Catalysis by Using TiO2 Nanoparticles and Nanotubes

TiO2 has attracted considerable attention due to its stability, non-toxicity, low cost, and great potential for use as a photocatalyst in environmental applications. Since strong metal-support interaction (SMSI) of titania-supported noble metals was first reported in 1978, titania supported catalyst has been intensively studied in heterogeneous catalysis. However, the effective catalytic activity was restricted due to the low surface area of TiO2. Recently, TiO2-based nanotubes were extensively investigated because of their potentials in many areas such as highly efficient photocatalysis and hydrogen sensor.In the present study, formation of titanium oxide (TiO2) nanotubes was carried out by hydrothermal method, with TiO2 nanoparticle-powders immersed in concentrated NaOH solution in an autoclave at 110 ℃. Preparation of nano-size Pt on TiO2-nanoparticles or TiO2-nanotubes was performed by photochemical deposition method with UV irradiation on an aqueous solution containing TiO2 and hexachloroplatinic acid or tetrachloroauric acid. The TEM micrographs show that TiO2-nanotubes exhibit ～300 nm in length with an inner diameter of ～ 6 nm and the wall thickness of ～ 2 nm, and homogeneous nanosize Pt particles (～ 2 nm) were well-dispersed on both nanoparticle- and nanotube- titania supports. It also shows the nanotube morphology was retained up2o n Pt-immobilization. Nitrogen adsorption isotherm at 77K resulted a high surface area (～ 200m/g) of TiO2-nanotubes, which is about 40 times greater than that of "mother" TiO2 nanoparticles (～5 m/g). All the spectroscopic results exhibited that the nanotube structure was not significantly affected by the immobilized Pt particles. Ti K-edge XANES spectra of TiO2 nanotube and Pt/TiO2-nanotube represent that most titanium are in a tetrahedral coordination with few retained in the octahedral structure.In the in-situ FT-IR experiments, an IR cell was evacuated to a pressure of 10-5 torr at room temperature as soon as the catalyst-pellet, Pt/TiO2 or Pt/TiO2-nanotube, was placed inside the cell.Then, 60 torr of hydrogen was introduced into the cell and subsequently the temperature was programmed to increase from room temperature to 300℃ at a constant heating rate of 5℃/min.For Pt/TiO2, an IR peak at 2083 em-1 started to appear at 200℃ with a maximum intensity at 250℃ and then decreasing as temperature increased. The 2083 em-1 IR peak corresponds to the linearly adsorption of CO on the well-dispersed Pt sites. Simultaneously, the IR bands of gaseous methane at 3016 em-1 started to appear at 225℃ and the peak intensity increased with temperature. The results reveal that Pt/TiO2 can adsorb gaseous CO2 and further catalyzes the reduction of CO2 by H2 through the intermediate CO, which further produces gaseous methane. While for the Pt/TiO2-nanotube catalyst, methane was produced at relatively low temperature, 100℃, and it catalyzed the direct conversion of CO2 to CH4. The absence of intermediate CO-adsorption signals durinng the temperature programmed process indicates that the prepared TiO2 nanotube-supported nanosize Pt possesses a potent capability for CO2 adsorption and highly catalytic activity in the hydrogenation of CO2, and was superior to the conventional Pt/TiO2 catalyst. The catalytic activity of Pt/TiO2-nanotube was indeed significantly enhanced by the high surface area of TiO2-nanotubes.Details will be discussed.     

Determination of bisbenzylisoquinoline alkaloids by high-performance liquid chromatography (II)

After the earlier analysis of nine bisbenzylisoquinoline alkaloids with ion pair chromatography, seven other bisbenzylisoquinoline alkaloids were analyzed using gradient elution with an acetonitrile-phosphate buffer (pH 8.0) mixture, and UV detection. Four alkaloids were detected in the stem woods of a Lauraceous plant, Dehaasia triandra Merr. and their contents determined. LC-MS suggested that a major unknown compound in the plant was also a bisbenzylisoquinoline alkaloid.     

New cyclopropyl-triterpenoids from the aerial roots of Ficus microcarpa

Four new cyclopropyl-triterpenes, 27-nor-3beta-hydroxy-25-oxocycloartane (1), (22E)-25,26,27-trinor-3beta-hydroxycycloart-22-en-24-al (2), 3beta-acetoxy-15alpha-hydroxy-13,27-cyclours-11-ene (3), 3beta-acetoxy-12alpha-formyloxy-13,27-cycloursan-11alpha-ol (4), together with (23E)-27-nor-3beta-hydroxycycloart-23-en-25-one (5) were isolated from the aerial roots of Ficus microcarpa. Compounds 3 and 4 are rare 13,27-cycloursane-type triterpenes. Their structures were elucidated by spectroscopic and chemical methods.     

Four new podocarpane-type trinorditerpenes from the bark of Taiwania cryptomerioides

Further studies on the bark of Taiwania cryptomerioides found four new podocarpane derivatives, 1beta,13-dihydroxy-8,11,13-podocarpatriene (1), 14,18-dihydroxy-13-methoxy-8,11,13-podocarpatriene (2), 1beta,14-dihydroxy-13-methoxy-8,11,13-podocarpatriene-2,7-dione (3), and 3beta,14-dihydroxy-13-methoxy-8,11,13-podocarpatrien-7-one (4), together with a known 1beta,13,14-trihydroxy-8,11,13-podocarpatrien-7-one (5). Those structures were elucidated principally from spectral evidence.     

New lignans from the heartwood of Chamaecyparis obtusa var. formosana

Four new lignans, 3',4'-O,O-demethylenehinokinin (1), chamalignolide (2), 8'beta-hydroxyhinokinin (3) and 7beta,8beta-epoxyzuonin A (4), as well as (-)-hinokinin (5), and (-)-zuonin A (6), were isolated from the heartwood of Chamaecyparis obtusa var. formosana. The structures of these lignans were unambiguously determined by spectroscopic methods. And the absolute configuration of 1 was elucidated with a circular dichroism (CD) spectrum.     

Stability of a dispersion of particles covered by a charge-regulated membrane: effect of the sizes of charged species

The influence of the sizes of charged species on the stability of a colloidal dispersion is investigated theoretically. We consider the case where a particle comprises a rigid core and an amphoteric, charge-regulated membrane layer, which simulates biocolloids and particles covered by artificial membranes. A modified Poisson-Boltzmann equation, which takes the sizes of all the charged species into account, is adopted to describe the electrical field. The effects of other key parameters such as electrolyte concentration, pH, and the valence of counterions on the behavior of a dispersion are also examined. We show that the larger the effective size of the counterions, the greater the stability ratio, which is consistent with experimental observations in the literature.     

Modified nucleosides in human serum.

Methylated purines and pyrimidines derived from the degradation of transfer ribonucleic acid have been shown to be excreted in abnormal amounts in the urine of patients with cancer. Recent technology developed by Gehrke and Kuo has allowed the separation and quantification of modified nucleosides in serum using reversed-phase high-performance liquid chromatography with diode-array measurement. Serum levels of ten modified nucleosides were measured in 37 normal healthy adults to establish normal values and to correlate activity with age and sex. In addition, serum levels of patients with several malignancies were measured to determine activity in these diseases. Levels of modified nucleosides in normal individuals were consistently reproducible and showed no significant variation among males versus females or with age. Patients with malignant diseases showed consistent elevations and these were highest in patients with more advanced disease. The evidence of no significant differences in the mean levels of modified nucleosides in serum with age or sex in normal adults and elevations in patients with malignancies demonstrate the potential value of modified nucleosides as cancer biomarkers.     

Electrical interaction between two cylinders with an ion-penetrable charged membrane in an oil/water interface

The electrical interaction between two long, parallel cylinders each is covered by an ion-penetrable charged membrane immersed in an oil/water interface is investigated. The effects of contact angle, radius of cylinder, and membrane thickness on the electrical interaction force are examined. The results of numerical simulation reveal that the following conditions lead to a greater electrical interaction force: (i) a larger contact angle, i.e. a larger fraction of a cylinder in the oil phase; (ii) a larger cylinder radius; and (iii) a thinner membrane. For a fixed ionic strength, the electrical interaction force is insensible to the type of electrolytes in the water phase, in general. However, if two cylinders are close enough, then the higher the valence of counterions the greater the electrical interaction force.     

Decolorization of AZO dyes using catalytic ozonation

Decolorization of C.I. Reactive Red 2 (RR2) and C.I. Acid Orange 6 (AO6) using a catalytic ozonation system was evaluated. The decolorization rates for RR2 and AO6 were accelerated by at least 30% by adding MnO₂ to the O₃ system; additionally, the decolorization rate increased as the MnO₂ dosage and ozone power consumption increased. Enhanced MnO₂ catalytic ozonation was more apparent for AO6 than for RR2.     

Aqueous polymerization of acrylamide initiated by oxygenated cobalt(III) triethylenetetramine complex

Polymerization of acrylamide was thermally initiated by the oxygenated cobalt( III ) triethylenetetramine complex. Rate, conversion, and molecular weights obtained are favorable comparable to those initiated by K₂S₂O₄ and K₂S₂O₈ initiators. An induction period is about 3 mins. The value of K_df at 60°C is 6.75 × 10^?5 s^?1, and the chain transfer to monomer constant is 1.2 × 10^?5. The rate dependence obtained are a half order on the initiator concentration and a 1.38 order on the monomer concentration. The mole fraction of combination termination occurred in the overall termination reactions evaluated is 0.746.