Adsorption of Phenol and 2,4‐Dinitrophenol on Activated Carbon Cloth: The Influence of Sorbent Surface Acidity and pH

Abstract

In this work the effect of the activated carbon cloth surface acidity and pH of the solution on phenols adsorption has been studied. Two phenols, widely different in the terms of their pKa values (phenol and 2,4‐dinitrophenol), have been chosen as the model compounds. It has been shown that phenol adsorption was favored by low pH values of solution and high point of zero charge values of activated carbon cloths. The adsorption of 2,4‐dinitrophenol was promoted at very low pH values of solution and it was less influenced by activated carbon cloth surface acidity.     

Influence of pH on the wet oxidation of phenol with copper catalyst

This work reports the influence of pH on the catalytic wet oxidation (CWO) of phenol performed with a commercial copper-based catalyst. The results obtained show that pH is a critical parameter able to modify the chemical stability of the catalyst, the significance of the oxidation reaction in the liquid phase, the reaction mechanism and, consequently, the oxidation route of phenol. Experiments have been carried out to study the mentioned aspects. Stirred basket and fixed bed reactors (FBRs) have been employed, at 140 °C and at 16 bar of oxygen pressure. Three initial pH values have been used: 6 (the pH of the phenol solution), 3.5 (adjusted by H₂SO₄) and 8 (by addition of Na₂CO₃). Furthermore, some phenol oxidation runs without solid catalyst but with different concentrations of copper in solution have been accomplish at pHo=3.5. At acid pH, important leaching of copper from the catalyst to the solution was achieved, finding this negligible at pH 8. It was found that the major contribution to the phenol conversion reached at acid pH by using the solid catalyst was due to the catalytic activity of the leached copper. Both oxidation mechanisms at acid and basic conditions have been elucidated to explain the differences in the type and distribution of the intermediates obtained. The catalytic phenol oxidation route found at pH=8 comprises intermediates less toxic than phenol while at acid pH the cyclic intermediates formed as first oxidation intermediates are far more toxic than phenol.     

苯酚的O_3/H_2O_2化学氧化反应动力学研究

应用 Stopped- flow光谱仪研究苯酚在 2 88～ 30 8K和 p H=3.2～ 9.8的 O3 / H2 O2 氧化反应动力学。通过实验及分析认为 :在不同酸度的实验条件下苯酚 O3 / H2 O2 氧化降解的途径及动力学不同。在酸性及弱酸性(p H=6 .5 )下苯酚 O3 / H2 O2 氧化反应机理是苯酚直接为 O3 氧化 ,在碱性 (p H=9.8)时为自由基机理     

异丙醇的O3/H2O2复合氧化动力学研究

采用停流光谱仪研究了异丙醇在T=298K和pH=3～11范围内O3 / H2O2复合氧化的反应动力学.结果表明异丙醇的O3 / H2O2复合氧化反应动力学随反应体系的pH值不同而不同.在酸性和中性条件下,反应相对于O3浓度、异丙醇浓度都为1级;在碱性条件下,异丙醇较容易被O3/H2O2复合氧化降解,总反应级数为2级,相对于O3浓度、异丙醇浓度和H2O2浓度分别为1级、0级和1级,可见异丙醇的降解速率与它的浓度无关.在T=298K,当pH值从9增大到11, 反应速率常数从3486.1(mol·L-1)-1·s-1增大到38239.2(mol·L-1)-1·s-1. 表明在酸性条件下,异丙醇的O3/H2O2复合氧化是O3分子直接攻击异丙醇的反应占主导;在碱性条件下,自由基型反应占主导.     

Copper‐Catalyzed Peroxide Oxidation Testing for Tetraphenylborate Decomposition

Abstract

A new processing option, copper‐catalyzed hydrogen peroxide oxidation of tetraphenylborate under alkaline conditions, was demonstrated in laboratory testing. Laboratory‐scale tests were conducted to evaluate the use of copper‐catalyzed hydrogen peroxide oxidation to treat simulants of the Savannah River Site tank waste. The oxidation process involves the reaction of hydrogen peroxide with a copper catalyst to form hydroxyl free radicals. With an oxidation potential of 2.8 volts, the hydroxyl free radical is a very powerful oxidant, second only to fluorine, and will react with a wide range of organic molecules. The goal is to oxidize the tetraphenylborate completely to carbon dioxide, with minimal benzene generation. Testing was completed in a lab‐scale demonstration apparatus at the Savannah River National Laboratory. Greater than 99.8% tetraphenylborate destruction was achieved in less than three weeks. Offgas benzene analysis by a gas chromatograph demonstrated low benzene generation. Analysis of the resulting slurry demonstrated >82.3% organic carbon destruction. The only carbon compounds detected were formate, oxalate, benzene (vapor), carbonate, p‐terphenyl, quaterphenyl, phenol, and phenol 3‐dimethylamino.     

Ozonation of the reactive dye intermediate 2‐naphthylamine 3,6,8‐trisulphonic acid (K‐Acid): kinetic assessment,ozonation products and ecotoxicity

Ozonation of the commercially important, recalcitrant reactive dye intermediate 2‐naphthylamine 3,6,8‐trisulphonic acid (K‐Acid) was investigated. Ozonation performance was examined by following ozone absorption rates and K‐Acid, chemical oxygen demand and total organic carbon removals. Mean oxidation states and unidentified organic products were also determined. At pH 3, where direct ozone reactions are dominant, the second‐order rate constant between K‐Acid and molecular ozone was determined as 20 m ^?1 s^?1 for steady‐state aqueous ozone concentration. The competition kinetics approach was also adopted where a reference compound, phenol, and K‐Acid were subjected to ozonation. By applying this method, the second‐order reaction rate constant was found to be 76 m ^?1 s^?1. Common oxidation products formed during ozonation at pH 3, pH 7 and pH 7 with 1 mm hydrogen peroxide were identified as methoxy‐phenyl‐oxime, phenol, benzene, benzaldehyde and oxalic acid via high‐performance liquid chromatography and gas chromatography/mass spectrometry analyses. Continuous nitrate and sulphate evolution were observed during K‐Acid ozonation as a consequence of the abrupt release and subsequent oxidation of its amino and sulphonate groups. The number and amount of reaction products were most intensive for K‐Acid ozonation at pH 7 with 1 mm hydrogen peroxide. According to the acute toxicity tests conducted with Vibrio fischeri, ozonation products were not less toxic than the original K‐Acid solution that caused only 15% inhibition.     

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     

Stimuli‐responsive properties of aminophenylboronic acid‐carrying thermosensitive copolymers

Thermosensitive copolymers of N‐isopropylacrylamide (NIPA) and N‐acryloxysuccinimide (NASI) were obtained by solution polymerization using azobisisobutyronitrile as the initiator in a tetrahydrofuran–toluene mixture at 65 °C. A boronic acid‐carrying ligand, m‐aminophenylboronic acid (APBA) was covalently attached to the thermosensitive copolymer via the reaction between amino and succinimide groups. APBA‐coupled thermosensitive copolymer exhibited both temperature and pH sensitivity. Thermally reversible phase transitions were observed both in the acidic and alkaline pH region for the APBA‐modified copolymers obtained with different NASI feed concentrations. In our study, ribonucleic acid (RNA) was selected as a biomolecule having reactive groups which could potentially interact with the boronic acid functionality. The response of boronic acid‐carrying thermosensitive copolymer against RNA was investigated in aqueous media in the pH range 4–9. In the acidic pH region, an increase was observed in the lower critical solution temperature (LCST) of the APBA‐coupled thermosensitive copolymer with increasing RNA concentration. However, LCST decreased with increasing RNA concentration at both neutral and alkaline pH values. The LCST of the APBA‐attached copolymer varied linearly with the RNA concentration at pH of 3, 4 and 7. © 2003 Society of Chemical Industry     

常温常压下δ-MnO_2对苯酚废水的处理研究

研究常温常压、pH值接近中性的条件下,δ-MnO2对苯酚的去除作用。通过气相色谱分析δ-MnO2处理前后苯酚溶液的变化,得到在该条件下,δ-MnO2对苯酚的氧化作用可以忽略;通过通入空气和氮气进行比较,得到在该条件下,空气作为氧化剂时,δ-MnO2没有催化氧化作用;δ-MnO2对苯酚的去除主要是吸附作用。     

Cloud-Point Extraction of Organic Compounds from Aqueous Solutions with Nonionic Surfactant

Abstract

Cloud-point extraction of organic compounds from aqueous solutions by using the nonionic surfactant PONPE10 has been investigated for phenol and three pyridines to clarify the effect of operating factors on its extractability. Phase separation of the surfactant solutions is attained at temperatures above the cloud point, and it is improved by adding NaCl or phenol. Phenol is extracted successfully in a wide pH range from acidic to neutral solutions with and without NaCl, where the extraction efficiency increases with an increase in the surfactant concentration. Backextraction of phenol from the surfactant-rich phase was found to be possible with alkaline solutions. Three pyridine derivatives can also be extracted from the solution under neutral and alkaline conditions, although the efficiencies are somewhat low compared with phenol. Moreover, selective separation of the pyridines from each other could be accomplished because of the difference in their hydrophobicities.     

Horseradish peroxidase‐catalysed oxidation of aqueous natural and synthetic oestrogens

The horseradish peroxidase (HRP)‐catalysed oxidation of selected potent oestrogens, including the natural oestrogens 17β‐oestradiol and oestriol and the synthetic oestrogen ethinyloestradiol, was studied and compared with that of phenol. HRP catalysed the oxidation of these oestrogens and phenol over a wide range of pH values, with optimal performance around neutral pH, which is in the range of typical urban wastewaters. In comparison with that of phenol, the oxidation of oestrogens consistently required less hydrogen peroxide. In addition, the rate of oxidation of oestradiol was equivalent, twofold faster and fivefold faster compared with that of ethinyloestradiol, oestriol and phenol respectively. For all substrates studied, similar kinetics of removal were observed provided that sufficient enzyme was added to reactions to compensate for differences in substrate affinity. In contrast with earlier studies with phenols in which HRP was observed to be susceptible to significant inactivation due to interactions with hydrogen peroxide and reaction products, minimal inactivation of HRP was observed during the present study, probably owing to the very low concentration of target substrates used here (i.e. 10 µmol dm^?3) relative to earlier studies with other phenolic substrates. These observations suggest that this enzymatic approach has strong potential to be used to target the treatment of oestrogenic compounds. Copyright © 2007 Society of Chemical Industry     

Microwave activation of electrochemical processes: High temperature phenol and triclosan electro-oxidation at carbon and diamond electrodes

The electrochemical oxidation of phenolic compounds in aqueous media is known to be affected by the formation of electro-polymerized organic layers which lead to partial or complete electrode blocking. In this study the effect of high intensity microwave radiation applied locally at the electrode surface is investigated for the oxidation of phenol and triclosan in alkaline solution at a 500 μm diameter glassy carbon or at a 500 μm × 500 μm boron-doped diamond electrode. The temperature at the electrode surface and mass transport enhancement are determined by calibration with the Fe(CN)₆^3−/4− redox system in aqueous 0.3 M NaOH and 0.2 NaCl (pH 12) solution. The calibration shows that strong thermal and mass transport effects occur at both glassy carbon and boron-doped diamond electrodes. The average electrode temperature reaches up to 390 K and mass transport enhancements of more than 20-fold are possible. For the phenol electro-oxidation at glassy carbon electrodes and at a concentration below 2 mM a multi-electron oxidation (ca. 4 electrons) occurs in the presence of microwave radiation. For the electro-oxidation of the more hydrophobic triclosan only the one-electron oxidation occurs. Although currents are enhanced in presence of microwave radiation, rapid blocking of the electrode surface in particular at high phenol concentrations still occurs.     

Decomposition of phenols in aqueous solution by a UV/O3 process

The decomposition of several non‐biodegradable phenols by the UV/O₃ and ozonation processes was studied and compared under various solution pH values, O₃ input mass flow rates and UV intensities to investigate the removal efficiencies of reactants and organic intermediates. The decomposition rate of phenols by the UV/O₃ process was found to increase with increasing O₃ input dosage, light intensity and solution pH value. The mineralization efficiencies of phenols in aqueous solution would be above 98% under adequate reaction conditions within three hours, but would be retarded for alkaline solutions because of the dissolution of CO₂ formed by mineralization of phenols. The increment of ozone input dosage had little effect on the mineralization of organic intermediates at the latter course of the reaction. The order of the decomposition rate of the phenols used in this research was 2,4‐dichlorophenol > 2‐chlorophenol > 2‐nitrophenol for low and neutral pH solutions, whereas they were nearly alike for alkaline solutions. The two‐step consecutive kinetic model was found to fit well in modeling the behavior of species during the decomposition of phenols in aqueous solutions by the UV/O₃ process.     

Photo‐oxidation of cyanide in aqueous solution by the UV/H2O2 process

Photo‐oxidation of cyanide was studied in aqueous solution using a low‐pressure ultra‐violet (UV) lamp along with H₂O₂ as an oxidant. It was observed that by UV alone, cyanide degradation was slow but when H₂O₂ was used with UV, the degradation rate became faster and complete degradation occurred in 40 min. The rate of degradation increased as the lamp wattage was increased. It was also observed that cyanide oxidation is dependent on initial H₂O₂ concentration and the optimum dose of H₂O₂ was found to be 35.3 mmol dm^?3. Photo‐oxidation reactions were carried out at alkaline pH values (10–11) as at acidic pH values, cyanide ions form highly toxic HCN gas which is volatile and difficult to oxidise. By the UV/H₂O₂ process, using a 25 W low‐pressure UV lamp and at alkaline pH of 10.5 with an H₂O₂ dose of 35.3 mmol dm^?3, cyanide (100 mg dm^?3) was completely degraded in 40 min when air was bubbled through the reactor, but when pure oxygen was bubbled the time reduced to 25 min. The cyanide degradation reaction pathway has been established. It was found that cyanide was first oxidised to cyanate and later the cyanate was oxidised to carbon dioxide and nitrogen. The kinetics of cyanide oxidation were found to be pseudo‐first order and the rate constant estimated to be 9.9 × 10^?2min^?1 at 40 °C. The power required for complete degradation of 1 kg of cyanide was found to be 167 kWh (kilowatt hour). Copyright © 2004 Society of Chemical Industry     

Electrochemical removal of phenol in alkaline solution. Contribution of the anodic polymerization on different electrode materials

The removal of organic pollutants based on electropolymerization on an anode was performed in the case of phenol in alkaline solution. The polymer formed by a process involving less than two electrons per molecule of phenol, is then precipitated by decreasing the pH and finally filtered and disposed. The electrochemical polymerization of phenol (C₀ = 0.105 M) in alkaline solution (pH = 13) at 86 °C has been studied by galvanostatic electrolysis, using a range of anode materials characterized by different O₂-overpotentials (IrO₂, Pt and β-PbO₂). Measurements of total organic carbon and HPLC have been used to follow phenol oxidation; the morphology of the polymer deposited on the electrode surface has been examined by SEM. Experimental data indicate that phenol concentration decreases by oxidation according to a first order reaction suggesting a mass transport limitation process. Polymeric films formed in alkaline solution did not cause the complete deactivation of the anodes. SEM results show that the polymeric films formed on Ti/IrO₂ and Pt anodes cannot be mineralized. On the other hand, complex oxidation reactions leading to the partial incineration of polymeric materials can take place on the Ta/β-PbO₂ surface due to electrogenerated HO radicals which have an oxidizing power much higher than that of intermediaries formed respectively on IrO₂ and Pt. It is assumed that the polymer films formed on these anodes have different permeability characteristics which determine the rate of mass transfer of the phenol. The fractions of phenol converted in polymers were 25, 32 and 39% respectively with Ti/IrO₂, Pt and Ta/β-PbO₂, a series of materials in which the O₂-overvoltage increases.     

Gemeinsame kondensation von phenol,melamin und formaldehyd. III. Vorkondensation

The condensation reaction between phenol, melamine, and formaldehyde at different conditions (pH-value, molar ratio of phenol and melamine) was investigated. Gel permeation chromatography, ¹³C NMR-spectroscopy and thermogravimetry showed the reactivity of phenol in the reaction with formaldehyde to be rather small at low pH values. At alkaline conditions this reactivity rises very fast. Melamine shows an inverse behaviour. Therefore neither at acidic nor at alkaline conditions cocondensates between melamine and phenol with formaldehyde are formed. Condensation, which involves both melamine and phenol, can be performed at pH-values between 6 and 9. In this range, the reaction can be controlled via acetone dilutability and turbidimetric titration.     

微电解接触氧化系统降解邻氯酚研究

在微电解接触氧化系统中,研究了邻氯酚的降解特性和机理。在酸性溶液中,邻氯酚的降解效率比其在中性和碱性溶液的高。向其中加入活性炭,由于表面催化的作用使得邻氯酚更易降解。溶液中的溶解氧参与电极反应并促进邻氯酚的降解。降解产物有1,2-苯二酚、丙三醇、草酸和乙酸。通过对中间产物的分析,提出了邻氯酚可能的降解途径。     

Phenol photodegradation over titanium dioxide

The heterogeneous photocatalytic oxidation of phenol in aqueous diluted solutions over TiO₂ particles under UV-illumination has been investigated. It has been observed that the yield of the phenol photooxidation depends strongly on the pH of the solution. Maximum yields are obtained at pH 8 and also in very alkaline media. These results are explained considering the processes that take place at the surface of the semiconductor, in which OH radicals have an important role. With respect to the initial charge transfer steps a kinetic analysis has been performed. From this analysis it was deduced that the constant rate of formation of OH radicals is about 4.0 × 10⁴ times greater than the constant rate of the direct reaction between phenol and photogenerated holes in the TiO₂ particles. Finally, from HPLC analysis, hydroquinone, paraquinone and 1,2.4-benzenetriol have been detected as intermediate products prior to the total phenol mineralization.     

Hydrogen peroxide promoted wet air oxidation of phenol: influence of operating conditions and homogeneous metal catalysts

The promoted wet air oxidation of phenol has been investigated through the addition of hydrogen peroxide as a source of free radicals. The reaction has been shown to proceed in two stages, an initial fast reaction associated with hydrogen peroxide consumption and a second slower step that occurs at a rate comparable with conventional wet air oxidation. An increase in temperature has a positive effect on both stages, while oxygen partial pressure only influences the second slower stage. The influence of pH on phenol oxidation is shown to be significant with the highest efficiency achieved at very alkaline conditions when phenol is completely dissociated. The catalytic activity of homogeneous metal salts was investigated in both the presence and absence of hydrogen peroxide. The combined addition of hydrogen peroxide and a bivalent metal (ie copper, cobalt or manganese) is shown to enhance the rate of phenol removal. However, in the absence of hydrogen peroxide only copper exhibited catalytic activity. Finally, a reaction mechanism involving different radical species has been proposed. From the experimental results the apparent activation energy (96.9 ± 3.5 kJ mol⁻¹) and pre‐exponential factor (1.6 ± 0.2 10¹⁰ s⁻¹) were calculated for hydrogen peroxide decomposition into hydroxyl radicals. © 1999 Society of Chemical Industry