Sonolytic, sonocatalytic and sonophotocatalytic degradation of chitosan in the presence of TiO2 nanoparticles

Abstract

The degradation of chitosan by means of ultrasound irradiation and its combination with heterogeneous (TiO(2)) was investigated. Emphasis was given on the effect 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 with increasing ultrasound power (in the range 30-90 W), while the presence of TiO(2) in the dark generally had little effect on degradation. On the other hand, TiO(2) sono-photocatalysis led to complete chitosan degradation in 60 min with increasing catalyst loading. TiO(2) 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. The degraded chitosans were characterized by X-ray diffraction (XRD), gel permeation chromatography (GPC) and Fourier transform infrared (FT-IR) spectroscopy and average molecular weight of ultrasonicated chitosan was determined by measurements of relative viscosity of samples. The results show that the total degree of deacetylation (DD) of chitosan did not change after degradation and the decrease of molecular weight led to transformation of crystal structure. A negative order for the dependence of the reaction rate on total molar concentration of chitosan solution within the degradation process was suggested.

Synthesis of Magnetic Sonophotocatalyst and its Enhanced Biodegradability of Organophosphate Pesticide

“…A desired concentration of DDVP was prepared by dissolving the 12 L of dechlorinated tap water aerated for 40 min at room temperature (19)(20)(21)(22)(23)(24)(25) o C). Then, the catalyst was added to the above DDVP solution.…”

“…Many studies have been reported on combining ultrasound with UV light irradiation in the presence of TiO 2 and sonophotocatalysis can enhance the efficiency of semiconductor mediated degradation of organic contaminants synergistically. [18][19][20] To the best of our knowledge, the combination of radial ultrasound and magnetic core-shell photocatalyst was seldom reported. Radial ultrasound can increase the distribution area of ultrasound wave, thus increasing the amounts of the reactive radical species.…”

Photocatalytic, Sonolytic and Sonophotocatalytic Degradation of 4-Chloro-2-Nitro Phenol

“…Actually the ultrasound promoted reactions increased the catalytic activity of TiO 2 by de-aggregating the catalyst particles, thus increasing the surface area for the reaction. Secondly, the increased production of hydroxyl radicals as per the following reactions [22]:…”

Photo-Assisted Sondegradation of Hydrogels in the Presence of TiO2Nanoparticles

“…The rate of chitosan degradation in mentioned conditions (sonophotocatalysis) increased with an increase in catalyst loading. The beneficial effect of coupling photocatalysis with sonolysis may be attributed to several reasons, namely: (i) increased production of hydroxyl radicals in the reaction mixture, (ii) enhanced mass transfer between the liquid phase and the catalyst surface, (iii) catalyst excitation by ultrasound-induced luminescence which has a wide wavelength range below 375 nm [63][64][65][66] and (iv) increased catalytic activity due to ultrasound de-aggregating catalyst particles, thus increasing surface area.…”