Development of carbon quantum dots for the selective and sensitive detection of nitrite ions

Nitrite ion is used as a preservative in food and beverages and is also a common pollutant emerging from industrial processes. The concentration of nitrite requires strict control due to its toxicity and reactivity. It is also an indicator of infections in the human body. Detection of nitrite concentration via effective, cheap, and sustainable methods will help regulation of industrial uses and early diagnosis of diseases mostly related with the respiratory system. Carbon dots are a relatively new class of luminescent nanoparticles and are highly promising in sensing applications due to their tunable, functional group-rich surface and fluorescence properties. The lack of heavy metals, ease of production and biocompatibility, the lack of surface capping agents make the luminescence of carbon dots highly sensitive to the surrounding media and favorable for sensing applications. The development of carbon dots from various carbon sources including small molecules and polyolefins has been studied to produce stable, reproducible, low-cost carbon dots with high quantum yield and various emission profiles. Red luminescent carbon dots were developed for highly selective and sensitive nitrite sensing with 0.01 ppm limit of detection (LOD). From the emergence of plastics in the early 20th century, plastics replaced many materials due to cost, light weight, durability, etc. Today, humanity faces the problem of plastic pollution as a result of the large volume of production but insufficient recycling. Chemical stability and corrosion resistance of plastics especially polyolefins like polyethylene (PE) and polypropylene (PP), make the recycle processes highly expensive and inefficient. Conversion of these polyolefins to the value-added carbon nanoparticles proposes an efficient way to handle plastic pollution. Upcycling of polyolefins to luminescent carbon dots with high quantum and conversion efficiency is demonstrated in this thesis as an alternative to polymer recycling.