Behavior of chitosan immobilized CdS nanocrystals with various crosslinking and drying treatments in textile dye photodegradation

Abstract

Chitosan based photocatalyst composites containing semiconducting CdS nanocyrstals with and without glutaraldehyde and epichlorohydrin crosslinking treatments were studied for the photodegradation of Methyl Orange and Acid Blue 25. The photocatalysts dried using oven and freeze dryer were investigated. Studies of the effects of crosslinking and various drying methods on photodegradation characteristics of the chitosan-based catalyst composites were rare, although these studies were not uncommon for the studies using chitosan as an adsorbent. The chitosan polymer embedded CdS nanocrystal photocatalyst composites were characterized by using X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscope (SEM), Fourier transform infrared (FT-IR) and visible reflectance spectroscopy. The degradation kinetics was investigated under the effects of catalyst dosage, initial dye concentration, initial pH of dye solution, on adsorption and photodegradation of dyes (Methyl Orange and Acid Blue 25) were investigated. The dye removal mechanism involved an initial sorption process following the photo-degradation. The sorption kinetics revealed that the sorption process undergo the pseudo second order adsorption kinetics. Photodegradation of Methyl Orange was pseudo first order kinetics. Unlike Methyl Orange, degradation profiles of CI Acid Blue 25 followed the rare second order kinetics. Nevertheless, degradation of CI Acid Blue 25 can be the first order kinetics if the reaction was commenced with high pH dye solution. Efficient colour removal was observed. The catalyst composite can remove 99% Methyl Orange at pH 4 and 98% Acid Blue 25 dye at pH10 with 75 minutes of illumination. The present study mainly carried out with the catalyst composites prepared without special shape forming technique and in form of flakes. Moreover, two innovative chitosan-based encapsulation systems, namely (1) chitosan micro-particles and (2) chitosan mini-particles with loaded CdS catalyst aiming at facilitating the practical application have been developed and preliminary tests were conducted.