Preparation of Lignin-Silica Hybrid Composite by Using the Alkaline Digestion Liquor of Rice Husk

The lignin-silica hybrid composites were prepared by using the black liquor of rice husk alkaline digestion. The application of acid to the black liquor resulted in the precipitation of the lignin-silica hybrid composites. The four pH conditions such as pH 8, pH 6, pH 4, pH 2 were applied for evaluating the effects of pH condition on the preparation of the lignin-silica hybrid composites. The lower pH condition resulted in the increase of the precipitation and the higher contents of lignin in the precipitate of the lignin-silica hybrid composite, especially at pH 2 condition. The analysis with FT-IR and TGA also showed the higher lignin contents of the lignin-silica hybrid composites prepared at pH 2 conditions. The micro-particles and micro pores of the lignin-silica hybrid composite prepared at pH 8 were not observed in the SEM images of the lignin-silica hybrid composites precipitated at pH 2, which might be caused by the higher portion of the combined lignin and the agglomeration of the lignin prepared at pH 2 condition.