Properties and morphology of CdS compounded TiO2 visible-light photocatalytic nanofilms coated on glass surface
Introduction
Photocatalytic nanomaterial, a new kind of eco-materials, is widely used nowadays. As a branch of it, TiO2 photocatalytic film applies sensitization technology of fine surface to efficiently degrade oil and other hazardous wastes in the air [1].
Traditionally, the photocatalytic film, which coated on the glass surface to make the glass as self-cleaning glass is based mainly on single component-titanium dioxide. As the forbidden-zone width of titanium dioxide is 3.2 eV, the photocatalytic ability of traditional self-cleaning glass is limited in ultraviolet wavelength [2]. Cadmium sulfide is a kind of semiconductor with forbidden-zone of 2.5 eV, and its valence electron can be easily evoked to conduction band when the wavelength of evoking light is less than or equal to 495 nm. However, cadmium sulfide is not so stabilized as titanium dioxide is. Based on the stability of titanium dioxide and thin forbidden-zone of cadmium sulfide we compound these two semiconductors and coat them on glass surface to get a new kind of nanofilms with higher degradation efficiency.
However, the films coated on glass surface contain cadmium which is harmful to people. Coating another layer on the CdS compounded TiO2 film surface can inhibit the dissolve of cadmium. And in order to promote the function of the inside layer, add some pore-producing agents in these additional layers, such as trifluoroacetic acid and polyethylene glycol, is valuable.
Section snippets
Experiment
The glass substrate is soda-lime–silicate plate glass and the compounded films were prepared by sol–gel processing. Films of different compounded ratio (0–45 atm%) of titanium and cadmium were made. The preparation processing is described in Fig. 1. Films with various thickness were made by using spinning method to coat the compounded sol–gel on the cleaned glass substrate. After heating-treatment under different temperature, the films with different degradation quality were obtained. Then,
Results and discussion
The attenuation rate of compounded films with time under different recycle treatments is described in Fig. 2. Hoffman and Martin reported that CdS can make spectral response red shift [3], however, CdS is light sensitive material and can be photo-decomposed by light when it exposes to air. The photodecomposition process is governed by the photochemical reaction:
With the presence of TiO2 during the process, the electrons will feed into TiO2 particles from CdS particles and be
Conclusion
CdS compounded TiO2 films can promote the visible light photocatalytic degradation efficiency of glass surface greatly. The additional layer of TiO2 can decrease the dissolved quantity of cadmium and the degradation attenuation of compounded films. After the outer layer of TiO2 was coated on the compounded film surface, the wetting capacity of the film will be also improved.
References (4)
Application of nano materials and technology and the industrialization chance in China
Mater. Rev.
(2001)The status of photo cleaning evoked by photo accelerant reaction
Ind. Mater.
(1997)