The influence of pH and cadmium sulfide on the photocatalytic degradation of 2-chlorophenol in titanium dioxide suspensions

The influence of pH and cadmium sulfide on the photocatalytic degradation of 2-chlorophenol (2-CP) in titanium dioxide suspensions was investigated to evaluate the feasibility of mixed semiconductors on the photodegradation of chlorinated organics in aqueous solution. Apparent first-order rate constants (k(obs)) and initial rate constants were used to evaluate the degradation efficiency of 2-CP. Higher degradation efficiency of 2-CP was observed at higher pH values. The apparent pseudo-first-order rate constant was 0.036 min(-1) at pH 12.5 in TiO2/UV system, while a 2- to 9-fold decrease in k(obs) was observed over the pH range of 2.5-9.5. The addition of phosphate buffer solutions at different pH values have different effects on the degradation of 2-CP. H2PO4- has little effect on the photodegradation of 2-CP, while HPO4(2-) could inhibit the photodegradation efficiency of 2-CP. Chlorocatechol, hydroquinone, benzoquinone and phenol were identified as the predominant aromatic intermediates for the photocatalytic degradation of 2-CP. Moreover, less aromatic intermediates at higher pH were observed. Direct oxidation contributed significantly to the photodegradation of 2-CP. An addition of a semiconductor decreased the initial and apparent first-order rate constants of 2-CP. The cutoff of wavelength of 320nm could diminish the contribution of direct photolysis of 2-CP. The combination of cadmium sulfide and titanium dioxide can lead to an enhanced rate of disappearance of 2-CP compared to those in single semiconductor system. A 1.2 to 2.5-fold increase in rate constant in coupled semiconductor system relative to the single semiconductor system was obtained.     

Destruction of cresols by Fenton oxidation process

The present study was used to probe the treatment of simulated wastewater containing cresols by Fenton process. Experiments were conducted in a batch reactor to examine the effects of operating variables like pH, hydrogen peroxide concentration (H(2)O(2)) and ferrous ion concentration (Fe(2+)) on chemical oxygen demand (COD) removal. The progress of the degradation reaction was monitored by the decrease in COD content in the treated solution. The optimal reacting conditions were experimentally determined and it was found to be [H(2)O(2)]=31.64 mM, [Fe(2+)]=0.90 mM for o- and p-cresol while 0.72 mM for m-cresol at pH=3.0+/-0.2. The degradation efficiency for cresol isomers was as high as 82% within 120 min at optimum conditions. A pseudo-first-order kinetic model was adopted to represent the Fenton oxidation for cresols. The mineralization rate for cresols obeys the following sequence: m->p->o-. Maximum degradation occurred at 30 degrees C for the temperature range of 20-50 degrees C studied. The global activation energy for the first-order reaction was estimated to be in the range of 12.90-16.25 kJ/mol. Air/nitrogen did not play an active role in completely mineralizing the organic intermediates at the experimental conditions adopted. Irrespective of the position of methyl group in o-, m- or p-position, the maximum dissolved organic carbon (DOC) removal efficiency was 42%. Only 2/5th of cresol was mineralized to CO(2) by Fenton process. The results showed that the cresols were completely oxidized and degraded into lower molecular weight aliphatic acids. Among the acids, acetic and oxalic acids were identified as the major products formed during the degradation.     

pH effect on OH radical production in photo/ferrioxalate system

In wastewater treatment using the Fenton and photofenton processes, pH is one of the critical operating parameters, due to the fact that the Fenton reaction can work only under acidic pH conditions. It is hoped that Ferric iron complexed with oxalate (Fe(III)-oxalate; ferrioxalate) will provide an alternative to the traditional Fenton process with its limited range of pH conditions, since its high solubility in aqueous media can broaden the available pH range of the Fenton reaction up to the near neutral pH regime. In this study, we investigated the pH dependency of OH production in the photo/ferrioxalate system, in the presence and absence of externally supplied H(2)O(2), where 2,4--D was used as the probe compound for OH production at a wide range of pH values (1.2--7.4). In the absence of externally supplied H(2)O(2), the 2,4--D degradation was considerably enhanced with increasing pH, whereas it was reduced with increasing pH in the presence of an excess amount of H(2)O(2). These variations in the degradation of 2,4--D were thus found to be precisely related to the formation of H(2)O(2), a factor to which little attention was paid in previous studies. In the absence of H(2)O(2) addition, the in situ formation of H(2)O(2) is facilitated with increasing pH by the reaction of Fe(II) with O(2)(-), which increases with pH, augmenting the production of OH and thereby leading to the faster degradation of 2,4--D. This same reaction can also provide an explanation for the opposite pH dependence of 2,4--D degradation in the presence of H(2)O(2).     

Dual roles of CO2*- for degrading synthetic organic chemicals in the photo/ferrioxalate system

In this study, the relative importance of the dual reaction pathways of CO2*- in the photo/ferrioxalate system, where it acts both as a reductant for reducing the ferric ion and as an agent for the formation of H(2)O(2), was investigated as a function of the concentrations of ferrioxalate and oxygen. We studied the two competitive reactions of CO2*- in the photo/ferrioxalate system, which depend on the relative concentrations of ferrioxalate to oxygen, with the degradation of 2,4-dichlorophenoxyacetic acid (2,4-D), which was used as a target pollutant. At high concentrations of ferrioxalate, almost all of the CO2*- reacted with ferrioxalate to reduce Fe(III) to Fe(II), whereas at low concentrations of ferrioxalate, a majority of the CO2*- contributed to the formation of H(2)O(2), as a result of its reaction with oxygen, which allows the Fenton reaction to occur without any external supply of H(2)O(2).     

Oxidative decomposition of atrazine by a Fenton-like reaction in a H2O2/ferrihydrite system

The oxidation of atrazine (ATZ) was studied in the presence of hydrogen peroxide (H(2)O(2)) and ferrihydrite at different concentrations and pHs. The rate of ATZ oxidation increased with H(2)O(2) concentration and is independent of pH ranging from 4 to 8. However, at pH 3 an increase of ten times in the rate of ATZ oxidation was observed due to the mineral dissolution. The decomposition rate of H(2)O(2) was three times higher at pH 8 than 3 and increased with increase of both H(2)O(2) and ferrihydrite concentrations. The results indicate that ferrihydrite controls oxidation of ATZ by H(2)O(2) in two different ways: (i) mineral dissolution at low pH allowing the Fenton reaction to proceed in solution and (ii) surface-mediated decomposition of H(2)O(2) producing non-reactive oxygen species in particular at higher pH. Three degradation products (desethylatrazine, desisopropylatrazine, and 2-hydroxyatrazine) were identified and corroborate with a Fenton reaction taking place in solution.     

Fenton试剂降解PAM催化剂的研究

采用Fenton试剂氧化降解含油废水中的聚丙烯酰胺,研究了H2O2用量、催化剂种类及用量对降解聚丙烯酰胺效果的影响。结果表明,H2O2用量为聚丙烯酰胺的20%为宜;CuCl2具有和FeSO4、Fe(NO3)3、FeCl3相近的催化效果,并且可以作为一种在较高pH值条件下应用的催化剂;在优选条件下该氧化体系可以使聚丙烯酰胺黏度大大降低。     

铁掺杂类石墨相氮化碳类芬顿/光催化氧化作用机制

采用热聚合法制备并优化了不同铁掺杂比的铁掺杂类石墨相氮化碳(Fe-g-C₃N₄)类芬顿光催化剂,铁元素可完全掺杂进入类石墨相氮化碳(g-C₃N₄)结构中并组成Fe—N配位键,最佳的Fe掺杂比为10%(质量分数)。Fe-g-C₃N₄类芬顿/光催化氧化对罗丹明B的降解速率和降解率均远高于g-C₃N₄的,反应10 min时降解率已达到87. 9%,反应过程中起主要作用的活性基团为羟基自由基,超氧自由基和空穴电子也有一定作用。在pH值为3～9范围内,Fe-g-C₃N₄类芬顿/光催化氧化对罗丹明B的降解率均高于90%,大幅度拓宽了适用范围; H₂O₂的投加量会显著影响Fe-g-C₃N₄类芬顿/光催化氧化的降解效能,H₂O₂最佳投量范围为1. 0～1....     

Solar photocatalytic degradation of reactive blue 4 using a Fresnel lens

The heterogeneous photocatalytic degradation of reactive blue 4 dye (RB4) solutions under Fenton reagent and TiO(2) assisted by concentrated solar light irradiation using a Fresnel lens has been studied. Multivariate experimental design was applied to study the kinetic process. The efficiency of photocatalytic degradation was determined from the analysis of color and total organic carbon (TOC) removal. Factorial experimental design allowed to determine the influence of four parameters (pH and initial concentrations of TiO(2), Fe(II) and H(2)O(2)) on the value of the decoloration kinetic rate constant. Experimental data were fitted using neural networks (NNs). The mathematical model reproduces experimental data within 86% of confidence and allows the simulation of the process for any value of parameters in the experimental range studied. Also, a measure of the saliency of the input variables was made based upon the connection weights of the neural networks, allowing the analysis of the relative relevance of each variable with respect to the others. Results showed that acidic pHs (pH=3.6) are preferred for the complete dye decoloration. The optimum catalyst concentration is 1.2g TiO(2)/l. The use of a low cost catalyst and its activation using a Fresnel lens to concentrate solar energy significantly accelerates the degradation process when compared with direct solar radiation alone and can offer an economical and practical alternative for the destruction of environmental organic compounds.     

Comparison of different advanced oxidation processes for phenol degradation

Advanced Oxidation Processes (O3, O3/H2O2, UV, UV/O3, UV/H2O2, O3/UV/H2O2, Fe2+ /H2O2 and photocatalysis) for degradation of phenol in aqueous solution have been studied in earlier works. In this paper, a comparison of these techniques is undertaken: pH influence, kinetic constants, stoichiometric coefficient and optimum oxidant/pollutant ratio. Of the tested processes, Fenton reagent was found to the fastest one for phenol degradation. However, lower costs were obtained with ozonation. In the ozone combinations, the best results were achieved with single ozonation. As for the UV processes, UV/H2O2 showed the highest degradation rate.     

高级氧化+SBR工艺处理聚乙二醇废水试验研究

研究了高级氧化+SBR组合工艺处理高浓度聚乙二醇(PEG)废水的效果及其影响因素。结果表明,采用芬顿试剂作为高级氧化剂,当FeSO4.7H2O投加量为800 mg/L,H2O2投加量为30 mL/L,反应时间为3.5 h时,CODCr去除率可达到50.5%;生化处理阶段所需采用两级SBR工艺,污泥浓度均为4 000 mg/L,一、二级厌氧及好氧反应时间分别为12和10 h;芬顿试剂氧化和厌氧处理对提高PEG废水的可生化性有明显效果;该组合工艺的出水水质可以达到《污水综合排放标准》(GB 8978—1996)中的二级排放标准。     

Degradation of 2,4-dichlorophenol by immobilized iron catalysts

The degradation of 2,4-Dichlorophenol (from now on 2,4-DCP) has been carried out on Nafion-Fe (1.78%) in the presence of H2O2 under visible light irradiation. A solution containing 2,4-DCP (TOC 72 mg C/L)) is seen to be mineralized in approximately 1 h in the presence of H2O2 (10 mM) under solar simulated visible light (80 mW cm-2) at pH values between 2.8 and 11. Homogeneous photo-assisted Fenton reactions were capable of mediating 2,4-DCP degradation only up to pH 5.4. The degradation kinetics of 2,4-DCP on Nafion-Fe membranes was more favorable than the one observed during Fenton photo-assisted processes at pH 2.8. The degradation of 2,4-DCP was investigated as a function of the substrate, oxidant concentration and applied light intensity. The Nafion-Fe was seen to be effective over many cycles during the photo-catalytic degradation of 2,4-DCP showing an efficient and stable performance during 2,4-DCP degradation without leaching out Fe(3+)-ions into the solution. Evidence is presented that the degradation at the surface of the Nafion-Fe membrane seems to be controlled by mass transfer and not by chemical reaction of the species in solution. The approach used to degrade 2,4-DCP is shown to be valid for other chloro-carbons like 4-chlorophenol, 2,3-chlorophenol and 2,4,5-trichlorophenol.     

Oxidation of p,p'-DDT and p,p'-DDE in highly and long-term contaminated soil using Fenton reaction in a slurry system

The degradation of DDT [1,1-bis(4-chlorophenyl)-2,2,2-trichloroethane] and DDE [2,2-bis(4-chlorophenyl)-1,1-dichloroethylene] in highly and long-term contaminated soil using Fenton reaction in a slurry system is studied in this work. The influence of the amount of soluble iron added to the slurry versus the mineral iron originally present in the soil, and the influence of H(2)O(2) concentration on the degradation process are evaluated. The main iron mineral species encountered in the soil, hematite (Fe(2)O(3)), did not show catalytic activity in the decomposition of H(2)O(2), resulting in low degradation of DDT (24%) and DDE (4%) after 6 h. The addition of soluble iron (3.0 mmol L(-1)) improves the reaction reaching 53% degradation of DDT and 46% of DDE. The increase in iron concentration from 3.0 to 24 mmol L(-1) improves slightly the degradation rate of the contaminants. However, similar degradation percentages were obtained after 24 h of reaction. It was observed that low concentrations of H(2)O(2) were sufficient to degrade around 50% of the DDT and DDE present in the soil, while higher degradation percentages were achieved only with high amounts of this reagent (1.1 mol L(-1)).     

Anodic Fenton process assisted by a microbial fuel cell for enhanced degradation of organic pollutants

The electro-Fenton process is efficient for degradation of organic pollutants, but it suffers from the high operating costs due to the need of power investment. Here, a new anodic Fenton system is developed for energy-saving and efficient treatment of organic pollutants by incorporating microbial fuel cell (MFC) into an anodic Fenton process. This system is composed of an anodic Fenton reactor and a two-chamber air-cathode MFC. The power generated from a two-chamber MFC is used to drive the anodic Fenton process for Acid Orange 7 (AO7) degradation through accelerating in situ generation of Fe²⁺ from sacrificial iron. The kinetic results show that the MFC-assisted anodic Fenton process system had a significantly higher pseudo-first-order rate constant than those for the chemical Fenton methods. The electrochemical analysis reveals that AO7 did not hinder the corrosion of iron. The anodic Fenton process was influenced by the MFC performance. It was also found that increasing dissolved oxygen in the cathode improved the MFC power density, which in turn enhanced the AO7 degradation rate. These clearly demonstrate that the anodic Fenton process could be integrated with MFC to develop a self-sustained system for cost-effective and energy-saving electrochemical wastewater treatment.     

Effect of inorganic, synthetic and naturally occurring chelating agents on Fe(II) mediated advanced oxidation of chlorophenols

This study examines the feasibility and application of Advanced Oxidation Technologies (AOTs) for the treatment of chlorophenols that are included in US EPA priority pollutant list. A novel class of sulfate/hydroxyl radical-based homogeneous AOTs (Fe(II)/PS, Fe(II)/PMS, Fe(II)/H₂O₂) was successfully tested for the degradation of series of chlorophenols (4-CP, 2,4-CP, 2,4,6-CP, 2,3,4,5-CP). The major objective of the present study was to evaluate the effectiveness of three representative chelating agents (citrate, ethylenediaminedisuccinate (EDDS), and pyrophosphate) on Fe(II)-mediated activation of three common peroxide (peroxymonosulfate (PMS), persulfate (PS), and hydrogen peroxide (H₂O₂)) at neutral pH conditions. Short term (4 h) and long term (7 days) experiments were conducted to evaluate the kinetics and longevity of different oxidative systems for 4-chlorophenol degradation. Results showed that each of the iron-chelating agent couple was superior in activating a particular oxidant and consequently for 4-CP degradation. In case of Fe(II)/PMS system, the inorganic chelating agent pyrophosphate showed effective activation of PMS whereas very fast dissociation of PMS was recorded in the case of EDDS without any apparent 4-CP degradation. In Fe(II)/H₂O₂ system, EDDS was proven to be the most effective whereas pyrophosphate showed negligible activation of H₂O₂. Fe(II)/Citrate system showed moderate activation of all three oxidants. PMS was found to be the most universal oxidant, which was activated by all three iron-chelating agent systems and Fe(II)/Citrate was the most universal chelating agent system, which was able to activate all three oxidants to a certain extent.     

Sonolytic degradation of methyl tert-butyl ether: the role of coupled Fenton process and persulphate ion

The sonolytic degradation of methyl tert-butyl ether (MTBE) has been investigated at ultrasonic frequency of 20 kHz. The observed pseudo-first-order rate constant decreased from 1.25 x 10(-4) to 5.32 x 10(-5) s(-1) as the concentration of MTBE increased from 2.84 x 10(-2) to 2.84 x 10(-1) mM. The rate of degradation of MTBE increased with the increase of the power density of ultrasonicator and also with the rise in reactor system temperature. In the presence of oxidising agent, potassium persulphate, the sonolytic rate of degradation of MTBE was accelerated substantially. Tert-butyl formate (TBF) and acetone were found to be the major intermediates of the degradation of MTBE. It is found that the ultrasound/Fe2+/H2O2 method is promising process for the degradation of MTBE. More than 95% degradation of MTBE (2.84 x 10(-2) mM) along with its intermediate products has been achieved during the coupled ultrasound/Fe2+/ H2O2 method. Hence, the coupled ultrasound/Fe2+/H2O2 may be a viable method for the degradation MTBE within a short period of time than the ultrasound irradiation process only. A kinetic model, based on the initial rates of degradation of MTBE and TBF, provides a good agreement with the experimental results.     

Kinetics and mechanisms of DMSO (dimethylsulfoxide) degradation by UV/H(2)O(2) process

The objective of this study was to elucidate the degradation pathways of dimethylsulfoxide (DMSO) during its mineralization caused by UV/H(2)O(2) treatment. In order to accomplish this, we measured the concentration time-profiles of DMSO and its degradation intermediates during the UV/H(2)O(2) treatment. In addition, we proposed a kinetic model that could account for the degradation pathways of DMSO during its UV/H(2)O(2) treatment. The results show that the degradation of DMSO by the UV/H(2)O(2) treatment can be classified into two major pathways, and this is supported by both the analysis of the intermediates and total organic carbon (TOC) measurements. Firstly, DMSO was degraded into sulfate (SO(4)(2-)) through the formation of methansulfinate (CH(3)SO(2)(-)) and methansulfonate (CH(3)SO(3)(-)) as sulfur-containing intermediates. One of the two carbon constituents of DMSO was highly resistant to mineralization, due to the formation of methansulfonate, which reacted very slowly with (.-)OH k = 0.8 x 10(7) M(-1)s(-1)). Secondly, the other carbon constituent of DMSO was relatively easily mineralized through the formation of formaldehyde (HCHO) and formate (HCO(2)(-)) as non-sulfur-containing intermediates. The kinetic model proposed in this study for the degradation of DMSO by (.-)OH in the UV/H(2)O(2) process was able to successfully predict the patterns of concentration time-profiles of all components during the UV/H(2)O(2) treatment of DMSO.     

Degradation of industrial waste waters on Fe/C-fabrics. Optimization of the solution parameters during reactor operation

This study addresses the pre-treatment of toxic and recalcitrant compounds found in the waste waters arriving at a treating station for industrial effluents containing chlorinated aromatics and non-aromatic compounds, anilines, phenols, methyl-tert-butyl-ether (MTBE). By reducing the total organic carbon (TOC) of these waste waters the hydraulic load for the further bacterial processing in the secondary biological treatment is decreased. The TOC decrease and discoloration of the waste waters was observed only under light irradiation in the reactor by immobilized Fenton processes on Fe/C-fabrics but not in the dark. The energy of activation for the degradation of the waste waters was of 4.2 kcal/mol. The degradation of the waste waters was studied in the reactor as a function of (a) the amount of oxidant used (H2O2), (b) the recirculation rate, (c) the solution pH and (d) the applied temperature. With these parameters taken as input factors, statistical modeling allows one to estimate the most economic use of the oxidant and electrical energy to degrade these waste waters. The concentration of the most abundant organic pollutants during waste waters degradation was followed by gas chromatography/mass spectrometry (GC-MS). The ratio of the biological oxygen demand to the total organic carbon BOD5/TOC increased significantly due to the Fe/C-fabric catalyzed treatment from an initial value of 2.03 to 2.71 (2 h). The reactor results show that the recirculation rate has no influence on the TOC decrease of the treated waters but affects the BOD increase of these solutions.     

Kinetic modeling of electro-Fenton reaction in aqueous solution

To well describe the electro-Fenton (E-Fenton) reaction in aqueous solution, a new kinetic model was established according to the generally accepted mechanism of E-Fenton reaction. The model has special consideration on the rates of hydrogen peroxide (H(2)O(2)) generation and consumption in the reaction solution. The model also embraces three key operating factors affecting the organic degradation in the E-Fenton reaction, including current density, dissolved oxygen concentration and initial ferrous ion concentration. This analytical model was then validated by the experiments of phenol degradation in aqueous solution. The experiments demonstrated that the H(2)O(2) gradually built up with time and eventually approached its maximum value in the reaction solution. The experiments also showed that phenol was degraded at a slow rate at the early stage of the reaction, a faster rate during the middle stage, and a slow rate again at the final stage. It was confirmed in all experiments that the curves of phenol degradation (concentration vs. time) appeared to be an inverted "S" shape. The experimental data were fitted using both the normal first-order model and our new model, respectively. The goodness of fittings demonstrated that the new model could better fit the experimental data than the first-order model appreciably, which indicates that this analytical model can better describe the kinetics of the E-Fenton reaction mathematically and also chemically.     

Application of the photo-Fenton process to the treatment of wastewaters contaminated with diesel

The application of the photo-Fenton process for the treatment of wastewaters contaminated with diesel oil was investigated. This particular process has been widely studied for the photochemical degradation of highly toxic organic pollutants. Experiments were performed according to a factorial experimental design at two levels and two variables: H(2)O(2) concentration (5-200 mM) and Fe(2+) concentration (0.01-1 mM). Experimental results demonstrated that the photo-Fenton process is technically feasible for the treatment of wastewaters containing diesel oil constituents, with total mineralization. A combination of factorial experimental design and gradient descent techniques was employed to optimize the amount of the Fenton reagents, resulting in Fe(2+) (0.1 mM) and H(2)O(2) (50 mM). These optimized levels did not exceed the limit for disposal of ferrous ions (0.27 mM) proposed at the local environmental legislation.     

Degradation of estrone in aqueous solution by photo-Fenton system

Photodegradation of estrone (E1) in aqueous solutions by UV-VIS/Fe(III)/H2O2 system (photo-Fenton system) was preliminarily investigated under a 250-W metal halide lamp (lambda > or = 313 nm). The influences such as initial pH value, initial concentration of Fe(III), H2O2 and E1 on degradation efficiency of E1 were discussed in detail. The results indicated that E1 could be decomposed efficiently in UV-VIS/Fe(III)/H2O2 system. After 160-min irradiation, the photodegradation efficiency of 18.5 micromol L(-1) E1 reached 98.4% in the solution containing 20.8 micromol L(-1) Fe(III), and 1664 micromol L(-1) H2O2 at initial pH value 3.0. The degradation efficiencies of E1 were dependent on initial pH value, Fe (III) concentration and H2O2 concentration. The degradation of four estrogens estrone (E1), estradiol (E2), 17alpha-ethynylestradiol (EE2) and diethylstibestrol (DES) in UV-VIS/Fe(III)/H2O2 system were also conducted. Under the conditions of pH 3.0, the E1 apparent kinetics equation -dC(E1)/dt=0.00093[H2O2]0.47[Fe(III)]0.63[E1]0.24 (r=0.9935, n=11) was obtained. The E1 mineralization efficiency was lower than degradation efficiency under the same conditions, which implied the mineralization occurred probably only at aromatic ring. There are several intermediate products produced during the course of E1 degradation. The comparison of the degradation efficiencies of E1, E2, EE2 and DES degradation in UV-VIS/Fe(III)/H2O2 system were also conducted, and the relative degradability among different estrogens were followed the sequence: DES>E2>EE2>E1.