Studies Of Sugar Production Of Miscanthus By Enzymatic Hydrolysis And Its Biochar For Cr(Ⅵ) Adsorption

In view of a series of energy crisis problems and environmental problems caused byheavy metal pollution and straw burning,the comprehensive utilization of biomass materials has been paid more and more attention.Among the biomass,Miscanthus can be used as both energy materials and biochar materials due to its rich lignocellulose and high content of carbon and oxygen elements,which has significant advantages.In this study,we selected Miscanthus as experimental materials,analyzed the effects of different pretreatment methods on sugar production by enzymatic hydrolysis and diacussed the mechanism of pretreatment methods on sugar production efficiency as well.In addition,we used Miscanthus to prepare biochar adsorption materials,explored the adsorption characteristics and related adsorption mechanism of Cr(Ⅵ)ions in solution.The main results are as follows:(1)The pretreatment method has a great influence on the sugar production efficiency by enzymatic hydrolysis of Miscanthus.Among the different pretreatments,the highest yield of 73.4% for hexoses was obtained from 12.0% Na OH solution pretreatment,whereas 1.0% Ca O and microwave pretreatment resulted in a lower hexose yield than the control.Microwave combined with alkali pretreatment can improve the enzymatic hydrolysis efficiency of Miscanthus in a short time.The sugar production efficiency of enzymatic hydrolysis from microwave combined with 1.0%Na OH pretreatment(27.59%)was 4.3 times higher than that of microwave combined with 1.0% Ca O(5.21%).Microwave combined with low concentration of alkali can promote the enzymatic hydrolysis,while microwave combined with high concentration of alkali can inhibit the enzymatic hydrolysis.Scanning electron microscopy(SEM),Congo red staining and Fourier Transform Infrared(FT-IR)analysis were used to study the changes of the structure and surface morphology of the residues of Miscanthus before and after different pretreatment.The results show that the different pretreatments destroy the cell wall cladding structure and reduce the bonding force between cellulose,hemicellulose and lignin to different degrees,therefore increasing the accessibility of cellulose and enhancing cellulose digestion.The porosity(the maximum adsorption capacity of Congo red)exhibited a significantly positive correlation with the hexose yield.(2)Miscanthus biochar has excellent adsorption preperties for Cr(Ⅵ)ions.Using thermogravimetric analysis(TG),the suitable preparation temperature of biochar is500 ℃.With the increase of the amount of biochar,the adsorption amount decreased.The adsorption of Cr(Ⅵ)ions by biochar was favorable at lower p H.When the adsorption temperature is 30 ℃,the initial concentration of Cr(Ⅵ)is 50 mg/L,the p H value is 2.0,and the addition amount of biochar is 0.02 g,the adsorption capacity of Cr(Ⅵ)ions by biochar reached 20.0 mg/g.The adsorption process was in line with the second-order adsorption kinetic model,and could be well described by the Freundlich adsorption isotherm.The adsorption process is mainly chemical adsorption process and the root reason is that the redox reaction between Cr(Ⅵ)and the oxygen-containing functional groups on the surface of biochar.Moreover,the characteristics of Miscanthus biochar were analyzed.The results show that the whole adsorption process may involve physical adsorption,electrostatic attraction and surface complexation.The above results not only elaborated the importance of pretreatment methods of Miscanthus for sugar production by enzymatic hydrolysis,but also evaluated the efficient absorption of its biochar for heavy metal ions.This study provides a valuable theoretical basis for the efficient and comprehensive utilization of Miscanthus,a typical biomass material.