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This paper presents an in situ, nondestructive method of monitoring [Cl.sup.-] concentrations and pH values at the steel/ concrete interface. The Ag/AgCl electrodes prepared by the electrochemical anodization and the Ir/Ir[O.sub.2] electrodes prepared by thermal oxidation in carbonate served as [Cl.sup.-] concentration and pH sensors, respectively. The potentiometric response of the Ag/AgCl electrode to the logarithm of [Cl.sup.-] concentrations ranging from 1 x [10.sup.-4] to 2 M in saturated Ca[(OH).sub.2] solution simulating the inner electrolytic medium of concrete shows good linearity. The Ir/Ir[O.sub.2] electrode also exhibits an ideal Nernstian response in the range of pH 1-14. The Ag/AgCl and Ir/ Ir[O.sub.2] electrodes were combined into a multiplex [Cl.sup.-]/pH sensor, and the sensor was embedded in concrete close to the steel/concrete interface to realize an in situ and long-term measurement of [Cl.sup.-] concentrations and pH values. The results indicate that the combined sensor is robust and sensitive enough to in situ measure [Cl.sup.-] concentrations and pH quantitatively at the steel/concrete interface, which is of indispensable importance to the study of corrosion and protection of the steel in concrete.

Abstract: Shell–core nanostructured ZnS/CdS quantum dots (QDs) were assembled uniformly on the surface of TiO2 nanotube arrays by sequence chemical bath deposition (CBD) of CdS and ZnS in alcohol solution system. The morphology and chemical composition of the obtained composite thin films were characterized by scanning electron microscopy, transmission electron microscopy and energy dispersive X-ray spectroscopy. The effect of solvent and immersion cycles for the photoanode preparation on the photoelectrochemical activity and photogenerated cathodic protection property was investigated. It is found that the nanostructured CdS QDs (20 cycles) coated on TiO2 nanotube arrays show a remarkably enhanced photoelectrochemical activity. The coating of ZnS QD shells (5 cycles) is able to improve the stability of the CdS@TiO2 photoanode under white-light irradiation. After the irradiation light is turned off, the photogenerated cathodic protection of 403 stainless steel (403SS) can be remained for several hours. [Copyright &y& Elsevier]