ABSTRACT
This chapter is devoted to the research that has been done using the sonochemical method for the deposition of metal oxide NPs on textiles. Sonochemistry is the scientific area where chemical reactions occur under ultrasound irradiation. Liquids irradiated with ultrasound produce bubbles. The reaction is dependent on the development of an acoustic bubble in the solution. Ultrasonic waves with the frequency range of 20 kHz–1 MHz are responsible for the process of acoustic cavitation, which means the formation, growth, and explosive collapse of the bubbles. There are a number of theories that explain how 20 kHz ultrasonic radiation can break chemical bonds (Suslick et al., 1986; Doktycz and Suslick, 1990; Mason, 1990). The first question that arises is how such a bubble can be formed, considering the fact that the forces required to separate water molecules to a distance of two van der Waals radii 368would require a power of 105 W/cm. On the other hand, it is well known that in a sonication bath with a power of 0.3 W/cm, water is readily converted into hydrogen peroxide. Different explanations have been offered, and they are all based on the existence of unseen particles or gas bubbles that decrease the intermolecular forces, enabling the creation of the bubble. The experimental evidence for the importance of unseen particles in sonochemistry is that when the solution undergoes ultrafiltration before the application of ultrasonic power, there is no chemical reaction and chemical bonds are not ruptured. The second stage is the growth of the bubble, which occurs through the diffusion of solvent and/or solute vapors into the volume of the bubble. The third stage is the collapse of the bubble, which occurs when the bubble size reaches its maximum value. From here on, we will adopt the hot spot mechanism, one of the theories that explain why, upon the collapse of a bubble, chemical bonds are broken. This theory claims that very high temperatures (5,000–25,000 K) (Suslick et al., 1986) are obtained upon the collapse of the bubble. Since this collapse occurs in less than a nanosecond, very high cooling rates in excess of 1011 K/s are obtained. These extreme conditions develop when the bubble’s collapse causes the chemical reactions to occur. The high cooling rate prevents the crystallization of the products. This is the reason why amorphous NPs are formed when volatile precursors are used and the gas-phase reaction is predominant. However, from this explanation, the reason for the formation of nanostructured material is not clear. Our explanation for the creation of nanoproducts is that the fast kinetics does not permit the growth of the nuclei, and in each collapsing bubble, a few nucleation centers are formed whose growth is limited by the short collapse. If the precursor is a nonvolatile compound, the reaction occurs in a liquid phase in a 200 nm ring surrounding the collapsing bubble (Doktycz and Suslick, 1990). The products are sometimes nano-amorphous particles and in other cases nanocrystalline, depending on the temperature in the ring region where the reaction takes place. In fact, when the sonochemical reactions were used for the synthesis of inorganic products, nanomaterials were obtained.
