Study On Preparation And Modification Of δ-MnO₂ And Its Catalytic Performance For Formaldehyde Oxidation At Low Temperature

Formaldehyde poses a serious threat to human health,not only has carcinogenic and teratogenic effects,but also has an adverse effect on air quality.Catalytic oxidation is an effective technology for formaldehyde removal.Noble‐metal catalysts can completely convert formaldehyde at room temperature,but its industrial application is limited because of its high price.Therefore,the development of low-cost catalytic materials for formaldehyde oxidation at room temperature has become a research hotspot.In recent years,manganese oxides have been found to have a good catalytic effect on formaldehyde.In addition,manganese oxides have attracted more and more attention because of their low cost,easy availability and environmental protection.In this paper,the performance of formaldehyde decomposition of sodium manganite is improved by changing the concentration of interlayer ions and interlayer ions of manganese oxide and using cotton fiber as carrier.The main research and conclusions of this paper are as follows:（1）The effect of different interlayer potassium content on the catalytic oxidation of formaldehyde byδ-MnO₂ was studied.It is found that when the potassium ion doping concentration is 0.01 M,the specific surface area ofδ-MnO₂-1 is the largest(429.6932 m² g^-1).With the further increase of potassium ion doping concentration,the specific surface area of the samples decrease gradually.However,the formaldehyde removal performance ofδ-MnO₂ with different interlayer potassium content shows that the specific surface area is not the most important factor affecting the formaldehyde removal performance ofδ-MnO₂.In a certain range,increasing the concentration of potassium ion will decrease the Mn-O bond energy,which is beneficial to the improvement of formaldehyde removal performance.However,when the concentration of potassium ion is too high,potassium ion will stabilize the interlayer structure ofδ-MnO₂,which is not conducive to the removal of formaldehyde.When the concentration of potassium chloride is 0.05M,the Mn-O bond energy ofδ-MnO₂ is the lowest and the content of adsorbed oxygen on the surface is higher.δ-MnO₂-5 has the best formaldehyde removal performance.（2）δ-MnO₂ with different interlayer ions was prepared by introducing a certain amount of chloride（lithium chloride,sodium chloride,potassium chloride,rubidium chloride,cesium chloride）into the redox reaction of potassium permanganate with manganese sulfate monohydrate.It is found that the interlayer ions have a certain influence on the formaldehyde removal performance ofδ-MnO₂.When doped with Rb⁺,the Mn-O bond energy ofδ-MnO₂ is the lowest and the surface adsorbed oxygen content is higher.Under the condition of 36℃and the initial formaldehyde concentration of 200 ppm,a 200 mg of Rb-MnO₂ could achieve the percentage of removal of formaldehyde 97.48%.（3）Rb-MnO₂/cotton fabric and K-MnO₂/cotton fabric composites were prepared by padding and in-situ loading.After testing,it is found that the two methods of loading manganese oxide can improve the removal performance of formaldehyde by manganese oxide to a certain extent.This is because the cotton fabric itself has a certain ability to adsorb formaldehyde to help manganese oxide to better contact with formaldehyde molecules.In addition,although the method of in-situ loading can load more manganese oxide on cotton fabric,the improvement of formaldehyde removal performance ofδ-MnO₂ is not as good as that of dip-rolling loading.The reason for this phenomenon may be that some of the manganese oxide particles loaded in situ are stacked together,which reduces the overall contact area with formaldehyde.