Degradation of 2,4,5-trichlorophenoxyacetic acid by a novel Electro-Fe(II)/Oxone process using iron sheet as the sacrificial anode

A novel electrochemically enhanced advanced oxidation process for the destruction of organic contaminants in aqueous solution is reported in this study. The process involves the use of an iron (Fe) sheet as sacrificial anode and a graphite bar as cathode. In the oxidation process, once an electric current is applied between the anode and the cathode, a predetermined amount of Oxone is added to the reactor. Ferrous ions generated from the sacrificed Fe anode mediate the generation of highly powerful radicals (SO(4)(•-)) through the decomposition of Oxone. The coupled process of Fe(II)/Oxone and electrochemical treatment (Electro-Fe(II)/Oxone) was evaluated in terms of 2,4,5-Trichlorophenoxyacetic acid degradation in aqueous solution. Various parameters were investigated to optimize the process, including applied current, electrolyte and Oxone concentration. In addition, low solution pH facilitates the system performance due to the dual effects of weak Fenton reagent generation and persulfate ions generation, whereas the system performance was inhibited at basic pH levels through non-radical self-dissociation of Oxone and the formation of ferric hydroxide precipitates. Furthermore, the active radicals involved in the Electro-Fe(II)/Oxone process were also identified. The Electro-Fe(II)/Oxone process demonstrates a very high 2,4,5-T degradation efficiency (over 90% decay within 10 min), which justifies the novel Electro-Fe(II)/Oxone a promising treatment process for herbicide removal in water.

Degradation of a xanthene dye by Fe(II)-mediated activation of Oxone process

A powerful oxidation process using sulfate radicals activated by transition metal mediated Oxone process has been evaluated in depth by monitoring the degradation of a xanthene dye Rhodamine B (RhB) in aqueous solution. Ferrous ion was chosen as the transition metal due to its potential catalytic effect and wide availability in dyeing industrial effluent. The effects of parameters including reactant dosing sequence, Fe(II)/Oxone molar ratio and concentration, solution pH, and inorganic salts on the process performance have been investigated. Total RhB removal was obtained within 90 min under an optimal Fe(II)/Oxone molar ratio of 1:1. The RhB degradation was found to be a two-stage kinetics, consisting of a rapid initial decay and followed by a retarded stage. Additionally, experimental results indicated that the presence of certain anions had either a positive or negative effect on the process. The inhibitory effect in the presence of SO(4)(2-) was elucidated by a proposed formula using Nernst equation. Furthermore, dye mineralization in terms of TOC removal indicates that stepwise addition of Fe(II) and Oxone can significantly improve the process performance by about 20%, and the retention time required can be greatly reduced comparing with the conventional one-off dosing method.

Mask Technology For X-Ray Nanolithography

In this report we describe a system of technologies we have developed for fabricating, patterning, and replicating x-ray masks with linewidths as fine as 50 nm (0.05 μm). This effort has evolved into a fairly routine service supporting a growing community of researchers at MIT interested in fabricating sub-micron and nanometer scale structures and devices. Strong, transparent, silicon-rich nitride (SiN) membranes bonded to optically-flat Pyrex rings and patterned with gold absorbers form the basic x-ray mask structure. We have recently completed the installation of a vertical thermal reactor (VTR) for the deposition of SiN coatings. Results indicate superb film uniformity, decreased defect counts, and increased strength over previously available nitrides. Patterning of the masks is performed at an off-site location by electron-beam lithography followed by development and gold electroplating at MIT. We describe a new fountain plating bath and mask chuck which allows us to obtain clean, uniform gold films of low stress. Once completed, the so-called “master” masks are replicated onto new x-ray mask substrates which are then processed into “daughter” masks. The resulting polarity-reversed patterns are required in order to achieve the desired pattern in positive resist when printed onto substrates. We will describe our in-house built x-ray aligner which features a high-power electron bombardment source and SiN vacuum isolation window to achieve exposures in a helium environment.

Degradation of linuron by UV, ozonation, and UV/O(3) processes--effect of anions and reaction mechanism

A comprehensive study of the degradation of linuron, one of the phenylurea herbicides, was conducted by using different treatment processes including UV, ozonation and UV/O(3). The effect of various anions on the performance of ozonation has been examined. N-terminus demethoxylation, photohydrolysis with or without dechlorination, and N-terminus demethylation have been found to be the major mechanisms in the linuron decay under the irradiation of UV at 254 nm while N-terminus demethoxylation, dechlorination and hydroxylation on benzene ring was observed to be involved in the ozonation process. Eight new intermediates were identified in UV process in this study compared with previous studies. Different decay pathways were proposed based on the identified intermediates in the three studied processes. UV/O(3) has demonstrated the best performance among these three processes in terms of LNR decay, mineralization, dechlorination and de-nitrogenation.

Heterogeneous lollipop-like V2O5/ZnO array: a promising composite nanostructure for visible light photocatalysis

ZnO/V(2)O(5) core-shell nanostructures have been prepared by a two-step synthesis route through combined hydrothermal growth and magnetron sputtering. After annealing under oxygen ambience, a ZnO/V(2)O(5) heterogeneous lollipop-like nanoarray formed. The microstructure and crystal orientation of those nanolollipops were investigated by scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM), which show single crystal structure. The optical properties were characterized by UV-vis spectroscopy and showed quite different absorption curves for the as-deposited and annealed samples. The ZnO/V(2)O(5) nanolollipops demonstrated excellent photocatalytic activity in terms of decomposing 2,6-dichlorophenol (2,6-DCP) under visible light, indicating their promising potential as catalysts for industrial wastewater and soil pollution treatments.

Reactor model development: the removal performance of ferrous-catalysed photo-oxidation process by examining the reaction parameters

The removal performance of the ferrous catalysed photo-oxidation process was investigated through the examination of major process parameters including pH levels and dosages of ferrous (Fe(2+)) and hydrogen peroxide (H(2)O(2)). A common used herbicide, alachlor, was used as a target compound in the degradation process. In the study, alachlor was found to be effectively degraded by hydroxyl radicals (HO) which were generated by UV/Fe(2+)/H(2)O(2) in the oxidation process. It was interesting to find that the pattern of reaction kinetics of alachlor varied depending on the initial concentrations of Fe(2+) and H(2)O(2). An optimum H(2)O(2) dosage was determined. This was practically useful because the overdose of H(2)O(2) would cause the process retardation. The conventional pseudo-first-order kinetics and two-stage first-order kinetics were observed at lower and higher Fe(2+) concentrations, respectively. Models were proposed and used to stimulate the kinetic process. Thus, design charts were established for determining the reaction time (i.e., reactor sizing) required for predetermined removal performance of alachlor under different concentrations of H(2)O(2) and Fe(2+).

Reaction mechanism of linuron degradation in TiO2 suspension under visible light irradiation with the assistance of H2O2

The application of TiO2/H2O/Vis (visible light) process for the aqueous degradation of linuron (LNR) has been investigated. The performance of TiO/H2O2/Vis process has been compared with other processes such as TiO2/H2O2 in the dark, TiO2/Vis, and H2O2 is in terms of LNR decay. The result showed that more than 70% LNR could be decomposed in the TiO2/H2O2/Vis. The degradation mechanism of LNR by TiO2/H2O2/Vis process has been verified through investigation of the effects of various radical scavengers on the performance of this system, monitoring the generation of photocurrent, and comparing the intermediates and decay pathways of LNR by UV-TiO2 and TiO2/ H2O2/Vis processes with 16 and 17 intermediates identified, respectively. It has been revealed that demethoxylation and demethylation through alkylic-oxidation is the major mechanism of LNR degradation while dechlorination (hydroxylation at the chlorine site) and direct hydroxylation on the benzene ring is minor in both processes. Mineralization and release of chlorine and nitrogen have been also studied.

Challenges in phenotype definition in the whole-genome era: multivariate models of memory and intelligence

Refining phenotypes for the study of neuropsychiatric disorders is of paramount importance in neuroscience. Poor phenotype definition provides the greatest obstacle for making progress in disorders like schizophrenia, bipolar disorder, Attention Deficit/Hyperactivity Disorder (ADHD), and autism. Using freely available informatics tools developed by the Consortium for Neuropsychiatric Phenomics (CNP), we provide a framework for defining and refining latent constructs used in neuroscience research and then apply this strategy to review known genetic contributions to memory and intelligence in healthy individuals. This approach can help us begin to build multi-level phenotype models that express the interactions between constructs necessary to understand complex neuropsychiatric diseases. These results are available online through the http://www.phenowiki.org database. Further work needs to be done in order to provide consensus-building applications for the broadly defined constructs used in neuroscience research.

Degradation of atrazine by cobalt-mediated activation of peroxymonosulfate: Different cobalt counteranions in homogenous process and cobalt oxide catalysts in photolytic heterogeneous process

The degradation of atrazine (ATZ) by cobalt-mediated activation of peroxymonosulfate (PMS) has been studied in this work. For the homogenous process, different cobalt counteranions: cobalt(II) nitrate Co(NO(3))(2), cobalt(II) sulfate CoSO(4), cobalt(II) chloride CoCl(2), and cobalt(II) acetate Co(CH(3)COO)(2), have been examined. The inhibitory effect was observed in the process initiated by CoCl(2). For the pH test, wide range of pH level (2-10) has been investigated. It was found that the higher rates were obtained in the normal pH levels. At extreme pH levels, the process was impeded by inactivation of PMS at acidic pH and prohibited by precipitation at basic pH. On the other hand, the recycling capability of cobalt oxide and the oxidative potential of cobalt-immobilized titanium dioxide Co-TiO(2) catalyst were analyzed in the heterogeneous process. It was found that the higher the cobalt content in the catalyst, the better the removal performance was resulted. At last, the Co-TiO(2) catalyst synthesized in this work was found to be very effective in transforming ATZ as well as its intermediate in the presence of UV-vis irradiation.

A new approach to quantify the degradation kinetics of linuron with UV, ozonation and UV/O3 processes

The degradation of linuron, one of phenylurea herbicides, was investigated for its reaction kinetics by different treatment processes including ultraviolet irradiation (UV), ozonation (O3), and UV/O3. The decay rate of linuron by UV/O3 process was found to be around 3.5 times and 2.5 times faster than sole-UV and ozone-alone, respectively. Experimental results also indicate overall rate constants increased exponentially with pH above 9.0 while the increase of rate constants with pH below 9 is insignificant in O3 system. All dominant parameters involved in the three processes were determined in the assistant of proposed linear models in this study. The approach was found useful in predicting the process performances through the quantification of quantum yield (Phi(LNR)) (rate constant for the formation of free radical HOO(.-) from ozone decomposition at high pH), rate constant of linuron with ozone ((k(O3,LNR)), rate constant of linuron with hydroxyl radical (k(OH,LNR)), and alpha (the ratio of the production rate of OH() and the decay rate of ozone in UV/O3 system).