Synergy effect of sulfite, visible light, and catalyst in highly efficient photocatalytic degradation of methyl orange with sulfite activation by ZnxMg3-xAl-LDH/g-C3N4 composite: Performances, roles, and mechanism

Zn_xMg_3-xAl-LDH/g-C₃N₄ (Z_xM_3-xACN, x = 0, 1, 2, 3) composites were prepared via the electrostatic self-assembly method by assembling Zn_xMg_3-xAl-LDH with g-C₃N₄ nanosheets. The photocatalytic degradation of methyl orange (MO) by Z_xM_3-xACN under the visible-light and the sulfite activation was investigated. The results show that the doping rate of Zn^2 + had an important effect on the microstructure, photoelectric properties, and photocatalytic performance of Z_xM_3-xACN composites. In cooperation with the Na₂SO₃ activation, the photocatalytic degradation efficiency of MO by Z_xM_3-xACN composites were significantly improved. Zn₁Mg₂Al-LDH/g-C₃N₄ (Z₁M₂ACN) composite achieved the optimum photocatalytic performance. With the addition of 5 mmol Na₂SO₃, 25 mg of Z₁M₂ACN could degrade 94.3 % of MO molecules (10 mg/L, 100 mL) after 30 min of photocatalytic reaction, and it also exhibited good stability and recyclability. In addition, the pH value and temperature of MO solution as well as the sulfite dosage influenced the degradation efficiency, and a possible mechanism for the degradation of MO by Zn_xMg_3-xAl-LDH/g-C₃N₄ composite in the photocatalysis-sulfite activation system was proposed. Therefore, this research not only provides a strategy for the efficient degradation of organic pollutants by ZnMgAl-LDH/g-C₃N₄ composite, but also reveals the relationship among the visible-light, photocatalyst, and sulfite oxidant for the organic pollutant degradation.