Characterization of surface functional groups by FT-near infrared spectroscopy

傅立叶变换近红外光谱（FT-NIR）是一种功能强大的分析方法，但除了农业领域外，还不太熟悉。近红外区（4000 cm-1 <-1>~ 10000 cm-1<-1>）覆盖了O-H键的泛音以及伸缩和弯曲振动的组合。研究的目的是确定O-H振动来源于酸性，特别是固体酸氧化物。由于近红外光谱的研究结果不多，因此采用标准样品，用CCl_4、C_6H_6和CHCl_3等稀释剂进行峰归属。液体样品中的酸强度与相应的OH基团的振动频率如下：1）当酸强度（pKa）约为4.5时，在CDCl_3溶液中观察到OH基团的振动频率在6890 Cm ~（-1）附近<-1>。2)当酸强度达到约。3、频率移到6850 cm ~ 2<-1>。3)当酸强度为4.5 ~ 3时，在CDCl_3溶液中，在6890 <-1>~ 6850 cm ~ 2<-1>处出现吸收峰，在固体样品中，结构和硅铝比已确定的沸石在6500- 7000 cm ~ 2和5000 cm ~ 2处出现特征峰肩<-1><-1>。峰肩的位置与Si/Al比的变化密切相关，表明峰肩可能归因于来自酸强度的OH基团。由于所观察的沸石暴露于空气中，因此也检测到来自吸附的H_2O的峰。为了明确识别酸强度对应的峰，原位和漫反射技术是先决条件。这项研究正在进行之中。

Fourier Transform Near Infrared Spectroscopy (FT-NIR) is a powerful analytical method but is not familiar except for in agricultural fields. The NIR region(4000cm^<-1>〜10000cm^<-1>) covers the overtones and combination of stretching and bending vibrations of O-H bonds. The aim of study is to identify O-H vibrations originated from the acid property, especially on solid acid oxides. As there are a few results on NIR studies, standard samples for the assignment of peaks have been employed using diluents such as CCl_4, C_6H_6 and CHCl_3. The acid strength in the liquid sample is associated to the vibration frequencies of the corresponding OH groups as follows : 1) When the acid strength(pKa) is about 4.5, the vibration frequency of OH groups is observed around 6890Cm^<-1> in CDCl_3 solution. 2) When the acid strength becomes ca. 3, the frequency is shifted to 6850cm^<-1>. 3) When the acid strength is between 4.5 and 3, the absorption peaks appear between 6890Cm^<-1> and 6850cm^<-1> in CDCl_3 solution.In solid samples, zeolites, where the structures and Si/Al ratios are identified already, show the characteristic peak shoulders at 6500-7000cm^<-1> and 5000cm^<-1>. The positions of peak shoulders are closely correlated with changes in the Si/Al ratio, suggesting that the peak shoulders might be attributed to the OH groups derived from the acid strength. Since the zeolites observed were exposed to air, the peaks from adsorbed H_2O also were detected. In order to identify clearly the peak corresponding to the acid strength, the in-situ and diffuse reflectance techniques are prerequisite. The study is under way.