Synthesis Of Manganese Oxide By A Several Organic Compounds Assisted Hydrothermal Process And Its Fenton-like Catalytic Properties

In recent years,advanced oxidation technology uses extremely active free radicals as the main oxidant for the catalytic degradation of organic pollutants,this has much attention.Among them,Fenton oxidation method has good removal effect on high toxicity,high concentration and poor sewage.Therefore,in this paper,a series of manganese oxides were prepared by hydrothermal synthesis using potassium permanganate as the manganese source and oxidant,adding a certain amount of organic matter as modifier.The Fenton-catalyzed H₂O₂ degradation of methylene blue（MB）,and the catalytic properties of the products were determined.The relationship between the crystal species,morphology,size and catalysis of the different organic species and dosage was also revealed.The research contents and results of this thesis are as follows:1.Effects of cyclohexane on degrading the performance of MB through catalyzing H₂O₂ with δ-MnO₂Unmodified（CHM-0）and modified（CHM-2,CHM-5 and CHM-10）δ-MnO₂ were prepared by simple hydrothermal method at 180 ℃ / 24 h with different volumes of cyclohexane as modifier.The adsorption and degradation properties of the product were determined.The products were characterized by microscopic techniques such as XRD,SEM,TEM and N₂ desorption.And the solution of CHM-5 was analyzed in the hydrothermal process using GC-MS technology.The mechanism of the reaction catalysis was preliminarily determined using free radical scavenger,and its stability was evaluated.The results show that:（1）Cyclohexane has a modification effect on the improvement of the performance of H₂O₂ degradation by δ-MnO₂.With the increase of the amount of cyclohexane,the adsorption rate of MB gradually increased,while the contribution rate of oxidative degradation and total removal rate were the highest in CHM-5.（2）Compared with CHM-0,the modified δ-MnO₂ reduces the intensity of the diffraction peak and the degree of crystallization.（3）CHM-5sample morphology not only δ-MnO₂ structure of the flower-like microspheres,as well as one-dimensional rod-like particles and particle size of about 30-60 nm irregular microspheres exist.（4）The CHM-5 sample had a specific surface area of 148.7 m²·g^-1and a pore volume of0.33 cm³·g^-1,which was much larger than CHM-0(specific surface area of only 15.9 m²·g^-1and pore volume of 0.084 cm³·g^-1).（5）Cyclohexane is gradually oxidized by KMnO₄ to produce three products of acetone,cyclohexanol and cyclohexanone.The oxidation products of cyclohexane adsorbed on the surface of δ-MnO₂ nuclei,changed the morphology and crystallinity of δ-MnO₂ and increased the specific surface area of δ-MnO₂,which affected the catalytic performance of the product.（6）The modified δ-MnO₂ catalyzes H₂O₂ resulting in the removal of MB by the formation of ·OH.（7）After repeated the experiment and recycled 3times,the removal efficiency remained at 91% or more.The modified δ-MnO₂ prepared by cyclohexane provides a new method for improving the catalytic degradation performance of MB.2.Comparative studys of four mono-substituted benzene on the structure and property of MnO₂The effects of toluene,ethylbenzene,benzaldehyde and benzoic acid on the molar ratio of potassium permanganate（0,2,5,10）were studied and prepared a series of manganese oxides.The catalytic degradation performance of the products was determined.The materials were characterized by XRD,SEM and N₂ desorption.The relationship between the microstructure and properties of MnO₂ was investigated.The results shows:（1）For example,at the molar ratio of 5,the modified products prepared by four mono-substituted benzenes improved the removal ability,and hydrocarbons and carbonic acid substitutes was compared to aldehydes were higher the removal efficiency of MB.（2）When adding toluene,ethylbenzene and benzoic acid,the product obtained is δ-MnO₂,but the addition of organic matter reduces the degree of crystallization of the product.When adding benzaldehyde,the crystal form of the product is composed of δ-MnO₂ gradually converted to α-MnO₂.（3）The modified products prepared by adding toluene,the morphology is the flower-like microspheres,which was the same as that of δ-MnO₂,but its diameter to be slightly smaller;adding ethylbenzene and benzoic acid preparation of the change in the sexual products,not only the δ-MnO₂ structure of the flower-like microspheres,as well as the emergence of nanorods;adding benzaldehyde prepared modified products,the morphology of the structure of the nanorods.（4）Addition of toluene obtained the product,the adsorption rate of MB and the total removal rate is the highest（94.9%）at molar ratio of 5.With the increase of the molar ratio of ethylbenzene,the degradation contribution rate increased gradually.The modifiedproduct MnO₂ obtained by adding benzoic acid enhances the adsorption and degradation properties of on MB,but its removal effect is not as good as that of functional groups.When the molar ratio is 10 of benzoic acid and potassium permanganate,the catalytic effect is obviously worse,which may have a direct relationship with the crystal form and morphology of the product.In conclusion,the addition of organic matter changed the microstructure of theδ-MnO₂,the crystalline phase of modified product was δ-MnO₂ and the morphology of the flower and the rod structure,which can increase the specific surface area,and then improve the catalytic performance of MB.3.Effects of cyclohexane on degrading the performance of MB through catalyzing H₂O₂ with α-MnO₂The unmodified and modified α-MnO₂ was prepared by hydrothermal method with using hydrochloride and potassium permanganate as the raw material and cyclohexane as modifier.The effect of the product on the catalytic performance of MB was determined.Finally,the products were analyzed by XRD,SEM and BET techniques,the results shows:（1）Compared with Mn-0,the modified α-MnO₂ showed higher degradation performance.Among them,when the amount of cyclohexane was 1mL,the removal efficiency was 97.1%;（2）Mn-1reduces the degree of crystallization and the micro-particle size of the product;（3）The addition of cyclohexane increases the specific surface area of α-MnO₂.The specific surface area and pore volume of Mn-1 sample are the largest and the pore size is the smallest in all products.Therefore,more surface active sites can be provided,which shows a higher catalytic activity performance;（4）The catalytic oxidation of modified α-MnO₂ prepared by cyclohexane resulted in the generation of ·OH and leaded to the degradation of MB.