Evaporation kinetics during containerless chemical synthesis of ZIF-8 in levitated droplets.

Zeolitic imidazolate framework-8 was synthesized in a containerless state acoustic levitation. The cavitation effect of ultrasound affected the coordination connection of organic ligands in acoustically levitated droplets and they exhibited a conspicuous difference in the particle size distribution as compared with those under normal conditions. Herein, methanol was chosen as the solvent to investigate the influence of droplet evaporation on acoustic levitation synthesis. The kinetic parameters of droplet evaporation such as geometrical morphology transformation, concentration change and temperature evolution were measured for the levitation state. Surface evaporation resulted in the drastic deformation of the droplet during ZIF-8 synthesis and caused its vertical vibration and shape oscillation. The abrupt change of the levitation state aggravated the sound field effect on the containerless synthesis and caused a decrease of particle size distribution. A two-dimensional axis-symmetry model was used to visually simulate the sound field distribution during acoustic levitation synthesis based on the finite element method. The fabricated ZIF-8 was able to remove phthalic acid in wastewater through adsorption, and its kinetic features followed a pseudo second-order rate model.