Preparation And Properties Of Manganese Oxide/Porous Carbon Composties

Porous carbon materials are widely used in the fields of separation,electrode,catalyst carrier,environmental protection and energy storage due to their high specific surface area and pore volume,well-developed pore structure,good academic stability and low price.As a catalyst carrier,porous carbon can not only effectively prevent the aggregation of catalysts,but also promote the enrichment of pollutants,and have a synergistic effect with the catalysts,which is beneficial to the improvement of the catalytic performance of the catalysts.However,the preparation of such materials and the loading of catalysts usually require cumbersome steps.In order to reduce the preparation process of composites and obtain the composites with good properties by simple and effective method,polyacrylic acid-manganese ion colloids(PAA-Mn)were prepared by Mn ion-induced method as template.Manganese oxide-porous carbon composites with different structures were prepared by one-step carbonization,and the catalytic properties of the composites were improved from the aspects of structure,specific surface area,size and valence state of manganese oxide.The main contents of the study are as follows:(1)Poly(acrylic acid)stabilized ultra-small MnO2 nanoparticles(around 1.0 nm)are first produced and then in situ incorporated into the RF resin matrix.Manganese oxide/solid porous carbon composites(MnOx-C)were prepared by one-step carbonization.The MnO2 are reduced to Mn3O4 and MnO(denoted as MnOx)during carbonization,which are more active in heterogeneous Fenton catalysis.Under the optimized synthesis condition,the average size of the MnOx particles is only 2.9 nm.,and homogeneously dispersed in the carbon matrix.Moreover,the BET surface area of the composite is as large as 227.7 m3 g-1.Within 60 min,the degradation rate of methylene blue at the concentration of 100 mg/1 reached 96%,showing a good catalytic performance.(2)In order to improve the specific surface area and hydrophilicity of the composites,a core-shell type nano-catalyst(MnOx-C@SiO2)with manganese oxide-carbon composite as core and SiO2 as shell is prepared by using a SiO2 coated polyacrylic-manganese dioxide composite micelle(PAA-MnO2@SiO2).The results showed that the SiO2 shell can effectively prevent manganese oxide from growing up(d<1 nm)to prevent the aggregation of productsduring carbonation,and the hydrophilicity of the material was greatly increased.Its internal carbon component can further stabilize manganese oxide nanoparticles and promote the enrichment of organic pollutants around the catalyst.The specific surface area of MnOx-C@SiO2 is 317.3 m2 g-1 In the process of catalytic degradation of methylene blue(MB)solution by fenton reaction,the degradation rate of MB solution can reach 96.8%within 40 min,and the catalytic efficiency is significantly higher than before.(3)Hollow structure can effectively improve the exchange rate of internal and external substances and make pollutants accumulate around them.In this paper,a soft template method for the synthesis of mnox-hollow carbon composites(HC-Mn)is proposed.The hollow structure is formed by simple water washing,and the residual manganese ions in situ form mnox.during carbonation.In addition,the formation process was well studied and a plausible formation mechanism was proposed.The Mn ions played two key roles in the synthesis:first,they promoted the aggregation of the PAA molecules,thus forming the PAA-Mn colloids in solution with high water content,which were suitable for the subsequent RF coating.Secondly,considerable Mn ions were retained after template removal,which were transformed into MnOx particles(d<1 nm)simultaneously during carbonization.Because of the hollow structure of the material,the prepared hc-mn has a higher specific surface area(386 m2 g-1).The degradation rate of methylene blue by hc-mn-0.7 reached 99%in 60 min,and decreased by 3%after 4 cycles of recycling,and the cycling stability was significantly improved compared with the previous one.The degradation rate of methylene blue reached 99%in 60 mol/L and decreased by 3%after 4 cycles of recycling.