A simple method for production of humidity indicating silica gel from rice husk ash

Abstract

The objective of the present work is to develop a procedure for obtaining and characterizing active blue silica from rice husk ash. About 25 wt.% silica powder (from total mass of rice husk) of 95% pure silica could be produced after heat-treating at 700°C for 6 hours. A simple method based on alkaline extraction followed by acid precipitation was developed to produce pure silica hydrogel from RHA. A well-defined very minimum amount CoCl2-containing blue silica gel was prepared by impregnation of the aqueous solution of the salt to silica hydrogel, ageing and drying method. The sharp colour changing from blue to pink of the dried blue silica gel of amorphous characteristics was obtained at 3% moisture adsorption, and total moisture adsorption capacity was 39.5% at 80% RH. The gel was characterized using X-ray diffraction (XRD), Scanning Electron Microscope (SEM), energy dispersive X-ray (EDX), FT-infrared spectroscopy (FT-IR), thermal analysis (DSC/TG) and UV-vis reflectance spectroscopy (UV-vis) techniques. The results show that this novel preparation procedure provides an easy pathway to produce blue silica gel from rice husk according to specification.