Showing papers on "Phenol published in 2015"

Heterogeneous degradation of organic pollutants by persulfate activated by CuO-Fe3O4: Mechanism, stability, and effects of pH and bicarbonate ions

Abstract: Magnetic CuO-Fe3O4 composite was fabricated by a simple hydrothermal method and characterized as a heterogeneous catalyst for phenol degradation. The effects of pH and bicarbonate ions on catalytic activity were extensively evaluated in view of the practical applications. The results indicated that an increase of solution pH and the presence of bicarbonate ions were beneficial for the removal of phenol in the CuO-Fe3O4 coupled with persulfate (PS) process. Almost 100% mineralization of 0.1 mM phenol can be achieved in 120 min by using 0.3 g/L CuO-Fe3O4 and 5.0 mM PS at pH 11.0 or in the presence of 3.0 mM bicarbonate. The positive effect of bicarbonate ion is probably due to the suppression of copper leaching as well as the formation of Cu(III). The reuse of catalyst at pH0 11.0 and 5.6 showed that the catalyst remains a high level of stability at alkaline condition (e.g., pH0 11.0). On the basis of the characterization of catalyst, the results of metal leaching and EPR studies, it is suggested that pheno...

A new magnetic nano zero-valent iron encapsulated in carbon spheres for oxidative degradation of phenol

Abstract: In this study, magnetic carbon encapsulated nano iron hybrids (nano Fe0/Fe3C@CS) were synthesized via a novel one-pot hydrothermal method followed by self-reduction in N2 atmosphere. The structural, morphological, and physicochemical properties of the samples were thoroughly investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), N2 sorption isotherms and thermogravimetric analysis–differential scanning calorimetry (TGA–DSC). Catalytic performance of the as-synthesized nanoparticles was tested in activation of oxone® for phenol degradation in aqueous solutions. Superior catalytic performance was observed by complete removal of 20 ppm phenol within 10 min. The formation of Fe3C was found to contribute to a better stability and magnetic separation of Fe0/Fe3C@CS in its repeated uses. Both electron paramagnetic resonance (EPR) and classic quenching tests were carried out to investigate the mechanism of radical generation and evolution in phenol oxidation. Different from Co- and Mn-based catalysts in generation of sulfate radicals, Fe0/Fe3C@CS selectively induced hydroxyl radicals for phenol degradation.

Low temperature combustion synthesis of nitrogen-doped graphene for metal-free catalytic oxidation

Abstract: Nitrogen-doped reduced graphene oxide (N-rGO) was prepared by a simple process of simultaneous reduction and nitrogen doping on graphene oxide (GO) at low temperatures using ammonium nitrate as a N precursor. Characterization techniques indicated that N-rGO materials with a high N loading (5–8 at%) can be easily produced and that the crystal/micro-structures and chemical compositions of N-rGO materials are dependent on the calcination conditions. The metal-free catalysis of N-rGO was investigated by catalytic activation of peroxymonosulfate (PMS) for phenol oxidative degradation in water. It was found that N-rGO samples are promising green catalysts for phenol degradation. Kinetic studies showed that phenol degradation follows first order reaction kinetics on N-rGO-350 with an activation energy of 31.6 kJ mol−1. The mechanism of PMS activation and phenol oxidation was elucidated by employing both electron paramagnetic resonance (EPR) studies and quenching tests with ethanol and tert-butanol.

Role of Dissociation of Phenol in Its Selective Hydrogenation on Pt(111) and Pd(111)

Abstract: The adsorption, dissociation, and hydrogenation of phenol on the Pt(111) and Pd(111) surfaces have been studied using density functional theory slab calculations. The results show that phenol favors adsorption through a mixed σ–π interaction on both surfaces through its phenyl ring, with the hydrogen atoms and hydroxyl tilted away from the surface. The dissociation of phenol to phenoxy is both thermodynamically and kinetically favored on Pd but not on Pt. The phenoxy adsorbs on Pd through both the phenyl ring and the oxygen atom, whereas the O atom points away from the surface on Pt. On Pt, the barrier for adding one hydrogen atom to the adsorbed phenol is 0.49 eV lower than the overall barrier for phenol dissociation to phenoxy followed by adding the hydrogen atom to its phenyl ring, resulting in direct hydrogenation of the adsorbed phenol to cyclohexanol as the dominant reaction pathway. In contrast, on Pd, the barrier for direct hydrogenation (1.22 eV) is higher than the overall barrier of dissociation...

Switching Oxygen Reduction Pathway by Exfoliating Graphitic Carbon Nitride for Enhanced Photocatalytic Phenol Degradation

Abstract: The selectivity of molecular oxygen activation on the exfoliated graphitic carbon nitride (g-C3N4) and its influence on the photocatalytic phenol degradation process were demonstrated. Compared with bulk g-C3N4, the exfoliated nanosheet yielded a 3-fold enhancement in photocatalytic phenol degradation. ROS trapping experiments demonstrated that although the direct hole oxidation was mainly responsible for phenol photodegradation on both g-C3N4 catalysts, molecular oxygen activation processes on their surface greatly influenced the whole phenol degradation efficiency. Reactive oxygen species and Raman spectroscopy measurements revealed that oxygen was preferentially reduced to ·O2– by one-electron transfer on bulk g-C3N4, while on g-C3N4 nanosheet the production of H2O2 via a two-electron transfer process was favored due to the rapid formation of surface-stabilized 1,4-endoperoxide. The latter process not only promotes the separation of photogenerated electron–hole pairs but also greatly facilitates reacti...

Eco-friendly asbestos free brake-pad: Using banana peels

Abstract: The use of asbestos fibre is being avoided due to its carcinogenic nature that might cause health risks. A new brake pad produced using banana peel waste to replace asbestos and Phenolic resin (phenol formaldehyde), as a binder was investigated. The resin was varying from 5 to 30 wt% with an interval of 5 wt%. Morphology, physical, mechanical and wear properties of the brake pad were studied. The results show that compressive strength, hardness and specific gravity of the produced samples were seen to be increasing with an increase in wt% of resin addition, while oil soak, water soak, wear rate and percentage charred decreased as the wt% of resin increased. Overall samples, containing 25 wt% in uncarbonized banana peels (BUNCp) and 30 wt% in carbonized (BCp) gave better properties. The result of this research indicates that banana peel particles can be effectively used as a replacement for asbestos in brake pad manufacture.

Direct Hydroxylation of Benzene to Phenol Using Hydrogen Peroxide Catalyzed by Nickel Complexes Supported by Pyridylalkylamine Ligands

Abstract: Selective hydroxylation of benzene to phenol has been achieved using H2O2 in the presence of a catalytic amount of the nickel complex [NiII(tepa)]2+ (2) (tepa = tris[2-(pyridin-2-yl)ethyl]amine) at 60 °C. The maximum yield of phenol was 21% based on benzene without the formation of quinone or diphenol. In an endurance test of the catalyst, complex 2 showed a turnover number (TON) of 749, which is the highest value reported to date for molecular catalysts in benzene hydroxylation with H2O2. When toluene was employed as a substrate instead of benzene, cresol was obtained as the major product with 90% selectivity. When H218O2 was utilized as the oxidant, 18O-labeled phenol was predominantly obtained. The reaction rate for fully deuterated benzene was nearly identical to that of benzene (kinetic isotope effect = 1.0). On the basis of these results, the reaction mechanism is discussed.

Comparative study on steam reforming of model aromatic compounds of biomass tar over Ni and Ni–Fe alloy nanoparticles

Abstract: Steam reforming of tar model compounds (benzene, toluene and phenol) was carried out using Ni–Fe/Mg/Al catalysts prepared by calcination and reduction of hydrotalcite-like precursor. Ni–Fe/Mg/Al (Fe/Ni = 0.25) catalyst showed higher activity (∼twice conversion rate based on catalyst weight) and better resistence to carbon deposition (∼one order smaller amount of deposited carbon) than Ni/Mg/Al. The difference in the weight-based rate and carbon deposition amount between catalysts with and without Fe was large when benzene or toluene was used as a substrate and high steam/carbon (S/C) ratio was applied. On the other hand, when phenol was used as a substrate, relatively large amount of carbon derived from decomposition of phenol was deposited on Ni–Fe/Mg/Al catalyst even with high (3.8) S/C ratio. The catalyst loses some activity for steam reforming of toluene when treated with phenol (untreated catalyst: ∼80% conversion of toluene (rate 51 μmol g −1 -cat s −1 ); treated catalyst ∼60% (rate 38 μmol g −1 -cat s −1 )), probably because of the deposited carbon from phenol. Kinetic studies and O 2 - or H 2 O-TPO studies showed that phenol was strongly adsorbed on Fe site as well as Ni site, and the adsorbed phenol could be converted into carbonaceous species under the reaction conditions. On the other hand, the adsorbed phenol on Ni site underwent steam reforming, and the reaction was promoted by Fe.

Understanding the role of manganese dioxide in the oxidation of phenolic compounds by aqueous permanganate.

Abstract: Recent studies have shown that manganese dioxide (MnO2) can significantly accelerate the oxidation kinetics of phenolic compounds such as triclosan and chlorophenols by potassium permanganate (Mn(VII)) in slightly acidic solutions. However, the role of MnO2 (i.e., as an oxidant vs catalyst) is still unclear. In this work, it was demonstrated that Mn(VII) oxidized triclosan (i.e., trichloro-2-phenoxyphenol) and its analogue 2-phenoxyphenol, mainly generating ether bond cleavage products (i.e., 2,4-dichlorophenol and phenol, respectively), while MnO2 reacted with them producing appreciable dimers as well as hydroxylated and quinone-like products. Using these two phenoxyphenols as mechanistic probes, it was interestingly found that MnO2 formed in situ or prepared ex situ greatly accelerated the kinetics but negligibly affected the pathways of their oxidation by Mn(VII) at acidic pH 5. The yields (R) of indicative products 2,4-dichlorophenol and phenol from their respective probes (i.e., molar ratios of product formed to probe lost) under various experimental conditions were quantified. Comparable R values were obtained during the treatment by Mn(VII) in the absence vs presence of MnO2. Meanwhile, it was confirmed that MnO2 could accelerate the kinetics of Mn(VII) oxidation of refractory nitrophenols (i.e., 2-nitrophenol and 4-nitrophenol), which otherwise showed negligible reactivity toward Mn(VII) and MnO2 individually, and the effect of MnO2 was strongly dependent upon its concentration as well as solution pH. These results clearly rule out the role of MnO2 as a mild co-oxidant and suggest a potential catalytic effect on Mn(VII) oxidation of phenolic compounds regardless of their susceptibility to oxidation by MnO2.

Catalytic ozonation with γ-Al2O3 to enhance the degradation of refractory organics in water

Abstract: Nowadays, heterogeneous catalytic ozonation appears as a promising way to treat industrial wastewaters containing refractory pollutants, which resist to biological treatments. Several oxides and minerals have been used and their behavior is subject to controversy with particularly the role of Lewis acid sites and/or basic sites and the effect of salts. In this study, millimetric mesoporous γ-Al2O3 particles suitable for industrial processes were used for enhancing the ozonation efficiency of petrochemical effluents without pH adjustment. A phenol (2,4-dimethylphenol (2,4-DMP)) was first chosen as petrochemical refractory molecule to evaluate the influence of alumina in ozonation. Single ozonation and ozonation in presence of γ-Al2O3 led to the disappearance of 2,4-DMP in 25 min and a decrease in pH from 4.5 to 2.5. No adsorption of 2,4-DMP occurred on γ-Al2O3. Adding γ-Al2O3 in the process resulted in an increase of the 2,4–DMP oxidation level. Indeed, the total organic carbon (TOC) removal was 14% for a single ozonation and 46% for ozonation with γ-Al2O3. Similarly, chemical oxygen demand (COD) removal increases from 35 to 75%, respectively. Various oxidized by-products were produced during the degradation of 2,4-DMP, but after 5 h ozonation 90% of organic by-products were acetic acid > formic acid ≫ oxalic acid. Some of the carboxylic acids were adsorbed on γ-Al2O3. The use of radical scavengers (tert-butanol) highlighted the involvement of hydroxyl radicals during catalytic ozonation with γ-Al2O3 in contrary to single ozonation, which mainly involved direct ozone reaction. γ-Al2O3 is an amphoteric solid with Lewis acid AlOH(H+) sites and basicAl-OH sites. After ozonation the amount of basic sites decreased due to carboxylates adsorption, while the Lewis acid sites remained constant as evidenced by FTIR. Several ozonation runs with γ-Al2O3 reported a progressive decrease of its catalytic activity due to the cumulative sorption of carboxylates on the basic sites. After 80 h of ozonation, a calcination at 550 °C allowed to recover allAl-OH basic sites and the initial activity of γ-Al2O3. A synthetic petrochemical effluent containing various petrochemicals (phenol, acetic acid, naphtenic acid, pyrene, naphtalene) was then treated with γ-Al2O3 with and without NaCl. Sodium ions prevented carboxylates adsorption on γ-Al2O3 leading to a higher efficiency of γ-Al2O3 in presence of NaCl and allowed to decrease the toxicity of the petrochemical effluent.

Quantitative prediction of generation of hydroxyl radicals from ozone microbubbles

Abstract: Concentration of hydroxyl radicals generated from ozone microbubbles was determined by using an indirect method over a wide range of pH (i.e. pH 3–10). p-Chlorobenzoic acid (PCBA) was used as the probe compound to calculate the concentration of hydroxyl radicals. A constant, Rct, was defined as the ratio of OH and O3 exposures, which was employed to estimate the concentration of hydroxyl radicals. The effects of pH and carbonate ions on the generation of hydroxyl radicals were studied. It was observed that the O3 exposure and the depletion of PCBA were higher at acidic pH than at the alkaline pH. At acidic pH, C O 3 2 − acted as the ·OH scavenger only, whereas at alkaline pH, it inhibited ozone decomposition. This changed the values of ·OH exposure, O3 exposure, and hence, Rct. The degradation of phenol was performed at pH 3–10 by using ozone microbubbles. The contributions of ·OH and O3 on the oxidation of phenol were calculated. A mechanism of the generation of ·OH from the ozone microbubbles under acidic and alkaline conditions was developed.

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

Abstract: 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). The materials were characterized using X-ray Powder Diffraction (XRD), Fourier Transform Infrared (FT-IR) spectroscopy, Scanning Electron Microscopy (SEM), and Energy Dispersive X-ray (EDX) spectroscopy. By comparison, the Cu(BDC) exhibited a better catalytic degradation performance. and was selected for further experiments. Several parameters including temperature, H2O2 dose, catalyst dose and initial pH of the phenol wastewater which could affect the catalytic degradation efficiency by the Cu(BDC) were investigated. Under optimum conditions, a phenol conversion of 99% and a COD (Chemical Oxygen Demand) removal of 93% were achieved. The degradation of phenol solutions of different concentrations (100 to 1000 mg L−1) was also carried out. No matter whether a low or high concentration of the phenol solution was used, satisfactory results with a phenol conversion of 99% and a COD removal of over 90% were obtained. After being reused twice, the Cu(BDC) still maintained a good catalytic performance with a phenol conversion of 99% and a COD removal of over 85%. Like other copper catalysts, the mechanism of the degradation process was a hydroxyl radical mechanism. The leaching of Cu2+ was also monitored by Inductively Coupled Plasma-Atomic Emission Spectroscopy (ICP-AES) and a negligible release of copper (7 ppm) was observed. Overall, Cu-MOFs could be promising heterogeneous catalysts for the catalytic oxidation of phenol with H2O2 as the oxidant.

The generation of hydroxyl radicals by hydrogen peroxide decomposition on FeOCl/SBA‐15 catalysts for phenol degradation

Abstract: Iron oxychloride (FeOCl) supported on mesoporous silica (SBA-15), as a Fenton-like solid catalyst for phenol degradation, showed supreme activity for production of hydroxyl radical (HO·) by H2O2 decomposition, and the generation capacity was comparable to the conventional Fenton reagent (Fe2++H2O2). The structure of FeOCl was characterized with spectroscopies. The generation of HO· species during the reaction was detected using 5,5-dimethyl-1-pyrroline N-oxide trapped electron paramagnetic resonance. Furthermore, the kinetics in detail was driven for the creation and diffusion of HO· by H2O2 decomposition over FeOCl, which follows a first-order rate through a two-step reaction. With the combination of the catalyst structure and kinetic parameters, the plausible mechanism for H2O2 decomposition during the oxidative degradation of phenol was rationalized. As a Fenton-like solid catalyst, FeOCl/SBA-15 is a promising alternative for the removal of low-level organic contaminates from water. © 2014 American Institute of Chemical Engineers AIChE J, 61: 166–176, 2015

Selective Hydrogenation of Phenol to Cyclohexanone over Pd–HAP Catalyst in Aqueous Media

Abstract: The production of pure cyclohexanone under mild conditions over catalysts with high reactivity, selectivity, compatibility, stability, and low cost is still a great challenge. Here we report a hydroxyapatite-bound palladium catalyst (Pd-HAP) to demonstrate its excellent performance on phenol hydrogenation to cyclohexanone. Based on catalyst characterization, the Pd nanoclusters (approximate to 0.9nm) are highly dispersed and bound to phosphate in HAP. Only basic active sites on HAP surface are detected. At 25 degrees C and ambient H-2 pressure in water, phenol can be 100% converted into cyclohexanone with 100% selectivity. This system shows a universal applicability to temperature, pH, solvent, low H-2 purity, and pressure. The catalyst reveals high stability to be recycled without deactivation or morphology change; and Pd nano-clusters barely aggregate even at 400 degrees C. During the reaction, HAP adsorbs phenol, and Pd nanoclusters activate and spillover H-2. The mechanism is also investigated, proposed, and verified.

C3N4-H5PMo10V2O40: a dual-catalysis system for reductant-free aerobic oxidation of benzene to phenol

Abstract: Hydroxylation of benzene is a widely studied atom economical and environmental benign reaction for producing phenol, aiming to replace the existing three-step cumene process. Aerobic oxidation of benzene with O2 is an ideal and dream process, but benzene and O2 are so inert that current systems either require expensive noble metal catalysts or wasteful sacrificial reducing agents; otherwise, phenol yields are extremely low. Here we report a dual-catalysis non-noble metal system by simultaneously using graphitic carbon nitride (C3N4) and Keggin-type polyoxometalate H5PMo10V2O40 (PMoV2) as catalysts, showing an exceptional activity for reductant-free aerobic oxidation of benzene to phenol. The dual-catalysis mechanism results in an unusual route to create phenol, in which benzene is activated on the melem unit of C3N4 and O2 by the V-O-V structure of PMoV2. This system is simple, highly efficient and thus may lead the one-step production of phenol from benzene to a more practical pathway.

Low temperature supercritical water gasification of biomass constituents: glucose/phenol mixtures.

Abstract: Supercritical water gasification (SCWG) is an interesting technology for the production of energy from wet and residual biomass. To date, the complete understanding of the fundamental phenomena involved in SCWG is still an open issue. An interesting aspect to be investigated is represented by the interactions among the single constituents of biomass, such as cellulose and lignin. This can be accomplished by using glucose and phenol as model compounds. In the present study, four glucose/phenol mixtures were utilized. All mixtures presented a constant organics mass fraction of 5%, where the relative fraction of phenol ranged from 0% (pure glucose) to 30%. The mixtures were gasified at 400 °C and 25.0 MPa in a continuous tubular reactor, with a residence time between 10 and 240 s. Results showed that, at the considered reaction conditions, phenol mostly behaves as a sort of inert in terms of total gas production, although it plays an inhibitory action towards H 2 . The analysis of the liquid phase revealed that phenol likely inhibits Cannizzaro and de-carbonylation reactions and it advantages the pathways involving de-hydration reactions.