Photodestruction of Acid Orange 7 (AO7) in aqueous solutions by UV/H2O2: influence of operational parameters

Fabrication of ZnO-SnO2 nanocomposite and its photocatalytic activity for enhanced degradation of Biebrich scarlet

The n-n-type ZnO-SnO₂ nanocomposite was fabricated using malic acid following a simple one-pot co-precipitation method. The fabricated ZnO-SnO₂ nanocomposite was employed as a photocatalyst in the degradation of Biebrich scarlet dye under UV₂₅₄ light. TEM, SAED, XRD, XPS, EDX, FTIR, and UV spectra have been recorded to characterize the synthesized ZnO-SnO₂ nanostructures. TEM studies found that the average particle size was 10-12 nm, and the SAED confirmed the polycrystalline nature of the synthesized nanocomposite. It was found that 97% of 10 mg/L Biebrich scarlet dye was degraded by 25 mg/L of photocatalyst within 40-min irradiation of UV₂₅₄ light at an optimum pH of 6. Further studies showed that the degradation followed pseudo-first-order kinetics with a rate constant of 5.48 × 10^-2 min^-1. The fabricated ZnO-SnO₂ nanocomposite was reusable up to 8 times; hence, it proved to be an efficient catalyst for the photodegradation of Biebrich scarlet dye.

Two Coordination Polymers Synthesized from Various N-Donor Clusters Spaced by Terephthalic Acid for Efficient Photocatalytic Degradation of Ibuprofen in Water under Solar and Artificial Irradiation

Two coordination polymers CP1 {[Zn(II)(BIPY)(Pht)] _n } and CP2 {[Zn(HYD)(Pht)] _n } (BIPY = 4,4'-bipyridine, Pht = terephthalic acid, and HYD = 8-hydroxyquinoline) have been successfully synthesized by a hydrothermal process using zinc aqueous solution. The so-prepared compounds were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, UV-visible spectroscopy, thermogravimetric analysis (TGA), and cyclic voltammetry. XRD pointed to a crystalline phase for CP1, while CP2 required recrystallization, FTIR spectroscopy established the presence of characteristic bands for all the ligands, and TGA showed thermal stability up to 100 °C. The electrochemical study showed a good charge transfer between the ligands and Zn metal for both materials. The UV-vis spectra displayed a strong absorption band spreading over a wide wavelength range, encompassing UV and visible light, with a band gap of 2.69 eV for CP1 and 2.56 eV for CP2, both of which are smaller than that of ZnO. This provides an advantageous alternative to using ZnO. The 5 × 10^-5 mol L^-1 ibuprofen decomposition kinetics under solar and UV light were studied under different irradiation conditions. Good photocatalytic properties were observed due to their high surface area.

Synthesized Cr/TiO2 immobilized on pumice powder for photochemical degradation of acid orange-7 dye under UV/visible light: influential operating factors, optimization, and modeling

The current study aimed to investigate the removal efficiency of acid orange-7 (AO7) using synthesized Cr/TiO₂ immobilized on pumice powder under visible light and UV irradiation. The characterization of synthesized nanocatalyst examined by scanning electron microscope, X-ray diffraction, and Fourier transforms infrared. The optimum of experimental parameters including catalyst dosage, dye concentration, time and pH, D-optimal Design (DOD) along with response surface methodology obtained by R software. The initial and outlet concentration was measured using a spectrophotometer. Besides, Analysis of variance results for the quadratic model showed simple linear regression with high significance and provided as a predicting model. The differences less than 0.2 between multiple and adjusted R² in two models indicate that two examined models fitted suitably. The highest removal efficiency of AO7 was 95 and 74% under visible and UV irradiation, respectively. Therefore, the higher removal efficiency in visible light reduces the costs and energy, moreover, offers an environmentally friendly method. The results showed that the removal efficiency of AO7 increased considerably with rising catalyst dosage and time, as well as minimizing dye concentration, and pH.

Microbial use for azo dye degradation-a strategy for dye bioremediation

Azo dyes are aromatic compounds with one to many -N=N- groups as well as the leading class of synthetic dyes utilised in commercial solicitations. Azo dyes, released in the environment through textile effluents, have hazardous effects on the aquatic as well as human life. Their persistence and discharge into the environment are becoming a global concern; thus, the remediation of these contaminants has acquired great attention. The current review comprehensively discusses some of the main aspects of biodegradation of azo dyes. A variety of physicochemical approaches has already been utilised for treatment of textile effluents counting filtration, coagulation and chemical flocculation. Though these conventional techniques are effective, yet they are lavish and also comprise formation of concentrated sludge that makes a secondary disposal problem. In this regard, microbial usage is an effective, economical, bio-friendly and ecologically benign approach.

Photocatalytic Degradation of Azo Dye Reactive Violet 5 on Fe-Doped Titania Catalysts under Visible Light Irradiation

The presence of azo dyes in textile effluents is an issue of major concern due to their potential impact on the environment and human health. In this study we investigate the photocatalytic degradation under visible light of Reactive Violet 5 (RV5), an azo dye widely used in the textile industry. A preliminary screening of different titania-based catalysts was carried out to identify the best candidate for RV5 removal. The selected catalyst was then tested in a stirred and aerated lab-scale reactor illuminated with a blue light-emitting diode (LED) source emitting in the wavelength range of 460–470 nm. The effects of pH, catalyst load, and hydrogen peroxide additions on the efficiency of dye removal were evaluated. Under the best conditions (pH 10, 3 g/L of catalyst, and 60 mM hydrogen peroxide), the dye solution was completely decolorized in about 2 h. Overall, the results obtained suggest that the proposed process may represent a suitable method for the removal of RV5 from textile effluents.

Degradation of malachite green by a pulsed light/H2O2 process

Pulsed light (PL) is a type of photonic technology characterized by intense short light pulses that enhance the speed of photochemical reactions, and which might be useful as light source in advanced oxidation processes. This work aimed to test PL as light source for the degradation of the dye malachite green (MG) by combining PL with H₂O₂. To this end, the effect of dye and H₂O₂ concentrations and pH on the degradation rate of MG was studied and a degradation pathway was proposed. Dye degradation followed a pseudo-first order kinetics; it increased with low initial dye concentration, high H₂O₂ concentration and low pH. Complete decolourization was achieved after 35 light pulses (75 J/cm²), with a degradation rate of 0.0710 cm²/J. The degradation was initiated by the attack of hydroxyl radicals to the central carbon of MG generating 4-(dimethylamino)benzophenone (DLBP) followed by the addition of hydroxyl radicals to the non-amino aromatic ring of DLBP and the demethylation of the amino group. Results indicate that PL technology has potential to be implemented to decrease the environmental impact of dyeing industries.

Dielectric barrier discharge plasma microbubble reactor for pretreatment of lignocellulosic biomass

A novel lignocellulosic biomass pretreatment reactor has been designed and tested to investigate pretreatment efficacy of miscanthus grass. The reactor was designed to optimize the transfer of highly oxidative species produced by dielectric barrier discharge plasma to the liquid phase immediately after generation, by arranging close proximity of the plasma to the gas-liquid interface of microbubbles. The reactor produced a range of reactive oxygen species and reactive nitrogen species, and the rate of production depended on the power source duty cycle and the temperature of the plasma. Ozone and other oxidative species were dispersed efficiently using energy efficient microbubbles produced by fluidic oscillations. A 5% (w/w) miscanthus suspension pretreated for 3 h at 10% duty cycle yielded 0.5% acid soluble lignin release and 26% sugar release post hydrolysis with accelerated pretreatment toward the latter stages of the treatment demonstrating the potential of this approach as an alternative pretreatment method. © 2018 The Authors. AIChE Journal published by Wiley Periodicals, Inc. on behalf of American Institute of Chemical Engineers. © 2018 The Authors. AIChE Journal published by Wiley Periodicals, Inc. on behalf of American Institute of Chemical Engineers. AIChE J, 64: 3803-3816, 2018.

Solvothermal synthesis, characterization and photocatalytic property of zirconium dioxide doped titanium dioxide spinous hollow microspheres with sunflower pollen as bio-templates

Zirconium dioxide (ZrO₂) doped titanium dioxide (TiO₂) spinous hollow microspheres were successfully prepared through a facile solvothermal method using sunflower pollen as bio-templates. The products were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), N₂ adsorption-desorption isotherms and UV-Vis diffuse reflectance spectroscopy. It was found that the products have spinous microsphere morphology with an approximate diameter of 12 μm. The ZrO₂ doped TiO₂ hollow microspheres exhibited a higher photocatalytic activity in the degradation of Rhodamine B (RhB) in aqueous solutions under UV-light irradiation compared with TiO₂ hollow microspheres and ZrO₂-doped TiO₂ particles. In particular, the removal of RhB followed pseudo-first-order kinetics, and 96.3% of RhB was degraded in 60 min under UV-light irradiation when ZrO₂ doped TiO₂ spinous hollow microspheres were used as the photocatalysts. Neutral and alkaline conditions were found to favor over acidic conditions for the photocatalytic degradation of RhB. Furthermore, scavenging experiments indicated that photogenerated holes (h⁺) and radicals (OH and O^-₂) were the main reactive species in the photocatalytic process using ZrO₂ doped TiO₂ hollow microspheres as the catalysts under UV light irradiation.

The use of reactive index of hydroxyl radicals to investigate the degradation of acid orange 7 by Fenton process

This study suggested the amount of hydroxyl radicals (OH) reacting with organics as a new index to evaluate the reaction efficiency (RE) of Fenton process, and used it to investigate the degradation mechanism of target pollution, Acid Orange 7 (AO7). The effects of initial concentrations of Fe(II), H₂O₂, and AO7 on RE were quantified by using response surface methodology (RSM). The main factors affecting RE were Fe(II), H₂O₂, and their interaction, and their percentage effects were 65.75, 11.99 and 22.23%, respectively. Moreover, based on the analysis result of RSM, a condition for good RE was proposed that it should ensure a higher amount of OH reacted with organics, and reduce the amount of OH scavenged by Fe(II). Liquid chromatography-mass spectrometry (LC/MS) analysis was used to identify the products of AO7 degradation in Fenton process, and there were three possible mechanisms to be observed, such as azo bond cleavage, hydroxylation, and oxidation of naphthalene ring. The trend of mechanisms might vary with the amount of OH attacks, and therefore the use of estimated RE could provide more particular information to better understand the relationship between organic degradation and OH attacks.

Effects of water chemistry on decolorization in three photochemical processes: Pro and cons of the UV/AA process

The poor selectivity of hydroxyl radicals is a major restriction in the practical application of the UV/H₂O₂ process for dyeing wastewater treatment. As an alternative, the target-selective UV/acetylacetone (AA) process was found highly efficient for dye decolorization. For the proper selection and application of the two photochemical processes, the effects of water matrices, including common inorganic anions (Cl^-, SO₄^2-, NO₃^-, HCO₃^-), natural organic matter, metal cations (Mg²⁺, Mn²⁺, Cu²⁺, Fe³⁺, Cr³⁺), and temperature, on the photo-degradation of an azo dye, Acid Orange 7 (AO7), were systematically investigated. The experimental results demonstrate that the UV/AA process was more sensitive to inner filter effect. NO₃^-, Cu²⁺, and Fe³⁺ were all detrimental to the UV/AA process, whereas at certain concentrations they were beneficial to the UV/H₂O₂ process. However, even with severe inhibitory effects, the decolorization efficiency of the UV/AA process was still several times higher than that of the UV/H₂O₂ process. The results are helpful for us to better understand the mechanisms behind the UV/AA process and may shed light on the application of UV-based advanced oxidation processes for wastewater treatment.

Enhanced photo-catalytic activity of Sr and Ag co-doped TiO2 nanoparticles for the degradation of Direct Green-6 and Reactive Blue-160 under UV & visible light

This work is focused on sol-gel synthesis of silver and strontium co-doped TiO2 nanoparticles and their utilization as photo-catalysts in degradation of two textile dyes. Effect of pH, intensity of light, amount of photo-catalyst, concentration of dye, sensitizers, etc., were studied to optimize conditions for obtaining enhanced photo-catalytic activity of synthesized nanoparticles. XRD, BET, HR-TEM, EDAX and UV-Vis (diffused reflectance mode) techniques were used to characterize the nanoparticles. Interestingly, band gap of Sr and Ag co-doped TiO2 nanoparticles showed considerable narrowing (2.6 eV) when compared to Ag doped TiO2 (2.7 eV) and undoped TiO2 (3.17 eV) nanoparticles. Incorporation of Ag and Sr in the lattice of TiO2 could bring isolated energy levels near conduction and valence bands thus narrowing band gap. The XRD analysis shows that both Ag and Sr nanoparticles are finely dispersed on the surface of titania framework, without disturbing its crystalline structure. TEM images indicate that representative grain sizes of Ag-doped TiO2 & Sr and Ag co-doped TiO2 nanoparticles are in the range of 8-20 nm and 11-25 nm, respectively. Effective degradation of Direct Green-6 (DG-6) and Reactive Blue-160 (RB-160) under UV and visible light has been achieved using the photo-catalysts. Sr and Ag co-doped TiO2 photo-catalysts showed higher catalytic activity during degradation process in visible region when compared to Ag-doped and undoped TiO2 nanoparticles which could be attributed to the interactive effect caused by band gap narrowing and enhancement in charge separation. For confirming degradation of the dyes, total organic carbon (TOC) content was monitored periodically.

Sonophotocatalytic treatment of Bismarck Brown G dye and real textile effluent using synthesized novel Fe(0)-doped TiO2 catalyst

Using a novel Fe(0)-TiO₂-doped catalyst, the degradation of Bismarck Brown G dye was compared by means of advanced oxidation processes, such as sonolysis, photolysis (UV light) and sonophotolysis. The sonophotolysis methodology was also adopted for real textile effluent.

Photodegradation of Acid Orange 7 in a UV/acetylacetone process

Acetylacetone (AcAc) was employed as a photo-activator for the degradation of Acid Orange 7 (AO7) under UV irradiation. The feasibility of this process (named as UV/AcAc) was evaluated through comparison with the well-established UV/H2O2 process in terms of absorption spectrum and the biodegradability of the solutions. A complete decoloration of the AO7 solution could be fulfilled with AcAc at mM level. A self-acceleration phenomenon was observed for the UV/AcAc process. The pseudo first-order decoloration rate constant of AO7 in the UV/AcAc process was several times higher than that in the UV/H2O2 process, depending on the irradiation conditions. The BOD to COD ratio of the solutions increased from below 0.1 to above 0.3, along with a slight mineralization. Based on degradation product analysis, the possible pathways for AO7 degradation in the UV/AcAc process were proposed.

Application of zeolite-activated carbon macrocomposite for the adsorption of Acid Orange 7: isotherm, kinetic and thermodynamic studies

In this study, the adsorption behavior of azo dye Acid Orange 7 (AO7) from aqueous solution onto macrocomposite (MC) was investigated under various experimental conditions. The adsorbent, MC, which consists of a mixture of zeolite and activated carbon, was found to be effective in removing AO7. The MC were characterized by scanning electron microscopy (SEM), energy dispersive X-ray, point of zero charge, and Brunauer-Emmett-Teller surface area analysis. A series of experiments were performed via batch adsorption technique to examine the effect of the process variables, namely, contact time, initial dye concentration, and solution pH. The dye equilibrium adsorption was investigated, and the equilibrium data were fitted to Langmuir, Freundlich, and Tempkin isotherm models. The Langmuir isotherm model fits the equilibrium data better than the Freundlich isotherm model. For the kinetic study, pseudo-first-order, pseudo-second-order, and intraparticle diffusion model were used to fit the experimental data. The adsorption kinetic was found to be well described by the pseudo-second-order model. Thermodynamic analysis indicated that the adsorption process is a spontaneous and endothermic process. The SEM, Fourier transform infrared spectroscopy, ultraviolet-visible spectral and high performance liquid chromatography analysis were carried out before and after the adsorption process. For the phytotoxicity test, treated AO7 was found to be less toxic. Thus, the study indicated that MC has good potential use as an adsorbent for the removal of azo dye from aqueous solution.

Effectiveness of photochemical and sonochemical processes in degradation of Basic Violet 16 (BV16) dye from aqueous solutions

In this study, degradation of Basic Violet 16 (BV16) by ultraviolet radiation (UV), ultrasonic irradiation (US), UV/H2O2 and US/H2O2 processes was investigated in a laboratory-scale batch photoreactor equipped with a 55W immersed-type low-pressure mercury vapor lamp and a sonoreactor with high frequency (130kHz) plate type transducer at 100W of acoustic power. The effects of initial dye concentration, concentration of H2O2 and solution pH and presence of Na2SO4 was studied on the sonochemical and photochemical destruction of BV16 in aqueous phase. The results indicated that in the UV/H2O2 and US/H2O2 systems, a sufficient amount of H2O2 was necessary, but a very high H2O2 concentration would inhibit the reaction rate. The optimum H2O2 concentration was achieved in the range of 17 mmol/L at dye concentration of 30 mg/L. A degradation of 99% was obtained with UV/H2O2 within 8 minutes while decolorization efficiency by using UV (23%), US (<6%) and US/H2O2(<15%) processes were negligible for this kind of dye. Pseudo-first order kinetics with respect to dyestuffs concentrations was found to fit all the experimental data.

A comparative study on the degradation of RB-19 dye in an aqueous medium by advanced oxidation processes

The effectiveness of photolysis (UV), peroxidation (H(2)O(2)), peroxidation combined with UV light (UV/H(2)O(2)), Fenton reagent (H(2)O(2)/Fe(2+)), and the photo-Fenton process (H(2)O(2)/Fe(2+)/UV) at degrading the textile dye Reactive Blue 19 was evaluated. The efficiency of the photo-Fenton process for degrading raw textiles and biologically pre-treated effluents was also evaluated. H(2)O(2) (100-800 mg L(-1)) and UV light did not degrade dye when used separately. The UV/H(2)O(2) process was effective but slow: 91% of dye degraded within 3 h of reaction at a concentration of 500 mg L(-1) H(2)O(2). Fenton reagent reduced dissolved organic carbon by 36.8% and color was reduced by >98% within a few minutes of reaction. The photo-Fenton process was the most efficient, reducing 94.5% of dissolved organic carbon and 99.4% of color. The combination of a biological system and the photo-Fenton process degraded a high level of textile effluent degradation, reducing dissolved organic carbon by 88%, color by 85%, chemical oxygen demand by 80%, and biochemical oxygen demand by 93%.

Fabrication of titanium dioxide and tungstophosphate nanocomposite films and their photocatalytic degradation for methyl orange

Photocatalytic multilayer films with different numbers of bilayers were prepared via an electrostatic layer-by-layer (LbL) self-assembly method. These LbL films were characterized by UV-vis spectroscopy, atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). Our results indicate that TiO(2) and tungstophosphate (H(3)PW(12)O(40), abbreviated as PW(12)) are successfully incorporated into the thin films. The as-prepared (TiO(2)/PW(12))(n) films show good photocatalytic performance toward methyl orange (MO) solution at pH 2.0, which is attributed to the synergistic effect between TiO(2) and PW(12). The effect of experimental parameters including number of bilayers, initial concentration, and pH value of dye solution were also studied. The multilayer films can be easily recovered and reused several times with little change of degradation, indicating that they are stable under the ultraviolet (UV) irradiation. The detection of active species displays that active holes (h(+)) play a dominant role for MO photodegradation in the TiO(2)/PW(12) system. Taking advantage of immobilization of catalysts on glass slides, the problem of recovery is solved. It is expected that photocatalytic multilayer films have substantial applications in industry.

Degradation of Active Brilliant Red X-3B by a microwave discharge electrodeless lamp in the presence of activated carbon

Degradation of Active Brilliant Red X-3B (X-3B) in aqueous solution by a microwave discharge electrodeless lamp (MDEL) in the presence of activated carbon was investigated. The preliminary results proved this method could effectively degrade X-3B in aqueous solution. The removal percentages of colour and chemical oxygen demand were up to approximately 99% and 66%, respectively, at the conditions of 0.8 g/L dye concentration, 20 g/L activated carbon, pH 7.0 and 8 min microwave irradiation time. The degradation basically belonged to first-order reaction kinetics and its rate constant was 0.42 min(-1). No aromatic organics were detected in the final treated solution, indicating that the mineralization was relatively complete. By studying the change in solution properties, it could be concluded that MDEL-assisted oxidation was the dominant reaction mechanism. In addition, the influence of operational parameters and reuse of activated carbon were also discussed.

Photo-degradation of acid red 44 using Al and Fe modified silicates

Al and Fe modified silicates were synthesized using the hydrothermal method. The obtained materials were calcined at different temperatures (250, 500 and 750 degrees C) and characterized using XRD, FTIR, UV and SEM spectroscopy. The obtained materials were applied for the photo-decolorization of acid red 44 as a member of azo dye family, in aqueous medium using UV irradiation (lambda=254 nm) under different experimental conditions. The effect of calcination temperature, catalyst concentration and pH on the decolorization of acid red 44 dye were investigated. The decolorization of acid red 44 dye and the decreasing in concentration of the formed intermediates have been followed using UV-vis spectrophotometry and high performance liquid chromatography (HPLC). Results showed that the addition of Al and Fe-silicate to the dye solution as well as pH change greatly enhanced the rate of degradation. The decolorization followed the pseudo first order kinetics model and a significant mineralization of AR44 was observed.

Effect of operational parameters on degradation of Malachite Green by ultrasonic irradiation

The aim of the present study was to apply ultrasonic technique to remove Malachite Oxalate Green (MG) from aqueous solution. An ultrasonic bath with frequency of 35 kHz was used to investigate the effect of different operational parameters such as MG concentration, power density, temperature, mechanical agitation and addition of EtOH, 2-PrOH and iso-BuOH. Decolorization of MG follows a first order kinetics and hydroxyl radicals have an important role in degradation of MG. The apparent reaction rate constant (k(ap)) was influenced by variation of operational parameters. The activation energy was 30.95 kJ/mol in temperature range of 21-34 degrees C, suggesting a diffusion-controlled reaction. Alcohols act as hydroxyl radicals scavengers having undesirable contribution. UV-vis spectral change of MG showed hypsochromic shift occurred with increasing sonication time, proposing N-demethylation process of MG.

Photodegradation of metolachlor applying UV and UV/H2O2

Metolachlor is one of the most widely used herbicides in the world for controlling weeds. It has been detected in both ground and surface waters in the United States, and there are rising concerns in regard to its health risks and in developing effective treatment processes for its removal from water. Degradation of metolachlor via ultraviolet (UV) photolysis and an UV/hydrogen peroxide advanced oxidation process (AOP) was studied. The quantum yield of metolachlor at 254 nm was found to be 0.302 +/- 0.001 mol E-1 through direct UV photolysis in the range of pH 6-8. The second-order rate constant of the reaction between metolachlor and hydroxyl radical was determined to be 9.07 (+/-0.21) x 10(9) M-1 s-1 by using a competition kinetics model that utilized nitrobenzene as a reference compound. In addition, these parameters were successfully applied in modeling the kinetics of elimination of metolachlor using an UV/H2O2 process in both laboratory and natural waters. The formation of several photolysis byproducts was identified using gas chromatography/mass spectrometry, and a scheme for the metolachlor photodegradation pathway is proposed.

Application of several advanced oxidation processes for the destruction of terephthalic acid (TPA)

Terephthalic acid (TPA) is widely applied as a raw material in making polyester fiber, polyethylene terephthalate (PET) bottles, polyester films, etc. TPA is toxic and is known to act as endocrine disruptor. TPA wastewater is traditionally treated by biological process and this study aims to evaluate the effectiveness of several advanced oxidation processes on TPA removal. The oxidation processes studied were: UV-TiO(2), UV-H(2)O(2), UV-H(2)O(2)-Fe, O(3), O(3)/Fe, O(3)/TiO(2), UV-O(3)-H(2)O(2)-Fe and UV-O(3)-H(2)O(2)-Fe-TiO(2). The results indicate that the time required for the complete destruction of 50 ppm of TPA can be minimized from 10h using UV-TiO(2) system, to less than 10 min by UV-H(2)O(2)-Fe-O(3) system. Some of the likely organic intermediates identified during TPA destruction include, benzoquinone, benzene, maleic acid and oxalic acid. Possible destruction pathway of TPA has been proposed. TPA degradation by various systems was also analyzed based on the reaction kinetics and operating costs.

Kinetics of oxidative decolorization and mineralization of Acid Orange 7 by dark and photoassisted Co2+-catalyzed peroxymonosulfate system

A kinetic model was proposed and used to interpret the experimental data for degradation of Acid Orange 7 (AO7) in aqueous solution induced by Co(2+)/peroxymonosulfate (Co/PMS) reagent in terms of both decolorization and mineralization. The pseudo first-order decolorization rate constants are related to [Co(2+)], [PMS], reciprocal of [H(+)] and [AO7](0). Activation energy of the AO7 decolorization process was determined to be 75.7 kJ mol(-1). UV and visible light can accelerate the decolorization and mineralization process due to different mechanisms. In the combined UV/Co/PMS system, UV light can decompose PMS to generate hydroxyl ((*)OH) and sulfate radicals (SO(4)(*-)), while in the Vis/Co/PMS system, excited AO7 molecules can transfer electrons to PMS or Co(3+) and thus accelerate the decomposition of PMS and catalytic cycle of Co(3+)/Co(2+).

Photocatalytic degradation of C.I. Acid Red 27 by immobilized ZnO on glass plates in continuous-mode

The photocatalytic degradation of C.I. Acid Red 27 (AR27), an anionic monoazo dye of acid class, in aqueous solutions was investigated with immobilized ZnO catalyst on glass plates in a continuous-mode. In the slurry ZnO system the separation and recycling of the photocatalyst is practically difficult. Thus, ZnO was immobilized on solid supports to solve this problem. The removal percent increases with increasing the photoreactor volume and light intensity but it decreases when the flow rate is increased. With decreasing flow rate from 43 to 15mlmin(-1), the complete decolorization and degradation was obtained at around 748 and 1080cm(3) from photoreactor volume. The increase in the light intensity from 21.4 to 58.5Wm(-2) increases the decolorization from 23 to 57.6% and degradation from 17.5 to 37.8% for 374cm(3) of photoreactor volume. NH(4)(+), NO(3)(-), NO(2)(-) and SO(4)(2-) ions were analyzed as mineralization products of nitrogen and sulfur heteroatoms. Results showed that final concentration of SO(4)(2-) ions and N-containing mineralization products were less than the finally expected stoichiometric values. The positive slope of production of NH(4)(+), NO(3)(-) and NO(2)(-) shows that these compounds are initial products resulting directly from the initial attack on the nitrogen-to-nitrogen double bond (-NN-) of the azo dye.

Photooxidative degradation of 4-nitrophenol (4-NP) in UV/H2O2 process: influence of operational parameters and reaction mechanism

The photooxidative degradation of 4-nitrophenol (4-NP) was studied in the UV/H2O2 process. The effects of applied H2O2 dose, initial 4-NP concentration and UV light intensity have been studied. Degradation was complete in 13 min and follows apparent first-order kinetics. The removal efficiency of 4-NP depends on the operational parameters and increases as the initial concentration of H2O2 and light intensity are increased but it decreases when the initial concentration of 4-NP is increased. From HPLC analysis, major intermediate products were hydroxyl derivatives of 4-NP as a result of photooxidative hydroxylation.

Simple, sensitive and on-line fluorescence monitoring of photodegradation of phenol and 2-naphthol

A simple molecular fluorescence spectrometer based on a hand-held CCD spectrometer was constructed for on-line monitoring of the photodegradation of pollutants. A high-pressure Hg vapour lamp was used for the UV photodegradation and simultaneously for the fluorescence excitation. Phenol and 2-naphthol were selected as the targets for this preliminary study. Using peak fluorescence, figures of merit for monitoring these two hydroxybenzene were obtained. Degradation efficiencies with different homogeneous photocatalyst systems were investigated, including UV only, UV/H(2)O(2) and UV/Fe(3+) degradation systems. The kinetics modelling showed that their photodegradation fitted the Langmuir-Hinshelwood model. Results showed that the proposed method is potentially applicable to both on-line real-time monitoring and field analysis.

Kinetic modeling on photooxidative degradation of C.I. Acid Orange 7 in a tubular continuous-flow photoreactor

The decolorization of C.I. Acid Orange 7 (AO7), an anionic monoazo dye of acid class, was investigated using UV radiation in the presence of H2O2 in a tubular continuous-flow photoreactor as a function of oxidant and dye concentrations, reactor length and volumetric flow rate. The removal efficiency of AO7 depends on the operational parameters and increases as the initial concentration of H2O2 is increased but it decreases when the flow rate and initial concentration of AO7 are increased. The decolorization rate follows pseudo-first order kinetic with respect to the dye concentration. A rate equation for decolorization of AO7 was achieved by kinetic modeling. This model allows predicting concentration of AO7 in different photoreactor lengths for different volumetric flow rates and initial concentrations of H2O2 and AO7. The calculated results obtained from kinetic model were in good agreement with experimental data.