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 V_max. 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 K_m, maximum reaction rate V_max and initial reaction rate, correlating with ultrasonic conditions. Also, values of K_m and V_max were calculated in the absence and presence of ultrasonic and sonophoto waves.