Silica synthesis from biomass

Abstract

Agribusiness activities are generating large amounts of waste due to production processes and society’s high consumption standard. The most common types of crop biomass waste are straw, bark, cob and bagasse. The amount of agricultural waste generated in the world (million tons/year) is: Rice husk: 130-170; Corn Cob: 164; Sugarcane Bagasse: 700. Most of this waste is disposed of by burning, dumping, or landfilling. Incorrect disposal raises serious questions related to human health and the environment, mainly associated with air pollution, water and soil contamination. The strategy to mitigate the effects of disposal is the reuse of agricultural biomass waste. Wastes such as rice husk, corn cob, wheat straw and sugarcane bagasse present high content of silica in the composition, thus can be utilized for the production of nanosilica (SiNPs). SiNPs present a variety of applications due to their distinctive properties such as stability, biocompatibility, surface reactivity, tunable pore size, and high surface area. Extracting silica from agricultural waste is an excellent alternative to obtain high added-value products. Methods of extracting silica from agricultural waste are divided into thermal, biological and chemical. The chemical synthesis method has the advantage of size and shape control, as well as purity improvement. Among the chemical methods, SiNPs are mainly synthesized via a sol-gel polymeric route. The silica is extracted from the waste as sodium silicate, then treated with acid to convert it into a gel. A transformation occurs in colloidal suspension of sol into gel through 3D interconnecting network. The sol–gel technique allows control the size, distribution, and morphology of particles with a large specific area and high porosity. Pure amorphous silica was successfully extracted at a 99.1% from sugarcane waste ash. The synthesized SiNPs can be characterized by a combination of spectroscopic and chemical techniques, such as XRD, XRF, SEM, TEM, particle size distribution, N2 adsorption-desorption isotherms, TGA, and FTIR. In this approach, the adoption of the circular economy in agroindustrial waste management contributes significantly to the achievement of the Sustainable Development Goals (SDGs), specifically, SDG 12: “By 2030, substantially reduce waste generation through prevention, reduction, recycling and reuse”.