Showing papers on "Phenol published in 2007"
TL;DR: In this paper, the authors investigated the use of three carbonaceous materials, activated carbon (AC), bagasse ash (BA) and wood charcoal (WC), as adsorbents for removal of phenol from water.
223 citations
TL;DR: In this article, the adsorption behavior of phenol onto the porous carbon was studied by varying the parameters such as agitation time, phenol concentration, pH and temperature, and the results showed that the sorption process was found to be exothermic in nature.
206 citations
TL;DR: Four different antioxidant tests were used to determine the free-radical scavenging activity of 39 extra virgin olive oils and compare the total phenol content by the Folin-Ciocalteu method; the Picual variety of extra-virgin olive oil showed high antioxidant activity.
169 citations
TL;DR: Photocatalytic degradation of phenol in water was examined using Pr-doped TiO(2) nanoparticles and it was shown that photodegradation followed a pseudo-first-order kinetics and the rate constant changed with phenol concentration.
154 citations
TL;DR: In this article, the photocatalytic degradation of phenol was performed at room temperature in aqueous suspended mixtures of TiO2 and activated carbon (AC) for three consecutive runs.
Abstract: The photocatalytic degradation of phenol was performed at room temperature in aqueous suspended mixtures of TiO2 and activated carbon (AC). The main objective of the present work was to verify the potential of TiO2/AC system in the photocatalytic degradation of phenol and the principal intermediate products after performing three consecutive runs. The phenol disappearance follows a first-order kinetics. Therefore, the apparent first-order rate constant of phenol and total organic carbon photodegradations were selected to evaluate the photoefficiency of the system. From the present results it can be concluded that there is a synergistic effect between both solids which is determined by the numbers of photocatalytic runs. From a practical point of view, TiO2/AC is able to photomineralize phenol and total organic carbon for three and two, respectively, consecutive runs more efficiently than TiO2 alone.
147 citations
TL;DR: The results indicate that the p-substituted phenols are mainly degraded by indirect electrochemical oxidation with hydroxyl radicals on a boron-doped diamond electrode.
Abstract: Electrochemical oxidation of some p-substituted phenols (p-nitrophenol, p-hydroxybenzaldehyde, phenol, p-cresol, and p-methoxyphenol) with electron-donating and -withdrawing substituents was studied to reveal the relationship between the structure and the electrochemical reactivity of p-substituted phenols using a boron-doped diamond electrode by voltammetry and bulk electrolysis. Voltammetric study shows that the oxidation peak potentials of p-substituted phenols become more positive with an increase of Hammett's constants, that is, the direct electrochemical oxidation of p-substituted phenol with an electron-withdrawing group is more difficult than that of p-substituted phenol with an electron-donating group. However,the p-substituted phenols with electron-withdrawing groups are degraded faster than those with electron-donating groups in bulk electrolysis, which is opposite to the result obtained on the Pt electrode. These results indicate that the p-substituted phenols are mainly degraded by indirect electrochemical oxidation with hydroxyl radicals on a boron-doped diamond electrode. Under the attack of hydroxyl radicals, the release of p-substituted groups from the aromatic ring is the rate-limiting step. Since electron-withdrawing groups are easy to be released, the p-substituted phenols with these groups are degraded faster than those with electron-donating groups. Therefore, the degradation rates of the p-substituted phenols rise with an increase of Hammett's constants.
140 citations
TL;DR: In this paper, the catalytic wet peroxide oxidation of phenolic aqueous solutions over a novel Fe 2 O 3 /SBA-15 nanocomposite material was deeply studied.
133 citations
TL;DR: In this paper, the photocatalytic oxidation of different benzene derivatives has been investigated in order to understand how the substituent group affects the selectivity to hydroxylated compounds.
124 citations
TL;DR: Formation of complexes between hydroquinone and p-benzoquinone at increasing pH can remove from solution those highly toxic intermediates whose very low EC50 values give rise to a high ecotoxicity even at fairly low concentrations.
Abstract: This work deals with the evolution of intermediates and ecotoxicity upon Fenton's oxidation of phenol in aqueous solution. The EC50 values of the intermediates identified in the oxidation pathway of phenol have been measured. Some of these compounds, mainly hydroquinone and p-benzoquinone, showed toxicity levels much higher than phenol itself. Depending on the operating conditions, these intermediates could be completely transformed into organic acids, mainly oxalic and formic. Ecotoxicity values substantially lower than those expected from the chemical composition were measured in the reaction samples. This is explained by a reduction of the concentration of aromatic intermediates when the pH was adjusted at 6-8 (according to what is required by the standard bioassay ISO 11348-3). Formation of complexes between hydroquinone and p-benzoquinone at increasing pH can remove from solution those highly toxic intermediates whose very low EC50 values give rise to a high ecotoxicity even at fairly low concentrations. This together with the enhanced decomposition of residual H202 at increasing pH represent important beneficial effects of the neutralization step following Fenton treatment which allow a complementary cleaning of the effluent.
123 citations
TL;DR: In this paper, a nanocomposite material of crystalline iron oxides supported over mesostructured SBA-15 material is shown the most successful catalyst for degradation of phenolic aqueous solutions by photo-Fenton processes, achieving an outstanding overall catalytic performance accompanied with a noteworthy stability.
Abstract: Iron-containing catalysts have been prepared following different synthesis routes and silica supports (amorphous, zeolitic and mesostructured materials). Activity and stability of these materials were assessed on the photo-Fenton degradation of phenolic aqueous solutions using near UV irradiation (higher than 313 nm) at room temperature and initial neutral pH. Their catalytic performance was monitored in terms of phenol and total organic carbon (TOC) conversions. Aromatic compounds and carboxylic acids as by-products coming from incomplete mineralization of phenol as well as the efficiency of each catalytic system in the use of the oxidant were also studied. Stability of the materials throughout the photo-Fenton reaction was evaluated in terms of metal leachibility. Activity and stability depend on the environment of iron species and features of silica support. The evolution of pH with the reaction time and their relationship with TOC degradation and leaching degree has been discussed. A nanocomposite material of crystalline iron oxides supported over mesostructured SBA-15 material is shown the most successful catalyst for degradation of phenolic aqueous solutions by photo-Fenton processes, achieving an outstanding overall catalytic performance accompanied with a noteworthy stability.
121 citations
TL;DR: The results indicate that, contrary to many other electrodes, the oxidation of phenolic compounds on CILE is highly stable and does not result in electrode fouling.
Abstract: A carbon ionic liquid electrode (CILE) was used for the investigation of the electrochemical oxidation of phenolic compounds in acidic media using cyclic voltammetry, chronoamperometry and square wave voltammetry techniques. The results indicate that, contrary to many other electrodes, the oxidation of phenolic compounds on CILE is highly stable and does not result in electrode fouling. Cyclic voltammetry showed that phenolic compounds such as phenol, 2,4-dichlorophenol and catechol were oxidized at CILE and remained electroactive after multiple cycles and at high concentrations of phenol. The cyclic voltammetric response of the CILE is very stable with more than 99% of the initial activity remaining after 20 s of stirring of a 0.5 mM solution of phenol.
TL;DR: In this paper, the authors used oxovanadium(IV) exchanged zeolite-Y with the Schiff base derived from salicylaldehyde and 2-aminomethylbenzimidazole (Hsal-ambmz) in refluxing methanol followed by aerial oxidation leads to the formation of encapsulated dioxovanadium (V) complex, [VO2(sal-ambermz)]-Y(1).
Abstract: Interaction of oxovanadium(IV) exchanged zeolite-Y with the Schiff base derived from salicylaldehyde and 2-aminomethylbenzimidazole (Hsal-ambmz) in refluxing methanol followed by aerial oxidation leads to the formation of encapsulated dioxovanadium(V) complex, [VO2(sal-ambmz)]-Y(1). Similar reaction with copper(II) exchanged zeolite-Y followed by its treatment with aqueous NaCl gave encapsulated copper(II) complex, [Cu(sal-ambmz)Cl]-Y(2). These encapsulated complexes have been characterized by spectroscopic studies, thermal analysis and scanning electron micrographs (SEMs) as well as X-ray diffraction patterns. 3D model structure generated for neat complex [VO2(sal-ambmz)] suggests that zeolite-Y can accommodate these complexes in its nano-cavity without any strain. The encapsulated materials are active catalysts for the oxidation of phenol, styrene and methyl phenyl sulfide using H2O2 as an oxidant. Under the optimised reaction conditions about 42% conversion of phenol was obtained with these catalysts where the selectivity of catechol varied in the order: 2 (73.9%) >1 (65.2%). With the conversion of 97.0% with 1 or 56.7% with 2, the oxidation of styrene gave styrene oxide, benzaldehyde, benzoic acid, 1-phenylethane-1,2-diol and phenylacetaldehyde as major products. A maximum of 96.1% (with 1) conversion of methyl phenyl sulfide was observed in which the selectivity of major product methyl phenyl sulfoxide was found to be ca. 98%.
TL;DR: In this paper, the hydrogenation of phenol in aqueous phase was studied in a continuous trickle bed reactor using commercial and some home-made Pd/activated carbon (AC) catalysts with the aim to explore a possible way for the treatment of phenolic wastewaters.
TL;DR: In this paper, the authors report on the gasification of guaiacol and phenol in supercritical water at 400−700 °C, at times with added Ni wires that ran the entire length of the reactor.
Abstract: We report on the gasification of guaiacol and phenol in supercritical water at 400−700 °C The reactions were conducted in sealed quartz tubes, at times with added Ni wires that ran the entire length of the reactor These reactors allowed the homogeneous and heterogeneous SCWG rates to be quantified separately for the first time Guaiacol is mainly gasified into hydrogen, carbon dioxide, carbon monoxide, and methane The rest of the guaiacol decomposes to phenol and o-cresol or reacts to form char Nickel does not affect the conversion of guaiacol to phenol and o-cresol, but it significantly changes the gas product compositions Phenol is mainly gasified into hydrogen, carbon dioxide, and methane Hydrogen was the most abundant product at high phenol conversions The gas compositions measured experimentally were largely consistent with those anticipated from chemical equilibrium calculations In the absence of nickel, phenol conversions up to 68% were reached after 1 h In the presence of Ni wire, complet
TL;DR: It is shown that, for both a synthetic phenol wastewater and an aqueous extract of Brazilian gasoline, the inhibition of the photo-Fenton degradation of the organic material in the presence of chloride ion can be circumvented by maintaining the pH of the medium at or slightly above 3 throughout the process, even in the absence of significant amounts of added chloride ion.
Abstract: The inhibition of the photo-Fenton (Fe2+/Fe3+, H2O2, UV light) degradation of synthetic phenol wastewater solutions by chloride ions is shown to affect primarily the photochemical step of the process, having only a slight effect on the thermal or Fenton step. Kinetic studies of the reactions of oxoiron (IV) (FeO2+) with phenol indicate that, if FeO2+ is formed in the photo-Fenton degradation, its role is probably minor. Finally, it is shown that, for both a synthetic phenol wastewater and an aqueous extract of Brazilian gasoline, the inhibition of the photo-Fenton degradation of the organic material in the presence of chloride ion can be circumvented by maintaining the pH of the medium at or slightly above 3 throughout the process, even in the presence of significant amounts of added chloride ion (0.5 M).
TL;DR: In this paper, the performance of a fixed-bed FBR for the catalytic wet hydrogen peroxide oxidation (CWHPO) of phenolic aqueous solutions is investigated.
Abstract: Iron oxide supported over mesostructured SBA-15 material (Fe2O3/SBA-15) has been used in a fixed-bed reactor (FBR) for the catalytic wet hydrogen peroxide oxidation (CWHPO) of phenolic aqueous solutions. This catalyst is agglomerated by extrusion with different particle sizes (0.35−2 mm) using bentonite mineral clay and methyl cellulose as inorganic and organic binders, respectively. Several variables, such as the feed flow rate, the weight of the catalyst bed, and the particle size, have been studied in order to optimize the operation conditions for phenol mineralization. Activity of catalyst in terms of phenol degradation and TOC reduction has been monitored. Internal diffusional problems by the increase of the particle size seem not to play a dominant role in the overall catalytic performance. Loadings of catalysts higher than 2.9 g for 1 cm3/min of 1 g/L phenolic aqueous solution, equivalent to residence times ≈ 3.1−3.8 min, have not substantially affected the phenol and TOC reduction. Under the best ...
TL;DR: The obtained results revealed that degradation efficiency of phenol could be increased by the addition of TiO( 2) in pulsed discharge system, and the gas of Ar and O(2) bubbled into the reaction system was found to be favorable for phenol degradation and H(2).
TL;DR: A series of palladium supported on activated carbon catalysts, with Pd varying from 0.5 to 6.0%, were tested for vapour phase phenol hydrogenation in a fixed-bed all glass micro-reactor at a reaction temperature of 453 K under normal atmospheric pressure as discussed by the authors.
TL;DR: In this paper, the effects of parameters such as pH, reaction time and initial phenol concentration on the photolytic degradation and toxicity assay have been studied and the experimental results have shown that lower pH and lower concentration of phenol favor the phenol degradation.
Abstract: The photodegradation of phenol was studied in a batch reactor system illuminated with a 400 W medium pressure mercury lamp. The effects of parameters such as pH, reaction time and initial phenol concentration on the photolytic degradation and toxicity assay have been studied. The experimental results have shown that lower pH and lower concentration of phenol favor the phenol degradation. The disappearance of phenol in each case approximately obeyed first-order kinetics with the apparent rate constants increasing with decreasing solute concentration. Bioassay tests showed that phenol was toxic to Daphnia magna and so resulted in quite low LC50 values. Comparison of toxicity units (TU) between phenol and effluent toxicity has shown that TU value for effluent was 2.18 times lower than that obtained for phenol. Thus, photolysis is able to decrease the toxicity of by-products formed during the degradation of phenol.
TL;DR: It was found that ozonation at alkaline pH was an effective method of phenol destruction, but it was considerably more effective when applied simultaneously with ultrasonic irradiation, which was attributed to combined effects of increased ozone mass transfer and excess hydroxyl radical formation.
TL;DR: In this article, the authors investigated the hydroxylation of benzene to phenol with hydrogen peroxide using different solvents and a series of catalysts, obtained by modification of titanium silicalite (TS-1).
Abstract: The hydroxylation of benzene to phenol with hydrogen peroxide was investigated using different solvents and a series of catalysts, obtained by modification of titanium silicalite (TS-1). The best results were obtained after post-synthesis treatment of TS-1 with NH 4 HF 2 and H 2 O 2 . The new catalyst (TS-1B), used in the presence of a particular co-solvent (sulfolane) is able to protect the produced phenol from over-oxidation and dramatically enhanced the selectivity of the reaction.
TL;DR: The nano-crystalline sulfated-zirconia catalysts, prepared by one-step as well as two-step sol-gel technique, showed excellent catalytic activity with a high substrate to catalyst weight ratio for the synthesis of 7-substituted 4-methyl coumarins via solvent free Pechmann reaction.
Abstract: The nano-crystalline sulfated-zirconia catalysts, prepared by one-step as well as two-step sol–gel technique, showed excellent catalytic activity with a high substrate to catalyst weight ratio for the synthesis of 7-substituted 4-methyl coumarins via solvent free Pechmann reaction. The m-amino phenol was found to be more reactive than m-hydroxy phenol. The catalyst results 100% conversion of m-amino phenol with ∼100% selectivity of 7-amino 4-methyl coumarin at 110 ◦ C within 2 min. For 7-hydroxy 4-methyl coumarin, 94% yield was obtained after 3 h at 170 ◦ C with phenol to catalyst weight ratio of 80. Slow kinetics was observed in polar nitrobenzene as well as in non-polar toluene for both coumarin derivatives, due to the slow bulk diffusion of reactant molecules in presence of solvent. The solvent free microwave assisted synthesis seems advantageous way to synthesize the hydroxy derivative resulting excellent yield (99%) in much lesser time (15 min) at lower temperature (150 ◦ C) as compared to thermal heating. The use of very small catalytic amount of sulfated-zirconia catalyst for the synthesis of coumarins and the reusability of the catalyst after simple activation for several times with similar catalytic activity are novel properties of the catalyst. © 2007 Elsevier B.V. All rights reserved.
TL;DR: In this article, the effects of concentrations of cerium and nitric acid on phenol degradation were found to be moderate within the range investigated, and the influence of the concentration of phenol, temperature, amount of ceranium, and concentration of the electrolyte were studied on phenolic degradation in a batch type reactor.
TL;DR: A kinetic model based on phenol diffusion within the pores of the adsorbent was in agreement with the results obtained for high initial concentrations of phenol, allowing the determination of diffusion coefficients.
TL;DR: The effects of methanol as HO scavenger demonstrated that the relative contribution of HO-based reactions to the decomposition of phenol in UV/VUV-irradiated solutions decreased strongly with increase of the initial phenol concentration as discussed by the authors.
Abstract: The UV (254 nm) and UV/VUV (254/185 nm) photolysis of phenol and the distribution of the products in solutions saturated with oxygen or nitrogen were investigated and compared. The initial rate of degradation of phenol in UV/VUV-irradiated solutions exceeded that determined in UV-irradiated solutions, but the difference decreased dramatically with increase of the initial phenol concentration. The effects of methanol as HO scavenger demonstrated that the relative contribution of the HO -based reactions to the decomposition of phenol in UV/VUV-irradiated solutions decreased strongly with increase of the initial phenol concentration. The same aromatic (1,2- and 1,4-dihydroxybenzene) and aliphatic (maleic, malic, tartaric and oxalic acids) intermediates were detected in UV- and UV/VUV-irradiated solutions saturated with oxygen. The decompositions of 1,2- and 1,4-dihydroxybenzene, 1,4-benzoquinone and oxalic acid were also investigated both in UV/VUV- and in UV-irradiated solutions.
TL;DR: In this paper, a commercial activated carbon was modified by different oxidative treatments to introduce different oxygen surface groups, and the resulting activated carbons and the corresponding Fe-impregnated (2.5% Fe) ones were tested for the wet air oxidation of phenol.
Abstract: A commercial activated carbon was modified by different oxidative treatments to introduce different oxygen surface groups. A gentle oxidation in gas phase with a poor oxygen stream and a more severe oxidation in liquid phase with a HNO 3 solution were used. The resulting activated carbons and the corresponding Fe-impregnated (2.5% Fe) ones were tested for the wet air oxidation of phenol. A trickle-bed reactor at 400 K and 8 atm of total pressure in a wide range of space time (20–320 g CAT h/g Phenol ) was used. The performance of the carbon supports and Fe catalysts was assessed by following phenol and TOC conversions, as well as the toxicity of the effluents. The fresh and used catalysts were characterized by nitrogen adsorption, TPD analyses and pH slurry . Gas-phase oxidation increased mainly the carbonyl/quinone groups and also carboxylic anhydride groups, whereas HNO 3 oxidation significantly increased all the oxygen surface groups, but more significantly phenol, carbonyl/quinone and lactone groups. Regarding the preparation of the catalysts, Fe itself plays a promoting role in the formation or destruction of oxygen surface groups during calcinations, the latter being only observed when the activated carbon was oxidized with HNO 3 . Phenol and TOC conversions increased with the initial acidity of the catalyst. The introduction of Fe enhanced the activity and toxicity abatement at high enough space times, compared to an activated carbon with the same amounts of oxygen surface groups. This can be attributed to the increase in the acidity that the Fe itself provokes and the promoter role of Fe in the oxidation reaction of phenol. After the catalytic wet air oxidation process, surface area and micropore volume decreased whereas the amount of oxygen surface groups increased, as well as the total acidity, except for the activated carbon treated with HNO 3 . Also Fe dispersion significantly diminishes. However, the final surface distribution did not affect the catalyst activity. The presence of Fe reduced the detrimental effect of wet oxidation on the porous structure of the activated carbons.
TL;DR: The obtained results indicated that catechol adsorption is much higher than those of the other phenolics and its interaction occurs preferentially through the formation of a catecholate monodentate.
TL;DR: A preliminary kinetic analysis of the data shown that the rate of phenol disappearance is not first order with respect to the phenol, and temperature strongly enhances phenol conversion.
TL;DR: In this paper, a clean synthesis of both carboxylic anhydrides and esters has been set up, which involves a double addition of the acid to the dicarbonate, affording a carboxyl anhydride [(RCO) 2 O], R 1 OH and carbon dioxide.
Abstract: The reaction between carboxylic acids (RCOOH) and dialkyl dicarbonates [(R 1 OCO) 2 O], in the presence of a weak Lewis acid such as magnesium chloride and the corresponding alcohol (R 1 OH) as the solvent, leads to the esters RCOOR 1 in excellent yields. The mechanism involves a double addition of the acid to the dicarbonate, affording a carboxylic anhydride [(RCO) 2 O], R 1 OH and carbon dioxide. The esters arise from the attack of the alcohols on the anhydrides. Exploiting the lesser reactivity of tert-butyl alcohol in comparison with other alcohols, a clean synthesis of both carboxylic anhydrides and esters has been set up. In the former reaction, an acid/Boc 2 O molecular ratio of 2:1 leads to the anhydride in good to excellent yields, depending on the stability of the resulting anhydride to the usual workup conditions. In the latter reaction, stoichiometric mixtures of the acid and Boc 2 O are allowed to react with a twofold excess of a primary alcohol, secondary alcohol or phenol (R 2 OH) to give the corresponding esters (RCOOR 2 ). Purification of the products is particularly easy since all byproducts are volatile or water soluble. A very easy chromatography is required only in the case of nonvolatile alcohols. A broad variety of sensitive functional groups is tolerated on both the acid and the alcohol, in particular a high chemoselectivity is observed. In fact, no transesterification processes occur with the acid-sensitive acetoxy group and methyl esters.
TL;DR: In this paper, the reactivity of horseradish peroxidase with water insoluble phenolic compounds has been studied in 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF 4 ])/water mixtures.
Abstract: The reactivity of horseradish peroxidase (HRP) with water insoluble phenolic compounds has been studied in 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF 4 ])/water mixtures. The enzyme retained some catalytic activity up to 90% ionic liquid in water at 25 °C only at pH values higher than 9.0. Activity steadily decreased towards neutral and acidic conditions, as judged by 4-aminoantypirin/phenol activity tests. Inhibition of horseradish peroxidase under neutral acidic condition was due to the binding of fluoride anions released from tetrafluoroborate anion to the heme iron as demonstrated by the sharp UV–visible absorption transition diagnostic of the conversion from a five coordinated to a six coordinated high spin ferric heme iron. Thus, reactions with water insoluble phenols were carried out under alkaline reaction conditions and 75% [BMIM][BF 4 ]/water mixture. Under these conditions, the distribution of the reaction products was much narrower with respect to that observed in aqueous buffers or water/dimethylformamide or water/dimethylsulfoxide mixtures, and polymeric species other than dimers were not observed. Technical scale preparations of a novel 4-phenylphenol ortho dimer [2,2′-bi-(4-phenylphenol)] with a high yield of the desired product were obtained.