Degradation of Orange G Using PMS Triggered by NH2-MIL-101(Fe): An Amino-Functionalized Metal-Organic Framework

As an azo dye, OG has toxic and harmful effects on ecosystems. Therefore, there is an urgent need to develop a green, environmentally friendly, and efficient catalyst to activate peroxymonosulfate (PMS) for the degradation of OG. In this study, the catalysts MIL-101(Fe) and NH2-MIL-101(Fe) were prepared using a solvothermal method to carry out degradation experiments. They were characterized by means of XRD, SEM, XPS, and FT-IR, and the results showed that the catalysts were successfully prepared. Then, a catalyst/PMS system was constructed, and the effects of different reaction systems, initial pH, temperature, catalyst dosing, PMS concentration, and the anion effect on the degradation of OG were investigated. Under specific conditions (100 mL OG solution with a concentration of 50 mg/L, pH = 7.3, temperature = 25 °C, 1 mL PMS solution with a concentration of 100 mmol/L, and a catalyst dosage of 0.02 g), the degradation of OG with MIL-101(Fe) was only 36.6% within 60 min; as a comparison, NH2-MIL-101(Fe) could reach up to 97.9%, with a reaction constant k value of 0.07245 min-1. The NH2-MIL-101 (Fe)/PMS reaction system was able to achieve efficient degradation of OG at different pH values (pH = 3~9). The degradation mechanism was analyzed using free-radical quenching tests. The free-radical quenching tests showed that SO4•-, •OH, and 1O2 were the main active species during the degradation of OG.

The Performance Evaluation of Meso-Tetraphenyl Porphyrin and Azo Dyes as Photosensitizers in Dye-sensitized Solar Cells

The photovoltaic properties of five different mono-azo function and meso-tetraphenyl porphyrin dyes have been investigated by computational DFT/TDDFT calculations and measurement of the J-V properties of their cells. The photovoltaic efficiency of the cells based on these dyes were determined by both experimental and theoretical methods. The efficiency-to-cost ratios of the azo-dye cells showed that they could be cheaper substitutes to porphyrin-based cells. Eriochrome blue black (EBB) and eriochrome black T (EBT) cells were shown to possess the best photovoltaic properties by the two methods employed (theory and experiment). The presence of two naphthol moieties at both ends of their -N = N- group has been adduced as possible reason for their relatively outstanding performance. The extremely low efficiency-to-cost ratio obtained for cell-POR suggests that the use of porphyrin as sensitizer may not be as economically viable as some azo dyes. MTO, EBB and EBT were found to be the most cost-effective among the investigated dyes. The porphyrin's low performance may have been amplified by the absence of an effective anchor group in its molecular structure.

Orange G degradation by heterogeneous peroxymonosulfate activation based on magnetic MnFe2O4/α-MnO2 hybrid

Wastewater containing an azo dye Orange G (OG) causes massive environmental pollution, thus it is critical to develop a highly effective, environmental-friendly, and reusable catalyst in peroxymonosulfate (PMS) activation for OG degradation. In this work, we successfully applied a magnetic MnFe₂O₄/α-MnO₂ hybrid fabricated by a simple hydrothermal method for OG removal in water. The characteristics of the hybrid were investigated by X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, Brunauer-Emmett-Teller method, vibrating sample magnetometry, electron paramagnetic resonance, thermogravimetric analysis, and X-ray photoelectron spectroscopy. The effects of operational parameters (i.e., catalytic system, catalytic dose, solution pH, and temperature) were investigated. The results exhibited that 96.8% of OG degradation was obtained with MnFe₂O₄/α-MnO₂(1:9)/PMS system in 30 min regardless of solution pH changes. Furthermore, the possible reaction mechanism of the coupling system was proposed, and the degradation intermediates of OG were identified by mass spectroscopy. The radical quenching experiments and EPR tests demonstrated that SO₄^•̶, O₂^•̶, and ¹O₂ were the primary reactive oxygen species responsible for the OG degradation. The hybrid also displayed unusual stability with less than 30% loss in the OG removal after four sequential cycles. Overall, magnetic MnFe₂O₄/α-MnO₂ hybrid could be used as a high potential activator of PMS to remove orange G and maybe other dyes from wastewater.

Orange G is a potential inhibitor of human insulin amyloid fibrillation and can be used as a probe to study mechanism of amyloid fibrillation and its inhibition

The extracellular insoluble deposits of highly ordered cross-β-structure-containing amyloid fibrils form the pathological basis for protein misfolding diseases. As amyloid fibrils are cytotoxic, inhibition of the process is a therapeutic strategy. Several small molecules have been identified and used as fibrillation inhibitors in the recent past. In this work, we investigate the effect of Orange G on insulin amyloid formation using fluorescence-based assays and negative-stain electron microscopy (EM). We show that Orange G effectively attenuates nucleation, thereby inhibiting amyloid fibrillation in a dose-dependent manner. Fluorescence quenching titrations of Orange G showed a reasonably strong binding affinity to native insulin. Binding isotherm measurements revealed the binding of Orange G to pre-formed insulin fibrils too, indicating that Orange G likely binds and stabilizes the mature fibrils and prevents the release of toxic oligomers which could be potential nuclei or templates for further fibrillation. Molecular docking of Orange G with native insulin and amyloid-like peptide structures were also carried out to analyse the contributing interactions and binding free energy. The findings of our study emphasize the use of Orange G as a molecular probe to identify and design inhibitors of amyloid fibrillation and to investigate the structural and toxic mechanisms underlying amyloid formation.

Photocatalytic Degradation of Orange G Dye by Using Bismuth Molybdate: Photocatalysis Optimization and Modeling via Definitive Screening Designs

In the current study, Bismuth molybdate was synthesized using simple co-precipitation procedure, and their characterization was carried out by various methods such as FT-IR, SEM, and P-XRD. Furthermore, the photocatalytic degradation of Orange G (ORG) dye using synthesized catalyst under visible light irradiation was studied. Response surface Method was used for the optimization of process variables and degradation kinetics evaluated by modeling of experimental data. Based on the experimental design outcomes, the first-order model was proven as a practical correlation between selected factors and response. Further ANOVA analysis has revealed that only two out of six factors have a significant effect on ORG degradation, however ORG concentration and irradiation time indicated the significant effects sequentially. Maximum ORG degradation of approximately 96% was achieved by keeping process parameters in range, such as 1 g L-1 loading of catalyst, 50 mg L-1 concentration of ORG, 1.4 mol L-1 concentration of H2O2 at pH 7 and a temperature of 30 °C. Kinetics of ORG degradation followed the pseudo first order, and almost complete degradation was achieved within 8 h. The effectiveness of the Bi2MoO6/H2O2 photo-Fenton system in degradation reactions is due to the higher number of photo-generated e- available on the catalyst surface as a result of their ability to inhibit recombination of e- and h+ pair.

Role of weak magnetic field for enhanced oxidation of orange G by magnetic Fenton

The role of weak magnetic field (WMF) on the degradation of a common textile azo-dye, orange G (OG), by magnetic Fenton system was investigated in detail. The results showed that the presence of WMF can provide better performance of the Fe₃O₄/H₂O₂ system for OG degradation. The optimized reaction conditions were contained at 1 mM Fe₃O₄ as Fe, 20 mT of magnetic field intensity, 20 mM H₂O₂, and initial pH of 3.0. The removal efficiency of OG by Fe₃O₄/H₂O₂ coupling with WMF increased largely from 56.3 to 82.3% compared with Fe₃O₄/H₂O₂ process. Both the electron paramagnetic resonance (EPR) analysis and the quenching effect of tert-butyl alcohol (TBA) confirmed that hydroxyl radical (•OH) was the primary reactive oxygen species in WMF-Fe₃O₄/H₂O₂ system. The improving effect of WMF was explained by the magnetoconvection theory. The presence of WMF could accelerate the corrosion rate of Fe₃O₄ and thus promoted the release of Fe(II), which led to the increased production of •OH and enhanced the degradation of OG. Moreover, it was surprising to observe that the WMF induced improvement in OG degradation by heterogeneous Fenton involving the iron sludge, namely FeOOH and Fe₂O₃, as catalysts. These results indicated that WMF could be utilized as an efficient and cost-effective strategy to improve the removal of organic pollutants by iron oxide-based Fenton process.

Characterization and performance evaluation of synthesized ZnO nanoflowers, nanorods, and their hybrid nanocomposites with graphene oxide for degradation of Orange G

Nanoflowers and nanorods of ZnO were synthesized via hydrothermal route. These morphologies of zinc oxide (ZnO) were then decorated over graphene oxide (GO) to yield hybrid nanocomposites, namely, GO-ZnO_nR and GO-ZnO_nF. The decoration of ZnO nanorods and nanoflowers on GO layers was confirmed through FESEM images. The synthesized nanocomposites were subjected to degrade the Orange G under identical conditions. The band gap energies determined using diffused reflectance spectra were 2.87, 2.89 eV for GO-ZnO_nR, and GO-ZnO_nF, whereas, for both ZnO_nR and ZnO_nF, it was 3.14 eV. For 50 min of UV irradiations (at 6 pH), 100% degradation was achieved corresponding to GO-ZnO_nR (44.1 m² g^-1) followed by 90.1%, 70.2%, and 68.3% with GO-ZnO_nF (35.9 m² g^-1), ZnO_nR (20 m² g^-1), and ZnO_nF (15.1 m² g^-1), respectively. Significant boost in the degradation of Orange G, with GO-ZnO_nR, was attributed to its reduced band gap, higher surface area, and enhanced charge separation. Kinetic study confirms the pseudo-first-order reaction rate. Mineralization efficiency of 91% in 120 min indicated the efficient reduction of Orange G and its intermediates. Further, reactive species trapping experiments revealed that photo-induced ^•OH are dominant radicals for the degradation followed by ^•O₂^- and h⁺. Liquid chromatography mass spectra data has been used to predict the plausible reaction pathways. Reusability studies indicated that GO-ZnO_nR can be used for four successive degradation cycles, without any significant activity loss.

Ligninolytic Enzyme Production and Decolorization Capacity of Synthetic Dyes by Saprotrophic White Rot, Brown Rot, and Litter Decomposing Basidiomycetes

An extensive screening of saprotrophic Basidiomycetes causing white rot (WR), brown rot (BR), or litter decomposition (LD) for the production of laccase and Mn-peroxidase (MnP) and decolorization of the synthetic dyes Orange G and Remazol Brilliant Blue R (RBBR) was performed. The study considered in total 150 strains belonging to 77 species. The aim of this work was to compare the decolorization and ligninolytic capacity among different ecophysiological and taxonomic groups of Basidiomycetes. WR strains decolorized both dyes most efficiently; high decolorization capacity was also found in some LD fungi. The enzyme production was recorded in all three ecophysiology groups, but to a different extent. All WR and LD fungi produced laccase, and the majority of them also produced MnP. The strains belonging to BR lacked decolorization capabilities. None of them produced MnP and the production of laccase was either very low or absent. The most efficient decolorization of both dyes and the highest laccase production was found among the members of the orders Polyporales and Agaricales. The strains with high MnP activity occurred across almost all fungal orders (Polyporales, Agaricales, Hymenochaetales, and Russulales). Synthetic dye decolorization by fungal strains was clearly related to their production of ligninolytic enzymes and both properties were determined by the interaction of their ecophysiology and taxonomy, with a more relevant role of ecophysiology. Our screening revealed 12 strains with high decolorization capacity (9 WR and 3 LD), which could be promising for further biotechnological utilization.

Functionalized Graphene Derivatives and TiO2 for High Visible Light Photodegradation of Azo Dyes

Functionalized graphene derivatives including graphene oxide (GO), reduced graphene oxide (rGO), and heteroatom (nitrogen/sulphur (N/S) or boron (B))-doped graphene were used to synthesize composites with TiO₂ (T). The photocatalytic performance of composites was assessed for the degradation of Orange G dye (OG) under simulated solar light. All the prepared graphene derivatives—TiO₂ composites showed better photocatalytic performance than bare TiO₂. A higher photocatalytic activity was found for the composites containing GO and N/S co-doped rGO (k_app = 109.2 × 10⁻³ and 48.4 × 10⁻³ min⁻¹, for GO-T and rGONS-T, respectively). The influence of both initial solution pH and the reactive species involved in the OG degradation pathway were studied. The photocatalytic activity of the samples decreased with the increase of the initial pH (from 3.0 to 10.0) due to the occurrence of electrostatic repulsive forces between the photocatalysts surface and the molecules of OG, both negatively charged. The use of selective scavengers showed that although the photogenerated holes dominate the degradation mechanism, radicals and singlet oxygen also participate in the OG degradation pathway. In addition, reutilization experiments indicated that the samples were stable under the reaction conditions used.

Functionalized Cellulose for the Controlled Synthesis of Novel Carbon-Ti Nanocomposites: Physicochemical and Photocatalytic Properties

Carbon-Ti nanocomposites were prepared by a controlled two-step method using microcrystalline cellulose as a raw material. The synthesis procedure involves the solubilization of cellulose by an acid treatment (H3PO4 or HNO3) and the impregnation with the Ti precursor followed of a carbonization step at 500 or 800 °C. The type of acid treatment leads to a different functionalization of cellulose with phosphorus- or oxygen-containing surface groups, which are able to control the load, dispersion and crystalline phase of Ti during the composite preparation. Thus, phosphorus functionalities lead to amorphous carbon-Ti composites at 500 °C, while TiP2O7 crystals are formed when prepared at 800 °C. On the contrary, oxygenated groups induce the formation of TiO2 rutile at an unusually low temperature (500 °C), while an increase of carbonization temperature promotes a progressive crystal growth. The removal of Orange G (OG) azo dye in aqueous solution, as target pollutant, was used to determine the adsorptive and photocatalytic efficiencies, with all composites being more active than the benchmark TiO2 material (Degussa P25). Carbon-Ti nanocomposites with a developed micro-mesoporosity, reduced band gap and TiO2 rutile phase were the most active in the photodegradation of OG under ultraviolet irradiation.

Role of exposed facets and surface OH groups in the Fenton-like reactivity of lepidocrocite catalyst

Heterogeneous Fe-based Fenton-like reaction is an efficient technology in wastewater treatment. However, few studies reveal the effects of exposed facets and surface OH groups of iron oxides on its reactivity. In this study, two lepidocrocite samples with lath- and rod-like morphologies were synthesized and applied to the adsorption and degradation of Orange G (OG). The OG molecule could be adsorbed vertically on the lath-like sample by the interaction with the μ-OH groups of the (010) facet. The molecule could also be adsorbed laterally on the rod-like sample by the interactions with the μ-OH and μ₃-OH groups of the (010) and (001) facets. When the data were normalized to the unit surface area, the adsorption capacity of OG, the production efficiency of OH, the degradation rate in dark, and the total degradation rates under visible light irradiation in the lath-like system were 9.625-, 3.34-, 2.75-, and 1.98-fold higher than those in the rod-like system, respectively.

A dual TiO2/Ti-stainless steel anode for the degradation of orange G in a coupling photoelectrochemical and photo-electro-Fenton system

A dual-anode consists of stainless steel and TiO₂/Ti electrodes is used to study the kinetics of the degradation of hazardous chemicals exemplified by azo dye orange G (OG) using a coupling photoelectrochemical catalytic and photoelectro-Fenton (PEC/PEF) system. Concurrent generation of hydroxyl radicals on the TiO₂/Ti photocatalyst and in-situ generation of Fenton reagents on the stainless steel electrode greatly enhances the performance of the PEC/PEF electrodes over that of the PEC and the PEF alone process. The efficiency of the PEC/PEF process is a function of Fe²⁺ and H₂O₂ concentration OH⋅ in the solution bulk, which promotes the oxidative degradation of OG and its byproducts. The mean carbon oxidation state (COS) is estimated to reflect the degree of mineralization. Based on the pseudo first-order kinetics with respect to OH, OG, Fe²⁺, the corresponding reaction rates is established. UV-Vis spectrometry reveals the presence of four major intermediates, which helps establish the OG degradation pathways.

Efficient degradation of Orange G with persulfate activated by recyclable FeMoO4

In this study, FeMoO₄ was applied to activate persulfate (PS, S₂O₈^2-) for azo dye Orange G (OG) degradation. The catalyst was characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS) and nitrogen adsorption-desorption isotherms. FeMoO₄ showed excellent efficiency in activating PS for OG removal. More than 95% could be removed after 40 min under reaction conditions of 4 mM PS, 0.3 g L^-1 FeMoO₄ and 0.2 mM OG. The effect of different parameters (PS doses, FeMoO₄ doses and pH) were evaluated. The results showed that acid condition provided higher efficiency and overdosing FeMoO₄ and PS presented a scavenging effect. Major intermediates were identified and possible degradation pathway was proposed. Recycle tests presented that FeMoO₄ had excellent recyclable stability in activating PS for OG removal. Sulfate radicals and hydroxyl radicals all occurred in the oxidation reactions and the former came first. The oxidation reaction was involved in the translation of Fe²⁺/Fe³⁺ occurred on the surface layer. This study revealed that the FeMoO₄/PS system is a very promising method for degrading organic contaminants in the environment.

Effective degradation of Orange G and Rhodamine B by alkali-activated hydrogen peroxide: roles of HO2- and O2·

Advanced oxidation processes offer effective solutions in treating wastewater from various industries. The process of alkali-activated hydrogen peroxide (H₂O₂) was superior for the treatment of alkaline dye wastewater because no additional reagents were required except H₂O₂. However, an important and interesting phenomenon had been observed that the primary reactive species were found different for degrading organic pollutants with the process of alkali-activated H₂O₂. Azo dye of Orange G (OG) and triphenylmethane dye of Rhodamine B (RhB) were chosen as the target organic pollutants. The influences of various parameters on OG and RhB degradation by alkali-activated H₂O₂ were evaluated. Furthermore, different scavengers, including ascorbic acid, methanol, t-butanol, isopropyl alcohol, furfuryl alcohol, and nitro blue tetrazolium, have been tested to identify the active species involved in dye degradation, and it was found that O₂^·- was mainly responsible for degrading OG, while HO₂^- anion was the primary oxidant for degrading RhB.

On the Interactions and Synergism between Phases of Carbon⁻Phosphorus⁻Titanium Composites Synthetized from Cellulose for the Removal of the Orange-G Dye

Carbon–phosphorus–titanium composites (CPT) were synthesized by Ti-impregnation and carbonization of cellulose. Microcrystalline cellulose used as carbon precursor was initially dissolved by phosphoric acid (H₃PO₄) to favor the Ti-dispersion and the simultaneous functionalization of the cellulose chains with phosphorus-containing groups, namely phosphates and polyphosphates. These groups interacted with the Ti-precursor during impregnation and determined the interface transformations during carbonization as a function of the Ti-content and carbonization temperature. Amorphous composites with high surface area and mesoporosity were obtained at low Ti-content (Ti:cellulose ratio = 1) and carbonization temperature (500 °C), while in composites with Ti:cellulose ratio = 12 and 800 °C, Ti-particles reacted with the cellulose groups leading to different Ti-crystalline polyphosphates and a marked loss of the porosity. The efficiency of composites in the removal of the Orange G dye in solution by adsorption and photocatalysis was discussed based on their physicochemical properties. These materials were more active than the benchmark TiO₂ material (Degussa P25), showing a clear synergism between phases.

Study of interaction between ionic liquids and orange G in aqueous solution with UV-vis spectroscopy and conductivity meter

The interactions between Orange G (OG) with three kinds of ionic liquid surfactants (C₁₀mimBF₄, C₁₂mimBF₄, C₁₆mimBF₄) and CTAB were studied with UV-Vis spectra and conductivity measurements. The systematic changes in UV-Vis spectra with an increase of carbon-chain length may be observed in presence of OG. They correspond to CMC of every system, respectively, and the CMCs of four systems have exhibit the decrease of CMCs compared to pure surfactant. The binding constants are calculated from the results of conductivity measurements in the order of C₁₆mimBF₄>CTAB>C₁₂mimBF₄>C₁₀mimBF₄. Furthermore, system behaviors presented significant association of complex formation and micelles formation, i.e. the change in UV-Vis spectra before and after the formation of micelles in mixed systems. In addition, Fourier-transform infrared (FT-IR) spectroscopy and ¹H NMR analysis further confirmed that the complexes are formed by hydrogen bond and van der Waal force. These findings could provide scientific guidance for extraction and separation of dyes.

Degradation of Orange G by Fenton-like reaction with Fe-impregnated biochar catalyst

This study was conducted to evaluate the catalytic activity of Fe-impregnated sugarcane biochar (FSB) for removing azo dye Orange G (OG) from solution under various Fenton-like oxidation conditions. The optimum molar Fe concentration for impregnation to achieve maximum catalytic activity of FSB in Fenton-like reaction with acceptable effluent Fe release was 0.25 M (163.4 Fe mg/g in FSB). High removal efficiency of 99.7% was achieved within 2 h of reaction at optimum conditions of 0.075 g/L H₂O₂, 0.5 g/L FSB for 0.1 g/L OG at initial pH 5.5 under 25 °C. For every 10 °C increase, the time for maximum OG degradation efficiency decreased by 0.5 h. The OG removal by FSB exhibited a slow induction reaction followed by fast OG decomposition. FSB can be used successively for at least 4 runs with >89.3% OG removal. The FSB was more economical, efficient, and recyclable than other conventional Fenton oxidation catalysts.

Magnetic EDTA functionalized CoFe2O4 nanoparticles (EDTA-CoFe2O4) as a novel catalyst for peroxymonosulfate activation and degradation of Orange G

EDTA functionalized CoFe₂O₄ nanoparticles (EDTA-CoFe₂O₄) synthesized using a facile one-pot solvothermal method were employed as catalysts to activate peroxymonosulfate (PMS) with Orange G (OG) as the target pollutant. Effects of operating parameters including initial solution pH, catalyst dosage, PMS dosage, and water matrix components such as Cl^-, NO₃^-, CO₃^2-, and humic acid were evaluated. A degradation efficiency of 93% was achieved in 15 min with 1 mM PMS and 0.2 g/L EDTA-CoFe₂O₄ catalyst, while only 57% of OG was degraded within 15 min in CoFe₂O₄/PMS system. The degradation of OG followed pseudo-first-order kinetics, and the apparent first-order date constant (k _obs) for OG in EDTA-CoFe₂O₄/PMS and CoFe₂O₄/PMS system was determined to be 0.152 and 0.077 min^-1, respectively. OG degradation by EDTA-CoFe₂O₄/PMS was enhanced with the increase of catalyst and PMS doses at respective range of 0.1-2.0 g/L and 0.5-10.0 mM. Higher efficiency of OG oxidation was observed within a wide pH range (3.0-9.0), implying the possibility of applying EDTA-CoFe₂O₄/PMS process under environmental realistic conditions. Humic acid (HA) at low concentration accelerated the removal of OG; however, a less apparent inhibitive effect was observed at HA addition of 10 mg/L. The k _obs value was found to decrease slightly from 0.1601 to 0.1274, 0.1248, and 0.1152 min^-1 with the addition of NO₃^-, CO₃^2-, and Cl^-, respectively, but near-complete removal of OG could still be obtained after 15 min. Both of the sulfate radicals and hydroxyl radicals were produced in the reaction, and sulfate radicals were the dominant according to the scavenging tests and electron paramagnetic resonance (EPR) tests. Finally, a degradation mechanism was proposed, and the stability and reusability of the EDTA-CoFe₂O₄ were evaluated.

Rapid decolorization of dye Orange G by microwave enhanced Fenton-like reaction with delafossite-type CuFeO2

Bimetallic oxide CuFeO₂ as a new heterogeneous catalyst has shown much higher catalytic ability for activating peroxide than single-metal oxides. The present work demonstrated a synergistic microwave (MW) enhanced Fenton-like process with CuFeO₂ for rapid decolorization of azo dye Orange G (OG). The MW irradiation dramatically enhanced the OG degradation efficiency, achieving 99.9% decolorization within 15min at pH5. The XRD analysis of reused CuFeO₂, together with metal leaching tests, indicated merits of recycling for CuFeO₂. The subsequent surface element analysis by XPS for fresh and used CuFeO₂ showed a complex network for reactions between copper-iron redox pairs and surface hydroxyl groups, leading to a synergistic Fenton-like system accelerated by MW irradiation. In the CuFeO₂ initiated Fenton-like reactions, several oxidant species (i.e., OH, O₂^-, electron hole, and Fe^IVO) responsible to the OG oxidation were identified by quenching experiments, showing the MW generated high temperature and "hot spots" enhanced the yield of OH by generation of electron-hole pairs. Further, the 26 detected degradation products confirmed the OH dominant oxidation of OG. This study shows that the MW-enhanced Fenton-like reaction using CuFeO₂ has potential applications for rapid decolorization of dye effluent.

A novel magnetic nanoscaled Fe3O4/CeO2 composite prepared by oxidation-precipitation process and its application for degradation of orange G in aqueous solution as Fenton-like heterogeneous catalyst

In this work, magnetic nanoparticles (MNPs) Fe₃O₄/CeO₂ were firstly synthesized using three different preparation methods, including coprecipitation, impregnation oxidation-precipitation and impregnation reduction-precipitation, respectively. The catalytic activities of Fe₃O₄/CeO₂ MNPs, prepared by above three methods, were compared systematically in terms of the degradation of orange G (OG). The impregnation oxidation-precipitation process was economical and maneuverable due to the usage of air, no need of nitrogen protection and higher utilization efficiency of iron. Response surface methodology based on central composite design were used to investigate the individual and interactive effects of three process parameters on the OG degradation, i.e. the initial pH of the solution, the dosage of H₂O₂ and the initial concentration of OG. Under the optimal conditions of pH 2.5, H₂O₂ 30 mM, OG 50 mg L^-1, catalyst 2.0 g L^-1 and 35 °C, the degradation percentage of OG was 98.2% within 120 min, which agreed well with the modeling prediction (R² = 0.9984, and Adj-R² = 0.9969). And the degradation reaction well followed the first-order kinetic with R² = 0.9969. The Fe₃O₄/CeO₂-OX MNPs showed high catalytic activity, stability and reusability in the degradation of OG.

[Activated Carbon Supported Co3O4 Catalysts to Activate Peroxymonosulfate for Orange G Degradation]

Activated carbon supported cobalt catalysts (Co/AC) were prepared through wet impregnation and high temperature calcination methods. The X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) characterization results showed that Co₃O₄ was the major form of Co species distributed on AC. The performance of Co/AC was evaluated as catalyst to activate peroxymonosulfate (PMS) to produce sulfate radicals (SO₄^-·) for Orange G (OG) degradation in solution. The activation mechanism and several influential factors were also investigated. The results demonstrated that SO₄^-·played a dominant role in OG degradation. And the degradation efficiency of OG increased with increasing Co/AC dosage, higher PMS concentration or elevating reaction temperature. Initial pH had a significant effect on OG degradation, with pH range of 4 to 8 as the optimal pH for degradation. In addition, the strong acidic or alkaline conditions were unfavorable for OG degradation. A dual effect of chloride ions (Cl^-) was observed. The high Cl^- concentration promoted degradation, while low concentration led to inhibition. The Co/AC also exhibited excellent reusability and its activating performance toward PMS was still observed after 6 rounds of tests. Finally, the degradation process and intermediate products of OG were analyzed with UV-visible spectroscopy and gas chromatography-mass spectrometry (GC/MS).

[Kinetics for Degradation of Orange G with Peroxymonosulfate Activated by Carbon Nanotubes]

Carbon nanotube (CNT) was used as an activator to activate peroxymonosulfate (PMS) to degrade azo dye orange G (OG) in aqueous solution. The results indicated that CNT exhibited a much better performance in activating PMS to decolorize OG than activated carbon (GAC), with 99% decolorization of OG achieved within 45 min. Afterwards, the degradation mechanism of OG in CNT activated PMS system was explored, and SO₄^-·was found to be dominantly responsible for OG degradation, which mainly took place on the surface of CNT. Effects of various factors, including temperatures, initial concentration of OG, CNT loadings, PMS dosage, and initial pH, on degradation of OG were then investigated, and OG degradation in these cases well conformed to first-order kinetics. From the analysis of UV-vis spectra of OG during the reaction, the peaks at 479 nm and 330 nm were found to be significantly decreased, suggesting that the azo band and naphthaline ring were destructed, respectively. Finally, TOC analysis indicated that a certain degree of OG mineralization was obtained in CNT activated PMS system.

Synthesis, characteristics and sonocatalytic activities of calcined γ-Fe2O3 and TiO2 nanotubes/γ-Fe2O3 magnetic catalysts in the degradation of Orange G

In this work, γ-Fe2O3 and TiO2 NTs/γ-Fe2O3 composites with good magnetism and sonocatalytic activity were prepared by a facile polyol method and utilize the principle of isoelectric point method, respectively. The structural and magnetic features of the prepared calcined γ-Fe2O3 and composite catalysts were investigated by transmission electron microscopy (TEM), powder X-ray diffraction (XRD), surface analysis, UV-Vis diffuse reflectance spectra (UV-Vis DRS), vibrating sample magnetometry (VSM) and zeta potential analysis. The effects of calcination temperature on γ-Fe2O3 phase variation, physical properties and sonocatalytic properties were investigated. The porosity, specific surface area, band gap energy and sonocatalytic activity of γ-Fe2O3 were gradually decreased with calcination temperature increased. TiO2 NTs/γ-Fe2O3 with appropriate composition and specific structural features possess synergetic effects such as efficient separation of charge carriers and hydroxyl radicals produced by heterogeneous fenton and fenton-like reactions. This enhanced the sonocatalytic activity for the degradation of Orange G under ultrasonic irradiation. The sonocatalytic reactions obeyed pseudo first-order kinetics. All these information provide insight into the design and development of high-efficiency catalyst for wastewater treatment.

Anodic fabrication of advanced titania nanotubes photocatalysts for photoelectrocatalysis decolorization of Orange G dye

Titania nanotubes (TNTs) were fabricated on Ti mesh substrates by the anodizing technique. The effects of preparation variables, such as anodizing voltage, time and calcination temperature on the textural characteristics and photocatalytic activity of TNTs were investigated. The surface morphology, crystalline phase, and chemical composition were analyzed using field emission-scanning electron microscopy and X-ray diffraction. The photo-electrochemical properties of TNTs were examined by voltammetry. The TNTs were tested as a photoanode for advanced oxidation processes, such as photocatalytic, electrocatalytic, and photoelectrocatalytic decolorization of Orange G dye. The well-arranged TNTs electrode prepared in this work showed a high photocurrent density of 101 µA cm(-2) at an optimum length-to-diameter aspect ratio of 31.2. In dye decolorization tests, the electrochemical photocatalytic system using TNTs as the photoanode achieved total decolorization and 64% mineralization under extended reaction time. These results show that TNTs prepared by this method is greatly stable in prolonged use and suitable as a photoanode in the photocatalytic/photoelectrocatalytic treatments of dye wastewater.

Decolorization of azo dyes Orange G using hydrodynamic cavitation coupled with heterogeneous Fenton process

The present work demonstrates the application of the combination of hydrodynamic cavitation (HC) and the heterogeneous Fenton process (HF, Fe(0)/H2O2) for the decolorization of azo dye Orange G (OG). The effects of main affecting operation conditions such as the inlet fluid pressure, initial concentration of OG, H2O2 and zero valent iron (ZVI), the fixed position of ZVI, and medium pH on decolorization efficiency were discussed with guidelines for selection of optimum parameters. The results revealed that the acidic conditions are preferred for OG decolorizaiton. The decolorization rate increased with increasing H2O2 and ZVI concentration and decreased with increasing OG initial concentration. Besides, the decolorization rate was strongly dependent on the fixed position of ZVI. The analysis results of degradation products using liquid chromatography-ESI-TOF mass spectrometry revealed that the degradation mechanism of OG proceeds mainly via reductive cleavage of the azo linkage due to the attack of hydroxyl radical. The present work has conclusively established that the combination of HC and HF can be more energy efficient and gives higher decolorization rate of OG as compared with HC and HF alone.

Decolorization of azo dye Orange G by aluminum powder enhanced by ultrasonic irradiation

In this work, the decolorization of azo dye Orange G (OG) in aqueous solution by aluminum powder enhanced by ultrasonic irradiation (AlP-UI) was investigated. The effects of various operating operational parameters such as the initial pH, initial OG concentration, AlP dosage, ultrasound power and added hydrogen peroxide (H2O2) concentration were studied. The results showed that the decolorization rate was enhanced when the aqueous OG was irradiated simultaneously by ultrasound in the AlP-acid systems. The decolorization rate decreased with the increase of both initial pH values of 2.0-4.0 and OG initial concentrations of 10-80mg/L, increased with the ultrasound power enhancing from 500 to 900W. An optimum value was reached at 2.0g/L of the AlP dosage in the range of 0.5-2.5g/L. The decolorization rate enhanced significantly by the addition of hydrogen peroxide in the range of 10-100mM to AlP-UI system reached an optimum value of 0.1491min(-1). The decolorization of OG appears to involve primarily oxidative steps, the cleavage of NN bond, which were verificated by the intermediate products of OG under the optimal tested degradation system, aniline and 1-amino-2-naphthol-6,8-disulfonate detected by the LC-MS.

Activating persulfate by Fe⁰ coupling with weak magnetic field: performance and mechanism

Weak magnetic field (WMF) and Fe(0) were proposed to activate PS synergistically (WMF-Fe(0)/PS) to degrade dyes and aromatic contaminants. The removal rates of orange G (OG) by WMF-Fe(0)/PS generally decreased with increasing initial pH (3.0-10.0) and increased with increasing Fe(0) (0.5-3.0 mM) or PS dosages (0.5-3.0 mM). Compared to its counterpart without WMF, the WMF-Fe(0)/PS process could induce a 5.4-28.2 fold enhancement in the removal rate of OG under different conditions. Moreover, the application of WMF significantly enhanced the decolorization rate and the mineralization of OG. The degradation rates of caffeine, 4-nitrophenol, benzotriazole and diuron by Fe(0)/PS were improved by 2.1-11.1 fold due to the superimposed WMF. Compared to many other sulfate radical-based advanced oxidation technologies under similar reaction conditions, WMF-Fe(0)/PS technology could degrade selected organic contaminants with much greater rates. Sulfate radical was identified to be the primary radical species responsible for the OG degradation at pH 7.0 in WMF-Fe(0)/PS process. This study unraveled that the presence of WMF accelerated the corrosion rate of Fe(0) and thus promoted the release of Fe(2+), which induced the increased production of sulfate radicals from PS and promoted the degradation of organic contaminants. Employing WMF to enhance oxidation capacity of Fe(0)/PS is a novel, efficient, promising and environmental-friendly method since it does not need extra energy and costly reagents.

Oxidation of Orange G by persulfate activated by Fe(II), Fe(III) and zero valent iron (ZVI)

Persulfate (PS) was employed in the oxidation of Orange G (OG), an azo dye commonly found in textile wastewaters. Activation of PS was conducted with iron to generate sulfate free radicals (SO4(-)) with high redox potential capable to oxidize most of the organics in water. Identification of oxidation intermediates was carried out by analyzing at different times organic by-products generated from treatment of a concentrate dye solution (11.6 mM) with 153 mM of PS and 20 mM of Fe(II) at 20 °C. Intermediate reaction products (mainly phenol (PH) and benzoquinone (BQ), and in less extent aniline, phenolic compounds and naphthalene type compounds with quinone groups) were identified by GC/MS and HPLC, and an oxidation pathway was proposed for the oxidation of OG with iron activated PS. The effect of iron valence (0, II and III) in the oxidation of an aqueous solution of OG (containing 0.1 mM) was studied in a 0.5 L batch reactor at 20 °C. Initial activator and PS concentrations employed were both 1 mM. Complete pollutant removal was achieved within the first 30 min when iron II or III were employed as activators. Quinone intermediates generated during pollutant oxidation may act as electron shuttles, allowing the reduction of Fe(III) into Fe(II) in the redox cycling of iron. Therefore, activation of PS by Fe(III) allowed complete OG removal. When zero valent iron (ZVI) was employed (particle diameter size 0.74 mm) the limiting step in SO4(-) generation was the surface reaction between ZVI and the oxidant yielding a lower oxidation rate of the dye. An increase in the oxidant dosage (0.2 mM OG, 2 mM Fe(III) and 6 mM PS) allowed complete pollutant and ecotoxicity removal, as well as mineralization close to 75%.