Sonochemical degradation of Basic Blue 41 dye assisted by nanoTiO2 and H2O2

The sonolysis of Basic Blue 41 dye in aqueous solution was performed at 35 kHz using ultrasonic power of 160 W and aqueous temperature of 25+1 degrees C within 180 min. The TiO2 nanoparticles were used as a catalyst to assist the sonication process. The effect of experimental parameters such as pH, H2O2 concentration and initial dye concentration on the reaction were investigated. It was recognized that in lower pH values the dye removal rate decreased. However, dye removal increased via increase in H2O2 concentration and lowering the initial dye concentration. All intermediate compounds were detected by integrated gas chromatography-mass spectrometry (GC/MS) and also ion chromatograph (IC). During the decolorization, all nitrogen atoms and aromatic groups of Basic Blue 41 were converted to urea, nitrate, formic acid, acetic acid and oxalic acid, etc. Kinetic studies revealed that the degradation process followed pseudo-first order mechanism with the correlation coefficient (R2) of 0.9918 under experimental conditions. The results showed that power ultrasound can be regarded as an appropriate tool for degradation of azo dyes to non-toxic end products.     

Oxidative decomposition of atrazine in water in the presence of hydrogen peroxide using an innovative microwave photochemical reactor

The simultaneous application of microwave (MW) power and UV light leads to improved results in photochemical processes. This study investigates the oxidative decomposition of atrazine in water using an innovative MW and UV photochemical reactor, which activates a chemical reaction with MW and UV radiation using an immersed source without the need for a MW oven. We investigated the influence of reaction parameters such as initial H(2)O(2) concentrations, reaction temperatures and applied MW power and identified the optimal conditions for the oxidative decomposition of atrazine. Atrazine was completely degraded by MW/UV/H(2)O(2) in a very short time (i.e. t(1/2) = 1.1 min for 20.8 mg/L in optimal conditions). From the kinetic study, the disappearance rate of atrazine can be expressed as dX/dt = k(PH)[M](0)(b-X)(1-X), where b ≡ [H(2)O(2)](0)/[M](0)+k(OH)[·OH]/k(PH)[M](0), and X is the atrazine conversion, which correlates well with the experimental data. The kinetic analysis also showed that an indirect reaction of atrazine with an OH radical is dominant at low concentrations of H(2)O(2) and a direct reaction of atrazine with H(2)O(2) is dominant when the concentration of H(2)O(2) is more than 200 mg/L.     

Oxidation of dichlorvos with hydrogen peroxide using ferrous ion as catalyst.

This study examines how Fenton's reagent (Fe2+ and H2O2) decomposed dichlorvos insecticide. Results showed that dichlorvos decomposed in a two-stage reaction. The first stage is a Fe2+/H2O2 reaction in which dichlorvos swiftly decomposed. In the second stage, dichlorvos decomposed somewhat less rapidly, and it is a Fe3+/H2O2 reaction. The detection of ferrous ions also supports the theory of the two-stage reaction for the dichlorvos oxidation with Fenton's reagent. The dissolved oxygen of the solution decreased rapidly in the first stage reaction, but it slowly increased in the second stage with a zero-order kinetics. The Fenton system decomposed dichlorvos most rapidly when the initial pH in the solution is 3-4. In addition, increasing the concentration of hydrogen peroxide or ferrous ions can enhance the decomposition of dichlorvos. Consequently, the relationship of rate constant (kobs), [H2O2] and [Fe2+] at initial pH 3 is determined as kobs = 2.67 x 10(4)[H2O2]0.7[Fe2+]1.2.     

Photochemical degradation of diethyl phthalate with UV/H2O2

The decomposition of diethyl phthalate (DEP) in water using UV-H2O2 process was investigated in this paper. DEP cannot be effectively removed by UV radiation and H2O2 oxidation alone, while UV-H2O2 combination process proved to be effective and could degrade this compound completely. With initial concentration about 1.0mg/L, more than 98.6% of DEP can be removed at time of 60 min under intensity of UV radiation of 133.9 microW/cm2 and H2O2 dosage of 20mg/L. The effects of applied H2O2 dose, UV radiation intensity, water temperature and initial concentration of DEP on the degradation of DEP have been examined in this study. Degradation mechanisms of DEP with hydroxyl radicals oxidation also have been discussed. Removal rate of DEP was sensitive to the operational parameters. A simple kinetic model is proposed which confirms to pseudo-first order reaction. There is a linear relationship between rate constant k and UV intensity and H2O2 concentration.     

Decomposition of two haloacetic acids in water using UV radiation, ozone and advanced oxidation processes

The decomposition of two haloacetic acids (HAAs), dichloroacetic acid (DCAA) and trichloroacetic acid (TCAA), from water was studied by means of single oxidants: ozone, UV radiation; and by the advanced oxidation processes (AOPs) constituted by combinations of O(3)/UV radiation, H(2)O(2)/UV radiation, O(3)/H(2)O(2), O(3)/H(2)O(2)/UV radiation. The concentrations of HAAs were analyzed at specified time intervals to elucidate the decomposition of HAAs. Single O(3) or UV did not result in perceptible decomposition of HAAs within the applied reaction time. O(3)/UV showed to be more suitable for the decomposition of DCAA and TCAA in water among the six methods of oxidation. Decomposition of DCAA was easier than TCAA by AOPs. For O(3)/UV in the semi-continuous mode, the effective utilization rate of ozone for HAA decomposition decreased with ozone addition. The kinetics of HAAs decomposition by O(3)/UV and the influence of coexistent humic acids and HCO(3)(-) on the decomposition process were investigated. The decomposition of the HAAs by the O(3)/UV accorded with the pseudo-first-order mode under the constant initial dissolved O(3) concentration and fixed UV radiation. The pseudo-first-order rate constant for the decomposition of DCAA was more than four times that for TCAA. Humic acids can cause the H(2)O(2) accumulation and the decrease in rate constants of HAAs decomposition in the O(3)/UV process. The rate constants for the decomposition of DCAA and TCAA decreased by 41.1% and 23.8%, respectively, when humic acids were added at a concentration of 1.2mgTOC/L. The rate constants decreased by 43.5% and 25.9%, respectively, at an HCO(3)(-) concentration of 1.0mmol/L.     

Oxidative degradation of diethyl phthalate by photochemically-enhanced Fenton reaction

A kinetic investigation into the photo-degradation of aqueous diethyl phthalate by Fenton reagent was conducted in this study. The obtained results showed the enhancement of diethyl phthalate (DEP) decomposition by UV irradiation with the Fenton reaction. It was found that H2O2 concentration, Fe2+ concentration, and aqueous pH value were the three main factors that could significantly influence the degradation rates of DEP. The highest degradation percentage (75.8%) of DEP was observed within 120 min at pH 3 in the UV/H2O2/Fe2+ system, with original H2O2 and Fe2+ concentrations of 5.00 x 10(-4) and 1.67 x 10(-4)mol L(-1), respectively. The present study provides an effective approach to the treatment of wastewater containing DEP.     

Rate of dibutylsulfide decomposition by ozonation and the O3/H2O2 advanced oxidation process

A process of dibutylsulfide (DBS) oxidation using advanced methods of oxidation with ozone and hydrogen peroxide was studied. It was demonstrated that depending on pH value there are two mechanisms of DBS oxidation present: ionic and radical. The ionic mechanism predominates in acidic environment and the radical mechanism predominates in alkaline environment. At high pH ozone stability decreases and hydrogen peroxide has a deciding effect on DBS oxidation rate. At pH 9, and at high concentration of hydrogen peroxide (ranging from 0.1 to 1 mol/L), a clear increase in DBS decomposition rate was observed. That was caused by production of hydroperoxide radicals in reaction of hydrogen peroxide and ozone. In solutions pH value of which is close to 2, the rate of DBS oxidation by ozone alone is slower than in a O(3)/H(2)O(2) system, regardless the H(2)O(2) concentration. For higher H(2)O(2) concentrations (ranging from 0.1 to 1 mol/L), regardless the pH value of the solution, oxidation in a O(3)/H(2)O(2) system is faster, compared to a situation in which ozone is a sole oxidizer. For H(2)O(2) concentrations below 0.1 mol/L and when pH>2DBS oxidation in O(3)/H(2)O(2) system is slower compared to the situation in which ozone was the only oxidizer.     

Degradation of cyanobacteria toxin by advanced oxidation processes

Advanced oxidation processes (AOPs) using O(3), H(2)O(2), O(3)/H(2)O(2), O(3)/Fe(II), and Fenton treatment were investigated for the degradation of aqueous solutions of cyanobacteria. The effects of concentration of reactants, temperature, and pH on toxins degradation were monitored and the reaction kinetics was assessed. O(3) alone or combined with either H(2)O(2) or Fe(II) were efficient treatment for toxins elimination. A higher toxin oxidation tendency was observed with Fenton reaction; total toxins degradation (MC-LR and MC-RR) was achieved in only 60s. The ozonation treatment was successfully described by second-order kinetics model, with a first-order with respect to the concentration of either ozone or toxin. At 20 degrees C, with initial concentration of MC-LR of 1mg/L, the overall second-order reaction rate constant ranged from 6.79 x 10(4) to 3.49 x 10(3)M(-1)s(-1) as the solution pH increased from 2 to 11. The reaction kinetics of the other AOPs (O(3)/H(2)O(2), O(3)/Fe(II), and Fenton), were fitted to pseudo first-order kinetics. A rapid reaction was observed to took place at higher initial concentrations of O(3), H(2)O(2) and Fe(II), and higher temperatures. At pH 3, initial concentration of toxin of 1mg/L, the pseudo first-order rate constant, achieved by Fenton process, was in order of 8.76+/-0.7s(-1).     

Kinetics of decolorization of an azo dye in UV alone and UV/H(2)O(2) processes

The decolorization of C.I. Acid Red 27 (AR27), a monoazo anionic dye, was studied in the ultraviolet radiation (UV) alone and UV plus hydrogen peroxide (UV/H(2)O(2)) processes. The experimental results indicated that the kinetics of both oxidation processes fit well by pseudo-first order kinetics. The reaction rate was sensitive to the operational parameters and increased with increasing H(2)O(2) concentration and light intensity. The reaction orders of H(2)O(2) concentration and light intensity in both processes were obtained with linear regression method. A regression model was developed for pseudo-first order rate constant (k(ap,UV/H(2)O(2))) as a function of the Cconcentration and UV light intensity. (k(ap,UV/H(2)O(2)))=(2 x 10(-4)I(0.75)(0) + k(3)I(1.38)(0)[H(2)O(2)](n)(0))phi(AR27). As a result of two opposing effects of H(2)O(2) concentration at low and high concentrations, n has a value of 0.49 and -0.39 and k(3) has a value of 3 x 10(-4) and 0.1 for the regions of 0 mg l(-1) < [H(2)O(2)](0) < 650 mg l(-1) and 650 mg l(-1) < [H(2)O(2)](0) < 1500 mg l(-1)1, respectively. PhiAR27 is the initial dye concentration correlation index for developing of model for different initial concentrations of AR27. This rate expression can be used for predicting k(ap,UV/H(2)O(2) at different conditions in UV alone and UV/H2O2 processes. The results show that UV alone cannot be an efficient method for decolorization of AR27 in comparison with UV/H(2)O(2) process, therefore the first term of the model can be neglected.     

铜包裹碳化硅颗粒复合粉体的化学原位沉积制备与表征

以铜氨离子为铜源, 水合肼为还原剂, 在表面预氧化的SiC表面, 采用一步原位化学沉积法制备了均匀包裹Cu颗粒的SiC复合粉体. 采用扫描电子显微镜(SEM)、X射线衍射(XRD)、傅立叶红外光谱(FT-IR)、Zeta电位等测试表征手段研究了工艺条件对原位沉积反应的影响. 研究发现SiC表面预氧化形成的SiO2层能显著增强对铜氨离子吸附能力, 有助于原位还原生成单质Cu, 形成近乎连续包裹层. 控制反应体系中铜氨离子浓度和反应温度可以影响反应速率, 从而控制Cu颗粒的沉积速率和包裹效果. 对比研究表明, 在0.2 mol/L铜氨离子溶液中70℃反应, 在预氧化的SiC表面能够获得最佳包裹层.     

Non-isothermal kinetics of the dehydration reaction of 3-nitro-1,2,4-triazol-5-one rubidium and cesium complexes

3-Nitro-1,2,4-triazol-5-one (NTO) rubidium and cesium complexes were synthesized by mixing the aqueous solution of NTO and their respective metal carbonates. Their thermal decomposition and the non-isothermal kinetics of the dehydration reaction were studied under the non-isothermal condition by DSC and TG-DTG methods. The kinetic parameters were obtained from analysis of the DSC and TG-DTG curves by Kissinger method, Ozawa method, the differential method and the integral method. The most probable mechanism functions for the dehydration reaction of the title complexes were suggested by comparing the kinetic parameters. The dehydration decomposition reaction of RbNTO.H2O and CsNTO.H2O appears to be the same as Avrami-Erofeev equation: f(alpha) = (5/2)(1-alpha)[-ln(1-alpha)](3/5), G(alpha)=[-ln(1-alpha)](2/5), n = 2/5. The critical temperature of thermal explosion is 240.88 degrees C for RbNTO.H2O and 246.27 degrees C for CsNTO.H2O.     

Optimized photocatalytic degradation of Alcian Blue 8 GX in the presence of TiO2 suspensions

The photocatalytic degradation of Alcian Blue 8 GX, a cationic copper phthalocyanine dye, has been investigated in aqueous suspensions containing the commercial catalyst TiO(2) P-25. The photodegradation of the organic molecule follows approximately a pseudo-first kinetic order, according to the Langmuir-Hinshelwood model. The effect of catalyst concentration, pH of the initial solution and the H(2)O(2) concentration upon the reaction rate was ascertained. It was shown that the photocatalytic degradation reaction can be mathematically described as a function of parameters such as pH, H(2)O(2) concentration and irradiation time, being modeled by the use of the response surface methodology. Optimized values for oxidizing agent, concentration, pH and UV exposure time for the studied system were determined.     

Novel active heterogeneous Fenton system based on Fe3-xMxO4 (Fe, Co, Mn, Ni): the role of M2+ species on the reactivity towards H2O2 reactions

In this work, the effect of incorporation of M2+ species, i.e. Co2+, Mn2+ and Ni2+, into the magnetite structure to increase the reactivity towards H2O2 reactions was investigated. The following magnetites Fe3-xMnxO4, Fe3-xCoxO4 and Fe3-xNixO4 and the iron oxides Fe3O4, gamma-Fe2O3 and alpha-Fe2O3 were prepared and characterized by M?ssbauer spectroscopy, XRD, BET surface area, magnetization and chemical analyses. The obtained results showed that the M2+ species at the octahedral site in the magnetite strongly affects the reactivity towards H2O2, i.e. (i) the peroxide decomposition to O2 and (ii) the oxidation of organic molecules, such as the dye methylene blue and chlorobenzene in aqueous medium. Experiments with maghemite, gamma-Fe2O3 and hematite, alpha-Fe2O3, showed very low activities compared to Fe3O4, suggesting that the presence of Fe2+ in the oxide plays an important role for the activation of H2O2. The presence of Co or Mn in the magnetite structure produced a remarkable increase in the reactivity, whereas Ni inhibited the H2O2 reactions. The obtained results suggest a surface initiated reaction involving Msurf2+ (Fe, Co or Mn), producing HO radicals, which can lead to two competitive reactions, i.e. the decomposition of H2O2 or the oxidation of organics present in the aqueous medium. The unique effect of Co and Mn is discussed in terms of the thermodynamically favorable Cosurf3+ and Mnsurf3+ reduction by Femagnetite2+ regenerating the active species M2+.     

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.     

Nafion-coating of the electrodes improves the flow-stability of the Ag/SiO2/Ag2O electroosmotic pump

When a current or a voltage is applied across the ceramic membrane of the nongassing Ag/Ag(2)O-SiO(2)-Ag/Ag(2)O pump, protons produced in the anodic reaction 2Ag(s) + H(2)O → Ag(2)O(s) + 2H(+) + 2e(-) are driven to the cathode, where they are consumed by the reaction Ag(2)O(s) + H(2)O + 2e(-) → 2Ag(s) + 2 OH(-). The flow of water is induced by momentum transfer from the electric field-driven proton-sheet at the surface of the ceramic membrane. About 10(4) water molecules flowed per reacted electron. Because dissolved ions decrease the field at the membrane surface, the flow decreases upon increasing the ionic strength. For this reason Ag(+) ions introduced through the anodic reaction and by dissolution of Ag(2)O decrease the flow. Their accumulation is reduced by applying Nafion-films to the electrodes. The 20 μL min(-1) flow rate of 6 mm i.d. pumps with Nafion coated electrodes operate daily for 5 min at 1 V for 1 month, for 70 h when the pump is pulsed for 30 s every 30 min, and for 2 h when operating continuously.     

Photodegradation of 17beta-estradiol in water by UV-vis/Fe(III)/H2O2 system

Photodegradation of 17beta-estradiol (E2) in aqueous solutions by UV-vis/Fe(III)/H(2)O(2) system, namely Photo-Fenton system, was preliminarily investigated under a 250 W metal halide lamp (lambda > or = 313 nm). The influences of initial pH value, initial concentration of H(2)O(2) and E2 on photodegradation efficiency of E2 were discussed and the amount of CO(2) produced by the photodegradation reaction was measured. The results indicates that E2 could be decomposed efficiently in UV-vis/Fe(III)/H(2)O(2) system. Under the condition of 10.0 micromol L(-1) Fe(III), 1000 micromol L(-1) H(2)O(2) and pH 3.0, the degradation efficiency of 18.4 micromol L(-1) E2 reach 75.2% after the irradiation of 160 min. Over the range of pH 3.0-6.0, the higher acidity, the higher the degradation efficiency of E2 and initial reaction rate are. The degradation efficiency of E2 increases with increasing of initial concentration of H(2)O(2) and with decreasing of initial concentration of E2. The E2 mineralization efficiency increases with reaction time but the mineralization efficiency was lower. When the initial concentration of Fe(III) and H(2)O(2) were 10.0 and 1000 micromol L(-1), respectively, the mineralization efficiency of 18.4 micromol L(-1) E2 solution with pH 3.0 was only 21.6% after 160 min irradiation. It is suggested that the mineralization occurred probably only at aromatic ring.     

Effect of content of Mg(NO3)2 x 6H2O on fabrication of alpha-alumina nanopowders by thermal decomposition of ammonium aluminum carbonate (AACH)

An alpha-Al2O3 and MgAl2O3 spinel phase doped alpha-Al2O3 nanopowders were fabricated by the thermal decomposition and synthetic of ammonium aluminum carbonate hydroxide (AACH). Crystallite size of 5 to 8 nm were fabricated when reaction temperature of AACH was low, 8 degrees C, and the highest [NH4+][AlO(OH)2-][HCO3] ionic concentration of pH 10 from the ammonium hydrogen carbonate (AHC) aqueous solution. The phase transformation of amorphous-s, theta-, alpha-Al2O3, MgAl2O3 spinel phases was examined at each temperature according to the amount of Mg(NO3)2 x 6H2O and AACH. A time-temperature-transformation (TTT) diagram for thermal decomposition in air was determined. Homogeneous, spherical alpha-Al2O3 nanopowders with a particle size of 60 nm were obtained by firing the crystallites, which had been synthesized from AACH at pH 10 and 8 degrees C, at 1050 degrees C for 6 h in air.     

Photochemical mineralization of di-n-butyl phthalate with H2O2/Fe3+

This study evaluated the performance of photo-Fenton reaction initiated by the UV irradiation with H(2)O(2)/Fe(3+), denoted as UV/H(2)O(2)/Fe(3+), to decompose di-n-butyl phthalate (DBP) in the aqueous solution. The concentration of total organic carbon (TOC) was chosen as a mineralization index of the decomposition of DBP by the UV/H(2)O(2)/Fe(3+) process. A second-order kinetic model with respect to TOC was adequately adopted to represent the mineralization of DBP by the UV/H(2)O(2)/Fe(3+) process. The experimental results of this study suggested that the dosages with 4.74 x 10(-5) mol min(-1)L(-1) H(2)O(2) and initial Fe(3+) loading concentration of 4.50 x 10(-4) mol L(-1) in the solution at pH 3.0 with 120 microW cm(-2) UV (312 nm) provided the optimal operation conditions for the mineralization of DBP (5 mg L(-1)) yielding a 92.4% mineralization efficiency at 90 min reaction time.     

Monitoring the speciation of aqueous free chlorine from pH 1 to 12 with Raman spectroscopy to determine the identity of the potent low-pH oxidant

The speciation of aqueous free chlorine above pH 5 is a well-understood equilibrium of H2O + HOCl <==> OCl- + H3O+ with a pKa of 7.5. However, the identity of another very potent oxidant present at low pH (below 5) has been attributed by some researchers to Cl2(aq) and by others to H2OCl+. We have conducted a series of experiments designed to ascertain which of these two species is correct. First, using Raman spectroscopy, we found that an equilibrium of H2O + H2OCl+ <==> HOCl + H3O+ is unlikely because the "apparent pKa" increases monotonically from 1.25 to 2.11 as the analytical concentration is increased from 6.6 to 26.2 mM. Second, we found that significantly reducing the chloride ion concentration changed the Raman spectrum and also dramatically reduced the oxidation potency of the low-pH solution (as compared to solutions at the same pH that contained equimolar concentrations of Cl- and HOCl). The chloride ion concentration was not expected to impact an equilibrium of H2O + H2OCl+ <==> HOCl + H3O+, if it existed. These observations supported the following equilibrium as pH is decreased: Cl2(aq) + 2H2O <==> HOCl + Cl- + H3O+. The concentration-based equilibrium constant was estimated to be approximately 2.56 x 10(-4) M2 in solutions whose ionic strengths were approximately 0.01 M. The oxidative potency of the species in low pH solutions was investigated by monitoring the oxidation of secondary alcohols to ketones. These and other results reported here argue strongly that Cl2(aq) is the correct form of the potent low-pH oxidant in aqueous free-chlorine solutions.     

A kinetic study on the degradation of p-nitroaniline by Fenton oxidation process

A detailed kinetic model was developed for the degradation of p-nitroaniline (PNA) by Fenton oxidation. Batch experiments were carried out to investigate the role of pH, hydrogen peroxide and Fe(2+) levels, PNA concentration and the temperature. The kinetic rate constants, k(ap), for PNA degradation at different reaction conditions were determined. The test results show that the decomposition of PNA proceeded rapidly only at pH value of 3.0. Increasing the dosage of H(2)O(2) and Fe(2+) enhanced the k(ap) of PNA degradation. However, higher levels of H(2)O(2) also inhibited the reaction kinetics. The k(ap) of PNA degradation decreased with the increase of initial PNA concentration, but increased with the increase of temperature. Based on the rate constants obtained at different temperatures, the empirical Arrhenius expression of PNA degradation was derived. The derived activation energy for PNA degradation by Fenton oxidation is 53.96 kJ mol(-1).