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In this study, a chemical-free cleaning method for biofilms removal is presented, which is based on intermittent low-intensity ultrasonication (US) triggered bursting of microbubbles (MB) in such a sequence that MB were continuously introduced into the reaction vessel for 15 min, while US was activated for 2 s after every 2 min of microbubbling. It was found that the fixed biomass, and the extracellular proteins and polysaccharides of 24-h old biofilms grown on a nylon membrane surface were reduced, respectively, by 75, 79 and 72% after treatment by the US + MB method. Fourier transform infrared (FTIR) analysis further revealed that the chemical composition of the biofilms was not altered by the US + MB treatment, suggesting that biofilms were removed through physical forces due to the generation of a shock wave and a high-speed water jet through US-triggered bursting of the MB. The proposed method can be considered a chemical-free technology for biofilm removal.

Microbubbles (MBs) have been known for their ability to generate pressure waves through shrinking and subsequent self-collapsing phenomenon. In the present study, we have investigated the potential of air MBs for biofilm detachment from a nylon membrane surface in comparison to chemical cleaning by sodium hypochloride (NaOCl). About 88% of fixed biomass detachment was observed after 1 h air microbubbling, while only 10% of biofilm detachment was achieved in the control experiment without microbubbles. Images taken with a confocal laser scanning microscope (CLSM) clearly showed that nearly all extracellular polysaccharides and proteins in biofilms were removed from the membrane surface, indicating a complete disruption of the extracellular polymeric matrix of biofilms. It was further demonstrated that microbubbling is much more efficient than chemical cleaning with 0.5% NaOCl solution in terms of removal of fixed biomass and extracellular polysaccharides and proteins. This study provides experimental evidence showing that self-collapsing air MBs is a chemical-free and eco-friendly technology for biofilm detachment.

Large‐scale synthesis of van der Waals (vdW) metal–organic framework (MOF) nanosheets with controlled crystallinity and interlayer coupling strength is one of the bottlenecks in 2D materials that has limited its successful transition to large‐scale applications. Here, scalable synthesis of mBDC (m = Zn and Cu) 2D MOFs at large scales through a biphase method is demonstrated. The results show replacing water molecules with pyridine eliminates hydrogen bond formation at metal cluster sites. This prohibits tight coupling across adjacent MOF layers and sustains controllable 2D vdW MOF growth. It is further shown that control over the growth speed, crystallinity, and thickness can be achieved by addition of a controlled amount of triethylamine and formic acid to achieve highly crystalline vdW MOF nanosheets with extraordinarily high aspect ratio. The described synthesis route can easily be scaled up for large‐scale production either by deposition onto desired substrates or in crystalline layered powder form. Owing to its large lateral size, vdW nature, and high crystallinity, it is possible to perform atomic force microscopy, Kelvin probe force microscopy, and Raman measurements on the 2D MOFs. The results not only establish their vibrational properties and layer‐dependent responses but also show striking differences from other 2D inorganic materials.