Assembling flower-like MgAl-LDH nanospheres and g-C3N4 nanosheets for high efficiency removal of methyl orange

Flower-like Mg-Al-CO3 layered double hydroxide (MgAl-LDH) nanospheres with specific surface area of 221.95 m2/g were synthesized by modified aqueous miscible organic solvent treatment method. Via the electrostatic self-assembly method, MgAl-LDH and g-C3N4 nanosheets (CNNS), with the mass ratio of 1:10, 3:10, 5:10, 7:10, and 10:10, respectively, were assembled to prepare MgAl-LDH/g-C3N4 composites (MCN-X, X = 1, 3, 5, 7, and 10). The mass ratio of MgAl-LDH to g-C3N4 nanosheets affected the microstructure, optical and photoelectrochemical properties, and the removal efficiency toward methyl orange (MO), of MCN-X composites. The adsorption and photocatalytic degradation performance for MO by all MCN-X composites were better than those by pure g-C3N4 nanosheets. With the increasing of MgAl-LDH content, the adsorption rate and removal rate of MO by MCN-X composites increased firstly and then decreased gradually. The optimum performance was achieved by MCN-5, which removed 93.58 % of MO molecules after 30 min of dark adsorption and 120 min of photocatalytic degradation, and its pseudo-first-order reaction rate constants (k) value (0.0177 min-1) was 3.4 times that of CNNS. Reasons for these results were the enhanced specific surface area, the narrowed band gap, the inhibited recombination and the improved separation and migration of photo-generated carriers, as well as the excellent adsorption ability of MCN-5. This work provides a feasible strategy for synthesizing high performance MgAl-LDH/g-C3N4 composite photocatalyst.