| Summary: | Rice husk (RH) in the rice industry is often air-burnt to obtain energy in the form of heat and RH ash (RHA) residue. In this work, RHA was applied as a starting material to obtain silica-supported carbon nanomaterials, resulting in a new reuse of a globally produced industrial waste product, in a circular economy approach. The preparation involves ultrasound-assisted one-pot oxidation with a sulfonitric mixture followed by wet oven treatment in a closed vessel. A study of oxidation times and RHA amount/acid volume ratio led to a solid material (nC-RHA@SiO<sub>2</sub>) and a solution containing silica-supported carbon quantum dots (CQD-RHA@SiO<sub>2</sub>). TEM analyses evidenced that nC-RHA@SiO<sub>2</sub> consists of nanoparticle aggregates, while CQD-RHA@SiO<sub>2</sub> are carbon-coated spherical silica nanoparticles. The presence of oxygenated carbon functional groups, highlighted by XPS analyses, makes these materials suitable for a wide range of analytical applications. As the main product, nC-RHA@SiO<sub>2</sub> was tested for its affinity towards steroid hormones. Solid-phase extractions were carried out on environmental waters for the determination of target analytes at different concentrations (10, 50, and 200 ng L<sup>−1</sup>), achieving quantitative adsorption and recoveries (RSD < 20%, <i>n</i> = 3). The method was successfully employed for monitoring lake, river, and wastewater treatment plant water samples collected in Northern Italy.
|
|---|