The rice process generates a large amount of husk, which can become an environmental contaminant if it does not receive an adequate management. Because rice husk is a natural source of silica, in this work silica nanoparticles were obtained as an alternative use for this residue. The synthesis was carried out with the incineration, acid leaching process, and particle size reduction through high-energy mechanical ball milling. For its characterization, thermal, chemical, morphological, structural and superficial area analyses were performed with thermogravimetric analysis, X-ray fluorescence method, scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and Nitrogen adsorption/desorption isotherm techniques. The results indicated that between 150-450°C the organic material of the rice husk was released, and above 550°C was obtained ash rich in silica. The silica purity was effectively increased to 98.48%, through acid leaching with acid nitric. The reduction of particle size by mechanical milling at 600 rpm for 3 h was achieved up to nanometer size. Most of the nanoparticles were spherical with a diameter between 14 and 28 nm. Silicon oxide was the principal structural phase of the nanoparticles corroborated by the broad peak corresponding to the (101) plane shown by XRD pattern. A substantial increase of two magnitude orders of the specific surface area of nanoparticles was reached in comparison with particles without milling. The nanosilica particles obtained from rice husk can be used for the production of high-performance silicon or they can be also used as supplementary cementitious materials. 

Graphical Abstract

Production and characterization of silica nanoparticles from rice husk