Scanning Electrochemical Microscopy (SECM) feedback mode and substrate generation-tip collection (SG-TC) mode coupled with chronoamperometric approach were used to investigate H-2 oxidation and hydrogen evolution reaction (HER) at a polyaniline (PAni) coated highly oriented pyrolytic graphite (HOPG) electrode. Using the former mode, the heterogeneous electron transfer (ET) kinetics for H-2 oxidation was studied, while the latter mode allowed mapping of the distribution of local [H-2] at the nanoparticulate/aqueous interface, followed by monitoring the transients at the tip. These preliminary studies demonstrate that SECM is useful in evaluating the activity of nanophase electrocatalysts. Particularly, if one employs nanometer-sized tips or hydrodynamic microjet electrodes where the mass transfer rate is significantly high, it should be possible to investigate the ET kinetics more accurately.

Key words: Ceramic tile; water absorption; bulk density; firing shrinkage; modulus of ruptureDOI: http://dx.doi.org/10.3329/bjsr.v24i2.10775 Bangladesh J. Sci. Res. 24(2):169-180, 2011 (December)

Scanning electrochemical microscopy (SECM) has been used to investigate quantitatively the photodegradation kinetics of 4-chlorophenol (4-CP), in aerated and oxygenated aqueous solutions, at back-illuminated TiO2 films deposited from a suspension of Degussa P25 TiO2 powder at the end of an optical fibre. A potentiometric Ag/AgCl ultramicroelectrode (UME), positioned at a known distance above the TiO2 film, was used to monitor directly the Cl- production from the photodegradation of 4-CP. The effects of both light intensity and 4-CP concentration were investigated and the associated kinetics were determined. Amperometric measurements with a Pt UME demonstrated that O-2 was depleted significantly adjacent to the TiO2 surface under these conditions. A theoretical model, which employs a Langmuir-Hinshelwood type kinetic equation, has been developed to interpret the kinetics of the photodegradation process and determine the associated quantum efficiency.

The channel flow method with electrochemical detection (CFMED) has been used to investigate the photoelectrochemical reduction of O-2 at UV-illuminated TiO2 surfaces in both aerated and oxygenated solutions. This approach detects O-2 amperometrically at a working detector electrode strategically positioned downstream of a TiO2 surface, comprising a thin film of particulate material (Degussa P-25). By monitoring the transport-limited current as a function of flow rate with and without illumination, it has been possible to analyze the reaction kinetics in terms of various models proposed in the literature. The kinetics of the reduction process are reported, and the implications for semiconductor photocatalysis, are discussed.

The channel flow method with electrochemical detection (CFMED) has been used to investigate the photoelectrochemical reduction of O2 at UV-illuminated TiO2 surfaces in both aerated and oxygenated solutions. This approach detects O2 amperometrically at a working detector electrode strategically positioned downstream of a TiO2 surface, comprising a thin film of particulate material (Degussa P-25). By monitoring the transport-limited current as a function of flow rate with and without illumination, it has been possible to analyze the reaction kinetics in terms of various models proposed in the literature. The kinetics of the reduction process are reported, and the implications for semiconductor photocatalysis are discussed.

A new in situ electrochemical actinometry method has been developed and used to determine the light flux through a quartz fibre, employed in a scanning electrochemical microscopy (SECM) system developed to study the kinetics of interfacial photochemical processes. In this system an ultramicroelectrode (UME) probe is positioned with high precision at a known distance close to the end of the fibre, through which light is guided, and used to detect reactants or products of the ongoing photochemical process. The microelectrochemical actinometer was developed using the well-known liquid phase potassium ferrioxalate actinometer. The approach involved recording the steady-state current for Fe( iii ) reduction at a 25 µm diameter disc-shaped ultramicroelectrode (UME) positioned close to the fibre. A step function in the light flux through the fibre (off-on) was then applied which led to a depletion in the local Fe( iii ) concentration. The resulting chronoamperometric behaviour at the UME, as a consequence of the solution photochemical process, was measured. A theoretical model has been developed to simulate experimental current-time profiles, which enabled measurements of the light flux initiating the photoprocess.

Using scanning electrochemical microscopy (SECM) we have measured quantitatively the depletion of O-2 during the photodegradation of 4-chlorophenol at supported TiO2 films for the first time and established the connection between Cl- formation and O-2 depletion rates.

The channel flow method with electrochemical detection (CFMED) of Cl− ion product has been applied to the photodegradation kinetics of four chlorophenols (CPs) undergoing photolysis (λ>300nm) at a TiO2 film. The effects on the rate of photomineralisation of (i) varying CP concentration, (ii) O2 concentration, (iii) flow rate, (iv) light intensity and (v) supporting electrolyte, have been examined. Of particular note are the accelerative effects of increasing [O2] and removing background electrolyte. The kinetics have been shown to fit models derived from Langmuir–Hinshelwood kinetics; at high [CP], the rates fit a surface-limited model, but at low [CP], this model proves inadequate and a mixed-control model, incorporating mass transfer as an additional parameter, is shown to be necessary. The approach developed allows the conditions under which mass transfer is important in controlling photomineralisation rates to be identified.

Pakistan's security environment has deteriorated through its adoption of a declared nuclear weapons posture in May 1998. Internal fissures have widened along regional and sectarian lines as the Pakistani economy falters, unable to sustain even limited external sanctions following decades of internal mismanagement. Tensions with India have also increased as Pakistan's security managers adopt interventionist policies, based on a misplaced belief in the deterrent value of nuclear weapons. The international community, in particular, the USA's failure to reverse South Asian nuclear proliferation, has emboldened Indian advocates of nuclear deployment. If India deploys nuclear weapons and their delivery systems, Pakistan will follow suit. Operation-ready nuclear weapons will increase the prospects of an India-Pakistan conflict that could assume a nuclear dimension. Pakistan's nuclear weapons capability will not prevent an Indian conventional attack nor will the presence of nuclear weapons deter an Indian accidental, unauthorised or preventive nuclear attack. Changed domestic and external priorities alone can buttress Pakistani security.

The kinetics of Cl- production from the UV-photocatalysed degradation of aqueous 4-chlorophenol (CP), by a thin TiO2 (Degussa P25) film, in both aerated and oxygenated solutions, have been determined by the channel flow method with electrochemical detection. The experimental approach allows surface kinetics and mass transport effects to be readily resolved. For typical irradiation intensities of (0.7–2.0)×1017 quanta cm-2 s-1, the results obtained with dilute CP solutions (⩽0.5 mM), in particular, clearly demonstrate that there is a range of practically important conditions where mass transport plays a role in controlling the kinetics of the process. When these effects are considered, the surface kinetics are consistent with the Langmuir–Hinshelwood model.

Research Article| August 01 1998 Public Opinion and Nuclear Options for South Asia Samina Ahmed, Samina Ahmed Search for other works by this author on: This Site PubMed Google Scholar David Cortright, David Cortright Search for other works by this author on: This Site PubMed Google Scholar Amitabh Mattoo Amitabh Mattoo Search for other works by this author on: This Site PubMed Google Scholar Asian Survey (1998) 38 (8): 727–744. https://doi.org/10.2307/2645580 Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Cite Icon Cite Search Site Citation Samina Ahmed, David Cortright, Amitabh Mattoo; Public Opinion and Nuclear Options for South Asia. Asian Survey 1 August 1998; 38 (8): 727–744. doi: https://doi.org/10.2307/2645580 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAsian Survey Search This content is only available via PDF. Copyright 1998 The Regents of the University of California Article PDF first page preview Close Modal You do not currently have access to this content.