Sonophotocatalytic degradation of paracetamol using TiO2 and Fe3+
Highlights
► The sonophotocatalytic degradation of paracetamol using TiO2 and Fe3+ has been reported. ► In the presence of TiO2, both sonophotocatalytic degradation and mineralization were found to be additive. ► In the presence of Fe3+, sonophotocatalytic degradation was additive whereas mineralization was synergistic. ► The formation of hydroxylated derivative of paracetamol was observed in LC-MS analysis.
Introduction
Paracetamol is an analgesic and antipyretic drug, mostly used to relieve pains due to tension headache, migraine headache, muscular aches, neuralgia, backache, joint pain, rheumatic pain, general pain, tooth-ache and teething pain. Paracetamol contamination in the environment occurs because of the release of industrial effluents from the production sites, direct disposal in households, excretion and waste from human and animal medical care centers. So, the treatment of wastewater containing paracetamol is of interest in order to reduce its presence in aqueous environments. Advanced oxidation processes (AOPs), such as heterogeneous photocatalysis, Fenton and photo-Fenton oxidation, ozonation, sonolysis and UV/H2O2, are widely employed for the treatment of many recalcitrant organic compounds [1], [2], [3], [4]. Recently, ultrasonic irradiation mediated by suitable catalysts has received attention as a promising technique for the treatment of hazardous organic pollutants in wastewater [5], [6], [7], [8].
In sonolysis, there is no requirement to use any added chemicals or catalysts for the oxidation of organic pollutants. The chemical reactions occurring from the ultrasonic irradiation of a solution are produced through the phenomenon of cavitation. The process of cavitation refers to the rapid growth and implosive collapse of bubbles in a liquid resulting in the creation of an unusual reaction environment within and in the vicinity of the bubbles. During acoustic cavitation, hydroxyl radicals are produced from the water molecules entrapped inside the cavitation bubbles. These sonochemically produced hydroxyl radicals can be exploited for the treatment of polluted waters [9], [10].
It has been reported that combining US and ultraviolet (UV) irradiation with both homogeneous and heterogeneous photocatalysts can enhance the efficiency of the degradation of pollutants synergistically [11], [12], [13], [14]. Although, sonolysis and photocatalysis make use of different reaction systems, the principle process underlying these two techniques is the production of OH radicals, which are powerful oxidizing species with an oxidation potential of 2.5 V. Instead of operating sonolysis or photocatalysis alone, their combination can significantly enhance the degradation of target pollutants.
Isariebel et al. [15] have reported the sonochemical degradation of pharmaceutical drugs like paracetamol and levodopa at high US frequencies of 574, 860 and 1134 kHz at 9, 17, 22 and 32 W at 20 °C. The photocatalytic degradation of paracetamol using TiO2 and other AOPs has also been reported in the literature [16], [17]. In the present investigation, we report the sonophotocatalytic degradation of paracetamol at 213 kHz. The objective of the present investigation is to separately study the sonolytic and photocatalytic degradation of paracetamol using TiO2 and Fe3+ and then combine the two processes to examine whether or not synergistic effects are at play.
Section snippets
Experimental conditions
All experiments involving sonolysis were carried out with an ELAC LVG-60 RF 213 kHz ultrasound generator coupled with an ELAC allied signal transducer with a plate diameter of 54.5 mm. The experiments were carried out in a continuous wave mode and the total power delivered was ∼13.8 W (measured calorimetrically; intensity ∼0.6 W/cm2). The experimental set-up employed for the sonophotochemical experiments consists of the above mentioned sonolytic reactor, a mechanical stirrer and a lamp (450 W xenon
Effect of [Paracetamol]
The effect of concentration of paracetamol on the sonochemical degradation was studied by varying its concentration from 0.03 to 0.12 mM. The concentration changes as a function of sonication time are shown in Fig. 1. The linear ln(C0/C) vs sonication time plots suggest that the sonochemical degradation follow first-order like kinetics. However, the rate constant values change with an increase in the concentration showing that the degradation does not follow true first order behavior. This may
Summary
The sonolytic, photocatalytic and sonophotocatalytic degradation of paracetamol was studied in the presence of homogeneous (Fe3+) and a heterogeneous photocatalyst (TiO2). Rate of degradation values have been calculated for optimized conditions for sonolysis, photocatalysis and sonophotocalysis in the presence of TiO2 or Fe3+. It was inferred from the rate values that the combination of sonolysis with photocatalysis (TiO2 or Fe3+) showed an additive effect of combining the two processes.
Acknowledgements
The authors thank DIISR, Australia and DST, New Delhi for the financial support from India–Australian strategic research fund (INT/AUS/P-1/07 dated 19 September 2007).
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