Removal of organic contaminants such as azo dyes is highly desirable because of their toxicity, stability, and mutagenic properties. Herein an efficient method for the photodegradation of two well-known model azo dyes, namely metanil yellow (MY) and methyl orange (MO), under sunlight by multiple-heteroatomdoped carbon dots (CD) (nitrogen-, sulfur-, and phosphorusdoped-CD (NSP-CD)) is presented. The photodegradation results favored sunlight as a sustainable light source, as its value of t 1/2 is significantly less than that of artificial light (100 W tungsten bulb). Various parameters, such as the concentrations of individual dyes (20−100 ppm), a mixture of both dyes, changes in pH, and foreign/interfering ions, were investigated to understand the photocatalytic activity of NSP-CD. Under sunlight, photodegradation of ∼20 ppm of dye was observed in ∼60 min (for MY) and ∼90 min (for MO), respectively. A comparative NMR investigation was performed to confirm the photodegradation of the complex structural framework of azo dyes by NSP-CD. Moreover, to explore the real-life utility of the process, sunlight-promoted photodegradation experiments were conducted by externally spiking four different types of industrial samples. Spiking of MY and MO dyes with concentrations in the range of ∼15−23 ppm showed similar results of photodegradation.

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