2.5 Ultrasound
Ultrasound, recognized for its cleanliness, efficiency, and cost-effectiveness, is garnering
significant interest in wastewater treatment. Many studies have been conducted on the use of
ultrasound alone or in combination with hybrid techniques to remediate wastewater
contaminants. High-intensity ultrasonic radiation is used in ultrasonic synthesis, an unusual
chemical synthesis technique, to encourage chemical reactions. This method uses the mechanical
vibration of sound waves to gradually raise the reactants' temperature and local high pressure,
enabling quick reaction system activation and reaction completion (Li et al., 2023). A reaction
system's chemical processes can be induced, strengthened, or even weakened by ultrasound
stimulation (Z. Li et al., 2020).
The study by Malika and Sonawane (2022) reveals that with calcination at increasing
temperatures, the surface area of the nanoparticle decreased, and samples are in the anatase phase
at all temperatures studied. Adding Fe2O3 nanoparticles to the TiO₂ structure as a defect solved
the problem at the same time. The visible light absorption spectrum of the Fe2O3-TiO₂
nanocomposite will be investigated. The spectrum, in particular, indicated that increasing the
calcination temperature above 400 ◦C enhanced the crystallinity of Fe2O3 while reducing
amorphous TiO₂ to anatase structure. Moreover, with the inclusion of the Fe2O3 energy levels,
the total band gap energy will be reduced, increasing BET surface area; the same will be used in
the present photodegradation analysis. The research study shows that the photoluminescence
(PL) spectra of the TiO₂ nanosheet calcined at 350–550 ◦C in the range of 400–750 nm. It is
worth noting that the photocurrent densities are sharply increased with an increase in the
calcination temperature up to 500 °C and then started decreasing at 550 °C. Because of the lower
crystallinity, the TiO₂ nanosheet calcined at 450 ◦C had the lowest PL intensity, affecting the
synergistic effect between the Fe2O3 and TiO₂ nanoparticles by significantly reducing the PL
intensity and hindering the separation efficiency of electron-hole pair recombination rate to
enhance the photocatalytic performance of the Fe2O3-TiO₂ nanocomposite than bare TiO₂.
The 450 ◦C calcination temperature had promising results for the photocatalytic activity of the
Fe2O3-TiO₂ nanocomposite (FTN) by forming an anatase phase with reduced band gap energy
and higher thermal stability, BET surface area, and adsorption capacity. Thus, FTN/water hybrid
nanofluid photocatalytic performance is superior to TiO₂/water and Fe2O3/water nanofluid. After
that, RSM optimized degradation efficiency to 99% by setting the input parameters in
comparison with its initial dye concentration at 2 vol%, reaction time at 50 ppm, and
ultrasonication time also at 120 min, meanwhile keeping dye degradation performance constantly
at 120 min. Moreover, before degradation investigation, hybrid nanofluid ultrasound cavitation
increased the number of extremely reactive H and OH free radicals from acoustic cavity
implosion and proved to be the best approach for treating effluents. According to this outstanding
performance, it may be the novel source for treating industrial fluids, with the synergistic effect
of hybrid nanofluid and sono-photocatalysis.