Fabrication of green, fluorescent N-doped carbon quantum dots via microwave-assisted method: the effect of microwave power

Abstract

There seem to be fewer research methodically examining the luminous mechanisms of carbon quantum dots (CQDs), despite the general interest in comprehending their features. Preparing N-CQDs with desired optical properties and comprehending the mechanisms underlying photoluminescence (PL) that regulate emission characteristics are the main goals of this work. The functional groups (-NH₂, -OH, -CO, -CHO, -COOH, -COO) that form on the surface of the dots have a significant impact on the optical characteristics of N-CQDs. The preparation techniques and the precursor components are the main determinants of the kind and quantity of functional groups. In this study, CQDs were produced using a microwave-assisted synthesis process, beginning with urea and citric acid. The impact of the microwave power level on the surface functional groups on the dots' surface was then carefully evaluated. It was discovered that raising the microwave power level improves the PL by increasing the density of functional groups on the exterior of CQDs. On the other hand, heating at high microwave power lowers the PL intensity and functional group concentration. The produced N-CQDs' stability, catalytic activity, and sensing were investigated. This study emphasizes how surface functional groups affect PL emission and how to physically control them. Fluorescence quenching effect was produced by the addition of Fe³⁺ and Zn²⁺ ions to the N-CQD solution. Moreover, the samples were evaluated in the degradation of methylene blue, and the sample synthesized at medium microwave power showed the highest degradation rate. These findings demonstrated the as-synthesized N-CQDs samples can be used as sensors and photocatalyst.