Study On Preparation Of Nano-SiO₂ Based-composite Particles And Hydrophobic Protection Of Concrete Surfaces

Due to the excellent performance,SiO₂ nanoparticles are widely used in plastics,coatings,rubber,adhesive,and ceramics,and so on.SiO₂ nanoparticles with core-shell structure have advantages of controllable size,composition,shape,and structure,and which exhibit novel characteristics in optics,electricity,magnetics,catalysis,biomedicine,and photonic crystals.In the future,they will have great application prospects in new energy and materials and become a hot discussion.As the most widely used building materials,Concrete is often exposed to the atmosphere and vulnerable to damage by modes as corrosion,carbonation,and cracking,etc.Consequently,the durability and service life of concrete are affected seriously.The destruction of concrete usually begins from the surface,and it intrudes into the inner of the concretewith water as a carrier.The entry of water can be prevented by constructing hydrophobic protection coatings on concrete surface.As a result,the durability of the concrete can be enhanced.In this dissertation,SiO₂ and SiO₂@Ni composite microspheres,and hollow Ni microspheres are prepared,and the structure and catalytic property of the prepared microspheres are examinced in depth.In addition,a superhydrophobic protective agent containing SiO₂ nanoparticles are prepared by a simple method,and the hydrophobic property and its functionality are investigated in detail.The main contents and conclusion are as follows:?1?SiO₂ microspheres with particle size of 200-500 nm are prepared according to the classical St?ber method.Then SiO₂@Ni composite microspheres with raspberry-like morphology and core-shell structure are prepared by the reduction and deposition of Ni2+ on the surface of SiO₂ microspheres.Finally,the morphology,microstructure,phase structure,and chemical composition of the as-prepared nano-SiO₂ and SiO₂@Ni microspheres are characterized.?2?SiO₂ cores in SiO₂@Ni microspheres are removed by NaOH solution etching in order to prepare the hollow Ni microspheres.The effects of immersion time in NaOH solution on the surface morphology,phase structure,and composition of SiO₂@Ni composite microspheres are studied.The results show that the immersion time of NaOH solution has no influence on the surface morphology and phase structure of Si O₂@Ni composite microspheres.However,the ratio betweem Ni element and Si element in phase composition increases gradually with the extending of immersion time,indicating that SiO₂ cores are dissolved step by step.When NaOH solution etching time reaches 10 h,hollow Ni microspheres with perfect structure are obtained.?3?SiO₂@Ni composite microspheres,hollow Ni microspheres,and pure Ni nanoparticles as catalyst,by catalytic NaBH4 reduction of methylene blue solution reaction,SiO₂@Ni composite microspheres with higher catalytic performance,high stability and easy recycle performance.?4?A superhydrophobic protective agent containing SiO₂ microspheres is prepared successfully by a simple and environment-friendly method.After sprayed onto materials,superhydrophobic surfaces with a contact angle above 150 ° and a slidinging angle less than 5 ° can be resulted.Moreover,excellent superhydrophobic effect can be obtained when the protective agent is applied onto different substrates for a variety of hydrophilic liquids,indicating that the hydrophobic agent has good hydrophobic diversity and universality.Meanwhile,coatings prepared with the superhydrophobic protective agent exhibit good transparency and self-cleaning performance.It can realized for the effective separation of oil and water and the separation efficiency can reach 97% and 99%,respectively.?5?The superhydrophobic surface with a contact angle of 151.2° and a sliding angle less than 5° can be obtained by spraying nano-SiO₂ based superhydrophobic protective agent on concrete.It indicates that concrete has been endowed with good waterproof effect by coating the protective agent.The results from SEM and FT-IR show that the resultant concrete surface has the superhydrophobicity grounded on the combined effects of both micro-and nano-scaled rough structure and low surface energy materials.?6?The water absorption,penetration depth,acid and alkali resistance,resistance to organic solvents,UV resistance,and environmental stability are examined.Results show that the superhydrophobicity of the resultant superhydrophobic concretes maintains after acid and alkali corrosion,ultraviolet radiation,organic solvent soaking,and outdoor placement.Meanwhile,the superhydrophobic concretes have low water absorbancy and penetration depth.These indicate that superhydrophobic concretes can be used in various environments.