| Humic acids is widely found in soil,peat and low-order weathered coal in nature,and has a wide range of applications in agriculture,industry,medicine and so on.But the original weathered coal humic acids has a larger molecular weight,and direct extraction results in less active component content and lower activity.The traditional activation method of coal humic acids is usually to use KMnO4,HNO3,H2O2 and other oxidants in the solution to pre-treat the sample.This process requires heating,long reaction time,high equipment requirements,and consumes a lot of water.In addition,the activation process may release some toxic and harmful by-products,causing environmental pollution.These shortcomings greatly limit the development of low-order coal humic acid extraction process.Therefore,this paper synthesizes magnetically reusable Fe3O4/LaNiO3 catalyst and applies it to solid-phase grinding and oxidative degradation of weathered coal to prepare active small-molecule humic acid.Using E4/E6,humic acid content and molecular weight distribution as indicators,the study of this the best conditions of the process,the physical and chemical properties of the prepared humic acids were analyzed.The main research results and conclusions are as follows:1.ABO3 structured perovskite LaNiO3 was prepared by sol-gel method and combined with magnetic Fe3O4,and Fe3O4/LaNiO3 catalyst was synthesized.Through XRD,SEM,HRTEM,XPS,BET and other characterization analysis,it is found that the composite material is irregular particles with an average particle size of about 55 nm;in the material,LaNiO3 and Fe3O4 form an uneven heterojunction surface structure;the composite material has more than LaNiO3 larger specific surface area.2.With Ningxia weathered coal as raw materials,LaNiO3 as oxidants,the effects of the amount of activator,catalyst and grinding time on the humic acid content and E4/E6 ratio were investigated.The L9(33)orthogonal experiment method was used to optimize the preparation process of humic acids,and the best process conditions were obtained:weathered coal,catalyst(accounting for 1.0%of weathered coal mass),activator(accounting for 10.0%of weathered coal mass)and grinding 60 min.Compared with the experiment without catalyst,the content of humic acids produced by this method increased by 16.26%.3.Through four sets of controlled experiments,using elemental analysis,infrared spectroscopy,ultraviolet-visible spectroscopy,volume resistance chromatography,XPS,Py-GCMS,and 13C solid nuclear magnetic analysis,etc.The humic acids content and spectrum prepared by the above process were analyzed structural characteristics and relative molecular weight distribution.The results showed that the Fe3O4/LaNiO3 catalyst can effectively reduce the degree of aromatization of the molecular structure of humic acid;and the catalyst can effectively adjust the molecular weight distribution of humic acids.The weight average molecular weight(Mw)decreased from 59.7 kDa to 5.5 kDa,and the distribution range was narrower and more concentrated.In addition,the content of polar oxygen-containing functional groups in the humic acids prepared by this process increases,and weathered coal(HAs)is oxidized into polycyclic aromatic hydrocarbons,aliphatic and other polyfunctional small molecule compounds.4.Explore the mechanism of Fe3O4/LaNiO3's oxygen decomposition of weathered coal.The possible mechanism is:the metal ions in the perovskite as Lewis sites combine with oxygen-containing species to form Ni(?)OH,La(?)OH,Fe(?)OH and other species as active oxygen species directly oxidize humic acid,and O2 plays a vital role in this catalytic oxygenolysis process. |
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