No description available.

Phenol and its compounds are highly toxic even in low concentration, and have become the subject of intense research during the last two decades. Effluents from industries such as oil refining, paper milling, olive oil extraction, wood processing, coal gasification and textiles and resin manufacturing and agro-industrial wastes discharge phenols at levels much higher than the toxic levels set for this compound. Advanced Oxidation Processes (AOPs) such as UV, UV-TiO2, UV-H2O2, O3 and UV-O3 have become popular in recent years as efficient treatment methods for recalcitrant compounds like phenol. The effect of microwave (MW) and combined MW-UV treatment on degradation of phenol was studied in aqueous solution in the presence and absence of TiO2 under controlled temperature conditions. It was found that the efficiency of MW and MW-UV processes for the degradation of phenol was less than 10% after 120 minutes of treatment. However, the efficiencies of MW-TiO2 (hydrothermal) and MW-TiO2 (sol-gel) were slightly more than those of the above processes at 12 to 15% after 120 minutes, which might be due to adsorption of the phenol on the surface of TiO2 particles. It also was observed that MW-UV-TiO2 was superior to any other process studied for the degradation of phenol. At natural pH, the degradation efficiency of MW-UV-TiO2 (HT) on 1500 ppm of phenol in water was 23%, and for MW-UV-TiO2 (SG) it was 20%. Hence, it can be concluded that the catalyst (TiO2) prepared by the hydrothermal (HT) method had better catalytic activity than TiO2 prepared by the sol-gel (SG) method, which might be due to its structural and optical characteristics. Of the two developed reactors which are MW and a combined MW-UV reactor, MW-UV combined with TiO2 could be used for most successful degradation of phenol.

Thesis (Ph. D.)--University of Hong Kong, 2007. / Title proper from title frame. Also available in printed format.

The hitting the carbon material looks of hole of ordered structure relatively has its more apparent physics and chemical characteristic in the traditional powder sample, this research makes hitting the carbon material of hole in order to utilize the law of mask works and making and lying between the qualification of the view structure to it of preface structure. Utilize different carbon precursor containing carbon proportion, for instance: Carbon material of hole in cane sugar, phenol aldehyde tree ester and pitch come to prepare; And to the structure of hole, for instance: The hole shrinks the homogeneity, hole shrinking rate ,etc. the physical and not last comparison at chemical property. First of all, utilizing has no emulsification to get together (not add any to hand in and unite pharmaceutical) Styrene the single /last sulfic acid potassium / water prepare by polystyrene ball in system. The styrene thickness is reduced to adjust the single weight ratio to styrene of initial pharmaceutical and look on as, then the ball size of polystyrene is diminished, controlling all kinds of technology of the spheroid, can already produce the polystyrene ball under the diameter 100 nm. Use 4 second silicic acid / ammonia water / deionized water / ethanol prepare and oxidize the silicon ball two times on the other hand, experiment course make use of adjust ammonia water in not reacting ear count than may be controlled and oxidized the ball size of silicon 2 times relatively. Experiment to can produce by the twoes of the 100 nms diameter because it oxidize by silicon ball, cause accord with endure research to a the above-mentioned spheroid particle by rice grades of material size already all fully. The second part of experiment includes the carbon material of carbon proportion to prepare in order to utilize differently out and hit the carbon material of hole in order for the source, thereafter utilize SEM, X-ray and Ramam After the instrument analyzes, sum up the property difference of every carbon material and characteristic trend. The result of study reveals, in order to include carbons carbon material structure of hole prepared out of the carbon material source the lower in proportion, its diameter of average hole is smaller, the shrinking rate of hole is larger, the hole wall is thinner and slightly broken in shape. Another result reveals, the graphite intensity of the carbon material of hole relates to material source own one's share structure of carbon, contain benzene ring many line molecular structure and reticular formation facilitate, raise carbonization graphite intensity react, and molecule layer distance light; The influence containing benzene and surrounding the structure among them is superior to the reticular formation. In addition, the experimental result has revealed the material grade of hole in the average diameter of carbon material of hole has already reached for 350 nm.

Laccase (E.C 1.10.3.2) catalyzes the oxidation of aromatic substrates with the simultaneous reduction of molecular oxygen to water. It has significant potential for use in many applications due to its high reaction rates, broad substrate-specificity, and use of oxygen as an inexpensive co-factor. The objective of this research was to investigate the ability of laccase from Trametes versicolor to catalyze oxidation reactions under a variety of reaction conditions and to model the kinetics of these transformations. Phenol was selected as a model substrate. / Laccase was very stable when incubated at temperatures less than 30°C and pHs between 6 and 7. The optimum pH for phenol transformation was 6, but when present in sufficient quantities, laccase was able to significantly transform phenol at pHs from 4 to 7 and temperatures from 10 to 60°C. Laccase stability was negatively impacted by the presence of four common redox mediators. Of these, 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonate) (ABTS) and 2,2',6,6'-tetramethylpiperidine-N-oxyl (TEMPO) significantly enhanced phenol transformation but large quantities were required, which may limit the feasibility of the use of these mediators in many applications. / A series of kinetic models was developed in order to achieve a better understanding of the mechanisms and kinetics of laccase-catalyzed reactions and to eventually assist in the choice and design of suitable reactor systems. These models were designed to predict the transient oxygen and phenol concentrations during laccasecatalyzed reactions at pH 6 and 25°C. Over the course of developing and validating these models, it was observed that: (1) the rate-limiting step in the catalytic reactions is the reaction between the oxidized form of laccase and phenol; (2) the stoichiometric ratio, which is defined as the molar ratio of phenol transformed to oxygen consumed in the catalytic reaction, was found to increase with phenol concentration in the reaction mixture from a theoretical lower limit of 1 and to approach a theoretical upper limit of 4; and (3) laccase inactivation occurs over the course of the reaction and was found to be dependent on the rate of substrate transformation. / Ultimately, these findings were incorporated into a comprehensive kinetic model to predict transient species concentrations in an open-system environment where the degree of substrate transformation was not limited by oxygen availability. The model accounts for enzyme kinetics, oxygen mass-transfer, variable reaction stoichiometry, and inactivation related to reaction products. Excellent agreement was observed between measured and modeled phenol and oxygen concentrations for a wide range of initial phenol concentrations and enzyme activities. Simplified models were also developed by incorporating an assumption, referred to as the pseudo-steady-state assumption, that at any instant during the reaction, the enzyme achieves an approximate steady-state distribution of its various forms around the catalytic cycle. The pseudo-steady-state assumption had the advantage of reducing the complexity of model equations without sacrificing their predictive abilities and allowing enzyme quantities to be expressed in activity units instead of molar concentrations.

The biocatalysis of tyrosinase was investigated in selected organic solvent media, using catechin as substrate. The results showed that the optimal enzymatic activity was obtained at pH 6.2, 6.6, 6.0 and 6.2 in heptane, toluene, dichloromethane and dichloroethane media, respectively. The kinetic studies indicated that the Km values were 5.38, 1.03, 2.52 and 4.03 mM, for the enzymatic reaction in heptane, toluene, dichloromethane and dichloroethane media, respectively, whereas the Vmax values were 12.2 x 10--4, 3.3 x 10--4, 14.7 x 10--4 and 12.0 x 10--4 deltaA mug protein--1 sec--1 , respectively. The results showed that the change in acetone concentration, used as co-solvent for the tyrosinase biocatalysis, from 5 to 30% (v/v) in the heptane medium resulted in a decrease of 4.3 to 96.7% in enzymatic activity. However, the presence of 12.5, 22.0 and 22.0% of acetone in the media of dichloromethane, dichloroethane and toluene resulted in a maximal increase in enzymatic activity of 42.6, 71.8 and 92.1%, respectively. Moreover, the biocatalysis of tyrosinase in dichloromethane and heptane reaction media, using model phenolic substrates was also investigated. The Km values for the tyrosinase biocatalysis in dichloromethane medium, using 4-methyl catechol, catechol and catechin as substrates, were 2.21, 2.36 and 2.52 mM, respectively, whereas the Vmax values were 5.1 x 10--4 , 6.0 x 10--4 and 14.7 x 10 --4 deltaA mug protein--1 sec --1, respectively. In addition, the Km values for tyrosinase biocatalysis in the heptane medium, using p-cresol, catechol and catechin as substrates, were 1.07, 4.32 and 5.38 mM, respectively, whereas the Vmax values were 0.8 x 10--4, 1.0 x 10 --4 and 12.2 x 10--3 deltaA mug protein--1 sec--1, respectively. The characterization of the end products resulting from the tyrosinase biocatalysis, using selected substrates, was carried out by spectrophotometeric scanning, differential scanning calorimetry and pyrolysis/gas chromatography coupled to

Phenol oxidases mediate the degradation of recalcitrant compounds, polyphenolics, in wetland soils and are considered to play a key role in the microbial carbon cycle of peatlands which predominate in boreal biomes. In order to validate a method for quantification of oxidative enzyme activity in acidic wetland environments, the relationship between pH and substrate oxidation was studied using the standard enzyme tyrosinase and in soils collected from six freshwater wetlands including three marshes in north Florida and peatlands of northern Minnesota. Phenol oxidase (PO) activity was quantified with two commonly used assay substrates, ABTS (2,2'-azino-bis(3-ethylobenzthiazoline-6-sulfonic acid) and L-DOPA (L-3,4-dihydroxyphenylalanine), across a pH range of 4 to 7 which matched the in situ pH range of the studied wetlands. The PO assay is sensitive and activity could be detected with either substrate across a pH range of 4 to 7. However, with the standard enzyme tyrosinase, it was shown that a large change or threshold in oxidation rates occurred at pH 5. At pH < 5, L-DOPA oxidation rates were greatly diminished and ABTS oxidation was at a maximum. Above pH 5, ABTS oxidation occurred at much slower rates and L-DOPA oxidation was at a maximum. The pH response of PO activity in wetland soils corroborated observations made with tyrosinase. Thus, ABTS is recommended to be an effective substrate for the quantification of PO activity at an in situ pH of < 5, while L-DOPA is recommended at an in situ pH of > 5. In soils collected from a northern Minnesota peatland, assays conducted at an in situ pH of 4 showed one to two orders of magnitude higher rates of PO activity in solid phase peat in comparison to porewater, indicating that the majority of PO activity is associated with the peat. At three Minnesota peatland sites, PO activity was shown to attenuate with depth in agreement with the activities of other enzymes and with rates of peat decomposition.

Thesis (Ph. D.)--Columbia University, 1942. / Vita. Bibliography: p. 22.

Thesis (Ph. D.)--Columbia University, 1938. / Vita.

Thesis (Ph. D.)--Columbia University, 1945. / "Lithoprinted." Vita. Bibliography: p. 19.