Mineralization Of Phenol Research Articles

Magnéli phases Ti O2−1 as novel ozonation catalysts for effective mineralization of phenol

Magnéli phases TinO2n−1 have been demonstrated as promising environmentally friendly materials in advanced oxidation processes. In this study, Magnéli phases TinO2n−1 have been used as catalysts for the ozonation of phenol in aqueous solution for the first time. The materials exhibited excellent catalytic ozonation activities both in phenol degradation and mineralization. When Ti4O7 was added, the reaction rate was six-fold higher than that of with ozone alone, while the total organic carbon removal rate was substantially elevated from around 19.2% to 92%. By virtue of the good chemical stability of the materials, a low metal leaching of less than 0.15 mg·L− 1 could effectively avoid the secondary pollution by metal ions. Radical quenching tests revealed O2− and 1O2 to be active oxygen species for phenol degradation at pH 5. As semiconductor catalysts, TinO2n−1 materials show electronic transfer capability. Ozone adsorbed at B-acid sites of the catalyst surface can capture an electron from the conversion of Ti(III) to Ti(IV), and is thereby broken into the active oxygen species. It was interesting to observe that TinO2n−1 exhibit better catalytic activity for phenol degradation and mineralization with lower n value. The difference in electrical conductivity can be considered as a major factor for the catalytic performances. More highly conductive catalysts show a faster electron-transfer rate and better catalytic activity. Thus, significant evidences have been obtained for a single-electron-transfer mechanism of catalytic ozonation with Magnéli phases TinO2n−1.

Anodic oxidation-assisted O2 oxidation of phenol catalyzed by Fe3O4 at low voltage

Environmentally friendly and economically feasible technology is urgently needed for the management of phenolic compounds. Here, low-voltage degradation of phenol is achieved in an anodic oxidation (AO)-assisted O2 oxidation process with Fe3O4/graphite felt (GF) composite anode. Batch experiments on phenol degradation at 0.6 V achieve phenol removal in 78 h, and the total mineralization of phenol is obtained in 90 h at the first cycle. The time required for phenol removal is reduced to 48 h after three cycles of operation, meanwhile mineralization of phenol being completed in 51 h. The AO-assisted O2 oxidation process is confirmed to adopt a non-radical pathway in which the phenol is degraded at the catalytic sites of GF under the synergy of O2 and anodic electric field. Phenol degradation efficiency at the Fe3O4/GF composite anode is significantly higher than that at the GF, which is ascribed to the accelerated electron transfer by Fe3O4. The FeC and FeOC bonds are identified as inherent linkages responsible for electron transfer between the Fe3O4 and GF. Process efficiency is able to be spontaneously enhanced in recycling operation due to the intensification of FeC and FeOC bonds. The low energy cost and application of cheap carbonaceous anode endow the AO-assisted O2 oxidation process with great potential for use in the remediation of phenol pollutant.

Commercial aluminum oxides with different crystalline structures efficient for the mineralization of phenolic pollutants

There are several polymorphs of aluminum oxide, therefore, commercial aluminum oxides with different crystalline structures were selected to perform photocatalytic tests; boehmite, gamma, and alpha alumina polymorphs were chosen to analyze its photocatalytic activity for the mineralization of phenol and 4-chlorophenol using UV light. All the materials were characterized by X-ray diffraction, N2 physisorption, UV–vis diffuse reflectance spectroscopy, infrared spectroscopy, and nuclear magnetic resonance. Also, the type of photoinduced reactive species responsible to carry out the mineralization process, were evaluated, finding that the O2− radicals are determinants for the photocatalytic process. The reaction mechanism involving the sensitization of the phenolic pollutant on the surface of Al2O3 for its mineralization is proposed. Although Al2O3 is an insulator, in the present work, it is proved to be an efficient material for the mineralization of phenolic pollutants.

Electrocatalytic phenol degradation by a novel nanostructured carbon fiber brush cathode coated with graphene ink

A new promising electrochemically-exfoliated graphene-based cathode for the electrocatalytic Fenton process was elaborated by an ink-coating technique. For this purpose, a method to coat graphene ink over a carbon-fiber brush substrate (referred to as Gr-Brush) was optimized and a 1:3 (w/w) Nafion®:graphene ratio increased the H2O2 accumulation yield by 40% (4.23 mg-H2O2 L−1 cm−2), as compared to an uncoated brush. Such improvement was attributed to the higher electroactive surface area and conductivity of Gr-Brush, a fact confirmed by cyclic voltammetry and impedance measurements. Due to a remarkable raise of OH production during the electro-Fenton (EF) process, the phenol degradation rate more than doubled and the mineralization yield increased from 78% (final total organic carbon, TOC, concentration of 5.28 mg-C L−1) with an uncoated brush to 98.5% (final TOC concentration of 0.34 mg-C L−1) with Gr-Brush, following 6 h of EF treatment. Furthermore, the energy required to achieve 40% of phenol mineralization with Gr-Brush was as low as 0.10 kWh g-1 TOC, which outcompeted any other existing graphene-based carbon cathode material coated with either electrochemically-exfoliated graphene (e.g., 0.20 kWh g-1 TOC with carbon cloth) or reduced graphene oxide (rGO) (e.g., 0.53 kWh g-1 TOC with carbon felt), a crucial feature for prospective applications of the novel electrode.

Synthesis of ordered mesoporous manganese titanium composite oxide catalyst for catalytic ozonation

Abstract In this account, highly ordered mesoporous MnO x /TiO 2 composite catalysts with efficient catalytic ozonation of phenol degradation were synthesized by the sol–gel method. The surface morphology and properties of the catalysts were characterized by several analytical methods, including SEM, TEM, BET, XRD, FTIR, and XPS. Interestingly, Mn doping was found to improve the degree of order, and the ordered mesoporous structure was optimized at 3% doping. Meanwhile, MnO x was highly dispersed in the ordered mesoporous materials to yield good catalytic ozonation performance. Phenol could completely be degraded in 20 min and mineralized at 79% in 60 min. Thus, the catalyst greatly improved the efficiency of degradation and mineralization of phenol when compared to single O 3 or O 3 + TiO 2 . Finally, the reaction mechanism of the catalyst was discussed and found to conform to pseudo-first-order reaction dynamics.

P-, B- and N-doped carbon black for the catalytic wet peroxide oxidation of phenol: Activity, stability and kinetic studies

Doped carbon blacks with P, B and N were prepared and tested as catalysts for the wet peroxide oxidation of phenol. N precursors allowed incorporating a higher amount of the doping element on the outermost surface. Phosphoric and boric acids as well as urea and pyridine yielded doped carbons with significantly high activity for the oxidation and mineralization of phenol and its aromatic intermediates. The kinetic model applied, scarcely reported on doped-carbons, showed reaction rate constants values up to eight times larger than those of the original carbon. This behavior was attributed to the more acidic character of doped-carbons.

An efficient eco advanced oxidation process for phenol mineralization using a 2D/3D nanocomposite photocatalyst and visible light irradiations

Nanocomposites (CNTi) with different mass ratios of carbon nitride (C3N4) and TiO2 nanoparticles were prepared hydrothermally. Different characterization techniques were used including X-ray diffraction (XRD), UV-Vis diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS), transmission electron spectroscopy (TEM) and Brunauer-Emmett-Teller (BET). UV-Vis DRS demonstrated that the CNTi nanocomposites exhibited absorption in the visible light range. A sun light - simulated photoexcitation source was used to study the kinetics of phenol degradation and its intermediates in presence of the as-prepared nanocomposite photocatalysts. These results were compared with studies when TiO2 nanoparticles were used in the presence and absence of H2O2 and/or O3. The photodegradation of phenol was evaluated spectrophotometrically and using the total organic carbon (TOC) measurements. It was observed that the photocatalytic activity of the CNTi nanocomposites was significantly higher than that of TiO2 nanoparticles. Additionally, spectrophotometry and TOC analyses confirmed that degraded phenol was completely mineralized to CO2 and H2O with the use of CNTi nanocomposites, which was not the case for TiO2 where several intermediates were formed. Furthermore, when H2O2 and O3 were simultaneously present, the 0.1% g-C3N4/TiO2 nanocomposite showed the highest phenol degradation rate and the degradation percentage was greater than 91.4% within 30 min.

Sequential Combination of Electro-Fenton and Electrochemical Chlorination Processes for the Treatment of Anaerobically-Digested Food Wastewater.

A two-stage sequential electro-Fenton (E-Fenton) oxidation followed by electrochemical chlorination (EC) was demonstrated to concomitantly treat high concentrations of organic carbon and ammonium nitrogen (NH4+-N) in real anaerobically digested food wastewater (ADFW). The anodic Fenton process caused the rapid mineralization of phenol as a model substrate through the production of hydroxyl radical as the main oxidant. The electrochemical oxidation of NH4+ by a dimensionally stable anode (DSA) resulted in temporal concentration profiles of combined and free chlorine species that were analogous to those during the conventional breakpoint chlorination of NH4+. Together with the minimal production of nitrate, this confirmed that the conversion of NH4+ to nitrogen gas was electrochemically achievable. The monitoring of treatment performance with varying key parameters (e.g., current density, H2O2 feeding rate, pH, NaCl loading, and DSA type) led to the optimization of two component systems. The comparative evaluation of two sequentially combined systems (i.e., the E-Fenton-EC system versus the EC-E-Fenton system) using the mixture of phenol and NH4+ under the predetermined optimal conditions suggested the superiority of the E-Fenton-EC system in terms of treatment efficiency and energy consumption. Finally, the sequential E-Fenton-EC process effectively mineralized organic carbon and decomposed NH4+-N in the real ADFW without external supply of NaCl.

Photo-catalytic activity of hydrophilic-modified TiO2 for the decomposition of methylene blue and phenol

We applied hydrophilic surface modification to P-25 TiO2 nanoparticles via thermal deposition of polydimethylsiloxane (PDMS), followed by annealing at 800 °C under vacuum conditions. This process yielded a thin layer consisting of hydrophilic organic functional groups (e.g., -C=O) as well as SiOx structures on the surface of TiO2. Compared to bare TiO2, the surface-modified TiO2 showed a higher adsorption capacity and photo-catalytic decomposition rate toward methylene blue. However, regarding the photo-catalytic decomposition of phenol, total mineralization of phenol was more complete when bare TiO2 was used as a photo-catalyst, whereas partial oxidation of phenol (i.e., into hydroquinone) was more dominant and total oxidation of phenol was supressed in the presence of surface-modified TiO2. Overall, one cannot simply say that hydrophilic modification of TiO2 leads to a higher affinity to H2O molecules with a higher yield of strongly-oxidizing agents (OH radicals) to increase the photo-catalytic activity in aqueous solutions. Our results imply that a subtle balance of the adsorption energy or rates of H2O, reactants, and reaction intermediates can be important factors for determining the photo-catalytic reaction rate. Different types of photo-catalyst surface modification can be beneficial or detrimental depending on the reaction. It is highlighted that one should be wary of evaluating the overall photo-catalytic activities of dissimilar catalysts based on the results of only a couple of reactions.

Degradation and mineralization of phenol in aqueous medium by heterogeneous monopersulfate activation on nanostructured cobalt based-perovskite catalysts ACoO3 (A = La, Ba, Sr and Ce): Characterization, kinetics and mechanism study

This study reports the heterogeneous catalytic degradation and mineralization of phenol in aqueous solution by means of potassium monopersulfate (PMS or Oxone) process mediated by cobalt perovskite-based catalysts (P-Co). Four nanostructured perovskites oxides with formula ACoO3 (A=Ba, Ce, La, Sr) were synthesized as heterogeneous catalysts by the citrate sol gel method and characterized by means of nitrogen isotherm adsorption (BET), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectrometry (EDX), x-ray photoelectron spectroscopy (XPS), X-ray Diffraction (XRD), transmission electron microscopy (TEM) and Fourier transform infrared (FT-IR) techniques. All the examined samples had perovskite structure. The influences of PMS dosage, catalyst loading, initial target compound concentration and solution pH on the removal efficiency were studied. The activity showed an order of SrCoO3>LaCoO3>BaCoO3>CeCoO3. LaCoO3 and SrCoO3 catalysts exhibit the better performance in terms of reaction rate and stability for the phenol degradation and mineralization by advanced oxidation technology based on sulfate radicals. Catalyst stability was assessed by means of consecutive reuse cycles. No significant loss of activity was noticed after five consecutive cycles. The role of reactive oxygen species produced in the system, mainly SO4− and OH, in the overall oxidation of phenol was determined by using suitable scavenger compounds. Under optimal conditions (10−4M PMS, natural pH, 0.3 gL−1 catalyst loading) complete removal of 20mgL−1 phenol was achieved in 90min. In terms of organic carbon removal, about 81% mineralization yield was reached in the optimal conditions for 6h heterogeneous P-Co/PMS system, suggesting an effective process for phenol mineralization. Four organics intermediates were observed and three of them were identified as catechol, hydroquinone and benzoquinone. A reaction sequence was therefore proposed for the degradation according to the detected products. Subsequent attack of these intermediates by SO4− radicals led to the formation of short chain acids such as, acetic, formic and oxalic acid which were identified by ion-exclusion chromatography.

Visible-light photo-Fenton oxidation of phenol with rGO-α-FeOOH supported on Al-doped mesoporous silica (MCM-41) at neutral pH: Performance and optimization of the catalyst

In this study, α-FeOOH on reduced graphene oxide (rGO-α-FeOOH) supported on an Al-doped MCM-41 catalyst (RFAM) was optimized for the visible-light photo-Fenton oxidation of phenol at neutral pH. The stability of the catalysts, effect of bubbling aeration, and degradation intermediates were investigated. Results indicated that RFAM with a large Brunauer-Emmett-Teller (BET) area and mesoporous structure displayed excellent catalytic activity for the visible-light-driven (VLD) photo-Fenton process. Phenol degradation was well described by a pseudo-first-order reaction kinetics model. Raman analysis demonstrated that an rGO-α-FeOOH (RF) composite is formed during the ferrous-ion-induced self-assembly process. Al-MCM-41 could uniformly disperse RF nanosheets and promote the mobility and diffusion of matter. The activity of the main catalyst α-FeOOH was enhanced after the incorporation of rGO nanosheets. The α-FeOOH crystal in RFAM showed catalytic activity superior to those of Fe3O4 and Fe2O3. The RFAM catalyst, with an optimal GO-Fe2+mass ratio of 2.33, exhibited a larger BET area, pore size, and pore volume, and thus exhibited high performance and energy utilization efficiency in the VLD photo-Fenton reaction with remarkable stability. Bubbling N2 inhibited catalytic performance, while bubbling O2 or air only slightly accelerated the phenol degradation. Visible light played an important role in accelerating the formation of reactive oxygen species (·OH) for the highly efficient phenol degradation. Analysis of degradation intermediates indicated a high phenol mineralization level and the formation of low-molecular-weight organic acids. This work would be helpful in providing an insight into a new type of catalyst assembly and a possible route to a promising heterogeneous catalyst applicable in the visible light photo-Fenton process for effective wastewater remediation at neutral pH.

Kinetic modeling of wet peroxide oxidation with a carbon black catalyst

A kinetic model has been developed describing the rate of hydrogen peroxide consumption and target pollutant (phenol) degradation in CWPO with a commercial carbon black as catalyst. The model allows following the evolution of the oxidation by-products (up to 12) through a detailed reaction pathway. The kinetic parameters were obtained by fitting the experimental results in batch reactor runs at T=90–130°C, P=4bar, [Phenol]0=1g/L, [catalyst]=0–10gcat/L and the theoretical stoichiometric amount of hydrogen peroxide for complete mineralization of phenol (5g/L). The results were subjected to the analysis of variance (ANOVA). The model includes a set of power-law expressions with different reaction orders which provides a complete description of the process and allows obtaining the efficiency of hydrogen peroxide consumption under giving operating conditions.

Enhanced Photodegradation of Phenol by ZnO Nanoparticles Synthesized through Sol-gel Method

Zinc oxide (ZnO) utilization in advanced oxidation process (AOP) via solar-photocatalytic process was a promising method for alternative treating wastewater containing phenol. The ZnO photocatalyst semiconductor was synthesized by sol-gel method. The morphology of the ZnO nanostructures was observed by using scanning electron microscope (SEM) and the crystallite phase of the ZnO was confirmed by x-ray diffraction (XRD). The objective of this study was to synthesis ZnO nanoparticles through a sol-gel method for application as a photocatalyst in the photodegradation of phenol under solar light irradiation. The photodegradation rate of phenol increased with the increasing of ZnO loading from 0.2 until 1.0 g. Only 2 h were required for synthesized ZnO to fully degrade the phenol. The synthesized ZnO are capable to totally degrade high initial concentration up until 45 mg L-1 within 6 h of reaction time. The photodegradation of phenol by ZnO are most favoured under the acidic condition (pH3) where the 100% removal achieved after 2 h of reaction. The mineralization of phenol was monitored through chemical oxygen demand (COD) reduction and 92.6% or removal was achieved. This study distinctly utilized natural sunlight as the sole sources of irradiation which safe, inexpensive; to initiate the photocatalyst for degradation of phenol.

Gamma irradiation-induced complete degradation and mineralization of phenol in aqueous solution: Effects of reagent

This study aims to gain new insight into phenol degradation and mineralization in aqueous solution using ionizing radiation to control its radiolytic elimination under various experimental conditions and to present the different radical reactions involved in water radiolysis. The most obvious finding of this study is that the combination of a reagent, i.e., O3, H2O2, N2O, O2, or S2O82−, with γ-rays effectively enhances the radiolytic system for phenol degradation or mineralization. Radiolytic yield is higher with H2O2 than with S2O82−. For the γ-ray/free O2, γ-ray/H2O2, γ-ray/S2O82−, γ-ray/N2O, and γ-ray/N2 systems, the absorbed doses for 90% phenol elimination are 1.7, 0.85, 1.65, 1.2, and 6.4kGy, respectively; in contrast, phenol can be decomposed totally and directly via reaction with molecular ozone. The lowest dose constant for phenol removal is determined for γ-ray/HCO3−. 89% of mineralization is reached for an absorbed dose of 10kGy with a γ-ray/S2O82− combination.

Qualitative analysis of a mathematical model for kinetic mechanisms of complete mineralization of phenol by Fe_2^+, Fe_3^+ and H_2O_2

In this work we study the phenol degradation kinetics through the formulation and analysis of a nonlinear system of ordinary differential equations. The results suggest that the dynamics of the model is consistent with the phenomenon of phenol mineralization.

Efficient mineralization of phenol by a temperature-responsive polyoxometalate catalyst under wet peroxide oxidation at lower temperatures

Herein, a temperature-responsive polyoxometalate (POM) catalyst [C16H33(CH3)3N]3[PO4{WO(O2)2}4]/poly(N-isopropylacrylamide) (abbreviated as (C16PW(O2)2/PNIPAM) was prepared and used in the catalytic wet peroxide oxidation (CWPO) of phenol under mild conditions.

Facile, high yield ultrasound mediated protocol for ZnO hierarchical structures synthesis: Formation mechanism, optical and photocatalytic properties

Hierarchical flowers-like zinc oxide structures have been successfully obtained by a simple and fast ultrasound-assisted method performed in a ordinary ultrasonic bath using an ammonia solution and zinc acetate, in the absence of any surfactant or template. The composition, structure, crystallinity, morphology and optical properties of the materials obtained at different ultrasound irradiation times were characterized by infrared, UV–Vis and photoluminescence spectroscopy, X-ray diffraction, scanning and transmission electron microscopy investigations. It was proved that the ultrasound irradiation time manipulates both the defect content (implicit the photoluminescent properties) and morphology of the ZnO materials: shorter irradiation times leads to the synthesis of high-defected ZnO structures of flower morphology with triangular-shaped petals, while higher irradiation times favours the formation of low-defected ZnO structures with tipped rod-like petals. A plausible growth mechanism of the architectures that implies aggregation via oriented attachment followed by an Ostwald ripening is advanced based on these results. The ZnO flower-like structures present high photocatalytic activities, a total phenol mineralization being registered in the case of visible light experiments. Electron-spin resonance measurements demonstrate the generation of reactive oxygen species, namely hydroxyl radicals but also C centred radicals adducts derived most probable from the residual acetate adsorbed on ZnO surface.

Photocatalytic activity of Ag3PO4 and some of its composites under non-filtered and UV-filtered solar-like radiation

Silver phosphate is a promising photocatalyst since its energy band gap is situated in the visible range (Eg≈2.4eV), thus this material is a potential candidate for replacing titania which is photoactive only under UV. However, Ag3PO4 suffers of photocorrosion and therefore composites should be prepared to limit this detrimental effect. In this work, pure Ag3PO4 and its composites with AgI, TiO2, and hydroxyapatite were prepared by using various methods. The photoactivity of the materials was evaluated by their ability to decolorize methylene blue and to mineralize phenol under non-filtered and UV-filtered artificial solar-like radiation. The use of UV cut-off filter enhanced the photocatalytic activity of pure silver phosphate by limiting the photocorrosion of silver(I) into Ag°. For composites with AgI and TiO2, despite their lower photoactivity compared to pure Ag3PO4, the efficiency in mineralization of phenol after repeated run is stabilized by using UV cut-off filter. On the other hand, the photocatalytic efficiency of Ag3PO4 composites containing hydroxyapatite remained low mainly due to high absorption properties of hydroxyapatite. The photoactive samples showed excellent photoinduced antimicrobial properties where Gram-negative E. coli was more susceptible to photocatalytic deactivation than Gram-positive S. aureus (MRSA).

Degradation and mineralization of aqueous phenol by an atmospheric pressure catalytic plasma reactor

Aqueous phenol degradation and mineralization was carried out by using an atmospheric pressure plasma reactor operating under argon (Ar)/air plasma. The addition of CeO2, Ce0.90Ni0.10O2-δ and 10wt% NiO/CeO2 catalysts improved the efficiency of phenol degradation. The modified ceria catalysts were prepared by wet impregnation and characterized by using X-ray diffraction (XRD), BET surface area measurements and Raman spectroscopy, to ensure the fluorite phase and oxygen-deficient sites. The effect of plasma gas, the concentration of the pollutant, applied voltage and the catalyst was studied. Typical results indicated that Ar plasma favors the degradation due to the formation of the highest amounts of oxidants like hydrogen peroxide (H2O2), which may be converted into hydroxyl radicals (OH) in the presence of a solid catalyst. Optical emission spectrum (OES) of the discharge confirms the formation of OH, whereas total organic carbon (TOC) analysis indicated the mineralization of the pollutant.

Assessing the use of zero-valent iron microspheres to catalyze Fenton treatment processes

The application of Fenton processes is limited by the production of iron sludge and its pH-dependence efficiency. UV-light assistance and the use of alternative catalysts as zero-valent iron (ZVI) may avoid both drawbacks favoring its potential industrial application. The use of ZVI microspheres as the catalyst of Fenton processes is herein assessed and optimized in terms of reagents dosage, particle size and surface area. Microspheres providing a surface area of 0.8m2/g showed the best performance and the lowest tendency to be dissolved under acidic conditions, resulting a concentration ratio of [H2O2]/[Fe0]=60 under optimal reaction conditions. The optimized 450W UV-radiation photo-Fenton treatment addressed the almost complete mineralization of phenol (COD and TOC removal≈98–99%) at both acidic and neutral initial pH values; whereas good mineralization results of oxalic acid were only achieved under acidic conditions (COD removal≈100%; TOC removal≈83%). Only initial neutral pH conditions enabled the recovery of the catalyst. Although a more powerful oxidation treatment was performed under acidic conditions, it also implied a higher dissolution of the microspheres. The application of less powerful radiation (100W) limited catalyst losses under acidic conditions, but longer treatment time is required aiming to address similar degradation results.