Novel chitosan-based granular adsorbents were developed for enhanced and selective separation of heavy metal ions. The research included the synthesis of chitosan hydrogel beads, the cross-linking of the hydrogel beads with ethylene glycol diglycidyl ether (EGDE) in a conventional and a novel amine-shielded method, the functionalization of the chitosan beads through surface grafting of polyacrylamide via a surfaceinitiated atom transfer radical polymerization (ATRP) method, and the examination of the adsorption performance of the various types of chitosan beads in the removal of heavy metal ions. It was found that chitosan beads were effective in heavy metal adsorption, the conventional cross-linking method improved the acidic stability of the beads but reduced their adsorption capacity, the novel amine-shielded cross-linking method retained the good adsorption capacity while it improved the acidic stability of the beads, and the grafting of polyacrylamide on chitosan beads not only enhanced the adsorption capacity but also provided the beads with excellent selectivity for mercury over lead ions. XPS analyses indicated that the adsorption of metal ions on chitosan beads was mainly attributed to the amine groups of chitosan, the novel amine-shielded cross-linking method preserved most of the amine groups from being consumed by the cross-linking process and hence improved the adsorption capacity of the cross-linked chitosan beads, and the many amide groups from the polyacrylamide grafted on the chitosan beads increased the adsorption capacity and also made possible selective adsorption of mercury ions because the amide groups can form covalent bonds with mercury ions.

A high-temperature potentiometric CO sensor was developed by coating a mixture of CuO/ZnO over one of the .platinum electrodes of a cell with a yttria-stabilized zirconia solid electrolyte. It showed good CO sensing characteristics over the temperature range of 450-550~ and concentration range of 0-10,000 ppm of CO in air. In particular, high sensitivity coupled with reasonably fast response and baseline recovery characteristics were observed at 450~ for CO concentrations below 3,000 ppm. The sensing mechanism and operating system were adequately described by a proposed mathematical model. The model relates the induced cell EMF to the various rate phenomena occurring in the oxide layer such as diffusion, adsorption, and surface catalytic oxidation of the adsorbed carbon monoxide by the gaseous oxygen.High-temperature potentiemetric oxygen sensors with solid electrolyte such as yttria-stabilized zireonia are essentially oxygen concentration galvanic cells. An electromotive force (EMF) is induced when the concentration of the oxygen in the sample gas in contact with one of the electrodes is different from that in a reference gas in contact with the other electrode. These sensors have been used in industrial alarm and control systems for monitoring and control of the oxygen concentration in a gas stream 1-6 and for the control of air-fuel ratio in internal combustion engines as in automobiles. 3 In the oxygen concentration cell pie2, Pt/yttria stabilized ZrO2/Pt,P~= where the partial pressure of oxygen, Po2 > P~o2, the two half-cell reactions are 02 + 4e --> 2 02. the cathodic reaction at I 2 02 --> 02 + 4e the anodic reaction at II The net cell reaction is the transfer of oxygen from the high to the low pressure side and the electrons in the opposite direction. The EMF~ E, of the cell is given by the Nernst's equation aswhere R is the molar gas constant, T the temperature, and F the Faraday constant. Okamoto et al.7 used the same principle in their development of a high-temperature carbon monoxide sensor by coating one of the platinum electrodes with an alumina-platinum CO oxidation catalyst. In a gas stream where the partial pressure of 02 and CO are Po~2 and PcBo, respectively, the oxide catalyst catalyzes the oxidation of CO. The partial pressures, P1 and P~o, at the 02 catalyst-covered platinum electrode are, respectively, smaller than PoB2 and Pc~o at the bare electrode. An EMF is therefore induced in the cell. When all other operating conditions are constant, its magnitude depends on the CO concentration. Such a galvanic cell Po~, P~o/Catalyst/P~2, P~o, Pt/stabilized ZrO2/Pt, Po2,S Pco' B is a useful high-temperature CO sensor and is used simply by inserting it in the gas stream unlike those without the catalyst coating where one electrode is exposed to the test mixture while the other is exposed to a reference mixtureY CuO/ZnO/A12Q is an established industrial catalyst for water-gas generation and synthesis of methanol. 1~ Carbon monoxide was found to be strongly chemisorbed on Cue but rather weakly on ZnO. ...

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