Preparation,Properties And Mechanism Of High Efficiency Photocatalytic Degradation NO Coating On Tunnel Inner Wall

With the continuous development of transportation and automobile industry,the pollution caused by automobile exhaust dominated by nitric oxide is becoming more and more serious.As a functional building material,TiO₂ photocatalytic coating has the advantages of green,high efficiency,economy and strong universality.It provides an ideal solution in line with the"double carbon plan"for the degradation of nitric oxide in the air environment.However,the application of the coating in tunnel still has many limitations:（1）the visible light response is inferior due to special lighting source.（2）The long-term photocatalytic performance was crippled by high pollution environment.（3）High humidity environment reduced the degradation efficiency of nitric oxide.（4）The degradation of nitric oxide produces more toxic nitrogen dioxide.（5）The degradation mechanism of nitric oxide in photocatalytic coating is not clear.Therefore,it is urgent to explore a long-term effective coating material for photocatalytic degradation of nitric oxide in the special environment of tunnel.In this paper,TiO₂ was modified by ion doping and heterostructure fabrication to expand its optical response range.Furthermore,a durable visible light photocatalytic waterborne coating was prepared by using the coating as the catalyst carrier.Based on the structural mechanism of"lotus leaf effect",superhydrophobic and superamphiphobic characteristics are introduced into the photocatalytic coating to endow the coating self-cleaning and ensure the long-term effectiveness of the photocatalytic effect of the coating.Combined with the microstructure and physicochemical characteristics of the self-cleaning photocatalytic coating,the degradation mechanism of nitric oxide is explored.The specific research is as follows:（1）Fe/N/Co doped titanium dioxide was prepared by ion doping,which changed the electronic structure of titanium dioxide and refined the grains,resulting in a significant red shift in its absorption spectrum.At the same time,two porous adsorption degradation photocatalysts were prepared using Fe/N/Co doped titanium dioxide regulated and loaded by molecular sieve and activated carbon with large specific surface area and strong adsorption capacity.The degradation efficiency of nitric oxide under visible light irradiation was 56.7%and 51.6%.Then,two kinds of waterborne acrylic photocatalytic coatings with visible light response were prepared with waterborne acrylic coatings as matrix materials.Under visible light irradiation,it can play a certain role in the degradation of nitric oxide.Aiming at the problem that the UV stability and durability of the photocatalytic coating are greatly reduced due to photooxidation in the actual use process,the UV aging test of Fe/N/Co doped titanium dioxide@activated carbon coating is carried out,and a"peach pit effect"is proposed as the mechanism to improve the UV stability of the photocatalytic coating.（2）To improve the self-cleaning of the coating,a one-dimensional tungsten oxide/titanium dioxide nanorod material with visible light response was prepared by the means of semiconductor recombination.It was used as the constructor of surface micro nano rough structure and polydimethylsiloxane as the provider of low surface energy,a superhydrophobic coating with visible light response was constructed.The contact angle between the coating and water can reach about 160°,and the durability of the coating is greatly improved due to the network interpenetrating structure formed by one-dimensional nanostructure and polydimethylsiloxane.The coating showed excellent nitric oxide degradation efficiency under UV and visible light.Through the 30 days outdoor test,the changes of nitric oxide degradation efficiency of superhydrophobic and hydrophilic coatings were compared,which confirmed the synergistic effect of self-cleaning and photocatalytic characteristics and ensured the long-term effect of photocatalysis.（3）Aiming at the oil pollutants in the tunnel,fluorosiloxane as the provider of low surface energy materials,a superamphiphobic coating with nitric oxide degradation effect is prepared,which solves the problem that the superhydrophobic coating is not resistant to oil pollution and further improves the self-cleaning effect of the coating.The contact angle of the coating to water and oil can reach more than 150°.At the same time,based on the physicochemical characteristics of the superamphiphobic surface,the effects of the water repellent characteristics of the coating surface and the environmental relative humidity on the photocatalytic degradation efficiency of nitric oxide were systematically studied.Combined with molecular simulation technology,the influence mechanism of coating surface characteristics on nitric oxide degradation was explored,and a mechanism to improve the degradation efficiency of nitric oxide on superamphiphobic coating under high humidity environment was proposed.By detecting the change of nitrogen dioxide concentration in the process of nitric oxide degradation,it is found that the nitrogen dioxide concentration produced by superamphiphobic photocatalytic coating is significantly lower than that of pure photocatalyst.Then,combined with in-situ infrared spectroscopy and electron paramagnetic spectroscopy,the difference of nitric oxide degradation mechanism between superamphiphobic photocatalytic coating and photocatalyst was studied,and two possible reaction pathways of hydroxyl radical and superoxide radical degradation of nitric oxide were summarized.Combined with the results of density functional theory calculation and product analysis,a green degradation mechanism of nitric oxide by superamphiphobic photocatalytic coating was proposed.It provides some theoretical support for the application of photocatalytic technology and the development of environmental protection.（4）Based on the analysis of nitric oxide degradation products,a tungsten oxide/titanium dioxide nanorod/calcium carbonate insulating heterojunction photocatalyst with degradation-regeneration double sites was prepared by simple grinding and calcination.The effects of different calcium carbonate loading on the morphology,microstructure and composition of this photocatalyst were investigated by SEM,XRD,FT-IR and XPS.Also,this heterojunction photocatalyst exhibits nitrogen dioxide-inhibited and durable characteristics for nitric oxide degradation.In the process of nitric oxide degradation,the production of nitrogen dioxide has been at a relatively low level,and after 5 nitric oxide degradation cycles,the degradation efficiency has only decreased by 3.7%.Density functional theory calculation,the detection of active groups by EPR and capture test,the nitric oxide degradation pathway characterized by in-situ FT-IR spectra showed that the electron-rich region formed and the existence of regeneration sites are the main reasons for promoting the nitrogen dioxide-inhibited and durable nitric oxide degradation.Furthermore,the mechanism of nitrogen dioxide-inhibited and durable nitric oxide degradation by this photocatalyst was revealed.Finally,tungsten oxide/titanium dioxide nanorod/calcium carbonate superamphiphobic photocatalytic coating was prepared,which still exhibits similar nitrogen dioxide-inhibited and durable characteristics for nitric oxide degradation to tungsten oxide/titanium dioxide nanorod/calcium carbonate photocatalyst.This work may lay a theoretical foundation for the green photocatalytic process and hope to provide a new idea for the development and application of durable and high-efficiency photocatalysts.（5）Technology of coating process is an important guarantee for the effective performance of coatings.Based on the engineering application,this paper systematically studies the coating process,and gives the basic coating scheme of self-cleaning synergistic photocatalytic coating:grinding→cleaning→repairing→batching putty→coating the bottom coating→coating the surface coating.According to the coating substrates of different test roads,combined with the physical and chemical characteristics of the coating,a coating scheme adapted to local conditions is proposed,and the self-cleaning and photocatalytic ability of the coating after actual coating are evaluated.