Immobilized bilayer TiO2/chitosan system for the removal of phenol under irradiation by a 45ᅡᅠwatt compact fluorescent lamp

a r t i c l e i n f o A simple bilayer system consisting of TiO 2 and chitosan (CS) biopolymer has been fabricated and immobilized onto a glass plate. The deposition properties of TiO 2 powder were improved by adding epoxidized natural rubber (ENR 50) and phenol-formaldehyde resin (PF) in the coating formulation. SEM analysis indicated that the degraded ENR 50 acted as macro-pores forming agent to generate macro-pores within the surface of TiO 2 layer and was quantitatively determined by TGA and EDX analyses as well. The highly porous structure of immobilized TiO 2 layer allows better diffusion of pollutants, increases the light penetration and improves the optical property as indicated by photoluminescence spectroscopy (PLS) analysis. Consequently, the photocatalytic activity and mineralization rate of the immobilized bilayer TiO 2 /CS system becomes approximately twice as fast as an immobilized TiO 2 single layer system and as good as TiO 2 powder in a slurry system. Moreover, the adsorption effect was extremely negligible and the photodegradation of phenol was mainly due to the photocatalytic process. Among all of the semiconductors photocatalysts, titanium dioxide TiO 2 is close to be an ideal bench mark photocatalyst in the environmental photocatalysis applications because of its many desirable properties such as inexpensive and readily available, biologically and chemically inert, and good photoactivity [1]. In fact, there are two main technical challenges that really restricted the large-scale applications of TiO 2 , firstly is the relatively wide band gap of TiO 2 which absorbs only 3–4% energy of the solar spectrum and restricts its applications to UV excitation source [2] and secondly, the effective slurry or suspension mode application of TiO 2 requires post-treatment catalyst recovering step which is normally difficult, energy-consumptive and not cost-effective. Moreover, the TiO 2 powder has a great tendency to aggregate especially at high concentrations provides a real limitation to apply to continuous flow system and suffers from scattering of incident UV light by the suspended particles [3,4]. Thus, several methods have been made in order to extend the spectral sensitivity of TiO 2 towards visible light region as adequately reviewed by Chatterjee and Dasgupta [5] which generally involved sensitization by dyes, doping with metallic and non-metallic species, heterojunction systems and utilizing thin film. Moreover, immobili-zation of TiO 2 powder on solid supports is an alternative convenient method to solve the problem of the post-treatment catalyst powder …