Lung-Chuan Chen

In situ DRIFT and kinetic studies of photocatalytic degradation on benzene vapor with visible-light-driven silver vanadates.

The visible-light active silver vanadates with different types of crystallines (Ag(4)V(2)O(7) and Ag(3)VO(4) phases) were synthesized by an environmentally friendly aqueous process. The parameters of hydrothermal temperature and hydrothermal time were tuned to maximize the photocatalytic efficiency for the decomposition of benzene vapor under visible-light irradiation. The quantum efficiencies of the photocatalysts are compared on the basis of the crystalline phases, surface area, intensity of surface hydroxyl groups, and Brönsted acid sites. From the results of DRIFTS studies, the photocatalytic activities strongly depend on the intensities of the Brönsted acidity and hydroxyl groups presented on the silver vanadates. The sample synthesized at 140 degrees C and 4h (HM140) exhibits the best photocatalytic activity; it has a reaction rate constant (k(app)) of 1.42 min(-1), much higher than that of P25 (k(app)=0.13 min(-1)). For an irradiation time of 720 min, the mineralization yields of benzene were 48% and 11% for HM140 and P25, respectively. Based on the short-term decrease of benzene concentration and the long-term increase of CO(2) concentration, the photocatalytic ability of the HM140 sample is significantly superior to that of P25. The highest activity can be attributed to the synergetic effects of the richest Brönsted acid sites, and a favorable crystalline phase combined with abundant surface hydroxyl groups.

Preparation of methacrylic acid-modified rice husk improved by an experimental design and application for paraquat adsorption.

Methacrylic acid (MAA) grafted rice husk was synthesized using graft copolymerization with Fentons reagent as the redox initiator and applied to the adsorption of paraquat. The highest grafting percentage of 44.3% was obtained using the traditional kinetic method. However, a maximum grafting percentage of 65.3% was calculated using the central composite design. Experimental results based on the recipes predicted from the statistical analysis are consistent with theoretical calculations. A representative polymethacrylic acid-g-rice husk (PMAA-g-rice husk) copolymer was hydrolyzed to a salt type and applied to the adsorption of paraquat. The adsorption equilibrium data correlate more closely with the Langmuir isotherm than with the Freundlich equation. The maximum adsorption capacity of modified rice husk is 292.5mg/g-adsorbent. This value exceeds those for Fullers earth and activated carbon, which are the most common binding agents used for paraquat. The samples at various stages were characterized by solid-state (13)C NMR spectroscopy.

Preparation of acrylic acid-modified chitin improved by an experimental design and its application in absorbing toxic organic compounds.

Chitin grafted poly (acrylic acid) (chi-g-PAA) is synthesized and characterized as an adsorbent of toxic organic compounds. Chi-g-PAA copolymers are prepared using of ammonium cerium (IV) nitrate (Ce(4+)) as the initiator. The highest grafting percentage of AA in chitin obtained using the traditional technique is 163.1%. A maximum grafting percentage of 230.6% is obtained using central composite design (CCD). Experimental results are consistent with theoretical calculations. The grafted copolymer is characterized by Fourier transform Infrared spectroscopy and solid state (13)C NMR. A representative chi-g-AA copolymer is hydrolyzed to a type of sodium salt (chi-g-PANa) and used in the adsorption of malachite green (MG), methyl violet (MV), and paraquat (PQ) in aqueous. The monolayer adsorption capacities of these substances are 285.7, 357.1, and 322.6 mg/g-adsorbent, respectively. Thermodynamic calculations show that the adsorption of MG, MV, and PQ are more favored at diluted solutions. The high adsorption capacity of chi-g-PANa for toxic matter indicates its potential in the treatment of wastewater and emergency treatment of PQ-poisoned patients.

Effect of ZnO Seed Layer and TiO2 Coating Treatments on Aligned TiO2/ZnO Nanostructures for Dye-Sensitized Solar Cells

A chemical bath deposition (CBD) method was applied to grow zinc oxide nanorod arrays on transparent conductive oxides acting as templates for the synthesis of TiO2/ZnO nanostructures (TiO2/ZNR) followed by HCl etching, and then these nanostructures were assembled as anodes in dye-sensitized solar cells. The ZnO nanorods, predominantly grew with good crystallinity along c-axis, exhibit wurtzite structure with smooth surface. Etching of the TiO2/ZNR by HCl changes the most preferential crystal plane of ZnO from (002) to (100) and significantly increases the atomic ratio of Ti/Zn. Optical absorption measurements indicate a band gap energy of 3.1 eV for ZNR and TiO2/ZNR. Increasing the spin coating time (SCT) of TiO2 on ZNR increases the PL intensity. The seed layer number (SLN) of ZnO exerts moderate influence on the photo-to-electricity conversion and an optimum SLN was observed for this study.