Preparation of Biochar-Fe₃O₄ Magnetic Nanoparticles and Its Application of Detection of Silver in Water

Biochar-Fe₃O₄ magnetic nanoparticles (NC/Fe₃O₄NPs) were prepared through a one-step hydrothermal method using pomelo peel powder, ferric chloride hexahydrate, and urea as materials. 10.0 mL of water sample was taken, and 10.0 mg of NC/Fe₃O_4NPs was added and the mixture was shaken for 15 min. A magnet was used to adsorb NC/Fe₃O₄NPs and separate it from the solution. The solution was discarded, and NC/Fe₃O₄NPs was washed with 5.0 mL of water. The solution was discarded, and the washing process was repeated 3 times. 5.0 mL of 30% (volume fraction) nitric acid solution was added and the mixture was shaken for 15 min. The solution was collected by magnetic separation of NC/Fe₃O₄NPs, and the silver in water was determined by graphite furnace atomic absorption spectrometry. As shown by the results, linear relationship between the corresponding absorbance and mass concentration of silver was found in the range of 0.20-10.0 μg·L⁻¹, with detection limit (3s) of 0.13 μg·L⁻¹. 6.0 μg·L⁻¹ silver standard solution was determined 6 times, and RSDs of the determined values was 2.6%. Test for recovery was made by standard addition method on actual samples, giving results in the range of 91.5%-97.5%.