Degradation Efficiency Of Acid Orange 7 Research Articles

Understanding the biodegradation pathways of azo dyes by immobilized white-rot fungus, Trametes hirsuta D7, using UPLC-PDA-FTICR MS supported by in silico simulations and toxicity assessment

No biodegradation methods are absolute in the treatment of all textile dyes, which leads to structure-dependent degradation. In this study, biodegradation of three azo dyes, reactive black 5 (RB5), acid blue 113 (AB113), and acid orange 7 (AO7), was investigated using an immobilized fungus, Trametes hirsuta D7. The degraded metabolites were identified using UPLC-PDA-FTICR MS and the biodegradation pathway followed was proposed. RB5 (92%) and AB113 (97%) were effectively degraded, whereas only 30% of AO7 was degraded. Molecular docking simulations were performed to determine the reason behind the poor degradation of AO7. Weak binding affinity, deficiency in H-bonding interactions, and the absence of interactions between the azo (-NN-) group and active residues of the model laccase enzyme were responsible for the low degradation efficiency of AO7. Furthermore, cytotoxicity and genotoxicity assays confirmed that the fungus-treated dye produced non-toxic metabolites. The observations of this study will be useful for understanding and further improving enzymatic dye biodegradation.

Study on the catalytic degradation of Acid Orange 7 and the potential mechanism by ferrous-percarbonate.

Factors affecting the degradation of Acid Orange 7 (AO7) were evaluated and optimized when ferrous was used to catalyze percarbonate in the present study. The optimized conditions included the initial pH values ranging from 3 to 11 for AO7 solution, the initial level of AO7, sodium percarbonate (SPC), and Fe2+ . Some ions and natural organic materials, which commonly exist in natural water, were also tested to evaluate their potential impacts on the degradation of AO7. The degradation efficiency of AO7 was up to 95% under the optimized test conditions, where the ferrous/percarbonate/AO7 molar ratio was 15/10/1 in the 0.285 mmol/l AO7 aqueous solution. The presence of Cl- , SO4 2- , NO3 - , Na+ , and Mg2+ did not affect the removal of AO7. The addition of HCO3 - significantly inhibited its removal, even when the concentration of HCO3 - was low to 0.6mmol/l. A slight inhibition effect was observed when the added concentration of humic acid ranged from 0.5 to 5mg/l, whereas the residue of AO7 was significantly enhanced when the level of humic acid was continually increased from 50 to 100 mg/l. Hydroxyl radicals (•OH) were the main reactive intermediates controlling the oxidation of AO7 in the present Fe2+ /SPC system. The produced intermediates through the degradation of AO7 were identified to include 2-coumaranone, 2-naphthol, phthalic acid, phthalimide, N-methylnaphthylamine, and 2-methylphenol. The proposed degradation pathways are consistent with the radical formation and the identified intermediates. PRACTITIONER POINTS: The ferrous/percarbonate system can remove 95% of AO7 under the optimized conditions. AO7 removal was inhibited by adding HCO3 - and humic acid, but not affected by Cl- , SO4 2- , NO3 - , Na+ , and Mg2+ . Hydroxylation, ring opening, and mineralization driven by the generated hydroxyl radicals were derived as the major processes for degrading AO7.

Enhanced degradation of organic contaminants by Fe(III)/peroxymonosulfate process with l-cysteine

The difficulty in Fe(III)/Fe(II) conversion in the Fe(III)/peroxymonosulfate (PMS) process limits its efficiency and application. Herein, l-cysteine (Cys), a green natural organic ligand with reducing capability, was innovatively introduced into Fe(III)/PMS to construct an excellent Cys/Fe(III)/PMS process. The Cys/Fe(III)/PMS process, at room temperature, can degrade a variety of organic contaminants, including dyes, phenolic compounds, and pharmaceuticals. In subsequent experiments with acid orange 7 (AO7), the AO7 degradation efficiency followed pseudo-first-order kinetic which exhibited an initial “fast stage” and a second “slow stage”. The rate constant values ranged depending on the initial Cys, Fe(III), PMS, and AO7 concentrations, reaction temperature, and pH values. In addition, the presence of Cl−, NO3−, and SO42− had negligible impact while HCO3− and humic acid inhibited the degradation of AO7. Furthermore, radical scavenger experiments and methyl phenyl sulfoxide (PMSO) transformation assay indicated that sulfate radical, hydroxyl radical, and ferryl ion (Fe(IV)) were the dominant reactive species involved in the Cys/Fe(III)/PMS process. Finally, based on the results of gas chromatography-mass spectrometry, several AO7 degradation pathways, including N=N cleavage, hydroxylation, and ring opening were proposed. This study provided a new insight to improve the efficiency of Fe(III)/PMS process by accelerating Fe(III)/Fe(II) cycle with Cys.

Synthesis of magnetic hydrochar from Fenton sludge and sewage sludge for enhanced anaerobic decolorization of azo dye AO7

A novel magnetic hydrochar synthesized from Fenton sludge (FS) and sewage sludge (SS) was employed in the anaerobic decolorization of acid orange 7 (AO7). The stable presence of Fe3O4 in magnetic hydrochar was confirmed by physicochemical characterization. The degradation efficiency of AO7 in the anaerobic system with the addition of hydrochar prepared in an optimal proportion (SS:FS=1:3, named as HC-1:3) could reach 98.55%, which was 1.91 times higher than the control system. Particularly, superior electrical conductivity, electron transport system activity and azo reductase activity of the sludge in anaerobic system with HC-1:3 were achieved. The redox of Fe(Ⅲ)/Fe(Ⅱ) in anaerobic system was realized by dissimilatory iron-reducing bacteria enriched with HC-1:3. According to the six-cycle batch experiments and 120-day continuous-flow UASB experiments, the addition of HC-1:3 into the anaerobic system facilitated the diversity of microbiological community and increased the ecological stability of anaerobic system. The possible electron transfer mechanism involving in the magnetic hydrochar-based anaerobic system for AO7 removal was speculated preliminarily. The as-prepared magnetic hydrochar not only showed a promising future in anaerobic system for recalcitrant contaminants degradation, but also provided a new approach for the resource utilization of FS and SS.

Advanced treatment of dye wastewater using a novel integrative Fenton-like/MnO2-filled upward flow biological filter bed system equipped with modified ceramsite

The deposal of residual hydrogen peroxide (H2O2) in Fenton-like system and the requirement of oxygen in bioreactor are essential parts for the treatment of integrative Fenton-like/bioreactor. A novel low-cost integrative Fenton-like and MnO2-filled upward flow biological filter bed (Fenton-like/MBFB) equipped with the modified ceramsite was constructed to evaluate the main properties and catalytic activity of modified ceramsite, and the optimal conditions of integrative system and compare integrative and traditional systems. In this study, the Fenton-like reactor with modified ceramsite had higher catalytic ability whose Acid Orange 7 (AO7) degradation efficiency reached to 79.3% due to large surface area and high porosity, compared with that with raw ceramsite (44.3%). Furthermore, total utilization efficiency of H2O2 in integrative system (from 32.41% to 53.51%) and removal efficiencies of COD and AO7 were remarkably improved, which would effectively decrease the waste of H2O2 and the setting of regulation pool and aeration tank. Thus, the integrative system can save 0.51 CNY/m3 in construction cost and 0.21 CNY/m3 in operating cost. The average COD removal efficiency, AO7 degradation efficiency and effluent DO concentration were achieved to 64.8%, 79.5% and 9.3 mg/L respectively in integrative system were achieved in integrative system during sixty successive runs. Also, the potential degradation pathway of contaminants was also proposed according to the OH-enhanced at Fenton-like reactor due to catalyst and adsorption of modified ceramsite and the removal of microorganisms and modified ceramsite for contaminants at MBFB. This study demonstrated the feasibility of integrative Fenton-like/MBFB filled with modified ceramsite for simultaneously decreasing operational cost and complexity and enhancing removal efficiency, thus provided a one-step alternative for refractory dye wastewater.

Revealing the influences of functional groups in azo dyes on the degradation efficiency and power output in solar photocatalytic fuel cell.

In this study, the degradation efficiency and electricity generation of the azo dyes affected by the functional groups and molecular structure in a solar photocatalytic fuel cell (PFC) system were investigated and discussed in detail. Four different azo dyes such as, Acid Orange 7 (AO7), Acid Red 18 (AR18), Reactive Black 5 (RB5), Reactive Red 120 (RR120) with different molecular structure were evaluated. The degradation efficiency of AO7, AR18, RB5 and RR120 achieved 5.6 ± 0.3%, 11.1 ± 0.6%, 41.9 ± 0.9% and 52.1 ± 1.3%, respectively, after 6h irradiated under solar light. In addition, the maximum power density, Pmax for AO7, AR18, RB5 and RR120 was 0.0269 ± 0.01, 0.111 ± 0.03, 1.665 ± 0.67 and 4.806 ± 1.79mWcm-2, respectively. Meanwhile, the concentration of COD for AO7, AR18, RB5 and RR120 reduced to 16 ± 0.1, 10 ± 0.3, 7 ± 0.6 and 3 ± 0.9mgL-1, respectively. The concentration ratio of benzene / naphthalene, benzene / azo bond and naphthalene / azo bond, respectively, was analyzed to investigate the impact of the functional groups over photodegradation of the azo dyes in PFC. Electron releasing groups (-OH and -NH2) and electron withdrawing groups (-SO3Na) which attached to the naphthalene or benzene ring also played a pivotal role in the degradation mechanism.

Carbon Quantum Dots (CQDs) Decorated Bi2O3-x Hybrid Photocatalysts with Promising NIR-Light-Driven Photodegradation Activity for AO7

In this work, Bi2O3-x with surface oxygen vacancies was prepared through the NaBH4 reduction of Bi2O3. After that, carbon quantum dots (CQDs) were deposited onto the surface of the Bi2O3-x to obtain a series of the CQDs/Bi2O3-x composites. The HRTEM and XPS characterizations of the CQDs/Bi2O3-x composites suggest that the thickness of surface oxygen vacancies could be adjusted by changing the concentration of NaBH4 solution, and the intimate contact between CQDs and the Bi2O3-x is achieved. Acid orange 7 (AO7) was adopted as the target reactant for investigating the photocatalytic degradation activities of the CQDs/Bi2O3-x composites under simulated sunlight and NIR light irradiation. It is found that the photocatalytic activities of the samples are closely related to the concentration of NaBH4 and content of CQDs. The Bi2O3-x samples exhibit enhanced simulated-sunlight-driven photocatalytic activity compared with Bi2O3. Specifically, the optimal degradation efficiency of AO7 is achieved over the 3R-Bi2O3-x (concentration of NaBH4: 3 mmol/L), which is 1.38 times higher than the degradation AO7 efficiency over Bi2O3. After the decoration of the 3R-Bi2O3-x surface with CQDs, the simulated-sunlight-driven photocatalytic activity of the CQDs/Bi2O3-x composite could be further enhanced. Among the samples, the 15C/3R-Bi2O3-x sample reveals the highest photocatalytic activity, leading to an AO7 degradation percentage of ~97% after 60 min irradiation. Different from Bi2O3 and the 3R-Bi2O3-x, the 15C/3R-Bi2O3-x sample also exhibits near-infrared (NIR)-light-driven photocatalytic degradation activity. In addition, the intrinsic photocatalytic activity of CQDs/Bi2O3-x composite was further confirmed by the degradation of phenol under simulated sunlight and NIR light irradiation. The photocurrent response and electrochemical impedance spectroscopy (EIS) measurements confirm the efficient migration and separation of photogenerated charges in the CQDs/Bi2O3-x samples. The •OH and h+ are proved to be the main reactive species in the simulated sunlight and NIR light photocatalytic processes over the CQDs/Bi2O3-x composites. According to the above experiments, the photocatalytic degradation mechanisms of the CQDs/Bi2O3-x composites under simulated sunlight and NIR light illumination were proposed.

A study of photocatalytic and photoelectrochemical activity of as-synthesized WO3/g-C3N4 composite photocatalysts for AO7 degradation

Herein, we have examined the effect of tungsten trioxide (WO3) doping in graphitic carbon nitride (g-C3N4) photocatalysts towards photodegradation of organic pollutant in aqueous medium. A sequence of visible light driven WO3/g-C3N4 composites were synthesized at various mole ratios (1, 2, 3 and 5%) of WO3 into g-C3N4 via simple and short-time wet-impregnation method. The fabricated photocatalytic materials were investigated by X-ray diffraction (XRD), Fourier transform-infrared (FT-IR) spectroscopy, UV–vis diffuse reflection spectroscopy (DRS), photoluminescence (PL) and scanning electron microscopy (SEM). The photocatalytic performance of the fabricated photocatalysts were assessed by the degradation of acid orange 7 (AO7) in visible-light illumination. The WO3/g-C3N4 composites were found to be exhibit an improved visible-light induced photocatalytic performances compared to the pure WO3 and g-C3N4. However, among the different composites, the optimized 3 wt% WO3/g-C3N4 composite has shown complete (100%) degradation efficiency of AO7 after 75 min which is superior than the pure g-C3N4. This synergistic enhancement might be credited to its increased light absorption in visible-light region and the photoexcited electron transfer from g-C3N4 to WO3 catalyst surface and enhanced charge separation efficiency. Additionally, the photo-electrochemical measurements of 3 wt% WO3/g-C3N4 composite has exhibited a quicker migration of the photo-excited charge-carriers. The radical scavenging studies inferred that the O2− are the key species accountable for the degradation of AO7 for fabricated WO3/g-C3N4 composite materials. Hence, the higher photocatalytic activity, long-term stability and recyclability of WO3/g-C3N4 composite has displayed it is a auspicious material for the photocatlytic degradation of organic contaminant applications.

Enhanced activation of peroxymonosulfte by LaFeO3 perovskite supported on Al2O3 for degradation of organic pollutants

In this study, the effect of various supports on activation of peroxymonosulfate and consequent degradation of Acid Orange 7 (AO7) in aqueous solutions was examined at the presence of LaFeO3 perovskite as catalyst. Results showed that the AO7 degradation efficiency by LaFeO3 supported on different supports was in an order of LaFeO3/Al2O3 (86.2%) > LaFeO3 (70.8%) > LaFeO3/CeO2 (59.0%) > LaFeO3/SiO2 (52.3%) > LaFeO3/TiO2 (32.2%). Moreover, the pseudo first-order rate constant for AO7 degradation by LaFeO3/Al2O3 was 3.2 times than that by LaFeO3. The enhancement was attributed to its large surface area, abundant chemisorbed surface-active oxygen, redox property and faster electron transfer. AO7 degradation and the leaching of iron ions decreased with the increase of pH. Data of electron spin resonance spectroscopy and quenching experiments revealed that sulfate and hydroxyl radicals were generated on LaFeO3/Al2O3 surface, while sulfate radicals were identified to be the main reactive species responsible for AO7 degradation. Mechanisms for peroxymonosulfate activation were consequently proposed. Furthermore, LaFeO3/Al2O3 catalyst exhibited a superior stability after five cycles. This work provides a new approach for design of iron-based perovskite catalysts with high and stable catalytic activity for removal of organic pollutants from aqueous solutions.

Mechanochemical formation of highly active manganese species from OMS-2 and peroxymonosulfate for degradation of dyes in aqueous solution

The performance and mechanism of mechanochemical activation of peroxymonosulfate (PMS) by cryptomelane-type manganese octahedral molecular sieve (OMS-2) prepared by a refluxing method for degradation of Acid Orange 7 (AO7) have been demonstrated. Grinding of OMS-2 and PMS in presence of a small amount of H2O for a short time induced a much higher AO7 degradation efficiency compared with the OMS-2 + PMS system without pretreatment. Such degradation can also be efficiently performed by this system over a wide range of solution pH and for different organic dyes. For other manganese oxides such as OMS-2 prepared by a solvent-free method, amorphous manganese oxides, and γ-MnO2, with coexistence of Mn(III) and Mn(IV) species, great enhancement of catalytic activity was also observed. Characterization of the ground OMS-2 by X-ray diffraction (XRD) analysis, transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) suggested that, during grinding, low-valent manganese species are oxidized to Mn(IV) species, representing the main active species for AO7 degradation. The produced SO 4 −· and HO· radicals from Mn(III) and the rest of the PMS also take part in the degradation reaction, although their contribution is limited. In addition, the influence of some key factors including the water content and time on the grinding and AO7 degradation was explored. The results of this study provide deep insight into mechanochemical activation of PMS with manganese oxides for enhanced degradation of pollutants in aqueous solution.

Sol-Gel Hydrothermal Synthesis and Visible Light Photocatalytic Degradation Performance of Fe/N Codoped TiO₂ Catalysts.

Using Ti(OC4H9)4 as a precursor, Fe(NO3)3⋅9H2O as the source of iron, and NH4NO3 as the source of nitrogen, an Fe/N codoped TiO2 catalyst was prepared using a sol-gel hydrothermal method. The as-prepared powders were characterized using X-ray powder diffraction, electron spectroscopy for chemical analysis, Fourier-transform infrared spectroscopy, and ultraviolet-visible spectrophotometry. Fe and N codoping resulted in decreased crystallite size and increased specific surface area. Results of the photocatalytic degradation of acid orange 7 (AO7) in a continuous-flow fluidized-bed reactor indicated that the maximum decolorization (more than 90%) of AO7 occurred with the Fe/N-TiO2 catalyst (dosage of 20 g/L) when a combination of visible light irradiation for 10 h HRT (hydraulic retention time), and a heterogeneous system was used. The AO7 degradation efficiency was considerably improved by increasing the hydraulic retention time from 2.5 to 10 h or by reducing the initial AO7 concentration from 300 to 100 mg/L. The reaction rate increased with the light intensity and the maximum value occurred at 35 mW/cm2; moreover, the efficiency of the AO7 degradation increased when the pH decreased with maximum efficiency at pH 3.

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.

Zn(0)-Catalyzed Ozonation Degradation of Acid Orange 7 (AO7) in Aqueous Solution

In this paper, Zn(0)-catalyzed ozonation degradation of acid orange 7 (AO7) and its impact factors including solution pH, Zn loading, and AO7 initial concentration were investigated through a series of bath experiments. The results demonstrated that Zn could markedly accelerate the degradation of AO7 by ozone (O3) and the degradation efficiency of AO7 increased by 77 and 71 % within 30 min as compared with those in the systems of O3 alone and Zn/air, respectively. The reuse of Zn resulted in a slight decline in AO7 degradation, suggesting that a coating of ZnO on the surface of Zn particles weakened Zn catalytic activity. The optimal removal of AO7 was achieved in a wide pH range of 4 to 10, and a lower or higher pH was not conducive to the degradation of AO7. In addition, the degradation efficiency of AO7 increased with Zn loading but decreased with AO7 initial concentration. The introduction of free radical scavengers into the system of AO7/Zn/O3 confirmed that O2 •−, rather than •OH, was the main free radicals responsible for the rapid removal of AO7. The degradation of AO7 by O3 assisted with Zn could be well expressed with pseudo-first-order kinetic model.

Accelerated photocatalytic degradation of organic pollutant over metal-organic framework MIL-53(Fe) under visible LED light mediated by persulfate

Photocatalysis based on metal-organic frameworks (MOFs) is being actively investigated as a potential technology in visible light harvesting and utilizing processes. Herein we report that MIL-53(Fe), an earth-abundant Fe-containing MOF material, shows photocatalytic activity for the degradation of Acid Orange 7 (AO7) from aqueous solution under visible LED light irradiation, yet the photocatalytic performance of bare MIL-53(Fe) was not satisfactory due to the fast recombination of photoinduced electron-hole pairs. This can be effectively overcome by adding the external electron acceptor (e.g., persulfate, PS) to the catalytic process. The accelerated photocatalytic degradation of AO7 is demonstrated by the result that the degradation efficiency of AO7 in the MIL-53(Fe)/PS/Vis process reached almost 100% within 90min as compared to only 24% under the identical experimental conditions for the MIL-53(Fe)/Vis process. To investigate the mechanism of the MIL-53(Fe)/PS/Vis process, photoluminescence (PL) spectra, electrochemical measurements and electron paramagnetic resonance (EPR) analysis were performed. It was concluded that the efficient separation of photogenerated electrons and holes by the introduced PS and the subsequent formation of reactive radicals resulting from the activation of PS by photogenerated electrons accounted for the accelerated photocatalytic degradation of AO7 in the MIL-53(Fe)/PS/Vis process. Furthermore, the applicability of MIL-53(Fe) used in the persulfate-mediated photocatalytic process was systematically investigated in terms of the identification of reactive radicals, the reusability and stability of the photocatalyst, as well as the effect of operating parameters. The findings of this work highlighted the great potential of MOFs as photocatalysts and elucidated a new opportunity for persulfate remediation of contaminated water.

Coupling cathodic Electro-Fenton reaction to membrane filtration for AO7 dye degradation: A successful feasibility study

This work evidences the interest of coupling advanced oxidation process (Electro-Fenton reaction) to dynamic filtration technology, using a tubular electrochemically reactive carbon graphite membrane, acting as cathode. This original coupling would be ideally adapted to confine organic pollution while achieving the complete degradation of refractory molecules from wastewater (domestic or industrial). The investigation was carried out using Acid Orange 7 (AO7) as a model pollutant.The electrochemical behavior of the membrane was firstly characterized in batch reactor in term of cathodic reactivity, for H2O2 selective production (in situ production from air supply followed by catalyzed ●OH generation). The influence of various parameters was studied to mark out the experimental domain to be investigated in a dynamic cross-flow reactor for AO7 degradation. In the latter case, a 23 full factorial design of experiments was used to screen the effect of operating conditions on two target responses: AO7 degradation efficiency (%) and kinetic constant value. Results showed that interactions effects between pH, current density and catalyst concentration influenced the AO7 degradation efficiency significantly. Moreover, better kinetic performances were obtained under dynamic filtration conditions, compared to a batch reactor. HPLC–MS analyses enabled elucidating at least six by-products formed throughout the process.

Preparation of natural pyrite nanoparticles by high energy planetary ball milling as a nanocatalyst for heterogeneous Fenton process

In the present study pyrite nanoparticles were prepared by high energy mechanical ball milling utilizing a planetary ball mill. Various pyrite samples were produced by changing the milling time from 2h to 6h, in the constant milling speed of 320rpm. X-ray diffraction (XRD), scanning electron microscopy (SEM) linked with energy dispersive X-ray (EDX), Fourier transform infrared spectroscopy (FT-IR) analysis and Brunauer–Emmett–Teller (BET) were performed to explain the characteristics of primary (unmilled) and milled pyrite samples. The average particle size distribution of the produced pyrite during 6h milling was found to be between 20nm and 100nm. The catalytic performance of the different pyrite samples was examined in the heterogeneous Fenton process for degradation of C.I. Acid Orange 7 (AO7) solution. Results showed that the decolorization efficiency of AO7 in the presence of 6h-milled pyrite sample was the highest. The impact of key parameters on the degradation efficiency of AO7 by pyrite nanoparticles catalyzed Fenton process was modeled using central composite design (CCD). Accordingly, the maximum removal efficiency of 96.30% was achieved at initial AO7 concentration of 16mg/L, H2O2 concentration of 5mmol/L, catalyst amount of 0.5g/L and reaction time of 25min.

Effects of nitrogen content in monocrystalline nano-CeO2 on the degradation of dye in indoor lighting

Azo dyes are an abundant class of synthetic dyes, however their complex structure makes them difficult to biologically degrade. We sought to degrade acid orange 7 (AO7) using nitrogen-doped nano-CeO2, which is a promising alternative photocatalyst to nitrogen-doped TiO2. Nitrogen-doped monocrystalline CeO2 nanoparticles with various nitrogen contents were synthesized solvothermally at 120̊C from Ce(NO3)3·6H2O, triethanolamine, and ethanol. The CeO2 monocrystals were between 7 and 8nm in diameter. Nitrogen was shown to be incorporated into CeO2 lattice from the results of the lattice parameter calculations, X-ray photoelectron spectroscopy analysis and elemental analysis. The degradation of AO7 in water was investigated using a domestic 10W compact fluorescent lamp. The degradation efficiency of AO7 by monocrystalline CeO2 increased with increasing nitrogen content, reaching 97.6% for the sample with a N:Ce molar ratio of 0.3.

Accelerated TiO2 photocatalytic degradation of Acid Orange 7 under visible light mediated by peroxymonosulfate

In this study, a system involving visible light TiO2 photocatalysis (Vis/TiO2) coupled with SO4--based advanced oxidation technologies (AOTs) through the addition of the oxidant peroxymonosulfate (PMS, HSO5-) has been developed to oxidize the target pollutant Acid Orange 7 (AO7) in aqueous solutions. There existed a remarkable synergistic effect in the combined Vis/TiO2/PMS system, and the performance of this combined system was better than that of a system to which persulfate (PS, S2O82-) or hydrogen peroxide (H2O2) was added. The influence of humic acids (HAs) and inorganic anions (H2PO4- and HCO3-) on the degradation rates in the Vis/TiO2/PMS system was also investigated. The obtained results revealed that HAs had a positive effect on the AO7 degradation efficiency in the Vis/TiO2/PMS system. When added to the Vis/TiO2 system, PMS can abrogate the adverse interference of anions in this system, such that the Vis/TiO2/PMS system exhibits much better degradation rates. The primary degradation intermediates of AO7 identified by GC/MS were phthalic acid, 2,4,6-trichlorophenol, coumarin and two chlorinated aromatic compounds (7-chloro-2-naphthalenol and 2,4-dichloro-1-naphthalenol). A possible pathway was proposed based on the analysis of the degradation products.

Degradation of azo dye Acid Orange 7 in water by Fe 0/granular activated carbon system in the presence of ultrasound

Degradation of azo dye Acid Orange 7 (AO7) was investigated using zero-valent iron/granular activated carbon (Fe 0/GAC) in the absence and presence of ultrasound (US). The AO7 degradation efficiency by Fe 0/GAC was dramatically enhanced by ultrasound, ultrasound alone had a little effect on the degradation. Effects of Fe 0/GAC ratios and initial pH values on AO7 degradation were studied in the US–Fe 0/GAC system. The degradation followed the pseudo-first-order kinetics model. The pseudo-first-order rate constant of AO7 degradation by Fe 0/GAC was 8.74 × 10 −3 min −1 while that by US–Fe 0/GAC was 3.91 × 10 −2 min −1. A significant synergetic effect was observed between US and Fe 0/GAC. Ultrasound swept the reactive intermediates or products from Fe 0 surface, and thereby the surface of Fe 0 was cleaned and reactivated. Granular activated carbon was added as cathode to increase the unit of internal batteries and enhance the current efficiency of the internal electrolysis. The suitable Fe 0/GAC ratio (v/v) for the degradation of AO7 in the presence of ultrasound was 1:1. The degradation was highly dependent on pH, and a decrease of the initial pH values from 12.0 to 4.0 led to the increase of degradation efficiencies. Sulfanilamide was proved as the main residual degradation product in the solution by the analysis of high-performance liquid chromatograms.