Effect of synthesis conditions on the morphology of mesoporous silica from elephant grass and its application in the adsorption of cationic and anionic dyes

In this study, various low cost mesoporous silica (MS) were synthesised from elephant grass (EG) a biowaste material often regarded as a weed, by varying synthesis conditions, such as temperature and surfactant concentration (cetyltrimethyl ammonium bromide (CTAB)), thus revealing the transformation of mesoporous silica from silica nanoparticles to silica nanotubes. MS obtained were extensively characterised. Highly porous silica nanoparticles (SNP) were obtained at 2 wt. percent of surfactant to silica and at 45 wt. silica nanotubes (SNT) were obtained. It was observed that 600 °C was the optimum temperature in MS synthesis as it gave higher surface area and an all-round better textural property in the sorption of methylene blue (cationic dye) and methyl orange (anionic dye) from wastewater. Batch adsorption was carried out to determine the effect of time, temperature, initial concentration, pH and adsorbent dose. SNP had a higher qm value of 123.5 mg/g for MB and 83.3 mg/g for MO which may be attributed to its larger surface area. Adsorption mechanism was through ion exchange and pore filling. Thermodynamic study revealed the adsorption process was exothermic. This study showed the transformation of EG into highly efficient sorbents with desorption studies showing that adsorbents could be reapplied in adsorption.