Extraction and Characterization of Biosilica from Raphia Africana Fruit Shells and Borassus aethiopum Leaves

Abstract

Agricultural wastes which include leaves, shells, husk, stalks, bagasse and ash of plants are often residues of processing or growing of raw agricultural products [1]. These wastes may contain materials that are beneficial to man despite their contribution to environmental pollution. Increase in human population has led to increase in agricultural expansion with exponential increase in waste generation [2]. Converting these wastes to useful forms is of great significance. In this study, biosilica was extracted from the ash of Borassus aethiopum leaves (BALA) and Raphia africana fruit shells (RASA) using precipitation method. The ashes obtained were characterized using Atomic Absorption Spectrophotometry (AAS). Scanning Electron Microscope (SEM), Fourier Transform Infrared Spectroscopy (FTIR) and X-Ray Fluorescence (XRF) were used to characterize the extracted silica. Morphology of the extracted biosilica using SEM revealed fine globules of various sizes formed from aggregates of biosilica at different magnifications: 150x, 500x and 1000x. FTIR spectra of the extracted biosilica revealed the presence of hydroxyl (OH), silanol (Si-O-H) and siloxane (Si-O-Si) functional groups recorded at absorption bands: 3395.6, 1636.3 and 1062.3 cm-1 respectively for BALA and 3388.2, 1640.0 and 1058.6 cm-1 respectively for RASA. XRF of the extracted biosilica showed two major peaks which correspond to the presence of silicon and oxygen atoms respectively. Percentage extraction of biosilica from the two precursors was between 70-90%. AAS result revealed that BALA had biosilica 67% while RASA showed 82% biosilica content. This study revealed that the leaves of BALA and fruit shells of RASA are good sources of silica and as such, converting waste to wealth thereby reducing green-house gases like CO2 released into the atmosphere when left to decompose naturally.