Dependences of ZnO Photoinduced Hydrophilic Conversion on Light Intensity and Wavelengths

Abstract

The present study explored the effect of light intensity and spectral variation of the actinic light on the hydrophilic conversion of the surface of ZnO nanocoatings. The dependence on light intensity indicates that both formation and destruction of the surface hydrophilic states occurs in parallel. The proposed kinetic mechanism corresponds well with experimental dependences. The spectral dependence of the photoinduced hydrophilic conversion of the ZnO surface suggests the important role of electronic photoexcitation of the solid. Similarity between the spectral distributions of the efficiency of photoinduced hydrophilic conversion and the ratio between the surface concentrations of electrons and holes (estimated on the basis of the ratio between quantum yields of oxygen and methane photostimulated adsorption) infers that the reason for the hydrophilicity alteration is the surface charge redistribution caused by actinic light.

In Situ Determination of the Water Condensation Mechanisms on Superhydrophobic and Superhydrophilic Titanium Dioxide Nanotubes

“…This conclusion is also extensible to the similar behavior of other photoactive 1D nanostructured surfaces, like supported ZnO nanowires. [36][37] Our findings also support a revised description of the dropwise water condensation onto apparent superhydrophobic nanostructures on the illumination conditions, [56] as well as to the industrial fabrication of anti-freezing surfaces. [19] EXPERIMENTAL METHODS Sample preparation: Vertically oriented domed-TiO2 nanotubes samples, with typical individual thicknesses in the range of 200-500 nm and a length of several microns, were fabricated on Si(100) substrates by a full vacuum and plasma deposition method carried out at mild temperatures.…”

“…This would favor a diffusive water adsorption and migration toward the bottom of voids where capillary forces contribute to its condensation. Results gathered in this work might also add critical information to other interesting issues, like fabrication of water harvesting systems, time evolution of photoinduced hydrophilic surfaces, and their dependence on the illumination conditions, as well as to the industrial fabrication of antifreezing surfaces …”

“…This would favor a diffusive water adsorption and migration toward the bottom of voids where capillary forces contribute to its condensation. water harvesting systems, time evolution of photoinduced hydrophilic surfaces, and their dependence on the illumination conditions, 56 as well as to the industrial fabrication of antifreezing surfaces. 19 ■ EXPERIMENTAL METHODS Sample Preparation.…”

Internal stress induced natural self-chemisorption of ZnO nanostructured films

“…The sample Z125 was repeatedly recorded after stored in dark surroundings for one day in order to reverse the initial wettability state, it can be observed the CA value of Z125 with UV irradiation for 60 mins clearly changed from 110.5 ± 1° to 17.6 ± 1°. The rapidly decrease of CA value of ZnO film can be attributed to the photocatalystic behavior due to the band gap illumination generates electron-hole pairs in ZnO by photoelectron emission 58 . These electrons and holes can either recombine or move to the surface to react with species adsorbed on the surface.…”

Light-Controlled ZrO2 Surface Hydrophilicity

“…To obtain reproducible initial states of the ZrO 2 surfaces, we used a special procedure developed in our laboratory and described elsewhere 15 16 17 (see also “ Supplementary Information ”) to obtain a hydrated surface which is characterized by a water contact angle value of 12.0° ± 1°. This state could stay unchanged during several hours at ambient conditions and was used as the initial state for the subsequent set of photo-experiments.…”