Reversible Transition Mechanism Between Super-hydrophobicity And Super-hydrophilicity Of Metal-oxide Nanostructures Induced By Ultraviolet Irradiation

The realization of super-hydrophobicity on the surface of semiconductor oxide nanomaterials has effectively expanded their multifunctional applications in the fields of optics,electricity and magnetism,presenting some novel functional characteristics.The implementation of photo-controlled superhydrophobic-superhydrophilic reversible transition on oxide nanomaterials provides a useful way for the design of intelligent devices and controllable oil-water separation devices.However,the reversible transition mechanism between light-controlled super-hydrophobicity and super-hydrophibicity of oxide nanomaterials is still unclear.In this thesis,we selected ZnO,Ti O₂and Sn O₂ as model materials and researched the effect of ultraviolet（UV）irradiation,treatment atmosphere,and oxygen vacancy defects on the surface wettability.Furthermore,we investigated the mechanism of UV-induced surface hydrophobic-hydrophilic transition of oxide nanomaterials.We used the liquid phase method synthesizing ZnO,TiO₂and SnO₂nanomaterials,realizing the transition of these oxide nanomaterials irradiated by UV light.Then,we utilized UV light to induce the state of oxide nanomaterials to transform to super-hydrophilic and studied how the super-hydrophilic oxides nanomaterials recover their hydrophobic.The research showed the surface droplet contact angle（WCA）of super-hydropbilic ZnO,Ti O₂and Sn O₂ nanomaterials exposed to UV light upgraded from 0°to 50°during storage in an anechoic chamber protected by nitrogen atmosphere,while during storage in an anechoic chamber protected by oxygen atmosphere,the WCA of these nanomaterials upgraded from 0°to150°,which was the contact angle value before UV treatment.The above results indicated that the presence of oxygen molecules plays an important role during the hydrophobic properties recovery of hydrophilic oxide nanomaterials induced by UV light.We used Raman and X-ray photoelectron spectroscopy to study the surface state changes of oxide materials during ultraviolet-induced super-hydrophobic and super-hydrophilic reversible transformation.The surface oxygen vacancy defects on oxide nanomaterials increased after UV irradiation.Whereas in the process of dark storage,the surface oxygen vacancy defects on oxide nanomaterials decreased and were accompanied by adsorption of O₂ molecules.Therefore,we believed that the reversible transition between super-hydrophobicity and super-hydrophilicity of metal-oxide nanostructures induced by ultraviolet irradiation was caused by the ability of adsorbing O₂ by oxygen vacancy defects.Based on these results,we proposed a reversible transition mechanism between super-hydrophobicity and super-hydrophilicity of metal-oxide nanostructures induced by ultraviolet irradiation.The further understanding of the super-hydrophobicity and super-hydrophilicity transition mechanism provided a basis for the design and fabrication of novel functional devices related to surface wettability.