In our group’s previous blog post, acoustic cavitation was explained and how it affected both homogeneous and heterogeneous solutions. To summarize, acoustic cavitation is when the intermolecular forces cannot withstand the mechanical activation put on them. This process ultimately forms cavitation bubbles, or small bubbles of gas, that expand until they become too big and burst.
Many sonochemical reactions are done in an ultrasonic bath because of its experience with cavitation bubbles. Normally, ultrasonic baths help clean contaminated objects by using cavitation bubbles to excite a liquid, which puts force against the contamination. Ultrasonic baths are very easy to use, which is another reason why many chemists use them for many sonochemical reactions. Also, ultrasonic baths can be easily obtained. This is an important advantage for scientists because many types of sonochemical equipment are very expensive and are hard to find. Other advantages include its ability to distribute sound evenly throughout the bath, there is little to no other technology needed to operate the bath, and it works well for high frequency applications. However, there are also quite a few disadvantages.
In ultrasonic baths, it is extremely hard to control the temperature. This is because ultrasonic baths usually warm up when they are in use, resulting in an inconsistent temperature. Many sonochemical reactions need to be at a certain temperature, so this serves as a major disadvantage. Some baths come with cooling jackets, but if a cooling jacket is not available, the person doing the experiment must come up with a new way to regulate the temperature. In addition, the power that goes into the reaction is not very large. This means that in some reactions, there is not enough power to carry out the reaction. The amount of power that goes into the reaction depends on a variety of factors. These factors include the size of the bath, the type of the reaction vessel, and where the reaction vessel is situated. This harsh disadvantage causes scientists to think about purchasing a new ultrasonic bath, which can be aggravating for most. Finally, there are some types of ultrasonic baths that are specifically designed for sonochemistry. These types of baths are usually much more expensive than regular ultrasonic baths. These disadvantages when conducting sonochemical reactions in an ultrasonic bath can lead scientists conduct regular thermodynamical reactions rather than using sonochemistry.
In general, there still are some beneficial effects that come from sonochemical reactions. Nanoparticles can easily be formed at a steady rate and with similar shapes from sonochemical reactions. Also, ultrasonic cavitation uses forces to turn solids into tiny particles instead. Conducting sonochemical reactions to liquids can help eliminate gas particles when they are unnecessary in the reaction. Some other major benefits of sonochemical reactions include removing contamination from water and soil, breaking down smoke and other fumes, removing pollutants from organisms, called bioremediation, and many others. When looking at all the disadvantages shown above, sonochemistry does not look like an efficient way to conduct a reaction. However, all of these advantages and benefits from sonochemical reactions shows why many scientists today are using sonochemistry to conduct many reactions that regular thermodynamic reactions cannot.