Study On Design And Performance Of Photocatalytic Synergistic Superhydrophobic Cement Based Self-cleaning Coating

Increasing environmental pollution has resulted in the presence of large amounts of chemicals and particulate matter in the air.These pollutants tend to adhere to the surface of cement structures and also form acid rain that erodes the structure,greatly reducing the aesthetics,functionality and durability of cement-based structures.Based on this,superhydrophobic materials（SHM）were prepared by sol-gel method using silica nanoparticles,n-octyltriethoxysilane（OTES）and silane coupling agent（KH560）as raw materials in this study.To further enhance the anti-pollution ability and degradation effect of the superhydrophobic materials,photocatalytic synergistic superhydrophobic materials（PSSHM）were prepared by introducing Ti O₂nanoparticles with photocatalytic effect.The self-cleaning properties,mechanical wear resistance,chemical stability and weathering resistance of two self-cleaning coatings,SHM and PSSHM,have been systematically investigated using cement based materials as the substrates.（1）The optimum conditions for the preparation of SHM were determined by orthogonal experimental design using the static contact angle as the evaluation criterion:3 g Si O₂nanoparticles,5 ml n-octyltriethoxysilane,1 ml silane coupling agent KH-560and stirring temperature of 50℃.Comparative analysis of the surface morphology of Si O₂nanoparticles and SHM showed that the nanoparticles on the surface of SHM were uniformly distributed and dense,with an obvious micro-nano-rough structure,and the highest content of C elements in SHM;X-ray diffraction showed that the crystal structure of SHM did not change significantly;infrared spectra showed that new absorption peaks appeared in SHM,caused by the stretching and bending vibration of the-CH₂group The X-ray photoelectron spectroscopy shows that the Si element is present in SHM in the form of Si-O and Si-C,and that organosilanes have been successfully grafted on the surface of the silica nanoparticles.In summary,the long-chain alkanes grafted on the surface of SHM together with the multilayer rough structure enhance its surface hydrophobic properties.（2）Using contact angle and photocatalytic degradation efficiency as evaluation indicators,the optimal preparation conditions for PSSHM were determined comprehensively:the nano Si O₂-Ti O₂doping ratio was 6:1,the HDTMS content was4%,and the MTMS content was 2%.The microstructure analysis of PSSHM shows that the particle distribution on the surface of PSSHM is uniform and dense,and the three-dimensional network and composite rough structure are clearly visible;PSSHM contains a typical absorption peak of anatase type titanium dioxide.Compared with pure Ti O₂,the corresponding diffraction peak intensity of PSSHM is weaker and the diffraction peak is wider;PSSHM exhibits a unique Ti-O-Ti stretching vibration characteristic absorption peak,and the O element exists in the form of Si-O-Si and Si-O-Ti.The light absorption intensity in the ultraviolet region of PSSHM decreases,but the band gap width decreases by 0.49 e V,indicating that the absorption ability of PSSHM in the visible light range has improved;The adsorption desorption isotherm of PSSHM exhibits a type IV curve,with both pore size and specific surface area smaller than that of Ti O₂.The measured surface contact angle of PSSHM is as high as 153.4°,and the rolling angle is 2°.The photocatalytic degradation efficiency reaches 98.5%after 120 minutes of UV irradiation.In summary,the PSSHM surface has both superhydrophobic properties and catalytic degradation functions.（3）The superhydrophobic performance test shows that the static contact angle of CBSC is 156.7°,the surface free energy is 5.05 m J/m²,the surface contact angle of CBPSSC is 155.4°,and the surface free energy is 1.94 m J/m².The surface free energy of CBSC and CBPSSC is significantly lower than that of ordinary cement specimens,that is both CBSC and CBPSSC have ultra-high hydrophobic properties;The self-cleaning performance test shows that the surfaces of CBSC and CBPSSC have excellent dustproof and antifouling effects.In addition,CBPSSC also has the ability to degrade organic pollutants.After 16 hours of UV irradiation,the degradation rate of Rhodamine B solution reaches 94.1%;The durability of cement based surface coatings was tested by designing tests for mechanical wear resistance,chemical stability,UV resistance,and thermal cycling resistance.The test shows that the surfaces of CBSC and CBPSSC still have high hydrophobicity after 700 cm wear and 72 h immersion in acid,alkali and salt;After 120 hours of ultraviolet irradiation and 10 temperature difference cycles,the superhydrophobic property is still maintained,indicating that CBSC and CBPSSC have good durability.