Sonocrystallisation of ZIF-8 in water with high excess of ligand: Effects of frequency, power and sonication time

• Published in: Ultrasonics sonochemistry 2021-08, Vol.76, p.105616-105616, Article 105616
• Main Authors: Nalesso, Silvia, Varlet, Gaelle, Bussemaker, Madeleine J., Sear, Richard P., Hodnett, Mark, Monteagudo-Oliván, Rebeca, Sebastián, Victor, Coronas, Joaquín, Lee, Judy
• Format: Article
• Language: English
• Subjects: Crystal size; Crystallinity; Mixing; MOFs; Original; Ultrasound frequency; Ultrasound power
• ISSN: 1350-4177; 1873-2828
• DOI: 10.1016/j.ultsonch.2021.105616

•ZIF-8 synthesis under different mixing speeds, US frequencies, powers and time.•ZIF-8 crystals were formed after 5 s of reaction time.•Sonication produced smallest crystals with an average size of 80 nm.•Varying frequency and power did not significantly affect the crystal properties.•Ultrasound has both positive and negative impact on crystal properties. A systematic study on the sonocrystallisation of ZIF-8 (zeolitic imidazolate framework-8) in a water-based system was investigated under different mixing speeds, ultrasound frequencies, calorimetric powers and sonication time. Regardless of the synthesis technique, pure crystals of ZIF-8 with high BET (Brunauer, Emmett and Teller) specific surface area (SSA) can be obtained in water after only 5 s. Furthermore, 5 s sonication produced even smaller crystals (~0.08 µm). The type of technique applied for producing the ZIF-8 crystals did not have any significant impact on crystallinity, purity and yield. Crystal morphology and size were affected by the use of ultrasound and mixing, obtaining nanoparticles with a more spherical shape than in silent condition (no ultrasound and mixing). However, no specific trends were observed with varying frequency, calorimetric power and mixing speed. Ultrasound and mixing may have an effect on the nucleation step, causing the fast production of nucleation centres. Furthermore, the BET SSA increased with increasing mixing speed. With ultrasound, the BET SSA is between the values obtained under silent condition and with mixing. A competition between micromixing and shockwaves has been proposed when sonication is used for ZIF-8 production. The former increases the BET SSA, while the latter could be responsible for porosity damage, causing a decrease of the surface area.