Effect of UV Radiation on the Removal of Carboxylic Acids from Water by H2O2 and O3 in the Presence of Metallic Ions

The effect of UV radiation on the removal of formic, oxalic and maleic acids from water by metallic ion (Fe²⁺ or Cu²⁺)/H₂O₂ and metallic ion/O₃ was studied and compared. The results showed that metallic ion/O₃/UV has higher efficiency than metallic ion/H₂O₂/UV for oxalic acid removal. UV radiation significantly increases the efficiency of metallic ion/H₂O₂ for formic and maleic acids removal while its effect on the efficiency of metallic ion/O₃ for formic acid removal is minor_. However, at pH 2, O₃ alone showed higher efficiency than metallic ion/H₂O₂/UV for formic acid removal. Contrary to the relative efficiency of metallic ions in the previous systems, Cu²⁺ exhibited higher rate than Fe²⁺ for the removal of the degradation products of maleic acid by O₃. UV radiation exhibited a minor effect on the efficiency of Cu²⁺/O₃, while it exhibited a large effect on the efficiency of Fe²⁺/O₃ for the removal of the degradation products of maleic acid.     

Decomposition of Carboxylic Acids in Water by O3, O3/H2O2, and O3/Catalyst

This paper studies the decomposition of formic, oxalic and maleic acids by O₃, O₃/catalyst, and O₃/H₂O₂. The catalytic effect of Co²⁺, Ni²⁺, Cu²⁺, Mn²⁺, Zn²⁺, Cr³⁺, and Fe²⁺ ions is investigated. The results showed that—Co²⁺ and Mn²⁺ have the highest catalytic activity for the decomposition of oxalic acid while the catalytic effect of the studied ions is insignificant on the rate of decomposition of formic acid. Maleic acid decomposes by ozone into formic acid and glyoxylic acid, which subsequently oxidizes to oxalic acid. Though the studied ions have no effect on the decomposition of maleic acid, they have a significant effect on the produced oxalic and glyoxylic acids. In the presence of Cu²⁺ ions glyoxylic acid is mainly transformed into formic acid and traces of oxalic acid. In such case, a complete decomposition of maleic acid and its degradation products is achieved within 45 min. The results also show that combining H₂O₂ with O₃ results in an increase in the rate of decomposition of oxalic acid. However, O₃/H₂O₂ system is less active than O₃/Co²⁺ or O₃/Mn²⁺.     

Highly stable Fe/γ‐Al2O3 catalyst for catalytic wet peroxide oxidation

BACKGROUND: A highly stable Fe/γ‐Al₂O₃ catalyst for catalytic wet peroxide oxidation has been studied using phenol as target pollutant. The catalyst was prepared by incipient wetness impregnation of γ‐Al₂O₃ with an aqueous solution of Fe(NO₃)₃· 9H₂O. The influence of pH, temperature, catalyst and H₂O₂ doses, as well as the initial phenol concentration has been analyzed. RESULTS: The reaction temperature and initial pH significantly affect both phenol conversion and total organic carbon removal. Working at 50 °C, an initial pH of 3, 100 mg L^?1 of phenol, a dose of H₂O₂ corresponding to the stoichiometric amount and 1250 mg L^?1 of catalyst, complete phenol conversion and a total organic carbon removal efficiency close to 80% were achieved. When the initial phenol concentration was increased to 1500 mg L^?1, a decreased efficiency in total organic carbon removal was observed with increased leaching of iron that can be related to a higher concentration of oxalic acid, as by‐product from catalytic wet peroxide oxidation of phenol. CONCLUSION: A laboratory synthesized γ‐Al₂O₃ supported Fe has shown potential application in catalytic wet peroxide oxidation of phenolic wastewaters. The catalyst showed remarkable stability in long‐term continuous experiments with limited Fe leaching, < 3% of the initial loading. Copyright © 2010 Society of Chemical Industry     

Removal of Cu2+ Ions from Aqueous Solutions by Starch-Graft-Acrylic Acid Hydrogels

Gelatinized starch was prepared by constantly stirring a mixture of starch and water at 95°C for 1 hour. Starch-graft-acrylic acid (S-g-AA) hydrogels were prepared by grafting acrylic acid (AA) [monomer/starch (w/w) 0.5–1.5] onto gelatinized starch with ceric ammonium nitrate as initiator under nitrogen atmosphere. The surface morphology of samples was studied using a scanning electron microscope (SEM). The hydrogels were evaluated for the removal of Cu²⁺ ion from aqueous solutions at different pH. The concentration of Cu²⁺ ion in aqueous solution was kept constant at 4 mmol/L. The metal ion removal capacities changed depending on treatment time, initial pH of the solution, and monomer/starch (w/w) ratio of the S-g-AA hydrogels. Cu²⁺ ion removal capacities were determined by atomic absorption spectrometer (AAS).     

Effect of Cu doping on the SCR activity of CeO2 catalyst prepared by citric acid method

CeO₂–CuO catalyst prepared by citric acid method was investigated for selective catalytic reduction of NO with NH₃. The activity of the CeO₂ catalyst was enhanced about 8–27% in the temperature range of 125–225 °C at a space velocity of 28,000 h⁻¹ by the addition of Cu. It was found that the state of Cu species had great impact on the SCR performance of CeO₂–CuO catalyst. Cu²⁺ can enhance the low temperature activity of SCR reaction, while CuO would promote NH₃ oxidation before SCR reaction at high temperature, which would cause the decrease of its high temperature SCR activity.     

Radical polymerisation of ethyl acrylate in the presence of molecular oxygen

Oxygen as a promoter of radical polymerisation of ethyl acrylate was studied in the aqueous medium. Cu²⁺ was chosen as the catalyst for the ascorbic acid (AA)—0₂ redox reaction, constituting a three component initiating system. The rate of polymerisation, R_p, was observed to increase, remain constant and then decrease with increasing [Cu²⁺]. R_p increased with [O₂] upto ～ 6.5 × 10^?4M and thereafter remained constant. [AA] > 1.2 × 10^?3M did not influence the rate. R_p always increased with monomer [M] at fixed [Cu²⁺], [O₂] and [AA]. However, the order with respect to [M] increased with increasing [Cu²⁺]. The rate of polymerisation increased with ionic strength, μ and decreased with [H₂SO₄]. There was an initial increase in R_p followed by a decrease with increasing temperature. Conditions were identified where R_p depended only on [Cu²⁺] and [M] or [M] only for industrial exploitation. Kinetic chain length of the polymers obtained under various experimental conditions were determined viscometrically.     

Solar photoassisted anodic oxidation of carboxylic acids in presence of Fe using a boron-doped diamond electrode

This paper reports a comparative study on the anodic oxidation of 2.5 l of 50 mg l⁻¹ TOC of formic, oxalic, acetic, pyruvic or maleic acid in 0.1 M Na₂SO₄ solutions of pH 3.0 with and without 1.0 mM Fe³⁺ as catalyst in the dark or under solar irradiation. Experiments have been performed with a batch recirculation flow plant containing a one-compartment filter-press electrolytic reactor equipped with a 20 cm² boron-doped diamond (BDD) anode and a 20 cm² stainless steel cathode, and coupled to a solar photoreactor. This system gradually accumulates H₂O₂ from dimerization of hydroxyl radical (OH) formed at the anode surface from water oxidation. Carboxylic acids in direct anodic oxidation are mainly oxidized by direct charge transfer and/or OH produced on BDD, while their Fe(III) complexes formed in presence of Fe³⁺ can also react with OH produced from Fenton reaction between regenerated Fe²⁺ with electrosynthesized H₂O₂ and/or photo-Fenton reaction. Fast photolysis of Fe(III)-oxalate and Fe(III)-pyruvate complexes under the action of sunlight also takes place. Chemical and photochemical trials of the same solutions have been made to better clarify the role of the different catalysts. Solar photoassisted anodic oxidation in presence of Fe³⁺ strongly accelerates the removal of all carboxylic acids in comparison with direct anodic oxidation, except for acetic acid that is removed at similar rate in both cases. This novel electrochemical advanced oxidation process allows more rapid mineralization of formic, oxalic and maleic acids, without any significant effect on the conversion of acetic acid into CO₂. The synergistic action of Fe³⁺ and sunlight in anodic oxidation can then be useful for wastewater remediation when oxalic and formic acids are formed as ultimate carboxylic acids of organic pollutants, but its performance is expected to strongly decay in the case of generation of persistent acetic acid during the degradation process.     

Studies in mineralization of aqueous aniline using Fenton and wet oxidation (FENTWO) as a hybrid process

A hybrid process for mineralization of aqueous aniline using Fenton and wet oxidation (FENTWO) is studied. It is important to have maximum conversion of ‘N’ atoms from the waste to N₂. The conversion of input ‘N’ atoms in aniline to N₂ was 15% during wet oxidation without the Fenton process and was improved to 50% with the Fenton process. Therefore, a hybrid process of Fenton followed by wet oxidation was studied for mineralization of the aqueous aniline stream. The parameters for the Fenton process were optimized (pH, catalyst, H₂O₂ to catalyst (FeSO₄) ratio, quantity of H₂O₂). The waste obtained after the Fenton process was then treated by wet oxidation for mineralization by having homogeneous CuSO₄ as the catalyst by keeping FeSO₄ therein. This combined catalyst was found to be more effective for the degradation of the intermediates formed in the Fenton process. Wet oxidation (WO) was studied in the temperature range 473–513 K and the oxygen partial pressure range 0.345–1.38 MPa at pH 6.5. The kinetic data was modeled using a power law rate expression in terms of chemical oxygen demand (COD). The optimum temperature for formation of more N₂ gas was found to be 493 K. The treated waste stream was found to contain oxalic acid using HPLC, and NH₄⁺, NO₃^? and NO₂^? ions using ion chromatography analysis. Copyright © 2007 Society of Chemical Industry     

Regeneration of 4-Chlorophenol Exhausted GAC with a Microwave Assisted Wet Peroxide Oxidation Process

To improve the performance of wet oxidation for the regeneration of GAC, a microwave assisted wet peroxide oxidation process has been applied for the regeneration of 4-chlorophenol exhausted GAC. The effects of various factors including reaction temperature, H₂O₂ dosage, reaction time, and addition of catalyst have been studied. The regeneration improves with the increase in reaction temperature, H₂O₂ dosage, and reaction time. The addition of Cu²⁺ further promotes the regeneration process. Under the conditions of temperature 150°C, H₂O₂ dosage 15 mmol, reaction time 20 min, Cu²⁺ concentration 20 mg/L, the regenerated GAC recovers 93.5% of its adsorption capacity. A nearly complete degradation of 4-chlorophenol in the aqueous phase is observed based on UV-vis and high-performance liquid chromatography spectra studies.     

Distinct synergetic effects in the ozone enhanced photocatalytic degradation of phenol and oxalic acid with Fe3+/TiO2 catalyst

In this work, phenol and oxalic acid(OA) degradation in an ozone and photocatalysis integrated process was intensively conducted with Fe~(3+)/TiO_2 catalyst. The ferrioxalate complex formed between Fe~(3+) and oxalate accelerated the removal of OA in the ozonation, photolysis and photocatalytic ozonation process, for its high reactivity with ozone and UV. Phenol was degraded in ozonation and photolysis with limited TOC removal rates, but much higher TOC removal was achieved in photocatalytic ozonation due to the generation of ·OH. The sequence of UV light and ozone in the sequential process also influences the TOC removal, and ozone is very powerful to oxidize intermediates catechol and hydroquinone to maleic acid. Fenton or photo-Fenton reactions only played a small part in Fe~(3+)/TiO_2catalyzed processes, because Fe~(3+) was greatly reduced but not regenerated in many cases.The synergetic effect was found to be highly related with the property of the target pollutants. Fe~(3+)/TiO_2 catalyzed system showed the highest ability to destroy organics, but the TiO_2 catalyzed system showed little higher synergy.     

Efficient degradation of <Emphasis Type="Italic">para</Emphasis>-chlorobenzoic acid in water by catalytic ozonation with La–Ce–MCM-41

La–Ce–MCM-41 was directly synthesized by a hydrothermal method and applied as heterogeneous catalyst for the ozonation process of para chlorobenzoic-acid (pCBA). La³⁺ and Ce³⁺ were successfully incorporated into the framework of MCM-41 and the formation of degradation products (p-chlorophenol, p-dihydroxybenzene, maleic acid and oxalic acid) were monitored qualitatively using gas chromatography–mass spectrometer and high performance liquid chromatography. Due to the synergy of bimetal and the fast degradation of accumulated intermediates, total organic carbon (TOC) removal efficiency was significantly improved (92 %) in La–Ce–MCM-41/O₃ process compared with ozonation (40 %) at identical reaction condition. The presence of tert-butanol (TBA) in La–Ce–MCM-41/O₃ process indicated that the oxidation of pCBA was mainly due to the function of hydroxyl radicals in the liquid bulk, and a plausible degradation pathway was proposed. TOC removal slightly decreased from 90 to 86 % after La–Ce–MCM-41 being re-utilized three times, which illustrated that La–Ce–MCM-41 was an efficient of promising catalyst for ozonation of pCBA.     

Kinetic evaluation of mechanistic models for O2 release from ZSM-5-supported [Cu2+ –O–Cu2+] ions by thermal reduction or chemical interaction with impinging N2O molecules

For a series of oxidized Cu-ZSM-5 catalysts which were characterized in the catalytic amounts of the oxygen-bridged Cu²⁺-dimers, [Cu²⁺–O–Cu²⁺], activation energies required for the reduction of the Cu²⁺-dimer species by O₂ release were determined using the temperature-programmed experiments of thermal O₂ desorption (TPD) and N₂O decomposition reaction. The activation energy for the thermal reduction of the Cu²⁺-dimers during the TPD decreased linearly with increasing molar number of the Cu²⁺-dimers available on the ZSM-5, suggesting that the energy barrier of the O₂ formation via a Langmuir-Hinshelwood (LH) mechanism increased in proportion to the distance between the two Cu²⁺-dimers in the nearest neighbor. Activation energies of thermal O₂ release were comparable to the literature-reported binding energies of the differently spaced Cu²⁺-dimers. It was also revealed that the activation energy of O₂ release during the temperature programmed N₂O decomposition reaction over an oxidized catalyst was generally low as compared to that in the TPD, and that the degree of reduction of the Cu²⁺-dimers was much greater in the N₂O decomposition reaction than in the TPD at the same temperatures. These beneficial effects N₂O decomposition on the reduction of the Cu²⁺-dimers were discussed in respect of the removal mechanism of the Cu²⁺-dimer bridged oxygen.     

Kinetics of polymerization of styrene. The catalyst system Cu2Cl2 + AlEt3 in n-hexane

Studies on polymerization of styrene by the heterogeneous catalyst system Cu₂Cl₂ + AlEt₃ are reported. Kinetic studies carried out at an optimum catalyst composition [Al]/[Cu] = 0.8 and aging time of 4 h give a value of 55 kJ/mol for the activation energy. The rate law can be presented as R = K [cat] [mon]². A radical mechanism is proposed on the basis of the effect of hydroquinone and ESR spectra. The mechanism of polymerization with this catalyst system is different than that of CuCl₂ + AlEt₂X (X = Br, Cl), which was reported earlier.     

Simultaneous removal of NO and SO2 using aqueous peroxymonosulfate with coactivation of Cu2+/Fe3+ and high temperature

A novel process on simultaneous removal of NO and SO₂ using aqueous peroxymonosulfate (PMS) with synergic activation of Cu²⁺/Fe³⁺ and high temperature in an impinging stream reactor is developed for the first time. Effects of PMS concentration, Cu²⁺/Fe³⁺ concentration, reaction temperature, solution pH, flue gas flow, liquid–gas ratio, gas components, and inorganic ions on NO/SO₂ removals were investigated. Active species and products were determined by electron spin resonance spectroscopy and ion chromatography. Removal pathways of NO/SO₂ were revealed, and mass transfer‐reaction kinetics of NO removal was studied. The optimal experimental conditions are obtained. H₂SO₄ and HNO₃ are the main products. It is found that there is a clear synergy between Cu²⁺/Fe³⁺ and high temperature for activating PMS. and ·OH are found to be the main oxidants for NO removal. NO removals belong to pseudo‐first fast reactions in the two investigated oxidation systems. Besides, the kinetic parameters are also measured. © 2016 American Institute of Chemical Engineers AIChE J, 63: 1287–1302, 2017     

Basic rules of NO oxidation by Fe2+/H2O2/AA directional decomposition system

Basic rules of NO oxidation by a Fe²⁺/H₂O₂/AA directional decomposition system were researched based on the technical background of flue gas NO_x removal. Effects of gas‐liquid interfacial area, main gas, and solution parameters on NO oxidation efficiency (η) were analyzed. The results showed that adequate contact area was the precondition for high η by a Fe²⁺/H₂O₂/AA system. η decreased with the increase in NO concentration, which illustrated that this method would be efficient in oxidizing NO at a low concentration. η tended to decrease linearly with the growth in gas flow, however, the NO oxidation rate (v) rose with the increase in NO concentration and gas flow. η increased with the initial concentrations of H₂O₂ and Fe²⁺, but the amplitude decreased. Controlling the initial concentrations of H₂O₂ and Fe²⁺ to achieve reasonable synergies between generation rate and consumption rate of ·OH could weaken the invalid consumption of reactants. η increased with the increase in temperature in the range 30–60 °C, but it nearly did not change with temperature after 60 °C. This oxidation technology and the traditional wet flue gas desulphurization technology exhibited temperature synergy. Under typical pH of wet desulphurization, η and H₂O₂ consumption rate did not change obviously.     

Spatially resolved indiffusion behavior of Cu2+ and Ni2+ in polypropylene

Microplastics and their effects on the environment and food chain have become increasingly important in recent years. These polymer particles, which are only few millimeters in size or smaller, accumulate in the environment and can enter the human food chain via animals that ingest them. Moreover, they can accumulate impurities such as heavy metals. Therefore, this study focuses on the indiffusion behavior of metal ions into semicrystalline polypropylene (PP) applying time-of-flight secondary ion mass spectrometry (ToF-SIMS) at cryo-conditions. Diffusion coefficients of Cu²⁺ and Ni²⁺ in PP are determined by classical SIMS depth profiling in frozen state (T <−130°C) and subsequent data analysis according to Fick's second law of diffusion. The results show that diffusion of Cu²⁺ ions in dry PP (D_PP,Cu = [2.21 ± 0.15]·10⁻¹² cm²/s) is faster compared to Ni²⁺ ion diffusion of dry PP (D_PP,Ni = [4.43 ± 0.55]·10⁻¹³ cm²/s). Interestingly, the diffusion of Cu²⁺ ions in water-saturated PP (D_PP,H2O,Cu = [1.91 ± 0.28]·10⁻¹³ cm²/s) is slower compared to Cu²⁺ ion diffusion in dry PP. Furthermore, high-lateral resolution ToF-SIMS analysis shows that metal ions only diffuse in certain areas of PP, which are most likely amorphous.     

Conventional and wet proofed CuO/Al2O3 catalysts for phenol oxidation: deactivation studies in a trickle bed reactor

A large variety of catalytic systems have been studied for the catalytic wet air oxidation of phenolic solutions. Most of them show good activity, but serious stability problems. In this contribution, stability studies were performed over CuO/Al₂O₃ conventional (CNT) and polytetrafluorethylene coated (C3T) catalysts used for the oxidation of 5 g L^?1 phenol solutions in a trickle bed reactor (140 °C and 7 atm of oxygen pressure). For the hydrophilic catalyst, phenol conversion decreased with usage due to the formation of Cu₂O and copper oxalate phases. For the wet proofed catalyst, the hydrophobic layer prevented the appearence of those phases, and conversion levels remained practically constant with reaction time. After usage, both catalysts were oxidized at 400 °C and tested for reaction: in the case of the C3T catalyst, the phenol conversion was increased over its initial level; for CNT catalyst, the phenol conversion was also increased, but initial levels were not completely restored. The deactivation mechanism of the CNT catalyst is associated with the formation of the Cu₂O and copper oxalate phases during reaction. For catalyst C3T, practically no deactivation was observed. Copyright © 2007 Society of Chemical Industry     

Catalytic combustion of SOFC stack flue gas over CuO and Mn2O3 supported by La0.8Sr0.2Mn0.67Cu0.33O3 perovskite

An efficient oxidation catalyst was developed to increase the combustion efficiency of unreacted CO, H₂, and CH₄ in flue gas of solid oxide fuel cell (SOFC) stack. Amorphous Cu‐Mn oxide catalyst (CuMnLa/Alumina) showed high catalytic activity, but significant degradation occurred due to phase transition to spinel structure at high temperatures (T > 650°C). La_0.8Sr_0.2Mn_0.67Cu_0.33O₃ perovskite (LSMC(p)) supported CuO or Mn₂O₃ exhibited improved thermal stability than CuMnLa/Alumina catalyst. Especially in case of 50Mn/LSMC(p), after the catalyst was exposed to 800°C for 24 h, T₅₀ of CO, H₂ and CH₄ was achieved at 170, 230, and 600°C, respectively. This result is much lower than that of CuMnLa/Alumina, which was exposed to the same condition. The high combustion efficiency is due to retention of the Cu²⁺‐Mn³⁺ redox couple, and supply of lattice oxygen from LSMC(p), especially at high temperature. © 2017 American Institute of Chemical Engineers AIChE J, 64: 940–949, 2018     

Template synthesis and characterization of hexaaza macrocycles containing pyridine iron(II) complex nanoparticles dispersed within nanoreactors of zeolite-Y

Iron(II) complexes with 18- and 20-membered hexaaza macrocyclic ligands were entrapped in the nanoreactors of zeolite-Y by a two-step process in the liquid phase: (i) adsorption of [bis(diamine)iron(II)] (diamine = 1,2-diaminoethane, 1,3-diaminopropane, 1,2-diaminobenzene, 1,3-diaminobenzene); [Fe(N–N)₂]²⁺–NaY; in the nanoreactors of the zeolite, and (ii) template condensation of the iron(II) precursor complex with 2,6-diacetylpyridine.The mode of bonding and overall geometry of the complexes and new complex nanoparticles entrapped in the nanoreactor of zeolite-Y ([Fe([18 or 20]py₂N₄)]²⁺–NaY, [Fe(Bzo₂[18 or 20]py₂N₄)]²⁺–NaY) has been inferred through FT-IR, TGA, XRD, XPS spectroscopic techniques and elemental analysis as well as nitrogen adsorption.     

Adsorption of Cu2+ Cations from Aqueous Solution by S-doped TiO2

S-doped TiO₂ as a novel adsorbent for Cu²⁺ cations removal from aqueous solutions was synthesized by simple sol-gel process. Removal of Cu²⁺ cations from aqueous solutions was investigated with particular reference to the effects of initial Cu²⁺ cations concentration, pH-value, adsorbent dosage, and temperature on adsorption. It was found that the maximum adsorption capacity was 96.35 mg g^?1 at 328 K. The adsorption equilibrium isotherms and the kinetic data were well described by the Langmuir and pseudo-second-order kinetic models, respectively. The high uptake capability of S-doped TiO₂ makes it a potentially attractive adsorbent for the removal of heavy metal pollutants from aqueous solution.