Sonolytic, sonocatalytic and sonophotocatalytic degradation of carboxymethyl cellulose (CMC): kinetic and mechanisms

Abstract

In this research, enzymatic degradation of carboxymethyl cellulose (CMC) with different concentration of substrate was studied using stable available parameters of Michaelis-Menton and calculated maximum reaction rate Vmax. We also used effective approaches such as ultrasonic, sonocatalytic and sonophotocatalytic irradiation in the presence of TiO2 nanoparticles as pretreatment. Degradation of the cellulose by means of ultrasound irradiation and its combination with heterogeneous (TiO2) was investigated. The emphasis was on evaluating theeffect of additives on degradation rate constants. Ultrasound irradiation (24 kHz) was provided by a sonicator, while an ultraviolet source of 16 W was used for UV irradiation. The extent of sonolytic degradation increased when ultrasound power (in the range 1560 W) increased, and the presence of TiO2 did not have significant effect on degradation. We should also note that TiO2 sonophotocatalysis led to complete cellulose degradation in 120 min with increasing the catalyst loading. TiO2 sonophotocatalysis was always faster than the respective individual processes due to the enhanced formation of reactive radicals as well as the possible ultrasound-induced increase of the active surface area of the catalyst. Their efficacy on enhancement of reactivity was discussed based on the kinetic parameters including, Michaelis constant Km, maximum reaction rate Vmax and initial reaction rate, correlating with ultrasonic conditions. Also, values of Km and Vmax were calculated in the absence and presence of ultrasonic and sonophoto waves.