Interfacial nanobubbles produced by long-time preserved cold water

Interfacial gaseous nanobubbles which have remarkable properties such as unexpectedly long lifetime and significant potential applications, are drawing more and more attention. However, the recent dispute about the contamination or gas inside the nanobubbles causes a large confusion due to the lack of simple and clean method to produce gas nanobubbles.Here we report a convenient and clean method to effectively produce interfacial nanobubbles based on a pure water system.By adding the cold water cooled at 4℃ for more than 48 h onto highly oriented pyrolytic graphite(HOPG) surface, we find that the average density and total volume of nanobubbles are increased to a high level and mainly dominated by the concentrations of the dissolved gases in cold water. Our findings and methods are crucial and helpful for settling the newly arisen debates on gas nanobubbles.     

Enrichment of microplastic pollution by micro-nanobubbles

Microplastic pollution has become a global environmental concern. It has been reported that microplastics are easily accessible to a wide range of aquatic organisms and ultimately enter the human body along the food chain. They pose a severe threat to ecosystems, organisms and even human health due to their durability and persistence. However, how to reduce microplastic pollution still remains a challenge in terms of scientific techniques and policy-making. There is currently still a lack of effective methods for microplastic recycling and removal. Luckily, a new technique, micro-nanobubbles (MNBs), may provide a possible and highly effective method to enrich microplastic pollution: their great advantages^[1] include a high specific surface area, long lifetime and ability to adsorb microplastics of the same size and hydrophobicity. Then they further adsorb on larger bubbles such as microbubbles or millimeter bubbles and float to the water surface together. In this study, we present a new method using MNBs to enrich microplastic pollution with high efficiency. Two types of microplastics, millimeter-scale plastic fragments and microplastic particles, were chosen as the model microplastic pollution systems to study the enrichment efficiency of MNBs on microplastics. Results showed that MNBs can efficiently enrich these microplastics. The enrichment efficiency increases with flotation time until a maximum value is reached. It is proved that MNBs not only collect the microplastic pollution but also reduce detergent use in domestic laundry sewage. This is because detergent, as a surfactant, is easily absorbed on the surface of MNBs and can be collected together with the microplastic pollution. Our research has demonstrated that the MNB technique could be promising for use in microplastic recycling and reducing detergent pollution in daily life.     

The properties of surface nanobubbles formed on different substrates

The properties and stability of the reported surface nanobubbles are related to the substrate used and the generation method. Here, we design a series of experiments to study the influence of the hydrophobicity of the substrate and the production method on the formation and properties of nanobubbles. We choose three different substrates, dodecyltrichlorosilane(DTS) modified silicon, octadecyltrichlorosilane(OTS) modified silicon, and highly oriented pyrolytic graphite(HOPG)as nanobubble substrates, and two methods of ethanol–water exchange and 4-℃ cold water to produce nanobubbles. It is found that using ethanol-water exchange method could produce more and larger nanobubbles than the 4-℃ cold water method. The contact angle of nanobubbles produced by ethanol–water exchange depends on the hydrophobicity of substrates, and decreases with the increase of the hydrophobicity of substrates. More interestingly, nanoscopic contact angle approaches the macroscopic contact angle as the hydrophobicity of substrates increases. It is believed that these results would be very useful to understand the stability of surface nanobubbles.