A method for producing mesoporous magnesium hydroxide nanoplates involving solvothermal treatment of a solution of a magnesium salt, a base, a glycol, and water is disclosed. The method does not use a surfactant or template in the solvothermal treatment. The method yields mesoporous nanoparticles of magnesium hydroxide having a plate-like morphology with a diameter of 20 nm to 100 nm, a mean pore diameter of 2 to 10 nm, a surface area of 50 to 70 m2/g, and a type-III nitrogen adsorption-desorption BET isotherm with a H3 hysteresis loop. An antibacterial composition containing the mesoporous magnesium hydroxide nanoplates is also disclosed. A method for reducing nitroaromatic compounds with a reducing agent and the mesoporous magnesium hydroxide nanoplates as a catalyst is also disclosed.