Photooxidation Of Dyes Research Articles

Synthesis, Structure, and Properties of Dion–Jacobson Double‐Layered Perovskites A′SmNb2O7 (A′ = Rb, K, Na, Li, H)

Dion‐Jacobson‐type layered perovskite compounds A′SmNb2O7 (A′ = Rb, K, Na, Li, H) were synthesized using solid‐state and ion‐exchange methods. While the parent solid‐state product RbSmNb2O7, has previously been studied, the ion‐exchanged compounds were obtained and studied for the first time. The phase and chemical purity of the compounds were confirmed by X‐ray diffraction (XRD) and energy‐dispersive X‐ray spectroscopy (EDX). The crystal structures of RbSmNb2O7 (I2cm, a=0.54356(1) nm, b=0.53935(1) nm, c=2.1891(5) nm), KSmNb2O7 (I2cm, a=0.53660(7) nm, b=0.54481(6) nm, c=2.1527(1) nm) and LiSmNb2O7 (B2cm, a=0.54546(4) nm, b=0.53567(4) nm, c=2.04582(5) nm) were refined using the Rietveld method. Polyhedral distortions in these structures have been studied in detail. The thermal behavior of the compounds has been determined using differential thermal analysis (DTA), revealing that A′ = Na, Li and H compounds are metastable hydrates, while A′ = Rb and K compounds are stable. The optical band gap, valence band edge, and conduction band edge potentials of the compounds obtained were calculated using diffuse reflection spectroscopy data. A photocatalytic experiment was performed on the degradation of methylene blue under ultraviolet light. All of the samples obtained showed some activity in the reaction of dye photooxidation.

Band gap engineering of ADG/NiO nanocomposite and applications for photocatalytic reduction of nitrogen and photo-oxidation of dyes

The use of solar-driven semiconductor photocatalysis to solve energy and environmental issues is an intriguing and difficult subject. As a consequence, various types of photocatalysts have been developed subsequently to fulfill the requirements of photocatalysis.Since graphene was discovered, materials based on graphene have garnered considerable interest. The aloe-vera derived (ADG)/nickel oxide (NiO) nanocomposite is a notable example of a graphene derivative.The uniform structure of graphene fibre is altered by nickel oxide(NiO) which tunes its band gap and causes electronic arrangements within graphene that is requiste for photocatalysis. Herein, we have used a one-pot chemical approach to design aloe vera-derived graphene/nickel oxide nanocomposites (ADG/NiO), a novel photocatalyst that show high molar absorbance, suitable band gap of 2.68 eV, good photo-stability and reusability. Under solar light irradiation, the ADG/NiO nanocomposite exhibited remarkable photocatalytic activity. It effectively fixed nitrogen into ammonia with an apparent quantum efficiency(AQE) of 0.64% and efficiently photo-oxidized dyes. Specifically, it achieved a dye removal efficiency of 94.2% for methylene blue (MB) and 86.41% for Eosin-B, converting them into harmless inorganic species like CO2 and H2O within just 90 minutes. The cost-effective ADG/NiO nanocomposite shows significant potential as a photocatalyst activated by solar light for practical applications such as the selective generation of NH3 and the purification of industrial wastewater containing dyes.

Physical and photo-electrochemical properties of the hetero-junction ZnCo2O4/ZnO prepared by nitrate route: Application to photodegradation of Indigo Carmine

The semi conducting and photoelectrochemical properties of prepared ZnCo2O4 by nitrate route are investigated. The X-ray diffraction pattern of the red compound indicates a spinel type structure crystallizing in a cubic symmetry (a = 8.0989 Å). The direct optical transition of 2.10 eV, measured by diffuse reflectance spectroscopy, is assigned to unfilled Co3+: 3d orbital splitting in octahedral field (t2g → eg). The electrical conduction occurs by small lattice polaron hopping with an activation energy of 0.19 eV and a hole mobility µ300K (=3.5 × 10−4 cm2 V−1 s−1), thermally activated. ZnCo2O4 exhibits a chemical stability over the pH range (4 and 12) and a flat band potential (Efb) of 0.12 V, was deduced from the capacitance – potential (C−2 – E) plot. The positive slope characteristics p type conduction with a hole density of 1.6 × 1017 cm−3 due to mixed valences Co3+/2+. The energy of the conduction band (2.96 eV / −1.79 VSCE) makes the spinel attractive for the photo-oxidation of dyes by O2− radicals. The powder is successfully tested in the photo degradation of Indigo Carmine (10 10 mg/L) over the hetero-junction upon visible and solar lights. The best performance of the hetero- junction (ZnCo2O4 / ZnO) is obtained with (10 %/90 %) percentage with an abatement of 93 %, larger than the spinel alone (49 %) under sunlight. The kinetic follows pseudo-first order with a half-life of 23 min.

Developing efficient CuO nanoplate/ZnO nanoparticle hybrid photocatalysts for methylene blue degradation under visible light.

CuO/ZnO nanocomposites with different components can overcome the drawbacks of previously used photocatalysts owing to their promotion in charge separation and transportation, light absorption, and the photo-oxidation of dyes. In this study, CuO nanoplates were synthesized by the hydrothermal method, while ZnO nanoparticles were fabricated by the precipitation method. A series of CuO/ZnO nanocomposites with different ZnO-to-CuO weight ratios, namely, 2 : 8, 4 : 6, 5 : 5, 6 : 4, and 8 : 2 were obtained via a mixing process. X-ray diffraction patterns confirmed the presence of hexagonal wurtzite ZnO and monoclinic CuO in the synthesized CuO/ZnO nanocomposites. Scanning electron microscopy showed the dispersion of ZnO nanoparticles on the surface of CuO nanoplates. Ultraviolet-visible absorption spectra exhibited a slight red-shift in the absorption edge of binary oxides relative to pure ZnO or CuO. All samples were employed for the photocatalytic degradation of methylene blue (MB) under visible light irradiation. The composite samples exhibited enhanced photocatalytic performance compared with pristine CuO or ZnO. This study aimed to examine the effect of the ZnO-to-CuO weight ratio on their photocatalytic performance. The results indicated that among all the synthesized nanocomposites and pristine oxides, the nanocomposite with ZnO and CuO in a proportion of 4 : 6 shows the highest photodegradation activity for the removal of MB with 93% MB photodegraded within 60 min at an initial MB concentration of 5 ppm. The photocatalytic kinetic data were described well by the pseudo-first-order model with a high correlation coefficient of 0.95. The photocatalytic mechanism of the mixed metal oxide was proposed and discussed in detail. The photodegradation characteristic of CuO/ZnO nanostructures is valuable for methylene blue degradation from aqueous solutions as well as environmental purification in various fields.

Enhanced photocatalytic activity of hierarchical C/ZnO nanocomposite derived from solvothermally restructured Zn-BTC microspheres

Single step solvothermal synthesis of hierarchical and hollow microspheres (HHMs) assembly of 1D zinc-trimesic acid (Zn-BTC) MOF nanospikes, without using any external stabilizer as shape modifier is reported here. Detailed electron microscopy imaging revealed that the Zn-BTC HHMs form through a self-templating mechanism due to the typical reaction conditions. The Zn-BTC HHMs were annealed to form ZnO/C hierarchical nanocomposite microspheres (HNMs). HNMs were found to be quite active for the photocatalytic water remediation through the photo-oxidation of dyes as well as photo-reduction of Cr (VI). Thorough characterization revealed that the HNMs exhibited three-dimensional (3D) hierarchical morphology with comparatively higher mesoporosity, extended visible light absorption, and better separation of photogenerated charges (e-/h+), resulting in enhanced photocatalytic performance (0.40 and 1.89 mg·g−1·min−1 removal efficiency for MV and Cr (VI) respectively). The enhanced photocatalytic activities of the HNMs were found to be due to the synergism between carbon matrix and the well-dispersed ZnO quantum dots.

N,N'-Bis(3-methylphenyl)-N,N'-dyphenylbenzidine Based Distributed Feedback Lasers with Holographically Fabricated Polymeric Resonators.

The molecule N,N′-bis(3-methylphenyl)-N,N′-dyphenylbenzidine (TPD) has been widely used in optoelectronic applications, mainly for its hole-transporting properties, but also for its capability to emit blue light and amplified spontaneous emission, which is important for the development of organic lasers. Here, we report deep-blue-emitting distributed feedback (DFB) lasers based on TPD dispersed in polystyrene (PS), as active media, and dichromated gelatin layers with holographically engraved relief gratings, as laser resonators. The effect of the device architecture (with the resonator located below or on top of the active layer) is investigated with a dye (TPD) that can be doped into PS at higher rates (up to 60 wt%), than with previously used dyes (<5 wt%). This has enabled changing the index contrast between film and resonator, which has an important effect on the laser performance. With regards to thresholds, both architectures behave similarly for TPD concentrations above 20 wt%, while for lower concentrations, top-layer resonator devices show lower values (around half). Remarkably, the operational durability of top-layer resonator devices is larger (in a factor of around 2), independently of the TPD concentration. This is a consequence of the protection offered by the resonator against dye photo-oxidation when the device is illuminated with pulsed UV light.

Degradation of acriflavine using environmentally benign process involving singlet-oxygen-photo-Fenton: A comparative study

The present study was conducted to analyze the degradation efficiency of acriflavine (a dye) using the photo-Fenton reagent with singlet molecular oxygen. In the presence of singlet molecular oxygen, the photochemical oxidation rate of Acriflavine is increased. The rate of photooxidation of dye in aqueous medium has been compared among singlet-oxygen-photo-Fenton (SOPF), photo-Fenton (PF), singlet oxygen (SOP) and photo-Fenton (PF) (< 10 °C) processes. SOPF is more effective photooxidation process than PF, PF (< 10 °C) and SOP. The effect of some parameters like pH, the concentration of Fe3+ ions, concentration of acriflavine, amount of H2O2 and light intensity have been observed for the rate of photooxidation. The photochemical oxidation reaction follows pseudo-first order kinetics. A tentative mechanism has been suggested for the singlet-oxygen-photo-Fenton process (SOPF).

Advances and Challenges in Developing Efficient Graphene Oxide-Based ZnO Photocatalysts for Dye Photo-Oxidation.

The efficient remediation of organic dyes from wastewater is increasingly valuable in water treatment technology, largely owing to the tons of hazardous chemicals currently and constantly released into rivers and seas from various industries, including the paper, pharmaceutical, textile, and dye production industries. Using solar energy as an inexhaustible source, photocatalysis ranks among the most promising wastewater treatment techniques for eliminating persistent organic pollutants and new emerging contaminants. In that context, developing efficient photocatalysts using sunlight irradiation and effectively integrating them into reactors, however, pose major challenges in the technologically relevant application of photocatalysts. As a potential solution, graphene oxide (GO)-based zinc oxide (ZnO) nanocomposites may be used together with different components (i.e., ZnO and GO-based materials) to overcome the drawbacks of ZnO photocatalysts. Indeed, mounting evidence suggests that using GO-based ZnO nanocomposites can promote light absorption, charge separation, charge transportation, and photo-oxidation of dyes. Despite such advances, viable, low-cost GO-based ZnO nanocomposite photocatalysts with sufficient efficiency, stability, and photostability remain to be developed, especially ones that can be integrated into photocatalytic reactors. This article offers a concise overview of state-of-the-art GO-based ZnO nanocomposites and the principal challenges in developing them.

Photocatalytic degradation of rhodamine B, and phenol red dyes using NiMn2O4 nanoparticles prepared by a new approach

NiMn2O4 nanoparticles have been successfully prepared through sol-gel method. The effects of different factors such as the type of solvent, and amino acid temperature were investigated on the size and morphologies of products. The smallest particle size of NiMn2O4 nanoparticles was found to be 25 nm in diameter. The magnetic properties of the samples were also measured by an alternating gradient force magnetometer (AGFM). The optical property of the desired products was investigated by UV–vis diffuse reflectance spectroscopy , and the band gap of product was computed nearly 3 eV. The estimated band gap confirms that this product may be used as a photocatalyst, so the photocatalytic test was conducted by photooxidation of dyes under ultraviolet irradiation and in the presence of NiMn2O4 nanoparricles. The results demonstrated that rhodamine B degradation was about 98 % under ultraviolet light for 80 min. Therefore, the synthesized product can be employed as an effective photocatalyst.

Zinc Oxide–Nanoclinoptilolite as a Superior Catalyst for Visible Photo-Oxidation of Dyes and Green Synthesis of Pyrazole Derivatives

In this study a new ZnO doped nanoclinoptilolite was synthesized and the morphology and properties of this new nanocomposite were studied using X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and Field emission scanning electron microscopy (FESEM). The effective substance (ZnO) amount on clinoptilolite substrate was also determined by EDX method. Natural based nanocomposites are low cost and high efficient materials for photo oxidation of organic dyes and also synthesis of organic compounds. The ability of this new nanocomposite in photodegradation of methylene blue (MB) as a cationic dye and mixture cationic- anionic dyes (methylene blue and methyl red) under visible light irradiation was studied. The effect of various important factors on the degradation rate was studied. Under optimal conditions, the degradation efficiency of MB was achieved about 88% in 40 min. A first order kinetic was observed for the degradation of MB. Also, this nanocomposite was used as an ecofriendly and green nanocatalyst for the synthesis of pyrazole derivatives by condensation of substituted phenyl hydrazines with 1,3-diketone/ketoester with high performance. The reaction of synthesis of 5-methyl-2-phenyl-2,4-dihydro-3H-pyrazol-3-one (3a) in aqueous medium gave the required product in high yield (99%) and in shorter reaction time (10 min).

An efficient fabrication of ZnO–carbon nanocomposites with enhanced photocatalytic activity and superior photostability

Synthesis of carbon nanoparticles (CNPs) and their composite with ZnO has proposed for the first time by combustion of camphor and chemical precipitation method. TEM image shows the surface of ZnO covered by tiny CNPs and acts as structure directing agent that transforms ZnO nanorods to uniform spherical ZnO. CNPs play a vital role to improve the photocatalytic activity and photostability of ZnO up to five runs due to impeding the photo-corrosion of ZnO. Enhance in the photocatalytic activity of ZnO–carbon nanocomposite could be attributed to the excellent dye adsorption capacity, direct photooxidation of dye and suppression of photoinduced electron–hole recombination. The presence of CNPs in nanocomposite served as the main role in accepting the photogenerated electrons due to electronic interaction between ZnO and CNPs. The cytotoxicity studies of meristematic root tip cells of Allium cepa reveals that photocatalytically degraded products were less toxic.

Structure and Photocatalytic Properties of TiO2/MoO3 and TiO2/V2O5 Nanocomposites Obtained by Mechanochemical Activation

The TiO2/MoO3 and TiO2/V2O5 thin-film nanoheterogeneous photocatalysts obtained by mechanochemical activation of oxides were studied by using the test reactions of probing dye photooxidation, EPR spectroscopy, X-ray diffraction, and atomic force microscopy. It was shown that mechanochemical synthesis yields nanoheterostructures of the oxide–oxide type, in which optimum conditions were created for photogeneration of charge carriers and their accumulation and thus opens up an opportunity of obtaining photocatalytic systems with prolonged oxidative activity.

Catalytic Properties of Fe-containing Layered Aluminosilicates in Photo-oxidation of Dye “Methyl Green”

The iron-containing materials with an iron content of 40 mg/g and 52.5 mg/g, a specific surface area of 107 m2/g and 96 m2/g are developed on the basis of natural layered aluminosilicate (montmorillonite) and polyhydroxo complexes of iron. It is shown that the materials exhibit high catalytic activity in the photo-oxidation of dye “Methyl Green”. The influence of physicochemical parameters (loading of the catalyst, a ratio of initial concentrations [H2O2]/[MG] on the efficiency of the dye photo-oxidation was established. The optimum conditions, which made it possible to achieve high mineralization and 100 % the dye oxidation efficiency were determined: the catalyst loading equal to 1.0 g/l and the ratio of [H2O2] and [MG] equal to stoichiometric ratio (55 mol/mol). The decrease of the total organic carbon content after photo-oxidation reaction was 56.5%. The average value of the quantum yield of the dye photo-oxidation was to 0.30 mol/Einstein. The results of the conducted research show that the developed iron-containing materials are the promising catalysts for photo-Fenton processes of oxidative degradation of organic compounds. The materials are of interest for use in wastewater treatment processes from toxic organic pollutants.

Converting Fe-rich magnetic wastes into active photocatalysts for environmental remediation processes

Abstract Hematite/magnetite photocatalysts were prepared by thermal treatment at 500 and 1000 °C of a Fe-rich waste obtained from a niobium mining. Rietveld analysis of XRD data and 57 Fe Mossbauer spectroscopy indicated that during the heat treatment magnetite is partially converted into hematite, which was the active photocatalytic phase in the samples. The remaining magnetite in the composites was useful to retard the fast electron-hole recombination in hematite. Zeta potential measurements revealed that the point of zero charge (pzc) of the iron oxides increased due to the thermal treatment, which favored the adsorption of negatively charged dye molecules. Diffuse reflectance measurements indicated that the band gap energies of iron oxides increased after the heat treatment due to a higher amount of hematite in those samples. Moreover, the valence band edges of hematite were more positive after the treatment of samples, which increased its dye photo-oxidation power. The photo-oxidation of neat methylene blue and Congo red in the presence of all samples was more efficient than that of neat methyl orange. On the other hand, it was verified from the competitive studies using the three dyes simultaneously that the photo-oxidation of methyl orange was favored, while the methylene blue and Congo red photo-oxidation decreased due to the methyl orange is replacing Congo red in the active photocatalytic sites of hematite. The proposed mechanism of dyes degradation was based on two main processes: (i) direct electron transfer from the dyes to the valence band of hematite, and (ii) dye oxidation by photogenerated OOH radicals on the hematite surface.

Comparison of Ilmenite and Nano-Ilmenite for Dye Removal and Antibacterial Activities

Objective: There are differents methode for moving dyes from contaminated environment and textile industries, the gold of this study is using of nano Ilmenite with anti bacterial properties for dye degradation. Method: The Ilmenite nanoparticles were produced and their catalytic activities were determined by the color change of several dyes. The prepared FeTiO3 nanoparticles have hexagonal structure with average size of ~21 nm. Results: The results indicated that although the Ilmenite has catalytic activity for photo-oxidation of dyes but Nano- Ilmenite has higher activity for dye removal. Dye removal by Nano-Ilmenite for Malachite Green, Alkaline Fuchsin and Coomassie Blue were 97% 50% and 100% respectively. Ilmenite removed Alkalin Fusion in lower rate but increased the color of Malachite Green and Coomassie Blue. Although Ilmenite had antibacterial activity but antibacterial activity of Nano-Ilmenite was 50% more. Conclusion: These data indicate that this Ilmenite soil can be used for remediation of contaminated area.

Woolen bun shaped CdS microspheres enfolded 1D nanowires for the superior photooxidation of dyes: A comparative case study

Woolen bun shaped CdS microspheres (2–5μm) wrapped by highly crystalline one dimensional CdS nanowires (length=8–10μm and diameter ∼80nm) are synthesized via anodic alumina membrane to achieve the best photoactivity for the decomposition of rhodamine B (50μM) and methylene blue (20μM) dyes using sunlight (50mWcm−2) irradiations. The higher number of surface exposed molecules for improved interactions with dye molecules in CdS nanowires led to its excellent photocatalytic performance over its spherical [cubic (∼12 nm) and hexagonal (∼15 nm) phase] and rod like (170 nm × 10 nm) morphology. Though of having less surface area (35.55 < 76 m2g−1) than nanorods, the crystalline structure with least surface defects, higher spectral response to absorb more light for multiple generation of charge carriers (e−–h+), and their superior delocalization for better charge separation as evidenced from its maximum (>80%) photoluminescence quenching and higher photoexcited charge carrier relaxation lifetime (3.6 ns) seems to be the cause of its outstanding performance. Many intermediate products and nearly linear increase in CO2 production are quantified during rhodamine B degradation by CdS nanowires under different time periods of sunlight irradiation.

FM Dye Photo-Oxidation as a Tool for Monitoring Membrane Recycling in Inner Hair Cells

Styryl (FM) dyes have been used for more than two decades to investigate exo- and endocytosis in conventional synapses. However, they are difficult to use in the inner hair cells of the auditory pathway (IHCs), as FM dyes appear to penetrate through mechanotransducer channels into the cytosol of IHCs, masking endocytotic uptake. To solve this problem we applied to IHCs the FM dye photo-oxidation technique, which renders the dyes into electron microscopy markers. Photo-oxidation allowed the unambiguous identification of labeled organelles, despite the presence of FM dye in the cytosol. This enabled us to describe the morphologies of several organelles that take up membrane in IHCs, both at rest and during stimulation. At rest, endosome-like organelles were detected in the region of the cuticular plate. Larger tubulo-cisternal organelles dominated the top and nuclear regions. Finally, the basal region, where the IHC active zones are located, contained few labeled organelles. Stimulation increased significantly membrane trafficking in the basal region, inducing the appearance of labeled vesicles and cistern-like organelles. The latter were replaced by small, synaptic-like vesicles during recovery after stimulation. In contrast, no changes in membrane trafficking were induced by stimulation in the cuticular plate region or in the top and nuclear regions. We conclude that synaptic vesicle recycling takes place mostly in the basal region of the IHCs. Other organelles participate in abundant constitutive membrane trafficking throughout the rest of the IHC volume.

A small pool of vesicles maintains synaptic activity in vivo

Chemical synapses contain substantial numbers of neurotransmitter-filled synaptic vesicles, ranging from approximately 100 to many thousands. The vesicles fuse with the plasma membrane to release neurotransmitter and are subsequently reformed and recycled. Stimulation of synapses in vitro generally causes the majority of the synaptic vesicles to release neurotransmitter, leading to the assumption that synapses contain numerous vesicles to sustain transmission during high activity. We tested this assumption by an approach we termed cellular ethology, monitoring vesicle function in behaving animals (10 animal models, nematodes to mammals). Using FM dye photooxidation, pHluorin imaging, and HRP uptake we found that only approximately 1-5% of the vesicles recycled over several hours, in both CNS synapses and neuromuscular junctions. These vesicles recycle repeatedly, intermixing slowly (over hours) with the reserve vesicles. The latter can eventually release when recycling is inhibited in vivo but do not seem to participate under normal activity. Vesicle recycling increased only to ≈ 5% in animals subjected to an extreme stress situation (frog predation on locusts). Synapsin, a molecule binding both vesicles and the cytoskeleton, may be a marker for the reserve vesicles: the proportion of vesicles recycling in vivo increased to 30% in synapsin-null Drosophila. We conclude that synapses do not require numerous reserve vesicles to sustain neurotransmitter release and thus may use them for other purposes, examined in the accompanying paper.

Modulation of SCFβ-TrCP-dependent IκBα Ubiquitination by Hydrogen Peroxide

Reactive oxygen species are known to participate in the regulation of intracellular signaling pathways, including activation of NF-kappaB. Recent studies have indicated that increases in intracellular concentrations of hydrogen peroxide (H(2)O(2)) have anti-inflammatory effects in neutrophils, including inhibition of the degradation of I kappaB alpha after TLR4 engagement. In the present experiments, we found that culture of lipopolysaccharide-stimulated neutrophils and HEK 293 cells with H(2)O(2) resulted in diminished ubiquitination of I kappaB alpha and decreased SCF(beta-TrCP) ubiquitin ligase activity. Exposure of neutrophils or HEK 293 cells to H(2)O(2) was associated with reduced binding between phosphorylated I kappaB alpha and SCF(beta-TrCP) but no change in the composition of the SCF(beta-TrCP) complex. Lipopolysaccharide-induced SCF(beta-TrCP) ubiquitin ligase activity as well as binding of beta-TrCP to phosphorylated I kappaB alpha was decreased in the lungs of acatalasemic mice and mice treated with the catalase inhibitor aminotriazole, situations in which intracellular concentrations of H(2)O(2) are increased. Exposure to H(2)O(2) resulted in oxidative modification of cysteine residues in beta-TrCP. Cysteine 308 in Blade 1 of the beta-TrCP beta-propeller region was found to be required for maximal binding between beta-TrCP and phosphorylated I kappaB alpha. These findings suggest that the anti-inflammatory effects of H(2)O(2) may result from its ability to decrease ubiquitination as well as subsequent degradation of I kappaB alpha through inhibiting the association between I kappaB alpha and SCF(beta-TrCP).

Azo-dyes photocatalytic degradation in aqueous suspension of TiO2 under solar irradiation.

The photodegradation of two common and very stable azo-dyes, i.e. methyl-orange (C14H14N3SO3Na) and orange II (C16H11N2SO4Na), is reported. The photocatalytic oxidation was carried out in aqueous suspensions of polycrystalline TiO2 irradiated by sunlight. Compound parabolic collectors, installed at the "Plataforma Solar de Almería" (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 (H2O2, S2O8(2-)) and some ions (Cl-, SO4(2-)) on the process was also studied.