Carbon dots and nitrogen-doped carbon dots-metal oxide nanocomposites: robust agents for effective sensing of ions

Carbon dots-Manganese oxide (CDs-MnO₂) and Nitrogen-doped carbon dots-MnO₂ (NCDs-MnO₂) nanocomposites were constructed by a green ultrasonic approach using Jasminum sambac leaves extract as a carbon source and reducing agent. The constructed nanocomposites were characterized by UV–visible spectrophotometry, FTIR, XRD, EDX, and SEM. CDs-MnO₂ nanocomposites gave a UV–visible absorbance peak at λ_max 223 nm and NCDs-MnO₂ nanocomposite showed a peak at λ_max 225 nm. FTIR examination revealed that the produced nanocomposites included a variety of functional groups. The size of the nanocomposite was calculated from XRD data i.e. 22.04 nm for CDs-MnO₂ while NCDs-MnO₂ had an amorphous nature. EDX analysis showed that both nanocomposites have C, O, and Mn while only one nanocomposite has N. SEM investigation revealed that nanocomposites are agglomerated. The spectrophotometric method was used for the sensitive and selective perceiving of Cr(VI) ions using prepared nanocomposites. Different factors were studied to find an optimum environment for sensing Cr (VI) ions i.e. concentration of ions, reaction time, pH, temperature, and effect of interfering species. The calculated limit of detection was 16 μM for CDs-MnO₂ and 69 μM for NCDs-MnO₂. The results showed that both nanocomposites are good sensors of Cr (VI) ions but NCDs-MnO₂ nanocomposites require less harsh conditions for sensing which can be due to the existence of different functional groups and size of the nanocomposite. Real sample analysis was also done by spike recovery method and calculated recovery percentages were found to be 100.01–100.2% for CDs-MnO₂ and 99.9–100.01% for NCDs-MnO₂.