Fourier Transform Infrared Spectroscopy (FTIR)
The surface chemical bonding was determined by Fourier transform infrared spectroscopy (FTIR, Perkin Elmer, Spectrum One, USA). Diffuse reflectance infrared fourier transform (DRIFT) technique was used for all samples to identify types of chemical bonds (functional groups). The spectral resolution was 4 cm-1 and 256 scans were coded into the mid infrared region (4000-400 cm-1) [6].