DA-MIL-100(Fe)中乙醇对低挥发性香兰素的协同脱附研究

Synergistic desorption of low volatile vanillin with ethanol on DA-MIL-100(Fe)

通过多巴胺修饰MIL-100(Fe)水热合成了DA-MIL-100(Fe)。并通过XRD、SEM、EDS、XPS、Zeta电位、TG和N_(2)吸/脱附等温线对修饰前后的材料进行了表征,多巴胺修饰后的MIL-100(Fe)依旧具有良好的结晶度以及热稳定性,其比表面积仍然高达1139.4 m^(2)/g。另外,以低挥发度香料香兰素(沸点555 K)为控释香料分子,选择低沸点分子乙醇(沸点351 K)作为“携带”分子,在香兰素和乙醇分子被DA-MIL-100(Fe)共吸附的条件下,利用被吸附香兰素分子与被吸附乙醇分子间的氢键作用力,减弱香兰素与吸附材料DA-MIL-100(Fe)之间的吸附力,测定了不同温度下香兰素在MIL-100(Fe)与DA-MIL-100(Fe)上的等温吸附线,并计算对比了香兰素在两个材料上的等量吸附热以及脱附活化能,结果发现香兰素在DA-MIL-100(Fe)上的等量吸附热明显小于未经多巴胺修饰的MIL-100(Fe)上的等量吸附热,且香兰素在修饰前后的MIL-100(Fe)材料上的脱附活化能从90.9 kJ/mol降低至77.4 kJ/mol。然后,考察不同香兰素初始吸附量对香兰素在DA-MIL-100(Fe)中脱附率的影响发现,香兰素的脱附率随香兰素初始吸附量的增加呈现先增加后下降的趋势,并在香兰素吸附量约3.19 mmol/g条件时达到最大脱附率(73.0%),这是因为在低香兰素初始吸附量时DA-MIL-100(Fe)中的强吸附位会降低香兰素的脱附率,而在高香兰素初始吸附量条件下,DA-MIL-100(Fe)孔道中香兰素分子的增加会导致孔道内乙醇数量的相对减少,从而减弱乙醇对香兰素的协同脱附作用。

In this study,DA-MIL-100(Fe)was synthesized by modifying MIL-100(Fe)with dopamine.The materials before and after modification were characterized by XRD,SEM,EDS,XPS,Zeta potential,TG,and N_(2) adsorption/desorption isotherms.The characterization results revealed that the dopamine-modified MIL-100(Fe)retained good crystallinity and thermal stability while maintaining a surface area of 1139.4 m^(2)/g.Besides,a low volatility flavor-vanillin(boiling point 555 K)as a“controlled release”of spice molecules and low boiling point molecule-ethanol(boiling point 351 K)as a“carrying”molecule were chosen under the condition that vanillin and ethanol molecules were adsorbed over DA-MIL-100(Fe).Using the hydrogen bonding force between the adsorbed vanillin molecule and the adsorbed ethanol molecule and attenuating the adsorption force between vanillin and the adsorbed material DA-MIL-100(Fe),the isothermal adsorption curves of vanillin on MIL-100(Fe)and DA-MIL-100(Fe)at different temperatures were plotted.Concurrently,the equivalent adsorption heat and desorption activation energy of vanillin on the MIL-100(Fe)and DA-MIL-100(Fe)were calculated and compared.The results showed that the equivalent heat of adsorption for vanillin on DA-MIL-100(Fe)was significantly lower than that on MIL-100(Fe)without dopamine modification.The activation energy of vanillin desorption on MIL-100(Fe)before and after modification decreased from 90.9 kJ/mol to 77.4 kJ/mol.Furthermore,the effect of different initial vanillin adsorption amounts on the vanillin desorption rate in DA-MIL-100(Fe)was investigated.The desorption rate of vanillin increased first and then decreased with increasing vanillin initial adsorption amount,reaching 3.19 mmol/g maximum desorption rate(73%).This was due to the fact that at low initial vanillin adsorption over DA-MIL-100(Fe),strong adsorption sites in composite decreased vanillin desorption,whereas,at high initial vanillin adsorption conditions,the increase in vanillin molecules in DA-MIL-100(Fe)channels led to a relative decrease in the amount of ethanol in the pore,thus weakening the synergistic desorption of vanillin by ethanol.