Preparation and characterization of highly pure silica from sedge as agricultural waste and its utilization in the synthesis of mesoporous silica MCM-41

Sedge (Carex riparia) is a weed which produces large quantities of agricultural waste. The objective of the present study was to develop a procedure for obtaining and characterization of amorphous silica from sedge and its application for synthesize of mesopororous silica MCM-41. Combustion of sedge was studied at different temperatures in the range of 500–800 °C. The resultant silica and as-synthesized MCM-41 were characterized by X-ray diffraction (XRD), X-ray fluorescence (XRF), N2 adsorption–desorption isotherms, Fourier-transform infrared (FT-IR) spectrometry, thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and Transmission electron microscopy (TEM). The x-ray diffraction pattern of the resulting silica revealed that 600 °C is optimum temperature for obtaining amorphous silica. White ash, containing majority of SiO2 with trace amounts of CaO, K2O, Al2O3, MgO, P2O5, etc., was successfully produced by a combination of heating, leaching and refluxing schemes to facilitate decomposition and gasification of the organic materials while avoiding complete ignition. The XRF results revealed that the highest purity of amorphous silica (98%) was obtained by applying a combination of pretreatment of sedge using leaching and post-treatment of sedge ash with refluxing. SEM results reveals that sedge ash particles are not spherical in shape and exhibit irregularly fragmented particles. The XRD pattern of the resulting MCM-41 revealed a typical pattern of hexagonal mesophase. In agreement with the XRD, the hexagonal structure of pores of MCM-41 was confirmed by the TEM oservations. The N2 adsorption results revealed that synthesized MCM-41 having large pore sizes of about 4.1 nm, high surface areas up to 1174 m2/g and total pore volume of 0.98 cm3/g. Through a combination of XRD, N2 adsorption and TEM methods, porosity parameters were compared.

► The process of white ash synthesis of amorphous silica from sedge weed was studied.
► Successfully use of extracted silica precursor for synthesis of mesoporous MCM-41 material.
► MCM-41 shows well-ordered 2d-hexagonal mesostructure in basic conditions.