Effect of ferric ion added on photodegradation of alachlor in the presence of TiO2 and UV radiation

The effect of in situ photodeposited ferric ion onto TiO2 surface on the degradation of alachlor was investigated in the presence of the UV radiation. The photodegradation rate of alachlor could be described as an apparent first order. The rate constant (K(a)) of alachlor increased from 0.021 to 0.060 h(-1) as the number of coating times increased from 1- to 5-times in the absence of ferric ion, where the corresponding thicknesses of the TiO2 film were 67 and 174 nm. The rate constant (K(a)) increased from 0.030 to 0.060 h(-1) as pH value decreasd from pH 9 to 5 in the presence of only TiO2 immobilised with 5-times of coating. The rate constant increased slightly from 0.031 to 0.050 h(-1) as the concentration of ferric ion increased from 0.75 to 7.5 mg Fe3+ l(-1) in the absence of TiO2. However, those increased from 0.051 to 0.110 h(-1) in the presence of both TiO2 and ferric ion. In situ photodeposition of ferric ion onto the TiO2 surface enhanced the rate constant of photodegradation of alachlor by about 80% with an adding 7.5 mgFe3+ l(-1). During the alachlor photodegradation, three kinds of non-toxic organic compounds derived from alachlor were detected in 1 h.     

Surface modification of TiO2 by a ruthenium(II) polypyridyl complex via silyl-linkage for the sensitized photocatalytic degradation of carbon tetrachloride by visible irradiation

A new ruthenium(II) photosensitizer, [Ru(II)(py-pzH)(3)](2+) (where py-pzH=3-(2'-pyridyl)pyrazole), has been synthesized. The complex displayed outstanding excited state redox properties (estimated Ru(III)/Ru(II)* approximately -1.24 V vs. NHE) and was expected to sensitize the injection of electrons into the conduction band of anatase TiO(2) upon visible irradiation. The photosensitizer was anchored onto the surface of anatase TiO(2) particles via in situ silylation. The silyl-linkage displayed excellent stability in both aqueous media, over a wide pH range, and in common organic solvents. The resultant material, TiO(2)-[Ru(II)(py-pz-Si identical with )(3)], was found to be able to mediate degradation of CCl(4) in neutral aqueous medium under broad band visible irradiation (lambda>450 nm). The relation between the rate of degradation and concentration of substrate was explored and the mechanism of the photodegradation of the perhalogenated organic was discussed.     

Electrochemical regeneration of Fe2+ in Fenton oxidation processes

This study is to establish optimal conditions for the minimization of iron sludge produced in Fenton oxidation processes by electro-regenerating Fe(2+) with constant potential (CPM) or constant current mode (CCM). Results indicate that the optimal cathodic potential for Fe(2+) regeneration is -0.1 V vs. the saturated calomel electrode (SCE) in terms of current efficiency. Keeping the initial Fe(3+) concentration ([Fe(3+)](0)) constant, the average current density produced at -0.1 V vs. SCE (CPM) is approximately equal to the optimal current density applied in the CCM. The suitable pH range is below the pH value determined by Fe(3+) hydrolysis. As expected, increasing cathode surface area and solution temperature notably increases Fe(2+) regeneration rate. At the optimal potential, the average current density increases linearly with [Fe(3+)](0), exhibiting a slope of 8.48 x 10(-3)(A/m(2))(mg/L)(-1). The average current efficiency varies with [Fe(3+)](0), e.g., 75% and 96-98% at 100 and > or = 500 mg/L [Fe(3+)](0), respectively. Once reaching 75% of Fe(2+) regeneration capacity, further regeneration becomes difficult due to Fe(3+) mass transfer limitation. Fe(2+) can also be effectively regenerated by dissolving iron sludge at low pH (usually 相似文献   

Photocatalytic degradation of reactive black 5 in aqueous solutions: Effect of operating conditions and coupling with ultrasound irradiation

The degradation of reactive black 5 (RB 5), a representative diazo dye found in textile effluents, by means of ultraviolet irradiation (9W UVA) over TiO(2) suspensions, ultrasound irradiation (80kHz, 135W) and their combined application was investigated. Several commercial TiO(2) catalysts were screened and an anatase Hombicat UV 100 sample exhibited considerable activity in terms of solution decoloration, COD and ecotoxicity reduction. Photocatalytic degradation increased with increasing TiO(2) loading (in the range 0.05-1g/L) and decreasing dye concentration (in the range 120-20mg/L) and solution pH (in the range 9-2.6). At the typical conditions employed in this study (60mg/L dye, 0.25mg/L catalyst, ambient pH=5.8, oxygen sparging), complete decoloration was achieved after 60min of reaction. Addition of H(2)O(2) up to 0.01M hindered degradation, scavenging the photogenerated holes and hydroxyl radicals. Ultrasound irradiation resulted in low decoloration, e.g. less than 10% after 60min at 60mg/L dye and oxygen sparging and slightly improved under an argon atmosphere. The simultaneous application of ultraviolet and ultrasound irradiation resulted in increased decoloration compared to that achieved by photocatalysis and sonolysis operating separately; moreover, the overall sonophotocatalytic effect was greater than the additive effect of the two processes, implying possible synergy.     

Degradation of paracetamol in aqueous solutions by TiO2 photocatalysis

In this study, photo/photocatalytic oxidation of common analgesic and antipyretic drug, paracetamol (acetaminophen), was investigated to determine the optimal operating conditions for degradation in water. UVA (365 nm) radiation alone degraded negligible amount of paracetamol, whereas paracetamol concentration decreased substantially under an irradiation of UVC (254 nm) with marginal changes in total organic carbon (TOC). In the presence of TiO2, much faster photodegradation of paracetamol and effective mineralization occurred; more than 95% of 2.0mM paracetamol was degraded within 80 min. The degradation rate constant decreased with an increase in the initial concentration of paracetamol, while it increased with light intensity and oxygen concentration. The degradation rate also increased with TiO2 loading until a concentration of 0.8 g L(-1). The degradation rate slowly increased between pH 3.5 and 9.5, but significantly decreased with increasing pH between 9.5 and 11.0. Based on the experimental data, a kinetic equation describing paracetamol photocatalytic degradation with various process parameters is obtained.     

Study on Fe(VI) species as a disinfectant: quantitative evaluation and modeling for inactivating Escherichia coli

Ferrate (Fe(VI)) has high potentials as a multi-purpose water treatment chemical acting as an oxidant, coagulant, and disinfectant, but little detail has been reported concerning its biocidal ability. In this study, the inactivation efficiencies of three Fe(VI) species (H(x)FeO(4)(x-2), x=0, 1, 2) are quantified using Escherichia coli as a model microorganism. E. coli inactivation by Fe(VI) was performed in solutions buffered with 25 mM phosphate in the pH range of 5.6-8.2 and at 25 degrees C. Kinetics of E. coli inactivation were successfully fitted to the Modified Delayed Chick-Watson model in the tested pH range, indicating that log inactivation level of E. coli is linearly proportional to exposure amount of E. coli to Fe(VI). The rate constant of E. coli inactivation by Fe(VI) (k(obs)) that was obtained from the linear regression increased non-linearly from 0.33 to 6.25 l(mg min)(-1) with decreasing pH from 8.2 to 5.6. From the measured pH dependency of k(obs) and the known acidity constants of Fe(VI) species (pK(a), H(2)FeO(4)=3.50 and pK(a), HFeO(4)(-)=7.23), HFeO(4)(-) and H(2)FeO(4) were found to be 3 and 265 times as effective as FeO(4)(2-) in E. coli inactivation, respectively.     

流动方式和消光系数对TiO2光催化性能的影响

利用溶胶-凝胶法在陶瓷管内壁负载了TiO2薄膜，研究了流动方式和消光系数对光催化降解有机物的影响。结果表明，易直接被紫外线光解的苯酚适于采用溢流的方式进行降解，其反应速率常数约为降膜式的2倍；不易直接光解的亚甲基蓝则适于采用降膜的方式，所得速率常数约为溢流式反应的2～3倍；消光系数是影响光催化降解效果的一个重要因素，反应速率常数随消光系数的减小而增大，当消光系数固定时，存在最佳管径和速率常数的最大值。     

Removal of 1,4-dioxane from water using sonication: effect of adding oxidants on the degradation kinetics

This research investigates the effect of adding oxidants such as Fe0, Fe2+ and S2O8(2-) in the sonication of 1,4-dioxane (1,4-D). The results indicate that the degradation pattern of 1,4-D kinetically could be divided into three steps (initiation, acceleration, and stabilization), with the first two steps predominating. The initiation step agreed with zero order rate model, while the acceleration step was the pseudo-first order. In the presence of HCO3- as a radical scavenger, the degradations of 1,4-D and TOC were suppressed, indicating that OH radical is an important factor in the sonolysis, especially at the acceleration step. The overall degradation efficiency of 79.0% in the sonolysis of 1,4-D was achieved within 200 min. While Fe0, Fe2+ and S2O8(2-) were individually combined with sonication, the total degradation efficiency of 1,4-D increased 18.6%, 19.1% and 16.5% after 200 min, respectively. The addition of oxidants not only increased the rate constant in the acceleration step, but also changed the kinetic model from zero to pseudo-first order at the initiation step. The addition of oxidants such as Fe2+, Fe0 and S2O8(2-) in the sonication of 1,4-D also improved the mineralization of 1,4-D. However, the degradation efficiencies of 1,4-D and TOC were not statistically different (p = 0.709, ANOVA) with different oxidants such as Fe2+, Fe0 and S2O8(2-).     

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.     

Photodegradation of bisphenol-A with TiO2 immobilized on the glass tubes including the UV light lamps

Photodegradation experiments of bisphenol-A (BPA) were performed with TiO(2) particles as a photocatalyst, where particles were immobilized using a titanium sol-solution synthesized by a sol-gel method. The effects of immobilized TiO(2)-film thickness, UV radiation intensity, and pH on the photodegradation of BPA were investigated. Apparent rate constant of the first order increased with increasing TiO(2)-coating time from 1 to 3, however, decreased over 4-coating time. Rate constant (K) increased with increasing the UV light intensity, which was related with the number of inserted UV lamps. Rate constant (K) increased as the pH value shifted from basic to acidic regions. Four kinds of byproducts were derived during the photodegradation of BPA, which were identified as 1.1-ethenylidenebis-benzene, 4-isopropylphenol, 4-tert-butylphenol, and phenol.     

The preparation of TiO2 nanometer photocatalyst film by a hydrothermal method and its sterilization performance for Giardia lamblia

The photocatalytic property of TiO(2) is utilized to sterilize the Giardia lamblia in an aqueous solution in this study. The TiO(2) colloidal solution used for the film was prepared by the modified hydrothermal method and it was directly coated on a UV-lamp, which was set up using a photoreactor manufactured in our laboratory. The TiO(2) film was very stably attached to the UV-lamp, and it was transparent until 5-time coating. The size of the TiO(2) particle in the film was distributed around 20-30 nm and the film thickness was about 200 nm per 1-time coating.The G. lamblia cell was just partially damaged under UV-irradiation without a TiO(2) photocatalyst, but the dead cell became very small and the dead body finally disappeared with an increase in the intensity of UV-irradiation after 2 h. In addition, under the TiO(2)/UV-irradiation system, the sterilized (dead) rate of G. lamblia was very fast. The sterilizing power increased at lower pH in the initial step, but it rather increased at a higher pH in the final step. And the sterilization of G. lamblia was very sensitive to the temperature, and resulted in an increase in the sterilized rate at higher temperatures. On the basis of these experimental observations, it can be concluded that TiO(2) photocatalyst under UV-irradiation could be adopted as one of the sterilization modalities for the G. lamblia.     

A comparative study on oxidation of disperse dyes by electrochemical process, ozone, hypochlorite and Fenton reagent

The results of an experimental study on the destruction of disperse dyes by chemical oxidation using ozone, hypochlorite and Fenton reagent (H2O2 + Fe2+) are compared with the data obtained by electrochemical oxidation. While the results obtained during hypochlorite oxidation were not satisfactory (only 35% reduction of colour was achieved at a dose of 6 g dm(-3)), ozonation enabled colour to be reduced by up to 90% (ozone dose 0.5 g dm(-3)). A high decolourisation degree was however accompanied by a low removal (10% efficiency) of chemical oxygen demand (COD). Trials of electrochemical oxidation proved this process much more efficient. Under the conditions of an acidic pH in 40 min of electrolysis a 79% elimination of COD was achieved at the Ti/Pt-Ir anode, which proved the best of seven different tested materials. Simultaneously 90% colour was removed. Indirect oxidation, by means of chlorine-deriving compounds, was the predominating process leading to the pollutants depletion. The best treatment results were obtained with the Fenton process, which under the optimal pH equal to 3 and hydrogen peroxide and ferrous sulphide dose of 600 and 550 mg dm(-3), respectively, resulted in a final effluent being colourless and with the residual COD equal to 100 mg dm(-3).     

Removal of arsenic using hardened paste of Portland cement: batch adsorption and column study

Hardened paste of Portland cement (HPPC) has been used as a low-cost adsorbent for the removal of arsenic from water environment. Results from the batch experiments, conducted at an initial concentration of 0.2 ppm of arsenate, suggest arsenate removal up to 95%. Kinetic profiles were developed for various conditions. Effects of adsorbent dose, common ions such as Ca(2+), Mg(2+), Fe(3+), Fe(2+), Cl(-), SO(4)(2-), NO(3)(-), PO(4)(3-) and of pH were studied in detail. Adsorption isotherm studies revealed that the Freundlich isotherm was followed with a better correlation than the Langmuir isotherm. Arsenite could also be removed up to approximately 88% using the same material, HPPC. Finally, column studies were undertaken involving the new HPPC to check the suitability of the material for the removal of total arsenic content from water body. Kinetic experiments for the removal of arsenic by column studies revealed a film diffusion mechanism.     

Photodegradation of endocrine disrupting chemical nonylphenol by simulated solar UV-irradiation

The photolysis of nonylphenol (NP) was investigated using a solar simulator in the absence/presence of dissolved organic matter (DOM), HCO3-, NO3- and Fe(III) ions. The effects of different parameters such as initial pH, initial concentration of substrate, temperature, and the effect of hydrogen peroxide concentration on photodegradation of nonylphenol in aqueous solution have been assessed. The results indicate that the oxidation rate increases in the presence of H2O2, Fe(III) and DOM with dissolved organic carbon concentrations not higher than 3 mg L(-1). Phenol, 1,4-dihydroxylbenzene and 1,4-benzoquinone were identified as intermediate products of photodegradation of nonylphenol, through an HPLC method. In addition, the disappearance of the estrogenic activity of nonylphenol during irradiation using YES test was investigated. Based upon the YES test results, there was a strong decrease of estrogenic activity of nonylphenol after 80 h irradiation in the presence of hydrogen peroxide.     

Hybrid photocatalysis/membrane treatment for surface waters containing low concentrations of natural organic matters

Since the mid-1990s, numerous studies on the treatment of drinking water by photocatalysis have been reported. Once optimised, the photocatalytic process can completely degrade numerous natural and artificial organic compounds. In this study, a hybrid photocatalysis/membrane process was used as a polishing treatment of surface water containing a small concentration of natural organic matters (i.e. total organic carbon (TOC) concentration of around 3mg/L) which may be difficult to remove using conventional filtration or coagulation. An optimum pH of 4.5 and a TiO(2) concentration of 0.1g/L were found to lead to the highest removal efficiencies. The relative effect of the individual processes featuring in the hybrid system (UV radiation, TiO(2) adsorption and membrane filtration) was also assessed for different pH values. The membrane separation process was accounted to remove around 18% of the initial TOC concentration, while TiO(2) adsorption alone was generally responsible for less than 5% of TOC removal during the 120 min of the experiments. However, when the natural water was only radiated by UV light, up to 70% of TOC was removed. A synergetic effect was observed when the three processes (TiO(2), UV and membrane) were used together. Comparison of removal efficiencies obtained during real and model (International Humic Substance Society) waters treatment by photocatalysis is also presented, revealing the importance of the nature of the feed in this type of treatment.     

UV/H_2O_2降解水中痕量NDMA的效能研究

采用UV/H2O2降解水中的痕量NDMA,考察了水中NDMA初始浓度、H2O2投量、pH、天然有机物及常见阴离子等因素的影响,并分析了NDMA的降解产物。结果表明,在UV辐照度为1 000μW/cm2、NDMA初始浓度为0.1 mmol/L、H2O2投量为20 mg/L、pH值为4的条件下,UV/H2O2对NDMA的降解效果较好(反应5 min后对NDMA的去除率接近100%);水中的天然有机物和Cl-、SO42-、NO3-、HCO3-等阴离子对NDMA的降解均有抑制作用,腐殖酸浓度越大其抑制作用越强,阴离子的抑制作用由大到小依次为HCO3-、NO3-、SO24-、Cl-;NDMA的主要降解产物为二甲胺和硝酸盐,此外还有少量亚硝酸盐、甲酸盐和甲胺生成。     

Degradation and byproduct formation of parathion in aqueous solutions by UV and UV/H(2)O(2) treatment

The photodegradation of parathion in aqueous solutions by UV and UV/H(2)O(2) processes was evaluated. Direct photolysis of parathion both by LP (low pressure) and MP (medium pressure) lamps at pH 7 was very slow with quantum yields of 6.67+/-0.33x10(-4) and 6.00+/-1.06x10(-4)molE(-1), respectively. Hydrogen peroxide enhanced the photodegradation of parathion through the reaction between UV generated hydroxyl radical and parathion with a second-order reaction rate constant of 9.70+/-0.45x10(9)M(-1)s(-1). An optimum molar ratio between hydrogen peroxide and parathion was determined to be between 300 and 400. Photodegradation of parathion yielded several organic byproducts, of which the paraoxon, 4-nitrophenol, O,O,O-triethyl thiophosphate and O,O-diethyl-methyl thiophosphate were quantified and their occurrence during UV/H(2)O(2) processes were discussed. NO(2)(-), PO(4)(3-), NO(3)(-) and SO(4)(2-) were the major anionic byproducts of parathion photodegradation and their recover ratios were also discussed. A photodegradation scheme suggesting three simultaneous pathways was proposed in the study.     

Iron type catalysts for the ozonation of oxalic acid in water

Two iron catalysts (Fe(III) and Fe2O3/Al2O3) have been used in the ozonation of oxalic acid in water at pH 2.5. Percentage removals of oxalic acid were 1.8%, 7% and 30% corresponding to the non-catalytic, homogeneous (Fe(III)) and heterogeneous (Fe2O3/Al2O3) catalytic ozonations, respectively. Catalytic oxalic acid ozonation leads in all cases to total mineralization. The mechanism of ozonation likely develops through formation of iron-oxalate complexes that further react with ozone without the participation of hydroxyl radicals. Because of the stringent acidic conditions, some metal leaching has been observed and quantified in the heterogeneous process. In the homogeneous catalysis, the kinetics was found to be first order with respect to ozone and oxalic acid while for the heterogeneous catalysis, the kinetic order depends on the concentration of ozone in the gas fed. Thus, at ozone concentrations lower than 30 mg L(-1), the heterogeneous ozonation is between first and zero order with respect to both ozone and oxalic acid while at higher ozone gas concentrations, the kinetics was found to be first and zero order with respect to oxalic acid and ozone, respectively. This kinetics is supported through an Eley-Rideal mechanism that involves a surface reaction between non-adsorbed ozone and adsorbed oxalic acid. Apparent activation energies of the homogeneous and heterogeneous catalytic ozonations were found to be 18.2 and 13.6 kcal mol(-1), respectively.     

Effect of precursor concentration on the characteristics of nanoscale zerovalent iron and its reactivity of nitrate

Differing precursor concentrations, 1.0, 0.1, and 0.01 M FeCl(3) x 6H(2)O, were performed to produce nanoscale Fe(0) and the results were discussed in terms of the specific surface area, particle size and electrochemical properties. The results indicated that the nanoscale Fe(0) prepared by 0.01 M FeCl(3) had absolutely reduced in size (9-10nm) and possessed the greatest specific surface area (56.67 m(2) g(-1)). These synthesized nanoscale Fe(0) particles were attempted to enhance the removal of 40 mg-NL(-1) unbuffered nitrate solution. The first-order degradation rate constants (k(obs)) increased significantly (5.5-8.6 times) with nanoscale Fe(0) prepared by 0.01 M precursor solution (Fe(0.01 M)(0)). When normalized to iron surface area concentration, the specific rate constant (k(SA)) was increased by a factor of approximately 1.7-2.4 using Fe(0.01 M)(0) (6.84 x 10(-4) L min(-1) m(-2) for Fe(0.01 M)(0), 4.04 x 10(-4) L min(-1) m(-2) for Fe(0.1 M)(0) and 2.80 x 10(-4) L min(-1) m(-2) for Fe(1 M)(0)). The rise of reactivity of the reactive site on the Fe(0.01 M)(0) surface was indicated by the specific rate constant (k(SA)) calculation and the i(0) value of the electrochemical test.     

Discoloration and mineralization of Orange II by using a bentonite clay-based Fe nanocomposite film as a heterogeneous photo-Fenton catalyst

Discoloration and mineralization of an azo dye Orange II was conducted by using a bentonite clay-based Fe nanocomposite (Fe-B) film as a heterogeneous photo-Fenton catalyst in the presence of UVC light and H(2)O(2). Under optimal conditions (pH=3.0, 10 mM H(2)O(2), and 1 x 8W UVC), 100% discoloration and 50-60% TOC removal of 0.2 mM Orange II can be achieved in 90 and 120 min, respectively. The mineralization kinetics of 0.2 mM Orange II is much slower than the corresponding discoloration kinetics. Under the same conditions, the Fe leaching from the Fe-B-coated catalyst film is very low. The Fe-B-coated catalyst film could be used in the pre-treatment of wastewater for an integrated system consisting of a photochemical reactor and a biological reactor. Multi-run experimental results reveal that the Fe-B-coated catalyst film could have a long-term stability for the discoloration and mineralization of Orange II. A comparison between the performance of the Fe-B-coated catalyst film and a suspended Fe-B catalyst in the discoloration and mineralization of Orange II was also discussed.