ATR-IR分析氢氧化钠对水及离子液体/水体系氢键作用的影响

Studies on the Effects of Sodium Hydroxide on Hydrogen Bonding of Water and Ionic Liquid/H_(2)O Systems by ATR-IR Analyses

利用衰减全反射红外光谱(ATR-IR)分析NaOH对水及1-乙基-3-甲基咪唑醋酸酯离子液体水溶液(EmimAc/水)氢键网络的影响,研究结果表明,NaOH的加入会影响水分子的氢键对称性和类型,对称性氢键谱带Ⅰ(3218 cm^(-1))和Ⅱ(3375 cm^(-1))随着NaOH浓度的提高而降低。NaOH使水溶液氢键发生极化,产生连续吸收带,连续吸收带随着NaOH浓度的提高而增强。水对EmimAc的阳离子和阴离子均有影响。水分子的OH和EmimAc的COO-产生强的相互作用,在3400~3200 cm^(-1)产生宽的吸收谱带;而水分子的质子和COO-作用使得C=O吸收谱带红移。水的加入使得EmimAc指纹区的谱带蓝移或吸收强度下降,表明水可以破坏EmimAc原有的氢键网络,形成“阴离子…HOH…阴离子”团簇,减弱了离子液体阴、阳离子之间的相互作用。NaOH替代水与EmimAc混合,ATR-IR谱图的变化并不显著,主要表现在谱带的吸收强度上。与EmimAc/水相比,EmimAc/NaOH水溶液的ATR-IR谱的吸收强度更高,表明NaOH水溶液对EmimAc氢键网络的破坏不如水显著。由此可见,可利用EmimAc/NaOH体系降低离子液体体系黏度,并且降低离子液体使用成本,对木质纤维原料预处理有一定的指导意义。

In this study,attenuated total reflection spectroscopy(ATR-IR)was used to analyze the influence of NaOH on the hydrogen bonding network of H_(2)O and 1-ethyl-3-methylimidazolium acetate ionic liquid aqueous solution(EmimAc/H_(2)O).The results showed that the addition of NaOH affected the symmetry and type of hydrogen bond of water aqueous solution.The symmetric hydrogen bond bandsⅠ(3218 cm^(-1))andⅡ(3375 cm^(-1))decreased with NaOH concentration.The hydrogen bonds of the water were polarized in the presence of NaOH,thus producing continuous absorption bands;moreover,the absorptions of the continuous bands were enhanced with increasing NaOH concentration.In the case of the EmimAc,water affects both the cation and anion.The OH of H_(2)O interacts strongly with COO-of EmimAc and generates a wide absorption band between 3400 and 3200 cm^(-1),while the interaction of proton on H_(2)O and COO-makes the C=O absorption band red-shift.H_(2)O addition could cause a blue shift or a decrease of the absorption between the band 1600~1200 cm^(-1),which is referred that water could damage the original hydrogen bond network of EmimAc and form“anion…HOH…anion”and weaken the interaction between cation and anion of ionic liquid.When water was substituted by NaOH and mixed with EmimAc,the absorption strengthened.It is probably that destruction of the EmimAc hydrogen bond network by NaOH aqueous solution is not as significant as water.In summary,the EmimAc/NaOH system can be used to reduce the viscosity of the ionic liquid system and the application cost of EmimAc,which has a specific guiding significance for the pretreatment of lignocellulosic biomass.