Effect of various sono-oxidation parameters on the removal of aqueous 2,4-dinitrophenol

Mono and co-immobilization of imidazolium ionic liquids on silica: effects of the substituted groups on the adsorption behavior of 2,4-dinitrophenol

Ionic liquid modified silicas with high adsorption capacity for phenols prompt us to deeply explore the contribution of interactions between the adsorbent and adsorbate, with a particular focus on hydrophobicity, π–π, electrostatic and acid–base interactions. Herein, by introducing a series of typical substituent groups including N,N-dimethylaminopropyl (A), benzyl (B), dodecyl (D) and naphthylmethyl (N) in an imidazole ring (Im), three mono-immobilized and two co-immobilized imidazolium ionic liquid modified silicas, namely SilprAImCl, SilprBImCl, SilprNImCl, SilprDBImCl and SilprDAImCl, werre synthesized for removal and recovery of 2,4-dinitrophenol (2,4-DNP) from aqueous solutions. Adsorption kinetics, isotherms, thermodynamic analysis and desorption experiments have been carried out. The experimental results reveal that the substituent groups such as N,N-dimethylaminopropyl, benzyl and naphthylmethyl on the imidazole ring can significantly enhance the adsorption of 2,4-DNP via the acid–base interaction or π–π interaction and the adsorption capacity of 2,4-DNP follows the order: SilprNImCl > SilprAImCl > SilprBImCl. Furthermore, SilprDBImCl exhibits the largest adsorption capacity and SilprDAImCl has the lowest among the five adsorbents. These interesting finds indicate that the combination of hydrophobicity and π–π interactions lead to enhanced adsorption performance towards 2,4-DNP, while the combination of the hydrophobicity and acid–base interactions can restrain greatly adsorption of 2,4-DNP from aqueous medium. Adsorption mechanisms of 2,4-DNP on the five adsorbents have been clarified. These results will provide a deeper insight for efficient removal of phenols from water environments.

Ionic liquid modified silicas with high adsorption capacity for phenols prompt us to deeply explore the contribution of interactions between the adsorbent and adsorbate, with a particular focus on hydrophobicity, π–π, electrostatic and acid–base interactions.

Titanium dioxide-based sonophotocatalytic mineralization of bisphenol A and its intermediates

In this study, bisphenol A (BPA) removal by sonophotocatalysis coupled with commercially available titanium dioxide (TiO₂, P25) was assessed in batch tests using energy-based advanced oxidation combining ultrasound (US) and ultraviolet (UV). The kinetics of BPA removal were systematically evaluated by changing operational parameters, such as US frequency and power, mechanical stirring speed, and temperature, but also comparison of single and coupled systems under the optimum US conditions (35 kHz, 50 W, 300 rpm stirring speed, and 20 °C). The combination of US/UV/P25 exhibited the highest BPA removal rate (28.0 × 10^-3 min^-1). In terms of the synergy index, the synergistic effect of sonophotocatalysis was found to be 2.2. This indicated that sonophotocatalysis has a considerably higher removal efficiency than sonocatalysis or photocatalysis. The removal of BPA was further investigated to identify BPA byproducts and intermediates using high-performance liquid chromatography-mass spectrometry. Five main intermediates were formed during sonophotocatalytic degradation, and complete removal of BPA and its intermediates was obtained after 3 h of operation. The degradation pathway of BPA by sonophotocatalysis was also elucidated.

Sono-advanced Fenton decolorization of azo dye Orange G: Analysis of synergistic effect and mechanisms

In this study, a successful decolorization of Orange G was achieved by means of coupling zero valent iron (ZVI), H2O2 and ultrasound (US) under acidic pH conditions. The synergistic effect and characterization of potential roles of the factors including ZVI, tert-Butanol as radical scavenger, dissolved ferrous ions and H2O2 generated from sonication were evaluated in this sono-advanced Fenton process (SAFP) system. A clear synergy was evident in terms of decolorization rate and the TOC removal as the input of US enhanced the activity of the Fe(0)/H2O2 system. The results suggested that the ZVI was potential replacement for the Fe(2+) ion. This remarkable activity was attributed to the capacity of Fe(2+) formed and reduction of sonic-dissolved Fe(2+) concentration by the formation of {Fe·Fe(2+)}. The modification of the condition of H2O2 addition such as the dosage and input method showed significant variations in terms of decolorization rate. This result indicated that the optimal external addition of H2O2 and input method is a limited factor of decolorization rate due to its comparatively insufficient generated by ultrasound.

Effect of process intensifying parameters on the hydrodynamic cavitation based degradation of commercial pesticide (methomyl) in the aqueous solution

Methomyl, a carbamate pesticide, is classified as a pesticide of category-1 toxicity and hence shows harmful effects on both human and aquatic life. In the present work, the degradation of methomyl has been studied by using hydrodynamic cavitation reactor (HC) and its combination with intensifying agents such as H2O2, fenton reagent and ozone (hybrid processes). Initially, the optimization of operating parameters such pH and inlet pressure to the cavitating device (circular venturi) has been carried out for maximizing the efficacy of hydrodynamic cavitation. Further degradation study of methomyl by the application of hybrid processes was carried out at an optimal pH of 2.5 and the optimal inlet pressure of 5 bar. Significant synergetic effect has been observed in case of all the hybrid processes studied. Synergetic coefficient of 5.8, 13.41 and 47.6 has been obtained by combining hydrodynamic cavitation with H2O2, fenton process and ozone respectively. Efficacy of individual and hybrid processes has also been obtained in terms of energy efficiency and extent of mineralization. HC+Ozone process has proved to be the most effective process having highest synergetic coefficient, energy efficiency and the extent of mineralization. The study has also encompassed the identification of intermediate by-products generated during the degradation and has proposed the probable degradation pathway. It has been conclusively established that hydrodynamic cavitation in the presence of intensifying agents can effectively be used for complete degradation of methomyl.

Facilitated and selective oxidation of thiophenic sulfur compounds using MoOx/Al₂O₃-H₂O₂ system under ultrasonic irradiation

Oxidative desulfurization of thiophenic sulfur compounds of benzothiophene (BT), dibenzothiophene (DBT) and 4,6-dimethyl dibenzothiophene (4,6-DMDBT) with MoOx/Al₂O₃ catalyst and H₂O₂ oxidant has been facilitated and more selective under ultrasonic irradiation. The catalyst with the optimum 10% of Mo loading consisted of isolated tetrahedral molybdenum oxide species based on FTIR analysis. The increase of Mo loading to 15% and 20% caused to generation of polymolybdate and MoO₃ crystals which decreased desulfurization activity. Sonication enhanced the apparent reaction rate constants in oxidation of all three sulfur compounds. An increase in the Arrhenius factor (A0), which is the total number of collisions per second, could explain the acceleration in the rate constants by sonication. The apparent activated energy (Ea) of BT oxidation was reduced from 96.6 to 75.3 kJ/mol by using ultrasound. This indicated that ultrasound had also a chemical effect, like a catalytic influence, in the acceleration of BT removal. DBT oxidation was reduced when investigated in the presence of tetralin, naphthalene and 2-methyl naphthalene as the model aromatic compounds of actual light oils. A higher selectivity toward DBT elimination in the presence of aromatics was obtained by sonication when compared with the silent treatment. Ultrasound cleaned the catalyst surface from adsorbed aromatics. On the basis of the obtained results, a mechanistic proposal for this desulfurization was explained. Oxidation was performed by nucleophilic attack of sulfur atom to the molybdenum peroxide species of tetrahedral molybdates, which was more advanced by sonication.

Degradation of alachlor using an enhanced sono-Fenton process with efficient Fenton's reagent dosages

In this study, an enhanced sono-Fenton process for the degradation of alachlor is presented. At high ultrasonic power, low pH, and in the presence of adequate Fenton's reagent dosages, alachlor degradation can reach nearly 100%. The toxicity of treated alachlor wastewater, which was measured by changes in cell viability, slightly decreased after the Fenton or ultrasound/H2O2 process and significantly decreased after the enhanced sono-Fenton process. A satisfactory relationship was observed between the total organic carbon removal and cell viability increment, indicating that alachlor mineralization is a key step in reducing the toxicity of the solution. The formation of alachlor degradation byproducts was observed during the oxidation process, in which the first step was the substitution of a chloride by a hydroxyl group. In conclusion, the enhanced sono-Fenton process was effective in the degradation and detoxification of alachlor within a short reaction time. Thus, the treated wastewater can then be passed through a biological treatment unit for further treatment.

Sonocatalytic and sonophotocatalytic degradation of Rhodamine 6G containing wastewaters

The present work deals with degradation of aqueous solution of Rhodamine 6G (Rh 6G) using sonocatalytic and sonophotocatalytic treatment schemes based on the use of cupric oxide (CuO) and titanium dioxide (TiO2) as the solid catalysts. Experiments have been carried out at the operating capacity of 2 L and constant initial pH of 12.5. The effect of catalyst loading on the sonochemical degradation has been investigated by varying the loading over the range of 1.5-4.5 g/L. It has been observed that the maximum degradation of 52.2% was obtained at an optimum concentration of CuO as 1.5 g/L whereas for TiO2 maximum degradation was observed as 51.2% at a loading of 4 g/L over similar treatment period. Studies with presence of radical scavengers such as methanol (CH3OH) and n-butanol (C4H9OH) indicated lower extents of degradation confirming the dominance of radical mechanism. The combined approach of ultrasound, solid catalyst and scavengers has also been investigated at optimum loadings to simulate real conditions. The optimal solid loading was used for studies involving oxidation using UV irradiations where 26.4% and 28.9% of degradation was achieved at optimal loading of CuO and TiO2, respectively. Studies using combination of UV and US irradiations have also been carried out using the optimal concentration of the catalysts. It has been observed that maximum degradation of 63.3% is achieved using combined US and UV with TiO2 (4 g/L) as the photocatalyst. Overall it can be said that the combined processes give higher extent of degradation as compared to the individual processes based on US or UV irradiations.

Acetamiprid removal in wastewater by the low-temperature plasma using dielectric barrier discharge

Degradation of acetamiprid in wastewater was studied in a dielectric barrier discharge (DBD) reactor. This reactor produces ultraviolet light and reactive species like ozone (O₃) can be used for the treatment of wastewater. We examined the factors that could affect the degradation process, including the discharge power, and the initial concentrations of acetamiprid, and O₃ which is generated by the DBD reactor. We also investigated the effect of adding Na₂B₄O₇ as a radical scavenger to probe the role of hydroxyl radical in the reaction. The results indicated that acetamiprid could be removed from aqueous solution effectively and hydroxyl radicals played an important role during the degradation by the low temperature plasma. The degradation process of acetamiprid fits the first-order kinetics. The degradation efficiency was 83.48 percent at 200 min when the discharge power was 170 W and the initial acetamiprid concentration was 50 mg/L. The removal efficiency of acetamiprid decreased with the increasing concentration of Na₂B₄O₇ because B₄O₇(2-) is an excellent radical scavenger that inhibited the generation of OH during the DBD process. The removal efficiency of acetamiprid improved in the presence of O₃. The main reason was that O₃ can oxidize certain organic compounds directly or indirectly by generating hydroxyl radicals. The degradation products of acetamiprid were characterized qualitatively and quantitatively using high performance liquid chromatography, mass spectrometry and UV-vis spectroscopy.

Treatment of cyanide containing wastewater using cavitation based approach

Industrial wastewater streams containing high concentrations of biorefractory materials like cyanides should ideally be treated at source. In the present work, degradation of potassium ferrocyanide (K4Fe(CN)6) as a model pollutant has been investigated using cavitational reactors with possible intensification studies using different approaches. Effect of different operating parameters such as initial concentration, temperature and pH on the extent of degradation using acoustic cavitation has been investigated. For the case of hydrodynamic cavitation, flow characteristics of cavitating device (venturi) have been established initially followed by the effect of inlet pressure and pH on the extent of degradation. Under the optimized set of operating parameters, the addition of hydrogen peroxide (ratio of K4Fe(CN)6:H2O2 varied from 1:1 to 1:30 mol basis) as process intensifying approach has been investigated. The present work has conclusively established that under the set of optimized operating parameters, cavitation can be effectively used for degradation of potassium ferrocyanide. The comparative study of hydrodynamic cavitation and acoustic cavitation suggested that hydrodynamic cavitation is more energy efficient and gives higher degradation as compared to acoustic cavitation for equivalent power/energy dissipation. The present work is the first one to report comparison of cavitation based treatment schemes for degradation of cyanide containing wastewaters.

Wastewater treatment using hybrid treatment schemes based on cavitation and Fenton chemistry: a review

Advanced oxidation processes such as cavitation and Fenton chemistry have shown considerable promise for wastewater treatment applications due to the ease of operation and simple reactor design. In this review, hybrid methods based on cavitation coupled with Fenton process for the treatment of wastewater have been discussed. The basics of individual processes (Acoustic cavitation, Hydrodynamic cavitation, Fenton chemistry) have been discussed initially highlighting the need for combined processes. The different types of reactors used for the combined processes have been discussed with some recommendations for large scale operation. The effects of important operating parameters such as solution temperature, initial pH, initial pollutant concentration and Fenton's reagent dosage have been discussed with guidelines for selection of optimum parameters. The optimization of power density is necessary for ultrasonic processes (US) and combined processes (US/Fenton) whereas the inlet pressure needs to be optimized in the case of Hydrodynamic cavitation (HC) based processes. An overview of different pollutants degraded under optimized conditions using HC/Fenton and US/Fenton process with comparison with individual processes have been presented. It has been observed that the main mechanism for the synergy of the combined process depends on the generation of additional hydroxyl radicals and its proper utilization for the degradation of the pollutant, which is strongly dependent on the loading of hydrogen peroxide. Overall, efficient wastewater treatment with high degree of energy efficiency can be achieved using combined process operating under optimized conditions, as compared to the individual process.

Synergetic effect of combination of AOP's (hydrodynamic cavitation and H₂O₂) on the degradation of neonicotinoid class of insecticide

In the present work, degradation of imidacloprid (neonicotinoid class of insecticide) in aqueous solution has been systematically investigated using hydrodynamic cavitation and combination of hydrodynamic cavitation (HC) and H2O2. Initially, effect of different operating parameters such as inlet pressure to the cavitating device (5-20 bar) and operating pH (2-7.5) has been investigated. Optimization of process parameters was followed by the study of effect of combination of HC and H2O2 process on the rate of degradation of imidacloprid. Significant enhancement in the rate of degradation of imidacloprid has been observed using HC+H2O2 process which lead to a complete degradation of imidacloprid in 45 min of operation using optimal molar ratio of imidacloprid:H2O2 as 1:40. Substantial synergetic effect has been observed using HC+H2O2 process which confer the synergetic coefficient of 22.79. An attempt has been made to investigate and compare the energy efficiency and extent of mineralization of individual and combined processes applied in the present work. Identification of the byproducts formed during degradation of imidacloprid has also been done using LC-MS analysis. The present work has established a fact that hydrodynamic cavitation in combination with H2O2 can be effectively used for degradation of imidacloprid.

Degradation of 2,4-dinitrophenol using a combination of hydrodynamic cavitation, chemical and advanced oxidation processes

In the present work, degradation of 2,4-dinitrophenol (DNP), a persistent organic contaminant with high toxicity and very low biodegradability has been investigated using combination of hydrodynamic cavitation (HC) and chemical/advanced oxidation. The cavitating conditions have been generated using orifice plate as a cavitating device. Initially, the optimization of basic operating parameters have been done by performing experiments over varying inlet pressure (over the range of 3-6 bar), temperature (30 °C, 35 °C and 40 °C) and solution pH (over the range of 3-11). Subsequently, combined treatment strategies have been investigated for process intensification of the degradation process. The effect of HC combined with chemical oxidation processes such as hydrogen peroxide (HC/H2O2), ferrous activated persulfate (HC/Na2S2O8/FeSO4) and HC coupled with advanced oxidation processes such as conventional Fenton (HC/FeSO4/H2O2), advanced Fenton (HC/Fe/H2O2) and Fenton-like process (HC/CuO/H2O2) on the extent of degradation of DNP have also been investigated at optimized conditions of pH 4, temperature of 35 °C and inlet pressure of 4 bar. Kinetic study revealed that degradation of DNP fitted first order kinetics for all the approaches under investigation. Complete degradation with maximum rate of DNP degradation has been observed for the combined HC/Fenton process. The energy consumption analysis for hydrodynamic cavitation based process has been done on the basis of cavitational yield. Degradation intermediates have also been identified and quantified in the current work. The synergistic index calculated for all the combined processes indicates HC/Fenton process is more feasible than the combination of HC with other Fenton like processes.

Removal of 2,4-dinitrophenol using hybrid methods based on ultrasound at an operating capacity of 7 L

Sonochemical removal of 2,4-dinitrophenol (DNP) has been investigated using ultrasonic bath, with an operating capacity of 7 L, fitted with a large transducer with longitudinal vibrations having a 1 kW rated power output and operating frequency of 25 kHz. It has been revealed from calorimetric studies that maximum power is dissipated at a capacity of 7 L. The concentration of DNP has been monitored with an objective of evaluation of the efficacy of ultrasonic reactor in combination with process intensifying approaches for the removal of DNP. The effect of operating pH and additives such as hydrogen peroxide and ferrous iron activated persulfate on the extent of removal of DNP has been investigated. It has been observed that the extent of removal is greater at lower pH (pH 2.5 and 4) than at higher pH (pH 10). The combined treatment strategies such as ultrasound (US)/Fenton, US/advanced Fenton and US/CuO/H2O2 have also been investigated with an objective of obtaining complete removal of DNP using hybrid treatment strategies. The extent of removal has been found to increase significantly in US/Fenton process (98.7%) as compared to that using US alone (5.8%) which demonstrates the efficacy of the combined process. First order kinetics has been fitted for all the approaches investigated in the work. Calculations of cavitational yield indicated the superiority of the reactor design as compared to the conventional ultrasonic horn type reactors. The main intermediates formed during the process of removal of DNP have been identified.

Treatment of pharmaceutical effluent by ultrasound coupled with dual oxidant system

In this study, sonolysis (US), a dual oxidant system (DOX), and ultrasound coupled with a dual oxidant system (US/DOX) were employed to degrade real pharmaceutical effluent. In a DOX system, two effective oxidizing agents such as hydrogen peroxide and activated persulphate were used simultaneously. In this work, for the first time, an easily available waste material, iron swarf, was used as an activator for persulphate oxidation. Iron swarf coupled with an ultrasound system showed better activation. High iron dosage, acidic pH and high temperature favoured degradation with both DOX and US/DOX. Sequential addition of iron swarf produced better results compared to single-step addition. The activation energy was found to be 47.25 and 23.47 kJ/mol for DOX and US/DOX, respectively. The biodegradability index of the effluent was enhanced from 0.13 to 0.81 after treatment with US/DOX.

Photodegradation of p-Nitrophenol Catalyzed by ZnO/MWCNTs Composite Catalyst in Water

Photodegradation ofp-nitrophenol catalyzed by ZnO/MWCNTs composite in water was investigated. The effects of pH, irradiation time, catalyst loading, initial substrate concentration and MWCNTs content on the degradation were investigated. Experiment results revealed that the optimal conditions were ap-nitrophenol concentration of 60.0 mg/L at pH 5.0 with catalyst loading of 10.0 g/L under solar irradiation for the illumination of 180 min. The highest efficiency on photodegradation ofp-nitrophenol can be achieved with an optimal MWCNTs/ZnO mass ratio of 0.16%. Possible decomposing mechanisms were also discussed. The repeatability of photocatalytic activity was tested. The photocatalyst was used ten cycles with degradation efficiency still higher than 95%. The results of the study showed the feasible and potential use of ZnO/MWCNTs composite in degradation of toxic organic pollutants.

Degradation of C.I. Acid Orange 7 by ultrasound enhanced heterogeneous Fenton-like process

The effect of ultrasonic power density, goethite addition, hydrogen peroxide concentration, initial pH, hydroxyl radical scavenger, and initial dye concentration on the decolorization of C.I. Acid Orange 7 by ultrasound/goethite/H(2)O(2) process was investigated. The results showed that the decolorization rate increased with power density, goethite addition, and hydrogen peroxide concentration, but decreased with the increase of initial dye concentration. The ultrasonic power density, goethite addition, and initial dye concentration have little effect on decolorization efficiency after 30 min reaction, while the increase of hydrogen peroxide concentration results in the increase of decolorization efficiency. There existed an optimal initial pH to achieve the highest decololrization rate and decolorization efficiency. The presence of hydroxyl radical scavenger would inhibit the decolorization reaction. Only less than half of total organic carbon (TOC) was removed after 90 min reaction, indicating more aggressive conditions are required to achieve the complete mineralization than those employed to simply break the chromophore group.

Solar photocatalytic degradation of 2,6-dinitro-p-cresol (DNPC) using multi-walled carbon nanotubes (MWCNTs)-TiO(2) composite photocatalysts

Multi-walled carbon nanotubes (MWCNTs)-TiO(2) composite photocatalysts with excellent activity were prepared by sol-gel method in order to investigate its photocatalytic activity under solar irradiation for the degradation of 2,6-dinitro-p-cresol (DNPC) in aqueous solution. The prepared composite were analyzed by XRD, FTIR, SEM, TEM, TG-DTA and UV-vis absorption spectra techniques. The results showed that the composite can cause an obvious red shift of UV-vis spectra compared with pure TiO(2). The degradation of DNPC by MWCNTs-TiO(2) composite photocatalysts under solar irradiation was systematically studied by varying the experimental parameters such as pH value, irradiation time, the initial substrate concentration, reaction temperature, catalyst concentration, etc. The optimal conditions were a DNPC concentration of 33.4 mgL(-1) at pH 6.0 with MWCNTs-TiO(2) concentration of 6.0gL(-1) under solar irradiation for the illumination of 150 min. The presence of MWCNTs can enhance the photoefficiency of TiO(2). The highest efficiency on photodegradation of DNPC can be achieved with an optimal MWCNTs/TiO(2) mass ratio of 0.05%. The photocatalytic degradation of DNPC obeys a pseudo-first-order behavior according to the Langmuir-Hinshelwood model, and possible decomposing mechanisms are also discussed. The photocatalyst was used for five cycles with photocatalytic degradation efficiency still higher than 96%. The results of the study showed the feasible and potential use of MWCNTs-TiO(2) composite in degradation of toxic organic pollutants.

Ultrasonic irradiation-induced degradation of low-concentration bisphenol A in aqueous solution

The treatment of bisphenol A (BPA)-contaminated water has attracted great interest recently. In this contribution, ultrasound (US) was applied to remove low-concentration BPA in aqueous solution at the frequency of 20 kHz, and the effects of ultrasonic intensity and ozone on BPA removal were evaluated for the first time. Considering the coexistence of halomethanes and BPA in chlorinated drinking water, BPA was degraded under US in the presence of CCl(4). In addition, the main intermediates resulting from BPA ultrasonic degradation were identified by gas chromatography-mass spectrometry. On the basis of these studies, OH radical induced oxidation was identified as the major destruction pathway during BPA sonolysis.

Degradation of C.I. Direct Black 168 from aqueous solution by fly ash/H2O2 combining ultrasound

Degradation of C.I. Direct Black 168 from aqueous solution using Fenton-like reactions combining ultrasound was investigated. In the presence of H(2)O(2), the effect of the heterogeneous catalysts, such as fly ash, kaolinite or diatomaceous earth on the degradation of Direct Black 168 was observed under ultrasound. The fly ash was the most efficient catalyst. It is apparent that ultrasound can prompt the reaction to take place and give in higher degradation. In the combination of ultrasound and fly ash/H(2)O(2), the effect of different system variables namely concentration of the dye, dosage of fly ash, concentration of H(2)O(2), pH of solution and the addition of NaCl were studied. 99.0% removal ratio was achieved at initial concentration 100mg/L, pH 3.0, and dosage of fly ash 2.0 g/L, as well as 2.94 mM H(2)O(2). NaCl exhibited only a minor effect on the dye removal.

Degradation of 2,4-dinitrophenol by combining sonolysis and different additives

Based on the effects of various additives on ultrasonic degradation of 2,4-dinitrophenol (DNP) in aqueous solution, the degradation mechanisms and reaction kinetics of DNP in different processes were proposed. The results showed that some additives, such as CuO, CCl(4), O(3), NaCl and KI, were favorable for DNP sonochemical degradation. On the contrary, DNP degradation efficiency was restrained by Na(2)CO(3), indicating that OH radicals oxidation played an important role in DNP ultrasonic removal. The significant increases in DNP degradation in US/CuO/H(2)O(2), US/CCl(4) and US/O(3) systems were also related to the intermediates formed during the reactions, such as HO(2)/O(2)(-) radicals, chlorine-containing radicals and HClO. In addition, DNP ultrasonic removal was observed to behave as pseudo-first-order kinetics under different experimental conditions tested in the present work.

Decolorizing of azo dye Reactive red 24 aqueous solution using exfoliated graphite and H2O2 under ultrasound irradiation

At its natural pH (6.95), the decolorization of Reactive red 24 in ultrasound, ultrasound/H2O2, exfoliated graphite, ultrasound/exfoliated graphite, exfoliated graphite/H2O2 and ultrasound/exfoliated graphite/H2O2 systems were compared. An enhancement was observed for the decolorization in ultrasound/exfoliated graphite/H2O2 system. The effect of solution pH, H2O2 and exfoliated graphite dosages, and temperature on the decolorization of Reactive red 24 was investigated. The sonochemical treatment in combination with exfoliated graphite/H2O2 showed a synergistic effect for the decolorization of Reactive red 24. The results indicated that under proper conditions, there was a possibility to remove Reactive red 24 very efficient from aqueous solution. The decolorization of other azo dyes (Reactive red 2, Methyl orange, Acid red 1, Acid red 73, Acid red 249, Acid orange 7, Acid blue 113, Acid brown 75, Acid green 20, Acid yellow 42, Acid mordant brown 33, Acid mordant yellow 10 and Direct green 1) was also investigated, at their natural pH.

Low-temperature plasma-induced degradation of aqueous 2,4-dinitrophenol

The degradation behavior of 2,4-dinitrophenol (DNP) by low-temperature plasma was investigated and the effect of some factors that might affect the degradation process was further examined. The results indicated that DNP could be effectively removed from aqueous solution. The degradation value was 83.6% when the input power was 150 W and 60 s was selected as the discharge time. Increasing the input power increased the degradation efficiency. The degradation process fitted first-order dynamics and the reduction was mainly caused by the reaction of DNP with OH. The degradation efficiency decreased with the increase of initial concentration at the same discharge time. H2O2 at the concentration of 0.25% enhanced the degradation process, however, hindered the degradation at 1.00 and 2.00%. The presence of Fe2+ could benefit DNP degradation. However, the increment in degradation efficiency might be suppressed to some extent at a high concentration level. Cu2+ inhibited the degradation process within 30 s and enhanced the reduction after 30 s. Furthermore, the increment of Cu2+ concentration could enhance the effect. A little acid environment was conducive to DNP degradation and the pH value became lower with increasing discharge time by low-temperature plasma.

Sonochemical decolorization of acid black 210 in the presence of exfoliated graphite

The decolorization of acid black 210 by ultrasonic irradiation in the presence of exfoliated graphite was investigated. Low pH value and large exfoliation volume of exfoliated graphite favored the ultrasonic decolorization of acid black 210. The combination method of ultrasonic waves and exfoliated graphite achieved better results than either exfoliated graphite or ultrasound alone. Improved decolorization efficiency has been observed in the present system compared to the process using a combination of ultrasound and activated carbon. In the combination method of ultrasonic waves and exfoliated graphite, approximately 99.5% of acid black 210 was removed using 0.8 g/l exfoliated graphite at a pH of 1 within 120 min at 51 degrees C.

Intensification of hydroxyl radical production in sonochemical reactors

The efficacy of sonochemical reactors in chemical processing applications has been well established in the laboratory scale of operation though at a given set of operating parameters and no efforts have been directed in terms of maximizing the free radical production. In the present work, the effect of different operating parameters viz. pH, power dissipation into the system, effect of additives such as air, haloalkanes, titanium dioxide, iron and oxygen on the extent of hydroxyl radical formation in a sonochemical reactor have been investigated using salicylic acid dosimetry. Possible mechanisms for oxidation of salicylic acid in the presence of different additives have also been established. It has been observed that acidic conditions under optimized power dissipation in the presence of iron powder and oxygen result in maximum liberation of hydroxyl radicals as quantified by the kinetic rate constant for production of 2,5- and 2,3-dihydroxybenzoic acid. The study has enabled the optimization of the conditions for maximum efficacy of sonochemical reactors where free radical attack is the controlling mechanism for the chemical processing applications.

Comparison of Fenton and sono-Fenton bisphenol A degradation

Degradation of bisphenol A (BPA) was carried out with the Fenton reagent with and without additional sonochemical treatment. The Fenton and the sono-Fenton decomposition of BPA showed that ultrasound irradiation of wastewater improved the wet oxidation process of 25 mg l(-1) BPA solutions. The sonochemical degradation of BPA was monitored using UV absorption and large volume injection packed capillary LC measurements.

Sonodegradation of halomethane mixtures in chlorinated drinking water

Ultrasonic degradation of halomethane mixtures, with very low initial concentration in chlorinated drinking water was investigated. It was observed that the removal efficiencies of four halomethanes after 1 h ultrasonic irradiation followed the increasing order: CHCl(3) < CHBr(2)Cl < CHBrCl(2) < CCl(4) and the degradation reactions of the halomethanes were well described by the pseudo-first-order kinetics model. Molecular polarity was found to be an important factor controlling the sonodegradation of halomethane mixtures. Increasing acoustic intensity enhanced the removal of halomethanes in chlorinated drinking water. In addition, ultrasonic irradiation led to a slightly decrease of pH and TOC of chlorinated drinking water.