How does H2O2 Chemical Treatments Influence the Hydrophilicity and Decontaminate Ability of ZnO Nanowire Surfaces

Abstract:

ZnO is a biocompatible, economic, and nontoxic nanomaterial that guarantees safety for researchers, widely used in optoelectronic applications and functional coatings. The control of surface hydrophilicity, a vital property manipulated by surface tension and morphology, is significant for sanitizing applications made from nanomaterials. Recently, the tunable wettability shown by ZnO nanowires in storage has generated a lot of research interest. Several papers have reported on the phenomenon of ZnO nanostructures turning from hydrophilic to hydrophobic after storing for 1~2 months without illumination (Bhavsar and Prabhu 2014), which will degrade the performance of hydrophilic nanomaterial applications (e.g. self-cleaning surface, hydrophilic clothes). This phenomenon may be attributed to the impurities attached to the surface of ZnO nanowires during its exposure to air, mostly hydrocarbons. As the covalent hydrocarbon compounds accumulate, the originally ionic and polarized ZnO nanowires are likely to become apolar, losing their hydrophilic property (hydrophilicity can be evaluated by measuring the water contact angle). Therefore, this research aims to seek suitable chemical treatments that can remove hydrocarbon impurities on the surface of ZnO nanowires. To be specific, the nanowires will be produced through thermal evaporation (similar to CVD) method. Taking into account that H2O2 is a strong oxidizer, the hydrocarbons will oxidize to become water and carbon dioxide after reacting with it, diffusing in the air. As a result, hydrogen peroxide solution with different concentrations and volumes will be used to perform both direct and indirect treatments, evaluating how effective they are in restoring the hydrophilicity of ZnO nanowires. Relevant parameters like surface bonding measurement of the nanowires may also be considered in the research. Hypothetically, H2O2 solution with higher concentration will have greater effects on increasing the wettability. Besides hydrophilicity, relationships between the wettability and the surface decontaminate ability of ZnO nanowire surfaces will also be investigated, indicating the possibility to apply ZnO nanomaterial in self-cleaning surfaces.