, based on the optimization of the binary NH2-MIL-125(Ti)/C3N4 composite proportion, Ag6Si2O7 can be deposited in situ on the surface of NH2-MIL-125(Ti)/C3N4 composite, the ternary photocatalytic composite material Ag6Si2O7/C3N4/NH2-MIL-125(Ti) has been fabricated with success. The ternary material was characterized using X-ray diffraction (XRD), scanning electron microscope (SEM), field emission scanning electron microscope (FESEM), energy dispersive spectrometer (EDS), transmission electron microscope (TEM), high-resolution transmission electron microscopy (HRTEM), Fourier transforms infrared spectroscopy (FT-IR), ultraviolet–visible diffuse reflectance spectrum (UV-Vis DRS), photoluminescence (PL), electrochemical impedance spectroscopy (EIS) as well as X-ray photoelectron spectroscopy (XPS) analysis. The effects of the mass proportions of NH2-MIL-125(Ti) to C3N4 as well as Ag6Si2O7 to NH2-MIL-125(Ti)/C3N4 on the visible light catalytic performance were investigated. It was found that the binary composite material with a mass proportion of 1:5 of NH2-MIL-125(Ti) to C3N4 and the tertiary material with a mass proportion of 1:20 of Ag6Si2O7 to NH2-MIL-125(Ti)/C3N4 exhibited superior photocatalytic performance towards Rhodamine B (RhB) and various colorless organic contaminants, the apparent photocatalytic rate constants of the tertiary composite material for RhB, tetracycline, and ethenzamide were 15.6, 1.69 and 1.75 times that of the Ag6Si2O7 alone, and 1.30, 1.42 and 7.98 times that of the NH2-MIL-125(Ti)/C3N4 binary composite, individually. The composite maintains high efficiency after completing three cycles. The formation of active species and the effective degradation of organic contaminants during photocatalysis can be attributed to the compact double Z-scheme heterostructure among the three semiconductors in the ternary composite. The development of the double Z-scheme composite is of great significance for the economical and highly efficient elimination of organic contaminants.