Parameters affecting the photocatalytic degradation of dyes using TiO2: a review

Abstract

Traditional chemical, physical and biological processes for treating wastewater containing textile dye have such disadvantages as high cost, high energy requirement and generation of secondary pollution during treatment process. The advanced oxidation processes technology has been attracting growing attention for the decomposition of organic dyes. Such processes are based on the light-enhanced generation of highly reactive hydroxyl radicals, which oxidize the organic matter in solution and convert it completely into water, CO 2 and inorganic compounds. In this presentation, the photocatalytic degradation of dyes in aqueous solution using TiO 2 as photocatalyst under solar and UV irradiation has been reviewed. It is observed that the degradation of dyes depends on several parameters such as pH, catalyst concentration, substrate concentration and the presence of oxidants. Reaction temperature and the intensity of light also affect the degradation of dyes. Particle size, BETsurface area and different mineral forms of TiO 2 also have influence on the degradation rate.

Photocatalytic degradation and photo-Fenton oxidation of Congo red dye pollutants in water using natural chromite—response surface optimization

“…Under the irradiation of UV light, the outer surface electrons from chromium octahedral sites can be excited from the valence band to the conduction band. This will result in the formation of the electron-hole pair in the valence band (Reza et al 2015). The holes can react with an electron donor (water molecules or hydroxide ions) and produce oxidizing free radical (hydroxyl radical), which will oxidize dyes on the surface (Ng et al 2012;Akbal 2005).…”

“…The holes can react with an electron donor (water molecules or hydroxide ions) and produce oxidizing free radical (hydroxyl radical), which will oxidize dyes on the surface (Ng et al 2012;Akbal 2005). Also, the holes can oxidize the dye pollutants by direct electron transfer (Reza et al 2015). Such mechanism can be summarized in Fig.…”

“…The chemical methods involved oxidation of dye into CO 2 and inorganic ions through the production of hydroxyl radical (Herrmann 1999). The hydroxyl radical can be generated by direct photolysis of oxidants as O 3 and H 2 O 2 , with UV irradiation, Fenton, and photo-Fenton process or by photocatalytic process using semiconductors (Reza et al 2015). The combination of the previous techniques can enhance the generation of the hydroxyl radical.…”

A Review on the Factors Affecting the Photocatalytic Degradation of Hazardous Materials

“…The initial concentration of dye in a given photocatalytic reaction is an important factor which needs to be taken into account. Generally speaking the percentage degradation decreases with increasing amount of dye concentration, while keeping a fixed amount of catalyst [35].…”

“…The initial concentration of dye in a given photocatalytic reaction is an important factor which needs to be taken into account. Generally speaking the percentage degradation decreases with increasing amount of dye concentration, while keeping a fixed amount of catalyst [35].This can be rationalized on the basis that as dye concentration increases, more organic substances are adsorbed on the surface of TiO 2 , whereas less number of photons are available to reach the catalyst surface and therefore less •OH are formed, thus resulting in less degradation percentage. Figure 1 is showing the photodegradation of methyl orange with different photocatalyst.…”