THz time-domain spectroscopy of selected molecular sieves and their related compounds

The spectral characteristics of selected molecular sieves (3A, 4A, 5A, 13X and synthetic zeolite) in a terahertz (THz) range were studied by THz time-domain spectroscopy technologies (THz-TDS). The chemical composition of a molecular sieve is M x/n [(AlO 2 )x·(SiO 2 )y]·zH 2 O, where M is metal cation and n is the valence of the metal cation. The absorption coefficients and refractive indices were extracted in the spectra. Different from that of the A-type molecular sieves, the absorption curves and refractive indices of synthetic zeolite and 13X molecular sieve display large fluctuation as the frequency change. In addition, two kinds of related compounds (Al 2 O 3 and quartz sand) were studied by using THz-TDS. The Al 2 O 3 shows weak absorption and quartz sand has three typical absorption peaks at 0.89, 1.3, 1.55 THz. The refractive index of Al 2 O 3 is kept at about 1.27 while that of quartz sand show large fluctuations. The present results suggested that the THz spectra of molecular sieves are in dependent of their types and indicated the potential of THz technology for the molecular sieve industry.