Investigation of the effect of ultrasonic waves on the enhancement of efficiency of direct photolysis and photooxidation processes on the removal of a model contaminant from textile industry

The effect of ultrasonic waves (US) was studied on the degradation of Malachite Green (MG)
as a model contaminant from textile industry by direct photolysis with ultraviolet (UV) radiation
and UV/H2O2 processes. The US (35 kHz) and UV (253.7 nm) radiations were carried out with
an ultrasonic bath and a 15 W low-pressure mercury lamp, respectively. Degradation of MG
follows pseudo-first order kinetics in all cases. The apparent reaction rate constant (kap) for
UV/US process is greater than sum of the UV and US processes but it is relatively low for
practical uses. However UV/H2O2 treatment more efficiently decomposes this organic
contaminant and combining this process with US can improve its efficiency. kap is influenced
by variation of operational parameters such as power density, temperature, initial
concentration of MG and H2O2 for US/UV/H2O2 process and activation energy was 9 kJ mol-1
in the range of 294-307 K for this process. UV-vis spectral change of MG showed
hypsochromic shift occurred with increasing sonication time, suggested N-demethylation
process of MG.