An overview on the photocatalytic degradation of azo dyes in the presence of TiO2 doped with selective transition metals (original) (raw)
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Synthesis of Fe3+ doped TiO2 photocatalysts for the visible assisted degradation of an azo dye
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2011
The nano-sized, Fe 3+ doped TiO 2 photocatalyst was successfully prepared by a simple wet impregnation method with an attempt to extend the light absorption of TiO 2 into the visible region and reduce the rapid recombination of electrons and holes. The transmission electron microscopy (TEM), diffuse reflectance spectroscopy (DRS) and X-ray diffraction (XRD) results showed that the crystallite size of the as prepared Fe-TiO 2 particles is in the nano regime and indicated that Fe 3+ was substituted for Ti 4+ in the lattice of TiO 2 . The photocatalytic activities of the samples were evaluated for the degradation of an azo dye, acid red 88 in aqueous solutions under visible light irradiation. It was observed that the photocatalytic degradation of acid red under visible light irradiation in the presence of Fe 3+ doped TiO 2 (1.8 g/L) followed pseudo-first order reaction kinetics with a rate constant of 5.24 × 10 −4 s −1 . Significant enhancement in the photodegradation rate was observed upon the addition of electron acceptors (peroxomonosulphate (PMS), peroxodisulphate (PDS) and hydrogen peroxide (H 2 O 2 )) to the reaction medium. The extent of photocatalytic mineralization of the target pollutant and the degradation products were analyzed by total organic carbon (TOC) analyzer and electrospray mass spectrometry (ESMS).
Azo-dyes photocatalytic degradation in aqueous suspension of TiO2 under solar irradiation
Chemosphere, 2002
The photodegradation of two common and very stable azo-dyes, i.e. methyl-orange (C 14 H 14 N 3 SO 3 Na) and orange II (C 16 H 11 N 2 SO 4 Na), is reported. The photocatalytic oxidation was carried out in aqueous suspensions of polycrystalline TiO 2 irradiated by sunlight. Compound parabolic collectors, installed at the ''Plataforma Solar de Almer ı ıa'' (PSA, Spain) were used as the photoreactors and two identical reacting systems allowed to perform photoreactivity runs for the two dyes at the same time and under the same irradiation conditions. The disappearance of colour and substrates together with the abatement of total organic carbon content was monitored. The main sulfonate-containing intermediates were found to be in lower number in respect to those obtained under artificial irradiation. In particular there were no more evidence of the presence of hydroxylated transients. The dependence of dye photooxidation rate on: (i) substrate concentration; (ii) catalyst amount; and (iii) initial pH was investigated. The influence of the presence of strong oxidant species (H 2 O 2 , S 2 O 2À 8 ) and some ions (Cl À , SO 2À 4 ) on the process was also studied.
Environmental Technology & Innovation, 2018
The photocatalytic degradation of a model azo dye acid orange 7 (AO7) by Fe 3+-doped TiO 2 nanocatalyst has been studied under UV, Visible (λ > 400 nm) and solar light irradiation. The role of hydrogen peroxide to enhance the catalyst's efficiency was examined. The reaction pathway of complete mineralization was investigated by monitoring the temporal evolution of reaction intermediates and low molecular weight organic acids (LMWOA) as final products in solution. These LMWOAs are oxidized eventually to inorganic ions such a nitrate, sulfate, oxalate etc, which are confirmed using GC-MS, UV-Vis and Ion Chromatographic analyses. The optimized condition of photocatalytic degradation were obtained for degradation under different light source. The Fe 3+-doped TiO 2 showed high dye degradation efficiency under both UV (100%), visible (100%) and solar light (90%) which distinguishes Fe 3+-doped TiO 2 from materials in literature that are only efficient in particular light source for dye degradation. Furthermore, the Fe 3+ doped titania photocatlysts are stable and can maintain performance upto 6 recycle use. Reaction kinetics for UV and solar light induced degradation followed first order reaction whereas visible light degradation followed a zero-order reaction.
The total annual production of synthetic dye is more than 7 Â 10 5 tons. Annually, through only textile waste effluents, around one thousand tons of non-biodegradable textile dyes are discharged into natural streams and water bodies. Therefore, with growing environmental concerns and environmental awareness there is a need for the removal of dyes from local and industrial water effluents with a cost effective technology. In general, these dyes have been found to be resistant to biological as well as physical treatment technologies.
Optimised photocatalytic degradation of a mixture of azo dyes using a TiO 2 /H 2 O 2 /UV process
Water Science & Technology, 2012
The aim of the present study was to optimise the photocatalytic degradation of a mixture of six commercial azo dyes, by exposure to UV radiation in an aqueous solution containing TiO2-P25. Response surface methodology, based on a 32 full factorial experimental design with three replicates was employed for process optimisation with respect to two parameters: TiO2 (0.1–0.9 g/L) and H2O2 (1–100 mmol/L). The optimum conditions for photocatalytic degradation were achieved at concentrations of 0.5 g TiO2/L and 50 mmol H2O2/L, respectively. Dye mineralisation was confirmed by monitoring TOC, conductivity, sulfate and nitrate ions, with a sulfate ion yield of 96% under optimal reactor conditions. Complete decolorisation was attained after 240 min irradiation time for all tested azo-dyes, in a process which followed a pseudo-first kinetic order model, with a kinetic rate constant of approximately 0.018 min−1. Based on these results, this photocatalytic process has promise as an alternative f...
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.
Chemistry & Chemical Technology, 2010
In this work a detailed investigation of heterogeneous photocatalytic degradation of Navy blue HE2R 1 (NB), azo dye of the reactive class is presented using UV/TiO2/H2O2 process in the aqueous suspension under 8W low-pressure mercury vapor lamp irradiation. Here we also report about optimization of various experimental parameters such as effect of catalyst concentration, effect of substrate concentration, effect of H2O2 addition. The effect of the UV/TiO2/H2O2 process employment and selection of optional operational parameters on complete decolorization and substantial decrease of Chemical Oxygen Demand (COD) and Total Organic Carbon (TOC) of dye solution has been established.
Catalysis Letters, 2009
A donor-acceptor conjugated-type polymer, poly(thiophene-1,3,4-oxadiazole) (PThOD), was synthesized by one-step polycondensation in polyphosphoric acid. PThOD was confirmed and characterized using Fourier transform infrared spectra, thermogravimetric analysis, X-ray diffraction and UV-visible spectra. The UV-visible spectra showed that PThOD could absorb not only in the whole ultraviolet range from 200 to 400 nm but also in the visible light range up to 500 nm. Considering the conjugated structure of PThOD, studies were carried out of its performance for the photocatalytic degradation of various dyes, such as methyl orange, methylene blue, rhodamine B and reactive brilliant blue (RBB), under medium-pressure Hg light source irradiation. The results showed that PThOD was an effective photocatalyst, which could degrade the four types of dye solution. Besides, visible light was also used to investigate the degradation of RBB, and the results showed that RBB could be degraded as well, though the efficiency was not as high as using the Hg lamp. The superoxide anion radical (O 2 •−), which is one of the reactive oxide species, was detected using the nitrotetrazolium blue chloride method and considered to play a key role in photodegradation of dyes. Moreover, various scavengers were also used to further prove the function of O • 2 −. Furthermore, it was found that degradation rate could be changed by adding H + , which might be attributed to a change of adsorption capacity of PThOD. Finally, the reusability of PThOD as photocatalyst was investigated. The results indicated that the reusability efficiency of PThOD was excellent even after ten continuous rounds of use.
Optimization of the photocatalytic degradation of commercial azo dyes in aqueous TiO2 suspensions
Reaction Kinetics, Mechanisms and Catalysis, 2014
The photocatalytic degradation of three textile azo dyes, Remazol Yellow Gold RGB, Remazol Blue RGB and Remazol Carbon RGB has been studied in model effluents regarding the variation of parameters as concentration of titanium dioxide (TiO 2 ), concentration of the dyes, effect of hydrogen peroxide (H 2 O 2 ), effect of pH, recycling of TiO 2 . The concentration of 1 g L -1 of TiO 2 degraded around 100 % of Remazol Blue RGB and Remazol Carbon RGB and around 90 % for the Remazol Yellow Gold RGB after 120 min of photodegradation. The remaining concentrations of added TiO 2 were found to be less efficient, except for Remazol Blue RGB, which still reaches about 80 % photodegradation, for 0.1 g L -1 of TiO 2 . The efficiency of photodegradation of all dyes decreased with an increase of the initial dye concentration. For a concentration of 30 mg L -1 , all dyes showed around 100 %. However, upon increasing the concentration of the dye until 150 mg L -1 , the photodegradation becomes very slow, with photodegradation rates off only 11 % for Remazol Yellow Gold RGB and Remazol Blue RGB and 9.7 % for the Remazol Carbon RGB. Photodegradation of the three dyes was found to be pH dependent. The maximum reaction rate was observed with 0.3 9 10 -3 mol L -1 120 min). At higher concentrations of H 2 O 2 , the degradation efficiency decreased significantly for all dyes. In what regards the reuse of the photocatalyst, the first cycle degraded 100 % of the Remazol Carbon RGB after 60 min of irradiation and the second and third cycles degraded 44 and 36 % of the dye. The effect of the simultaneous photodegradation of the three azo dyes in water was further investigated for distilled and natural lake water. It was observed that the degradation rates achieved in mono and three-component system were identical. The degradation yield in lake water observed to be smaller than in distillated water with 75, 72 and 53 % (99, 98 and 88 % in distilled water) of degradation for Remazol Blue RGB, Remazol Carbon RGB and Remazol Yellow Gold RGB, respectively.