The Construction Of Wood Nanofiber Photocatalytic Coating And Its Bonding Mechanism With Wood Interface

Indoor volatile organic compound(VOCs)pollution seriously endangers people’s life and health.As the photocatalytic oxidation technology can oxidize and degrade VOCs pollutants into water and carbon dioxide under the function of light,it is considered to be a reliable indoor VOCs purification technology.However,because the photocatalyst is all powder,it is difficult to avoid the use of organic polymer resin as a film-forming agent to construct a photocatalytic coating realizing the dispersion and fixation of the photocatalyst.While the polymer resin is unstable and easy to be aging in the photocatalytic process,which leads to the decline of the bonding performance of the photocatalytic coating and affects the service life of the photocatalytic coating.At the same time,the photoaging process will generate a large amount of aldehydes and ketones VOCs,which will bring about secondary pollution problems and aggravate indoor environmental pollution.Therefore,the rational design of photocatalytic coatings is of great significance for the safe and efficient purification of indoor VOCs pollution.Wood cellulose nanofibers(CNFs)are widely sourced and have certain photostability.It also has been demonstrated that CNF have a significant effect on the reinforcement construction of coatings.Based on this,this article proposes to construct an environmentally friendly TiO2 photocatalytic coating by using wood cellulose nanofibers to efficiently disperse and stabilize the photocatalytic coating with the stable rheological properties of CNF.And there are utilizing its keratinization force after dehydration to build a high-strength bonding interface.The relationship between CNF on the viscosity characteristics of photocatalytic coatings and the effect of coatings on formaldehyde degradation performance were studied.The construction stability and catalytic stability of CNF photocatalytic coatings also were evaluated.The binding mechanism between CNF photocatalytic coatings and wood surfaces was established.The main research contents and results are as follows:(1)TiO2 photocatalytic coatings were constructed by using CNF as a film-forming agent through multi-stage dispersion.The relationship between CNF on the viscosity test of photocatalytic coatings and the catalytic degradation performance of catalytic coatings on formaldehyde was studied.The results show that CNF has a significant effect on the viscosity and stability of TiO2 photocatalytic waterborne coatings.With the increase of CNF addition,the viscosity of the paint first decreases and then increases,and its viscosity stability increases with the increase of CNF addition.After the CNF addition is higher than 0.4%,the CNF photocatalytic coating has a stable static viscosity.When the CNF-TiO2 photocatalytic coating was constructed on wood surfaces,the catalytic degradation test of formaldehyde showed that the content of CNF had little influence on the catalytic degradation performance.The photocatalytic coating with 0.0%-0.6%CNF content also have close and excellent formaldehyde degradation rate and conversion rate,and the conversion rate in 4 h can reach more than 90%.Based on the coating catalytic properties and coating viscosity properties,it is concluded that 0.4%CNF-TiO2 is the more suitable CNF photocatalytic coating.Morphology analysis of the coating showed that amorphous CNF only existed on the surface of TiO2 in a very thin layer of 3-5 nm,without very thick coating on TiO2.There is a very tight interfacial bond between CNF and TiO2.The UV-Vis and XRD studies of the photocatalytic coating found that the addition of 0.4%CNF did not have a significant adverse effect on the light absorption characteristics and crystal structure of the TiO2 photocatalyst.(2)The construction stability and catalytic stability of the CNF photocatalytic coating were evaluated.The results showed that the dispersion stability of CNF photocatalytic coatings showed a trend of first weakening and then strengthening with the increase of CNF content.When the CNF content is higher than 0.4%,the coatings can be maintained for 200 days without delamination,which is more stable than common PEG-TiO2 and W-PU-TiO2 photocatalytic coating.In-depth zeta potential analysis showed that the higher zeta potential(-54.07±0.54 mV)of CNFs provided strong electrostatic repulsion and achieved stable dispersion of the coating.And the 0.4%CNF-TiO2 coating has universal applicability to different materials surfaces(wood,glass,metal,paper)and different coating preparation methods(painting,spraying and immersion),showing strong build stability.In addition,the 0.4%CNF-TiO2 photocatalytic coating also has excellent cyclic catalytic stability and excellent catalytic stability in different temperature and humidity environments.(3)The bonding strength test,theoretical simulation,and experimental verification of the 0.4%CNF-TiO2 photocatalytic coating on the wood surface were carried out.The results show that the mass loss of 0.4%CNF-TiO2 is 60.26%lower than that of 0.0%CNF-TiO2 in the abrasion of 120 cm sandpaper.And the 0.4%CNF-TiO2 photocatalytic coating can withstand more than 40 times of tape peeling without obvious peeling,showing excellent interfacial bonding strength and anti-peeling properties.The theoretical simulation results show that the hydroxyl-rich CNF in the CNF-TiO2 photocatalytic coating can form a highdensity strong hydrogen bond interaction with the low electrostatic potential TiO2 particles and the surface of the substrate.The CNF-CNF,CNF-TiO2 interface inside the coating and the interface of CNF-substrate all have very high formation energy(up to 2 eV)and strong bond.The experimental research also confirmed that the bonding strength of CNF to TiO2 photocatalytic coating was significantly improved.And the strengthening function was significantly stronger than that of common photocatalytic coating binders.In addition,the TiO2 photocatalytic coating had more abundant TiO2 photocatalytic coating after 0.4%CNF was added.The red-shift of 32.78 cm-1 on hydroxyl absorption peak in FTIR test also shows that the hydrogen bond interaction inside of this coating is significantly strengthened.(4)The main binding mechanism of CNF photocatalytic coating and wood surface shows that CNF rich in hydroxyl groups can form high-density strong hydrogen bond with TiO2 nanoparticles and wood surface.It will induce the keratinization force and form a hydrogen bond network through the connection of heterogeneous interfaces and the crosslinking of CNF itself.This hydrogen bond network between the interior of the coating and the wood substrate achieves the high-strength bonding between the CNF photocatalytic coating and the wood surface.In this paper,an environmentally friendly TiO2 photocatalytic coating was successfully constructed on wood surface by using green,renewable and photostable wood cellulose nanofibers as film-forming and binder for photocatalytic coatings.The relationship between the influence of CNF on the viscosity characteristics and the formaldehyde degradation characteristics of catalytic coatings was obtained.And the construction stability and catalytic stability of CNF photocatalytic coatings were comprehensively evaluated.Combined theoretical simulation and experimental research,the binding mechanism of CNF photocatalytic coating and wood surface was established.This study provides a new idea and corresponding theoretical basis for rationally designing photocatalytic coatings to purify indoor VOCs pollution in a green and safe manner.