Degradation of phenol by heterogeneous Fenton reaction using Fe/clinoptilolite

Development of ceramic honeycomb monolith from natural zeolite tested as adsorbent to remove methylene blue in aqueous media

This work presents a ceramic monolith with a honeycomb structure obtained from a natural zeolite (clinoptilolite), bentonite, and alumina. The monolith obtained by extrusion had a cell density of 57 CPSI (cells per square inch), an open frontal area of 52% w/w, and a wall thickness of 0.9 mm. The raw materials and the natural zeolite ceramic monolith (NZCM) were characterized by X-ray diffraction, N₂ adsorption-desorption at 77 K, CO₂ adsorption at 273 K, mercury intrusion-extrusion, axial compression tests, resistance to leaching at acidic and basic pH, and point of zero charge. The NZCM presented an S_BET = 31 m²∙g^-1, a modal micropore size of 0.44 nm, a porosity of 39%, the compressive stress = 14 MPa, and a pH_PZC = 7.5. The NZCM was used as an inexpensive and easy-to-handle adsorbent to remove methylene blue (MB) dye in batch studies of kinetics and adsorption isotherms. From modeling of adsorption kinetic data, the predominant phenomenon in this system was physisorption. The modeling of adsorption isotherm data shows that the material has homogeneous active sites. The adsorption occurs by monolayer formation, finding a maximum capacity removal rate of 27 mg MB per gram of NZCM. Compared to other structured materials, a high capacity for removing MB with the ceramic monolith was obtained along with good mechanical properties and resistance in acidic and alkaline environments.

Efficient treatment of saline recalcitrant petrochemical wastewater using heterogeneous UV-assisted sono-Fenton process

An effective hybrid system was applied as a first report for successful treatment of recalcitrant petrochemical wastewater (PCW). In this regards, magnetic powdered activated carbon (MPAC), as a heterogeneous catalyst, was coupled with ultrasound (US) and UV irradiations for activation of H₂O₂ (marked as MPAC/US/UV/H₂O₂). Chemical oxygen demand (COD) removal ratio was evaluated with various influencing operating factors including solution pH, MPAC and H₂O₂ concentrations, US power and quenchers. A possible mechanism for catalytic degradation and generation of reactive species was proposed. To evaluate the biodegradability of both raw and treated PCWs, the activated sludge inhibition experiments were performed based on Zahn-Wellens test. MPAC indicated high catalytic activity, reusability and stability in the studied system. Over 87% of COD was removed under optimum conditions within 80 min treatment and the residual COD concentration reached 82.9 mg/L, which was permissible to discharge surface water sources based on the environmental standards. Leaching of transition metals from catalyst textural was negligible. Compared to homogeneous system (Fe²⁺/US/UV/H₂O₂), heterogeneous system (MPAC/US/UV/H₂O₂) represented a better performance in COD removal. Identification of intermediates by GC-MS showed that a wide range of recalcitrant compounds was removed and/or degraded into small molecular compounds effectively after treatment. A biodegradability ratio of 64% and the residual COD of 28 mg/L for treated PCW, indicating that the biodegradability was improved and refractory organic matters removed effectively. As conclusion, MPAC/US/UV/H₂O₂ hybrid system can be introduced as a successful advanced treatment process for efficient remediation of refractory PCWs.

Effects of iron (hydr)oxides on the degradation of diethyl phthalate ester in heterogeneous (photo)-Fenton reactions

This work studied the structural effects of hematite (α-Fe₂O₃), 2-line ferrihydrite (HFO) and goethite (α-FeOOH) on diethyl phthalate ester (DEP) degradation. The results showed that the degradation of DEP was faster under 365 nm light irradiation than in the dark in the presence of iron (hydr)oxides. The apparent kinetic rates of DEP degradation followed the order HFO > goethite ≈ hematite in the dark and HFO > hematite > goethite under 365 nm light irradiation. Two pathways governed H₂O₂ decomposition efficiency on iron (hydr)oxide surfaces: (1) forming OH on inherent surface hydroxyl groups (Fe-OH) and (2) producing O₂ and H₂O on the surface oxygen vacancies. X-ray photoelectron spectroscopy (XPS) analyses indicated that HFO not only has high Fe-OH content but also has high Vo content, resulting in its low H₂O₂ utilization efficiency (η). DEP was degraded through hydrogen abstraction and de-esterification, and the major products were (OH)₂-DEP, mono-ethyl phthalate (MEP), OH-MEP, and phthalate acid (PA). The study is important in understanding the transformation of phthalate esters in top surface soils and surface waters under ultraviolet light.

Towards understanding of heterogeneous Fenton reaction using carbon-Fe catalysts coupled to in-situ H2O2 electro-generation as clean technology for wastewater treatment

Iron-supported catalyst on granular activated carbon was prepared for its use in heterogeneous Fenton reaction coupled to an in situ H₂O₂ electro-generation. For this process, an electrolysis cell was employed, using carbon felt as cathode and graphite as anode. A solution of H₂O₂ (electrogenerated at a rate of 30 mg L^-1 h^-1) was obtained using a current intensity of 12 mA. In order to promote the decomposition of H₂O₂ to OH, a Carbon-Fe catalyst was used. This catalyst was prepared by incipient wet impregnation using FeSO₄ as precursor salt to obtain samples with 9% wt of iron. Samples were characterized by EDX, FTIR and XPS spectroscopy before and after wastewater treatment using phenol as model molecule. Two iron oxidation states on the samples were found, Fe²⁺ and Fe³⁺. The ratio between Fe²⁺/Fe³⁺ was 1.29 which was later reduced to 0.92 after Fenton process; this might be associated with the metal oxidation (Fe²⁺ to Fe⁺³) occurring during Fenton-reaction, thus indicating that H₂O₂ decomposition was carried out by Fe²⁺ on carbon surface. Detection and quantification of hydroxyl radical were carried out by fluorescence spectroscopy, obtaining a radical concentration of 3.5 μM in solution. Iron in solution were determined, showing a concentration of 0.1 mg L^-1, making evident that the supported metal is stable and the reaction is carried out in a heterogeneous phase. Results showed an environmentally friendly process that can generate reagents in situ, with high efficiencies in the degradation of pollutants and minimizing the formation of toxic byproducts, which are common in conventional treatments.

UiO-66-supported Fe catalyst: a vapour deposition preparation method and its superior catalytic performance for removal of organic pollutants in water

A vapour deposition (VD) method was established for preparation of the UiO-66-supported Fe (Fe/UiO-66) catalyst, which provided the first case of the metal-organic framework (MOF)-supported Fe catalyst prepared by using the vapour-based method. The Fe loading was around 7.0-8.5 wt% under the present preparation conditions. The crystal structure of UiO-66 was not obviously influenced by the Fe loading, while the surface area significantly decreased, implicating most of the Fe components resided in the pores on UiO-66. The results for the methyl orange (MO) removal tests showed that MO in aqueous solution can be removed by UiO-66 by adsorption, and in contrast, it can be oxidized by H2O2 with the catalysis of Fe/UiO-66. Further catalytic tests showed that Fe/UiO-66 was rather effective to catalyse the oxidation of benzene derivatives like aniline in water in terms of chemical oxygen demand (COD) removal efficiency. The catalytic test results for Fe/UiO-66 were compared to those of Fe/Al2O3 with the same Fe loading and to the catalysts reported in the literature. This paper provides a general strategy for VD preparation of MOF-supported Fe catalyst on the one hand, and new catalysts for removing organic pollutants from water, on the other hand.

Basic Treatment in Natural Clinoptilolite for Improvement of Physicochemical Properties

Natural zeolites are low in cost and exhibit interesting properties for applications in adsorption and catalysis. However, the fact that they are natural materials, not obtained in pure form, and can incorporate various compensating ions can compromise their properties and restrict their use. As their textural and chemical properties are of great relevance for adsorption and catalysis applications, this work aims to study the modification of the natural zeolite clinoptilolite to obtain materials with better physicochemical properties. Clinoptilolite was treated with NaOH under various conditions. The treated material was characterized by X-ray diffraction, X-ray fluorescence, N2 adsorption and desorption at 77 K, CO2 adsorption at 273 K, and pyridine adsorption. The treatment allowed the removal of silicon from the material, improving the textural properties and preserving the structural Al. With the removal of Si, the Si/Al ratio decreased, and consequently, the number of acid and adsorptive sites increased. In addition, statistical planning revealed that the concentration of NaOH is the parameter that most influences the improvement of the textural properties.

Fe1-xZnxS ternary solid solution as an efficient Fenton-like catalyst for ultrafast degradation of phenol

Heterogeneous Fenton-like system has been proved to be an promising alternative to Fenton system due to its easy separation. However, it's a challenge to design heterogeneous Fenton-like catalysts with high activity and great durability. Here, ternary solid solution Fe_1-xZn_xS were prepared via hydrothermal synthesis as heterogeneous Fenton-like catalysts. The Fe_0.7Zn_0.3S sample exhibited state of the art activity for yielding OH by H₂O₂ decomposition, and the ultrafast degradation of phenol was achieved in 4 min at initial acidic condition under room temperature. The phenol degradation rate constant of Fe_0.7Zn_0.3S was 99 and 70 times of ZnS and FeS, respectively. Further, we show that the unique structural configuration of iron atoms, the formation of FeS₂-pyrite with (200) plane, are responsible for the excellent activity. The intermediate products were identified by LC-MS and a possible pathway was accordingly proposed to elucidate the mechanism of phenol degradation by OH. Overall, this work provides an idea for the rational design of the relevant heterogeneous Fenton-like catalysts.

The preparation of Fe2O3-ZSM-5 catalysts by metal-organic chemical vapour deposition method for catalytic wet peroxide oxidation of m-cresol

Fe₂O₃-ZSM-5 catalysts (0.6 wt% Fe load) prepared by metal-organic chemical vapour deposition (MOCVD) method were evaluated in the catalytic wet peroxide oxidation (CWPO) of m-cresol in a batch reactor. The catalysts have a good iron dispersion and small iron crystalline size, and exhibit high stability during reaction. In addition, the kinetics of the reaction were studied and the initial oxidation rate equation was given. Catalysts were first characterized by N₂ adsorption-desorption isotherms, scanning electronic microscopy, energy-dispersive spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy. Results show that extra-framework Fe³⁺ species (presenting in the form of Fe₂O₃) are successfully loaded on ZSM-5 supports by MOCVD method. Performances of catalysts were tested and effects of different temperature, stirring rate, catalyst amount on hydrogen peroxide, m-cresol, total organic carbon (TOC) conversion and Fe leaching concentration were studied. Results reveal that catalytic activity increased with higher temperature, faster stirring rate and larger catalyst amount. In all circumstances, m-cresol conversion could reach 99% in 0.5-2.5 h, and the highest TOC removal (80.5%) is obtained after 3 h under conditions of 60°C, 400 r.p.m. and catalyst amount of 2.5 g l^-1. The iron-leaching concentrations are less than 1.1 mg l^-1 under all conditions. The initial oxidation rate equation [Formula: see text] is obtained for m-cresol degradation with Fe₂O₃-ZSM-5 catalysts.

Adsorption and catalytic oxidation of organic pollutants using Fe-zeolite

In this work, a natural zeolite, modified and loaded with iron (NZ-A-Fe) as a heterogeneous catalyst, was characterized for its suitability as a permeable reactive barrier (PRB) material for treatment of aromatic hydrocarbons in groundwater. Adsorption and oxidation processes were analyzed. Batch adsorption tests for benzene, toluene and xylene (BTX) aqueous concentrated solutions were performed at neutral pH. Kinetic adsorption was described with the pseudo-second-order model. Experiments were performed using a stirred batch reactor with near 11 mM initial BTX concentration applying NZ-A-Fe as solid catalyst and H₂O₂ as an oxidant. BTX removal reached 80% in 600 min in these experimental conditions. Catalytic oxidation was described with a pseudo-first-order kinetic model. No significant iron leaching was detected during all the experiences. These investigations show that coupling adsorption with catalytic oxidation with this novel system is a promising procedure to simultaneously remove BTX from moderately concentrated aqueous solution at neutral pH in groundwater.

Phenol degradation catalyzed by a peroxidase mimic constructed through the grafting of heme onto metal-organic frameworks

The aim of this work was to construct a peroxidase mimic for achieving the phenol degradation through Fenton reaction. The enzyme mimic was synthesized through the conjugation of heme with the amino group of 2-amino-1,4-benzene dicarboxylate in UiO-66-NH₂ (ZrMOF), namely Heme-ZrMOF. Compared to free heme, the composite Heme-ZrMOF exhibited an obviously enhanced ability for phenol degradation with up to 97.3% of phenol removal after 2h. Meanwhile, it could achieve the easy separation of catalyst from the system and the elimination of iron residues in the process of phenol degradation. Finally, the catalyst Heme-ZrMOF was observed to possess good recyclability in the phenol degradation with still 76.2% of phenol removal after 4 cycles.

VUV/UV light inducing accelerated phenol degradation with a low electric input

This study presents the first evidence for the accelerated degradation of phenol by Fenton's reagent in a mini-fluidic VUV/UV photoreaction system (MVPS). A low-pressure mercury lamp used in the MVPS led to a complete degradation of phenol within 4-6 min. The HO˙ and HO₂˙ originating from both Fenton's reagent and VUV photolysis of water were identified with suitable radical scavengers. The effects of initial concentrations of phenol, H₂O₂ and Fe³⁺ as well as solution pH on phenol degradation kinetics were examined. Increasing the initial phenol concentration slowed down the phenol degradation, whereas increasing the initial H₂O₂ or Fe³⁺ concentration accelerated the phenol degradation. The optimal solution pH was 3.7. At both 254 and 185 nm, increasing phenol concentration enhanced its absorption for the incident photons. The reaction mechanism for the degradation of phenol was suggested consistent with the results obtained. This study indicates that the VUV/UV photo-Fenton process has potential applications in the treatment of industrial wastewater containing phenol and related aromatic pollutants.

Synthesis, characterization and performance of high energy ball milled meso-scale zero valent iron in Fenton reaction

Understanding contaminant degradation by different sized zero valent iron (ZVI) particles is one important aspect in addressing the long-term stability of these particles in field studies. In this study, meso zero valent iron (mZVI) particles were synthesised in a milling time of 10 h using ball milling technique. The efficacy of mZVI particles for removal of phenol was quantitatively evaluated in comparison with coarse zero valent iron (cZVI) and nano zero valent iron (nZVI) particles. Phenol degradation experiments were carried out in sacrificial batch mode at room temperature independently with cZVI, nZVI and mZVI under varied pH conditions of 3, 4, 6, 7, 8 and 10. Batch experiments substantiating the reactivity of mZVI under unbuffered pH system were also carried out and compared with buffered and poorly buffered pH systems. mZVI particles showed consistent phenol degradation at circum-neutral pH with efficiency of 44%, 67%, and 89% in a span of 5, 10 and 20 min respectively. The dissolved iron species and residual iron formation were also measured as a function of pH. Unbuffered systems at circum-neutral pH produced less residual iron when compared to buffered and poorly buffered systems. At this pH, oxidation of Fe(2+) produced a different oxidant Ferryl ion, which was found to effectively participate in phenol degradation.

Fenton Process Coupled to Ultrasound and UV Light Irradiation for the Oxidation of a Model Pollutant

The Fenton process coupled to photosonolysis (UV light and Us), using Fe2O3catalyst supported on Al2O3, was used to oxidize a model pollutant like acid green 50 textile dye (AG50). Dye degradation was followed by AG50 concentration decay analyses. It was observed that parameters like iron content on a fixed amount of catalyst supporting material, catalyst annealing temperature, initial dye concentration, and the solution pH influence the overall treatment efficiency. High removal efficiencies of the model pollutant are achieved. The stability and reusability tests of the Fe2O3catalyst show that the catalyst can be used up to three cycles achieving high discoloration. Thus, this catalyst is highly efficient for the degradation of AG50 in the Fenton process.

Degradation of phenol by a heterogeneous photo-Fenton process using Fe/Cu/Al catalysts

Cu²⁺ and Fe³⁺ can react with H₂O₂, producing Cu⁺, Fe²⁺, and ˙OH. Then ˙OH can react with phenol directly. The degradation of phenol leads to the formation of the mixed byproducts, such as catechol, benzoquinone, resorcinol and hydroquinone.

Degradation of tetracycline hydrochloride by heterogeneous Fenton-like reaction using Fe@Bacillus subtilis

In this work, a novel heterogeneous catalyst Fe@Bacillus subtiliswas firstly fabricatedviaa simple impregnation method and its catalytic efficiency was examined for removal of tetracycline hydrochloride.

Synthesis of magnetic alginate beads based on Fe3O4 nanoparticles for the removal of 3-methylindole from aqueous solution using Fenton process

A novel magnetic heterogeneous catalyst has been developed by incorporation of iron(II) and magnetic functionalized nanoparticles Fe3O4 in alginate beads with the aim of using them in the advanced Fenton oxidation of a malodorous compound (3 methyl-indole: 3-MI). The effects of significant operational parameters such as initial pH, oxidant concentration and catalyst amount were investigated and optimized for a better removal of 3-MI at initial concentration of 20mgL(-1). Besides, the catalyst stability was evaluated according to the iron leached into the aqueous solution. Results revealed that the parameters affecting Fenton catalysis must be carefully chosen to avoid excessive iron release. Under optimized conditions, the magnetic catalyst exhibited a good catalytic performance. Total removal of 3 methyl indole and a remarkable organic mineralization, without significant leaching of iron, were attained within 120min at pH 3.0 by using 0.4gL(-1) of Fe-MABs and 9.8mmolL(-1) of H2O2. The novel magnetic catalyst would be of potential application due to its high efficiency, easy recovery and good structural stability.

Degradation and mineralization of phenol compounds with goethite catalyst and mineralization prediction using artificial intelligence

The efficiency of phenol degradation via Fenton reaction using mixture of heterogeneous goethite catalyst with homogeneous ferrous ion was analyzed as a function of three independent variables, initial concentration of phenol (60 to 100 mg /L), weight ratio of initial concentration of phenol to that of H₂O₂ (1: 6 to 1: 14) and, weight ratio of initial concentration of goethite catalyst to that of H₂O₂ (1: 0.3 to 1: 0.7). More than 90 % of phenol removal and more than 40% of TOC removal were achieved within 60 minutes of reaction. Two separate models were developed using artificial neural networks to predict degradation percentage by a combination of Fe³⁺ and Fe²⁺ catalyst. Five operational parameters were employed as inputs while phenol degradation and TOC removal were considered as outputs of the developed models. Satisfactory agreement was observed between testing data and the predicted values (R²_Phenol = 0.9214 and R²TOC= 0.9082).

Heterogeneous catalytic wet peroxide oxidation of simulated phenol wastewater by copper metal–organic frameworks

Two different porous copper metal–organic frameworks (Cu-MOFs) named as Cu₃(BTC)₂ and Cu(BDC) were synthesized and applied as heterogeneous catalysts for the catalytic wet peroxide oxidation (CWPO) of simulated phenol wastewater (100 mg L⁻¹).

Kinetic modeling of a heterogeneous Fenton oxidative treatment of petroleum refining wastewater

The mineralisation kinetics of petroleum refinery effluent (PRE) by Fenton oxidation were evaluated. Within the ambit of the experimental data generated, first-order kinetic model (FKM), generalised lumped kinetic model (GLKM), and generalized kinetic model (GKM) were tested. The obtained apparent kinetic rate constants for the initial oxidation step (k₂′), their final oxidation step (k₁′), and the direct conversion to endproducts step (k₃′) were 10.12, 3.78, and 0.24 min⁻¹ for GKM; 0.98, 0.98, and nil min⁻¹ for GLKM; and nil, nil, and >0.005 min⁻¹ for FKM. The findings showed that GKM is superior in estimating the mineralization kinetics.

Preparation of magnetic recoverable nanosize Cu-Fe2O3/Fe photocatalysts

Iron based catalysts generally have the advantage of the easily operated magnetically recovery from application sites. In the present work, paramagnetic iron and copper core-shell nanoparticles having the iron fractions (X(Fe) = Fe/(Cu+Fe)) of 0.33-1.0 were prepared and characterized by in situ synchrotron X-ray absorption and scattering spectroscopy. During the temperature-programmed carbonization (TPC) of Cu(2+)- and Fe(3+)-β-cyclodextrin (CD) complexes, a rapid reduction of Cu(II) occurs at about 453 K together with a growth of the metallic copper (Cu). Iron proceeds in the distinct growth path. At 453-513 K, the Fe(III) → Fe(II) → Fe consecutive reduction is observed. The unreduced Fe(III) (7-13%) is coated on the surfaces of the Fe nanoparticles (as Fe2O3/Fe). Growth of the Fe nanoparticle is inhibited by the surface Fe2O3, while the steady growth in Cu is observed. The Cu has a size range of 14-18 nm in diameter, compared to the small Fe2O3/Fe ones (3-6 nm). Under the UV-visible light irradiation for four hours, methylene blue can be photocatalytically degraded (>90%) by the (Cu-Fe2O3/Fe)@C. The (Cu-Fe2O3/Fe)@C photocatalysts can effectively oxidize dye molecules, providing a promising alternative for dye degradation using solar energy. Recovery of the (Cu-Fe2O3/Fe)@C photocatalysts can be attained by applying external magnetic field to trap the ferromagnetic Cu-Fe2O3/Fe nanoparticles, which suggests an economically attractive process, especially applied in photocatalytic degradation of dye-contaminated wastewater.