Modification And Spectral Characteristics Of Soil Organic Matter And Pectin

In this paper,soil organic matter and pectin were used as raw materials to further improve the utilization of natural biomass resources.The soil organic matter was extracted and modified by hydrothermal method.A new method for the determination of soil organic matter by this solution was proposed and compared with potassium dichromate method.At the same time,natural pectin was used as raw material,its molecular structure was changed by plasma treatment,and the fluorescence characteristics of modified pectin and optical and mechanical properties of the final solid film were studied.1.Taking soil organic matter as the research object,the soil organic matter was modified by hydrothermal treatment with high temperature and high pressure,and its physical and chemical properties were analyzed by carbon and nitrogen analyzer,fluorescence spectrometer,UV-visible spectrophotometer and p H tester.The fluorescence properties of the solution were studied by using fluorescence spectrometer and UV-vis spectrophotometer,and the correlation between soil organic matter content and potassium dichromate volumetric method was analyzed by using its optical properties.A better linear relationship（R²>0.7）was found when SOM content was controlled by soil mass than by humic acid.Using the calibration curves of Beibei soil and humic acid,the SOM of the selected samples was measured using optical properties.The relationship between SOM and the potassium dichromate volumetric method can be extrapolated with a linear relationship of R² approaching 0.7 at 250,300,400 and 420nm wavelengths.If the A₂₅₀ from Beibei soil is used as the calibration curve,R² peak value is 0.74,at which time the correlation between soil organic matter content measured and potassium dichromated volumetric method is the highest.2.Apple pectin solution（PE）was modified by low-temperature plasma to obtain PPE,PPN solution and corresponding film(PPE stands for pectin solution obtained after 20min of pectin solution was treated by low-temperature plasma airsickness.PPN stands for pectin solution obtained after the pectin solution containing ammonia was treated by low-temperature plasma airsickness for 20min.It was found that the modification of plasma made PPE and PPN solution have fluorescence properties.When the ultraviolet flashlight was used,PPN solution produced strong blue-green fluorescence,while PPE solution showed weak blue-green fluorescence.Compared with PE solution,PPE solution and PPN solution have significantly higher photoluminescence intensity and absorbance in the ultraviolet and visible region.In the range of 10^-10 to 10^-1 M,the PL quenching（I₀/I）of PPN solution with different concentrations of K⁺,Na⁺,Mg²⁺,Al³⁺and Zn²⁺has little change.There is a good linear relationship between I₀/I and Cu²⁺concentration.Compared with PE films,PPE and PPN films have more intermolecular interactions,and the film matrix has a dense structure and better flexibility.The absorbance trend of PPN film is similar to that of PPE film,but the absorbance value is higher than that of PE film.The absorbance of the three films is similar to that of solution.The thermal degradation temperature of PPE and PPN films increased,and PPE film had higher thermal stability.At the same time,the tensile strength and elastic modulus of PPN film（938.35mpa）were higher than those of PPE film（578.28mpa）,and the glass transition temperature of PPN film increased.Hydrothermal treatment can be used to modify soil organic matter.Two methods,fluorescence spectrometry and absorption spectrometry,were established to determine soil organic matter content and compared with potassium dichromate volumetric method.When absorption spectrometry was used,the correlation with potassium dichromic volumetric method was the highest at 250 nm,and the test effect was the best,with a peak R² of 0.74.Fluorescence spectrometry is not a good way to detect soil organic matter.These two methods are green and do not use chemical reagents to detect soil organic matter,which can avoid the disadvantages of environmental pollution caused by chemical reagents in traditional methods,and provide a reference for the rapid detection of soil organic matter content and the utilization of biomass resources of soil organic matter.Plasma can be used to modify pectin,the intermolecular interaction is stronger,and the mechanical properties and thermal stability of thin films are improved.The PPE solution treated by plasma with pectin solution had the highest thermal stability.The surface structure is the most smooth and compact;The tensile strength and storage modulus are higher than those of original pectin film but lower than those of PPN film.The absorbance and fluorescence intensity of PPN solution treated with ammonia and plasma increased significantly,which can be used for the detection of copper ions.The surface structure is rough,and the cross section has tiny holes;Compared with the original pectin film,the tensile strength and energy storage modulus of the film are significantly improved,the glass transition temperature is increased,and the film has higher thermal stability.Under the background of abundant pectin resources but serious waste in China,new applications of pectin were developed to provide a reference for improving the modification and utilization of pectin biomass resources.