The effect of operational parameters on the photocatalytic degradation of pesticide

The photocatalytic degradation of Cartap Hydrochloride, a synthetic pesticide. has been investigated over coated TiO2 photocatalysts irradiated with a ultraviolet (UV) light. The effect of operational parameters, i.e., Cartap Hydrochloride concentration, reaction time, light intensity and additive on the degradation rate of aqueous solution of Cartap Hydrochloride has been examined. Results show that the employment of efficient photocatalysts and the selection of optimal operational parameters may lead to degradation of Cartap Hydrochloride solutions.     

Superior photodecomposition of pyrene by metal ion-loaded TiO₂ catalyst under UV light irradiation

BACKGROUND: The photocatalytic degradation of pyrene under UV (125 W Hg-Arc, 10.4 mW/cm2) irradiation of TiO2 aqueous suspension has been found to be highly improved with the dissolved transition metal ions like Cu2+, Fe3+, Ag+, and Au3+, etc. As the reduction potential of these metals lies below the conduction band (CB) position (?0.1 eV) of TiO2, the photoexcited electron transfer occurs more readily and reduces electron–hole recombination rate. Therefore, it has a beneficial influence on the photocatalytic ability of TiO2 because of rapid Fermi energy equilibrium between the CB of TiO2 and its surface adsorbed metal ions. RESULTS AND DISCUSSION: The Fermi level is referred to as the electrochemical potential and plays an important role in the band theory of solids. When metal and semiconductor are in contact, electron migration from photoirradiated semiconductor to the deposited metal occurs at the interface until two Fermi levels equilibrate and enhanced the photocatalytic activity of semiconductor photocatalyst. Ni2+ having more negative reduction potential (?0.25 eV) than the CB of TiO2 imparts negligible co-catalytic activity to TiO2 photoreaction. It also revealed that loading of Au3+ ions displayed higher degradation rate of pyrene than Au photodeposition. Furthermore, when the amount of dissolved Fe+3 and Au3+ ions gradually increases from 0.1 to 2 wt.%, the pyrene photodecomposition rate also become faster.     

负载TiO2/Fe3+的玻璃纤维反应器光催化苯酚

以玻璃纤维为载体,将TiO2负载到其表面形成了空间玻璃纤维反应器,引入Fe3+作为掺杂改性离子,形成了负载TiO2/Fe3+的空间玻璃纤维光催化反应器,并以高压汞灯为光源进行了光催化降解水中苯酚的实验研究,考察了影响苯酚光催化降解的因素,确定了在UV365～250 W光源照射下,pH为3～5,O2通入量1.0 L/(min.L),反应器内上升流速为0.7 m/min等实验条件下,初始浓度为30 mg/L的苯酚废水经120 min光催化反应后,降解率可达到85%,矿化率可达80%。     

TiO2光催化降解水中土霉素的动力学研究

环境中抗生素的出现及其引起的危害正受到越来越多的关注。以高压汞灯为光源,选用较为广泛的抗生素土霉素（OTC）为处理对象。考察了初始质量浓度、反应过程中光照、催化剂投加量、溶液起始pH、溶液中DOM和NO^-₃对光催化降解的影响,研究了其光降解动力学。结果表明,TiO₂光催化氧化法能够有效去除水中半微量的OTC,OTC的光降解过程符合一级反应动力学模型;UV/TiO₂联用工艺对TOC也有很好的去除效果,反应90 min,TOC去除率可达74%;OTC的初始浓度从30 mg/L增大到90 mg/L,反应速率从0.0619 min^-1降低到0.0130 min^-1;随着光催化剂投加量的增大,光降解速率常数先增大后减小;增加溶液的pH值,速率常数逐渐减小;溶液中的DOM和NO^-₃也可以影响光降解效率。     

Continuous monitoring of photocatalytic treatments by flow injection. Degradation of dicamba in aqueous TiO2 dispersions.

The possible use of flow injection (FI) to monitor the photocatalytic mineralization of dicamba (3,6-dichloro-2-methoxybenzoic acid) present at the trace level in aqueous solutions containing TiO2 suspensions has been evaluated. Experiments were performed in a stirred photochemical reactor equipped with a simple FI manifold, integrating an online filtration unit able to perform the monitoring of the UV absorbance of the irradiated solution every 4 min. The light source used was a medium pressure mercury lamp (125 W). During the initial steps of the reaction the formation of UV absorbing intermediates, which completely disappear in less than 80 min, was evidenced. Additional HPLC, DOC and chloride ion measurements carried out on manually taken samples confirmed the complete mineralization of dicamba within about 90 min. The proposed on-line monitoring looks particularly suitable for the control of degradation treatments where primary degradation and mineralization steps take place after a comparable irradiation time.     

Risks of using membrane filtration for trace metal analysis and assessing the dissolved metal fraction of aqueous media--a study on zinc, copper and nickel

Membrane filtration is commonly performed for solid-liquid separation of aqueous solutions prior to trace metal analysis and when assessing “dissolved” metal fractions. Potential artifacts induced by filtration such as contamination and/or adsorption of metals within the membrane have been investigated for different membrane materials, metals, applied pressures and pre-cleaning steps. Measurements have been conducted on aqueous solutions including well-defined metal standards, ultrapure water, and on runoff water from corroded samples.Filtration using both non-cleaned and pre-cleaned filters revealed contamination and adsorption effects, in particular pronounced for zinc, evident for copper but non-significant for nickel. The results clearly show these artifacts to be non-systematic both for non-cleaned and pre-cleaned membranes. The applied pressure was of minor importance.Measurements of the labile fraction by means of stripping voltammetry clearly elucidate that membrane filtration followed by total metal analysis cannot accurately assess the labile or the dissolved metal fraction.     

Photocatalytic degradation of an organophosphorus pesticide phosalone in aqueous suspensions of titanium dioxide

The present work deals with photocatalytic degradation of an organophosphorus pesticide, phosalone, in water in the presence of TiO2 particles under UV light illumination (1000 W). The influence of the basic photocatalytic parameters such as pH of the solution, amount of TiO2, irradiation time, stirring rate, and distance from UV source, on the photodegradation efficiency of phosalone was investigated. The degradation rate of phosalone was not high when the photolysis was carried out in the absence of TiO2 and it was negligible in the absence of UV light. The half-life (DT50) of a 20 ppm aqueous solution of phosalone was 15 min in optimized conditions. The plot of lnC (phosalone) vs. time was linear, suggesting first order reaction (K=0.0532 min(-1)). The half-life time of photomineralization in the concentration range of 7.5-20 ppm was 13.02 min. The efficiency of the method was also determined by measuring the reduction of Chemical Oxygen Demand (COD). During the mineralization under optimized conditions, COD decreased by more than 45% at irradiation time of 15 min. The photodegradation of phosalone was enhanced by addition of proper amount of hydrogen peroxide (150 ppm).     

负载TiO2/Fe^3＋的玻璃纤维反应器光催化苯酚

以玻璃纤维为载体,将TiO2负载到其表面形成了空间玻璃纤维反应器,引入Fe3＋作为掺杂改性离子,形成了负载TiO2/Fe^3＋的空间玻璃纤维光催化反应器,并以高压汞灯为光源进行了光催化降解水中苯酚的实验研究,考察了影响苯酚光催化降解的因素,确定了在UV365-250 W光源照射下,pH为3-5,O2通入量1.0 L/（min.L）,反应器内上升流速为0.7 m/min等实验条件下,初始浓度为30 mg/L的苯酚废水经120 min光催化反应后,降解率可达到85%,矿化率可达80%。     

The enhanced PC and PEC oxidation of formic acid in aqueous solution using a Cu-TiO2/ITO film

The photocatalytic (PC) and photoelectrocatalytic (PEC) activity of Cu-TiO2/ITO films for degrading formic acid in aqueous solution was investigated in this study. Compared with a TiO2/ITO film, the degradation efficiency of formic acid on the Cu-TiO2 films increased markedly in both the PC and PEC oxidation processes. However, it was found that the photodeposited Cu metal on the Cu-TiO2 films could electrochemically dissolute during the PEC reaction, while an electrical bias with the voltage higher than 1.48 V was applied. It is believed this is a common problem occurred for several metals deposition on the TiO2 films, which results in a poor stability of the metal-deposited TiO2 electrode in PEC processes. To improve the stability of the Cu-TiO2 electrode, an alternative process between PC and PEC reactions was investigated. It was found that the dissolute Cu metal during the PEC process was re-deposited on the Cu-TiO2 film again during the PC process. The experiments with repeated runs demonstrated that this alternative process could not only overcome the loss of Cu, but also enhance the PEC oxidation efficiency of the Cu-TiO2 films.     

Elemental uptake by seaweed, Plocamium corallorhirza along the Kwazulu-natal coast of Indian Ocean, South Africa

This study reports the elemental uptake by Plocamium corallorhiza, a Rhodophyta class of coralline alga grown richly along KwaZulu-Natal coastline. The uptake of seven important elements, namely Fe, Mn, As, B, Ti, Zn and Hg, selected based on their abundance in the samples, were investigated for a one-year cycle, from June 2002 to May 2003, at four chosen sites located along the KwaZulu-Natal coastline. The sites spread over 150 km from North to South Coast are Zinkwasi, Ballito, Treasure Beach and Park Rynie. P. corallorhiza possess good manganese and arsenic-accumulating ability and has potential to be an excellent indicator for most of the metals studied. A typical P. corallorhiza sample at Park Rynie (winter) recorded Mn (14 ppm), Fe (6.02 ppm), As (8.4 ppm), B (1580 ppb), Zn (234 ppb), Ti (751 ppb) and Hg (15.8 ppb). The general trend found at all sites was a large decrease in iron concentration in spring and summer and increase in winter. Mercury uptake was lowest in winter and autumn at all sites. The highest mercury levels in the seaweeds were recorded during spring or summer.     

Comparative effects of mine wastes on the benthos of an acid and an alkaline pond

Benthic invertebrates collected from an acid (pH 3.2) and an alkaline (pH 7.9) tailing pond in the Rouyn-Noranda mining region were compared with those of a control pond in order to assess the effects of the pH on the benthic community structure and on metal accumulation by invertebrates. The acid pond showed high mean soluble concentrations of aluminium (2600 ppb), copper (230 ppb), iron (6500 ppb) and zinc (4900 ppb) in the water and high mean concentrations of copper (340 ppm), iron (15,238 ppm) and zinc (445 ppm) in the sediments. The benthic fauna was dominated by Chironomus spp and the water beetle Ilybius sp. The Shannon-Weaver diversity index was 0.04. The alkaline pond had high mean sediment concentrations of cadmium (21 ppm), iron (15,823 ppm), manganese (658 ppm) and nickel (146 ppm). A total of 37 insect genera and a diversity index of 3.4 were recorded for this pond. Of the seven metals studied only copper and aluminium showed greater accumulations in the biota of the contaminated ponds than in that of the control. Insects dominated the benthic fauna in both contaminated ponds and crustacea in the control.     

Photomineralization of n-alkanoic acids in aqueous solution by photocatalytic membranes. Influence of trialkyl vanadates as catalytic promoters of immobilized titanium dioxide

The Ti0₂-mediated photomineralization of 8–1000 ppm of methanoic acid, of 6–100 ppm of ethanoic acid, of 6–180 ppm of propanoic acid, and of 6–90 ppm of n-decanoic acid in aqueous solutions was studied at 296± 2 K or 308 ± 2 K, with low and high pressure mercury arc lamps (radiant power in the absorption range 8 and 145 W respectively), using PHOTOPERM® CPP/313 membranes containing immobilized 30±3 wt.% Ti0₂, and, in parallel runs, 7 wt.% of a synergic mixture of tri(t-butyl)- and tri-(i-propyl) vanadate(V) as photocatalytic promoter. Stoichiometric H₂0₂ was used or, in some of the runs, 0₃, at saturation, as oxygen suppliers. Disappearance of total organic carbon (TOC) was followed as a function of time. To fit kinetic curves up to complete photomineralization, a kinetic model was employed, already used successfully in previous studies, which considers appearance and disappearance of all intermediates, as if they were represented by a hypothetical single molecule, mediating all of them. The photocatalytic activity of trialkyl vanadates was evaluated from quantum yields at “infinite” concentration, with respect to the maximum allowable efficiencies. When using O₃, a dark catalysis effect clearly appeared towards intermediate species produced during the photocatalysed degradation.     

The light transmission and distribution in an optical fiber coated with TiO2 particles

The light delivery and distribution phenomena along the optical fiber coated with the P-25 TiO(2) particles by dipping was investigated. The surface properties (coverage, roughness and thickness) of the TiO(2) layer coated on the optical fiber were characterized by SEM micrographs. For TiO(2) layer prepared from solutions containing less than 20 wt.% of TiO(2) slurry, the thickness of layer was increased linearly with the TiO(2) slurry content in solutions. The UV light intensity transmitted along a TiO(2)-coated optical fiber decreased more rapidly than that transmitted along a non-coated fiber. Based on the experimental results, the light intensity distribution around a coated optical fiber was modeled to determine the optimum configuration for the design of optical fiber reactors under various operational conditions.     

Elemental Uptake by Seaweed,Plocamium corallorhirza Along the KwaZulu-Natal Coast of Indian Ocean,South Africa

This study reports the elemental uptake by Plocamium corallorhiza, a Rhodophyta class of coralline alga grown richly along KwaZulu-Natal coastline. The uptake of seven important elements, namely Fe, Mn, As, B, Ti, Zn and Hg, selected based on their abundance in the samples, were investigated for a one-year cycle, from June 2002 to May 2003, at four chosen sites located along the KwaZulu-Natal coastline. The sites spread over 150 km from North to South Coast are Zinkwasi, Ballito, Treasure Beach and Park Rynie. P. corallorhiza possess good manganese and arsenic-accumulating ability and has potential to be an excellent indicator for most of the metals studied. A typical P. corallorhiza sample at Park Rynie (winter) recorded Mn (14 ppm), Fe (6.02 ppm), As (8.4 ppm), B (1580 ppb), Zn (234 ppb), Ti (751 ppb) and Hg (15.8 ppb). The general trend found at all sites was a large decrease in iron concentration in spring and summer and increase in winter. Mercury uptake was lowest in winter and autumn at all sites. The highest mercury levels in the seaweeds were recorded during spring or summer.     

Effect of adsorbents coated with titanium dioxide on the photocatalytic degradation of propoxur

Photocatalytic oxidation of pesticides in aqueous media irradiated by UV light is a rapidly growing field of research. Therefore, the treatment technology for degradation of propoxur (an insecticide) using titanium dioxide coated on the supports such as activated carbon, zeolite, brick, quartz and glass beads, was performed in this research. Results show that GAC/TiO2 is the best complexing agent for oxidizing propoxur because of its adsorption properities. The others follow the sequence: plain TiO2 > glass beads > zeolite > brick > quartz. The degradation rate of propoxur with plain TiO2 is higher than that with TiO2/GAC complexing agent. But the mineralization rate of propoxur with plain TiO2 is lower than that with TiO2/GAC complexing agent. However, it can be concluded that using GAC as the support can improve the photocatalytic efficiency.     

Photocatalytic oxidation of sulfamethazine

The photocatalytic degradation of sulfamethazine (SMT), a sulfonamide drug, has been investigated in aqueous heterogeneous solutions containing n-type oxide semiconductors as photocatalysts. The disappearance of the organic molecule follows approximately a pseudo-first-order kinetics according to the Langmuir-Hinshelwood model. It was observed that, with TiO2 P-25 and ZnO as photocatalysts, quantitative degradation of the organic molecule occurs after 4 h. During this time the desulfurization of the substrate is complete, while only 30% of the nitrogen in the organic compound was recovered in the form of nitrate and ammonium ions, indicating that various other nitrogen-containing organic compounds remain in the solution. The addition of H2O2 leads, in the case of TiO2 P-25, to a twofold increase on the reaction rate, while a negative effect has been observed in the presence of ZnO. The initial apparent photonic efficiency (zeta0) of the photooxidation and the mineralization under various experimental conditions have been calculated.     

Removal and degradation of aromatic compounds from a highly polluted site by coupling soil washing with photocatalysis

The possible application of two environmental remediation technologies - soil washing and photocatalysis - to remove and decompose various aromatic pollutants present in excavated soils of a contaminated industrial site has been investigated. Aqueous solutions containing the non-ionic surfactant Brij 35 were used to extract the contaminants from the soil samples. The photocatalytic treatment of the obtained washing wastes, performed in the presence of TiO(2) suspensions irradiated with simulated sunlight, showed a slow abatement of the toxic compounds due to the relevant concentrations of organics in the waste. A neat improvement of the process performances, obtained by operating in the presence of added potassium peroxydisulfate, suggests a feasible treatment route.     

Study on the indoor volatile organic compound treatment and performance assessment with TiO2/MCM-41 and TiO2/quartz photoreactor under ultraviolet irradiation

Volatile organic compounds (VOCs) are the cause of indoor air pollution and are readily emitted from furniture and cleaning agents. In Taiwan, the concentrations of indoor VOCs range roughly from 1 to 10 ppm. It is important to effectively reduce indoor VOC emissions and establish the implementation of long-term, low-cost, controlled techniques such as those found in the ultraviolet/titanium dioxide (UV/TiO2) control systems. This study evaluates the performance of a photoreactor activated by visible irradiation and packed with TiO2/quartz or TiO2/mobile catalytic material number 41 (MCM-41). The photocatalysts tested include commercial TiO2 (Degussa P-25) and synthesized TiO2 with a modified sol-gel process. The UV light had a wavelength of 365 nm and contained an 8-W, low-pressure mercury lamp. Reactants and products were analyzed quantitatively by using gas chromatography with a flame-ionization detector. It is important to understand the influence of such operational parameters, such as concentration of pollutant, temperature, and retention time of processing. The indoor concentrations of VOCs varied from 2 to 10 ppm. Additionally, the temperatures ranged from 15 to 35 degrees C and the retention time tested from 2 to 8.2 sec. The results show that quartz with TiO2 had a better photoreductive efficiency than quartz with MCM-41. The toluene degradation efficiency of 77.4% with UV/TiO2/quartz was larger than that of 54.4% with the UV/TiO2/MCM-41 system under 10-min reaction time. The degradation efficiency of the UV/TiO2 system decreased with the increasing concentrations of indoor VOCs. The toluene degradation efficiency at 2 ppm was approximately 5 times greater than that at 10 ppm. The photoreduction rate of the VOCs was also evaluated with the Langmuir-Hinshewood model and was shown to be pseudo-first-order kinetics.     

Photocatalytic degradation of pentachlorophenol on TiO2 sol-gel catalysts

The photocatalytic degradation of pentachlorophenol (PCP) in aqueous solution was investigated using TiO2 catalysts. The samples were prepared by the sol-gel method using different gelation pH and different calcination temperatures. The solids were characterized by specific surface area, X-ray diffraction, UV-Vis absorbance, FTIR and pentachlorophenol adsorption. The catalytic activity of the solids was evaluated in a conventional photoreactor at 298 K using 30 ppm of pentachlorophenol. It was found that the reaction follows a first-order reaction and the kinetic constant values change slightly with the pH of gelation and more significantly with the calcination temperature.     

Effect of four alcohols on adsorption, desorption, and movement of cadmium, nickel, and zinc through soils

Miscible-displacement experiments were conducted to compare the effects of aqueous soil solutions with ethyl alcohol, ethylene glycol, diethylene glycol, and triethylene glycol on the movement of metals through soils. Aqueous or alcohol solutions containing 1 mM each Cd, Ni, and Zn and 5 mM Ca were perfused through columns containing River Sand, Canelo loam (Canelo 1) or Mohave sandy clay loam (Mohave scl) until effluent metal concentrations (C) equaled influent concentrations (C₀) or CC₀⁻¹ = 1. In general, the order of sorption was Zn > Ni > Cd in aqueous-perfused columns, while in alcohol-perfused columns sorption of Ni Cd ≥ Zn. In comparison to aqueous solutions, alcohols reduced total metal sorption by at least 25%. Metal sorption was best correlated to cation exchange capacity of the soil, sorption of metals being greatest in the Mohave scl and least in the River Sand. After CC₀⁻¹ = 1 was reached, columns were leached with deionized water. While leaching did not affect the sorption of metals in columns which had been perfused with aqueous solvents, sorption behavior of metals changed significantly in columns which had been perfused with alcohol solvents. Leaching caused desorption of 5 to 30% of the sorbed Ni. In general, Cd was desorbed (up to 45%) from the soils tested. The exceptions were River Sand columns perfused with diethylene and triethylene glycol in which additional Cd was sorbed to the soil from the soil solution. Additional Zn was sorbed in all columns tested with the exception of the Canelo 1 column perfused with ethyl alcohol.