Adsorption/combustion-type gas sensors employing mesoporous γ-alumina (mp-Al2O3) powders loaded with core(Au)/shell(Pd) nanoparticles, which were synthesized by sonochemical reduction, (n(Au/Pd)/mp-Al2O3, n: the amount of Au/Pd nanoparticles loaded, Pd loaded onto the mp-Al2O3 powders was reduced (≤ 0.5 wt%). These sensing properties seem to be largely dependent on the morphological and compositional characteristics of Au and Pd loaded on the γ-alumina surface. In addition, the n(Au/Pd)/mp-Al2O3 sensors showed much larger response to ethanol than those to toluene and n-hexane, probably because of the difference in the magnitude of polarity (dipole moment and dielectric constant) of their molecules. However, the sensors obviously detected even 10 ppm n-hexane with the extremely low dipole moment and dielectric constant. These results promise that the n(Au/Pd)/mp-Al2O3 sensors can detect the lower concentration of these gases as well as other VOCs.

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On the added-row reconstructed Ag(110)(nx1)-O surfaces where one-dimensional -Ag-O-Ag-O- chains arrange periodically, the clean-off reaction of O adatoms by CO was investigated using variable temperature scanning tunneling microscopy (VT-STM). Based on the in situ STM observations of the surface structure variation in the course of the reaction at various temperatures, we found that the reaction kinetics are significantly affected by the structural transition of AgO chains from a solid straight line configuration to dynamically fluctuating configurations. Below 230 K where the chains are straight, the reaction takes place only at the end of the chains, so that the reaction progresses in the zero-order kinetics with the reaction front propagating along the chain. The temperature dependence of the reaction rates yields the activation barrier of 41 kJ/mol and the preexponential factor of 1.7 x 10(3) cm(-2) s(-1). At room temperature, the reaction rate is drastically accelerated when almost half of the O adatoms are eliminated and the chains start fluctuating. The dynamic formation of active sites equivalent to the end of chains upon the chain fluctuation results in the nonlinear increase of the reaction rate.

The angular distribution of desorbing product N 2 was studied in N 2 O decompositions on Rh͑110͒ in the temperature range of 60-700 K. The N 2 desorption collimates along 62°-68°off normal toward either the ͓001͔ or ͓001͔ direction in a transient N 2 O decomposition below ca. 470 K or in the steady-state N 2 O + CO reaction above 540 K. In the steady-state reaction at the temperature from ca. 470 to 540 K, however, the collimation angle shifts from 62°to 45°with decreasing surface temperature. This angle shift is ascribed to the steric hindrance by coadsorbed CO because the N 2 collimation in transient N 2 O decomposition at around 65°is recovered in the range of 380-500 K by an abrupt CO pressure drop followed by the decrease in CO coverage. N 2 O is oriented along the ͓001͔ direction before dissociation. A scattering model of the nascent N 2 by adsorbed CO is proposed, yielding smaller collimation angles.

The effectiveness of hypochlorite cleaning for fouling mitigation of a prototype chlorineresistant nanofiltration (NF) membrane was assessed for direct filtration of a secondary treated effluent. The chlorine resistance and separation performance of the prototype NF membrane were also compared to commercial NF and reverse osmosis membranes. The prototype chlorine resistant NF membrane did not show any changes in permeability and conductivity rejection after exposing a NaOCl solution for up to 5×10 4 ppm-h. By contrast, a considerable deterioration in rejection was observed for the other two commercial membranes. Direct filtration of a secondary treated effluent by the prototype NF membrane resulted in a progressive permeability reduction by up to 25% after 10 h of filtration. The membrane permeability was fully restored by hypochlorite cleaning with a 2,000 ppm NaOCl solution for 1 h. Effective permeability recovery by hypochlorite cleaning was demonstrated with multiple hypochlorite cleaning cycles. Membrane fouling and hypochlorite cleaning were also simulated using solutions containing a model foulant (sodium alginate, humic acids or bovine serum albumin). Among them, an insufficient permeability recovery was observed for membrane fouling caused by humic acids. Further research is recommended to develop an improved hypochlorite cleaning protocol to control various membrane fouling.

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The kinetics of the clean-off reaction of O adatoms by CO on Ag(110)-(2x1)-O is investigated by scanning tunneling microscopy. The reaction is accelerated in the lower O coverage range where AgO chains with (nx1) (n> or =4) configurations show significant structural fluctuation. Simulations based on the Ising model are used to provide a quantitative understanding of the acceleration, which originates from the dynamical formation of active O adatoms by fluctuation of AgO chains.

Mesoporous (mp-) Al2O3 powders loaded with n wt% MO (Bi2O3, CeO2, Fe2O3, NiO, RuO2 or ZrO2 (n = 1, 5, 10)) and/or 1 wt% Pt nanoparticles (1.0Pt/nMO-mp-Al2O3) were synthesized by an impregnation or a sonochemical reduction method. The sensor-signal profiles typically consist of one large dynamic response and subsequent static response, which originate from the flash catalytic combustion of these adsorbates and general catalytic combustion, respectively, during the pulse heating. The 1.0Pt/nCeO2-mp-Al2O3 sensor showed the largest static response to all target VOCs (ethanol, ethyl acetate, acetone, benzene and toluene), probably due to the largest specific surface area (ca. 187 m2 g-1) among the sensors examined. In addition, the sensor also showed the largest dynamic response to most of target VOCs except for toluene. On the other hand, 1.0Pt/10Bi2O3-mp-Al2O3 sensor showed the largest dynamic response to toluene and the dynamic response speed of the 1.0Pt/10Bi2O3-mp-Al2O3 sensor to toluene was faster than that of the 1.0Pt/10CeO2-mp-Al2O3 sensor. This is probably because of more accelerated catalytic combustion behavior and the adsorption property of toluene over 1.0Pt/10Bi2O3-mp-Al2O3 than those over 1.0Pt/10CeO2-mp-Al2O3.