Preparation Of Green Porous Cross-linked Starch And Adsorption Properties

As a green,safe and degradable adsorbent,porous starch has been widely used in the fields of drug carrier,pollutant adsorbent and dietary supplement encapsulation agent.However,compared with inorganic adsorbents such as activated carbon,porous starch has much smaller surface area,lower mechanical strength and poor heat resistance.Therefore,in order to improve the limitations of the industrial application of porous starch.In this thesis,native corn starch hydrolyzed by malt endogenous enzymes was used as raw material,and crosslinked with sodium trimetaphosphate,citric acid and malic acid,respectively.To explore the physical and chemical properties of cross-linked porous starch and use it as adsorbent to study the adsorption properties of cross-linked porous starch on water,soybean oil,volatile essential oil and cationic methylene blue dye.The specific research results are as follows:（1）Porous starch（MPS）was prepared by endogenous maltase.The effects of starch internal structure on the porosity,adsorption capacity and thermal stability of porous starch were studied by comparing the properties of corn starch hydrolyzed by malt endogenous enzymes with those treated by traditional commercial enzymes.The results showed that the crystal type had no change after enzyme modification,but the order degree decreased.The proportion of short chains（DP6-12）in MPS increased by9.36%and the average chain length decreased from 18.97 to 18.54.Compared withα-amylase hydrolysis,the specific surface area and pore volume of MPS after maltase treatment increased by 306.97%and 124.53%,and compared withβ-amylase hydrolysis,increased by 130.26%and 73.13%,respectively.The specific surface area and pore volume of porous starch were positively correlated with the adsorption properties.The water absorption and methylene blue absorption of porous starch were 196.00%and110.82%higher than those of native starch,respectively.The adsorption capacity of MPS to soybean oil increased by 50.15%compared with that of AA-BA-PS.The adsorption capacity of MPS for essential oil was increased by 2 times after enzyme hydrolysis;（2）Native corn starch was hydrolyzed by maltase and crosslinked with different crosslinking agents.The cross-linked porous starch（STMP-MPS）,malic acid cross-linked porous starch（MA-MPS）and citric acid cross-linked porous starch（CA-MPS）were prepared.After crosslinking,starch particles clustered together,and the two organic acids crosslinked to adhere to each other more closely.MA-MPS and CA-MPS showed a new C=O stretching absorption peak at 1738 cm^-1.The characteristic absorption peaks P-O(1242 cm^-1)and P-O-C(1025 cm^-1)of STMP-MPS did not appear in the spectrum of starch samples due to the low degree of crosslinking.The degradation temperature of MA-MPS and CA-MPS was increased by the introduction of ester bond.The pore size distribution and specific surface area were affected by different crosslinkers.Compared with the average pore size of 12.43 nm of STMP-MPS,CA-MPS（14.02 nm）and MA-MPS（14.79 nm）were increased more significantly.The surface area of MA-MPS was 36%higher than that of STMP-MPS.Compared with STMP-MPS,water absorption of MA-MPS and CA-MPS increased by64%and 32%,respectively.The adsorption capacity of MA-MPS to essential oil was the strongest,about 4 times that of STMP-MPS.（3）The results of the first two parts show that porous crosslinked starch has a good adsorption effect on methylene blue（MB）.Therefore,porous organic acid cross-linked starch as adsorbent and STMP-MPS was used as the control sample,the adsorption kinetics model of CA-MPS and MA-MPS for methylene blue dyes was constructed.The experimental results showed that the adsorption capacity of MA-MPS and CA-MPS for MB increased by 108.51%and 107.45%,compared with STMP-MPS.With the increase of contact time,the adsorption capacity of methylene blue also increased,and the adsorption capacity reached the adsorption equilibrium at 50 min,and the maximum adsorption capacity at the same time.The adsorption process of CA-MPS and MA-MPS on MB conformed to Langmuir model and pseudo-first-order internal diffusion model,which was endothermic spontaneous adsorption process.The adsorption of MB by porous crosslinked starch was mainly dependent on hydrogen bond and electrostatic interaction.Under the optimal adsorption conditions,the maximum adsorption capacity of CA-MPS and MA-MPS was 0.54 mg/g and 0.52 mg/g,respectively,and could be reused after two cycles;In this thesis,corn starch was hydrolyzed by malt enzyme to solve the shortcomings of commercial amylase,such as high preparation cost,complicated extraction process and short storage time.At the same time,it was proved that the porous cross-linked starch prepared by cross-linking treatment could further increase the pore size and specific surface area of porous starch,thus expanding the adsorption capacity of porous cross-linked starch,which has certain important significance for increasing the adsorption capacity of porous starch materials.The introduction of chemical bonds in the crosslinking process provides a new perspective for improving its thermal stability.In addition,porous crosslinked starch,as a new green degradable adsorbent with high efficiency,convenience and low cost,provides a direction for the treatment of high concentration organic cationic dye wastewater.