Study on the ability to treat methylene blue in water and textile dyeing wastewater from sedge mats of the ZnAlCO3 hydrotalcite modified by Cu2+ ion under visible light

Abstract

Hydrotalcite ZnAlCO3 and modified hydrotalcite CuZnAlCO₃ were synthesized by a co-precipitation method from nitrate salts of Al, Zn and Cu as precursors. Using Na₂CO₃ salt to provide CO₃^2- interlayer ion and NaOH 2N solution to adjust the pH of the reaction mixture to pH = 9.5. The obtained samples were characterized by physical analysis methods: XRD, EDX, SEM image, BET, UV-Vis DRS. The characterization results showed that the two synthesized samples H and 3CuH (molar ratio of Zn:Al and Cu:Zn:Al are 7:3 and 3:4:3 for H and 3CuH, respectively) had a lamellar structure similar to hydrotalcite with ions CO₃^2- in the interlayer. The molar ratio of Zn:Al and Cu:Zn:Al in the samples is quite similar to the amount taken to synthesize the samples. The specific surface area  increased from 16.1 to 33.9 m²/g, while the band gap energy Eg decreased from 3.02 to 1.25 eV, corresponding to  H and 3CuH. The photocatalytic activity of the 3CuH sample in the decomposition reaction of methylene blue (MB) was much better than that of the sample H at the concentrations of MB investigated (10, 25, 50 ppm). The catalytic activity of the 3CuH material  depended on the initial concentration of MB solution and the pH of the medium. Free radicals OH• and holes h⁺play an important role in the photocatalytic activity of 3CuH material. In addition, the 3CuH sample is capable of effectively treating blue sedge textile dyeing wastewater with the decomposition efficiency of blue substances reaching over 94% after 4 hours of illumination, the mineralization efficiency of pigments reaching nearly 88% after 7 hours of lighting.