Indian Journal of Chemical Technology Vol. 22, Jan-Mar 2015, pp. 73-77 Sonochemical degradation of p-chlorophenol assisted by H 2 O 2 and Ag-TiO 2 / TiO 2 catalyst Shilpa K Nandwani*, A K Mungray & Mausumi Chakraborty Department of Chemical Engineering, S. V. National Institute of Technology, Surat, India. E-mail: sknandwani80@gmail.com Received 29 September 2013; accepted 15 May 2014 The degradation of p-chlorophenol in aqueous solution by low frequency ultrasound (30 kHz) has been studied. The degradation of p-chlorophenol in US/H 2 O 2 , US/ Ag- TiO 2 US/TiO 2 , US/TiO 2 /H 2 O 2 and US/ Ag-TiO 2 /H 2 O 2 systems is also compared. The maximum removal of p-chlorophenol i.e 75% is observed in US/ Ag-TiO 2 /H 2 O 2 system where as 37% removal is observed in US/TiO 2 /H 2 O 2 system. Further the effect of initial substrate concentration, pH and temperature on the initial rate of degradation of the model pollutant have also been investigated. Studies reveal that the initial rate of degradation increases with increase in initial substrate concentration whereas the initial rate of degradation decreases with an increase in pH and reaction temperature. Keywords: Ag-loaded TiO 2 catalyst, Hydrogen peroxide, p-Chlorophenol (PCP), Ultrasound. p-Chlorophenol (PCP) is used in pesticides and antiseptics. It is mainly produced in pulp and paper industry, in bleaching process with chlorine. PCP being much more toxic than its parent compound, phenol, affects liver and immune system. Discharge of these chemicals into the environment poses significant health risks due to their high carcinogenicity. Also high toxicity and its physiochemical properties make PCP difficult to decompose by the conventional waste-water treatment processes. Ultrasonic irradiation has received considerable interest as an advanced oxidation process since this process leads to complete demineralization of the harmful pollutant, which are not easily biodegradable, by oxidizing them to less toxic intermediates. Sonochemical techniques utilize ultrasound to produce an oxidative environment via acoustic: formation, growth and implosive collapse of micro- bubbles that entrap molecules of gases and water vapor from the surrounding liquid. During collapse of cavitation bubbles intense localized temperatures (5000°K), pressures (1000 atm), electrical charges as well as plasma effects are induced 1,2 . The entrapped molecules are thus subjected to extremes of temperature and pressure generated during transient and adiabatic collapse of bubbles and dissociation generating radicals. With fragmentation of these bubbles during collapse, these radicals are released into the bubble liquid medium where they induce various chemical reactions 3 . Depending on the physiochemical properties of organic pollutants there are two different mechanisms for their degradation: thermal decomposition due to direct pyrolysis inside the cavitation bubbles and decomposition via oxidizing the pollutant by ˚OH radicals and H 2 O 2 released into the bubble liquid medium when the cavitation bubbles collapse 4 . Hydrophobic and volatile compounds degrade mainly by pyrolysis in the cavitation bubbles. Hydrophilic compounds, compounds with a low vapour pressure e.g., phenol, PCP, degrade ultrasonically mainly by reaction with ˚OH radicals and H 2 O 2 in the bulk solution or in the interface between the collapsing cavitation bubble and the bulk solution 5 . Studies regarding the ultrasonic degradation of hydrophilic organic compounds reveal that though ultrasonic irradiation has potential for treatment of hazardous wastewater, the use of ultrasound alone cannot provide high enough rate of degradation 5,6 . Accelerating the ultrasonic degradation of such compounds by coupling it with other advanced oxidation processes is another possibility to increase the efficiency of this technique 4 . Heterogeneous sonocatalytic degradation of recalcitrant organic contaminants using different catalysts such as metal oxides is an alternative way to solve the problem of transforming persistent organic contaminants to non-persistent substances. The most common type of catalyst to be used is TiO 2 and its advantages are such as inexpensive, non-toxic, biologically stable and reusable. Loading of metal particles into TiO 2 catalysts either through doping or used as their composites can inhibit charge recombination between holes and electrons produced during the ultrasonic irradiation of TiO 2 to enhance the degradation efficiency 4 . In the present study, the degradation of PCP, the model hazardous organic compound, by ultrasonic