Antisolvent crystallization of paracetamol was conducted using ultrasound. The effect of various ultrasonic frequencies and power on the mean crystal size, crystal size distribution, induction time, and type of polymorph obtained was studied. Multibubble sonoluminescence intensity was used to correlate the crystallization results with cavitation activity. Results showed that under optimum conditions ultrasound can significantly (i) reduce the mean crystal size from 170 to 13 μm, (ii) lower the induction time from 360 to 30 s, and (iii) narrow the size distribution. A close association between cavitation activity and rate of nucleation was observed. In addition, crystallization under sonication led to the formation of not only monoclinic polymorph (form I) but also orthorhombic polymorph (form II) of paracetamol, which is otherwise difficult to obtain in the absence of ultrasoun

Sonochemistry refers to ultrasound-initiated chemical processes in liquids. The interaction between bubbles and sound energy in liquids results in acoustic cavitation. This review presents the fundamental aspects of acoustic cavitation and theoretical aspects behind sonochemistry such as dynamics of bubble oscillation, the rectified diffusion process that is responsible for the growth of cavitation bubbles, near adiabatic collapse of cavitation bubbles resulting in extreme reaction conditions and several chemical species generated within collapsing bubbles that are responsible for various redox reactions. Specifically, a detailed discussion on single bubble sonochemistry is provided.

The out-of-equilibrium self-assembly of simple aromatic amino acid molecules is driven by high frequency ultrasound, where acoustic energy acts as a fuel to form uniform supramolecular nanostructures with multifarious optical and biological properties.

The production of biodiesel was carried out from canola oil and methanol catalysed by lipase from Candida rugosa under different ultrasonic experimental conditions using horn (20kHz) and plate (22, 44, 98 and 300kHz) transducers. The effects of experimental conditions such as horn tip diameter, ultrasonic power, ultrasonic frequency and enzyme concentrations on biodiesel yield were investigated. The results showed that the application of ultrasound decreased the reaction time from 22-24h to 1.5h with the use of 3.5cm ultrasonic horn, an applied power of 40W, methanol to oil molar ratio of 5:1 and enzyme concentration of 0.23wt/wt% of oil. Low intensity ultrasound is efficient and a promising tool for the enzyme catalysed biodiesel synthesis as higher intensities tend to inactivate the enzyme and reduce its efficiency.

A sustainable, reagent-less and one-pot ultrasonic methodology has been developed to transform amorphous tannic acid into regularly shaped crystalline ellagic acid particles.

In the past few decades, several studies have used nanoparticles for photocatalytic reactions. For practical applications, the use of nanomaterials may not be advantageous due to the difficulties in removing them from processed liquids, and they also pose possible health risks. We have developed a procedure that uses chitosan to convert nanosized photocatalysts into micron sized materials without losing their efficiency or surface area. Additionally, the synthetic method offers the possibility of adding functionality like macroporosity and doping carbon or gold nanoparticles. The synthesis involves ultrasonic emulsification of tetradecane in an aqueous chitosan solution containing photocatalytic nanoparticles.Tetradecane-core chitosan/photocatalyst composite-shelled microspheres were produced during the ultrasonic emulsification process. Calcination of these microspheres resulted in the formation of carbon doped micron-sized photocatalytic particles with macroporous structure. Detailed characterisations were carried out using dynamic light scattering, zeta potential, SEM, TEM, BET, XRD and XPS measurements. A possible mechanism for the formation of micron-sized photocatalytic particles is proposed. The photocatalytic efficiencies of synthesised microparticles and their reusability through filtration were evaluated and compared with that of starting nanomaterials using two organic dyes as model pollutants. One of the catalysts (gold doped photocatalyst) was also tested for H 2 S gas removal by adsorption. The regeneration of the adsorbent was also achieved after room temperature photocatalysis.The results indicate that the synthetic procedure can be used to produce macroscale photocatalysts with a size range of 10-20 mm as efficient as the starting nanopowders (size range of 20-50 nm).

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Fluorescent oligomeric structures were synthesized from the phenolic moieties by a simple one-step sonochemical approach without the use of enzymes, metal catalyst, or other toxic reagents. The formation of phenol dimers, trimers, and oligomers was confirmed by absorption spectroscopy, fluorescence spectroscopy, HPLC, and mass spectroscopy. We have demonstrated that the cavitation bubble surface acted as a catalytic binding site to generate such oligomers, and the ultrasonic frequency, concentration, and other physicochemical properties (surface activity) of phenolic building blocks can affect the formation of these oligomers. The sonochemically produced phenolic oligomers showed antioxidant activity which was determined by DPPH assay. The study suggests that acoustic cavitation could promote polymerization of simple phenolic molecules to generate bioactive oligomers and nanostructures with varying functional properties.