Bio-silica production from rice husk for environmental remediation: Removal of methylene blue from aqueous solutions

In this work, a methodology was thus structured to obtain bio-silica (SiO2) from rice husk (RH). The rice husk ash (RHA) obtained was characterized using X-ray diffraction (XRD), infrared and UV-Vis absorption spectroscopy, scanning electron microscopy (SEM) and elemental analysis (EDS), as well as nitrogen adsorption-desorption isotherms to determine its specific surface area and porosity. The results showed that the synthesized biosilica was amorphous, with highly agglomerated submicron particles (<200 nm) and a specific surface area of similar to 202.31 m(2)/g. Considering the potential use of this bio-silica, its ability to remove methylene blue (MB) from aqueous solutions was evaluated. The results indicate that the chemical treatments carried out on the RH favored the removal of MB from the solution, going from a removal percentage of similar to 30%, for a sample without chemical treatment, to similar to 50% when the RH was treated with a 3 N HCl solution. The capacity of bio-silica to remove MB was increased by pre-irradiating the synthesized RHA with UV for 5 min, achieving removal percentages of up to similar to 73% for the sample chemically treated with a 3 N solution and at a temperature of 650 degrees C.