Preparation of lignin–MgAl layered double hydroxide composites by hydrothermal method using lignin as carrier and intercalation modifier agent

Abstract

To improve the dispersion and crystallization of layered double hydroxides (LDHs), black liquor lignin was used as both the carrier and the intercalation modifier agent to prepare lignin–MgAl layered double hydroxide (Lignin-LDH) composites by a hydrothermal method. Fourier-transform infrared spectroscopy showed that the amount of NO3− inserted into the LDH interlayers decreased significantly with the increase of the lignin content. X-ray diffraction revealed that the crystallization of LDH in the Lignin-LDH composites was enhanced by the hydrothermal treatment, and the crystal structure of the LDH was more disordered with the increase of the lignin content. Thermogravimetric analysis showed that hydrothermal treatment and the addition of lignin were beneficial for enhancing the thermal stability of the Lignin-LDH composites. The basal spacing of the LDH was unchanged based on Bragg equation calculations. Based on the infrared and thermogravimetric analysis results, it can be inferred that the molecules of dissolved hydroxyl compounds were inserted into the LDH interlayers. Scanning electron microscopy showed that the hydrothermal treatment promoted the growth of LDH crystals, and the increase of the lignin amount resulted in the dispersion of LDH in lignin and a decrease of the LDH thickness.