Microscale flower-like magnesium oxide for highly efficient photocatalytic degradation of organic dyes in aqueous solution

摘要

Flower-like MgO microparticles with excellent photocatalytic performance in degradation of various organic dyes ( e.g. , methylene blue, Congo red, thymol blue, bromothymol blue, eriochrome black T, and their mixture) were synthesized by a facile precipitation method via the reaction between Mg ~(2+) and CO _(3) ~(2?) at 70 °C. The reaction time was found to be crucial in determining the final morphology of flower-like MgO. After studying the particles from time-dependent experiments, scanning electron microscope observation, Fourier transform infrared spectra and thermogravimetric analyses demonstrated that the formation of flower-like particles involved a complex process, in which agglomerates or rod-like particles with a formula of x MgCO _(3) · y H _(2) O ( x = 0.75–0.77 and y = 1.87–1.96) were favorably formed after the initial mixture of the reactants. Owing to the chemical instability, they would turn into flower-like particles, which had a composition of x MgCO _(3) · y Mg(OH) _(2) · z H _(2) O ( x = 0.84–0.86, y = 0.13–0.23, and z = 0.77–1.15). After calcination, the generated product not only possessed a superior photocatalytic performance in degradation of organic dyes (100 mg L ~(?1) ) under UV light irradiation in contrast to other morphologies of MgO and other related state-of-the-art photocatalysts ( e.g. , N-doped TiO _(2) , Degussa P25 TiO _(2) , ZnO, WO _(3) , α-Fe _(2) O _(3) , BiVO _(4) , and g-C _(3) N _(4) ), but also could be used for five cycles, maintaining its efficiency above 92.2%. These capacities made the flower-like MgO a potential candidate for polluted water treatment. Also, the underlying photocatalysis mechanism of MgO was proposed through radical trapping experiments.