SPECIAL DATA HANDLING TECHNIQUES FOR FOURIER-TRANSFORM INFRARED PHOTOACOUSTIC SPECTRA - ESTIMATION AND CHARACTERIZATION OF THE N-CONTENTS ON AMMONIATED TRICHLOROSILYLATED SILICA-GEL, USING PARTIAL LEAST-SQUARES REGRESSION AND CURVE FITTING ON THE SI-H STRETCHING VIBRATION

The reaction of silica gel with trichlorosilane (HSiCl3) and subsequently with gaseous NH3, resulting in a surface covered with =Si-O-Si(H)(NH2), and NH4Cl species, has been studied. The Si-H stretching vibration (2270 cm-1) of the trichlorosilylated silica perturbs, upon ammonia adsorption, into three overlapping bands. It is shown that partial least-squares regression (PLSR) is able to predict the concentration of the different surface species, using the Si-H stretching vibration region as the only spectral dataset. It is noticeable that this vibration has a constant intensity, since the Si-H species are generated during the trichlorosilylation step, and not during the ammoniation. The mechanisms, causing this perturbation are investigated in more detail, using curve fitting and Si-29 cross-polarisation magic-angle-spinning (CP MAS) NMR. The occurrence of an ammoniated secondary species [(=Si-O),-Si(H)(NH2)] on the silica surface is proposed and its infrared (IR) absorbing frequency is determined. An introduction to PLS for the spectroscopist is included.