Photo-degradation of di azo dye Bismarck Brown by advanced photo-Fenton process: Influence of inorganic anions and evaluation of recycling efficiency of iron powder

Development of persulfate-based advanced oxidation processes to remove synthetic azo dyes from aqueous matrices

Azo dyes are largely used in many industries and discharged in large volumes of their effluents into the aquatic environment giving rise to non-esthetic pollution and health-risk problems. Due to the high stability of azo dyes in ambient conditions, they cannot be abated in conventional wastewater treatment plants. Over the last fifteen years, the decontamination of dyeing effluents by persulfate (PS)-based advanced oxidation processes (AOPs) has received a great attention. In these methods, PS is activated to be decomposed into sulfate radical anion (SO4•-), which is further partially hydrolyzed to hydroxyl radical (•OH). Superoxide ion (O2•-) and singlet oxygen (1O2) can also be produced as oxidants. This review summarizes the results reported for the discoloration and mineralization of synthetic and real waters contaminated with azo dyes covering up to November 2023. PS activation with iron, non-iron transition metals, and carbonaceous materials catalysts, heat, UVC light, photocatalysis, photodegradation with iron, electrochemical and related processes, microwaves, ozonation, ultrasounds, and other processes is detailed and analyzed. The principles and characteristics of each method are explained with special attention to the operating variables, the different oxidizing species generated yielding radical and non-radical mechanisms, the addition of inorganic anions and natural organic matter, the aqueous matrix, and the by-products identified. Finally, the overall loss of toxicity or partial detoxification of treated azo dye solutions during the PS-based AOPs is discussed.

Fenton-Like Reaction: Recent Advances and New Trends

The Fenton reaction refers to the reaction in which ferrous ions (Fe2+) produce hydroxyl radicals and other reactive oxidizing substances by decomposing hydrogen peroxide (H2O2). This paper reviews the mechanism, application system, and materials employed in the Fenton reaction including conventional homogeneous and non-homogeneous Fenton reactions as well as photo-, electrically-, ultrasonically-, and piezoelectrically-triggered Fenton reactions, and summarizes the applications in the degradation of soil oil pollutions, landfill leachate, textile wastewater, and antibiotics from a practical point of view. The mineralization paths of typical pollutant are elucidated with relevant case studies. The paper concludes with a summary and outlook of the further development of Fenton-like reactions.

Natural iron minerals in an electrocatalytic oxidation system and in situ pollutant removal in groundwater: Applications, mechanisms, and challenges

Natural iron-bearing minerals are widely distributed in the environment and show prominent catalytic performance in pollutant removal. This work provides an overview of groundwater restoration technologies utilizing heterogeneous electro-Fenton (HEF) techniques with the aid of different iron forms as catalysts. In particular, applications of natural iron-bearing minerals in groundwater in the HEF system have been thoroughly summarized from either the view of organic pollutant removal or degradation. Based on the analysis of the catalytic mechanism in the HEF process by pyrite (FeS₂), goethite (α-FeOOH), and magnetite (Fe₃O₄) and the geochemistry analysis of these natural iron-bearing minerals in groundwater, the feasibility and challenges of HEF for organic degradation by using typical iron minerals in groundwater have been discussed, and natural factors affecting the HEF process have been analyzed so that appropriate in situ remedial measures can be applied to contaminated groundwater.

Microwave assisted sol-gel approach for Zr doped TiO2 as a benign photocatalyst for bismark brown red dye pollutant

A microwave supported sol-gel approach was developed in this study to fabricate Zr-doped TiO2 mesoporous nanostructures for efficient photocatalytic activity on bismark brown red (BBR) dye under visible light illumination. Sophisticated analytical techniques such as X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), high resolution transmission electron microscopy (HRTEM), field emission scanning electron microscopy (FESEM) with energy dispersive X-ray spectroscopy (EDX), X-ray fluorescence analysis (XRF), Fourier transform infrared (FT-IR), ultraviolet-visible diffuse reflectance (UV-vis-DRS) spectroscopy and Brunauer-Emmet-Teller (BET) surface area analyses were used to obtain their structural, electrical: optical and spectroscopic characteristics. The analysis results revealed that the developed nanostructures exhibited strong broad absorption in the visible region with good adsorption capacity and thus enhanced photocatalytic performance. The average crystallite size was found to be 12.5 nm (UTO), 6.4 nm (ZT4), and 4.7 nm (ZT4M4) respectively. The nanocatalysts (ZT4M4) showed a decrease in bandgap and particle size with an increase in the surface area of the Zr-TiO2 nanoparticles (119 m2 g-1). In comparison to previous studies on the photocatalytic degradation of BBR dye under visible light irradiation employing Ni-S co-doped (110 min), Cu-doped TiO2 (75 min), etc., ZT4M4 exhibited a remarkable degradation rate of 99% in 50 minutes. This may be due to the hydroxyl radicals being the principle reactive species responsible for the BBR dye oxidative degradation. The present study showed that ZT4M4 was found to be the best photocatalyst for the BBR dye degradation under the optimal conditions.

Reconstruction of Electronic Structure of MOF-525 via Metalloporphyrin for Enhanced Photoelectro-Fenton Process

Photoelectro-Fenton (PEF) process can continuously promote the occurrence of Fenton reaction and the generation of active species, which is an advanced oxidation technology for pollutant degradation. However, the lack of bifunctional catalysts restricts the development of PEF technology. In this study, the electronic rearrangement MOF-525 modified by metalloporphyrin (named MOF-525-Fe/Zr) was prepared, to load on the carbon felt as a novel cathode catalyst, which is used in PEF process. A series of characterization and photoelectric chemical properties tests combined with DFT calculation showed that the modification of MOF-525 could not only have the large specific surface area and multistage pore structure but also co-stimulate the metal-to-ligand charge transfer (MLCT) and ligand-to-cluster charge transfer (LCCT) by photoelectric synergy. These charge transitions provide periodic electron donor-acceptor conduction paths in MOF-525-Fe/Zr, which can improve the active species formation and transfer efficiency. Owing to their favorable pore and electronic structure as well as stability, MOF-525-Fe/Zr shows great promise for the application in the catalytic process of PEF. Sulfamethoxazole (SMX) degradation was enhanced by MOF-525-Fe/Zr with the TOC removal rate above 75% both in river water and tap water. Finally, the reasonable pathway of PEF catalytic degradation of SMX was proposed by HPLC-MS analysis. In conclusion, this study provides a new idea for reconstructing the electronic structure of MOFs catalyst and broadening the practical application of PEF technology.

Pattern, Forms and Bibliometric Analysis for Systematic Study of Silica-Supported Heterogeneous Solar Photocatalyst for Lannate Insecticide Abatement from Aqueous Stream

Agro-industrial streams with high toxic loadings must undergo for treatment prior to final disposal. Thus, the current investigation aimed to apply cheap and naturally available materials to explore sustainable heterogeneous solar/Fenton reaction for insecticide abatement form waste streams. Iron was collected from the wastewater stream after coal industry. The sand pellets were used as iron support material which acts as a heterogeneous solar photo-catalyst like modified Fenton reaction. The prepared catalysts were characterized using X-ray diffraction (XRD) and scanning electron microscope (SEM) for characterization. System parameters variables were studied using the modified catalysts. Although the acidic pH showed maximal removal efficiency, the catalyst could also work at a wide pH range with a reduced activity. The optimum conditions of the newly synthesized modified Fenton composite showed 103, 45 mg/L for H2O2 and catalyst, respectively, at pH 2.8 within 90 min under solar irradiation for maximal Lannate oxidation reached to 98%. Moreover, the increase in Lannate concentration loading results in a reduction in the removal efficiency from 98 to 96% when the Lannate loading increased from 10 to 50 ppm, although further increase of Lannate (100 ppm) results in only 2% removal. Also, temperature effect was displayed and the high temperature range was unfavorable. The kinetics of Lannate removal was dependent on operation temperature and following the first-order kinetic model. The thermodynamic parameters values settled the system is non-spontaneous in nature, proceeds in endothermic circumstances and working in a low energy barrier (34.54 kJ mol−1). Recyclability confirms the sustainability of the catalyst, and the third cycle catalytic use attained 28% Lannate removal.

Comparison of naphthalene removal performance using H2O2, sodium percarbonate and calcium peroxide oxidants activated by ferrous ions and degradation mechanism

The presence of polycyclic aromatic hydrocarbons (PAHs) in groundwater is making a great threat to human health in the world which has received an increasing environmental concern. Among various Fenton oxidation processes, 97.6%, 92.1% and 89.4% naphthalene (NaP) removals were observed using hydrogen peroxide (H₂O₂), sodium percarbonate (SPC) and calcium peroxide (CP) as oxidants activated by Fe(II) in ultrapure water tests, respectively. While, the inhibitory effect on NaP degradation caused by the weak alkaline solution pH and the presence of HCO₃^- in actual groundwater could be compensated by doubling dosages of oxidants and Fe(II) to different extent. 98.0%, 49.8% and 11.5% of NaP were degraded by using H₂O₂, SPC and CP, respectively, strongly suggesting the best H₂O₂ performance among them. It was observed that 83.3% and 9.6% inhibition on NaP degradation in H₂O₂/Fe(II)/NaP system occurred in the presence of isopropyl alcohol and chloroform, confirming that both hydroxyl radical (HO) and superoxide anion radical () contributed to NaP degradation in Fenton process and HO was the prominent radical. The presence of HO was further demonstrated by electro-spin resonance spectrometer analysis. The identification of transformation products of NaP revealed that hydroxylation and ring rupture were the main NaP degradation pathways.

Degradation of 2,4-Dichlorophenol by Ethylenediamine-N,N′-disuccinic Acid-Modified Photo-Fenton System: Effects of Chemical Compounds Present in Natural Waters

This paper describes a study of the treatment of 2,4-dichlorophenol (2,4-DCP) with an ethylenediamine-N,N′-disuccinic-acid (EDDS)-modified photo-Fenton system in ultrapure water and different natural waters. The results showed that the EDDS-modified photo-Fenton system is adequate for 2,4-DCP degradation. Compared with a medium containing a single organic pollutant, the removal of pollutants in a more complex medium consisting of two organic compounds is slower by around 25 to 50% as a function of the organic pollutant. Moreover, 2,4-DCP can be further effectively degraded in the presence of organic materials and various inorganic ions. However, the photodegradation of 2,4-DCP in different natural waters, including natural lake water, effluent from domestic sewage treatment plants, and secondary effluent from pulp and paper mill wastewaters, is inhibited. Chemical compounds present in natural waters have different influences on the degradation of 2,4-DCP by adopting the EDDS-modified photo-Fenton system. In any case, the results obtained in this work show that the EDDS-modified photo-Fenton system can effectively degrade pollutants in a natural water body, which makes it a promising technology for treating pollutants in natural water bodies.

Photo-Fenton-like degradation of bisphenol A by persulfate and solar irradiation

This work evaluates the feasibility of a solar-enhanced Fenton-like process using S₂O₈^2- (PS) and Fe²⁺ for the elimination of BPA, a model endocrine-disruption compound. This comparative study of BPA removal showed that among the approaches employed, the effectiveness of BPA degradation (10 mg/L) decreased in the order: Solar/PS/Fe²⁺> Solar/PS > PS/Fe²⁺> Solar/Fe²⁺> Solar. The complete degradation of BPA was achieved by Solar/PS/Fe²⁺ treatment at a [PS]:[BPA] ratio of 20 in less than t_30W 5 in deionised water. The high efficiency of the Solar/PS/Fe²⁺ process revealed a synergistic effect (ϕ = 2.38) between the applied activation agents on the formation of reactive oxygen species (ROS) and subsequent decomposition of BPA. The treatment was accompanied by total organic carbon (TOC) removal (44%) in 45 min. Sequential generation of reactive oxygen species has made Solar/PS/Fe²⁺ a kinetically effective process for removing BPA without accumulation of toxic intermediates. The reaction rate followed pseudo-first-order kinetics that increased with increasing PS and Fe²⁺ concentrations. Experimental evidence suggests that exposure to solar irradiation maintains suitable quantities of free Fe²⁺ in the reaction mixture, even at low catalyst concentrations (the molar ratio of [PS]:[Fe²⁺] varied from 1:0.01 to 1:0.08). The effects of HCO₃^-, SO₄^2-, and Cl^- were also examined. As expected, HCO₃^- and SO₄^2- inhibited BPA oxidation. The effect of Cl^- on the oxidation efficiency of BPA in Fenton-like systems depends not only on actual Cl^- concentrations but it is also highly influenced by molar ratios of Cl^- to oxidant and catalyst. Inhibition, which was caused by Cl^- in the mM range can be overcome by prolonging the reaction time or increasing the initial Fe²⁺concentration. Finally, the efficiency of Solar/PS/Fe²⁺ process was examined in diluted natural surface water and wastewater effluent. On eliminating the buffering action of HCO₃^-/CO₃^2- ions by lowering the pH value to 4.5, complete BPA degradation was achieved in all real water matrices.

Enhanced heterogeneous Fenton-like systems based on highly dispersed Fe0-Fe2O3 nanoparticles embedded ordered mesoporous carbon composite catalyst

Acceleration of Fe³⁺/Fe²⁺ cycle and simultaneous reduction of particle size with enhanced stability is extremely important for iron-based heterogeneous Fenton catalysts. In this work, Fe⁰-Fe₂O₃ composite nanoparticles embedded ordered mesoporous carbon hybrid materials (Fe⁰-Fe₂O₃/OMC) were rationally designed as efficient heterogeneous Fenton catalysts. Because of the confinement and reduction of OMC, highly dispersed Fe⁰-Fe₂O₃ active species with diameter of ∼8 nm were generated by an optimized carbothermic reduction process. In addition, Fe⁰-Fe₂O₃/OMC possesses ordered mesoporous structure with uniform mesopore, high surface area and pore volume. For comparison, two other catalysts, including solely Fe⁰ nanoparticles supported on ordered mesoporous carbon (Fe⁰/OMC) and solely Fe₂O₃ nanoparticles supported on ordered mesoporous carbon (Fe₂O₃/OMC) were also prepared. The Fenton catalytic performance of synthesized catalysts was evaluated by using H₂O₂ as oxidizing agent to degrade Acid Orange II (AOII). The results show that almost 98.1% of 100 mg L^-1 AOII was removed by Fe⁰-Fe₂O₃/OMC in condition of neutral pH and nearly room temperature, which is much higher than those of compared catalysts. The enhanced catalytic activity of Fe⁰-Fe₂O₃/OMC for AOII removal is due to the efficient electron transfer between the Fe⁰ and iron oxide and the accelerated Fe³⁺/Fe²⁺ cycle. The stability and reusability of the catalyst was also investigated, which showed a good performance even after five consecutive runs. The as-synthesized catalyst is proved to be an attractive candidate in heterogeneous Fenton chemistry and practical application.

Comparison of photo-Fenton, O3/H2O2/UV and photocatalytic processes for the treatment of gray water

This research was carried out to compare and optimize the gray water treatment performance by the photo-Fenton, photocatalysis and ozone/H₂O₂/UV processes. Experimental design and optimization were carried out using Central Composite Design of Response Surface Methodology. The results of experiments showed that the most effective and influencing factors in photo-Fenton process were H₂O₂/Fe²⁺ ratio, in ozone/H₂O₂/UV experiment were O₃ concentration, H₂O₂ concentration, reaction time and pH and in photocatalytic process were TiO₂ concentration, pH and reaction time. The highest COD removal in photo-Fenton, ozone/H₂O₂/UV and photocatalytic process were 90%, 92% and 55%, respectively. The results were analyzed by design expert software and for all three processes second-order models were proposed to simulate the COD removal efficiency. In conclusion the ozone/H₂O₂/UV process is recommended for the treatment of gray water, since it was able to remove both COD and turbidity by 92% and 93%, respectively.

Catalytic performances of Ni/Fe layered double hydroxides fabricated via different methods in Fenton-like processes

Nickel-iron hydrotalcites (NiFe-LDH) with various [Ni]/[Fe] ratios were prepared using co-precipitation method (NiFe-LDH CP) and hydrothermal method (NiFe-LDH HT), respectively. The crystal structure and chemical composition of NiFe-LDHs were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetry and differential scanning calorimetry (TGA-DSC) and scanning electron microscopy, and NiFe-LDHs were occupied as catalysts to establish heterogeneous Fenton systems for the degradation of methylene blue (MB). The catalytic potential of the catalysts was investigated through cyclic voltammetry analysis. The effects of the dosage of catalyst, initial solution pH and the amount of hydrogen peroxide on the removal of MB were investigated. The results showed that the optimum ratio of [Ni]/[Fe] in the preparation of NiFe-LDHs was 3. NiFe-LDH HT is much smaller and in uniform particle size, with better redox reversible characteristic and catalytic potential. The optimum conditions for the removal of MB catalyzed by NiFe-LDH CP and NiFe-LDH HT were both determined to be 0.15 g/L catalyst, 0.88 mmol/L hydrogen peroxide at pH 2, under which the chemical oxygen demand (COD) removal were 58.96% and 67.87%, respectively. The maximum apparent generation efficiency of ·OH were 46.21% and 49.24%, and NiFe-LDH CP and NiFe-LDH HT were verified to be of high stability.

Degradation of the UV-filter benzophenone-3 in aqueous solution using persulfate activated by heat, metal ions and light

The goals of this study were to bring forward new data and insights into the effect of activation methods, operational variables and reaction pathways during sulfate radicals-based oxidation of benzophenone-3 (BP-3) in aqueous solution. Heat, transition metal ions (Fe²⁺, Cu²⁺, Co²⁺), UV and visible light irradiation were used to activate persulfate (PS) to degrade BP-3. The results showed that these three activation methods can remarkably enhance BP-3 removal efficiency. Under the conditions of [BP-3]₀: [PS]₀ = 1: 500, pH = 7.0, and 40 °C, complete removal of BP-3 (1.31 μM) was observed in 3 h. In the pH range of 3.0-9.0, the degradation of BP-3 decreased with increasing pH. Increasing the PS dosage accelerated the reaction, while the presence of humic acid (HA) significantly inhibited the efficiency of BP-3 removal. Based on electron paramagnetic resonance (EPR) and radical quenching studies, sulfate and hydroxyl radicals contributed to the oxidation process. According to the evolution of BP-3 and its 7 by-products, as well as frontier electron densities (FED) calculation, two routes were proposed involving hydroxylation, demethylation and direct oxidation. On the whole, this work is a unique contribution to the systematic elucidation of BP-3 removal by PS.

Influence of aromatic additives on Bismarck Brown Y dye color removal treatment by Fenton processes

The influence of diverse aromatic additives on Fenton processes (Fe²⁺/H₂O₂, Fe³⁺/H₂O₂) has been evaluated by using the Bismarck Brown Y (BBY) di azo dye as target pollutant. Results indicate that all tested Fe³⁺-reducing additives (gallic, 3,4-dihydroxyphenylacetic, 2,3-dihydroxybenzoic, and 2,5-dihydroxybenzoic acids, catechol, and hydroquinone) exhibited pro-oxidant properties during BBY dye color removal, mainly during Fe³⁺/H₂O₂ treatments. For example, in the presence of hydroquinone BBY color removal was increased from 22 to 83% for 60 min through the Fe³⁺/H₂O₂ process. The effect of non-reducing additives was less pronounced, among which salicylic and 2,4-dihydroxybenzoic acids were more efficient at removing dye color than benzoic acid and methylene blue. It was suggested that OH radicals may have converted non-reducing additives into Fe³⁺-reducing intermediates, which had a positive effect on the treatments. On the other hand, antioxidant properties were observed during BBY color removal in the presence of higher concentrations of gallic and salicylic acids. These items of data indicate that a minimum amount of aromatic additive was enough to increase BBY dye color removal by Fenton processes.

2,4-D abatement from groundwater samples by photo-Fenton processes at circumneutral pH using naturally iron present. Effect of inorganic ions

This study evaluated, at laboratory scale, if the using iron naturally present (0.3 mg L^-1) and adding 10 mg L^-1 of hydrogen peroxide was effective to remove 24.3 mgL^-1 of 2,4-dichlorophenoxyacetic acid (2,4-D) from groundwater samples by simulated solar irradiation (global intensity = 300 W m^-2). Under these conditions, the degradation of 2,4-D reached 75.2 % and the apparition of its main oxidation byproduct 2,4-dichlorophenol (DCP) was observed. On the other hand, pH exhibited an increasing from 7.0 to 8.3 during the experiment. Experiments using Milli-Q water at pH 7.0, iron, and H₂O₂ concentrations of 0.3 and 10 mg L^-1, respectively, were carried out in order to study the effect of ions such as carbonate species, phosphate, and fluoride in typical concentrations often found in groundwater. Ion concentrations were combined by using a factorial experimental design 2³. Results showed that carbonates and fluoride did not produce a detrimental effect on the 2,4-D degradation, while phosphate inhibited the process. In this case, the pH increased also from 7.0 to 7.95 and 8.99. Effect of parameters such as pH, iron concentration, and hydrogen peroxide concentration on the 2,4-D degradation by the photo-Fenton process in groundwater was evaluated by using a factorial experimental design 2³. Results showed that the pH was the main parameter affecting the process. This study shows for the first time that using the photo-Fenton process at circumneutral pH and iron naturally present seems to be a promising process to remove pesticides from groundwater.

Removal of antibiotic cloxacillin by means of electrochemical oxidation, TiO2 photocatalysis, and photo-Fenton processes: analysis of degradation pathways and effect of the water matrix on the elimination of antimicrobial activity

This study evaluates the treatment of the antibiotic cloxacillin (CLX) in water by means of electrochemical oxidation, TiO₂ photocatalysis, and the photo-Fenton system. The three treatments completely removed cloxacillin and eliminated the residual antimicrobial activity from synthetic pharmaceutical wastewater containing the antibiotic, commercial excipients, and inorganic ions. However, significant differences in the degradation routes were found. In the photo-Fenton process, the hydroxyl radical was involved in the antibiotic removal, while in the TiO₂ photocatalysis process, the action of both the holes and the adsorbed hydroxyl radicals degraded the pollutant. In the electrochemical treatment (using a Ti/IrO₂ anode in sodium chloride as supporting electrolyte), oxidation via HClO played the main role in the removal of CLX. The analysis of initial by-products showed five different mechanistic pathways: oxidation of the thioether group, opening of the central β-lactam ring, breakdown of the secondary amide, hydroxylation of the aromatic ring, and decarboxylation. All the oxidation processes exhibited the three first pathways. Moreover, the aromatic ring hydroxylation was found in both photochemical treatments, while the decarboxylation of the pollutant was only observed in the TiO₂ photocatalysis process. As a consequence of the degradation routes and mechanistic pathways, the elimination of organic carbon was different. After 480 and 240 min, the TiO₂ photocatalysis and photo-Fenton processes achieved ∼45 and ∼15 % of mineralization, respectively. During the electrochemical treatment, 100 % of the organic carbon remained even after the antibiotic was treated four times the time needed to degrade it. In contrast, in all processes, a natural matrix (mineral water) did not considerably inhibit pollutant elimination. However, the presence of glucose in the water significantly affected the degradation of CLX by means of TiO₂ photocatalysis.

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.

Biphasic reduction model for predicting the impacts of dye-bath constituents on the reduction of tris-azo dye Direct Green-1 by zero valent iron (Fe0)

Influence of common dye-bath additives, namely sodium chloride, ammonium sulphate, urea, acetic acid and citric acid, on the reductive decolouration of Direct Green 1 dye in the presence of Fe⁰ was investigated. Organic acids improved dye reduction by augmenting Fe⁰ corrosion, with acetic acid performing better than citric acid. NaCl enhanced the reduction rate by its 'salting out' effect on the bulk solution and by Cl^- anion-mediated pitting corrosion of iron surface. (NH₄)₂SO₄ induced 'salting out' effect accompanied by enhanced iron corrosion by SO₄^2- anion and buffering effect of NH₄⁺ improved the reduction rates. However, at 2g/L (NH₄)₂SO₄ concentration, complexating of SO₄^2- with iron oxides decreased Fe⁰ reactivity. Urea severely compromised the reduction reaction, onus to its chaotropic and 'salting in' effect in solution, and due to it masking the Fe⁰ surface. Decolouration obeyed biphasic reduction kinetics (R²>0.993 in all the cases) exhibiting an initial rapid phase, when more than 95% dye reduction was observed, preceding a tedious phase. Maximum rapid phase reduction rate of 0.955/min was observed at pH2 in the co-presence of all dye-bath constituents. The developed biphasic model reckoned the influence of each dye-bath additive on decolouration and simulated well with the experimental data obtained at pH2.

Iron–copper bimetallic nanoparticles supported on hollow mesoporous silica spheres: the effect of Fe/Cu ratio on heterogeneous Fenton degradation of a dye

A series of iron–copper bimetallic nanoparticles supported on hollow mesoporous silica spheres with different Fe/Cu ratios were prepared using a simple post-impregnation and sodium borohydride reduction strategy.

Recent advances and prospects of catalytic advanced oxidation process in treating textile effluents

In the past few years, there have been many researches on the use of different types of homogenous catalyst for the degradation of textile wastewater in conventional advanced oxidation processes (AOPs). However, homogenous AOPs suffer from few limitations, including large consumption of chemicals, acidic pH, high cost of hydrogen peroxide, generation of iron sludge, and necessity of post-treatment. Therefore, recently, there have been more researches that focus on improving the performance of conventional AOPs using heterogeneous catalysts such as titanium dioxide, nanomaterials, metal oxides, zeolite, hematite, goethite, magnetite, and activated carbon (AC). Besides, different supports such as AC that have been incorporated with transition metals and clays have been proven to have excellent catalytic activity in AOPs. This paper presents a comprehensive review of advances and prospects of catalytic AOPs for the decontamination of a wide range of synthetic and real textile wastewater. This review provides an up-to-date critical review of the information on the degradation of various textile dyes by a wide range of heterogeneous catalysts and adsorbents. The future challenges of AOPs, including chemical consumption, toxicity assessment, reactor design, and limitation of catalysts, are discussed in this paper. In addition, this paper also discusses the presence of ions, generation of by-products, and industrial applications of AOPs. Special emphasis is given to recent studies and large-scale combination of AOPs for wastewater treatment. This review paper concludes that more studies are needed for the kinetics, reactor design, and modeling of hybrid AOPs and the production of their corresponding intermediate products and secondary pollutants. A better economic model should also be developed to predict the cost of AOPs, as the treatment cost varies with dyes and textile effluents.

Bio-inspired route for the synthesis of spherical shaped MgO:Fe(3+) nanoparticles: Structural, photoluminescence and photocatalytic investigation

MgO:Fe(3+) (0.1-5 mol%) nanoparticles (NPs) were synthesized via eco-friendly, inexpensive and simple low temperature solution combustion route using Aloe vera gel as fuel. The final products were characterized by SEM, TEM and HRTEM. PXRD data and Rietveld analysis revealed the formation of cubic system. The influence of Fe(3+) ion concentration on the structure morphology, UV absorption, PL emission and photocatalytic activity of MgO:Fe(3+) NPs were investigated. The yellow emission with CIE chromaticity coordinates (0.44, 0.52) and average correlated color temperature value was found to be 3540 K which corresponds to warm light of NPs. The control of Fe(3+) on MgO matrix influences the photocatalytic decolorization of methylene blue (MB) under UV light. The enhanced photocatalytic activity of MgO:Fe(3+) (4 mol%) was attributed to dopant concentration, effective crystallite size, textural properties, decreased band gap and capability for reducing the electron-hole pair recombination. Further, the trends of inhibitory effect in the presence of different radical scavengers were explored. These findings open up new avenues for the exploration of Fe-doped MgO in eco-friendly water applications and in the process of display devices.

Bio-inspired synthesis of Y2O3: Eu(3+) red nanophosphor for eco-friendly photocatalysis

We report the synthesis of Y2O3: Eu(3+) (1-11 mol%) nanoparticles (NPs) with different morphologies via eco-friendly, inexpensive and simple low temperature solution combustion method using Aloe Vera gel as fuel. The formation of different morphologies of Y2O3: Eu(3+) NPs were characterized by PXRD, SEM, TEM, HRTEM, UV-Visible and PL techniques. The PXRD data and Rietveld analysis confirms the formation of single phase Y2O3 with cubic crystal structure. The influence of Eu(3+) ion concentration on the morphology, UV-Visible absorption, PL emission and photocatalytic activity of Y2O3: Eu(3+) nanostructures were investigated. Y2O3: Eu(3+) NPs exhibit intense red emission with CIE chromaticity coordinates (0.50, 0.47) and correlated color temperature values at different excitation ranges from 1868 to 2600 K. The control of Eu(3+) ion on Y2O3 matrix influences the photocatalytic decolorization of methylene blue (MB) as a model compound was evaluated under UVA light. Enhanced photocatalytic activity of conical shaped Y2O3: Eu(3+) (1 mol%) was attributed to dopant concentration, crystallite size, textural properties and capability of reducing the electron-hole pair recombination. The trend of inhibitory effect in the presence of different radical scavengers followed the order SO4(2-)>Cl(-)>C2H5OH>HCO3(-)>CO3(2-). These findings show great promise of Y2O3: Eu(3+) NPs as a red phosphor in warm white LEDs as well as eco-friendly heterogeneous photocatalysis.

Iron–copper bimetallic nanoparticles supported on hollow mesoporous silica spheres: an effective heterogeneous Fenton catalyst for orange II degradation

Iron–copper bimetallic nanoparticles supported on hollow mesoporous silica spheres as a composite catalyst (FeCu/HMS) was synthesized.

Zinc oxide based photocatalysis: tailoring surface-bulk structure and related interfacial charge carrier dynamics for better environmental applications

Surface-bulk modification of zinc oxide for efficient photocatalysis.

Two novel octamolybdate nanoclusters as catalysts for dye degradation by air under room conditions

Two new octamolybdate-based hybrid materials as catalysts for the wet air oxidation of dyes under mild conditions.

Toxicity of the azo dyes Acid Red 97 and Bismarck Brown Y to Western clawed frog (Silurana tropicalis)

Azo compounds are used in a variety of industrial applications, such as textile colorant. Azo dyes have been found to contaminate aquatic environments and it has been shown that these compounds could potentially be toxic or induce endocrine disruption in aquatic organisms. However, there are few data available on the toxicity of these dyes, specifically Acid Red 97 (AR97) and Bismarck Brown Y (BBY). The aim of this study was to determine the toxicity and the endocrine-disrupting properties of AR97 and BBY in frogs. As fugacity modeling predicted that both compounds would sorb to sediment, sediment exposures were performed using a geometric range of concentrations (0, 1, 10, 100 and 1,000 ppm). Both AR97 and BBY dyes were not lethal to Silurana tropicalis embryos; however, BBY significantly induced malformations. Gene expression analysis of oxidative stress and mutagen-related genes was performed in BBY-treated larvae. There were significant two-fold increases of the tumor-suppressing protein p53 and heat shock protein 70 mRNA at 1,000 ppm suggesting that BBY induces cellular stress in early S. tropicalis development. Transcripts of the heat shock protein 90 did not change. Furthermore, reproductive-related genes were assessed and a 2.1-fold change was observed in the mRNA of the steroidogenic acute regulatory protein while steroid 5 alpha-reductase type 2 and androgen receptor transcript levels did not vary among treatments. In conclusion, high concentrations of BBY lead to increased developmental defects in frog embryogenesis and early larval development.

Perfluorooctanoic acid degradation in the presence of Fe(III) under natural sunlight

Due to the high bond dissociation energy (BDE) of CF bonds (116 kcal/mol), perfluorooctanoic acid (PFOA) is a highly recalcitrant pollutant. Herein, we demonstrate a novel method to decompose PFOA in the presence of sunlight and ferric iron (Fe(III)). Under such conditions, 97.8 ± 1.7% of 50 μM PFOA decomposed within 28 days into shorter-chain intermediates and fluoride (F(-)), with an overall defluorination extent of 12.7 ± 0.5%. No PFOA was removed under visible light, indicating that UV radiation is required for PFOA decomposition. Spectroscopic analysis indicates that the decomposition reaction is likely initiated by electron-transfer from PFOA to Fe(III), forming Fe(II) and an unstable organic carboxyl radical. An alternative mechanism for the formation of this organic radical involves hydroxyl radicals, detected by electron paramagnetic resonance (EPR). The observation that PFOA can be degraded by Fe(III) under solar irradiation provides mechanistic insight into a possibly overlooked natural attenuation process. Because Fe(III) is abundant in natural waters and sunlight is essentially free, this work represents a potentially important step toward the development of simple and inexpensive remediation strategies for PFOA-contaminated water.