Kinetics of the decoloration of reactive dyes over visible light-irradiated TiO2 semiconductor photocatalyst (original) (raw)
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Kinetics of photocatalytic degradation of reactive dyes in a TiO 2 slurry reactor
Journal of Photochemistry and Photobiology A-chemistry, 2002
The textile industry consumes considerable amounts of water during the dyeing and finishing operations. Dyes are extensively used and hence wastewaters discharged in rivers or public sewage treatment plants are highly contaminated. In this work, a detailed investigation of the adsorption and photocatalytic degradation of the safira HEXL dye, an anionic azo dye of reactive class, is presented. H 2 O 2 and UV light have a negligible effect when they are used on their own. The adsorption of dye on the semiconductor shows a strong dependence on the pH and follows a Langmuir adsorption model. The photodegradation kinetics is discussed in terms of the Langmuir-Hinshelwood model.
This paper presents the review of the effects of operating parameters on the photocatalytic degradation of textile dyes using TiO 2-based photocatalysts. It further examines various methods used in the preparations of the considered photocatalysts. The findings revealed that various parameters, such as the initial pH of the solution to be degraded, oxidizing agents, temperature at which the catalysts must be calcined, dopant(s) content and catalyst loading exert their individual influence on the photocatalytic degradation of any dye in wastewaters. It was also found out that sol–gel method is widely used in the production of TiO 2-based photocatalysts because of the advantage derived from its ability to synthesize nanosized crystallized powder of the photocatalysts of high purity at relatively low temperature.
A review on Parameters Affecting the Photocatalytic Degradation of Dyes using Photocatalysts
2013
Production of clean hydrogen energy and removal of environmental pollutants using photocatalysis technique have received a great deal of interest in recent few decades. Photocatalytic reaction catalyzed by semiconductors has been approved as a promising process for solving energy and environmental issues. This paper presents an overview of photocatalytic degradation of dyes in presence of UV light. We highlight here the effects of various parameters, such as the amount of the catalyst loading, initial concentrations of dye and pH along with the study of reaction mechanism of photocatalysis. A case study is examined which gives an overview of different operating parameters affecting the photocatalytic degradation of Rhodamine-B in aqueous solution with titanium dioxide (TiO 2 ) and niobium pentaoxide (Nb 2 O 5 ) as photocatalyst in slurry form has been carried out using UV-A light (254 nm). The effect of various parameters such as catalyst loading, pH and initial concentration of the RB dye on degradation is determined. The maximum rate of degradation was observed in acidic medium at pH 3 for catalyst TiO 2 and Nb 2 O 5 respectively. It was observed that the photocatalytic activity of TiO 2 is greater than Nb 2 O 5 .
Environmental Progress, 2005
The photocatalytic degradation of methylene blue and methyl orange have been studied in the presence of titanium dioxide powder illuminated with a 300-W UV lamp. The effect of hydrogen peroxide on the degradation process was also determined. It was found that the color removal efficiency was affected by the concentration of dye, amount of TiO 2 added, and the pH of the solution. The degradation of dyes obeys first-order kinetics, with the apparent first-order rate constant increasing with decreasing dye concentration. The rate constants were evaluated as a function of the concentration of dye, amount of TiO 2 , and pH.
A kinetic approach to the photocatalytic decolorization of acid dyes
Research into the photocatalytic decolorization of four acid dyes was\nguided by a kinetic approach. The kinetic approach was adapted as a\nresult of observing constant rates of decolorization when H2O2 from the\nstart was added to immobilized TiO2 photocatalysis. Three different\nfrequencies of UV were applied to the dyes. It was theorized that, on\nillumination at different UV frequencies, the electrons within the\nsemiconductor were excited from the valence band to the conduction band,\nyielding the electron-hole pairs at the constant rate. CPT, the time of\nUV exposure required to cause 90% of vibrations between the double and\nsingle bonds along the molecular, chain of the dyes to be oxidized, was\ntaken and used as a measure of the activities. It is called Critical\nPhotonic Time or CPT. The CPTs varied according to the frequencies of\nthe UV intensities. The CPTs were correlated with the resistivity of the\ntextile dyes, and the assessment of photon efficiency (PEhv) and photon\ndeficiency (PDhv) in UV lamps. The derivatization of CPT from the\nfirst-order-kinetic law is presented.
Simultaneous degradation of non-emissive and emissive dyes on visible light illuminated TiO2 surface
Journal of Molecular Catalysis A: Chemical, 2006
Simultaneous photocatalytic degradation of non-emissive dye, acid blue1 (AB1) and emissive dyes (eosinY or thionine) in air-equilibrated aqueous suspension of TiO 2 semiconductor photocatalyst has been achieved at ambient conditions. Under visible light irradiation AB1 undergoes appreciable degradation in presence of a sensitizing dye (eosinY or thionine). However, concomitant decoloration of eosinY (EY) or thionine (Th) due to self-sensitized degradation was also noticed. Mechanistic proposals for the photocatalytic degradation of AB1 using a 150 W Xe lamp with a UV-filter (λ > 420 nm) as well as without a UV-filter, are discussed. Formation of reactive • O 2 − / • HO 2 radicals is proposed to be responsible for the degradation of the selected dyes, AB1, EY and Th.
Decolouration of textile dyes in wastewaters by photocatalysis with TiO2
Solar Energy, 2005
The photocatalytic removal of colour of a synthetic textile effluent, using TiO 2 suspensions under solar radiation, has been studied at pilot plant scale. A synthetic dye solution was prepared by a mix of six commercial textile dyes. A photochemical reactor of parallel CPC reflectors with UV-transparent tubular receivers was used. The study of photodegradation was carried out using the TaguchiÕs parameter design method. Following this methodology, the reaction was conducted under different flow conditions, pH and H 2 O 2 concentrations. The results show that all dyes used in the experiences can be degraded successfully by photo-oxidation. The process shows a significant enhancement when it is carried out at high flows, alkaline media and high H 2 O 2 concentration. Colour removal from the effluent was reached at 55 min operating time.
Kinetics of Photocatalytic Degradation of Dyes Using Semiconductor Nanomaterials
Aim: To conduct photocatalytic degradation of dyes using the semiconductor material (usually TiO 2) catalyst under ultraviolet radiation, and to evaluate the kinetic parameters, viz. rate constant and order of reaction, using integral and differential methods. Theory: Photolysis involves the use of ultraviolet (UV) or visible light radiation to effect chemical transformations. Photocatalysis uses a catalyst, usually, a semiconducting oxide to accelerate the photoreaction. The mechanism of UV photocatalysis is well documented [1-7], and the following reactions represent the key steps in the generation of charge-carriers and hydroxyl radicals, which mediate photocatalytic reactions. A pictorial representation of the mechanism of TiO 2 photocatalysis is shown in Figure 1.