Comparison of several advanced oxidation processes for the decolorization of Reactive Red 120 azo dye in aqueous solution

In this study UV/TiO2, electro-Fenton (EF), wet-air oxidation (WAO), and UV/electro-Fenton (UV/EF) advanced oxidation processes (AOPs) have been applied to degrade Reactive Red 120 (RR120) dye in aqueous solution. The most efficient method on decolorization and mineralization of RR120 was observed to be WAO process. Photocatalytic degradation of RR120 by UV/TiO2 have been studied at different pH values. At pH 3 photocatalytic degradation kinetics of RR120 successfully fitted to Langmuir-Hinshelwood (L-H) kinetics model. The values of second order degradation rate (k") constant and adsorption constant (K) were determined as 4.525 mg L(-1) min(-1) and 0.387 L mg(-1), respectively. Decolorization efficiency observed in the order of WAO > UV/TiO2 = UV/EF > EF while WAO > UV/TiO2 > UV/EF > EF order was observed in TOC removal (mineralization). For all AOPs, it was found that degradation products in reaction mixture can be disposed safely to environment after 90 min treatment.     

Studies on photodegradation of two commercial dyes in aqueous phase using different photocatalysts

The present study involves the photocatalytic degradation of Methyl Orange (MO) and Rhodamine 6G (R6G), employing heterogeneous photocatalytic process. Photocatalytic activity of various semiconductors such as titanium dioxide (TiO(2)), zinc oxide (ZnO), stannic oxide (SnO(2)), zinc sulphide (ZnS) and cadmium sulphide (CdS) has been investigated. An attempt has been made to study the effect of process parameters viz., amount of catalyst, concentration of dye and pH on photocatalytic degradation of MO and R6G. The experiments were carried out by irradiating the aqueous solutions of dyes containing photocatalysts with UV and solar light. The rate of decolorization was estimated from residual concentration spectrophotometrically. Similar experiments were carried out by varying pH (2-10), amount of catalyst (0.25-2.0g/l) and initial concentration of dye (5-200mg/l). The experimental results indicated that the maximum decolorization (more than 90%) of dyes occurred with ZnO catalyst and at basic pH and the maximum adsorption of MO was noticed at pH 4 and of R6G at pH 10. The percentage reduction of MO and R6G was estimated under UV/solar system and it was found that COD reduction takes place at a faster rate under solar light as compared to UV light. In case of R6G, highest decolorizing efficiency was achieved with lower dose of catalyst (0.5g/l) than MO (1g/l) under similar conditions. The performance of photocatalytic system employing ZnO/solar light was observed to be better than ZnO/UV system.     

Decolorization of C.I. Reactive Red 2 by catalytic ozonation processes

This study adopted O3, UV/TiO2/O3, O3/Mn(II) and O3/MnO2 systems to assess the decolorization efficiency of C.I. Reactive Red 2 (RR2). The decolorization rate increased with concentrations of Mn(II) and MnO2 in the ranges 0.05-0.1 and 0.05-0.8 g/l, respectively. However, when 0.5-3g/l TiO2 was added, the effect of TiO2 dosage for RR2 decolorization was insignificant in the UV/TiO2/O3 system. At pH 2, the decolorization rate constants of O3, O3/Mn(II) (0.05 g/l), O3/Mn(II) (0.1g/l), O3/Mn(II) (0.15 g/l), O3/MnO2 (0.05 g/l) and O3/MnO2 (0.8 g/l) were 0.816, 2.001, 3.173, 3.087, 1.040 and 1.648 min(-1), respectively. After 5 min of reaction, the decolorization rates followed the order O3/Mn(II)>O3/MnO2>O3>UV/TiO2/O3; however, the TOC removal did not vary among these systems. Adding ethanol reduced the decolorization rate of the UV/TiO2/O3 and O3/MnO2 systems and did not affect the decolorization rate of O3/Mn(II). Decolorization in UV/TiO2/O3, O3/Mn(II) and O3/MnO2 systems is suggested to proceed by mainly radical-, surface- and radical-type mechanisms, respectively. Additionally, direct ozonation cannot be ignored in O3/Mn(II) and O3/MnO2 systems.     

The use of artificial neural networks (ANN) for modeling of decolorization of textile dye solution containing C. I. Basic Yellow 28 by electrocoagulation process

In this paper, electrocoagulation has been used for removal of color from solution containing C. I. Basic Yellow 28. The effect of operational parameters such as current density, initial pH of the solution, time of electrolysis, initial dye concentration, distance between the electrodes, retention time and solution conductivity were studied in an attempt to reach higher removal efficiency. Our results showed that the increase of current density up to 80 Am(-2) enhanced the color removal efficiency, the electrolysis time was 7 min and the range of pH was determined 5-8. It was found that for achieving a high color removal percent, the conductivity of the solution and the initial concentration of dye should be 10 mS cm(-1) and 50 mg l(-1), respectively. An artificial neural networks (ANN) model was developed to predict the performance of decolorization efficiency by EC process based on experimental data obtained in a laboratory batch reactor. A comparison between the predicted results of the designed ANN model and experimental data was also conducted. The model can describe the color removal percent under different conditions.     

The decolorization of C.I. Reactive Black 5 in aqueous solution by electrocoagulation using sacrificial iron electrodes

The removal of color from synthetic wastewater containing Reactive Black 5 was experimentally investigated using direct current electrocoagulation at iron electrodes. The effects of operational parameters such as current density, initial pH, electrolysis time, initial dye concentration and solution conductivity on color removal efficiency were investigated in this study. The optimum operating range for each of these operating variables was experimentally determined. The experimental results show that the color of Reactive Black 5 in the aqueous phase was removed effectively. Under the conditions of an initial dye concentration of 100 mg L(-1), initial pH of 5, current density of 4.575 mAcm(-2), salt concentration of 3000 mg L(-1), temperature of 20 degrees C, and interelectrode distance of 2.5 cm, the color removal efficiency reached 98.8%. Electrical energy consumption in the above conditions for the decolorization of the dye solution containing Reactive Black 5 was 4.96 kWh/kg dye. Results show that the first-order rate equation provides the best correlation for the decolorization rate of Reactive Black 5.     

The decolorization and mineralization of acid orange 6 azo dye in aqueous solution by advanced oxidation processes: a comparative study

The comparison of different advanced oxidation processes (AOPs), i.e. ultraviolet (UV)/TiO(2), O(3), O(3)/UV, O(3)/UV/TiO(2), Fenton and electrocoagulation (EC), is of interest to determine the best removal performance for the destruction of the target compound in an Acid Orange 6 (AO6) solution, exploring the most efficient experimental conditions as well; on the other hand, the results may provide baseline information of the combination of different AOPs in treating industrial wastewater. The following conclusions can be drawn: (1) in the effects of individual and combined ozonation and photocatalytic UV irradiation, both O(3)/UV and O(3)/UV/TiO(2) processes exhibit remarkable TOC removal capability that can achieve a 65% removal efficiency at pH 7 and O(3) dose=45mg/L; (2) the optimum pH and ratio of [H(2)O(2)]/[Fe(2+)] found for the Fenton process, are pH 4 and [H(2)O(2)]/[Fe(2+)]=6.58. The optimum [H(2)O(2)] and [Fe(2+)] under the same HF value are 58.82 and 8.93mM, respectively; (3) the optimum applied voltage found in the EC experiment is 80V, and the initial pH will affect the AO6 and TOC removal rates in that acidic conditions may be favorable for a higher removal rate; (4) the AO6 decolorization rate ranking was obtained in the order of O(3)相似文献   

Decolorization of C.I. Acid Yellow 23 solution by electrocoagulation process: investigation of operational parameters and evaluation of specific electrical energy consumption (SEEC)

This study investigates the evaluation of specific electrical energy consumption (SEEC) and the influence of operating parameters on the color removal efficiency of a dye solution containing C.I. Acid Yellow 23 by electrocoagulation process. Firstly, the operational parameters including current density, initial dye concentration, initial pH and time of electrolysis were optimized. Then the effects of the conductivity, the interelectrode distance and the area of cross-section of the electrodes on specific electrical energy consumption (SEEC) were studied under the optimum conditions. Our results indicated that for a solution of 50mg/l C.I. Acid Yellow 23, almost 98% color and 69% chemical oxygen demand (COD) were removed, when the pH was about 6, the time of electrolysis was 5min and the current density was approximately 112.5A/m(2). In addition, the results of our study revealed that when the conductivity and area of cross-section of the electrodes increased and interelectrode distance decreased, the cell voltage and specific electrical energy consumption would be decreased.     

Treatment of levafix orange textile dye solution by electrocoagulation

The decolorization of the levafix orange textile dye in aqueous solution by electrocoagulation using aluminum sacrificial anode has been investigated. The process performance is analyzed in terms of decolorization efficiency and the important cost-related parameters such as electrode and energy consumptions, as a function of initial pH, conductivity, current density, initial dye concentration and electrolysis time. The present study proves the effectiveness of electrochemical treatment for the textile dye solution. 95% decolorization efficiency may be obtained at suitable operating conditions such as; current density 100 A/m(2), operating time 12 min and initial pH 6.4. The corresponding electrode and energy consumptions during the electrolysis were found to be 1.8 kg Al/kg dye and 35 k Wh/kg dye.     

Decolorization of Reactive Red 2 by advanced oxidation processes: Comparative studies of homogeneous and heterogeneous systems

This study investigated the decolorization of the Reactive Red 2 in water using advanced oxidation processes (AOPs): UV/TiO2, UV/SnO2, UV/TiO2+SnO2, O3, O3+MnO2, UV/O3 and UV/O3+TiO2+SnO2. Kinetic analyses indicated that the decolorization rates of Reactive Red 2 could be approximated as pseudo-first-order kinetics for both homogeneous and heterogeneous systems. The decolorization rate at pH 7 exceeded pH 4 and 10 in UV/TiO2 and UV/TiO2+SnO2 systems, respectively. However, the rate constants in the systems (including O3) demonstrated the order of pH 10>pH 7>pH 4. The UV/TiO2+SnO2 and O3+MnO2 systems exhibited a greater decolorization rate than the UV/TiO2 and O3 systems, respectively. Additionally, the promotion of rate depended on pH. The variation of dye concentration influenced the decolorization efficiency of heterogeneous systems more significant than homogeneous systems. Experimental results verified that decolorization and desulfuration occurred at nearly the same rate. Moreover, the decolorization rate constants at pH 7 in various systems followed the order of UV/O3 > or = O3+MnO2 > or = UV/O3+TiO2+SnO2 > O3 > UV/TiO2+SnO2 > or = UV/TiO2 > UV/SnO2.     

Adsorption and photocatalytic decolorization of a synthetic dye erythrosine on anatase TiO2 and ZnO surfaces

The UV radiation assisted photocatalytic decolorization/degradation kinetics of an anionic dye erythrosine (ER), has been studied over TiO2 and ZnO surfaces. Since adsorption is the prerequisite condition for decolorization/degradation of dye molecules in presence of heterogeneous catalysis, the Langmuir and Freundlich isotherms were examined to verify the adsorption intensity. Standard adsorption free energy measurement implies that the adsorption of ER on both TiO2 and ZnO surfaces is spontaneous endothermic process. The effect of catalyst loading (TiO2/ZnO) revealed the fact that the maximum decolorization rate is obtained under an optimized catalyst loading condition. The decolorization efficiency was also investigated over the pH range of 5.0-10.0 indicating that increasing pH enhances decolorization efficiency. The influence of H2O2 on decolorization efficiency was found noticeable since it is a hydroxyl radical provider. The kinetic study of this degradation indicates that under the experimental condition, the decolorization mechanism follows zero order kinetics on the basis of Langmuir-Hinshelwood (L-H) heterogeneous reaction mechanism.     

Decolorization of alkaline TNT hydrolysis effluents using UV/H(2)O(2)

Effects of H(2)O(2) dosage (0, 10, 50, 100 and 300 mg/l), reaction pH (11.9, 6.5 and 2.5) and initial color intensity (85, 80 and 60 color unit) on decolorization of alkaline 2,4,6-trinitrotoluene (TNT) hydrolysis effluents were investigated at a fixed UV strength (40 W/m(2)). Results indicated that UV/H(2)O(2) oxidation could efficiently achieve decolorization and further mineralization. Pseudo first-order decolorization rate constants, k, ranged between 2.9 and 5.4 h(-1) with higher values for lower H(2)O(2) dosage (i.e., 10 mg/l H(2)O(2)) when the decolorization occurred at the reaction pH of 11.9, whereas a faster decolorization was achieved with increase in H(2)O(2) dosage at both pH 6.5 and 2.5, resulting in the values of k as fast as 15.4 and 26.6 h(-1) with 300 mg/l H(2)O(2) at pH 6.5 and 2.5, respectively. Difference in decolorization rates was attributed to the reaction pH rather than to the initial color intensity, resulting from the scavenging of hydroxyl radical by carbonate ion. About 40% of spontaneous mineralization was achieved with addition of 10 mg/l H(2)O(2) at pH 6.5. Efficient decolorization and extension of H(2)O(2) longevity were observed at pH 6.5 conditions. It is recommended that the colored effluents from alkaline TNT hydrolysis be neutralized prior to a decolorization step.     

Comparison of the treatment methods efficiency for decolorization and mineralization of Reactive Black 5 azo dye

Degradation of Reactive Black 5 (RB5), a well-known non-biodegradable disazo dye, has been studied using UV/TiO2, wet-air oxidation (WAO), electro-Fenton (EF) and UV/electro-Fenton (UV/EF) advanced oxidation processes (AOPs). The efficiency of substrate decolorization and mineralization in each process has been comparatively discussed by decreases in concentration and total organic carbon content of RB5 solutions. The most efficient method on decolorization and mineralization was observed to be WAO process. Mineralization efficiency was observed in the order of WAO>UV/TiO2>UV/EF>EF. Final solutions of AOPs applications after 90 min treatment can be disposed safely to environment. Photocatalytic degradation kinetics of RB5 successfully fitted to Langmuir-Hinshelwood (L-H) kinetics model. The values of second order degradation rate constant (k') and adsorption constant (K) were determined as 5.085 mg L(-1)min(-1) and 0.112 L mg(-1), respectively.     

Effect of surface plasmon resonance on the photocatalytic activity of Au/TiO2 under UV/visible illumination

In this study, gold-loaded titanium dioxide was prepared by an impregnation method to investigate the effect of surface plasmon resonance (SPR) on photoactivity. The deposited gold nanoparticles (NPs) absorb visible light because of SPR. The effects of both the gold content and the TiO2 size of Au/TiO2 on SPR and the photocatalytic efficiency were investigated. The morphology, crystal structure, light absorption, emission from the recombination of a photoexcited electron and hole, and the degree of aggregation were investigated using transmission electron microscopy (TEM), X-ray diffraction (XRD), UV-visible-diffuse reflectance spectra (UV-VIS-DRS), photoluminescence (PL) spectroscopy, and turbidimetry, respectively. Photocatalytic activity was evaluated by the decolorization of methyl orange solution over modified titania under UV and UV/GLED (green light emitting diode) illumination. Au/TiO2 NPs exhibited an absorption peak (530-570 nm) because of SPR. The results of our photocatalytic experiments indicated that the UV-inducedly photocatalytic reaction rate was improved by simultaneously using UV and green light illumination; this corresponds to the adsorption region of SPR. Au/TiO2 could use the enhanced electric field amplitude on the surface of the Au particle in the spectral vicinity of its plasmon resonance and thus improve the photoactivity. Experimental results show that the synergistic effect between UV and green light for the improvement of photoactivity increases with increasing the SPR absorption, which in turn is affected by the Au content and TiO2 size.     

Decolorization of basic dye solutions by electrocoagulation: an investigation of the effect of operational parameters

Electrocoagulation (EC) is one of the most effective techniques to remove color and organic pollutants from wastewater, which reduces the sludge generation. In this paper, electrocoagulation has been used for the removal of color from solutions containing C. I. Basic Red 46 (BR46) and C. I. Basic Blue 3 (BB3). These dyes are used in the wool and blanket factories for fiber dyeing. The effect of operational parameters such as current density, initial pH of the solution, time of electrolysis, initial dye concentration and solution conductivity were studied in an attempt to reach higher removal efficiency. The findings in this study shows that an increase in the current density up to 60-80 A m(-2) enhanced the color removal efficiency, the electrolysis time was 5 min and the range of pH was determined between 5.5 and 8.5 for two mentioned dye solutions. It was found that for, the initial concentration of dye in solutions should not be higher than 80 mg l(-1) in order to achieve a high color removal percentage. The optimum conductivity was found to be 8 mS cm(-1), which was adjusted using proper amount of NaCl with the dye concentration of 50 mg l(-1). Electrical energy consumption in the above conditions for the decolorization of the dye solutions containing BR46 and BB3 were 4.70 kWh(kgdye removed)(-1) and 7.57 kWh(kgdye removed)(-1), respectively. Also, during the EC process under the optimized conditions, the COD decreased by more than 75% and 99% in dye solutions containing BB3 and BR46, respectively.     

Preparation, characterization, and photocatalytic activity of Gd3+ doped TiO2 nanoparticles

TiO2 and Gd3+ doped TiO2 nanoparticles were prepared by sol-gel method and the materials were characterized by XRD, TEM, SEM-EDX, BET, FT-IR, UV-Vis absorption, and Raman spectral analysis. The photocatalytic activity of nano TiO2 and Gd/TiO2 nanoparticles was evaluated using a model pollutant propoxur, a carbamate pesticide, in a batch type UV photoreactor. The results revealed higher photocatalytic activity for Gd/TiO2 nanoparticles than both TiO2 nanoparticles and commercial TiO2 (Degussa P-25). The enhanced photocatalytic activity of Gd/TiO2 relative to TiO2 is attributed to its increased band gap energy as evidenced from the blue shift to shorter wavelength observed in the UV-Vis abso4ption spectra. The recombination rate of photogenerated electron-hole pair decreased due to increase in the band gap, which enhanced the charge transfer efficiency of Gd/TiO2 nanoparticles. Gd3+ with its half filled 7 f subshell facilitated rapid electron transfer at solid-liquid interface by shallowly trapping the electrons. Among the various dopant level of gadolinium, 0.3 wt% Gd/TiO2 nanoparticles showed higher activity than others due to its higher surface area.     

Treatment of pulp and paper industry bleaching effluent by electrocoagulant process

The experiments were carried out in an electrocoagulation reactor with aluminum as sacrificial electrodes. The influence of electrolysis time, current density, pH, NaCl concentration, rotational speed of the stirrer and electrode distance on reduction of color, COD and BOD were studied in detail. From the experimental results, 15 mA/cm(2) current density, pH of 7, 1 g/l NaCl, 100 rpm, 28°C temperature and 3 cm electrode distance were found to be optimum for maximum reduction of color, COD and BOD. The reduction of color, COD and BOD under the optimum condition were found to be 94%, 90% and 87% respectively. The electrode energy consumption was calculated and found to be varied from 10.1 to 12.9 kWh/m(3) depending on the operating conditions. Under optimal operating condition such as 15 mA/cm(2) current density, pH of 7, 1 g/l NaCl, 100 rpm, 28°C temperature and 3 cm electrode distance, the operating cost was found to be 1.56 US $/m(3). The experimental results proved that the electrocoagulation is a suitable method for treating bleaching plant effluents for reuse.     

An integrated technique using zero-valent iron and UV/H2O2 sequential process for complete decolorization and mineralization of C.I. Acid Black 24 wastewater

The zero-valent iron (ZVI) reduction succeeds for decolorization, while UV/H(2)O(2) oxidation process results into mineralization, so that this study proposed an integrated technique by reduction coupling with oxidation process in order to acquire simultaneously complete both decolorization and mineralization of C.I. Acid Black 24. From the experimental data, the zero-valent iron addition alone can decolorize the dye wastewater yet it demanded longer time than ZVI coupled with UV/H(2)O(2) processes (Red-Ox). Moreover, it resulted into only about 30% removal of the total organic carbon (TOC), which was capable to be effectively mineralized by UV/H(2)O(2) process. The proposed sequential ZVI-UV/H(2)O(2) integration system cannot only effectively remove color and TOC in AB 24 wastewater simultaneously but also save irradiation power and time demand. Furthermore, the decolorization rate constants were about 3.77-4.0 times magnitude comparing with that by UV/H(2)O(2) process alone.     

Decolorization of dye solution containing Acid Red 14 by electrocoagulation with a comparative investigation of different electrode connections

This study was performed to investigate the variables that influence the efficiency of decolorization of a solution containing an azo dye (Acid Red 14) by electrocoagulation (EC) in order to compare the efficiency of different electrode connections for color removal. Current density, time of electrolysis, interelectrode distance, and pH of the solution were the variables that most influenced color removal. Initially, a simple electrochemical cell was prepared with an anode and a cathode. Then the effect of each variable was studied separately using synthetic wastewater in a batch mode. The efficiency of the method tested was determined by measurement of color removal and reduction of Chemical Oxygen Demand (COD). For dye solutions with COD of approximately 30 ppm and dye concentrations less than 150 ppm, high color removal (93%) was obtained when the pH ranged from 6 to 9, time of electrolysis was approximately 4 min, current density was approximately 80 A/m2, the temperature was approximately 300 K, and interelectrode distance was 1 cm. During the EC process under these conditions, the COD decreased by more than 85%. In the second series of experiment, the efficiency of EC cells with monopolar electrodes in series and parallel connections and an EC cell with bipolar electrodes were compared with results using a simple electrochemical cell. The experimental results showed that an EC cell with several electrodes was more effective than a simple electrochemical cell in color removal. The results also showed that an EC cell with monopolar electrodes had a higher color removal efficiency than an EC cell with bipolar electrodes. Furthermore, within an EC cell, the series connection of the monopolar electrodes was more effective for the treatment process than the parallel connection in color removal.     

Photocatalytic degradation of triazinic ring-containing azo dye (Reactive Red 198) by using immobilized TiO2 photoreactor: bench scale study

The decolorization and degradation of triazinic ring-containing azo dye by using TiO(2)-immobilized photoreactor is reported. A simple and easy method was used for the immobilization of photocatalyst. Reactive Red 198 (RR 198) was used as model compound. Photocatalytic degradation processes were performed using a 5 L (bench scale) solution containing dye. Batch mode immersion type method was used for the treatment of dye solution. UV-vis, ion chromatography (IC) and chemical oxygen demand (COD) analyses were employed to evaluate the results of the photocatalytic degradation of RR 198. Dye solution was completely decolorized in relatively short time (35 min) after UV irradiation in combination with hydrogen peroxide. The results verified that all of the dye molecules were destructed. Kinetics analysis indicates that the dye photocatalytic decolorization rates followed first order model (R(2) = 0.99). Ion chromatography analysis was used to investigate the formation and destruction of aliphatic carboxylic acids and formation of inorganic anions during the process. Formate and oxalate anions were detected as main aliphatic carboxylic intermediates, which were further oxidized slowly to CO(2). UV/TiO(2)/H(2)O(2) process proved to be capable of successful decolorization and degradation of the RR 198.     

Photocatalytic degradation of azo dyes using Au:TiO2, gamma-Fe2O3:TiO2 functional nanosystems

We report photocatalytic degradation studies on Navy Blue HE2R (NB) dye on significant details as a representative from the class of azo dyes using functional nanosystems specifically designed to allow a strong photocatalytic activity. A modified sol-gel route was employed to synthesize Au and gamma-Fe2O3 modified TiO2 nanoparticles (NPs) at low temperature. The attachment strategy is better because it allows clear surface of TiO2 to remain open for photo-catalysis. X-ray diffraction, Raman and UV-VIS spectroscopy studies showed the presence of gold and iron oxide phases along-with the anatase TiO2 phase. TEM studies showed TiO2 nanocomposite particles of size approximately 10-12 nm. A detailed investigation on heterogeneous photocatalytic performance for Navy Blue HE2R dye was done using the as-synthesized catalysts Au:TiO2 and gamma-Fe2O3:TiO2 in aqueous suspension under 8 W low-pressure mercury vapour lamp irradiation. Also, the photocatalytic degradation of Amranth and Orange G azo dyes were studied. The surface modified TiO2 NPs showed significantly improved photocatalytic activity as compared to pure TiO2. Exposure of the dye to the UV light in the presence of pure and gold NPs attached TiO2 catalysts caused dye degradation of about approximately 20% and approximately 80%, respectively, in the first couple of hours. In the presence of gamma-Fe2O3 NPs attached TiO2, a remarkable approximately 95% degradation of the azo dye was observed only in the first 15 min of UV exposure. The process parameters for the optimum catalytic activity are established which lead to a complete decoloration and substantial dye degradation, supported by the values of the Chemical Oxygen Demand (COD) approximately 93% and Total Organic Carbon (TOC) approximately 65% of the treated dye solution after 5 hours on the employment of the UV/Au:TiO2/H2O2 photocatalytic process.