Efficient degradation of Acid Orange 7 in aqueous solution by iron ore tailing Fenton-like process

Freezing-enhanced degradation of azo dyes in the chloride-peroxymonosulfate system

In this study, we investigated the freezing-induced acceleration of dye bleaching by chloride-activated peroxymonosulfate (PMS). It has been observed that the oxidation of chloride by PMS generates a free chlorine species, such as hypochlorous acid (HOCl), under mild acidic and circumneutral pH condition. This process is the major reason for the enhanced oxidation capacity for electron-rich organic compounds (e.g., phenol) in the chloride-PMS system. However, we demonstrated that the chloride-PMS system clearly reduced the total organic carbon concentration (TOC), whereas the HOCl system did not lead to decrease in TOC. Overall, the chemical reaction is negligible in an aqueous condition if the concentrations of reagents are low, and freezing the solution accelerates the degradation of dye pollutants remarkably. Most notably, the pseudo-first order kinetic rate constant for acid orange 7 (AO7) degradation is approximately 0.252 h-1 with 0.5 mM PMS, 1 mM NaCl, initial pH 3, and a freezing temperature of -20 °C. AO7 degradation is not observed when the solution is not frozen. According to a confocal Raman-microscope analysis and an experiment that used an extremely high dose of reactants, the freeze concentration effect is the main reason for the acceleration phenomenon. Because the freezing phenomenon is spontaneous at high latitudes and at mid-latitudes in winter, and the chloride is ubiquitous elsewhere, the frozen chloride-PMS system has potential as a method for energy-free and eco-friendly technology for the degradation of organic pollutants in cold environments.

Reuse of iron ore tailings as an efficient adsorbent to remove dyes from aqueous solution

In this work, an iron ore tailings sample (IOT), collected from a tailings dam in Minas Gerais, Brazil, was characterized. The IOT presented point of zero charge of ∼ 6, specific surface area of 4 m2 g-1, and was mainly composed of hematite and quartz. Subsequently, experiments were performed to evaluate the adsorption of an anionic dye, Direct Red 80 (DR80), and a cationic dye, Methylene Blue (MB), by the IOT, studying the effects of its dose (doseIOT) and the solution initial pH (pH0). The DR80 removal increased with the decrease of the pH0 while the opposite effect occurred in the experiments with the MB, suggesting the process is governed by the adsorption resulting from electrostatic forces. The increase in the doseIOT increased the DR80 and MB removal, which can be attributed to the greater availability of adsorption sites. Pseudo-second order kinetic (R2 > 0.9994) and the Langmuir equilibrium isotherm (R2 > 0.9842) models described well the DR80 adsorption by the IOT, being the reaction rate and maximum adsorption capacity higher at lower pH0. In a regeneration experiment, it was possible to desorb almost entirely the DR80 using a NaOH solution. Additionally, the regenerated IOT was able to adsorb the DR80, demonstrating its reusability. In a preliminary assay, the IOT decreased the colour of the textile wastewater sample at pH0 3. Therefore, the results indicate the potential use of IOT for removing electric-charged pollutants by adsorption, especially anionic ones under acidic conditions.

Pyrite Cinder as an Effective Fenton-like Catalyst for the Degradation of Reactive Azo Dye: Effects of Process Parameters and Complete Effluent Characterization

This research investigates the potential use of pyrite cinder (PC) as an efficient Fenton-like catalyst for the removal of the reactive azo dye Reactive Red 120 (RR120) from aqueous solutions. The characterization of its PC structure and composition confirmed its great potential to act as catalytic iron source in a heterogeneous Fenton system. Dye removal optimization was performed in terms of PC dosage (0.4–8 g/L), H2O2 concentration (2–25 mM), pH value (2–4.6), initial dye concentration (50–200 mg/L), and mixing time. The highest decolorization efficiency (92%) was achieved after a reaction time of 480 min under following conditions: RR120 = 50 mg/L, PC = 4 g/L, H2O2 = 10 mM, and pH = 3. After decolorization, an extensive analysis of the generated effluent was performed regarding metal leaching, mineralization, toxicity, and degradation product formation. The metal leaching indicated the necessity for a pH increase in order to remove the settled metal hydroxides. The mineralization efficiency was satisfactory, reaching 85% and 62% of the COD and TOC removal, respectively. The respirometry measurements and bioluminescence tests indicated the detoxification of the treated solution. The absorption spectra and GC/MS analysis confirmed the changes in the molecular structure in the form of the destruction of the azo bond, with a simpler aromatic and aliphatic intermediates formation. This study provides an effective method for removing azo dye in polluted water by employing waste tailings as alternative Fenton-like catalysts, while also using waste tailings as the secondary resource.

Highly active Fenton-like catalyst derived from solid waste-iron ore tailings using wheat straw pyrolysis

The pollutants degradation rate of iron ore tailings-based heterogeneous catalysts is the main factor limiting its application. Herein, an iron ore tailings-based Fenton-like catalyst (I/W(3:1)-900-60) with a relatively fast catalysis rate was constructed by co-pyrolysis (900°C, 60 min holding time) of iron ore tailings and wheat straw with a mass ratio of 3:1. With wheat straw blending, the generated I/W(3:1)-900-60 presented a larger surface area (24.53 m²/g), smaller pore size (3.76 nm), reduced iron species (Fe²⁺ from magnetic), and a higher catalytic activity (0.0229 min^-1) than I-900-60 (1.32 m²/g, 12.87 nm, 0.012 min^-1) pyrolyzed using single iron ore tailing under the same pyrolysis conditions. In addition, biochar and iron ore tailings in I/W(3:1)-900-60 were tightly combined through chemical bonding. The optimal catalyst remains active after three cycles, indicating its catalytic stability and recyclability. The good Fenton-like methylene blue degradation efficiency of I/W(3:1)-900-60 was ascribed to the sacrificial role of biochar, as well as the electron transfer between biochar and iron active sites or the redox cycles of ≡Fe³⁺/Fe²⁺. This finding provides a facile construction strategy for highly active iron ore tailings-based Fenton-like catalyst and thereby had a great potential application in wastewater treatment.

Coal mining pyritic waste in Fenton-like processes: Raw and purified catalysts in Reactive Blue 21 dye discoloration

Raw pyritic waste (RPW) from South Brazilian coal deposits and pure pyritic waste (PPW) were used as catalysts for organic dyes discoloration. Samples were characterized for their chemical, morphological, and structural properties. There was a significant content of Fe and S in both samples from the presence of iron sulfide. The average particle size is 10.9 μm for RPW and 7.4 μm for PPW, demonstrating that the beneficiation process could remove the larger quartz particles, interfered in the distribution, and average particle size. Smaller particle sizes promoted a larger surface area for the PPW. The influence of the pyritic waste in dosage, H₂O₂ concentration, and pH was evaluated, obtaining discoloration values above 95% for 0.5 g/L of pyritic waste, 2 g/L of H₂O_2, and pH 4.3 for both pyritic wastes. The degradation kinetics of the Reactive Blue 21 using the raw pyritic waste obtained a dye concentration removal above 93% in 90 min, with an iron release of 5.4 mg/L into the solution. Using PPW, the dye concentration removal was over 92% in 40 min, with the iron release of 15.5 mg/L into the solution. Discoloration rate for the PPW sample is 7 times greater than the rate obtained for RPW, indicating a faster decay rate for the purified sample. A decrease in discoloration efficiency is observed for PPW after 6 cycles of use, due to the higher concentration of iron leached into the medium. From the results, it was concluded that the raw pyritic waste has excellent potential for use as a catalyst for Fenton reaction, especially for dye-containing water discoloration, thus demonstrating the excellent applicability potential of pyritc waste in the degradation of organic pollutants in wastewater.

A strategy to enhance the photocatalytic efficiency of α-Fe2O3

The photocatalytic dye degradation of pure α-Fe₂O₃ and different concentration of Co doped α-Fe₂O₃ is explored. Facile hydrothermal method were employed to prepare pristine, 2% and 4% Co-Fe₂O₃ nanoparticles. Further, synthesized product confirmation studies were employed from X-ray diffraction, UV-vis spectrometry, Fourier-transform infrared, Raman, scanning electron microscope and transmission electron microscope studies. The rhombohedral nanoparticles developed were enhanced photocatalytic action. Photocatalytic dye degradation studies were analyzed for prepared three samples and the photocatalytic efficacy of the obtained photocatalysts was compared experimentally. Methylene blue dye was degraded under UV-light irradiation with 364 nm. The results showed that 4% Co doped α-Fe₂O₃ sample exhibited better dye degradation with 92% efficiency. The 4% doping of cobalt ions enhanced the photocatalytic property of Fe₂O₃ and is a good candidate for methylene blue dye degradation above 90%. In addition, strategy for photocatalytic efficiency enhancement was proposed.

Efficient activation of peroxymonosulfate by composites containing iron mining waste and graphitic carbon nitride for the degradation of acetaminophen

In this work, the potential to use an iron mining waste (IW), rich in α-Fe₂O₃ and α-FeOOH, for the development of composites based on graphitic carbon nitride (CN) is demonstrated. These materials were synthesized through a simple thermal treatment at 550 °C of a mixture containing melamine and different IW mass percentages, giving rise to the catalysts xIWCN (where x is related to the initial mass percentage of IW). The iron phases of the precursor were partially transformed throughout the formation of the composites, in such a way that a mixture of α-Fe₂O₃ and γ-Fe₂O₃ was observed in their final composition. Furthermore, structural defects were produced in the carbonaceous matrix of the materials, causing the fragmentation of g-C₃N₄ and an increase of surface area. The catalytic activities of these composites were evaluated in reactions of peroxymonosulfate activation for the degradation of paracetamol. Among these materials, the composite 20IWCN showed the best catalytic activity, being able to degrade almost 90 % of the total paracetamol in only 20 min of reaction. This catalyst also demonstrated high chemical stability, being successfully utilized in five consecutive reaction cycles, with negligible iron leaching.

Anion-Dominated Copper Salicyaldimine Complexes-Structures, Coordination Mode of Nitrate and Decolorization Properties toward Acid Orange 7 Dye

A salicyaldimine ligand, 3-tert-butyl-4-hydroxy-5-(((pyridin-2-ylmethyl)imino)methyl)benzoic acid (H₂L_salpyca) and two Cu(II)−salicylaldimine complexes, [Cu(HL_salpyca)Cl] (1) and [Cu(HL_salpyca)(NO₃)]_n (2), have been synthesized. Complex 1 has a discrete mononuclear structure, in which the Cu(II) center is in a distorted square-planar geometry made up of one HL_salpyca⁻ monoanion in an NNO tris-chelating mode and one Cl⁻ anion. Complex 2 adopts a neutral one-dimensional zigzag chain structure propagating along the crystallographic [010] direction, where the Cu(II) center suits a distorted square pyramidal geometry with a τ value of 0.134, consisted of one HL_salpyca⁻ monoanion as an NNO tris-chelator and two NO₃⁻ anions. When the Cu∙∙∙O semi coordination is taken into consideration, the nitrato ligand bridges two Cu(II) centers in an unsymmetrical bridging-tridentate with a μ, κ⁴O,O′:O′,O″ coordination. Clearly, anion herein plays a critical role in dominating the formation of discrete and polymeric structures of copper salicyaldimine complexes. Noteworthy, complex 2 is insoluble but highly stable in H₂O and various organic solvents (CH₃OH, CH₃CN, acetone, CH₂Cl₂ and THF). Moreover, complex 2 shows good photocatalytic degradation activity and recyclability to accelerate the decolorization rate and enhance the decolorization performance of acid orange 7 (AO7) dye by hydrogen peroxide (H₂O₂) under daylight.

Novel quantification of formation trend and reaction efficiency of hydroxyl radicals for investigating photocatalytic mechanism of Fe-doped TiO2 during UV and visible light-induced degradation of acid orange 7

A detailed mechanistic investigation of the hydroxyl radical (•OH) formation and organic pollutant degradation over transition metal-doped and undoped TiO₂ photocatalysts was performed by the quantitative measurement of •OH and the identification of intermediate products under various experimental conditions. The Fe-doped TiO₂ as a typical subject was prepared, characterized and used to degrade an azo dye Acid Orange 7 (AO7). It is indicated that the enhanced photocatalytic activity of Fe-doped TiO₂ for AO7 degradation was attributed to the increase in surface area, the facilitated charge transfer via Fe-dopant, and a red shift of absorbable wavelength, maintaining a great formation of •OH under visible irradiation. The oxidation of H₂O by holes was estimated as the major pathway of •OH formation rather than the reduction of dissolved O₂ by electrons, and their formation trends reached to approximately 75% and 25%, respectively. Meanwhile the synergistic effect of Fe-dopant produced nearly 10% of extra •OH by visible light photoactivation. The intermediate products and pathways of AO7 degradation varied greatly with different photocatalysts and conditions of the process, involving several reaction mechanisms such as the azo bond cleaving, naphthalene oxidation, desulfonation, and hydroxylated products generation. Through the quantification of •OH-reacted efficiency we proposed, a stoichiometry of •OH affecting overall reaction mechanisms in the TiO₂-assisted photodegradation of AO7 was further established. This study can provide new insights on how to better clarify the variation regularity of organic pollutant degradation from different treatments of the •OH-based advanced oxidation processes.

Synergistic degradation of acid orange 7 dye by using non-thermal plasma and g-C3N4/TiO2: Performance, degradation pathways and catalytic mechanism

In order to harness the full capability of ultraviolet and visible light in the dielectric barrier discharge induced non-thermal plasma (DBD-NTP) process, g-C₃N₄/TiO₂ catalysts were prepared and utilized in this process. Synergistic degradation of acid orange 7 (AO7) dye by DBD-NTP and g-C₃N₄/TiO₂ was conducted, and the performance, degradation pathways and synergistic catalytic mechanism were investigated. The results showed that the degradation rate of AO7 in the DBD-NTP and g-C₃N₄-15/TiO₂ process increased by 39.1% compared with that in the single DBD-NTP process at 12 min discharge time. At 20 W input power, initial concentration of AO7 was 5 mg/L, catalytic dosage was 0.5 g/L, initial pH value was 10.0 and air flow rate was 52 L/h, the degradation rate of AO7 reached 100.0% after 12 min discharge time. Higher discharge power and initial concentration of AO7 inhibited AO7 degradation, whereas increasing the air flow rate and initial pH value of the solution promoted AO7 degradation. The degradation pathways of AO7 consisted of azo structure destruction, ring opening reaction, hydroxylation, carboxylation and mineralization reaction. The results of radical trapping experiment showed that O₂^-, h⁺, OH, O₃ and H₂O₂ were the main reactive species for AO7 degradation in the DBD-NTP and g-C₃N₄-15/TiO₂ process. The Z-scheme photocatalytic mechanism for the g-C₃N₄/TiO₂ catalyst was proposed.

Surface composition and catalytic activity of an iron mining residue for simultaneous degradation of sulfonamide antibiotics

Iron mining residue was evaluated as a potential catalyst for heterogeneous Fenton/photo-Fenton degradation of sulfonamide antibiotics. The residue contained 25% Fe₂O₃ and 8% CeO₂, as determined by X-ray fluorescence spectroscopy, as well as other minor phases such as P₂O₅, SiO₂, and TiO₂. X-ray photoelectron spectroscopy analysis revealed a lower content of iron oxides on the surface, which restricted interaction of the residue with H₂O₂. Despite this limitation and the relatively low specific surface area (26 m² g^-1) of the crude iron mining residue (without any pretreatment), the material presented high catalytic activity for Fenton degradation of sulfonamide antibiotics. The degradation was strongly dependent on the initial pH, showing the highest efficiency at pH 2.5. For this condition, a concentration of sulfathiazole below the detection limit was obtained within 30 min, under black light irradiation and using 0.3 g L^-1 residue, with low H₂O₂ consumption (0.2 mmol L^-1). The residue also provided highly efficient sulfathiazole degradation in the dark, with the concentration of the antibiotic decreasing to an undetectable level after 45 min. Simultaneous degradation of two sulfonamide antibiotics revealed higher recalcitrance of sulfamethazine, compared to sulfathiazole, but the levels of both antibiotics decreased to below the detection limit after 45 min. The residue was very stable, since no significant concentration of soluble iron was detected after the degradation process. Furthermore, high catalytic activity was maintained during up to five cycles, showing the potential of this material for use as a low-cost and environmentally compliant catalyst in Fenton processes.

Heterogeneous Fenton-like catalyst for treatment of rhamnolipid-solubilized hexadecane wastewater

The treatment of wastewater containing hydrophobic organic pollutants solubilized by surfactants is of great environmental importance. In this work, the removal of rhamnolipid-solubilized hexadecane via a salicylic acid-methanol-acetone modified steel converter slag (SMA-SCS) catalyzed Fenton-like process was studied. First, we investigated the adsorption of rhamnolipid and hexadecane onto SCS and SMA-modified SCS. Compared to that of SCS, SMA-SCS exhibited better adsorption performance with maximum adsorption capacities of 0.23 and 0.28 mg/g for hexadecane and rhamnolipid, respectively. Degradation experiments showed that hexadecane was more readily degraded by the Fenton-like process than rhamnolipid. Up to 81.1% of hexadecane removal was achieved over 20 g/L of SMA-SCS within 24 h, whereas only 36% of rhamnolipid was degraded. On the other hand, the results indicated that increased rhamnolipid concentration had a negative effect on the degradation of hexadecane. During the oxidation reaction, the pH value of solution remained between 6.0 and 6.72. All these results demonstrated that the SMA-SCS/H₂O₂ Fenton-like process could be a cost-effective and promising approach for the treatment of surfactant-solubilized hydrophobic organic compounds.

Parameters affecting LED photoreactor efficiency in a heterogeneous photo-Fenton process using iron mining residue as catalyst

In this article, a light-emitting diode (LED)-based photoreactor was designed and evaluated for degradation of the antibiotic sulfathiazole (STZ), using heterogeneous photo-Fenton process with an iron ore residue as catalyst. The effects of the type of magnetic stirrer bar, use of baffles, rotation speed, and type and intensity of irradiation source were evaluated. The results showed that the degradation of STZ was strongly influenced by rotation speed (1100 rpm) and that the use of an octagonal stirrer bar favoured high dispersion and greater contact of the catalyst with the reaction medium. Although the presence of baffles had little influence on STZ degradation, their use enabled good dispersion of the catalyst (due to axial flow) and eliminated the vortex formed at high stirring speeds. It was found that the iron mining residue could be activated by UV LEDs, visible light LEDs, and black light irradiation, with similar degradation efficiencies achieved. Using the LEDs, STZ concentrations below the detection limit were obtained after 40 min, with power consumption 38-fold (UV LEDs) and 22-fold (visible light LEDs) lower than required for black light irradiation. The results demonstrated the advantages of the use of LED devices as irradiation systems in heterogeneous photo-Fenton processes.

Polyaniline-Grafted RuO2-TiO2 Heterostructure for the Catalysed Degradation of Methyl Orange in Darkness

Massive industrial and agricultural developments have led to adverse effects of environmental pollution resisting conventional treatment processes. The issue can be addressed via heterogeneous photocatalysis as witnessed recently. Herein, we have developed novel metal/semi-conductor/polymer nanocomposite for the catalyzed degradation and mineralization of model organic dye pollutants in darkness. RuO2-TiO2 mixed oxide nanoparticles (NPs) were modified with diphenyl amino (DPA) groups from the 4-diphenylamine diazonium salt precursor. The latter was reduced with ascorbic acid to provide radicals that modified the NPs and further served for in situ synthesis of polyaniline (PANI) that resulted in RuO2/TiO2-DPA-PANI nanocomposite catalyst. Excellent adhesion of PANI to RuO2/TiO2-DPA was noted but not in the case of the bare mixed oxide. This stresses the central role of diazonium compounds to tether PANI to the underlying mixed oxide. RuO2-TiO2/DPA/PANI nanocomposite revealed superior catalytic properties in the degradation of Methyl Orange (MO) compared to RuO2-TiO2/PANI and RuO2-TiO2. Interestingly, it is active even in the darkness due to high PANI mass loading. In addition, PANI constitutes a protective layer of RuO2-TiO2 NPs that permitted us to reuse the RuO2-TiO2/DPA/PANI nanocomposite nine times, whereas RuO2-TiO2/PANI and RuO2-TiO2 were reused seven and five times only, respectively. The electronic displacements at the interface of the heterojunction metal/semi-conductor under visible light and the synergistic effects between PANI and RuO2 result in the separation of electron-hole pairs and a reduction of its recombination rate as well as a significant catalytic activity of RuO2-TiO2/DPA/PANI under simulated sunlight and in the dark, respectively.

Pre-magnetization for enhancing the iron-catalyzed activation of peroxymonosulfate via accelerating the corrosion of Fe0

Our findings proved that micron-scale zero-valent iron (mZVI) particles with pre-magnetization combined with peroxymonosulfate (PMS) can markedly enhance the removal of acid orange 7 (AO7). Investigation into the mechanism showed that PMS accelerated the corrosion of ZVI to release Fe²⁺ under acidic conditions, and the in-situ generated Fe²⁺ further activated PMS to produce SO₄•^- and •OH, resulting in AO7 removal. Further, the Lorentz force strengthened the convection in the solution and the field gradient force tended to move Fe²⁺ from a higher to a lower field gradient at the pre-magnetized ZVI (Pre-ZVI) particle surfaces, thus indicating that pre-magnetization promoted the corrosion of ZVI to release Fe²⁺, which resulted in the enhancement of PMS activation. Nano-scale ZVI (nZVI) was more effective than mZVI in activating PMS to degrade AO7, but the pre-magnetization effect on mZVI was better than on nZVI. AO7 removal increased with higher ZVI and PMS dosage, lower AO7 concentration, and acidic conditions (pH = 2, 3). This study helps to understand the reactive radicals-based oxidation process with application of pre-magnetized ZVI in activating PMS.

Different adsorption-degradation behavior of methylene blue and Congo red in nanoceria/H2O2 system under alkaline conditions

The Fenton-like activity of nanoceria has attracted intensive attention for wastewater treatment in recent years. During the Fenton-like reaction, the adsorption of organic pollutants on catalyst surface plays a key role in their degradation. In this work, the adsorption-degradation of methylene blue (MB) and Congo red (CR) in nanoceria/H2O2 system was investigated under alkaline conditions. The MB exhibited weak adsorption on nanoceria surface via electrostatic attraction, while strong Lewis acid-base interactions between CR and cerium ions was observed. Moreover, the adsorption of MB was enhanced in the presence of H2O2 by the formation of surface peroxide species, but an adsorption competition existed between H2O2 and CR. With more Ce3+, CeO2 nanorods could degrade CR efficiently as Fenton-like catalyst. But the degradation of MB catalyzed by ceria was much lower than that of CR in the presence of H2O2.

The use of steel slags in the heterogeneous Fenton process for decreasing the chemical oxygen demand of oil refinery wastewater

The Fenton process is a useful and inexpensive type of advanced oxidation process for industrial wastewater treatment. This study was performed with the aim of using the steel slag as a catalyst in the heterogeneous Fenton process in order to reduce the chemical oxygen demand (COD) of oil refinery wastewater. The effects of various parameters including the reaction time (0.5, 1.0, 2.0, 3.0 and 4.0 h), pH (2.0, 3.0, 4.0, 5.0, 6.0 and 7.0), the concentration of steel slag (12.5, 25.0 and 37.5 g/L), and H₂O₂ concentration (100, 250, 400 and 500 mg/L) on the Fenton process were investigated. Furthermore, the effect of microwave irradiation on the process efficiency was studied by considering the optimum conditions of the mentioned parameters. The results showed that using 25.0 g/L of steel slag and 250 mg/L H₂O₂, at pH = 3.0, could reduce COD by up to 64% after 2.0 h. Also, microwave irradiation decreased the time of the process from 120 min to 25 min in the optimum conditions, but it consumed a high amount of energy. It could be concluded that steel slags had a high potential in the treatment of oil refinery wastewater through the Fenton process.

Simultaneous removal of Cr(VI) and acid orange 7 from water solution by dielectric barrier discharge plasma

A feasibility study was conducted for simultaneous removal of hexavalent chromium (Cr(VI)) and azo dye acid orange 7 (AO7) by the dielectric barrier discharge (DBD) plasma. The results showed that there was a synergistic effect between Cr(VI) reduction and AO7 degradation. The presence of Cr(VI) enhanced the degradation efficiency of AO7. Meanwhile, the removal efficiency of Cr(VI) also increased in the presence of AO7. Under acidic conditions (pH = 3.0), the reduction efficiency of Cr(VI) was higher (approximately 94%). However, the presence of Cr(VI) diminished the effect of pH on the AO7 degradation efficiency. By increasing the input voltage from 80 to 120 V, the removal efficiencies of Cr(VI) and AO7 were observably increased from 54% to 88% and 62% to 89%, respectively. Adding organic matters inhibited the degradation of AO7 and promoted the reduction of Cr(VI). The addition of Cu(II), Co(II), Ni(II), Mn(II) and Fe(III) could inhibit the Cr(VI) reduction, but not significantly affect the degradation of AO7. The degradation intermediates of AO7 were identified by LC-MS/MS system and a possible degradation pathway was proposed. This study showed that the DBD plasma can simultaneously remove Cr(VI) and AO7, which provided a new idea for the actual wastewater treatment.

Core–shell microspheres for the ultrafast degradation of estrogen hormone at neutral pH

In the past few years there has been growing concern about human exposure to endocrine disrupting chemicals. This kind of pollutants can bioaccumulate in aquatic organisms and lead to serious health problems, especially affecting child development. Many efforts have been devoted to achieving the efficient removal of such refractory organics. In this regard, a novel catalyst based on the combination of α-FeOOH and MnO₂@MnCO₃ catalysts has been developed by up-scalable techniques from cheap precursors and tested in the photo-Fenton-like degradation of an endocrine disruptor. Almost total degradation of 17α-ethynylestradiol hormone was achieved after only 2 min of simulated solar irradiation at neutral pH. The outstanding performance of FeOOH@MnO₂@MnCO₃ microspheres was mainly attributed to a larger generation of hydroxyl radicals, which are the primary mediators of the total oxidation for this hormone. This work contributes to the development of more cost-effective systems for the rapid and efficient removal of persistent organic pollutants present in sewage plant effluents under direct solar light.

Ultrafast photo-Fenton degradation of 17α-ethynylestradiol under simulated solar 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.

New insights into the electrochemical behavior of acid orange 7: Convergent paired electrochemical synthesis of new aminonaphthol derivatives

Electrochemical behavior of acid orange 7 has been exhaustively studied in aqueous solutions with different pH values, using cyclic voltammetry and constant current coulometry. This study has provided new insights into the mechanistic details, pH dependence and intermediate structure of both electrochemical oxidation and reduction of acid orange 7. Surprisingly, the results indicate that a same redox couple (1-iminonaphthalen-2(1H)-one/1-aminonaphthalen-2-ol) is formed from both oxidation and reduction of acid orange 7. Also, an additional purpose of this work is electrochemical synthesis of three new derivatives of 1-amino-4-(phenylsulfonyl)naphthalen-2-ol (3a-3c) under constant current electrolysis via electrochemical oxidation (and reduction) of acid orange 7 in the presence of arylsulfinic acids as nucleophiles. The results indicate that the electrogenerated 1-iminonaphthalen-2(1 H)-one participates in Michael addition reaction with arylsulfinic acids to form the 1-amino-3-(phenylsulfonyl)naphthalen-2-ol derivatives. The synthesis was carried out in an undivided cell equipped with carbon rods as an anode and cathode.

Environmental application of millimetre-scale sponge iron (s-Fe0) particles (IV): New insights into visible light photo-Fenton-like process with optimum dosage of H2O2 and RhB photosensitizers

In this study, we firstly develop the photo-Fenton-like system with millimetric sponge iron (s-Fe⁰), H₂O₂, visible light (vis, λ≥420nm) and rhodamine B (RhB), and present a comprehensive study concerning the mechanism. Thus, we investigate (1) the adsorption of RhB onto s-Fe⁰, (2) the photo-Fenton-like removal of RhB over iron oxides generated from the corrosion of s-Fe⁰, (3) the homogeneous photo-Fenton removal of RhB over Fe²⁺ or Fe³⁺, (4) the Fe³⁺-RhB complexes, and (5) the photo-Fenton-like removal of tetrabromobisphenol A (TBBPA). The results show that neither the adsorption process over s-Fe⁰ nor the photo-Fenton-like process over FeOOH, Fe₃O₄ and Fe₂O₃, achieved efficient removal of RhB. For comparison, in homogeneous photo-Fenton process, the presence of Fe³⁺ ions, rather than Fe²⁺ ions, effectively eliminated RhB. Furthermore, the UV-vis spectra showing new absorbance at∼285nm indicate the complexes of RhB and Fe³⁺ ions, adopting vis photons to form excited state and further eject one electron via ligand-to-metal charge-transfer to activate H₂O₂. Additionally, efficient TBBPA removal was obtained only in the presence of RhB. Accordingly, the s-Fe⁰- based photo-Fenton-like process assisted with dyestuff wastewater is promising for removing a series of persistent organic pollutants.

Effect of heterogeneous Fenton-like pre-treatment on anaerobic granular sludge performance and microbial community for the treatment of traditional Chinese medicine wastewater

The effect of a heterogeneous Fenton-like pre-treatment on the anaerobic processes, characteristics and microbial community of sludge was investigated for traditional Chinese medicine (TCM) wastewater containing rhein. When the concentrations of rhein were 50mg/L and 100mg/L, the toxic effect was physiological toxicity for anaerobic granular sludge. Using a single double circle (DC) reactor for the treatment of TCM wastewater containing rhein at concentrations of 15-20mg/L, the chemical oxygen demand (COD) removal rate was 69%, and coenzyme F420 was nearly undetectable in the 3D-excitation-emission matrix (EEM) spectra of soluble microbial products (SMP). The abundances of Methanoregula, Methanobacterium, Methanosphaerula were only 5.57%, 2.39% and 1.08% in the DC reactor, respectively. TCM wastewater containing rhein could be successfully treated by the combination of the heterogeneous Fenton-like pre-treatment and the DC reactor processes, and the COD removal rate reached 95%. Meanwhile, the abundances of Methanoregula, Methanobacterium, Methanosphaerula increased to 22.5%, 18.5%, and 13.87%, respectively. For the bacterial community, the abundance of Acidobacteria_Gp6 decreased from 6.99% to 1.07%, while the abundances of Acidobacteria_Gp1 and Acidobacteria_Gp2 increased from 1.61% to 6.55% and from 1.28% to 5.87%, respectively.